TY - CONF A1 - Würth, Christian A1 - Resch-Genger, Ute T1 - Absolute determination of photoluminescence quantum yields of scattering led converter materials how to get it right 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. A key performance parameter is the photoluminescence quantum yield (Φf), i.e., the number of emitted per number of absorbed photons. Φf of transparent luminophore solutions can be obtained relative to a fluorescence Φf standard of known Φf, meanwhile available as certified reference materials.[1] The determination of Φf of scattering liquid and solid samples requires, however, absolute measurements with an integrating sphere setup. Fist we present the results of an interlaboratory comparison of 3 labs from academia and industry on measurements of transparent and scattering dye solutions and YAG:Ce optoceramics, an optical converter material, with commercial stand-alone integrating sphere setups of different illumination and detection geometries.[2] Second we present results for a series of 500 μm-thick polymer films containing different concentrations of photoluminescent and scattering YAG:Ce microparticles.[3] We systematically explored and quantified pitfalls of absolute Φf measurements with special emphasis dedicated to the influence of measurement geometry, optical properties of the blank for determining the number of incident photons absorbed by the sample, and sample-specific surface roughness. Matching Φf values could be easily obtained for transparent dye solutions and scattering dispersions with a blank with scattering properties closely matching those of the sample, Φf measurements of optoceramic samples with different blanks revealed substantial differences of more than 20 %. Our results further reveal that setup configurations can introduce systematic errors resulting in under- or overestimation of the absorbed photon flux and hence an under- or overestimation of Φf. T2 - Shift 2025 CY - La Laguna, Tenerife, Spain DA - 13.10.2025 KW - Quantum Yield KW - LED Converter KW - Luminescent KW - Microparticles PY - 2025 AN - OPUS4-64785 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Würth, Christian T1 - Time resolved spectroscopy of upconverting lanthanide based upconversion nanocrystals N2 - This presentation gives an overview of time correlated population and depopulation processes of the electronic states of lanthanide doped nanoparticles. The fundamental principles of sensitized photon upconversion are explained. Theoretical principles and the correlation to experimental results are shown. Examples are given for particle growth, dissolution as well as influences of size, doping concentration and microenvironment. T2 - Principles and Applications of Time-resolved Fluorescence Spectroscopy CY - Berlin, Germany DA - 12.11.2024 KW - Upconversion KW - Time domain PY - 2024 AN - OPUS4-61652 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Petrov, Eugene A1 - Würth, Christian A1 - Richter, Maria A1 - Resch-Genger, Ute T1 - Fluorescence Standards from BAM - Dye Solutions and Polymer systems N2 - For fluorescence microscopy, there is an increasing need for suitable calibration tools and reference materials for microscope calibration, the determination of performance parameters, and the regular control and validation of instrument performance. This is addressed in the BmWk-financed project FluMikal (WIPANO program) by two research groups from academia and two companies, that is coordinated by BAM. Here we present different approaches to liquid and solid fluorescence standards for the determination of the wavelength-dependent spectral sensitivity of fluorescence microscopes and ideas concerning the choice of suitable fluorescence lifetime standard for increasingly utilized fluorescence lifetime imaging (FLIM). T2 - FluMiKal Projectmeeting CY - Munich, Germany DA - 27.11.2023 KW - Reference material KW - Reference product KW - Fluorescence microscopy KW - Quality assurance KW - Instrument performance validation KW - Lifetime standard PY - 2023 AN - OPUS4-59120 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Würth, Christian A1 - Resch-Genger, Ute T1 - Project Status report IEC TS 62607-3-1 ED2 N2 - Project Status report IEC TS 62607-3-1 ED2 reklative and absolute quantum yield determinations T2 - IEC TC 113 Plenary Meeting CY - Online meeting DA - 17.04.2023 KW - Quantum yield KW - Standardization KW - Nanomaterials KW - Nanomanufacturing KW - IEC PY - 2023 AN - OPUS4-57477 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Würth, Christian T1 - Time resolved spectroscopy of upconverting lanthanide based upconversion nanocrystals N2 - The optical properties of these materials strongly depend on the excitation power density, i.e., the number of photons absorbed per time interval. The upconversion quantum efficiencies (ΦUC) of these materials, the excitation power dependent population i.e. the emission characteristics, and the deactivation dynamics are influenced by nanoparticle architecture, doping concentration, and the microenvironment. We will discuss how time resolved measurements can help to understand the fundamental photophysical mechanisms and discuss differences to other nanocrystals like quantum dots. T2 - 19th International Course on “Principles and Applications of Time-resolved Fluorescence Spectroscopy” CY - Berlin, Germany DA - 16.11.2022 KW - Nanoparticle KW - Lanthanide KW - Upconversion KW - Energy transfer PY - 2022 AN - OPUS4-57000 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Resch-Genger, Ute A1 - Würth, Christian A1 - Pauli, Jutta A1 - Weigert, Florian T1 - Quantitative optical-spectroscopic characterization of luminescent nanomaterials - Photoluminescence Quantum Yields N2 - Accurate and quantitative photoluminescence measurements are mandatory for the comparison of different emitter classes and the rational design of the next generation of molecular and nanoscale reporters as well as for most applications relying on their luminescence features in the life and material sciences and nanobiophotonics. In the following, procedures for the determination of the spectroscopic key parameter photoluminescence quantum yield, i.e., the number of emitted per absorbed photons, in the UV/vis/NIR/SWIR are presented including pitfalls and achievable uncertainties and material-specific effects related to certain emitter classes are addressed. Special emphasis is dedicated to luminescent nanocrystals. T2 - International Workshop on "Emerging Nanomaterials for Displays and SSL" CY - Dresden, Germany DA - 11.11.2021 KW - Nano KW - Nanomaterial KW - Nanocrystal KW - Semiconductor quantum dot KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Lifetime KW - Surface chemistry KW - Brightness KW - NIR KW - SWIR KW - Method KW - Uncertainty KW - Rreference material PY - 2021 AN - OPUS4-53783 LA - deu AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Resch-Genger, Ute A1 - Würth, Christian A1 - Frenzel, Florian A1 - Weigert, Florian A1 - Andresen, Elina A1 - Grauel, Bettina A1 - Wegner, Karl David T1 - Semiconductor (SCNC) & Upconversion Nanocrystals (UCNC) – Optical Properties, Applications & Challenges N2 - Inorganic nanocrystals with linear and nonlinear luminescence in the ultraviolet, visible, near infrared and shortwave infrared like semiconductor quantum dots and spectrally shifting lanthanide-based nanophosphors have meanwhile found applications in the life and material sciences ranging from optical reporters for bioimaging and sensing over security barcodes to solid state lighting and photovoltaics. These nanomaterials commonly have increasingly sophisticated core/shell particle architectures with shells of different chemical composition and thickness to minimize radiationless deactivation at the particle surface that is usually the main energy loss mechanism [1]. For lanthanide-based spectral shifters, particularly for very small nanoparticles, also surface coatings are needed which protect near-surface lanthanide ions from luminescence quenching by high energy vibrators like O-H groups and prevent the disintegration of these nanoparticles under high dilution conditions. [2,3,4]. The identification of optimum particle structures requires quantitative spectroscopic studies focusing on the key performance parameter photoluminescence quantum yield [5,6], ideally flanked by single particle studies to assess spectroscopic inhomogeneities on a particle-to-particle level for typical preparation methods [7], Moreover, in the case of upconversion nanoparticles with a multi-photonic and hence, excitation power density (P)-dependent luminescence, quantitative luminescence studies over a broad P range are required to identify particle architectures that are best suited for applications in fluorescence assays up to fluorescence microscopy. Here, we present methods to quantify the photoluminescence of these different types of emitters in the vis/NIR/SWIR and as function of Pand demonstrate the importance of such measurements for a profound mechanistic understanding of the nonradiative deactivation pathways in semiconductor and upconversion nanocrystals of different size and particle architecture in different environments. T2 - 27th Annual Meeting of the Slovenian Chemical Society CY - Portoroz-Portorose, Slovenia DA - 21.09.2021 KW - Nano KW - Nanomaterial KW - Upconversion nanoparticle KW - Lanthanide KW - Photoluminescence KW - Quantum yield KW - Photophysics KW - Lifetime KW - Surface chemistry KW - Single particle KW - Brightness KW - NIR KW - Synthesis KW - Semiconductur KW - Quantum dot KW - Nanocrystal KW - SWIR PY - 2021 AN - OPUS4-53723 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Pauli, Jutta A1 - Würth, Christian A1 - Güttler, Arne A1 - Resch-Genger, Ute T1 - Reliable Determination of the Signal-Relevant Spectroscopic Key Characteristics of Luminescent Reporters and Optical Probes for Imaging in the vis/NIR/SWIR N2 - Introduction. Comparing different emitter classes and rationally designing the next generation of molecular and nanoscale probes for bioimaging applications require accurate and quantitative methods for the measurement of the key parameter photoluminescence quantum yield f.1 f equals the number of emitted per number of absorbed photons. This is particularly relevant for increasingly used fluorescence imaging in the short wave-infrared region (SWIR) ≥ 900 nm providing deeper penetration depths, a better image resolution, and an improved signal-to-noise or tumor-to-background ratio.2, 3 However, spectroscopic measurements in the SWIR are more challenging and require specific calibrations and standards. T2 - EMIM 2021 CY - Göttingen, Germany DA - 24.08.2021 KW - Fluorescence KW - Optical probe KW - Dye KW - Photophysics KW - Quantum yield KW - Mechanism KW - NIR KW - SWIR KW - Imaging KW - Reference material KW - Reliability KW - Nano KW - Particle KW - Method KW - Quality assurance PY - 2021 AN - OPUS4-53233 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Würth, Christian T1 - Systematic characterization of Upconversion nanoparticles: Effect of size, microenvironment, Energy transfer, shells N2 - Solid state multi-band emitters like lanthanide doped up-conversion nanoparticles (UCNPs) are promising materials for energy and biotechnologies. These materials are excitable in the near infrared (NIR) and show emission bands from UV to SWIR with excellent photostability, and long luminescence lifetimes in the µs range. The efficiency of these materials, i.e. the multiphoton absorption processes, the excitation power dependent population, and deactivation dynamics are strongly influenced by the particle size, structure, doping concentration, surface chemistry, and microenvironment. For applications UCNPs have to be optimized to meet the application relevant optical properties like the upconversion quantum yield (UC) and downshifting quantum yield (PL), luminescence lifetime and emission spectra. We investigated ß-NaYF4 NPs co-doped with Yb3+ and Er3+ in aqueous and organic media and as powder. For the later, bulk and nanomaterial is compared. For dispersed particles the influence of surface chemistry (ligands), microenvironment (solvent) and size (10 to 43 nm) was studied. Especially for bioapplications the Förster-Resonance-Energy-Transfer (FRET) efficiency from UCNPs to organic dye molecules (rose bengal and sulforhodamine B) was optimized with respect to the UCNP size. T2 - UpCon 2018 CY - Valencia, Spanien DA - 02.04.2018 KW - Nanoparticle KW - Upconversion KW - Quenching PY - 2018 AN - OPUS4-44762 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - CONF A1 - Würth, Christian T1 - New Trends in Fluorometry - Fluorescence Measurements above 1000 nm N2 - Trends in fluorometry and fluorescence imaging are increasing applications of molecular and nanoscale reporters with emission > 800 nm and recently also > 1000 nm for bioanalysis, medical diagnostics, bioimaging, and safety barcodes. Mandatory for the comparison of different emitter classes and the rational design of the next generation of reporters for the short wavelength infrared (SWIR) region are reliable and quantitative photoluminescence measurements in this challenging wavelength region. This is of special relevance for nanocrystalline emitters like semiconductor quantum dots and rods as well as lanthanide-based upconversion and downconversion nanocrystals, where surface states and the accessibility of emissive states by quenchers largely control accomplishable photoluminescence quantum yields and hence, signal sizes and detection sensitivities from the reporter side. Such measurements are currently hampered by the lack of suitable methods and standards for instrument calibration and validation and quantum yield standards with emission > 800 nm and especially > 1000 nm. In this respect, we present the design of integrating sphere setups for absolute and excitation power density-dependent measurements of emission spectra and photoluminescence quantum yields in the wavelength region of 650 to 1650 nm including calibration strategies and first candidates for potential fluorescence standards. Subsequently, selected examples for spectroscopic studies of different types of nanocrystals are presented including the upconversion and downconversion emission of differently sized and surface functionalized lanthanide-doped nanoparticles T2 - COSP-Colloquium Optical Spectroscopy CY - Berlin, Germany DA - 27.11.2017 KW - Yield KW - IR fluorescence KW - Quantum dot KW - Upconversion nanocrystal KW - Lanthanide emitter KW - NIR KW - Integrating sphere spectroscopy KW - Absolute fluorescence quantum PY - 2017 AN - OPUS4-43327 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -