Chemie und Prozesstechnik
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Luminescence techniques are amongst the most commonly used analytical methods in the life and material sciences due to their high sensitivity and their nondestructive and multiparametric character. Photoluminescence signals are, however, affected by wavelength-, polarization- and time-dependent instrument specific effects. This hampers the comparability of fluorescence measurements and calls for simple tools for instrument characterization and the quantification of measured fluorescence intensities. Well characterized fluorescence standards for instrument calibration and performance validation (IPV) can be used also to reference fluorescence signals. Of special importance is the reliable and accurate determination of photoluminescence quantum yields (Ф f), that equals the number of emitted per absorbed photons and presents the key performance parameter for emitter efficiency and the comparison of different luminophores. The determination of Ф f is typically done with the aid of so-called quantum yield standards with well-known Ф f values. These standards can also be applied to evaluate integrating sphere setups, which are increasingly being used for absolute measurements of Ф f values. In this respect, division biophotonics of BAM has certificated a set of Ф f standards, which absorb and fluorescence in the wavelength range from 350 to 1100 nm. In the following, the route to Ф f standards with reliable and traceable Ф f values with a complete uncertainty budget will be presented.
The comparison of different emitter classes and the rational design of the next generation of molecular and nanoscale reporters require accurate and quantitative photo-luminescence measurements. This is of special importance for all photoluminescence applications 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.
The reassessment of bridges is becoming increasingly important. The basic requirement for analyses of structural safety is reliable knowledge about individual structures. This paper introduces the new approach to evaluate the quality of measured data gained from non-destructive testing (NDT) to provide reliable, objective, and relevant information about existing bridges. The purpose is to relate this validated knowledge to probabilistic analyses. Bridging the gap between NDT and numerical reassessments indicates reduced numerical uncertainties and residual service time extensions. This paper deals with an application of this approach using measurement data collected by ultrasonic technique at a prestressed concrete bridge.
Relative and Absolute Methods for Measuring Photoluminescence Quantum Yields of UV/vis/NIR Emitters
(2019)
One of the key spectroscopic performance parameters of molecular and particulate emitters is the photoluminescence quantum yield (PL QY) that provides a direct measure for the number of emitted per absorbed photons. This triggered the interest in methods suitable for measuring this property for emitters in various environments in the UV/vis/NIR and above 1000 nm as well as on the ensemble and single emitter level. Moreover, for nonlinear emitters like lanthanide-based upconversion nanocrystals methods including instrumentation for power density-dependent PL QY studies are required.
An overview of the research activities in Division Biophotonics of BAM is given and suitable relative and absolute methods for the deter-mination of PL QY of organic dyes and different types of application-relevant nanomaterials in dispersion and in the solid state are presen-ted. This covers also the design and calibration of integrating sphere setups, achievable uncertainties, and candidates for PL QY reference materials.