TY - JOUR A1 - Amouroux, B. A1 - Eftekhari, A. A1 - Roux, C. A1 - Micheau, J. A1 - Roblin, P. A1 - Pasturel, M. A1 - Gauffre, F. A1 - Würth, Christian A1 - Resch-Genger, Ute A1 - Sliwa, M. A1 - Bouchet, A. A1 - Coudret, C. T1 - Synthesis and Emission Dynamics of Sub-3 nm Upconversion Nanoparticles N2 - Reducing the size of upconversion nanoparticles (UCNPs) down to a few nm yields luminescent materials containing a very small number of emitters. Considering the bottom limit of one activator per particle ultrasmall UCNPs offer an unprecedented platform to study the contributions of the energy transfers at play in upconversion luminescence. Maintaining detectable emission despite the limited number of emitting ions and the high surface-to-volume ratio requires suitable particle architectures. Na(Gd-Yb)F4:Tm3+ emissive sub-3 nm diameter 𝜷-phase UCNPs are prepared using a gadolinium-rich composition in situ mixing of the precursors and a microwave high-temperature cycling sequence allowing precise control of the particle size and dispersity. These cores are coated with a NaGdF4 inert shell to minimize the deleterious influence of surface quenching (SQ). Time-resolved luminescence measurements combining standard NIR excitation of the Yb3+ sensitizer and direct UV excitation of the Tm3+ activator are performed to quantify cross relaxation and surface quenching processes. The fine tuning of the number of activators per particle via an optimized synthesis pathway along with the use of an appropriate excitation scheme enabled to provide an accurate analysis of the different mechanisms at play in these model nanoparticles and to characterize the structure of the core-shell architecture. KW - Lanthanide KW - Nanoparticle KW - Luminescence KW - Quantitative spectroscopy KW - Quantum yield KW - Energy transfer KW - Quality assurance KW - Synthesis KW - Surface modification KW - Photophysics PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-606877 DO - https://doi.org/10.1002/adom.202303283 SN - 2195-1071 SP - 1 EP - 13 AN - OPUS4-60687 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Scholtz, Lena A1 - Eckert, J. G. A1 - Graf, Rebecca T. A1 - Kunst, A. A1 - Wegner, Karl David A1 - Bigall, N. C. A1 - Resch-Genger, Ute T1 - Correlating semiconductor nanoparticle architecture and applicability for the controlled encoding of luminescent polymer microparticles N2 - Luminophore stained micro- and nanobeads made from organic polymers like polystyrene (PS) are broadly used in the life and material sciences as luminescent reporters, for bead-based assays, sensor arrays, printable barcodes, security inks, and the calibration of fluorescence microscopes and flow cytometers. Initially mostly prepared with organic dyes, meanwhile luminescent core/shell nanoparticles (NPs) like spherical semiconductor quantum dots (QDs) are increasingly employed for bead encoding. This is related to their narrower emission spectra, tuneability of emission color, broad wavelength excitability, and better photostability. However, correlations between particle architecture, morphology, and photoluminescence (PL) of the luminescent nanocrystals used for encoding and the optical properties of the NP-stained beads have been rarely explored. This encouraged us to perform a screening study on the incorporation of different types of luminescent core/shell semiconductor nanocrystals into polymer microparticles (PMPs) by a radical-induced polymerization reaction. Nanocrystals explored include CdSe/CdS QDs of varying CdS shell thickness, a CdSe/ZnS core/shell QD, CdSe/CdS quantum rods (QRs), and CdSe/CdS nanoplatelets (NPLs). Thereby, we focused on the applicability of these NPs for the polymerization synthesis approach used and quantified the preservation of the initial NP luminescence. The spectroscopic characterization of the resulting PMPs revealed the successful staining of the PMPs with luminescent CdSe/CdS QDs and CdSe/CdS NPLs. In contrast, usage of CdSe/CdS QRs and CdSe QDs with a ZnS shell did not yield luminescent PMPs. The results of this study provide new insights into structure–property relationships between NP stained PMPs and the initial luminescent NPs applied for staining and underline the importance of such studies for the performance optimization of NP-stained beads. KW - Quantitative spectroscopy KW - Energy transfer KW - Synthesis KW - Surface chemistry KW - Semiconductor quantum dot KW - Luminescence KW - Nano KW - Particle KW - Quantum yield KW - Lifetime KW - Quality assurance KW - Polymer particle KW - Quantum rod KW - Nanoplatelet PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-602206 DO - https://doi.org/10.1038/s41598-024-62591-1 VL - 14 SP - 1 EP - 16 AN - OPUS4-60220 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Reiber, T. A1 - Hübner, Oskar A1 - Dose, C. A1 - Yushchenko, D. A. A1 - Resch-Genger, Ute T1 - Fluorophore multimerization on a PEG backbone as a concept for signal amplification and lifetime modulation N2 - Fluorescent labels have strongly contributed to many advancements in bioanalysis, molecular biology, molecular imaging, and medical diagnostics. Despite a large toolbox of molecular and nanoscale fluorophores to choose from, there is still a need for brighter labels, e.g., for flow cytometry and fluorescence microscopy, that are preferably of molecular nature. This requires versatile concepts for fluorophore multimerization, which involves the shielding of dyes from other chromophores and possible quenchers in their neighborhood. In addition, to increase the number of readout parameters for fluorescence microscopy and eventually also flow cytometry, control and tuning of the labels’ fluorescence lifetimes is desired. Searching for bright multi-chromophoric or multimeric labels, we developed PEGylated dyes bearing functional groups for their bioconjugation and explored their spectroscopic properties and photostability in comparison to those of the respective monomeric dyes for two exemplarily chosen fluorophores excitable at 488 nm. Subsequently, these dyes were conjugated with anti-CD4 and anti-CD8 immunoglobulins to obtain fluorescent conjugates suitable for the labeling of cells and beads. Finally, the suitability of these novel labels for fluorescence lifetime imaging and target discrimination based upon lifetime measurements was assessed. Based upon the results of our spectroscopic studies including measurements of fluorescence quantum yields (QY) and fluorescence decay kinetics we could demonstrate the absence of significant dye-dye interactions and self-quenching in these multimeric labels. Moreover, in a first fluorescence lifetime imaging (FLIM) study, we could show the future potential of this multimerization concept for lifetime discrimination and multiplexing. KW - Imaging KW - Quantum yield KW - Quality assurance KW - Antibody KW - Conjugate KW - Cell KW - FLIM KW - PEG KW - Flow cytometry KW - Lifetime KW - Energy transfer KW - Quantitative spectroscopy KW - Nano KW - Particle KW - Fluorescence KW - Dye KW - Amplification KW - Microscopy PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-602197 DO - https://doi.org/10.1038/s41598-024-62548-4 VL - 14 IS - 1 SP - 1 EP - 11 AN - OPUS4-60219 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - López-Iglesias, C. A1 - Markovina, A. A1 - Nirmalananthan-Budau, N. A1 - Resch-Genger, Ute A1 - Klinger, D. T1 - Optically monitoring the microenvironment of a hydrophobic cargo in amphiphilic nanogels: influence of network composition on loading and release N2 - Amphiphilic nanogels (ANGs) are promising carriers for hydrophobic cargos such as drugs, dyes, and catalysts. Loading content and release kinetics of these compounds are controlled by type and number of hydrophobic groups in the amphiphilic copolymer network. Thus, understanding the interactions between cargo and colloidal carrier is mandatory for a tailor-made and cargo-specific ANG design. To systematically explore the influence of the network composition on these interactions, we prepared a set of ANGs of different amphiphilicity and loaded these ANGs with varying concentrations of the solvatochromic dye Nile Red (NR). Here, NR acts as a hydrophobic model cargo to optically probe the polarity of its microenvironment. Analysis of the NR emission spectra as well as measurements of the fluorescence quantum yields and decay kinetics revealed a decrease in the polarity of the NR microenvironment with increasing hydrophobicity of the hydrophobic groups in the ANG network and dye–dye interactions at higher loading concentrations. At low NR concentrations, the hydrophobic cargo NR is encapsulated in the hydrophobic domains. Increasing NR concentrations resulted in probe molecules located in a more hydrophilic environment, i.e., at the nanodomain border, and favored dye–dye interactions and NR aggregation. These results correlate well with release experiments, indicating first NR release from more hydrophilic network locations. Overall, our findings demonstrate the importance to understand carrier–drug interactions for efficient loading and controlled release profiles in amphiphilic nanogels. KW - Particle KW - Energy transfer KW - Limit of detection KW - Polymer KW - Luminescence KW - Quantitative spectroscopy KW - Nano KW - Quantum yield KW - Lifetime KW - Quality assurance KW - Dye KW - Probe KW - Sensor KW - Nile Red PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-601603 DO - https://doi.org/10.1039/d4nr00051j SN - 2040-3364 IS - 16 SP - 9525 EP - 9535 PB - The Royal Society of Chemistry AN - OPUS4-60160 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Fiedler, Saskia A1 - Frenzel, Florian A1 - Würth, Christian A1 - Tavernaro, Isabella A1 - Grüne, M. A1 - Schweizer, S. A1 - Engel, A. A1 - Resch-Genger, Ute T1 - Interlaboratory Comparison on Absolute Photoluminescence Quantum Yield Measurements of Solid Light Converting Phosphors with Three Commercial Integrating Sphere Setups N2 - Scattering luminescent materials dispersed in liquid and solid matrices and luminescent powders are increasingly relevant for fundamental research and industry. Examples are luminescent nano- and microparticles and phosphors of different compositions in various matrices or incorporated into ceramics with applications in energy conversion, solid-state lighting, medical diagnostics, and security barcoding. The key parameter to characterize the performance of these materials is the photoluminescence/fluorescence quantum yield (Φf), i.e., the number of emitted photons per number of absorbed photons. To identify and quantify the sources of uncertainty of absolute measurements of Φf of scattering samples, the first interlaboratory comparison (ILC) of three laboratories from academia and industry was performed by following identical measurement protocols. Thereby, two types ofcommercial stand-alone integrating sphere setups with different illumination and detection geometries were utilized for measuring the Φf of transparent and scattering dye solutions and solid phosphors, namely, YAG:Ce optoceramics of varying surface roughness, used as converter materials for blue light emitting diodes. Special emphasis was dedicated to the influence of the measurement geometry, the optical properties of the blank utilized to determine the number of photons of the incident excitation light absorbed by the sample, and the sample-specific surface roughness. While the Φf values of the liquid samples matched between instruments, Φf measurements of the optoceramics with different blanks revealed substantial differences. The ILC results underline the importance of the measurement geometry, sample position, and blank for reliable Φf data of scattering the YAG:Ce optoceramics, with the blank’s optical properties accounting for uncertainties exceeding 20%. KW - Nano KW - Fluorescence KW - Reference material KW - Luminescence KW - Quantitative spectroscopy KW - Particle KW - Quantum yield KW - Quality assurance KW - Phosphor KW - Converter material KW - Lifetime KW - Interlaboratory comparison KW - Method KW - Uncertainty PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-600945 DO - https://doi.org/10.1021/acs.analchem.4c00372 SN - 0003-2700 SP - 6730 EP - 6737 PB - ACS Publications AN - OPUS4-60094 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wegner, Karl David A1 - Resch-Genger, Ute T1 - The 2023 Nobel Prize in Chemistry: Quantum dots N2 - The 2023 Nobel Prize in Chemistry was awarded to Aleksey I. Ekimov (prize share 1/3), Louis E. Brus (prize share 1/3), and Moungi G. Bawendi (prize share 1/3) for groundbreaking inventions in the field of nanotechnology, i.e., for the discovery and synthesis of semiconductor nanocrystals, also termed quantum dots, that exhibit size-dependent physicochemical properties enabled by quantum size effects. This feature article summarizes the main milestones of the discoveries and developments of quantum dots that paved the road to their versatile applications in solid-state lighting, display technology, energy conversion, medical diagnostics, bioimaging, and image-guided surgery. KW - Quantum dots KW - Semiconductor nanocrystals KW - Luminescence KW - Quantitative spectroscopy KW - Quantum yield KW - Advanced nanomaterials KW - Quality assurance KW - Energy transfer PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-597843 DO - https://doi.org/10.1007/s00216-024-05225-9 VL - 2024 SP - 1 EP - 11 PB - Springer CY - Cham AN - OPUS4-59784 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Potopnyk, M. A1 - Mech-Piskorz, J. A1 - Angulo, G. A1 - Ceborska, M. A1 - Luboradzki, R. A1 - Andresen, Elina A1 - Gajek, A. A1 - Wisniewska, A. A1 - Resch-Genger, Ute T1 - Aggregation/Crystallization-Induced Emission in Naphthyridine-Based Carbazolyl-Modified Donor-Acceptor Boron Dyes Tunable by Fluorine Atoms N2 - Four donor-acceptor boron difluoride complexes based on the carbazole electron donor and the [1,3,5,2]oxadiazaborinino[3,4-a][1,8]naphthyridine acceptor were designed, synthesized, and systematically spectroscopically investigated in solutions, in the solid states, and dye-doped polymer films. The dyes exhibit an intense blue to red solid-state emission with photoluminescence quantum yields of up to 56% in pure dye samples and 86% in poly(methyl methacrylate) films. All boron complexes show aggregation-induced emission and reversible mechanofluorochromism. The optical properties of these dyes and their solid state luminescence can be tuned by substitution pattern, i.e., the substituents at the naphthyridine unit. Exchange of CH3- for CF3-groups does not only increase the intramolecular charge transfer character, but also provides a crystallization-induced emission enhancement. KW - Spectroscopy KW - Dye KW - Luminescence KW - Sensor KW - Fluorescence KW - Quantum yield KW - Lifetime KW - Quality assurance KW - Synthesis PY - 2024 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-597426 DO - https://doi.org/10.1002/chem.202400004 SN - 0947-6539 SP - 1 EP - 12 PB - Wiley VHC-Verlag AN - OPUS4-59742 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Oskolkova, Tatiana O. A1 - Matiushkina, Anna A. A1 - Borodina, Lyubov' N. A1 - Smirnova, Ekaterina S. A1 - Dadadzhanova, Antonina I. A1 - Sewid, Fayza A. A1 - Veniaminov, Andrey V. A1 - Moiseeva, Ekaterina O. A1 - Orlova, Anna O. T1 - FRET‐Amplified Singlet Oxygen Generation by Nanocomposites Comprising Ternary AgInS2/ZnS Quantum Dots and Molecular Photosensitizers N2 - Antibacterial photodynamic therapy (a‐PDT) has emerged as a promising non‐invasive therapeutic modality that utilizes the combination of a photosensitive agent, molecular oxygen, and excitation light to generate reactive oxygen species (ROS), demonstrating remarkable activity against multidrug‐resistant bacterial infections. However, the effective use of conventional photosensitizers is significantly limited by a number of their shortcomings, namely, poor water solubility and low selectivity. Herein, we present a novel biocompatible water‐soluble nanocomposite based on hydrophobic tetraphenylporphyrin (TPP) molecules and hydrophilic ternary AgInS2/ZnS quantum dots incorporated into a chitosan matrix as an improved photosensitizer for a‐PDT. We demonstrated that TPP molecules could be successfully transferred into chitosan solution while remaining primarily in the form of monomers, which are capable of singlet oxygen generation. We performed a detailed analysis of the Förster resonance energy transfer (FRET) between quantum dots and TPP molecules within the nanocomposite and proposed the mechanism of the singlet oxygen efficiency enhancement via FRET. KW - Nano KW - Particle KW - Quantum dot KW - Fluorescence KW - Synthesis KW - Optical spectroscopy KW - Energy transfer KW - Quality assurance KW - Lifetime KW - Quantum yield PY - 2024 DO - https://doi.org/10.1002/cnma.202300469 SN - 2199-692X VL - 10 IS - 3 SP - 1 EP - 11 PB - Wiley AN - OPUS4-59728 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Scholtz, Lena A1 - Tavernaro, Isabella A1 - Eckert, J. G. A1 - Lutowski, Marc A1 - Geißler, Daniel A1 - Hertwig, Andreas A1 - Hidde, Gundula A1 - Bigall, N. C. A1 - Resch-Genger, Ute T1 - Influence of nanoparticle encapsulation and encoding on the surface chemistry of polymer carrier beads N2 - Surface-functionalized polymer beads encoded with molecular luminophores and nanocrystalline emitters such as semiconductor nanocrystals, often referred to as quantum dots (QDs), or magnetic nanoparticles are broadly used in the life sciences as reporters and carrier beads. Many of these applications require a profound knowledge of the chemical nature and total number of their surface functional groups (FGs), that control bead charge, colloidal stability, hydrophobicity, and the interaction with the environment and biological systems. For bioanalytical applications, also the number of groups accessible for the subsequent functionalization with, e.g., biomolecules or targeting ligands is relevant. In this study, we explore the influence of QD encoding on the amount of carboxylic acid (COOH) surface FGs of 2 μm polystyrene microparticles (PSMPs). This is done for frequently employed oleic acid and oleylamine stabilized, luminescent core/shell CdSe QDs and two commonly used encoding procedures. This included QD addition during bead formation by a thermally induced polymerization reaction and a post synthetic swelling procedure. The accessible number of COOH groups on the surface of QD-encoded and pristine beads was quantified by two colorimetric assays, utilizing differently sized reporters and electrostatic and covalent interactions. The results were compared to the total number of FGs obtained by a conductometric titration and Fourier transform infrared spectroscopy (FTIR). In addition, a comparison of the impact of QD and dye encoding on the bead surface chemistry was performed. Our results demonstrate the influence of QD encoding and the QD-encoding strategy on the number of surface FG that is ascribed to an interaction of the QDs with the carboxylic acid groups on the bead surface. These findings are of considerable relevance for applications of nanoparticle-encoded beads and safe-by-design concepts for nanomaterials. KW - Optical spectroscopy KW - Particle KW - Optical assay KW - IR spectroscopy KW - Fluorescence KW - Quantum yield KW - Quality assurance KW - Nano KW - Synthesis KW - Surface chemistry KW - Quantification KW - Method KW - Conductometry PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-581502 DO - https://doi.org/10.1038/s41598-023-38518-7 SN - 2045-2322 VL - 13 IS - 1 SP - 1 EP - 15 PB - Springer Nature CY - London AN - OPUS4-58150 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pauli, J. A1 - Güttler, Arne A1 - Schneider, T. A1 - Würth, Christian A1 - Resch-Genger, Ute T1 - Fluorescence Quantum Yield Standards for the UV/Visible/NIR: Development, Traceable Characterization, and Certification N2 - The rational design of next generation molecular and nanoscale reporters and the comparison of different emitter classes require the determination of the fluorometric key performance parameter fluorescence quantum yield (Φf), i.e., the number of emitted photons per number of absorbed photons. Main prerequisites for reliable Φf measurements, which are for transparent luminophore solutions commonly done relative to a reference, i.e., a fluorescence quantum yield standard of known Φf, are reliable and validated instrument calibration procedures to consider wavelength-, polarization-, and time-dependent instrument specific signal contributions, and sufficiently well characterized fluorescence quantum yield standards. As the standard’s Φf value directly contributes to the calculation of the sample’s Φf, its accuracy presents one of the main sources of uncertainty of relative Φf measurements. To close this gap, we developed a first set of 12 fluorescence quantum yield standards, which absorb and emit in the wavelength region of 330−1000 nm and absolutely determined their Φf values with two independently calibrated integrating sphere setups. Criteria for standard selection and the configuration of these novel fluorescence reference materials are given, and the certification procedure is presented including homogeneity and stability studies and the calculation of complete uncertainty budgets for the certified Φf values. The ultimate goal is to provide the community of fluorescence users with available reference materials as a basis for an improved comparability and reliability of quantum yield data since the measurement of this spectroscopic key property is an essential part of the characterization of any new emitter. KW - Optical spectroscopy KW - Traceability KW - Reference product KW - Dye KW - Fluorescence KW - Quantum yield KW - Reference material KW - Reference data KW - Certification KW - Quality assurance PY - 2023 DO - https://doi.org/10.1021/acs.analchem.2c05530 VL - 95 SP - 5671 EP - 5677 PB - American Chemical Society AN - OPUS4-58151 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Würth, Christian A1 - Behnke, Thomas A1 - Gienger, J. A1 - Resch-Genger, Ute T1 - Efficiency scale for scatteringluminescent particles linkedto fundamental and measurablespectroscopic properties N2 - Comparing the performance of molecular and nanoscale luminophores and luminescent microand nanoparticles and estimating achievable signal amplitudes and limits of detection requires a standardizable intensity scale. This initiated the development of the relative MESF (number of molecules of equivalent soluble fluorochromes) and ERF (equivalent reference fluorophores) scales for flow cytometry and fluorescence microscopy. Both intensity scales rely on fluorescence intensity values assigned to fluorescent calibration beads by an intensity comparison to spectrally closely matching fluorophore solutions of known concentration using a spectrofluorometer. Alternatively, the luminophore or bead brightness (B) can be determined that equals the product of the absorption cross section (σa) at the excitation wavelength (σa(λex)) and the photoluminescence quantum yield (Φpl). Thereby, an absolute scale based on fundamental and measurable spectroscopic properties can be realized which is independent of particle size, material, and luminophore staining or labeling density and considers the sensitivity of the optical properties of luminophores to their environment. Aiming for establishing such a brightness scale for light-scattering dispersions of luminescent particles with sizes exceeding a few ten nanometers, we demonstrate how the brightness of quasi-monodisperse 25 nm, 100 nm, and 1 μm sized polystyrene particles (PSP), loaded with two different dyes in varying concentrations, can be obtained with a single custom-designed integrating sphere setup that enables the absolute determination of Φpl and transmittance and diffuse reflectance measurements. The resulting Φpl, σa(λex), imaginary parts of the refractive index, and calculated B values of these samples are given in dependence of the number of incorporated dye molecule per particle. Finally, a unitless luminescence efficiency (LE) is defined allowing for the direct comparison of luminescence efficiencies of particles with different sizes. KW - Brightness KW - Quantum yield KW - Cross section KW - Lluminescence PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-573680 DO - https://doi.org/10.1038/s41598-023-32933-6 VL - 13 IS - 1 SP - 14 PB - Nature AN - OPUS4-57368 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wang, Cui A1 - Ebel, Kenny A1 - Heinze, Katja A1 - Resch-Genger, Ute A1 - Bald, Ilko T1 - Quantum Yield of DNA Strand Breaks under Photoexcitation of a Molecular Ruby N2 - Photodynamic therapy (PDT) used for treating cancer relies on the generation of highly reactive oxygen species, for example, singlet oxygen 1O2, by light-induced excitation of a photosensitizer (PS) in the presence of molecular oxygen, inducing DNA damage in close proximity of the PS. Although many precious metal complexes have been explored as PS for PDT and received clinical approval, only recently, the potential of photoactive complexes of nonnoble metals as PS has been discovered. Using the DNA origami technology that can absolutely quantify DNA strand break cross sections, we assessed the potential of the luminescent transition metal complex [Cr(ddpd)2]3+ (ddpd=N,N’-dimethyl-N,N’-dipyridine-2-ylpyridine-2,6-diamine) to damage DNA in an air-saturated aqueous environment upon UV/Vis illumination. The quantum yield for strand breakage, that is, the ratio of DNA strand breaks to the number of absorbed photons, was determined to 1–4%, indicating efficient transformation of photons into DNA strand breaks by [Cr(ddpd)2]3+. KW - Fluorescence KW - Synthesis KW - Production KW - Optical spectroscopy KW - Ligand KW - Photophysics KW - Cr(III) KW - Mechanism KW - NIR KW - PDT KW - Singlet oxygen KW - DNA KW - Origami KW - Quantum yield PY - 2023 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-573631 DO - https://doi.org/10.1002/chem.202203719 SP - 1 EP - 7 AN - OPUS4-57363 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Meng, M. A1 - Zhang, T. A1 - Wang, J. A1 - Cheng, Z. A1 - Yang, J. A1 - Qiao, X. A1 - Wen, J. A1 - Resch-Genger, Ute A1 - Ou, J. T1 - Fluorescence temperature sensing of NaYF4:Yb3+/Tm3+@NaGdF4:Nd3+/Yb3+ nanoparticles at low and high temperatures N2 - NaYF4:Yb3+/Tm3+@NaGdF4:Nd3+/Yb3+ upconversion nanoparticles (UCNPs) were prepared using a solvothermal method, and the effects of key factors such as the content of sensitiser Nd 3+ and Yb3+ on their luminescence properties were investigated. The nanoparticles are homogeneous in size and well dispersed. Under 808 nm excitation, it can produce strong upconversion fluorescence. At the same time, the nanoparticles have good temperature-sensing properties at the thermally coupled energy levels of 700 nm and 646 nm for Tm3+. Using its fluorescence intensity ratio (FIR), accurate temperature measurements can be performed, and it has been found that it exhibits different temperature sensing properties in low and high-temperature regions. The maximum relative sensitivity was found to be 0.88% K-1 and 1.89% K-1 for the lowtemperature region of 285 K-345 K and the high-temperature region of 345 K-495 K. The nanoparticles were applied to the internal temperature measurement of lithium batteries and the actual high-temperature environment, respectively, and were found to have good temperature measurementt performance. KW - Fluorescence KW - Sensor KW - Temperature KW - Ratiometric KW - Lanthanide KW - Quantum yield KW - Integrating sphere spectroscopy KW - Absolute fluorescence KW - Quality assurance KW - Nano KW - Particle KW - Application KW - Upconversion nanoparticle PY - 2022 DO - https://doi.org/10.1088/1361-6528/ac84e4 SN - 1361-6528 VL - 33 IS - 34 SP - 1 EP - 15 PB - IOP Publishing CY - Bristol AN - OPUS4-55454 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stroyuk, O. A1 - Raievska, O. A1 - Barabash, A. A1 - Batentschuk, M. A1 - Osvet, A. A1 - Fiedler, Saskia A1 - Resch-Genger, Ute A1 - Hauch, J. A1 - Brabec, C. J. T1 - “Green” Synthesis of Highly Luminescent Lead-Free Cs2AgxNa1-xBiyIn1-yCl6 Perovskites N2 - A new “green” and mild synthesis of highly stable microcrystalline Cs2AgxNa1-xBiyIn1-yCl6 (CANBIC) perovskites under ambient conditions was developed that is scalable to the multi-gram production. Under UV illumination, the CANBIC perovskites emit intense broadband photoluminescence (PL) with a quantum yield (QY) of 92% observed for x = 0.35 and y = 0.01-0.02. The combination of strong UV absorbance and broadband visible emission, high PL QY, and long PL lifetimes of up to 1.4 μs, along with an outstanding stability makes these CANBICs a promising material class for many optical applications. KW - Fluorescence KW - Perovskites KW - Solar cell KW - Automated synthesis KW - Green synthesis KW - Quantum yield KW - Integrating sphere spectroscopy KW - Absolute fluorescence KW - Quality assurance KW - Nano KW - Particle KW - Application KW - Semiconductor KW - Quantum dot KW - Renewable energy PY - 2022 DO - https://doi.org/10.1039/d2tc02055f SN - 2050-7526 VL - 10 IS - 27 SP - 9938 EP - 9944 PB - Royal Society of Chemistry AN - OPUS4-55453 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zou, Q. A1 - Marcelot, C. A1 - Ratel-Ramond, N. A1 - Yi, X. A1 - Roblin, P. A1 - Frenzel, Florian A1 - Resch-Genger, Ute A1 - Eftekhari, A. A1 - Bouchet, A. A1 - Coudret, C. A1 - Verelst, M. A1 - Chen, X. A1 - Mauricot, R. A1 - Roux, C. T1 - Heterogeneous Oxysulfide@Fluoride Core/ Shell Nanocrystals for Upconversion-Based Nanothermometry N2 - Lanthanide (Ln3+)-doped upconversion nanoparticles (UCNPs) often suffer from weak luminescence, especially when their sizes are ultrasmall (less than 10 nm). Enhancing the upconversion luminescence (UCL) efficiency of ultrasmall UCNPs has remained a challenge that must be undertaken if any practical applications are to be envisaged. Herein, we present a Ln3+-doped oxysulfide@fluoride core/shell heterostructure which shows efficient UCL properties under 980nm excitation and good stability in solution. Through epitaxial heterogeneous growth, a ∼4 nm optically inert β-NaYF4 shell was coated onto ∼5 nm ultrasmall Gd2O2S:20%Yb,1%Tm. These Gd2O2S:20%Yb,1%Tm@NaYF4 core/shell UCNPs exhibit a more than 800-fold increase in UCL intensity compared to the unprotected core, a 180-fold increase in luminescence decay time of the 3H4 → 3H6 Tm3+ transition from 5 to 900 μs, and an upconversion quantum yield (UCQY) of 0.76% at an excitation power density of 155 W/cm2. Likewise, Gd2O2S:20%Yb,2%Er@NaYF4 core/shell UCNPs show a nearly 5000-fold increase of their UCL intensity compared to the Gd2O2S:20%Yb,2%Er core and a maximum UCQY of 0.61%. In the Yb/Er core−shell UCNP system, the observed variation of luminescence intensity ratio seems to originate from a change in lattice strain as the temperature is elevated. For nanothermometry applications, the thermal sensitivities based on thermally coupled levels are estimated for both Yb/Tm and Yb/Er doped Gd2O2S@NaYF4 core/shell UCNPs. KW - Upconversion nanoparticle KW - Nanosensor KW - Lanthanide KW - Surface coating KW - Quantum yield KW - Photophysic PY - 2022 DO - https://doi.org/10.1021/acsnano.2c02423 SN - 1936-0851 SP - 1 EP - 11 PB - ACS Publications AN - OPUS4-55440 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Srivastava, Priyanka A1 - Tavernaro, Isabella A1 - Genger, C. A1 - Welker, P. A1 - Huebner, Oskar A1 - Resch-Genger, Ute T1 - Multicolor Polystyrene Nanosensors for the Monitoring of Acidic, Neutral, and Basic pH Values and Cellular Uptake Studies N2 - A first tricolor fluorescent pH nanosensor is presented, which was rationally designed from biocompatible carboxylated polystyrene nanoparticles and two analyte-responsive molecular fluorophores. Its fabrication involved particle staining with a blue-red-emissive dyad, consisting of a rhodamine moiety responsive to acidic pH values and a pH-inert quinoline fluorophore, followed by the covalent attachment of a fluorescein dye to the particle surface that signals neutral and basic pH values with a green fluorescence. These sensor particles change their fluorescence from blue to red and green, depending on the pH and excitation wavelength, and enable ratiometric pH measurements in the pH range of 3.0−9.0. The localization of the different sensor dyes in the particle core and at the particle surface was confirmed with fluorescence microscopy utilizing analogously prepared polystyrene microparticles. To show the application potential of these polystyrene-based multicolor sensor particles, fluorescence microscopy studies with a human A549 cell line were performed, which revealed the cellular uptake of the pH nanosensor and the differently colored emissions in different cell organelles, that is, compartments of the endosomal-lysosomal pathway. Our results demonstrate the underexplored potential of biocompatible polystyrene particles for multicolor and multianalyte sensing and bioimaging utilizing hydrophobic and/or hydrophilic stimuli-responsive luminophores. KW - Microparticle KW - Fluorescence KW - Sensor KW - pH KW - Quantum yield KW - Multiplexing KW - Imaging KW - Cell KW - Quality assurance KW - Nano KW - Polymer KW - Bioimaging KW - Particle KW - Application PY - 2022 DO - https://doi.org/10.1021/acs.analchem.2c00944 VL - 94 IS - 27 SP - 9656 EP - 9664 PB - ACS AN - OPUS4-55365 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Clark, P.C.J A1 - Andresen, Elina A1 - Sear, M. J. A1 - Favaro, M. A1 - Girardi, L. A1 - van de Krol, R. A1 - Resch-Genger, Ute A1 - Starr, D.E. T1 - Quantification of the Activator and Sensitizer Ion Distributions in NaYF4:Yb3+, Er3+ Upconverting Nanoparticles Via Depth-Profiling with Tender X-Ray Photoemission N2 - The spatial distribution and concentration of lanthanide activator and sensitizer dopant ions are of key importance for the luminescence color and efficiency of upconverting nanoparticles (UCNPs). Quantifying dopant ion distributions and intermixing, and correlating them with synthesis methods require suitable analytical techniques. Here, X-ray photoelectron spectroscopy depth-profiling with tender X-rays (2000–6000 eV), providing probe depths ideally matched to UCNP sizes, is used to measure the depth-dependent concentration ratios of Er3+ to Yb3+, [Er3+]/[Yb3+], in three types of UCNPs prepared using different reagents and synthesis methods. This is combined with data simulations and inductively coupled plasma-optical emission spectroscopy (ICP-OES) measurements of the lanthanide ion concentrations to construct models of the UCNPs’ dopant ion distributions. The UCNP sizes and architectures are chosen to demonstrate the potential of this approach. Core-only UCNPs synthesized with XCl3·6H2O precursors (β-phase) exhibit a homogeneous distribution of lanthanide ions, but a slightly surface-enhanced [Er3+]/[Yb3+] is observed for UCNPs prepared with trifluroacetate precursors (α-phase). Examination of Yb-core@Er-shell UCNPs reveals a co-doped, intermixed region between the single-doped core and shell. The impact of these different dopant ion distributions on the UCNP's optical properties is discussed to highlight their importance for UCNP functionality and the design of efficient UCNPs. KW - Shell KW - Nanomaterial KW - Nano KW - Upconversion nanoparticle KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Excitation power density KW - Surface KW - Coating KW - Core-shell KW - XPS KW - Intermixing KW - HAXPES KW - Method PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-552075 DO - https://doi.org/10.1002/smll.202107976 SN - 1613-6813 SP - 1 EP - 13 PB - Wiley-VCH-Verlag CY - Weinheim, Germany AN - OPUS4-55207 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Würth, Christian A1 - Grauel, Bettina A1 - Pons, Monika A1 - Frenzel, Florian A1 - Rissiek, P. A1 - Rücker, Kerstin A1 - Haase, Markus A1 - Resch-Genger, Ute T1 - Yb- and Er concentration dependence of the upconversion luminescence of highly doped NaYF4:Yb,Er/NaYF4:Lu core/shell nanocrystals prepared by a water-free synthesis N2 - High sensitizer and activator concentrations have been increasingly examined to improve the performance of multi-color emissive upconversion (UC) nanocrystals (UCNC) like NaYF4:Yb,Er and first strategies were reported to reduce concentration quenching in highly doped UCNC. UC luminescence (UCL) is, however, controlled not only by dopant concentration, yet by an interplay of different parameters including size, crystal and shell quality, and excitation power density (P). Thus, identifying optimum dopant concentrations requires systematic studies of UCNC designed to minimize additional quenching pathways and quantitative spectroscopy. Here, we quantify the dopant concentration dependence of the UCL quantum yield (ΦUC) of solid NaYF4:Yb,Er/NaYF4:Lu upconversion core/shell nanocrystals of varying Yb3+ and Er3+ concentrations (Yb3+ series: 20%‒98% Yb3+; 2% Er3+; Er3+ series: 60% Yb3+; 2%‒40% Er3+). To circumvent other luminescence quenching processes, an elaborate synthesis yielding OH-free UCNC with record ΦUC of ~9% and ~25 nm core particles with a thick surface shell were used. High Yb3+ concentrations barely reduce ΦUC from ~9% (20% Yb3+) to ~7% (98% Yb3+) for an Er3+ concentration of 2%, thereby allowing to strongly increase the particle absorption cross section and UCNC brightness. Although an increased Er3+ concentration reduces ΦUC from ~7% (2% Er3+) to 1% (40%) for 60% Yb3+. Nevertheless, at very high P (> 1 MW/cm2) used for microscopic studies, highly Er3+-doped UCNC display a high brightness because of reduced saturation. These findings underline the importance of synthesis control and will pave the road to many fundamental studies of UC materials. KW - Upconverion KW - Nanoparticle KW - Lanthanides KW - Quantum yield PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-551346 DO - https://doi.org/10.1007/s12274-022-4570-5 SP - 1 EP - 8 PB - Springer AN - OPUS4-55134 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bertorelle, F. A1 - Wegner, Karl David A1 - Berkulic, M. P. A1 - Fakhouri, H. A1 - Comby-Zerbino, C. A1 - Sagar, A. A1 - Bernadó, P. A1 - Resch-Genger, Ute A1 - Bonacic-Koutecký, V. A1 - Le Guével, X. A1 - Antoine, R. T1 - Tailoring the NIR-II Photoluminescence of Single Thiolated Au25 Nanoclusters by Selective Binding to Proteins N2 - Atomically precise gold nanoclusters are a fascinating class of nanomaterials that exhibit molecule-like properties and have outstanding photoluminescence (PL). Their ultrasmall size, molecular chemistry, and biocompatibility make them extremely appealing for selective biomolecule labeling in investigations of biological mechanisms at the cellular and anatomical levels. In this work, we report a simple route to incorporate a preformed Au25 nanocluster into a model bovine serum albumin (BSA) protein. A new approach combining small-angle X-ray scattering and molecular modeling provides a clear localization of a single Au25 within the protein to a cysteine residue on the gold nanocluster surface. Attaching Au25 to BSA strikingly modifies the PL properties with enhancement and a redshift in the second near-infrared (NIR-II) window. This study paves the way to conrol the design of selective sensitive probes in biomolecules through a ligand-based strategy to enable the optical detection of biomolecules in a cellular environment by live imaging. KW - Fluorescence KW - Aggregation KW - Signal enhancement KW - Cluster KW - Nano KW - Metal KW - NIRII KW - SWIR KW - Sensor KW - Quantum yield KW - Lifetime KW - Photophysics KW - Synthesis KW - Protein KW - Imaging KW - Bioimaging KW - Ligand KW - Gold PY - 2022 DO - https://doi.org/10.1002/chem.202200570 SN - 1521-3765 VL - 28 IS - 39 SP - 1 EP - 8 PB - Wiley-VCH CY - Weinheim AN - OPUS4-55077 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kromer, Ch. A1 - Schwibbert, K. A1 - Gadicherla, A. K. A1 - Thiele, D. A1 - Nirmalananthan-Budau, Nithiya A1 - Laux, P. A1 - Resch-Genger, Ute A1 - Luch, A. A1 - Tschiche, H. R. T1 - Monitoring and imaging pH in biofilms utilizing a fluorescent polymeric nanosensor N2 - Biofilms are ubiquitous in nature and in the man-made environment. Given their harmful effects on human health, an in-depth understanding of biofilms and the monitoring of their formation and growth are important. Particularly relevant for many metabolic processes and survival strategies of biofilms is their extracellular pH. However, most conventional techniques are not suited for minimally invasive pH measurements of living biofilms. Here, a fluorescent nanosensor is presented for ratiometric measurements of pH in biofilms in the range of pH 4.5–9.5 using confocal laser scanning microscopy. The nanosensor consists of biocompatible polystyrene nanoparticles loaded with pH-inert dye Nile Red and is surface functionalized with a pH-responsive fluorescein dye. Its performance was validated by fluorometrically monitoring the time-dependent changes in pH in E. coli biofilms after glucose inoculation at 37 °C and 4 °C. This revealed a temperature-dependent decrease in pH over a 4-h period caused by the acidifying glucose metabolism of E. coli. These studies demonstrate the applicability of this nanosensor to characterize the chemical microenvironment in biofilms with fluorescence methods. KW - Dye KW - Fluorescence KW - Signal enhancement KW - Sensor KW - Quantum yield KW - Synthesis KW - Nanoparticle KW - Nano KW - Polymer KW - Ph KW - Biofilm KW - MIC KW - Corrosion KW - Microorganism KW - Bacteria PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-550751 DO - https://doi.org/10.1038/s41598-022-13518-1 SN - 2045-2322 VL - 12 IS - 1 SP - 1 EP - 10 PB - Nature Publishing Group CY - London AN - OPUS4-55075 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Biesen, L. A1 - Krenzer, J. A1 - Nirmalananthan-Budau, Nithiya A1 - Resch-Genger, Ute A1 - Müller, Th. J. J. T1 - Asymmetrically bridged aroyl-S,N-ketene acetalbased multichromophores with aggregationinduced tunable emission N2 - Asymmetrically bridged aroyl-S,N-ketene acetals and aroyl-S,N-ketene acetal multichromophores can be readily synthesized in consecutive three-, four-, or five-component syntheses in good to excellent yields by several successive Suzuki-couplings of aroyl-S,N-ketene acetals and bis(boronic)acid esters. Different aroyl-S,N-ketene acetals as well as linker molecules yield a library of 23 multichromophores with substitution and linker pattern-tunable emission properties. This allows control of different communication pathways between the chromophores and of aggregation-induced emission (AIE) and energy transfer (ET) properties, providing elaborate aggregation-based fluorescence switches. KW - Dye KW - Aggregation KW - Aggregation induced emission KW - Signal enhancement KW - Energy transfer KW - Switch KW - Sensor KW - Quantum yield KW - Lifetime KW - Photophysics KW - Sythesis KW - Nanaoparticle PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-550719 DO - https://doi.org/10.1039/d2sc00415a VL - 13 SP - 5374 EP - 5381 PB - Royal Society of Chemistry AN - OPUS4-55071 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Fa, X. A1 - Lin, Sh. A1 - Yang, J. A1 - Shen, Ch. A1 - Liu, Y. A1 - Gong, Y. A1 - Qin, A. A1 - Ou, Jun A1 - Resch-Genger, Ute T1 - −808 nm-activated Ca2+ doped up-conversion nanoparticles that release no inducing liver cancer cell (HepG2) apoptosis N2 - Anear-infrared (NIR) light-triggered release method for nitric oxide (NO) was developed utilizing core/shell NaYF4: Tm/Yb/Ca@NaGdF4:Nd/Yb up-conversion nanoparticles (UCNPs) bearing a mesoporous silica (mSiO2) shell loaded with theNOdonor S-nitroso-N-acetyl-DL-penicillamine (SNAP). To avoid overheating in biological samples, Nd3+ was chosen as a sensitizer, Yb3+ ions as the bridging sensitizer, andTm3+ ions as UV-emissive activator while co-doping with Ca2+ was done to enhance the luminescence of the activatorTm3+.NOrelease from SNAP was triggered by an NIR-UV up-conversion process, initiated by 808nmlight absorbed by the Nd3+ ions.NOrelease was confirmed by the Griess method. Under 808nmirradiation, the viability of the liver cancer cell line HepG2 significantly decreased with increasing UCNPs@mSiO2-SNAP concentration. For a UCNPs@mSiO2-SNAP concentration of 200 μgml−1, the cell survival probability was 47%. These results demonstrate that UCNPs@mSiO2-SNAP can induce the release of apoptosis-inducingNOby NIR irradiation. KW - Nano KW - Nanomaterial KW - Upconversion nanoparticle KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Lifetime KW - Sensor KW - Excitation power density KW - Brightness KW - NIR KW - Mechanism KW - Triggered KW - Release KW - Cell KW - PDT KW - Dye KW - Therapy KW - Surface KW - Coating PY - 2022 DO - https://doi.org/10.1088/2050-6120/ac5524 VL - 10 IS - 2 SP - 1 EP - 9 PB - IOP Publishing AN - OPUS4-54842 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wang, Cui A1 - Kitzmann, W.R. A1 - Weigert, Florian A1 - Förster, Ch. A1 - Wang, X. A1 - Heintze, K. A1 - Resch-Genger, Ute T1 - Matrix Effects on Photoluminescence and Oxygen Sensitivity of a Molecular Ruby N2 - The molecular ruby analogue [Cr(ddpd)2]3+ (ddpd=N,N’-dimethyl-N,N’-dipyridine-2-ylpyridine-2,6-diamine) exhibits near infrared (NIR) emission with a high photoluminescence (PL) quantum yield ΦPL of 11 % and a lifetime of 898 μs in deaerated water at room temperature. While ligand-based control of the photophysical properties has received much attention, influences of the counter anions and microenvironment are still underexplored. In this study, the luminescence properties of the molecular ruby were systematically examined for the counter anions Cl−, Br−, [BF4]−, [PF6]−, [BPh4]−, and [BArF24]− in acetonitrile (MeCN) solution, in crystals, and embedded into polystyrene nanoparticles (PSNP). Stern-Volmer analyses of the oxygen quenching studies in the intensity and lifetime domain showed the highest oxygen sensitivity of the complexes with the counter anions of [BF4]− and [BArF24]−, which also revealed the longest luminescence lifetimes. Embedding [Cr(ddpd)2][PF6]3 in PSNPs and shielding with poly(vinyl alcohol) yields a strongly NIR-emissive oxygen-insensitive material with a record ΦPL of 15.2 % under ambient conditions. KW - Fluorescence KW - Sensor KW - Oxygen KW - Quantum yield KW - Quality assurance KW - Complex KW - Cr(III) KW - Lifetime KW - Ligand KW - Solid state KW - X-Ray analysis KW - Structure-property relationship KW - Nano KW - Polymer KW - Particle PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-546057 DO - https://doi.org/10.1002/cptc.202100296 SN - 2367-0932 VL - 6 IS - 6 SP - 1 EP - 9 PB - Wiley-VCH CY - Weinheim AN - OPUS4-54605 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wang, Cui A1 - Reichenauer, F. A1 - Kitzmann, W.R. A1 - Kerzig, Ch. A1 - Heintze, K. A1 - Resch-Genger, Ute T1 - Efficient Triplet-Triplet Annihilation Upconversion Sensitized by a Chromium(III) Complex via an Underexplored Energy Transfer Mechanism N2 - Sensitized triplet-triplet annihilation upconversion (sTTA-UC) mainly relies on precious metal complexes thanks to their high intersystem crossing (ISC) efficiencies, excited state energies, and lifetimes, while complexes of abundant first-row transition metals were only rarely utilized and with often moderate UC quantum yields. [Cr(bpmp)2]3+ (bpmp = 2,6-bis(2-pyridylmethyl)pyridine) containing earth-abundant chromium possesses an absorption band suitable for green light excitation, a doublet excited state energy matching the triplet energy of 9,10-diphenyl anthracene (DPA), a close to millisecond excited state lifetime, and high photostability. Combined ISC and doublet-triplet energy transfer from excited [Cr(bpmp)2]3+ to DPA gives 3DPA with close-to-unity quantum yield. TTA of 3DPA furnishes greento-blue UC with a quantum yield of 12.0 % (close to the theoretical maximum). Sterically less-hindered anthracenes undergo a [4+4] cycloaddition with [Cr(bpmp)2]3+ and green light. KW - Fluorescence KW - Optical probe KW - Sensor KW - ph KW - Quantum yield KW - Quality assurance KW - Cr(III) KW - Lifetime KW - Ligand KW - Theory KW - TTA-UC KW - Energy transfer KW - Upconversion KW - Mechanism KW - Anthracene KW - Photochemistry KW - DFT KW - Cycloaddition KW - Transient absorbtion spectroscopy PY - 2022 DO - https://doi.org/10.1002/anie.202202238 VL - 61 IS - 24 SP - 1 EP - 8 PB - Wiley online library AN - OPUS4-54604 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bastos, V. A1 - Oskoei, P. A1 - Andresen, Elina A1 - Saleh, Maysoon I. A1 - Rühle, Bastian A1 - Resch-Genger, Ute A1 - Oliveira, H. T1 - Stability, dissolution, and cytotoxicity of NaYF4‑upconversion nanoparticles with different coatings N2 - Upconversion nanoparticles (UCNPs) have attracted considerable attention owing to their unique photophysical properties. Their utilization in biomedical applications depends on the understanding of their transformations under physiological conditions and their potential toxicity. In this study, NaYF4: Yb,Er UCNPs, widely used for luminescence and photophysical studies, were modified with a set of four different coordinatively bound surface ligands, i.e., citrate, alendronate (AA), ethylendiamine tetra(methylene phosphonate) (EDTMP), and poly(maleic anhydride-alt-1-octadecene) (PMAO), as well as silica coatings with two different thicknesses. Subsequently, the aging-induced release of fluoride ions in water and cell culture media and their cytotoxic profile to human keratinocytes were assessed in parallel to the cytotoxic evaluation of the ligands, sodium fluoride and the lanthanide ions. The cytotoxicity studies of UCNPs with different surface modifications demonstrated the good biocompatibility of EDTMP-UCNPs and PMAO-UCNPs, which is in line with the low amount of fluoride ions released from these samples. An efficient prevention of UCNP dissolution and release of cytotoxic ions, as well as low cytotoxicity was also observed for UCNPs with a sufficiently thick silica shell. Overall, our results provide new insights into the understanding of the contribution of surface chemistry to the stability, dissolution behavior, and cytotoxicity of UCNPs. Altogether, the results obtained are highly important for future applications of UCNPs in the life sciences and bioimaging studies. KW - Nano KW - Nanomaterial KW - Upconversion nanoparticle KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Excitation power density KW - Surface chemistry KW - Coating PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-544681 DO - https://doi.org/10.1038/s41598-022-07630-5 SN - 2045-2322 VL - 12 SP - 1 EP - 13 PB - Springer Nature CY - London AN - OPUS4-54468 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bandi, V.G. A1 - Luciano, M.P. A1 - Saccomano, M. A1 - Patel, N.L. A1 - Bischof, Th. S. A1 - Lingg, J.G.P. A1 - Tsrunchev, P.T. A1 - Nix, M.N. A1 - Ruehle, Bastian A1 - Sanders, C. A1 - Riffle, L. A1 - Robinson, C.M. A1 - Difilippantonio, S. A1 - Kalen, J.D. A1 - Resch-Genger, Ute A1 - Ivanic, J. A1 - Bruns, O.T. A1 - Schnermann, M. T1 - Targeted multicolor in vivo imaging over 1,000 nm enabled by nonamethine cyanines N2 - Recent progress has shown that using wavelengths between 1,000 and 2,000 nm, referred to as the shortwave-infrared or near-infrared (NIR)-II range, can enable high-resolution in vivo imaging at depths not possible with conventional optical wavelengths. However, few bioconjugatable probes of the type that have proven invaluable for multiplexed imaging in the visible and NIR range are available for imaging these wavelengths. Using rational design, we have generated persulfonated indocyanine dyes with absorbance maxima at 872 and 1,072 nm through catechol-ring and aryl-ring fusion, respectively, onto the nonamethine scaffold. Multiplexed two-color and three-color in vivo imaging using monoclonal antibody and dextran conjugates in several tumor models illustrate the benefits of concurrent labeling of the tumor and healthy surrounding tissue and lymphatics. These efforts are enabled by complementary advances in a custom-built NIR/shortwave-infrared imaging setup and software package for multicolor real-time imaging. KW - Photoluminescence KW - Fluorescence KW - Dye KW - Cyanine KW - Antibody KW - Bioconjugate KW - Conjugate KW - Quantum yield KW - Photophysics KW - Lifetime KW - Sensor KW - NIR KW - SWIR KW - Mechanism KW - Imaging KW - Application KW - Contrast agent KW - Bioimaging PY - 2021 DO - https://doi.org/10.1038/s41592-022-01394-6 VL - 19 IS - 3 SP - 353 EP - 358 PB - Nature Research AN - OPUS4-54465 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Le Guevel, X. A1 - Wegner, Karl David A1 - Würth, Christian A1 - Baulin, V. A. A1 - Musnier, B. A1 - Josserand, V. A1 - Resch-Genger, Ute A1 - Koll, J-C T1 - Tailoring the SWIR emission of gold nanoclusters by surface ligand rigidification and their application in 3D bioimaging N2 - The influence of solvent polarity and surface ligand rigidification on the SWIR emission profile of gold nanoclusters with an anistropic surface was investigated. A strong enhancement of the SWIR emission band at 1200 nm was observed when measuring in different local environments: in solution, in polymer composites, and in solids. SWIR in vivo imaging of mice assisted by deep learning after intravenous administration of these gold nanoclusters provides high definition pseudo-3D views of vascular blood vessels. KW - Nano KW - Nanomaterial KW - Metal cluster KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Lifetime KW - Sensor KW - NIR KW - SWIR KW - Ligand KW - Gold KW - Mechanism KW - Charge transfer KW - Enhancement strategy KW - Imaging KW - Application KW - Contrast agent PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-543582 DO - https://doi.org/10.1039/D1CC06737K VL - 58 IS - 18 SP - 2967 EP - 2970 PB - RSC AN - OPUS4-54358 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Daly, H.C A1 - Matikonda, S.S A1 - Steffens, H.C A1 - Rühle, Bastian A1 - Resch-Genger, Ute A1 - Ivanic, J. A1 - Schermann, M.J T1 - Daly_Photochem Photobiol 2021_Ketone Incorporation Extends the Emission Properties of the Xanthene Scaffold N2 - Imaging in the shortwave-infrared region (SWIR, λ = 1000–2500 nm) has the potential to enable deep tissue imaging with high resolution. Critical to the development of these Methods is the identification of low molecular weight, biologically compatible fluorescent probes that emit beyond 1000 nm. Exchanging the bridging oxygen atom on the xanthene scaffold (C10’ position) with electron withdrawing groups has been shown to lead to significant redshifts in absorbance and emission. Guided by quantum chemistry computational modeling studies, we investigated the installation of a Ketone bridge at the C10’ position. This simple modification extends the absorbance maxima to 860 nm and the emission beyond 1000 nm, albeit with reduced photon output. Overall, These studies demonstrate that broadly applied xanthene dyes can be extended into the SWIR range. KW - Flourescence KW - Optical probe KW - Dye KW - Photophysics KW - Quantum yield KW - Mechanism KW - NIR KW - SWIR KW - Imaging KW - Reliability KW - Method KW - Quality assurance PY - 2021 DO - https://doi.org/10.1111/php.13544 SN - 1751-1097 VL - 98 IS - 2 SP - 325 EP - 333 PB - Wiley Online Library AN - OPUS4-54080 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Ahiboz, D. A1 - Andresen, Elina A1 - Manley, P. A1 - Resch-Genger, Ute A1 - Würth, Christian A1 - Becker, C. T1 - Metasurface-Enhanced Photon Upconversion upon 1550 nm Excitation N2 - Photon upconversion upon 1550 nm excitation is of high relevance for applications in the third biological excitation window, for photovoltaics beyond current limitations, and enables appealing options in the field of glass Fiber telecommunications. Trivalent doped erbium ions (Er3+) are the material of choice for 1550 nm excited upconversion, however, they suffer from a low absorption cross-section and a low brightness. Therefore, the ability of Silicon metasurfaces to provide greatly enhanced electrical near-fields is employed to enable efficient photon upconversion even at low external Illumination conditions. Hexagonally shaped β-NaYF4:Er3+ nanoparticles are placed on large-area silicon metasurfaces designed to convert near-infrared (1550 nm) to visible light. More than 2400-fold enhanced photon upconversion luminescence is achieved by using this metasurface instead of a planar substrate. With the aid of optical simulations based on the finite-element method, this result is attributed to the coupling of the excitation source with metasurface resonances at appropriate incident angles. Analysis of the excitation power density dependence of upconversion luminescence and red-to-green-emission ratios enables the estimation of nanoscale near-field enhancement on the metasurface. The findings permit the significant reduction of required external excitation intensities for photon upconversion of 1550 nm light, opening perspectives in biophotonics, telecommunication, and photovoltaics. KW - Nano KW - Nanomaterial KW - Upconversion nanoparticle KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Lifetime KW - Sensor KW - Excitation power density KW - Single particle KW - Brightness KW - NIR KW - Mechanism KW - Single enhancement KW - SWIR KW - Method PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-537193 DO - https://doi.org/10.1002/adom.202101285. SN - 2195-1071 VL - 9 IS - 24 SP - 2101285 PB - Wiley-VCH-GmbH AN - OPUS4-53719 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pauli, Jutta A1 - Ramírez, A. A1 - Crasselt, C. A1 - Schmidt, W. A1 - Resch-Genger, Ute T1 - Utilizing optical spectroscopy and 2',7'-difluorofluorescein to characterize the early stages of cement hydration N2 - The increasingly sophisticated nature of modern, more environmentally friendly cementitious binders requires a better understanding and control particularly of the complex, dynamic processes involved in the early phase of cement hydration. In-situ monitoring of properties of a constantly changing system over a defined period of time calls for simple, sensitive, fast, and preferably also non-invasive methods like optical spectroscopy KW - Flourescence KW - Optical probe KW - Sensor KW - Dye KW - Flourescin KW - Photophysics KW - PH KW - Quantum yield KW - Quality assurance KW - Mechanism KW - Cement KW - Concrete KW - Building material KW - Hydration KW - Process monitoring PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-537176 DO - https://doi.org/10.1088/2050-6120/ac2da0 SN - 2050-6120 VL - 10 IS - 1 SP - 2 EP - 13 PB - IOP Science AN - OPUS4-53717 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Grauel, Bettina A1 - Würth, Christian A1 - Homann, C. A1 - Krukewitt, Lisa A1 - Andresen, Elina A1 - Roik, Janina A1 - Recknagel, Sebastian A1 - Haase, M. A1 - Resch-Genger, Ute T1 - Volume and surface effects on two-photonic and three-photonic processes in dry co-doped upconversion nanocrystals N2 - Despite considerable advances in synthesizing high-quality core/shell upconversion (UC) nanocrystals (NC; UCNC) and UCNC photophysics, the application of near-infrared (NIR)-excitable lanthanide-doped UCNC in the life and material sciences is still hampered by the relatively low upconversion luminescence (UCL) of UCNC of small size or thin protecting shell. To obtain deeper insights into energy transfer and surface quenching processes involving Yb3+ and Er3+ ions, we examined energy loss processes in differently sized solid core NaYF4 nanocrystals doped with either Yb3+ (YbNC; 20% Yb3+) or Er3+ (ErNC; 2% Er3+) and co-doped with Yb3+ and Er3+ (YbErNC; 20% Yb3+ and 2% Er3+) without a surface protection shell and coated with a thin and a thick NaYF4 shell in comparison to single and co-doped bulk materials. Luminescence studies at 375 nm excitation demonstrate backenergy transfer (BET) from the 4G11/2 state of Er3+ to the 2F5/2 state of Yb3+, through which the red Er3+ 4F9/2 state is efficiently populated. Excitation power density (P)-dependent steady state and time-resolved photoluminescence measurements at different excitation and emission wavelengths enable to separate surface-related and volume-related effects for two-photonic and threephotonic processes involved in UCL and indicate a different influence of surface passivation on the green and red Er3+ emission. The intensity and lifetime of the latter respond particularly to an increase in volume of the active UCNC core. We provide a threedimensional random walk model to describe these effects that can be used in the future to predict the UCL behavior of UCNC. KW - Nano KW - Nanomaterial KW - Upconversion KW - Nanoparticle KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Pphotophysics KW - Lifetime KW - Sensor KW - Excitation KW - Power density KW - Single particle KW - Brightness KW - NIR KW - Mechanism KW - Modeling KW - Simulation KW - Energy transfer PY - 2022 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-535317 DO - https://doi.org/10.1007/s12274-021-3727-y SN - 1998-0124 VL - 15 IS - 3 SP - 2362 EP - 2373 PB - Springer AN - OPUS4-53531 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute T1 - Tumore abbilden, Biomarker nachweisen, Messungen standardisieren N2 - Zu den am häufigsten eingesetzten Analysemethoden in den Lebens- und Materialwissenschaften gehören Lumineszenzmethoden. Sie nutzen die Emission von Licht nach Absorption von Energie, um Signale zu erzeugen, und umfassen spektroskopische und mikroskopische Messungen. KW - Quality assurance KW - Sensor KW - Imaging KW - Reference material KW - Nano KW - Particle KW - Nanomaterial KW - Upconversion KW - Nanoparticle KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Lifetime KW - Excitation KW - Power density KW - Single particle KW - Brightness KW - NIR PY - 2021 SP - 75 EP - 77 PB - GDCH AN - OPUS4-53526 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Witte, F. A1 - Rietsch, P. A1 - Nirmalananthan-Budau, Nithiya A1 - Weigert, Florian A1 - Götze, J. P. A1 - Resch-Genger, Ute A1 - Eigler, S. A1 - Paulus, B. T1 - Aggregation-induced emission leading to two distinct emissive species in the solid-state structure of high-dipole organic chromophores N2 - The concept of aggregation-induced emission represents a means to rationalise photoluminescence of usually nonfluorescent excimers in solid-state materials. In this publication, we study the photophysical properties of selected diaminodicyanoquinone (DADQ) derivatives in the solid state using a combined approach of experiment and theory. DADQs are a class of high-dipole organic chromophores promising for applications in non-linear optics and light-harvesting devices. Among the compounds investigated, we find both aggregation-induced emission and aggregation-caused quenching effects rationalised by calculated energy transfer rates. Analysis of fluorescence spectra and lifetime measurements provide the interesting result that (at least) two emissive species seem to contribute to the photophysical properties of DADQs. The main emission peak is notably broadened in the long-wavelength limit and exhibits a blue-shifted shoulder. We employ high-level quantum-chemical methods to validate a molecular approach to a solid-state problem and show that the complex emission features of DADQs can be attributed to a combination of H-type aggregates, monomers, and crystal structure defects. KW - Fluorescence KW - Optical probe KW - Dye KW - Photophysics KW - Theory KW - Quantum yield KW - Mechanism KW - Quantum chemistry KW - Modelling KW - Aggregation KW - Lifetime KW - Single particle KW - Microscopy KW - Solid KW - Crystal PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-531138 DO - https://doi.org/10.1039/d1cp02534a SP - 1 EP - 9 PB - Royal Society of Chemistry AN - OPUS4-53113 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Biesen, L. A1 - May, L. A1 - Nirmalananthan-Budau, Nithiya A1 - Hoffmann, Katrin A1 - Resch-Genger, Ute A1 - Müller, T. J. J. T1 - Communication of Bichromophore Emission upon Aggregation – Aroyl-S,N-ketene Acetals as Multifunctional Sensor Merocyanines N2 - Aroyl-S,N-ketene acetal-based bichromophores can be readily synthesized in a consecutive three-component synthesis in good to excellent yields by condensation of aroyl chlorides and an N-(p-bromobenzyl) 2-methyl benzothiazolium salt followed by a Suzuki coupling, yielding a library of 31 bichromophoric fluorophores with substitution patterntunable emission properties. Varying both chromophores enables different communication pathways between the chromophores, exploiting aggregation-induced emission (AIE) and energy transfer (ET) properties, and thus, furnishing aggregation-based fluorescence switches. Possible applications range from fluorometric analysis of alcoholic beverages to pH sensors. KW - Dye KW - Fluorescence KW - Aggregation induced emission KW - Signal enhancement KW - Energy transfer KW - Switch KW - Sensor KW - Quantum yield KW - Lifetime KW - Photophysics KW - Synthesis PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-531123 DO - https://doi.org/10.1002/chem.202102052 VL - 27 IS - 53 SP - 13426 EP - 13434 PB - Wiley-VCH AN - OPUS4-53112 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Andresen, Elina A1 - Radunz, Sebastian A1 - Resch-Genger, Ute T1 - Novel PET-Operated Rosamine Sensor Dyes with Substitution Pattern-Tunable pKa Values and Temperature Sensitivity N2 - We present the synthesis and characterization of a family of regioisomerically pure pH-sensitive rosamine fluorophores consisting of xanthene fluorophore cores, which determine the dyes’ photophysical properties such as excitation/emission wavelength, fluorescence quantum yield, and fluorescence lifetime, and differently substituted phenol moieties. The hydroxyl substituent of the phenol moiety introduces a pH sensitivity of the dyes’ fluorescence exploiting a photoinduced electron transfer (PET), that leads to a protonation-induced switching ON of the rosamine emission. Rational tuning of the pKa value of the rosamine fluorescence between 4 to 9 is achieved by altering the substitution pattern and degree of bromination of the phenolic subunits. Additionally, a temperature sensitivity of the fluorescence quantum yield is introduced or suppressed based upon the degree of rigidity of the xanthene scaffold. KW - Fluorescence KW - Optical probe KW - Sensor KW - Dye KW - Rosamine KW - Synthesis KW - Photophysics KW - PH KW - Quantum yield KW - Quality assurancemechanism KW - temperature PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-530562 DO - https://doi.org/10.1039/d1nj02505h VL - 45 IS - 31 SP - 13934 EP - 13940 PB - Royal Society of Chemistry AN - OPUS4-53056 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Srivastava, Priyanka A1 - Fürstenwerth, Paul Christian A1 - Witte, J. F. A1 - Resch-Genger, Ute T1 - Synthesis and spectroscopic characterization of a fluorescent phenanthrene-rhodamine dyad for ratiometric measurements of acid pH values N2 - We present the rational design, synthesis and spectroscopic characterization of a novel dual excitation, three color emitting, pH-responsive fluorescent probe consisting of two phenanthrene and one rhodamine B units linked by click chemistry. The rhodamine moiety, excitable at λEx = 315 nm and at λEx = 560 nm in its ring-opened form, provides the pH-responsive fluorophore, while the pH-insensitive phenanthrene, excited at λEx = 315 nm, serves as inert internal reference, The presence of two phenanthrene moieties enables a blue monomer and a blueish green excimer emission at 351 nm and 500 nm, respectively. Opening of the rhodamine B spirolactam ring at an acidic pH below 5.0 (pKa = 2.59 ± 0.04) switches on its emission at 580 nm. Simultaneously, the phenanthrene excimer emission decreases caused by a change in orientation of the phenanthrene units, while the monomer emission is barely affected. This sensor design enables ratiometric measurements in the low acidic pH range utilizing the intensity ratios of the rhodamine B and phenanthrene excimer emission at 580 nm and 500 nm. Alternatively, also the intensity ratios of the rhodamine B and the phenanthrene monomer emission could be exploited or the sum of the phenanthrene monomer and excimer fluorescence. To the best of our knowledge, this is the first report of ratiometric sensing utilizing such a versatile type of tricolor emissive dyad probe bearing phenanthrene moieties and showing phenanthrene monomer and excimer emission. KW - Fluorescence KW - Optical probe KW - Sensor KW - Dye KW - Rhodamine KW - Synthesis KW - Photophysics KW - PH KW - Quantum yield KW - Quality assurance KW - Mechanism KW - Chemodosimeter KW - Phenanthrene KW - Ratiometric KW - Dyad PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-530554 DO - https://doi.org/10.1039/d1nj01573g SN - 1144-0546 VL - 45 IS - 31 SP - 13755 EP - 13762 PB - Royal Society of Chemistry AN - OPUS4-53055 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Reichenauer, F. A1 - Wang, Cui A1 - Förster, C. A1 - Boden, P. A1 - Ugur, N. A1 - Báez-Cruz, R. A1 - Kalmbach, J. A1 - Carrella, L. M. A1 - Rentschler, E. A1 - Ramanan, C. A1 - Niedner-Schatteburg, G. A1 - Gerhards, M. A1 - Seitz, M. A1 - Resch-Genger, Ute A1 - Heinze, K. T1 - Strongly Red-Emissive Molecular Ruby [Cr(bpmp)2]3+ Surpasses [Ru(bpy)3]2+ N2 - Gaining chemical control over the thermodynamics and kinetics of photoexcited states is paramount to an efficient and sustainable utilization of photoactive transition metal complexes in a plethora of technologies. In contrast to energies of charge Transfer states described by spatially separated orbitals, the energies of spinflip states cannot straightforwardly be predicted as Pauli Repulsion and the nephelauxetic effect play key roles. Guided by multireference quantum chemical calculations, we report a novel highly luminescent spin-flip emitter with a quantum chemically predicted blue-shifted luminescence. The spin-flip emission band of the chromium complex [Cr(bpmp)2]3+ (bpmp = 2,6-bis(2-pyridylmethyl) pyridine) shifted to higher energy from ca. 780 nm observed for known highly emissive chromium(III) complexes to 709 nm. The photoluminescence quantum yields climb to 20%, and very long excited state lifetimes in the millisecond range are achieved at room temperature in acidic D2O solution. Partial ligand deuteration increases the quantum yield to 25%. The high excited state energy of [Cr(bpmp)2]3+ and its facile reduction to [Cr(bpmp)2]2+ result in a high excited state redox potential. The ligand’s methylene bridge acts as a Brønsted acid quenching the luminescence at high pH. Combined with a pH-insensitive chromium(III) emitter, ratiometric optical pH sensing is achieved with single wavelength excitation. The photophysical and Ground state properties (quantum yield, lifetime, redox potential, and acid/base) of this spin-flip complex incorporating an earth-abundant metal surpass those of the classical precious metal [Ru(α-diimine)3]2+ charge transfer complexes, which are commonly employed in optical sensing and photo(redox) catalysis, underlining the bright future of these molecular ruby analogues. KW - Fluorescence KW - Optical probe KW - Sensor KW - PH KW - Quantum yield KW - Quality assurance KW - Complex KW - Cr(III) KW - Lifetime KW - Ligand KW - Theory PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-530548 DO - https://doi.org/10.1021/jacs.1c05971 VL - 143 IS - 30 SP - 11843 EP - 11855 PB - ACS Publications AN - OPUS4-53054 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Dhamo, Lorena A1 - Carulli, F. A1 - Nickl, Philip A1 - Wegner, Karl David A1 - Hodoroaba, Vasile-Dan A1 - Würth, Christian A1 - Brovelli, S. A1 - Resch-Genger, Ute T1 - Efficient luminescent solar concentrators based on environmentally friendly Cd-free ternary AIS/ZnS quantum dots N2 - Luminescent solar concentrators (LSC) allow to obtain renewable energy from building integrated photovoltaic systems. As promising efficient and long-term stable LSC fluorophores semiconductor nanocrystals like Quantum dots (QDs) with size and composition tunable optoelectronic properties have recently emerged. The most popular II/VI or IV/VI semiconductor QDs contain, however, potentially hazardous cadmium or lead ions, which is a bottleneck for commercial applications. A simple aqueous based, microwaveassisted synthesis for environmentally friendly and highly emissive AgInS2/ ZnS QDs is developed using 3-mercaptopropionic acid (MPA) and glutathione (GSH) and their incorporation into polylaurylmethacrylate (PLMA) polymer slabs integrable in LSC devices (10.4 × 10.4 × 0.2 cm3, G = 12.98). With this simple approach, optical power efficiencies (OPE) of 3.8% and 3.6% and optical quantum efficiencies (OQE) of 24.1% and 27.4% are obtained, which are among the highest values yet reported. KW - Solar energy KW - Solar concentrator KW - Quantum dots KW - Advanced material KW - Quantum yield PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-529735 DO - https://doi.org/10.1002/adom.202100587 SN - 2195-1071 SN - 0935-9648 VL - 9 IS - 17 SP - 1 EP - 8 PB - Wiley-VCH CY - Weinheim AN - OPUS4-52973 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Xu, R. A1 - Teich, W. A1 - Frenzel, Florian A1 - Hoffmann, Katrin A1 - Radke, J. A1 - Rösler, J. A1 - Faust, K. A1 - Blank, A. A1 - Brandenburg, S. A1 - Misch, M. A1 - Vajkoczy, P. A1 - Onken, J. S. A1 - Resch-Genger, Ute T1 - Optical characterization of sodium fluorescein in vitro and ex vivo N2 - Objective: The utilization of fluorescein-guided biopsies and resection has been recently discussed as a suitable strategy to improve and expedite operative techniques for the resection of central nervous system (CNS) tumors. However, little is known about the optical properties of sodium fluorescein (NaFl) in human tumor tissue and their potential impact on ex vivo analyses involving fluorescence-based methods. Methods: Tumor tissue was obtained from a study cohort of an observational study on the utilization of fluorescein-guided biopsy and resection (n=5). The optical properties of fluorescein-stained tissue were compared to the optical features of the dye in vitro and in control samples consisting of tumor tissue of high-grade glioma patients (n=3) without intravenous (i.v.) application of NaFl. The dye-exposed tumor tissues were used for optical measurements to confirm the detectability of NaFl emission ex vivo. The tissue samples were fixed in 4%PFA, immersed in 30% sucrose, embedded in Tissue-Tek OCT compound, and cut to 10 mm cryosections. Spatially resolved emission spectra from tumor samples were recorded on representative slides with a Confocal Laser Scanning Microscope FV1000 (Olympus GmbH, Hamburg, Germany) upon excitation with lexc = 488 nm. Results: Optical measurements of fluorescein in 0.9% sodium chloride (NaCl) under in vitro conditions showed an absorption maximum of lmax abs = 479 nm as detected with spectrophotometer Specord 200 and an emission peak at lmax em = 538 nm recorded with the emCCD detection system of a custom-made microscope-based single particle setup using a 500 nm long-pass filter. Further measurements revealed pH- and concentration-dependent emission spectra of NaFl. Under ex vivo conditions, confocal laser scanning microscopy of fluorescein tumor samples revealed a slight bathochromic shift and a broadening of the emission band. Conclusion: Tumor uptake of NaFl leads to changes in the optical properties – a bathochromic shift and broadening of the emission band – possibly caused by the dye’s high pH sensitivity and concentration-dependent reabsorption acting as an innerfilter of the dye’s emission, particularly in the short wavelength region of the Emission spectrum where absorption and fluorescence overlap. Understanding the ex vivo optical properties of fluorescein is crucial for testing and validating its further applicability as an optical probe for intravital microscopy, immunofluorescence localization studies, and flow cytometry analysis. KW - Fluorescence KW - Optical probe KW - Sensor KW - Fluorescein KW - PH KW - Imaging KW - Tissue KW - Cancer KW - Medical diagnostics KW - Tumor KW - In vivo KW - Ex vivo KW - Quantum yield KW - Dye KW - Quality assurance KW - Microscopy PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-527843 DO - https://doi.org/10.3389/fonc.2021.654300 SN - 2234-943X VL - 11 SP - 1 EP - 8 PB - Frontiers Media CY - Lausanne AN - OPUS4-52784 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Witte, F. A1 - Rietsch, P. A1 - Sinha, S. A1 - Krappe, A. A1 - Joswig, J.-O. A1 - Götze, J. P. A1 - Nirmalananthan-Budau, Nithiya A1 - Resch-Genger, Ute A1 - Eigler, S. A1 - Paulus, B. T1 - Fluorescence Quenching in J‑Aggregates through the Formation of Unusual Metastable Dimers N2 - Molecular aggregation alters the optical properties of a system as fluorescence may be activated or quenched. This is usually described within the well-established framework of H- and J-aggregates. While H-aggregates show nonfluorescent blueshifted absorption bands with respect to the isolated monomer, Jaggregates are fluorescent displaying a redshifted peak. In this publication, we employ a combined approach of experiment and theory to study the complex aggregation features and photophysical properties of diaminodicyanoquinone derivatives, which show unusual and puzzling nonfluorescent redshifted Absorption bands upon aggregation. Our theoretical analysis demonstrates that stable aggregates do not account for the experimental observations. Instead, we propose an unprecedented mechanism involving metastable dimeric species formed from stable dimers to generate nonfluorescent J-aggregates. These results represent a novel kind of aggregation-induced optical effect and may have Broad implications for the photophysics of dye aggregates. KW - Fluorescence KW - Llifetime KW - Dye KW - Quantum yield KW - Label KW - Reporter KW - Aggregation KW - Monomer KW - Heory KW - Mechanism KW - photophysics PY - 2021 DO - https://doi.org/10.1021/acs.jpcb.1c01600 SN - 1520-5207 VL - 125 IS - 17 SP - 4438 EP - 4446 PB - ACS Publikations AN - OPUS4-52619 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Maisuls, I. A1 - Wang, Cui A1 - Gutierrez Suburu, M. E. A1 - Wilde, S. A1 - Daniliuc, C.-G. A1 - Brunink, D. A1 - Doltsinis, N. L. A1 - Ostendorp, S. A1 - Kösters, J. A1 - Resch-Genger, Ute A1 - Strassert, C. A. T1 - Ligand-controlled and nanoconfinement-boosted luminescence employing Pt(II) and Pd(II) complexes: from color-tunable aggregation-enhanced dual emitters towards self-referenced oxygen reporters N2 - In this work, we describe the synthesis, structural and photophysical characterization of four novel Pd(II) and Pt(II) complexes bearing tetradentate luminophoric ligands with high photoluminescence quantum yields (FL) and long excited state lifetimes (s) at room temperature, where the results were interpreted by means of DFT calculations. Incorporation of fluorine atoms into the tetradentate ligand favors aggregation and thereby, a shortened average distance between the metal centers, which provides accessibility to metal–metal-to-ligand charge-transfer (3MMLCT) excimers acting as red-shifted Energy traps if compared with the monomeric entities. This supramolecular approach provides an elegant way to enable room-temperature phosphorescence from Pd(II) complexes, which are otherwise quenched by a thermal population of dissociative states due to a lower ligand field splitting. Encapsulation of These complexes in 100 nm-sized aminated polystyrene nanoparticles enables concentration-controlled aggregation-enhanced dual emission. This phenomenon facilitates the tunability of the absorption and emission colors while providing a rigidified environment supporting an enhanced FL up to about 80% and extended s exceeding 100 ms. Additionally, these nanoarrays constitute rare examples for selfreferenced oxygen reporters, since the phosphorescence of the aggregates is insensitive to external influences, whereas the monomeric species drop in luminescence lifetime and intensity with increasing triplet molecular dioxygen concentrations (diffusion-controlled quenching). KW - Fluorescence KW - Multiplexing KW - Lifetime KW - Bead KW - Particle KW - Dye KW - Barcoding KW - Encoding KW - Quantum yield KW - Label KW - Reporter KW - Pd(II) KW - Pt(II) KW - Complex KW - NMR KW - X-ray KW - Sythesis KW - Aggregation KW - Monomer KW - Color PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-525288 DO - https://doi.org/10.1039/d0sc06126c VL - 12 IS - 9 SP - 3270 EP - 3281 PB - Royal Society of Chemistry AN - OPUS4-52528 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Frenzel, Florian A1 - Würth, Christian A1 - Dukhno, O. A1 - Przybilla, F. A1 - Wiesholler, L. M. A1 - Muhr, V. A1 - Horsch, T. A1 - Mély, Y. A1 - Resch-Genger, Ute T1 - Multiband emission from single β-NaYF4(Yb,Er) nanoparticles at high excitation power densities and comparison to ensemble studies N2 - Ensemble and single particle studies of the excitation power density (P)-dependent upconversion luminescence (UCL) of core and core–shell β-NaYF4:Yb,Er upconversion nanoparticles (UCNPs) doped with 20% Yb3+ and 1% or 3% Er3+ performed over a P regime of 6 orders of magnitude reveal an increasing contribution of the emission from high energy Er3+ levels at P > 1 kW/cm2. This changes the overall emission color from initially green over yellow to white. While initially the green and with increasing P the red emission dominate in ensemble measurements at P < 1 kW/cm2, the increasing population of higher Er3+ energy levels by multiphotonic processes at higher P in single particle studies results in a multitude of emission bands in the ultraviolet/visible/near infrared (UV/vis/NIR) accompanied by a decreased contribution of the red luminescence. Based upon a thorough analysis of the P-dependence of UCL, the emission bands activated at high P were grouped and assigned to 2–3, 3–4, and 4 photonic processes involving energy transfer (ET), excited-state absorption (ESA), cross-relaxation (CR), back energy transfer (BET), and non-radiative relaxation processes (nRP). This underlines the P-tunability of UCNP brightness and color and highlights the potential of P-dependent measurements for mechanistic studies required to manifest the population pathways of the different Er3+ levels. KW - Nano KW - Nanomaterial KW - Upconversion nanoparticle KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Llifetime KW - Sensor KW - Excitation power density KW - Single particle KW - Brightness KW - NIR KW - Mechanism KW - Color tuning PY - 2021 DO - https://doi.org/10.1007/s12274-021-3350-y SN - 1998-0124 VL - 14 IS - 11 SP - 4107 EP - 4115 PB - Nano Research AN - OPUS4-52364 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rietsch, P. A1 - Zeyat, M. A1 - Hübner, Oskar A1 - Hoffmann, Katrin A1 - Resch-Genger, Ute A1 - Kutter, M. A1 - Paskin, A. A1 - Uhlig, J. A1 - Lentz, D. A1 - Eigler, S. T1 - Substitution Pattern-Controlled Fluorescence Lifetimes of Fluoranthene Dyes N2 - The absorption and emission properties of organic dyes are generally tuned by altering the substitution pattern. However, tuning the fluorescence lifetimes over a range of several 10 ns while barely affecting the spectral features and maintaining a moderate fluorescence quantum yield is challenging. Such properties are required for lifetime multiplexing and barcoding applications. Here, we show how this can be achieved for the class of fluoranthene dyes, which have substitution-dependent lifetimes between 6 and 33 ns for single wavelength excitation and emission. We explore the substitution-dependent emissive properties in the crystalline solid state that would prevent applications. Furthermore, by analyzing dye mixtures and embedding the dyes in carboxyfunctionalized 8 μm-sized polystyrene particles, the unprecedented potential of these dyes as labels and encoding fluorophores for time-resolved fluorescence detection techniques is demonstrated. KW - Fluorescence KW - Label KW - Fluoranthene KW - Quantum yield KW - Reporter KW - Crystal KW - Encoding KW - Multiplexing KW - Particle KW - Bead KW - Lifetime KW - Dye KW - Barcoding PY - 2021 DO - https://doi.org/10.1021/acs.jpcb.0c08851 SN - 1520-5207 VL - 125 IS - 4 SP - 1207 EP - 1213 PB - American Chemical Society AN - OPUS4-52087 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Sun, C. A1 - Schäferling, Michael A1 - Resch-Genger, Ute A1 - Gradzielski, M. T1 - Solvothermal Synthesis of Lanthanide-doped NaYF4 Upconversion N2 - Lanthanide-doped NaYF4 upconversion nano- and microcrystals were synthesized via a facile solvothermal approach. Thereby, the influence of volume ratios of ethylene glycol (EG)/H2O, molar ratios of NH4F/RE3+ (RE3+ represents the total amount of Y3+ and rare-earth dopant ions), Gd3+ ion contents, types of activator dopant ions, and different organic co-solvents on the crystal phase, size, and morphology of the resulting particles were studied systematically. A possible formation mechanism for the growth of crystals of different morphology is discussed. Our results show that the transition from the α- to the β-phase mainly depends on the volume ratio of EG/H2O and the molar ratio of NH4F/RE3+, while the morphology and size could be controlled by the type of organic co-solvent and Gd3+ dopant ions. Furthermore, the reaction time has to be long enough to convert α-NaYF4 into β-NaYF4 during the growth process to optimize the upconversion luminescence. The formation of larger β-NaYF4 crystals, which possess a higher upconversion luminescence than smaller particles, proceeds via intermediates of smaller crystals of cubic structure. In summary, our synthetic approach presents a facile route to tailor the size, Crystal phase, morphology, and luminescence features of upconversion materials. KW - Nano KW - Nanomaterial KW - Upconversion nanoparticle KW - Photoluminescence KW - Lanthanide KW - Quantum yield KW - Photophysics KW - Lifetime KW - Surface chemistry KW - Single particle KW - Brightness KW - NIR KW - Synthesis PY - 2021 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-520307 DO - https://doi.org/10.1002/cnma.202000564 VL - 7 IS - 2 SP - 174 EP - 183 PB - Wiley AN - OPUS4-52030 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Weigert, Florian A1 - Müller, A. A1 - Häusler, I. A1 - Geißler, Daniel A1 - Skroblin, D. A1 - Unger, Wolfgang A1 - Radnik, Jörg A1 - Resch-Genger, Ute T1 - Combining HR‑TEM and XPS to elucidate the core–shell structure of ultrabright CdSe/CdS semiconductor quantum dots N2 - Controlling thickness and tightness of surface passivation shells is crucial for many applications of core–shell nanoparticles (NP). Usually, to determine shell thickness, core and core/shell particle are measured individually requiring the availability of both nanoobjects. This is often not fulfilled for functional nanomaterials such as many photoluminescent semiconductor quantum dots (QD) used for bioimaging, solid state lighting, and display technologies as the core does not show the applicationrelevant functionality like a high photoluminescence (PL) quantum yield, calling for a whole nanoobject approach. By combining high-resolution transmission electron microscopy (HR-TEM) and X-ray photoelectron spectroscopy (XPS), a novel whole nanoobject approach is developed representatively for an ultrabright oleic acid-stabilized, thick shell CdSe/CdS QD with a PL quantum yield close to unity. The size of this spectroscopically assessed QD, is in the range of the information depth of usual laboratory XPS. Information on particle size and monodispersity were validated with dynamic light scattering (DLS) and small angle X-ray scattering (SAXS) and compared to data derived from optical measurements. In addition to demonstrating the potential of this novel whole nanoobject approach for determining architectures of small nanoparticles, the presented results also highlight challenges faced by different sizing and structural analysis methods and method-inherent uncertainties. KW - Photoluminescence KW - Single particle KW - Microscopy KW - Particle architecture KW - Thickness KW - SAXS KW - Shell KW - XPS KW - TEM KW - Semiconductor KW - Quantum dot KW - Photophysics KW - Quantum yield PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-517911 DO - https://doi.org/10.1038/s41598-020-77530-z VL - 10 IS - 1 SP - 20712 PB - Springer Nature AN - OPUS4-51791 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rietsch, P. A1 - Sobottka, S. A1 - Hoffmann, K. A1 - Popov, A. A. A1 - Hildebrandt, P. A1 - Sarkar, B. A1 - Resch-Genger, Ute A1 - Eigler, S. T1 - Between Aromatic and Quinoid Structure: A Symmetrical UV to Vis/NIR Benzothiadiazole Redox Switch N2 - Reversibly switching the light absorption of organic molecules by redox processes is of interest for applications in sensors, light harvesting, smart materials, and medical diagnostics. This work presents a symmetrical benzothiadiazole (BTD) derivative with a high fluorescence quantum yield in solution and in the crystalline state and shows by spectroelectrochemical analysis that reversible switching of UV absorption in the neutral state, to broadband Vis/NIR absorption in the 1st oxidized state, to sharp band Vis absorption in the 2nd oxidized state, is possible. For the one-electron oxidized species, formation of a delocalized radical is confirmed by electron paramagnetic resonance spectroelectrochemistry. Furthermore, our results reveal an increasing quinoidal distortion upon the 1st and 2nd oxidation, which can be used as the leitmotif for the development of BTD based redox switches. KW - Dye KW - Electrochemistry KW - Switch KW - Redox KW - Sensor KW - Photophysics KW - Quantum yield KW - photoluminescence PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-517222 DO - https://doi.org/10.1002/chem.202004009 VL - 26 IS - 72 SP - 17361 EP - 17365 PB - Wiley-VCH GmbH AN - OPUS4-51722 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute A1 - Carl, F. A1 - Grauel, Bettina A1 - Pons, Monica A1 - Würth, Christian A1 - Haase, M. T1 - LiYF4:Yb/LiYF4 and LiYF4:Yb,Er/LiYF4 core/shell nanocrystals with luminescence decay times similar to YLF laser crystals and the upconversion quantum yield of the Yb,Er doped nanocrystals N2 - We developed a procedure to prepare luminescent LiYF4:Yb/LiYF4 and LiYF4:Yb,Er/LiYF4 core/shell nanocrystals with a size of approximately 40 nm revealing luminescence decay times of the dopant ions that approach those of high-quality laser crystals of LiYF4:Yb (Yb:YLF) and LiYF4:Yb,Er (Yb,Er:YLF) with identical doping concentrations. As the luminescence decay times of Yb3+ and Er3+ are known to be very sensitive to the presence of quenchers, the long decay times of the core/shell nanocrystals indicate a very low number of defects in the core particles and at the core/shell interfaces. This improvement in the performance was achieved by introducing two important modifications in the commonly used oleic acid based synthesis. First, the shell was prepared via anewly developed method characterized by a very low nucleation rate for particles of pure LiYF4 shell material. Second, anhydrous acetates were used as precursors and additional drying steps were applied to reduce the incorporation of OH− in the crystal lattice, known to quench the emission of Yb3+ ions. Excitation power density (P)-dependent absolute measurements of the upconversion luminescence quantum yield (Φ,UC) of LiYF4:Yb,Er/LiYF4 core/shell particles reveal a maximum value of 1.25% at P of 180 W·cm−2. Although lower than the values reported for NaYF4:18%Yb,2%Er core/shell nanocrystals with comparable sizes, these Φ, UC values are the highest reported so far for LiYF4:18%Yb,2%Er/LiYF4 nanocrystals without additional dopants. Further improvements May nevertheless be possible by optimizing the dopant concentrations in the LiYF4 nanocrystals. KW - Nano KW - Crystal KW - Quantum yield KW - LiYF4 KW - Synthesis KW - Lifetime KW - Fluorescence KW - NIR KW - Photoluminescence KW - Lanthanide KW - Upconversion nanoparticle KW - Nanomaterial PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-515395 DO - https://doi.org/10.1007/s12274-020-3116-y SN - 1998-0124 VL - 14 IS - 3 SP - 797 EP - 806 PB - Springer AN - OPUS4-51539 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Zhao, J. A1 - Hu, Y. A1 - wei Lin, S. A1 - Resch-Genger, Ute A1 - Zhang, R. A1 - Wen, J. A1 - Kong, X. A1 - Qin, A. A1 - Ou, J. T1 - Enhanced luminescence intensity of near-infraredsensitized sensitized upconversion nanoparticles via Ca²+ doping for a nitric oxide release platform N2 - Light-induced NO release based on exogenous NO donors has attracted substantial attention in clinical applications; the induction light source usually converts near-infrared light to blue or ultraviolet light. However, the low efficiency of near-infrared light-assisted chemical light energy conversion remains a challenge, especially for NaYF4:Yb3+/Tm3+ photoconverting near-infrared light to ultraviolet (UV) and blue light. In this paper, a luminescence-enhanced strategy is reported by doping Ca2+ into NaYF4:Yb3+/Tm3+ and coating it with NaGdF4 through a two-step solvothermal method. Then, UCNPs modified with methyl-b-cyclodextrin (M-b-CD) are loaded on a ruthenium nitrosyl complex [(3)Ru(NO)(Cl)] as nitric oxide release-molecules (NORMs). X-ray diffraction (XRD) and energy-dispersive X-ray spectroscopy (EDS) data demonstrated that Ca2+ was successfully doped into NaYF4:Yb3+/Tm3+ nanoparticles as the core, and a pure hexagonal phase, NaYF4, was obtained from the doping of Ca2+. TEM revealed that the crystallinity was significantly improved after Ca2+ doping, and the core–shell structure was successfully synthesized, with NaGdF4 directionally grown on the NaYF4:Ca/Yb/Tm core. Fluorescence tests showed that, especially in the ultraviolet and blue light excitation wavelength regions, the UC emission intensity of the Ca-doped NaYF4:Yb3+/Tm3+@NaGdF4 core–shell UCNPs increased by 302.95 times vs. NaYF4:Yb3+/Tm3+ UCNPs. Finally, the release of NO was tested by the Griess method. Under 980 nm irradiation, the cell viability distinctly decreased with increasing UCNPs@M-b-CD-NORMs concentration. This study Shows that NORM release of NO is triggered by enhanced up-converted UV and blue light, which can be used for the development of UV photo-sensitive drugs. KW - Nano KW - Nanomaterial KW - Upconversion nanoparticle KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Lifetime KW - Sensor KW - Surface chemistry KW - Single particle KW - Brightness KW - NIR KW - PDT PY - 2020 DO - https://doi.org/10.1039/d0tb00088d VL - 8 IS - 30 SP - 6481 EP - 6489 PB - Journal of Materials Chemistry B AN - OPUS4-51262 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kalmbach, J. A1 - Wang, Cui A1 - You, Yi A1 - Förster, C. A1 - Schubert, H. A1 - Heinze, K. A1 - Resch-Genger, Ute A1 - Seitz, M. T1 - Near-IR to near-IR upconversion luminescence in molecular chromium ytterbium salts N2 - Upconversion photoluminescence in hetero-oligonuclear metal complex architectures featuring organic ligands is an interesting but still rarely observed phenomenon, despite its great potential from a basic research and application perspective. In this context, a new photonic material consisting of molecular chromium(III) and ytterbium(III) complex Ions was developed that exhibits excitation-power density-dependent cooperative sensitization of the chromium-centered 2E/2T1 phosphorescence at approximately 775 nm after excitation of the ytterbium band 2F7/2!2F5/2 at approximately 980 nm in the solid state at ambient temperature. The upconversion process is insensitive to atmospheric oxygen and can be observed in the presence of water molecules in the crystal lattice. KW - Upconversion KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Lifetime KW - Sensor KW - NIR KW - Cr(III) KW - Yb(III) complex KW - Crystal KW - Triplet-triplet annihilation KW - Sensitization KW - Light harvesting PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-512619 DO - https://doi.org/10.1002/anie.202007200 SN - 1433-7851 SN - 1521-3773 VL - 59 IS - 42 SP - 18804 EP - 18808 PB - Wiley CY - Weinheim AN - OPUS4-51261 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Soares, J. X. A1 - Wegner, Karl David A1 - Ribeiro, D. S. M. A1 - Melo, A. A1 - Häusler, I. A1 - Santos, J. L. M. A1 - Resch-Genger, Ute T1 - Rationally designed synthesis of bright AgInS2/ZnS quantum dots with emission control N2 - In the blossoming field of Cd-free semiconductor quantum dots (QDs), ternary I–III–VI QDs have received increasing attention due to the ease of the environmentally friendly synthesis of high-quality materials in water, their high photoluminescence (PL) Quantum yields (QYs) in the red and near infrared (NIR) region, and their inherently low toxicity. Moreover, their oxygen-insensitive long PL lifetimes of up to several hundreds of nanoseconds close a gap for applications exploiting the compound-specific parameter PL lifetime. To overcome the lack of reproducible synthetic methodologies and to enable a design-based control of their PL properties, we assessed and modelled the synthesis of high-quality MPA-capped AgInS2/ZnS (AIS/ZnS) QDs. Systematically refined Parameters included reaction time, temperature, Ag:In ratio, S:In ratio, Zn:In ratio, MPA:In ratio, and pH using a design-of-experiment approach. Guidance for the optimization was provided by mathematical models developed for the application-relevant PL parameters, maximum PL wavelength, QY, and PL lifetime as well as the elemental composition in terms of Ag:In:Zn ratio. With these experimental data-based models, MPA:In and Ag:In ratios and pH values were identified as the most important synthesis parameters for PL Control and an insight into the connection of these parameters could be gained. Subsequently, the experimental conditions to synthetize QDs with tunable emission and high QY were predicted. The excellent agreement between the predicted and experimentally found PL features confirmed the reliability of our methodology for the rational design of high quality AIS/ZnS QDs with defined PL features. This approach can be straightforwardly extended to other ternary and quaternary QDs and to doped QDs. KW - Modelling KW - Nanoparticle KW - AIS KW - Semiconductor quantum dot KW - Design of experiment KW - Photoluminescence KW - Quantum yield KW - Surface chemistry KW - Synthesis KW - Lifetime PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-510075 DO - https://doi.org/10.1007/s12274-020-2876-8 VL - 13 IS - 9 SP - 2438 EP - 2450 PB - Springer AN - OPUS4-51007 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Nirmalananthan-Budau, Nithiya A1 - Budau, J. H. A1 - Moldenhauer, Daniel A1 - Hermann, G. A1 - Kraus, Werner A1 - Hoffmann, Katrin A1 - Paulus, Beate A1 - Resch-Genger, Ute T1 - Substitution pattern controlled aggregation-induced emission in donor-acceptor-donor dyes with one and two propeller-like triphenylamine donors N2 - We present a comparative study of the spectroscopic properties of the donor–acceptor–donor substituted dyes triphenylamine-allylidenemalononitrile-julolidine (TMJ) and triphenylamine-allylidenemalononitriletriphenylamine (TMT), bearing one and two propeller-like triphenylamine donor moieties, in solvents of varying polarity and viscosity and in the aggregated and solid state. Our results reveal control of the aggregation-induced spectroscopic changes and the packing motifs of the dye molecules in the solid state by the chemical nature and structure of the second nitrogen-containing donor, i.e., a planar and a rigid julolidine or a twisted triphenyl group. Assuming that the TMT and TMJ aggregates show a comparable arrangement of the molecules to the respective crystals, these different molecular interactions in the solid state are responsible for aggregation induced emission (AIE) in the case of TMT and its absence for TMJ. Moreover, a versatile strategy for the fluorescence enhancement of only weakly emissive AIE dyes is shown, turning these dyes into bright nanoscale fluorescent reporters by using them as stains for preformed polymer particles. KW - Nano KW - Nanoparticle KW - Photoluminescence KW - Fluorescence KW - Quantum yield KW - Photophysics KW - Lifetime KW - Sensor KW - Dye KW - Enhancement KW - Particle KW - Polarity KW - AIE KW - Aggregation KW - Aggregation-induced emission KW - Solid state emission PY - 2020 DO - https://doi.org/10.1039/d0cp00413h VL - 22 IS - 25 SP - 14142 EP - 14154 AN - OPUS4-50967 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Denißen, M. A1 - Hannen, R. A1 - Itskalov, D. A1 - Biesen, L. A1 - Nirmalananthan-Budau, Nithiya A1 - Hoffmann, Katrin A1 - Reiss, G. J. A1 - Resch-Genger, Ute A1 - Müller, T. J. J. T1 - One-pot synthesis of a white-light emissive bichromophore operated by aggregation-induced dual emission (AIDE) and partial energy transfer N2 - Merocyanine–triarylamine bichromophores are readily synthesized by sequentially Pd-catalyzed insertion alkynylation–Michael–Suzuki four-component reactions. White-light emissive systems form upon aggregation in 1 : 99 and 0.1 : 99.9 vol% CH2Cl2–cyclohexane mixtures, ascribed to aggregation-induced dual emission (AIDE) in combination with partial energy transfer between both chromophore units as supported by spectroscopic studies. KW - Energy transfer KW - Nano KW - Nanoparticle KW - Photoluminescence KW - Fluorescence KW - Quantum yield KW - Photophysics KW - Lifetime KW - Sensor KW - Dye KW - Enhancement KW - Particle KW - Polarity KW - AIE KW - Aggregation KW - Aggregation-induced emission KW - Solid state emission KW - Merocyanine PY - 2020 DO - https://doi.org/10.1039/d0cc03451g VL - 56 IS - 54 SP - 7407 PB - Royal Society of Chemistry AN - OPUS4-50936 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Tan, M. A1 - Monks, Melissa-Jane A1 - Huang, D. A1 - Meng, Y. A1 - Chen, X. A1 - Zhou, Y A1 - Lom, S.-F. A1 - Würth, Christian A1 - Resch-Genger, Ute A1 - Chen, G. T1 - Efficient sub-15 nm cubic-phase core/Shell upconversion nanoparticles as reporters for ensemble and single particle studies† N2 - Single particle imaging of upconversion nanoparticles (UCNPs) has typically been realized using hexagonal (β) phase lanthanide-doped sodium yttrium fluoride (NaYF4) materials, the upconversion luminescence (UCL) of which saturates at power densities (P) of several hundred W cm−2 under 980 nm nearinfrared (NIR) excitation. Cubic (α) phase UCNPs have been mostly neglected because of their commonly observed lower UCL efficiency at comparable P in ensemble level studies. Here, we describe a set of sub-15 nm ytterbium-enriched α-NaYbF4:Er3+@CaF2 core/shell UCNPs doped with varying Er3+ concentrations (5–25%), studied over a wide P range of ∼8–105 W cm−2, which emit intense UCL even at a low P of 10 W cm−2 and also saturate at relatively low P. The highest upconversion quantum yield (ΦUC) and the highest particle brightness were obtained for an Er3+ dopant concentration of 12%, reaching the highest ΦUC of 0.77% at a saturation power density (Psat) of 110 W cm−2. These 12%Er3+-doped core/shell UCNPs were also the brightest UCNPs among this series under microscopic conditions at high P of ∼102–105 W cm−2 as demonstrated by imaging studies at the single particle level. Our results underline the potential applicability of the described sub-15 nm cubic-phase core/shell UCNPs for ensemble- and single particle- level bioimaging. KW - Nano KW - Nanomaterial KW - Upconversion nanoparticle KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Lifetime KW - Sensor KW - Surface chemistry KW - Single particle KW - Brightness PY - 2020 DO - https://doi.org/10.1039/d0nr02172e VL - 12 IS - 19 SP - 10592 EP - 10599 PB - Nanoscale AN - OPUS4-50908 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Biesen, L. A1 - Nirmalananthan-Budau, Nithiya A1 - Hoffmann, Katrin A1 - Resch-Genger, Ute A1 - Müller, T. J. J. T1 - Solid-State Emissive Aroyl-S,N-Ketene Acetals with Tunable N2 - N-Benzyl aroyl-S,N-ketene acetals can be readily synthesized by condensation of aroyl chlorides and N-Benzyl 2-methyl benzothiazolium salts in good to excellent yields, yielding a library of 35 chromophores with bright solid-state emission and aggregation-induced emission characteristics. Varying the substituent from electron-donating to electronwithdrawing enables the tuning of the solid-state emission Color from deep blue to red. KW - Nano KW - Nanoparticle KW - Photoluminescence KW - Fluorescence KW - Quantum yield KW - Photophysics KW - Lifetime KW - Sensor KW - dye KW - Enhancement KW - Particle KW - Polarity KW - AIE KW - Aggregation KW - Aggregation-induced emission KW - Solid state emission PY - 2020 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-509072 DO - https://doi.org/10.1002/anie.201916396 VL - 59 IS - 25 SP - 10037 EP - 10041 PB - Wiley Online Libary AN - OPUS4-50907 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Saleta Reig, D. A1 - Grauel, Bettina A1 - Konyushkin, V. A. A1 - Nakladov, A. N. A1 - Federov, P. P. A1 - Busko, D. A1 - Howard, I. A. A1 - Richards, B. S. A1 - Resch-Genger, Ute A1 - Kuznetsov, S. V. A1 - Turshatov, A. A1 - Würth, Christian T1 - Upconversion properties of SrF2:Yb3+,Er3+ single N2 - Synthesis of new upconversion (UC) materials that can convert near-infrared excitation light into visible emission light with high efficiency has crucial importance for energy and bio-applications. Herein, SrF2 single crystals with a doping concentration of 2 mol% Er3+ and 2–8 mol% Yb3+ were synthesized and the optical properties were studied. The absorption cross-section of the different doping ions was calculated. To identify the most efficient and brightest material absolute excitation power dependent UC photoluminescence quantum yields (ϕUC) and brightness values were determined. In addition, excitation characteristics and luminescence lifetimes were analysed to understand the changes in population pathways and possible quenching mechanisms. A dominant two-photon population behaviour of the red and green emission bands was observed for all investigated doping concentrations of Yb3+ and Er3+. The ϕUC value of 6.5% measured using 230 W cm−2 of 976 nm excitation for SrF2 crystal co-doped with 2 mol% Er3+ and 3 mol% Yb3+. These findings broaden the scope of efficient UC materials apart from the record UC material β-NaYF4:Yb3+, Er3+ and provide benchmark values for cubic-phase and especially SrF2- nano and micrometer sized materials. KW - Luorescence KW - Upconversion KW - Crystal KW - Lanthanide KW - Quantum yield KW - Absolute KW - Lifetime KW - Er(III) KW - Quality assurance KW - Fluorescence standard KW - SrF2 PY - 2020 DO - https://doi.org/10.1039/c9tc06591a VL - 8 IS - 12 SP - 4093 EP - 4101 PB - Journal of Materials Chemistry C AN - OPUS4-50825 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Meyerhofer, F. A1 - Dissinger, F. A1 - Weigert, Florian A1 - Jungclaus, J. A1 - Müller-Caspary, K. A1 - Waldvogel, S. R. A1 - Resch-Genger, Ute A1 - Voss, T. T1 - Citric Acid Based Carbon Dots with Amine Type Stabilizers: pHSpecific N2 - We report the synthesis and spectroscopic characteristics of two different sets of carbon dots (CDs) formed by hydrothermal reaction between citric acid and polyethylenimine (PEI) or 2,3-diaminopyridine (DAP). Although the formation of amide-based species and the presence of citrazinic acid type derivates assumed to be responsible for a blue emission is confirmed for both CDs by elemental analysis, infrared spectroscopy, and mass spectrometry, a higher abundance of sp2-hybridized nitrogen is observed for DAP-based CDs, which causes a red-shift of the n-π* absorption band relative to the one of PEI-based CDs. These CD Systems possess high photoluminescence quantum yields (QY) of ∼40% and ∼48% at neutral pH, demonstrating a possible tuning of the optical properties by the amine precursor. pH-Dependent spectroscopic studies revealed a drop in QY to < 9% (pH ∼ 1) and < 21% (pH ∼ 12) for both types of CDs under acidic and basic conditions. In contrast, significant differences in the pHdependency of the n-π* transitions are found for both CD types which are ascribed to different (de)protonation sequences of the CD-specific fluorophores and functional groups using Zeta potential analysis. KW - Fluorescence KW - Particle KW - Nano KW - Surface group analysis KW - Carbon dot KW - C-dot KW - Fluorescent probe KW - Quantum yield KW - Synthesis KW - IR KW - MS KW - Polymer KW - Ligand PY - 2020 DO - https://doi.org/10.1021/acs.jpcc.9b11732 VL - 124 IS - 16 SP - 8894 EP - 8904 PB - American Chemical Society AN - OPUS4-50813 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Yu, Z. A1 - Musnier, B. A1 - Wegner, Karl David A1 - Henry, M. A1 - Chovelon, B. A1 - Desroches-Castan, A. A1 - Fertin, A. A1 - Resch-Genger, Ute A1 - Bailly, S. A1 - Coll, J.-L. A1 - Usson, Y, A1 - Josserand, V. A1 - Le Gúevel, X. T1 - High-Resolution Shortwave Infrared Imaging of Vascular Disorders Using Gold Nanoclusters N2 - We synthesized a generation of water-soluble, atomically precise gold nanoclusters (Au NCs) with anisotropic Surface containing a short dithiol pegylated chain (AuMHA/TDT). The AuMHA/TDT exhibit a high brightness (QY ∼ 6%) in the shortwave infrared (SWIR) spectrum with a detection above 1250 nm. Furthermore, they show an extended half-life in blood (t1/2ß = 19.54 ± 0.05 h) and a very weak accumulation in organs. We also developed a non-invasive, whole-body vascular imaging system in the SWIR window with high-resolution, benefiting from a series of Monte Carlo image processing. The imaging process enabled to improve contrast by 1 order of magnitude and enhance the spatial Resolution by 59%. After systemic administration of these nanoprobes in mice, we can quantify vessel complexity in depth (>4 mm), allowing to detect very subtle vascular disorders non-invasively in bone morphogenetic protein 9 (Bmp9)-deficient mice. The combination of these anisotropic surface charged Au NCs plus an improved SWIR imaging device allows a precise mapping at high-resolution and an in depth understanding of the organization of the vascular network in live animals. KW - Nanoparticle KW - Nanosensor KW - Fluorescence KW - Metal cluster KW - NIR KW - SWIR KW - Photophysics KW - Ligand KW - Size KW - Surface chemistry KW - Quantum yield KW - Mechanism KW - Lifetime KW - Decay kinetics PY - 2020 DO - https://doi.org/10.1021/acsnano.0c01174 VL - 14 IS - 4 SP - 4973 EP - 4981 PB - ACS Publication AN - OPUS4-50671 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kraft, Marco A1 - Würth, Christian A1 - Muhr, V. A1 - Hirsch, T. A1 - Resch-Genger, Ute T1 - Explaining the influence of dopant concentration and excitation power density on the luminescence and brightness of beta-NaYF_4:Yb~(3+),Er~(3+) nanoparticles: Measurements and simulations N2 - A systematic study of the luminescence properties of monodisperse β-NaYF4: 20% Yb3+, 2% Er3+ upconversion nanoparticles (UCNPs) with sizes ranging from 12–43 nm is presented utilizing steady-state and time-resolved fluorometry. Special emphasis was dedicated to the absolute quantification of size- and environment-induced quenching of upconversion luminescence (UCL) by highenergy O–H and C–H vibrations from solvent and ligand molecules at different excitation power densities (P). In this context, the still-debated Population pathways of the 4F9/2 energy level of Er3+ were examined. Our results highlight the potential of particle size and P value for color tuning based on the pronounced near-infrared emission of 12 nm UCNPs, which outweighs the red Er3+ emission under “strongly quenched” conditions and accounts for over 50% of total UCL in water. Because current rate equation models do not include such emissions, the suitability of these models for accurately simulating all (de)population pathways of small UCNPs must be critically assessed. Furthermore, we postulate population pathways for the 4F9/2 energy level of Er3+, which correlate with the size-, environment-, and P-dependent quenching states of the higher Er3+ energy levels. KW - Nanoparticle KW - Nanosensor KW - Fluorescence KW - Upconversion KW - Upconversion nanoparticle KW - NIR KW - Photophysics KW - Lanthanide KW - Size KW - Surface chemistry KW - Quantum yield KW - Mechanism KW - Lifetime KW - Decay kinetics KW - Quenching KW - Diameter KW - Cyclohexane KW - Water PY - 2018 DO - https://doi.org/10.1007/s12274-018-2159-9 VL - 11/12 SP - 6360 EP - 6374 PB - Springer Nature AN - OPUS4-50307 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gharaati, S. A1 - Wang, Cui A1 - Förster, C. A1 - Weigert, Florian A1 - Resch-Genger, Ute A1 - Heinze, K. T1 - Triplet–Triplet Annihilation Upconversion in a MOF with AcceptorFilled Channels N2 - In summary, we report a highly modular solid TTA-UC system comprising of a crystalline, thermally stable PCN222(Pd) MOF with CA-coated MOF channels and with a DPA annihilator embedded in a solution-like environment in the MOF channels. This solid material displays blue upconverted delayed emission with a luminescence lifetime of 373 us, a threshold value of 329 mW*cm-2 and a triplet–triplet energy transfer efficiency of 82%. This optical application adds another facet to the versatile chemistry of PCN-222 MOFs. The design concept is also applicable to other TTA-UC pairs and enables tuning of the UCL color, for example, by replacing DPA with other dyes as exemplarily shown for 2,5,8,11-tetra-tert-butyl-perylene, that yields UCL at 450 nm. Current work aims to reduce the oxygen sensitivity and to increase the retention of the trapped annihilators in organic environments, for example, by tuning the chain length of the carboxylic acid and by coating the MOF surface. In addition, the TTA-UC efficiency will be further enhanced by reducing the reabsorption of the UC emission caused by Pd(TCPP) and by optimizing the sensitizer/annihilator interface. KW - Porphyrin KW - Method KW - MOF KW - Fluorescence KW - Dye KW - Sensor KW - Oxygen sensitive KW - Single molecule KW - DPA KW - Lifetime KW - Upconverstion KW - Quantum yield KW - Triplet-triplet annihilation KW - Sensitization KW - Energy transfer KW - NMR PY - 2019 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-500580 DO - https://doi.org/10.1002/chem.201904945 VL - 26 IS - 5 SP - 1003 EP - 1007 PB - Wiley-VCH Verlag CY - Weinheim AN - OPUS4-50058 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hirsch, A. A1 - Lohmann, S.-H. A1 - Strelow, C. A1 - Kipp, T. A1 - Würth, Christian A1 - Geißler, Daniel A1 - Komoski, A. A1 - Wolter, C. A1 - Weller, H. A1 - Resch-Genger, Ute A1 - Mews, A. T1 - Fluorescence Quantum Yield and Single-Particle Emission of CdSe N2 - The fluorescence quantum yield (QY) of CdSe dot/CdS rod (DR) nanoparticle ensembles is dependent on the Shell growth and excitation wavelength. We analyze the origin of this dependency by comparing the optical properties of DR ensembles to the results obtained in single-particle experiments. On the Ensemble level, we find that the QY of DRs with shell lengths shorter than 40 nm exhibits no dependence on the excitation wavelength, whereas for DRs with shell lengths longer than 50 nm, the QY significantly decreases for excitation above the CdS band gap. Upon excitation in the CdSe core, the ensemble QY, the fluorescence wavelength, and the fluorescence blinking behavior of individual particles are only dependent on the radial CdS shell thickness and not on the CDs shell length. If the photogenerated excitons can reach the CdSe core region, the fluorescence properties will be dependent only on the surface passivation in close vicinity to the CdSe core. The change in QY upon excitation above the band gap of CdS for longer DRs cannot be explained by nonradiative particles because the ratio of emitting DRs is found to be independent of the DR length. We propose a model after which the decrease in QY for longer CdS shells is due to an increasing fraction of nonradiative exciton recombination within the elongated shell. This is supported by an effective-mass-approximation-based calculation, which suggests an optimum length of DRs of about 40 nm, to combine the benefit of high CdS absorption cross section with a high fluorescence QY. KW - Fluorescence KW - Quantum dot KW - Photophysics KW - Single particle spectroscopy KW - Mechanism KW - Theory KW - Ensemble measurements KW - Quantum yield KW - CdSe KW - CdS shell PY - 2019 DO - https://doi.org/10.1021/acs.jpcc.9b07957 VL - 123 IS - 39 SP - 24338 EP - 24346 PB - ACS Publications AN - OPUS4-49556 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Treiling, S. A1 - Wang, Cui A1 - Förster, C. A1 - Reichenauer, F. A1 - Kalmbach, J. A1 - Boden, P. A1 - Harris, J. P. A1 - Carrella, L. M. A1 - Rentschler, E. A1 - Resch-Genger, Ute A1 - Reber, C. A1 - Seitz, M. A1 - Gerhards, M. A1 - Heinze, K. T1 - Luminescence and Light-Driven Energy and Electron Transfer from an Exceptionally Long-Lived Excited State of a Non-Innocent Chromium(III) Complex N2 - Photoactive metal complexes employing Earth‐abundant metal ions are a key to sustainable photophysical and photochemical applications. We exploit the effects of an inversion center and ligand non‐innocence to tune the luminescence and photochemistry of the excited state of the [CrN6] chromophore [Cr(tpe)2]3+ with close to octahedral symmetry (tpe=1,1,1‐tris(pyrid‐2‐yl)ethane). [Cr(tpe)2]3+ exhibits the longest luminescence lifetime (τ=4500 μs) reported up to date for a molecular polypyridyl chromium(III) complex together with a very high luminescence quantum yield of Φ=8.2 % at room temperature in fluid solution. Furthermore, the tpe ligands in [Cr(tpe)2]3+ are redox non‐innocent, leading to reversible reductive chemistry. The excited state redox potential and lifetime of [Cr(tpe)2]3+ surpass those of the classical photosensitizer [Ru(bpy)3]2+ (bpy=2,2′‐bipyridine) enabling energy transfer (to oxygen) and photoredox processes (with azulene and tri(n‐butyl)amine). KW - Quantum yield KW - Cr(III) complex KW - Longst luminescence lifetime KW - Electron transfer PY - 2019 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-494870 DO - https://doi.org/10.1002/anie.201909325 VL - 58 SP - 2 EP - 13 PB - Wiley-VCH AN - OPUS4-49487 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Özelci, Ersan A1 - Rühle, Bastian A1 - Weigert, Florian A1 - Lubotzky, B. A1 - Kewes, G. A1 - Resch-Genger, Ute A1 - Benson, O. T1 - Quantitative measurements of the pH-sensitive quantum yield of fluorophores in mesoporous silica thin films using a drexhage-type experiment N2 - The photoluminescence quantum yield characterizes the performance of emitters for applications in optical devices, as reporters or probes in material and analytical sciences, and for sensing applications. Quantum yield measurements are challenging for luminescent molecules and nanocrystals immobilized in thin films for many sensor applications, particularly if spatially resolved quantitative luminescence information is desired. We show here that a Drexhage-type experiment, where a silver-coated millimeter-sized sphere is used to modify the local density of states, can provide an elegant approach to counter this challenge. As a representative example of the potential of this method, we measure the pH-dependent photoluminescence quantum yield of fluorescein isothiocyanate bound to a thin mesoporous silica film. The results were compared with those of the studies on the pH dependence of the same dye in solution. We found that our approach can link single fluorophore studies to ensemble measurements and pave the way for the spatially resolved fluorescence measurements of ultralow concentrations of emitters utilized as optically active elements and reporters in thin sensor films or incorporated into membranes. KW - Fluorescence KW - Quantum yield KW - Method KW - pH KW - Dye KW - Sensor KW - Fluorescein KW - Film KW - Silica KW - Single molecule KW - Lifetime KW - Absolute quantum yield PY - 2019 DO - https://doi.org/10.1021/acs.jpcc.9b03917 SN - 1932-7447 SN - 1932-7455 VL - 123 IS - 33 SP - 20468 EP - 20475 PB - ACS Publications AN - OPUS4-48984 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Rietsch, P. A1 - Witte, F. A1 - Sobottka, S. A1 - Germer, G. A1 - Becker, A. A1 - Güttler, Arne A1 - Sarkar, B. A1 - Paulus, B. A1 - Resch-Genger, Ute A1 - Eigler, S. T1 - Diaminodicyanoquinones: Fluorescent dyes with high dipole moments and electron-acceptor properties N2 - Fluorescent dyes are applied in various fields of research,includingsolarcellsandlight-emittingdevices,andas reporters for assays and bioimaging studies.Fluorescent dyes with an added high dipole moment pave the way to nonlinear optics and polarity sensitivity.Redox activity makes it possible to switch the moleculeQsphotophysical properties.Diaminodicyanoquinone derivatives possess high dipole moments,yet only lowfluorescence quantum yields,and have therefore been neglected as fluorescent dyes.Here we investigate the fluorescencepropertiesofdiaminodicyanoquinonesusingacombined theoretical and experimental approach and derive molecules with afluorescence quantum yield exceeding 90%. The diaminodicyanoquinone core moiety provides chemical versatility and can be integrated into novel molecular architectures with unique photophysical features. KW - Dipole moment KW - Fluorescence KW - Quantum yield KW - Quinones PY - 2019 DO - https://doi.org/10.1002/anie.201903204 SN - 1433-7851 SN - 1521-3773 VL - 58 IS - 24 SP - 8235 EP - 8239 PB - Wiley Online Libary CY - Weihnheim AN - OPUS4-48890 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute ED - Kaiser, Martin ED - Würth, Christian ED - Kraft, Marco ED - Soukka, T. T1 - Explaining the influence of dopant concentration and excitation power density on the luminescence and brightness of β-NaYF4:Yb3+,Er3+ nanoparticles: Measurements and simulations N2 - We assessed the influence of Yb3+ and Er3+ dopant concentration on the relative spectral distribution, quantum yield (  UC), and decay kinetics of the upconversion luminescence (UCL) and particle brightness (BUC) for similarly sized (33 nm) oleate-capped -NaYF4:Yb3+,Er3+ upconversion (UC) nanoparticles (UCNPs) in toluene at broadly varied excitation power densities (P). This included an Yb3+ series where the Yb3+ concentration was varied between 11%–21% for a constant Er3+ concentration of 3%, and an Er3+ series, where the Er3+ concentration was varied between 1%–4% for a constant Yb3+ concentration of 14%. The results were fitted with a coupled rate equation model utilizing the UCL data and decay kinetics of the green and red Er3+ emission and the Yb3+ luminescence at 980 nm. An increasing Yb3+ concentration favors a pronounced triphotonic population of 4F9/2 at high P by an enhanced back energy transfer (BET) from the 4G11/2 level. Simultaneously, the Yb3+-controlled UCNPs absorption cross section overcompensates for the reduction in  UC with increasing Yb3+ concentration at high P, resulting in an increase in BUC. Additionally, our results show that an increase in Yb3+ and a decrease in Er3+ concentration enhance the color tuning range by P. These findings will pave the road to a deeper understanding of the energy transfer processes and their contribution to efficient UCL, as well as still debated trends in green-to-red intensity ratios of UCNPs at different P. KW - Nanoparticle KW - Lanthanide KW - Upconversion nanoparticle KW - Fluorescence KW - Integration sphere spectroscopy KW - Mechanism KW - Lifetime, synthesis KW - Surface chemistry KW - Yb(III) KW - Er(III) KW - Energy transfer KW - Absolute measurement KW - Quantum yield PY - 2019 DO - https://doi.org/10.1007/s12274-019-2450-4 SN - 1998-0124 SN - 1998-0000 VL - 12 IS - 8 SP - 1871 EP - 1879 PB - Springer AN - OPUS4-48880 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute A1 - Brunet, G. A1 - Marin, R. A1 - Monk, Melissa-Jane A1 - Galico, D. A. A1 - Sigoli, F. A. A1 - Suturina, E. A. A1 - Hemmer, E. A1 - Murugesu, M. T1 - Exploring the dual functionality of an Ytterbium complex for luminescence thermometry and slow magnetic relaxation† N2 - We present a comprehensive investigation of the magnetic and optical properties of an ytterbium complex, which combines two desirable and practical features into a single molecular system. Based upon YbIII Ions that promote near-infrared optical activity and a chemical backbone that is ideal for an in-depth understanding of the magnetic behaviour, we have designed a multifunctional opto-magnetic species that operates as a luminescent thermometer and as a single-molecule magnet (SMM). Our magnetic investigations, in conjunction with ab initio calculations, reveal one of the highest energy barriers reported for an YbIII-based complex. Moreover, we correlate this anisotropic barrier with the Emission spectrum of the compound, wherein we provide a complete assignment of the energetic profile of the complex. Such studies lay the foundation for the design of exciting multi-faceted materials that are able to retain information at the single-molecule level and possess built-in thermal self-monitoring capabilities. KW - Magnetic KW - Fluorescence KW - NIR KW - Temperature KW - Dual sensing KW - Sensor KW - Yb(III) complex KW - Lanthanide KW - Quantum yield KW - Quality assurance PY - 2019 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-486659 DO - https://doi.org/10.1039/c9sc00343f VL - 10 IS - 28 SP - 6799 EP - 6808 PB - Royal Society of Chemistry AN - OPUS4-48665 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wiesholler, L. M. A1 - Frenzel, Florian A1 - Grauel, Bettina A1 - Würth, Christian A1 - Resch-Genger, Ute A1 - Hirsch, T. ED - Resch-Genger, Ute ED - Hirsch, Thomas T1 - Yb,Nd,Er-doped upconversion nanoparticles: 980 nm versus 808 nm excitation N2 - Yb,Nd,Er-doped upconversion nanoparticles (UCNPs) have attracted considerable interest as luminescent reporters for bioimaging, sensing, energy conversion/shaping, and anticounterfeiting due to their capability to convert multiple near-infrared (NIR) photons into shorter wavelength ultraviolet, visible or NIR luminescence by successive absorption of two or more NIR photons. This enables optical measurements in complex media with very little background and high penetration depths for bioimaging. The use of Nd3+ as substitute for the commonly employed sensitizer Yb3+ or in combination with Yb3+ shifts the excitation wavelength from about 980 nm, where the absorption of water can weaken upconversion luminescence, to about 800 nm, and laser-induced local overheating effects in cells, tissue, and live animal studies can be minimized. To systematically investigate the potential of Nd3+ doping, we assessed the performance of a set of similarly sized Yb3+,Nd3+,Er3+-doped core- and core–shell UCNPs of different particle architecture in water at broadly varied excitation power densities (P) with steady state and time-resolved fluorometry for excitation at 980 nm and 808 nm. As a measure for UCNPs performance, the P-dependent upconversion quantum yield (Φ) and its saturation behavior were used as well as particle brightness (B). Based upon spectroscopic measurements at both excitation wavelengths in water and in a lipid phantom and B-based calculations of signal size at different penetration depths, conditions under which excitation at 808 nm is advantageous are derived and parameters for the further optimization of triple-doped UCNPs are given. KW - Lanthanide KW - Upconversion KW - Nanoparticle KW - Photoluminescence KW - Quantum yield KW - Lifetime KW - Brightness KW - Nd excitation KW - Excitation power density KW - Modelling KW - NIR PY - 2019 DO - https://doi.org/10.1039/C9NR03127H SN - 2040-3372 SN - 2040-3364 VL - 11 IS - 28 SP - 13440 EP - 13449 PB - Royal Society of Chemistry CY - London AN - OPUS4-48608 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute A1 - Andresen, Elina A1 - Schäferling, M. T1 - Surface modifications for photon-upconversion-based energy-transfer nanoprobes N2 - An emerging class of inorganic optical reporters are nearinfrared (NIR) excitable lanthanide-based upconversion nanoparticles (UCNPs) with multicolor emission and long luminescence lifetimes in the range of several hundred microseconds. For the design of chemical sensors and optical probes that reveal analyte-specific changes in their spectroscopic properties, these nanomaterials must be combined with sensitive indicator dyes that change their absorption and/or fluorescence properties selectively upon interaction with their target analyte, utilizing either resonance energy transfer (RET) processes or reabsorption-related inner filter effects. The rational development of UCNP-based nanoprobes for chemical sensing and imaging in a biological environment requires reliable methods for the Surface functionalization of UCNPs, the analysis and quantification of Surface groups, a high colloidal stability of UCNPs in aqueous media as well as the chemically stable attachment of the indicator molecules, and suitable instrumentation for the spectroscopic characterization of the energy-transfer systems and the derived nanosensors. These topics are highlighted in the following feature article, and examples of functionalized core−shell nanoprobes for the sensing of different biologically relevant analytes in aqueous environments will be presented. Special emphasis is placed on the intracellular sensing of pH. KW - Nano KW - Nanomaterial KW - Upconversion nanoparticle KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Lifetime KW - Sensor KW - FRET KW - Surface chemistry PY - 2019 DO - https://doi.org/10.1021/acs.langmuir.9b00238 SN - 0743-7463 VL - 35 IS - 15 SP - 5093 EP - 5113 PB - ACS AN - OPUS4-47975 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Bergstrand, J. A1 - Li, Q. A1 - Huang, B. A1 - Peng, X. A1 - Würth, Christian A1 - Resch-Genger, Ute A1 - Zhan, Q. A1 - Widengren, J. A1 - Agren, H. A1 - Liu, H. T1 - On the decay time of upconversion luminescence N2 - In this study, we systematically investigate the decay characteristics of upconversion luminescence (UCL) under anti-Stokes excitation through numerical simulations based on rate-equation models. We find that a UCL decay profile generally involves contributions from the sensitizer’s excited-state lifetime, energy transfer and cross-relaxation processes. It should thus be regarded as the overall temporal response of the whole upconversion system to the excitation function rather than the intrinsic lifetime of the luminescence emitting state. Only under certain conditions, such as when the effective lifetime of the sensitizer’s excited state is significantly shorter than that of the UCL emitting state and of the absence of cross-relaxation processes involving the emitting energy level, the UCL decay time approaches the intrinsic lifetime of the emitting state. Subsequently, Stokes excitation is generally preferred in order to accurately quantify the intrinsic lifetime of the emitting state. However, possible cross-relaxation between doped ions at high doping levels can complicate the decay characteristics of the luminescence and even make the Stokesexcitation approach fail. A strong cross-relaxation process can also account for the power dependence of the decay characteristics of UCL. KW - Nano KW - Nanomaterial KW - Upconversion nanoparticle KW - Lanthanide KW - Photoluminescence KW - Mechanism KW - Quantum yield KW - Photophysics KW - Lifetime KW - Modeling PY - 2019 DO - https://doi.org/10.1039/c8nr10332a VL - 11 IS - 11 SP - 4959 EP - 4969 PB - RSC Royal Society of Chemistry AN - OPUS4-47888 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - EvstigneevT, Roman V. A1 - Parfenov, Peter S. A1 - Dubavik, Aliaksei A1 - Cherevkov, Sergei A A1 - Fedorov, Anatoly V A1 - Martynenko, Irina V. A1 - Resch-Genger, Ute A1 - Ushakova, Elena V. A1 - Baranov, Alexander V. T1 - Time-resolved FRET in AgInS2/ZnS-CdSe/ZnS quantum dot systems N2 - The fast and accurate detection of disease-related biomarkers and potentially harmful analytes in different matrices is one of the main challenges in the life sciences. In order to achieve high signal-to-background ratios with frequently used photoluminescence techniques, luminescent reporters are required that are either excitable in the first diagnostic window or reveal luminescence lifetimes exceeding that of autofluorescent matrix components. Here, we demonstrate a reporter concept relying on broad band emissive ternary quantum dots (QDs) with luminescence lifetimes of a few hundred nanoseconds utilized for prolongating the lifetimes of organic or inorganic emitters with lifetimes in the order of a very few 10 ns or less through fluorescence resonant energy transfer. Using spectrally resolved and time-resolved measurements of the system optical response we demonstrate the potential of lifetime multiplexing with such systems exemplarily for AgInS2/ZnS and CdSe/ZnS QDs. KW - Nano KW - Nanomaterial KW - Ternary quantum dots KW - AIS KW - Semiconductor nanocrystal KW - Photoluminescence KW - Mechanism KW - Quantum yield KW - Photophysics KW - Energy transfer KW - Lifetime KW - Time-gated emission PY - 2019 DO - https://doi.org/10.1088/1361-6528/ab0136 SN - 0957-4484 SN - 1361-6528 VL - 30 IS - 19 SP - 195501, 1 EP - 7 PB - IOP Publishing Ltd AN - OPUS4-47434 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kraft, Marco A1 - Würth, Christian A1 - Palo, Emilia A1 - Soukka, Tero A1 - Resch-Genger, Ute T1 - Colour-optimized quantum yields of Yb, Tm Co-doped upconversion nanocrystals N2 - Wepresent here a systematic analysis of the influence of Tm3+ Doping concentrations (xTm) on the excitation power (P)-dependent upconversion luminescence and -performance of hexagonal-Phase NaYF4: 20% Yb3+, xTm%Tm3+ upconversion nanoparticles (UCNPs) for xTm of 0.2, 0.5, 0.8, 1.2, and 2.0, respectively. Our results reveal the influence of these differentTm3+ doping concentrations with respect to optimized upconversion quantum yield (ΦUC) values of the variousTm3+ upconversion emission bands, with the highestΦUC values of theTm3+ emission bands above 700 nmresulting for different xTm values as theTm3+ emission bands below 700 nm. This underlines the potential ofTm3+ dopant concentration for colour tuning. Special emphasis was dedicated to the spectroscopic parameters that can be linked to the (de)population pathways of the variousTm3+ energy levels, like the P- and xTm-dependent slope factors and the intensity ratios of selected emission bands. The evaluation of all parameters indicates that not only energy transfer upconversion-, but also crossrelaxation processes between neighbouringTm3+ ions play a vital role in the (de)population of the excited energy levels of Yb3+, Tm3+ codoped nanocrystals. KW - Nano KW - Nanomaterial KW - Upconversion nanoparticle KW - Lanthanide KW - Photoluminescence KW - Mechanism KW - Quantum yield KW - Photophysics KW - Lifetime PY - 2019 DO - https://doi.org/10.1088/2050-6120/ab023b SN - 2050-6120 VL - 7 IS - 2 SP - 024001, 1 EP - 6 PB - IOP AN - OPUS4-47420 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Stroyuk, O. A1 - Weigert, Florian A1 - Raevskaya, A. A1 - Spranger, F. A1 - Würth, Christian A1 - Resch-Genger, Ute A1 - Gaponik, N. A1 - Zahn, D. R. T. T1 - Inherently broadband photoluminescence in Ag−In−S/ZnS quantum dots observed in ensemble and single-particle studies N2 - We present a series of results that demonstrate that the broadband photoluminescence (PL) of aqueous glutathione-capped Ag−In−S (AIS) nanocrystals (NCs) is an inherent property of each NC, rather than a collective characteristic of an NC ensemble. By analyzing parameters affecting the PL features such as the postsynthesis annealing and the deposition of a passivating ZnS shell, we found no correlation between the spectral width of the PL band of AIS (AIS/ZnS) NCs and the density of the lattice defects. Analysis of the PL spectra of a series of size-selected AIS/ZnS NCs revealed that the PL width of fractionated NCs does not depend on the NC size and size distribution. The PL measurements in a broad temperature window from 320 to 10 K demonstrated that the PL width does not decrease with decreasing temperature as expected for an emission arising from thermally activated detrapping processes. Also, we show that the model of the self-trapped exciton can be versatilely applied to reconstruct the PL spectra of different AIS NCs and can account for the effects typically attributed to variations in defect state energy. Measurements of the PL properties of single AIS/ZnS NCs highlighted the broadband nature of the emission of individual NCs. The presented results show that the broadband PL of ternary NCs most probably does not originate from lattice defects but involves the NC lattice as a whole, and, therefore, by tailoring the NC structure, PL efficiencies as high as those reported for binary cadmium or lead chalcogenide NCs can be potentially reached. KW - Nano KW - Nanomaterial KW - Ternary quantum dots KW - AIS KW - Semiconductor nanocrystal KW - Photoluminescence KW - Mechanism KW - Single particle spectroscopy KW - Quantum yield KW - Photophysics PY - 2019 DO - https://doi.org/10.1021/acs.jpcc.8b11835 SN - 1932-7447 VL - 123 IS - 4 SP - 2632 EP - 2641 PB - ACS AN - OPUS4-47419 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Otto, S. A1 - Förster, C. A1 - Wang, Cui A1 - Resch-Genger, Ute A1 - Heinze, K. T1 - A Strongly Luminescent Chromium(III) ComplexAcid N2 - The synthesis, structure, reactivity,and photophysical properties of anovel acidic,luminescentchromium(III) complex [Cr(H2tpda)2]3+ (23+ +)bearing the tridentate H2tpda (2,6-bis(2-pyridylamino)pyridine) ligand are presented. Excitation of 23+ + at 442 nm results in strong, long-lived NIR luminescence at 782 nm in water and in acetonitrile. X-ray diffraction analysis and IR spectroscopy revealhydrogen-bonding interactions of the counter ions to the NH groups of 23+ + in the solidstate. Deprotonation of the NH groups of 23+ + by using anon-nucleophilic Schwesinger base in CH3CN switches off the luminescence. Re-protonation by using HClO4 restores the emission. In water,the pKa value of 23+ + amountsto8 .8, yet deprotonation is not reversible in the presence of hydroxide ions. Dioxygen quenches the emission of 23+ +,but to aweaker extent than expected. This is possibly due to the strong ion-pairing properties of 23+ + even in solution, reducing the energy transfer efficiency to O2.Deuteration of the NH groups of 23+ + approximately doubles the quantum yield and lifetime in water,demonstrating the importance of multiphoton relaxation in these NIR emitters. KW - Cr(III) complex KW - Oxygen sensor KW - pH sensor KW - Luminescence KW - Luminescence lifetime KW - Quantum yield KW - NIR emitter PY - 2018 DO - https://doi.org/10.1002/chem.201802797 SN - 0947-6539 VL - 24 IS - 48 SP - 12555 EP - 12563 PB - Wiley‐VCH Verlag GmbH & Co. KGaA CY - Weinheim AN - OPUS4-45929 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Homann, C. A1 - Krukewitt, Lisa A1 - Frenzel, Florian A1 - Grauel, Bettina A1 - Würth, Christian A1 - Resch-Genger, Ute A1 - Haase, M. T1 - NaYF4:Yb,Er/NaYF4 Core/Shell Nanocrystals with High Upconversion Luminescence Quantum Yield N2 - Upconversion core/shell nanocrystals with different mean sizes ranging from 15 to 45 nm were prepared via a modified synthesis procedure based on anhydrous rare‐earth acetates. All particles consist of a core of NaYF4:Yb,Er, doped with 18 % Yb3+ and 2 % Er3+, and an inert shell of NaYF4, with the shell thickness being equal to the radius of the core particle. Absolute measurements of the photoluminescence quantum yield at a series of different excitation power densities show that the quantum yield of 45 nm core/shell particles is already very close to the quantum yield of microcrystalline upconversion phosphor powder. Smaller core/shell particles prepared by the same method show only a moderate decrease in quantum yield. The quantum yield of 15 nm core/shell particles, for instance, is reduced by a factor of three compared to the bulk upconversion phosphor at high power densities (100 W cm−2) and by approximately a factor of 10 at low power densities (1 W cm−2). KW - Core shell structure KW - Upconversion KW - Non lienear processes KW - Nanoparticle KW - Quantum yield PY - 2018 DO - https://doi.org/10.1002/anie.201803083 VL - 57 IS - 28 SP - 8765 EP - 8769 PB - Wiley-VCH AN - OPUS4-45574 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute A1 - Hoffmann, Katrin A1 - Abbandonato, Gerardo T1 - Determination of quantum yields of semiconductor nanocrystals at the single emitter level via fluorescence correlation spectroscopy N2 - Comparing the photoluminescence (PL) properties of ensembles of nanocrystals like semiconductor quantum dots (QDs) with single particle studies is of increasing interest for many applications of These materials as reporters in bioimaging studies performed under very dilute conditions or even at the single particle level. Particularly relevant is here the PL quantum yield (ΦF), which determines the signal size together with the reporter’s molar extinction coefficient and is a direct measure for nanocrystal quality, especially for the inorganic surface passivation shell and its tightness, which can be correlated also with nanocrystal stability and the possible release of heavy metal ions. Exemplarily for red and green emitting CdTe nanocrystals, we present a method for the determination of ΦF of nanoparticle dispersions at ultralow concentration compared to cuvette measurements using fluorescence correlation spectroscopy (FCS), a single molecule method, and compared to molecular dyes with closely matching spectral properties and known ΦF. Our results underline the potential of this approach, provided that material-inherent limitations like ligand- and QD-specific aggregation affecting particle diffusion and QD drawbacks such as their complex and power-dependent blinking behavior are properly considered as shown here. KW - Semiconductor nanocrystal KW - Quantum dot KW - Quantum yield KW - Fluorescence correlation spectroscopy FCS KW - Single molecule PY - 2018 DO - https://doi.org/10.1039/c7nr09332b SN - 2040-3364 SN - 2040-3372 VL - 10 IS - 15 SP - 7147 EP - 7154 PB - Royal Society of Chemistry AN - OPUS4-44894 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute ED - Wang, Cui ED - Otto, S. ED - Dorn, M. ED - Kreidt, E. ED - Lebon, J. ED - Srsan, L. ED - di Martino-Fumo, P. ED - Gerhards, M. ED - Seitz, M. ED - Heinze, K. T1 - Deuterated Molecular Ruby with Record Luminescence Quantum Yield N2 - The recently reported luminescent chromium(III) complex 13+ ([Cr(ddpd)2]3+; ddpd=N,N’-dimethyl-N,N’-dipyridine-2-yl-pyridine-2,6-diamine) shows exceptionally strong near-IR emission at 775 nm in water under ambient conditions (F=11%) with a microsecond lifetime as the ligand design in 13+ effectively eliminates non-radiative decay pathways, such as photosubstitution, back-intersystem crossing, and trigonal twists. In the absence of energy acceptors, such as dioxygen, the remaining decay pathways are energy transfer to high energy solvent and ligand oscillators, namely OH and CH stretching vibrations. Selective deuteration of the solvents and the ddpd ligands probes the efficiency of these oscillators in the excited state deactivation. Addressing these energytransfer pathways in the first and second coordination sphere furnishes a record 30% quantum yield and a 2.3 millisecond lifetime for a metal complex with an earth-abundant metal ion in solution at room temperature. KW - Fluorescence KW - Quantum yield KW - Ligand design KW - Cr(III) KW - Complex KW - Oxygen sensor KW - NIR KW - Fluorescence lifetime PY - 2018 DO - https://doi.org/10.1002/ange.201711350 SN - 1521-3773 VL - 57 IS - 4 SP - 1112 EP - 1116 PB - Wiley-VCH Verlag & Co. KGaA CY - Weinheim AN - OPUS4-44045 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute ED - Wang, Cui ED - Otto, S. ED - Dorn, M. ED - Kreidt, E. ED - Lebon, J. ED - Srsan, L. ED - di Martino-Fumo, P. ED - Gerhards, M. ED - Seitz, M. ED - Heinze, K. T1 - Deuterierter molekularer Rubin mit Rekord-Lumineszenzquantenausbeute N2 - Der kürzlich publizierte Chrom(III)-Komplex 13+([Cr(ddpd)2]3+) zeigt in wässriger Lösung unter Umgebungsbedingungen eine bemerkenswert starke Emission im nahen Infrarot-Bereich mit einer Emissionswellenlänge von 775 nm. Geschicktes Ligandendesign verhindert strahlungslose Desaktivierungsprozesse wie Photosubstitution, Rück-Intersystem-Crossing und trigonale Verzerrungen und führt damit zu einer Phosphoreszenzlebensdauer im Bereich von Mikrosekunden. In Abwesenheit von Energieakzeptoren wie molekularem Sauerstoff verbleibt nur Energietransfer zu hochenergetischen Oszillatoren der Liganden und Lösungsmittelmoleküle wie beispielsweise OH- und CH-Streckschwingungen als Desaktivierungspfad. Selektive Deuterierung der ddpd-Liganden und der Lösungsmittel l-sst die Effizienz dieser Oszillatoren bei der Desaktivierung angeregter Zustände erkennbar werden. Gezieltes Ausschalten dieser Relaxationspfade führt zu einer Quantenausbeute von 30% und einer Lebensdauer von 2.3 Millisekunden bei Raumtemperatur in Lösung – Rekordwerte für einen Komplex, der auf dem Element Chrom basiert. Diese fundamentalen Erkenntnisse ebnen den Weg für gezieltes Ligandendesign zur Synthese lumineszierender Komplexe mit gut verfügbaren Übergangsmetallen. KW - Fluorescence KW - Quantum yield KW - Ligand design KW - Cr(III) KW - Complex KW - Oxygen sensor KW - NIR KW - Fluorescence lifetime PY - 2018 DO - https://doi.org/10.1002/ange.201711350 SN - 1521-3757 VL - 130 IS - 4 SP - 1125 EP - 1130 PB - Wiley-VCH Verlag & Co. KGaA CY - Weinheim AN - OPUS4-44043 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Kothavale, S. A1 - Jadhav, A. G. A1 - Scholz, Norman A1 - Nirmalananthan-Budau, Nithiya A1 - Behnke, Thomas A1 - Resch-Genger, Ute A1 - Sekar, N. T1 - Corrigendum to "Deep red emitting triphenylamine based coumarin-rhodamine hybrids with large stokes shift and viscosity sensing: Synthesis, photophysical properties and DFT studies of their spirocyclic and open forms" [Dyes Pigments 137 (2017) 329-341] N2 - We designed and synthesized triphenylamine based and coumarin fused rhodamine hybrid dyes and characterized using 1H, 13C NMR and HR-LCMS analysis. Both the newly synthesized hybrid dyes were found to show red shifted absorption as well as emissions and large Stokes shift (40e68 nm) as compared to the small Stokes shift (25e30 nm) of reported dyes Rhodamine B and 101. Photophysical properties of these dyes were studied in different solvents and according to the solvents acidity or basicity they preferred to remain in their spirocyclic or open form in different ratio. We studied the spirocyclic as well as open form derivatives of these dyes for their viscosity sensitivity in three different mixture of solvents i.e. polar-protic [EtOH-PEG 400], polar-aprotic [toluene-PEG 400] and non-polaraprotic [toluene-paraffin]. They are found to show very high viscosity sensitivity in polar-protic mixture of solvents [EtOH-PEG 400] and hence concluded that both polarity as well as viscosity factor worked together for the higher emission enhancement rather than only viscosity factor. As these dyes showed very high viscosity sensitivity in their spirocyclic as well as open form, they can be utilized as viscosity sensors in visible as well as deep red region. We also correlated our experimental finding theoretically by using Density Functional theory computations. KW - Dye KW - Fluorescence KW - Synthesis KW - Quantum yield KW - Lifetime KW - Coumarin KW - Rhodamine KW - Probe KW - Viscosity PY - 2018 DO - https://doi.org/10.1016/j.dyepig.2017.06.021 SN - 0143-7208 SN - 1873-3743 N1 - Geburtsname von Nirmalananthan-Budau, Nithiya: Nirmalananthan, N. - Birth name of Nirmalananthan-Budau, Nithiya: Nirmalananthan, N. VL - 149 SP - 929 PB - Elsevier CY - Amsterdam AN - OPUS4-44038 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute ED - Martynenko, Irina ED - Baimuratov, A. S. ED - Osipova, V. A. ED - Kuznetsova, V. A. ED - Purcell-Milton, F. ED - Rukhlenko, I. D. ED - Fedorov, A. V. ED - Gun'ko, Y. K. ED - Baranov, A. V. T1 - Excitation energy dependence of the photoluminescence quantum yield of core/shell CdSe/CdS quantum dots and correlation with circular dichroism N2 - Quantum dot (QD) based nanomaterials are very promising materials for the fabrication of optoelectronic devices like solar cells, light emitting diodes (LEDs), and photodetectors as well as as reporters for chemo- and biosensing and bioimaging. Many of These applications involve the monitoring of changes in photoluminescence intensity and energy transfer processes which can strongly depend on excitation wavelength or energy. In this work, we analyzed the excitation energy dependence (EED) of the photoluminescence quantum yields (PL QYs) and decay kinetics and the circular dichroism (CD) spectra of CdSe/CdS core/shell QDs with different thicknesses of the surface passivation shell. Our results demonstrate a strong correlation between the spectral position of local maxima observed in the EED of PL QY and the zero-crossing points of the CD profiles. Theoretical analysis of the energy band structure of the QDs with effective mass approximation suggests that these structures could correspond to exciton energy levels. This underlines the potential of CD spectroscopy for the study of electronic energy structure of chiroptically active nanocrystals which reveal quantum confinement effects. KW - Fluorescence KW - Semiconductor KW - Nanoparticle KW - Surface chemistry KW - Quantum yield KW - Lifetime KW - Nanocrystal KW - Cysteine KW - Thiol KW - Ligand KW - Quantum dot KW - CdSe KW - Exciton KW - Circular dichroism KW - Theory KW - Excitation spectra KW - Excitation energy dependence PY - 2017 DO - https://doi.org/10.1021/acs.chemmater.7b04478 SN - 0897-4756 SN - 1520-5002 VL - 30 IS - 2 SP - 465 EP - 471 PB - ACS Publications AN - OPUS4-44034 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Huang, K. A1 - Liu, H. A1 - Kraft, Marco A1 - Shikha, S. A1 - Zheng, X. A1 - Agren, H. A1 - Würth, Christian A1 - Resch-Genger, Ute A1 - Zhang, Y. T1 - A protected excitation-energy reservoir for efficient upconversion luminescence N2 - Lanthanide-doped upconversion nanoparticles (UCNPs) are of great interest for biomedical applications. Currently, the applicability of UCNP bionanotechnology is hampered by the generally low luminescence intensity of UCNPs and inefficient energy Transfer from UCNPs to surface-bound chromophores used e.g. for photodynamic therapy or analyte sensing. In this work, we address the low-Efficiency issue by developing versatile core-Shell nanostructures, where high-concentration sensitizers and activators are confined in the core and Shell Region of representative hexagonal NaYF2:Yb,Er UCNPs. After Doping concentration optimization, the sensitizer-rich core is able to harvest/accumulate more excitation energy and generate almost one order of Magnitude higher luminescence intesity than conventional homogeneously doped nanostructures. At the same time, the activator Ions located in the Shell enable a ~6 times more efficient resonant energy Transfer from UCNPs to surface-bound acceptor dye molecules due to the short distance between donor-acceptor pairs. Our work provides new insights into the rational design of UCNPs and will greatly encrease the General applicability of upconversion nanotechnologies. KW - Fluorescence KW - Lanthanide KW - Upconversion KW - Brightness KW - Quantification KW - Nanoparticle KW - Absolute fluorometry KW - NIR KW - IR KW - Quantum yield KW - Integrating sphere spectroscopy KW - Method KW - Energy transfer KW - Shell KW - Particle architecture PY - 2017 DO - https://doi.org/10.1039/c7nr06900f SN - 2040-3372 SN - 2040-3364 VL - 10 IS - 1 SP - 250 EP - 259 PB - The Royal Society of Chemistry AN - OPUS4-43893 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute A1 - Pilch, A. A1 - Würth, Christian A1 - Kaiser, Martin A1 - Wawrzynczyk, D. A1 - Kurnatowska, M. A1 - Arabasz, S. A1 - Prorok, K. A1 - Samoc, M. A1 - Strek, W. A1 - Bednarkiewicz, A. T1 - Shaping luminescent properties of Yb3+ and Ho3+ co-doped upconverting core-shell ß-NaYF4 nanoparticles by dopant distribution and spacing N2 - At the core of luminescence color and lifetime Tuning of rare earth doped upconverting nanoparticles (UCNPs), is the understanding of the Impact of the particle architecture for commonly used sensitizer (S) and activator (A) Ions. In this respect, a series of core@Shell NaYF4 UCNPs doped with Yb3+ and Ho3+ ions are presented here, where the same dopant concentrations are distributed in different particle architectures following the scheme: YbHo core and YbHo@..., ...@YbHo, Yb@Ho, Ho@Yb, YbHo@Yb, and Yb@YbHo core-Shell NPs. As refealed by quantitative steady-state and time-resolved luminescence studies, the relative spatial Distribution of the A and S ions in the UCNPs and their protection from surface quenching has a critical Impact on ther luminescence characteristics. Although the increased amount of Yb3+ Ions boosts UCNP Performance by amplifying the Absorption, the Yb3+ ions can also efficiently dissipate the energy stored in the material through energy Migration to the surface, thereby reducing the Overall energy Transfer Efficiency to the activator ions. The results provide yet another proof that UC Phosphor chemistry combined with materials Engineering through intentional core@shell structures may help to fine-tune the luminescence Features of UCNPs for their specific future applications in biosensing, bioimaging, photovoltaics, and Display technologies. KW - Fluorescence KW - Upconversion KW - NIR KW - Nonlinear KW - Nanoparticle KW - Surface chemistry KW - Quantum yield KW - Liftetime KW - Nanocrystal KW - Lanthanide KW - Ho(III) KW - Yb(III) KW - Mechanism KW - Absolute flourescence KW - Excitation power density dependence PY - 2017 DO - https://doi.org/10.1002/smll.201701635 SN - 1613-6810 VL - 13 IS - 47 SP - 1701635, 1 EP - 13 PB - WILEY-VCH Verlag GmbH & co. KGaA CY - Weinheim AN - OPUS4-43629 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute ED - Guhrenz, C. ED - Sayevich, V. ED - Weigert, Florian ED - Hollinger, E. ED - Reichhelm, A. ED - Gaponik, N. ED - Eychmüller, A. T1 - Transfer of Inorganic-Capped Nanocrystals into Aqueous Media N2 - We report on a novel and simple approach to surface ligand design of CdSe-based nanocrystals (NCs) with biocompatible, heterobifunctional polyethylene glycol (PEG) molecules. This method provides high transfer yields of the NCs into aqueous media with preservation of the narrow and symmetric emission bands of the initial organic-capped NCs regardless of their interior crystal structure and surface chemistry. The PEG-functionalized NCs show small sizes, high photoluminescence quantum yields of up to 75%, as well as impressive optical and colloidal stability. This universal approach is applied to different fluorescent nanomaterials (CdSe/CdS, CdSe/CdSCdxZn1-xS, and CdSe/CdS/ZnS), extending the great potential of organic-capped NCs for biological applications. KW - Fluorescence KW - Ligand exchange KW - Quantum dot KW - Surface chemistry KW - Semiconductor nanocrystal KW - Quantum yield KW - Lifetime KW - Dispersibillity KW - Colloid PY - 2017 DO - https://doi.org/10.1021/acs.jpclett.7b02319 VL - 8 IS - 22 SP - 5573 EP - 5578 PB - The Journal of Physical Chemistry Letters AN - OPUS4-43377 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Martynenko, Irina A1 - Litvin, A.P. A1 - Purcell-Milton, F. A1 - Baranov, A. V. A1 - Fedorov, A.V. A1 - Gun´ko, Y.K. T1 - Application of semiconductor quantum dots in bioimaging and biosensing N2 - In this review we present new concepts and recent progress in the application of semiconductur quantum dots (QD) as labels in two important areas of biology, bioimaging and biosensing. We analyze the biologically relevant properties of QDs focusing on the following topics: QD surface treatment and stability labeling of cellular structures and receptors with QDs, incorporation of QDs in living cells, cytotoxicity of QDs and influence of the biolocical environment on the biological and optical properties of QDs. Initially, we consider utilization of QDs as agants in high-resolution bioimaging techniques that can provide information at the molecular levels. The deverse range of modern live-cell QD-based imaging techniques with resolution far beyond the diffraction limit of light is examined. In each technique, we discuss the pros and cons of QD use and deliberate how QDs can be further engineered to facilitate their application in the respective imaging techniques and to produce significant improvements in resolution. Then we review QD-based point-of-care bioassays, bioprobes, and biosensors designed in different formats ranging from analytic biochemistry assays and ELISA, to novel point-of-care smartphone integrated QD-based biotests. Here, a wide range of QD-based fluorescence bioassays with optical transduction, electrochemiluminescence and photoelectrochemical assays are discussedc. Finally, this review provides an analysis of the prospects of application of QDs in selected important Areas of biology. KW - Fluorescence KW - Semiconductor quantum dot KW - Imaging KW - Quantification KW - Nanoparticle KW - NIR KW - IR KW - Quantum yield KW - Method KW - Microscopy KW - Assay KW - Bioconjugate PY - 2017 DO - https://doi.org/10.1039/c7tb01425b VL - 5 IS - 33 SP - 6701 EP - 6727 PB - Royal Society of Chemistry AN - OPUS4-43027 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Scholz, Norman A1 - Jadhav, A. A1 - Shreykar, M. A1 - Behnke, Thomas A1 - Nirmalananthan-Budau, Nithiya A1 - Resch-Genger, Ute A1 - Sekar, N. T1 - Coumarin-rhodamine hybrids-novel probes for the optical measurements of viscosity and polarity N2 - A comprehensive systematic study of Absorption and fluorescence properties in solvents of varying viscosity and polarity of three novel and red-emitting coumarin-rhodamine hybrid derivatives with differences in the rigidity of their substituents is presented. This includes ethanol-polyethylene glycol, toluene-polyethylene glycol, and tolueneparaffin mixtures. Moreover, protonation-induced effects on the spectroscopic properties are studied. A viscosity-induced emission enhancement was observed for all coumarin-rhodamine hybrid derivatives. MCR2 bearing a julolidine donor showed the expected low sensitivity to viscosity whereas MCR3 with its freely rotatable diphenylamino Substituent revealed a particularly pronounced sensitivity to this parameter. Moreover, MCR2 shows an enhancement in Emission in the open, i.e., protonated form in conjunction with a largely Stokes shift fluorescence in the deep red spectral region. This enables the application of these dyes as viscosity sensors and as far red emitting pH-sensitive probes. KW - Fluorescence KW - Dye KW - Quantum yield KW - Viscosity KW - Polarity KW - Environment KW - Probe KW - Coumarin KW - Rhodamine KW - Synthesis PY - 2017 DO - https://doi.org/10.1007/s10895-017-2165-4 SN - 1573-4994 SN - 1053-0509 N1 - Geburtsname von Nirmalananthan-Budau, Nithiya: Nirmalananthan, N. - Birth name of Nirmalananthan-Budau, Nithiya: Nirmalananthan, N. VL - 27 IS - 6 SP - 1949 EP - 1956 PB - CrossMark AN - OPUS4-42584 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute ED - Mousavi, M. ED - Thomasson, B. ED - Li, M. ED - Kraft, Marco ED - Würth, Christian ED - Andersson-Engels, S. T1 - Beam-profile-compensated quantum yield measurements of upconverting nanoparticles N2 - The quantum yield is a critically important parameter in the development of lanthanide-based upconverting nanoparticles (UCNPs) for use as novel contrast agents in biological imaging and optical reporters in assays. The present work focuses on the influence of the beam Profile in measuring the quantum yield (f) of nonscattering dispersions of nonlinear upconverting probes, by establishing a relation between f and excitation light power density from a rate equation analysis. A resulting 60% correction in the measured f due to the beam profile utilized for excitation underlines the significance of the beam profile in such measurements, and its impact when comparing results from different Setups and groups across the world. KW - Fluorescence KW - Lanthanide KW - Upconversion KW - Brithtness KW - Quantification KW - Nanoparticle KW - Absolute fluoreometry KW - NIR KW - IR KW - Quantum yield KW - Integrating sphere spectroscopy KW - Method PY - 2017 DO - https://doi.org/10.1039/c7cp03785f SN - 1463-9076 SN - 1463-9084 VL - 19 IS - 33 SP - 22016 EP - 22022 PB - Royal Society of Chemistry AN - OPUS4-42583 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Radunz, Sebastian A1 - Tschiche, Harald Rune A1 - Moldenhauer, Daniel A1 - Resch-Genger, Ute T1 - Broad range ON/OFF pH sensors based on pKa tunable fluorescent BODIPYs N2 - A set of highly fluorescent, pH-responsive boron dipyrromethene dyes covering the pH range of 5-12 is presented for broad range pH measurements in mixed aqueous-organic median and polymer matrices. Readout in the intensity Domain with low cost and miniaturized Instrumentation utilizes reversible protonation induced switching ON of their initially completely quenched flourescence mediated by photoinduced electron Transfer. All dyes, rationally designed to reveal closely matching Absorption and Emission properties, are accessible via facile two-step reactions in Overall yields of up to 20%. By modifying the Substitution pattern of the meso-Aryl substiuent, the pKa values could be fine-tuned from 6 to 11. Integration of these molecules into polymeric films by a simple mixing procedure yielded reversible and longterm stable pH sensors for naked eye detection. KW - Fluorescence KW - Sensor KW - PH KW - Dye KW - BODIPY KW - Synthesis KW - Quantification KW - Film KW - Quantum yield KW - Lifetime KW - PET PY - 2017 DO - https://doi.org/10.1016/j.snb.2017.05.080 SN - 0925-4005 VL - 251 SP - 490 EP - 494 PB - Elsevier AN - OPUS4-41782 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Gorris, H.H. A1 - Resch-Genger, Ute T1 - Perspectives and challenges of photon-upconversion nanoparticles - Part II: Bioanalytical applications N2 - In Part II of this Review series on lanthanide-doped photon-upconversion nanoparticles (UCNPs), we present and critically discuss the Performance and suitability of UCNPs as background-free luminescent Reporters in bioimaging and bioanalytical applications. The preparation of a biocompatible nanoparticle surface is an integral step for all life - science-related applications. UCNPs have found their way into a large number of diagnostic platforms, homogeneous and heterogeneous assay formats, and sensor applications. Many bioanalytical detection schemes involve Förster resonance energy transfert (FRET), which is still debated for UCNPs and Needs to be much improved. The Need for dedicated and standardized instruments as well as recent studies on the Dissolution and potential toxicity of UCNPs are addressed. Finally we outline future Trends and challenges in the field of upconversion. KW - Fluorescence KW - Lanthanide KW - Upconversion KW - Brightness KW - Quantification KW - Nanoparticle KW - Absolute fluorometry KW - NIR KW - IR KW - Quantum yield KW - Assay KW - Bioconjugation KW - Imaging KW - FRET KW - Sensor PY - 2017 DO - https://doi.org/10.1007/s00216-017-0482-8 SN - 1618-2650 SN - 1618-2642 VL - 409 IS - 25 SP - 5875 EP - 5890 PB - Springer AN - OPUS4-41706 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute A1 - Gorris, H.H. T1 - Perspectives and challenges of photon-upconversion nanoparticles - Part I: routes to brighter particles and quantitative spectroscopic studies N2 - Lanthanide-doped photon-upconversion nanoparticles (UCNPs) have been the Focus of many Research activities in materials and life sciences in the last 15 years because of their potential to convert light between different spectral regions and their unique photophysical properties. To fully exploit the application potential of These facinating nanomaterials, a number of challenges have to be overcome, such as the low brightness, particularly of small UCNPs, and the reliable quantification of the excitation-power-density-dependent upconversion luminescence. In this series of critical Reviews, recent developments in the design, Synthesis, optical-spectroscopic characterization, and application of UCNPs are presented with Special Focus on bioanalysis and the life sciences. Here we guide the reader from the Synthesis of UCNPs to different concepts to enhance their luminescence, including the required optical-spectroscopic assessment to quantify material Performance; surface modification strategies and bioanalytical applications as well as selected examples of the use of UCNPs as reporters in different Assay formats are addressed in part II. Future Trends and challenges in the field of upconversion are discussed with Special emphasis on UCNP Synthesis and material characterization, particularly quantitative luminescence studies. KW - Fluorescence KW - Lanthanide KW - Upconversion KW - Brightness KW - Quantification KW - Nanoparticle KW - Absolute fluorometry KW - NIR KW - IR KW - Quantum yield PY - 2017 DO - https://doi.org/10.1007/s00216-017-0499-z SN - 1618-2650 SN - 1618-2642 VL - 409 IS - 25 SP - 5855 EP - 5874 PB - Springer AN - OPUS4-41665 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Geißler, Daniel A1 - Würth, Christian A1 - Wolter, C. A1 - Weller, H. A1 - Resch-Genger, Ute T1 - Excitation wavelength dependence of the photoluminescence quantum yield and decay behavior of CdSe/CdS quantum dot/quantum rods with different aspect ratios N2 - The excitation wavelength (lexc) dependence of the photoluminescence (PL) quantum yield (FPL) and decay behavior (tPL) of a series of CdSe/CdS quantum dot/Quantum rods (QDQRs), consisting of the same spherical CdSe core and rod-shaped CdS shells, with aspect ratios ranging from 2 to 20 was characterized. lexc between 400–565 nm were chosen to cover the first excitonic absorption band of the CdSe core material, the onset of absorption of the CDs shell, and the region of predominant shell absorption. A strong lexc dependence of relative and absolutely measured FPL and tPL was found particularly for the longer QDQRs with higher aspect ratios. This is attributed to combined contributions from a length-dependent shell-to-core exciton localization efficiency, an increasing number of defect states within the shell for the longest QDQRs, and probably also the presence of absorbing, yet non-emitting shell material. Although the FPL values of the QDQRs decrease at shorter wavelength, the extremely high extinction coefficients introduced by the shell outweigh this effect, leading to significantly higher brightness values at wavelengths below the absorption onset of the CdS Shell compared with direct excitation of the CdSe cores. Moreover, our results present also an interesting example for the comparability of absolutely measured FPL using an integrating sphere setup and FPL values measured relative to common FPL standards, and underline the Need for a correction for particle scattering for QDQRs with high aspect ratios. KW - Quantum dot KW - Quantum rod KW - Quantum yield KW - Integrating sphere KW - Decay time PY - 2017 DO - https://doi.org/10.1039/C7CP02142A SN - 1463-9076 SN - 1463-9084 VL - 19 IS - 19 SP - 12509 EP - 12516 PB - Royal Society of Chemistry (RSC) AN - OPUS4-40814 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pellegrino, F. A1 - Pellutiè, L. A1 - Sordello, F. A1 - Minero, C. A1 - Ortel, Erik A1 - Hodoroaba, Vasile-Dan A1 - Maurino, V. T1 - Influence of agglomeration and aggregation on the photocatalytic activity of TiO2 nanoparticles N2 - Particle aggregation and agglomeration influence the optical properties of materials and therefore theirability to absorb and scatter the incoming radiation, also affecting their photocatalytic activity. Wehave studied the correlation between aggregation and photocatalytic activity for titanium dioxide bymeans of experimental measurements of extinction and photocatalytic activity and calculations of theiroptical properties (extinction, absorption and scattering cross-sections). This approach can be adoptedto quantitatively assess the quantum yields of the heterogeneous photocatalytic systems. The study wasperformed on TiO2PC105 Cristal ACTiVTM, made of aggregated (and agglomerated) primary particles of anatase. The size of the aggregates has been reduced with ultra-sonication. Aqueous suspensions of the obtained materials were characterized by measuring the optical properties (UV–vis extinction), the sizing properties (DLS) and the photocatalytic activity (degradation of phenol under standard con-ditions). The extinction and absorption spectra of the suspensions were derived from the calculatedcoefficients, considering also the size distributions measured with DLS, and revealed that light absorptionis maximized when particle aggregation and agglomeration are avoided, while diffusion of the incomingradiation dominates when large aggregates and agglomerates are present. The present paper represents a valuable approach to the accurate and reproducible measurement of the photocatalytic activity ofTiO2nanoparticles suspensions, thus allowing a more reliable comparison of the properties of different materials. KW - Titanium dioxide KW - Nanoparticles KW - Agglomeration/aggregation KW - Photocatalysis KW - Quantum yield PY - 2017 DO - https://doi.org/10.1016/j.apcatb.2017.05.046 SN - 0926-3373 SN - 1873-3883 VL - 216 SP - 80 EP - 87 PB - Elsevier B.V. AN - OPUS4-40477 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Pauli, Jutta A1 - Wycisk, V. A1 - Welker, P. A1 - Justies, A. A1 - Resch-Genger, Ute A1 - Haag, R. A1 - Licha, K. T1 - Glycerol-Based Contrast Agents: A Novel Series of Dendronized Pentamethine Dyes N2 - The synthesis of water-soluble dyes, which absorb and emit in the range between 650 and 950 nm and display high extinction coefficients (ε) as well as high fluorescence quantum yields (Φf), is still a demand for optical imaging. We now present a synthetic route for the preparation of a new group of glycerol-substituted cyanine dyes from dendronized indole precursors that have been functionalized as Nhydroxysuccinimide (NHS) esters. High Φf values of up to 0.15 and extinction coefficients of up to 189 000 L mol−1 cm−1 were obtained for the pure dyes. Furthermore, conjugates of the new dendronized dyes with the antibody cetuximab (ctx) that were directed against the epidermal growth factor receptor (EGFR) of tumor cells could be prepared with dye to protein ratios between 0.3 and 2.2 to assess their potential as imaging probes. For the first time, ctx conjugates could be achieved without showing a decrease in Φf and with an increasing labeling degree that exceeded the value of the pure dye even at a labeling degree above 2. The incorporation of hydrophilically and sterically demanding dendrimers into cyanines prevented dimer formation after covalent conjugation to the antibody. The binding functionality of the resulting ctx conjugates to the EGFR was successfully demonstrated by cell microscopy studies using EGFR expressing cell lines. In summary, the combination of hydrophilic glycerol dendrons with reactive dye labels has been established for the first time and is a promising Approach toward more powerful fluorescent labels with less dimerization. KW - Dye KW - Quantum yield KW - Fluorescence KW - Contrast agent KW - Extinction coefficient PY - 2015 DO - https://doi.org/10.1021/acs.bioconjchem.5b00097 SN - 1043-1802 VL - 26 SP - 773 EP - 781 PB - ACS Publications CY - Washington AN - OPUS4-38880 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Meiling, T. A1 - Cywinski, P. A1 - Bald, Ilko T1 - White carbon: Fluorescent carbon nanoparticles with tunable quantum yield in a reproducible green synthesis N2 - In this study, a new reliable, economic, and environmentally-friendly one-step synthesis is established to obtain carbon nanodots (CNDs) with well-defined and reproducible photoluminescence (PL) properties via the microwave-assisted hydrothermal treatment of starch and Tris-acetate-EDTA (TAE) buffer as carbon sources. Three kinds of CNDs are prepared using different sets of above mentioned starting materials. The as-synthesized CNDs: C-CND (starch only), N-CND 1 (starch in TAE) and N-CND 2 (TAE only) exhibit highly homogenous PL and are ready to use without need for further purification. The CNDs are stable over a long period of time (>1 year) either in solution or as freeze-dried powder. Depending on starting material, CNDs with PL quantum yield (PLQY) ranging from less than 1% up to 28% are obtained. The influence of the precursor concentration, reaction time and type of additives on the optical properties (UV-Vis absorption, PL emission spectrum and PLQY) is carefully investigated, providing insight into the chemical processes that occur during CND formation. Remarkably, upon freeze-drying the initially brown CND-solution turns into a non-fluorescent white/slightly Brown powder which recovers PL in aqueous solution and can potentially be applied as fluorescent marker in bio-imaging, as a reduction agent or as a photocatalyst. KW - Carbon dots KW - Quantum yield KW - Fluorescence KW - Nanoparticles PY - 2016 UR - https://nbn-resolving.org/urn:nbn:de:kobv:b43-367204 DO - https://doi.org/10.1038/srep28557 VL - 6 SP - Article 28557, 1 EP - 9 PB - Nature Publishing Group AN - OPUS4-36720 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Resch-Genger, Ute A1 - Sloniec-Myszk, Jagoda ED - Hennig, Andreas T1 - Chiral, J-aggregate-forming dyes for alternative signal modulation mechanisms in self-immolative enzyme-activatable optical probes N2 - Enzyme-activatable optical probes are important for future advances in cancer imaging, but may easily suffer from low signal-to-background ratios unless not optimized. To address this shortcoming, numerous mechanisms to modulate the fluorescence signal have been explored. We report herein newly synthesized probes based on selfimmolative linkers containing chiral J-aggregate-forming dyes. Signal modulation by formation of chiral J-aggregates is yet unexplored in optical enzyme probe design. The comprehensive characterization of the probes by absorption, CD, fluorescence, and time-resolved fluorescence spectroscopy revealed dye−dye interactions not observed for the free dyes in solution as well as dye−protein interactions with the enzyme. This suggested that J-aggregate formation is challenging to achieve with current probe design and that interactions of the dyes with the Enzyme may interfere with achieving high signal-to-background ratios. The detailed understanding of the interactions provided herein provides valuable guidelines for the future design of similar probes. KW - Signal amplification KW - Fluorescence KW - Quantum yield KW - Optical spectroscopy KW - Dye KW - Cyanine KW - Characterization KW - Assay KW - Chiral KW - Aggregation KW - Activatable probe PY - 2016 DO - https://doi.org/10.1021/acs.jpcb.5b10526 SN - 1520-5207 SN - 1520-6106 VL - 120 IS - 5 SP - 877 EP - 885 PB - ACS Publications AN - OPUS4-35949 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Würth, Christian A1 - Geißler, Daniel A1 - Behnke, Thomas A1 - Kaiser, Martin A1 - Resch-Genger, Ute T1 - Critical review of the determination of photoluminescence quantum yields of luminescent reporters N2 - A crucial variable for methodical performance evaluation and comparison of luminescent reporters is the photoluminescence quantum yield (Φ pl). This quantity, defined as the number of emitted photons per number of absorbed photons, is the direct measure of the efficiency of the conversion of absorbed photons into emitted light for small organic dyes, fluorescent proteins, metal–ligand complexes, metal clusters, polymeric nanoparticles, and semiconductor and up-conversion nanocrystals. Φ pl determines the sensitivity for the detection of a specific analyte from the chromophore perspective, together with its molar-absorption coefficient at the excitation wavelength. In this review we discuss different optical and photothermal methods for measuring Φ pl of transparent and scattering systems for the most common classes of luminescent reporters, and critically evaluate their potential and limitations. In addition, reporter-specific effects and sources of uncertainty are addressed. The ultimate objective is to provide users of fluorescence techniques with validated tools for the determination of Φ pl, including a series of Φ pl standards for the ultraviolet, visible, and near-infrared regions, and to enable better judgment of the reliability of literature data. KW - Fluorescence KW - Photoluminescence KW - Quantum yield KW - Organic dye KW - Nanoparticle KW - Quantum dot KW - Up-conversion nanocrystal KW - Optical probe KW - Standard KW - Quality assurance KW - Integrating sphere spectroscopy KW - Photoacoustic spectroscopy KW - Thermal lensing KW - Nanocavity PY - 2015 DO - https://doi.org/10.1007/s00216-014-8130-z SN - 1618-2642 SN - 1618-2650 VL - 407 IS - 1 SP - 59 EP - 78 PB - Springer CY - Berlin AN - OPUS4-32406 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Schoetz, U. A1 - Deliolanis, N.C. A1 - Ng, D. A1 - Pauli, Jutta A1 - Resch-Genger, Ute A1 - Kühn, E. A1 - Heuer, S. A1 - Beisker, W. A1 - Köster, R.W. A1 - Zitzelsberger, H. A1 - Caldwell, R.B. T1 - Usefulness of a Darwinian system in a biotechnological application: evolution of optical window fluorescent protein variants under selective pressure N2 - With rare exceptions, natural evolution is an extremely slow process. One particularly striking exception in the case of protein evolution is in the natural production of antibodies. Developing B cells activate and diversify their immunoglobulin (Ig) genes by recombination, gene conversion (GC) and somatic hypermutation (SHM). Iterative cycles of hypermutation and selection continue until antibodies of high antigen binding specificity emerge (affinity maturation). The avian B cell line DT40, a cell line which is highly amenable to genetic manipulation and exhibits a high rate of targeted integration, utilizes both GC and SHM. Targeting the DT40's diversification machinery onto transgenes of interest inserted into the Ig loci and coupling selective pressure based on the desired outcome mimics evolution. Here we further demonstrate the usefulness of this platform technology by selectively pressuring a large shift in the spectral properties of the fluorescent protein eqFP615 into the highly stable and advanced optical imaging expediting fluorescent protein Amrose. The method is advantageous as it is time and cost effective and no prior knowledge of the outcome protein's structure is necessary. Amrose was evolved to have high excitation at 633 nm and excitation/emission into the far-red, which is optimal for whole-body and deep tissue imaging as we demonstrate in the zebrafish and mouse model. KW - Fluorescent protein KW - Quantum yield PY - 2014 DO - https://doi.org/10.1371/journal.pone.0107069 SN - 1932-6203 VL - 9 IS - 9 SP - e107069-1 EP - e107069-12 PB - PubMed Central AN - OPUS4-31976 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Mathejczyk, J. A1 - Pauli, Jutta A1 - Dullin, C. A1 - Napp, J. A1 - Tietze, L.-F. A1 - Kessler, H. A1 - Resch-Genger, Ute A1 - Alves, F. T1 - Spectroscopically well-characterized RGD optical probe as a prerequisite for lifetime-gated tumor imaging N2 - Labeling of RGD peptides with near-infrared fluorophores yields optical probes for noninvasive imaging of tumors overexpressing ανβ3 integrins. An important prerequisite for optimum detection sensitivity in vivo is strongly absorbing and highly emissive probes with a known fluorescence lifetime. The RGD-Cy5.5 optical probe was derived by coupling Cy5.5 to a cyclic arginine–glycine–aspartic acid–D-phenylalanine–lysine (RGDfK) peptide via an aminohexanoic acid spacer. Spectroscopic properties of the probe were studied in different matrices in comparison to Cy5.5. For in vivo imaging, human glioblastoma cells were subcutaneously implanted into nude mice, and in vivo fluorescence intensity and lifetime were measured. The fluorescence quantum yield and lifetime of Cy5.5 were found to be barely affected on RGD conjugation but dramatically changed in the presence of proteins. By time domain fluorescence imaging, we demonstrated specific binding of RGD-Cy5.5 to glioblastoma xenografts in nude mice. Discrimination of unspecific fluorescence by lifetime-gated analysis further enhanced the detection sensitivity of RGD-Cy5.5-derived signals. We characterized RGD-Cy5.5 as a strongly emissive and stable probe adequate for selective targeting of ανβ3 integrins. The specificity and thus the overall detection sensitivity in vivo were optimized with lifetime gating, based on the previous determination of the probés fluorescence lifetime under application-relevant conditions. KW - Time domain near-infrared fluorescence (NIRF) imaging KW - Fluorescence KW - Lifetime KW - Quantum yield KW - RGD-Cy5.5 KW - Spectroscopic analysis PY - 2011 DO - https://doi.org/10.2310/7290.2011.00018 SN - 1535-3508 SN - 1536-0121 VL - 10 IS - 6 SP - 469 EP - 480 PB - Decker CY - Hamilton, Ont. AN - OPUS4-25711 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Würth, Christian A1 - González, M.G. A1 - Niessner, R. A1 - Panne, Ulrich A1 - Haisch, C. A1 - Resch-Genger, Ute T1 - Determination of the absolute fluorescence quantum yield of rhodamine 6G with optical and photoacoustic methods - providing the basis for fluorescence quantum yield standards N2 - To establish the methodical basis for the development and certification of fluorescence quantum yield standards, we determined the fluorescence quantum yield Φf of rhodamine 6G (R6G) with two absolute methods with complementary measurement principles, here optical spectroscopy using an integrating sphere setup and pulsed laser photoacoustic spectroscopy (PAS). For the assessment of aggregation- and reabsorption-induced distortions of measured fluorescence quantum yields and procedures for the reliable consideration of such effects, this systematic comparison was performed in ethanol and in water employing different concentrations of R6G. In addition, the relative and absolute fluorescence quantum yields of these solutions were obtained with a calibrated spectrofluorometer and a commercialized integrating sphere setup. Based upon this systematic comparison, experimental advantages and systematic sources of variation were identified for both methods. KW - Fluorescence KW - Photoluminescence KW - Quantum yield KW - Photoacoustic spectroscopy KW - Absolute quantum yield KW - Integrating sphere KW - Rhodamine 6G KW - Aggregation KW - Reabsorption PY - 2012 DO - https://doi.org/10.1016/j.talanta.2011.12.051 SN - 0039-9140 VL - 90 SP - 30 EP - 37 PB - Elsevier CY - Amsterdam AN - OPUS4-25710 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Hodenius, M. A1 - Würth, Christian A1 - Jayapaul, J. A1 - Wong, J. E. A1 - Lammers, T. A1 - Gätjens, J. A1 - Arns, S. A1 - Mertens, N. A1 - Slabu, I. A1 - Ivanova, G. A1 - Bornemann, J. A1 - De Cuyper, M. A1 - Resch-Genger, Ute A1 - Kiessling, F. T1 - Fluorescent magnetoliposomes as a platform technology for functional and molecular MR and optical imaging N2 - Here, we present a detailed characterisation of rhodamine B-containing magnetoliposomes (FLU-ML), emphasising the dependence of their fluorescence properties on the presence of iron oxide cores, and the molar fraction of the fluorophore. The magnetoliposome types used exist as colloidally stable, negatively charged clusters with an average hydrodynamic diameter of 95 nm. The molar rhodamine B fractions were 0.67 % and 1.97 %. Rhodamine B normalised fluorescence, quantum yields and fluorescence lifetimes were substantially reduced by inner filter effects as the magnetoliposome concentration is increased, by increasing molar rhodamine B fraction, and by quenching originating from the iron oxide cores. MR relaxometry at 3 T revealed extremely high r2 relaxivities (440 to 554 s-1mM-1) and moderately high r1 values (2.06 to 3.59 s-1mM-1). Upon incubating human prostate carcinoma (PC-3) cells with FLU-ML, a dose-dependent particle internalisation was found by MR relaxometry. In addition, the internalised FLU-ML were clearly visible by fluorescence microscopy. At the FLU-ML concentrations used (up to 3 × 103 M Fe) cell viability was not substantially impaired. These results provide valuable insights on the fluorescence properties of bimodal magnetoliposomes and open promising perspectives for the use of these materials as a platform technology for advanced functional and molecular MR and optical imaging applications. KW - Fluorescent magnetoliposomes KW - Steady state and time resolved fluorometry KW - Quantum yield KW - Fluorescence lifetimes KW - MR relaxivities KW - PC-3 cells KW - Cell viability PY - 2012 DO - https://doi.org/10.1002/cmmi.467 SN - 1555-4309 SN - 1555-4317 VL - 7 IS - 1 SP - 59 EP - 67 PB - Wiley CY - Chichester AN - OPUS4-25577 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Würth, Christian A1 - Pauli, Jutta A1 - Lochmann, Cornelia A1 - Spieles, Monika A1 - Resch-Genger, Ute T1 - Integrating sphere setup for the traceable measurement of absolute photoluminescence quantum yields in the near infrared N2 - There is an increasing interest in chromophores absorbing and emitting in the near-infrared (NIR) spectral region, e.g., for applications as fluorescent reporters for optical imaging techniques and hence, in reliable methods for the characterization of their signal-relevant properties like the fluorescence quantum yield (Φf) and brightness. The lack of well established Φf standards for the NIR region in conjunction with the need for accurate Φf measurements in transparent and scattering media encouraged us to built up an integrating sphere setup for spectrally resolved measurements of absolute fluorescence traceable to radiometric scales. Here, we present the design of this setup and its characterization and validation including an uncertainty budget for the determination of absolute Φf in the visible and NIR. To provide the basis for better measurements of Φf in the spectral window from ca. 600 to 1000 nm used, e.g., for optical imaging, the absolute Φf of a set of NIR chromophores covering this spectral region are measured and compared to relative values obtained using rhodamine 101 as Φf standard. Additionally, the absolute Φf values of some red dyes that are among the most commonly used labels in the life sciences are presented as well as the absolute quantum yield of an optical probe for tumor imaging. KW - Fluorescence KW - Photoluminescence KW - Quantum yield KW - Dye KW - Uncertainty KW - Absolute quantum yield KW - Method comparison KW - Integrating sphere KW - NIR KW - Standards KW - Quantum yield standards PY - 2012 DO - https://doi.org/10.1021/ac2021954 SN - 0003-2700 SN - 1520-6882 VL - 84 IS - 3 SP - 1345 EP - 1352 PB - American Chemical Society CY - Washington, DC AN - OPUS4-25504 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Behnke, Thomas A1 - Würth, Christian A1 - Laux, Eva-Maria A1 - Hoffmann, Katrin A1 - Resch-Genger, Ute T1 - Simple strategies towards bright polymer particles via one-step staining procedures N2 - In order to develop simple and versatile procedures for the preparation of red emissive particles, various one-step swelling procedures for the loading of fluorophores into nanometer- and micrometer-sized polystyrene particles were systematically assessed. Parameters studied for model dyes from common dye classes include the composition of the swelling medium, dye charge and polarity, dye concentration, and particle surface chemistry. The dye loading procedures were compared based upon the efficiency of dye incorporation, fluorescence intensity, and colloidal stability of the resulting particles as well as the absence of dye leaking as determined by absorption and fluorescence spectroscopy, flow cytometry, and measurements of zeta potentials. In addition, for the first time, the influence of the amount of incorporated dye on the absolute fluorescence quantum yield and brightness of the fluorescent particles was investigated for selected chromophores in differently sized particles using a custom-made calibrated integrating sphere setup. Our results demonstrate the general suitability of these one-step loading procedures for efficient particle staining with neutral, zwitterionic, and charged fluorophores like oxazines, coumarines, squaraines, xanthenes, and cyanines emitting in the visible and near infrared. Dye polarity was identified as a suitable tool to estimate the loading efficiency of fluorophores into these polymer particles. KW - Fluorescence KW - Polystyrene KW - Particles KW - Encapsulation KW - Quantum yield KW - Zeta potential KW - Method KW - Label KW - Particle KW - Polymer KW - Absolute fluorescence quantum yield KW - Fluorophore KW - Dye content KW - Surface groups KW - Size KW - Brightness PY - 2012 DO - https://doi.org/10.1016/j.dyepig.2012.01.021 SN - 0143-7208 SN - 1873-3743 VL - 94 IS - 2 SP - 247 EP - 257 PB - Elsevier Ltd. CY - Kidlington AN - OPUS4-25481 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Würth, Christian A1 - Grabolle, Markus A1 - Pauli, Jutta A1 - Spieles, Monika A1 - Resch-Genger, Ute T1 - Comparison of methods and achievable uncertainties for the relative and absolute measurement of photoluminescence quantum yields N2 - The photoluminescence quantum yield (Φf) that presents a direct measure for the efficiency of the conversion of absorbed photons into emitted photons is one of the spectroscopic key parameters of functional fluorophores. It determines the suitability of such materials for applications in, for example, (bio)analysis, biosensing, and fluorescence imaging as well as as active components in optical devices. The reborn interest in accurate Φf measurements in conjunction with the controversial reliability of reported Φf values of many common organic dyes encouraged us to compare two relative and one absolute fluorometric method for the determination of the fluorescence quantum yields of quinine sulfate dihydrate, coumarin 153, fluorescein, rhodamine 6G, and rhodamine 101. The relative methods include the use of a chain of Φf transfer standards consisting of several 'standard dye' versus 'reference dye' pairs linked to a golden Φf standard that covers the ultraviolet and visible spectral region, and the use of different excitation wavelengths for standard and sample, respectively. Based upon these measurements and the calibration of the instruments employed, complete uncertainty budgets for the resulting Φf values are derived for each method, thereby providing evaluated standard operation procedures for Φf measurements and, simultaneously, a set of assessed Φf standards. KW - Fluorescence KW - Photoluminescence KW - Quantum yield KW - Dye KW - Uncertainty KW - Absolute quantum yield KW - Method comparison KW - Integrating sphere PY - 2011 DO - https://doi.org/10.1021/ac2000303 SN - 0003-2700 SN - 1520-6882 VL - 83 IS - 9 SP - 3431 EP - 3439 PB - American Chemical Society CY - Washington, DC AN - OPUS4-23632 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -