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 U6 - 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 - 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 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:kobv:b43-500580 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 - 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 U6 - 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 - 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 U6 - 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 - 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 U6 - 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 - CONF A1 - Resch-Genger, Ute A1 - Würth, Christian A1 - Frenzel, Florian A1 - Grauel, Bettina A1 - Nirmalananthan-Budau, Nithiya A1 - Pauli, Jutta A1 - Hoffmann, Katrin T1 - Photoluminescence at BAM – Photoluminescence at BAM – Photophysical Studies, Quantum Yield Measurements, Multiplexing Strategies, and Standards N2 - Photoluminescence applications in the life and material sciences require bright molecular and nanocrystalline emitters, stimuli-responsive optical probes, signal enhancement, multiplexing, and barcoding strategies and traceable methods to quantify the signal-relevant optical properties of luminescent materials at the ensemble and single molecule/particle level. In this context, current research at Division Biophotonics of BAM is presented ranging from dye and nanocrystal photophysics, absolute measurements of photoluminescence quantum yields in the UV/vis/NIR/SWIR, lifetime multiplexing, and the development of different types of fluorescence standards for validating optical-spectroscopic measurements. T2 - Institutskolloquium IPHT CY - Jena, Germany DA - 22.10.2019 KW - Surface group analysis KW - NIR KW - SWIR KW - Quantum dot KW - Lanthanide KW - Cleavable probe KW - Lifetime KW - Multiplexing KW - Sensor KW - Assay PY - 2019 AN - OPUS4-49360 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Resch-Genger, Ute A1 - Weigert, Florian A1 - Frenzel, Florian A1 - Würth, Christian A1 - Hoffmann, Katrin A1 - Martynenko, Iris A1 - Dhamo, Lorena T1 - Optical properties of different types of luminescent nanocrystals at the ensemble and single emitter level N2 - Applications of luminescent nanomaterials like semiconductor nanocrystals (QDs) and lanthanide-based upconversion nanocrystals (UCNPs) in the life sciences such as bioimaging studies or their use as reporter in assays call for a correlation of the photoluminescence (PL) properties of these nanomaterials on ensemble and single particle levels. This is particularly relevant within the context of continuously decreasing detection limits. Aiming at optimum nanomaterials for spectroscopic and microscopic applications, we examine the optical properties of QDs like II/VI QDs and cadmium-free AgInS2/ZnS QDs (AIS/ZnS) and UCNPs of different chemical composition, size, and particle architecture for ensembles and single particles. This includes PL spectra, PL quantum yields (ΦF), brightness values, blinking behavior, and PL decay kinetics. For UCNPs with their nonlinear spectrally converted PL excited by sequential multiphoton absorption, these measurements were also done as a function of excitation power density (P). Special emphasis is dedicated to the performance parameters ΦF and brightness, that determine signal size and provide a measure for nanocrystal quality.[1-5] Systematic studies of the excitation energy dependence (EED) [6] of the PL properties of II/VI and ternary AgInS2/ZnS QDs reveal the potential of this relatively simple method for providing insights into the electronic energy structure of QDs. The intrinsic nature of the inhomogeneous broadening of the PL bands of AIS/ZnS QDs was confirmed by single particle spectroscopy.[5] By combining P-dependent integration spectroscopy and single particle measurements of UCNPs, using a new custom-made setup, consisting of different lasers, an inverted microscope, different detectors, and an AFM, we could study the P-dependent optical properties of these nonlinear emitters from ~10 W/cm2 up to ~105 W/cm2. These results provide optimum dopant ion concentrations for bioanalytical, spectroscopic, and microscopic applications of UCNP. Acknowledgement. Financial support by grants RE1203/12-3 and RE1203/20-1 (support of F. Weigert, L. Dhamo, and F. Frenzel) from German Research Council (DFG) is acknowledged. T2 - 17th Internatinal Congress on Photobiology CY - Barcelona, Spain DA - 25.08.2019 KW - Nanoparticle KW - Quantum dot KW - Fluorescence KW - Single particle spectroscopy KW - Mechanism KW - Lifetime KW - Exciton KW - Ternary quantum dot KW - AIS QD KW - Synthesis KW - Shell KW - Surface chemistry PY - 2019 AN - OPUS4-48877 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 U6 - 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 - CONF A1 - Resch-Genger, Ute A1 - Würth, Christian A1 - Frenzel, Florian A1 - Grauel, Bettina A1 - Weigert, Florian A1 - Wegner, Karl David T1 - Nanocrystals with Luminescence in the vis, NIR and SWIR – Photophysics and Applications N2 - Luminescent nanocrystals like core/shell semiconductor quantum dots and lanthanide doped nanophosphors as well as gold nanoclusters with emission in the visible (vis) and particularly in the near infrared (NIR) and short wavelength infrared (SWIR) region have been increasingly used as reporters in the life sciences and for bioimaging studies in the last years. This has led to sophisticated core-shell particle architectures of different chemical composition utilizing semiconductor quantum dots and lanthanide-based nanocrystals and initiated the design of gold nanoclusters with different ligands. In addition, this led to an increasing number of quantitative spectroscopic studies focusing on the key performance parameter photoluminescence quantum yield to identify optimum particle structures. In the following, an overview of different classes of nanocrystalline emitters and their photophysics is provided and examples for the absolute characterization of the photoluminescence properties of these different vis/NIR/SWIR emitters are shown including excitation power density-dependent studies on the ensemble and single particle level. Also, the impact of such measurements on a profound mechanistic understanding of the underlying nonradiative deactivation pathways is highlighted as required for reporter design. T2 - MIMIT 2019 CY - Peking, People's Republic of China DA - 18.10.2019 KW - Fluorescence KW - Quantum yield KW - Integrating sphere spectroscopy KW - Dye KW - Nanocrystal KW - NIR KW - SWIR KW - Quantum dot KW - Lanthanide nanoparticle KW - Old nanocrystal KW - Imaging KW - Lifetime KW - Nanoparticle PY - 2019 AN - OPUS4-49361 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wang, Cui A1 - Otto, S. A1 - Dorn, M. A1 - Heinze, K. A1 - Resch-Genger, Ute T1 - Luminescent TOP nanosensors for simultaneously measuring temperature, oxygen, and pH at a single excitation wavelength N2 - Two nanosensors for simultaneous optical measurements of the bioanalytically and biologically relevant analytes temperature (“T”), oxygen (“O”), and pH (“P”) have been designed. These “TOP” nanosensors are based on 100 nmsized silica-coated polystyrene nanoparticles (PS-NPs) doped with a near-infrared emissive oxygen- and temperature-sensitive chromium(III) complex ([Cr(ddpd)2][BPh4]3, CrBPh4) and an inert reference dye (Nile Red, NR or 5,10,15,20tetrakis(pentafluorophenyl) porphyrin, TFPP) and are covalently labeled with pHsensitive fluorescein isothiocyanate (FITC). These emitters can be excited at the same wavelength and reveal spectrally distinguishable emission bands, allowing for ratiometric intensity-based and time-resolved studies in the visible and near-infrared wavelength region. Studies in PBS buffer solutions and in a model body liquid demonstrate the applicability of these nanosensors for the sensitive luminescence readout of TOP simultaneously at the same spatialposition. KW - Medical diagnostics KW - Sensor KW - Nanoparticle KW - Fluorescence KW - Nanosensor KW - Oxygen KW - Temperature KW - pH KW - Ratiometric KW - Lifetime KW - NIR KW - Cr(III) complex KW - Dye KW - FITC KW - Environment PY - 2019 U6 - https://doi.org/10.1021/acs.analchem.8b05060 SN - 0003-2700 VL - 91 IS - 3 SP - 2337 EP - 2344 PB - ACS AN - OPUS4-47455 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -