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 - 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 - 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 - 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 - 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 - 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 - Radunz, Sebastian A1 - Kraus, Werner A1 - Bischoff, F. A. A1 - Emmerling, Franziska A1 - Resch-Genger, Ute A1 - Tschiche, Harald T1 - Temperature- and Structure-Dependent Optical Properties and Photophysics of BODIPY Dyes N2 - We report on the temperature- and structural-dependent optical properties and photophysics of a set of boron dipyrromethene (BODIPY) dyes with different substitution patterns of their meso-aryl subunit. Single-crystal Xray diffraction analysis of the compounds enabled a classification of the dyes into a sterically hindered and a unhindered group. The steric hindrance refers to a blocked rotational motion of the aryl subunit around the bond connecting this moiety to the meso-position of the BODIPY core. The energy barriers related to this rotation were simulated by DFT calculations. As follows from the relatively low rotational barrier calculated to about 17 kcal/mol, a free rotation is only possible for sterically unhindered compounds. Rotational barriers of more than 40 kcal/mol determined for the sterically hindered compounds suggest an effective freezing of the rotational motion in These molecules. With the aid of temperature-dependent spectroscopic measurements, we could show that the ability to rotate directly affects the optical properties of our set of BODIPY dyes. This accounts for the strong temperature dependence of the fluorescence of the sterically unhindered compounds which show a drastic decrease in fluorescence quantum yield and a significant shortening in fluorescence lifetime upon heating. The optical properties of the sterically hindered compounds, however, are barely affected by temperature. Our results suggest a nonradiative deactivation of the first excited singlet state of the sterically unhindered compounds caused by a conical intersection of the potential energy surfaces of the Ground and first excited state which is accessible by rotation of the meso-subunit. This is in good agreement with previously reported deactivation mechanisms. In addition, our results suggest the presence of a second nonradiative depopulation pathway of the first excited singlet state which is particularly relevant for the sterically hindered compounds. KW - Fluorescence KW - Sensor KW - Switch KW - pH KW - BODIPY KW - Dye KW - Probe KW - Synthesis KW - Photophysics KW - Mechanism PY - 2020 DO - https://doi.org/10.1021/acs.jpca.9b11859 SN - 1089-5639 VL - 124 IS - 9 SP - 1787 EP - 1797 PB - American Chemical Society AN - OPUS4-50639 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -