Chemie und Prozesstechnik
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Correlating the photoluminescence (PL) properties of nanomaterials like semiconductor nanocrystals (QDs) and upconversion nanocrystals (UCNPs) assessed in ensemble studies and at the single particle level is increasingly relevant for applications of these nanomaterials in the life sciences like bioimaging studies or their use as reporters in microfluidic assays. Here we present a comparison of the spectroscopic properties of ensembles and single emitters for QDs like II/VI QDs and cadmium-free AIS/ZnS QDs as well as different UCNPs. The overall goal of this study was to derive particle architectures well suited for spectroscopic and microscopic applications.
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.
Biophotonics and analytics - Photoluminescence properties of nanocrystals and surface group analysis
(2018)
Correlating the photoluminescence (PL) properties of nanomaterials like semiconductor nanocrystals (QDs) and upconversion nanocrystals (UCNPs) assessed in ensemble studies and at the single particle level and studying their surface chemistry is increasingly relevant for applications of these nanomaterials in the life and material sciences. Here we present a comparison of the spectroscopic properties of ensembles and single nanocrystalline emitters and simple methods for the quantification of functional groups and ligands on particle surfaces. The overall goal of this study was to derive particle architectures and surface chemistries well suited for spectroscopic and microscopic applications.
Common approaches to improve the optical properties of semiconductor quantum dots and lanthanide doped nanophosphors present core/shell structures as radiationless deactivation at the particle surface is usually the main energy loss mechanism. This has led to increasingly sophisticated particle architectures using multishell systems with shells of different chemical composition and thickness and initiated an increasing number of quantitative spectroscopic studies focusing on the key performance parameter photoluminescence quantum yield to identify optimum particle structures. This is particularly challenging in the long wavelength region > 1000 nm and for nonlinear emitters like upconversion nanocrystals. Here, we present suitable absolute methods to quantify the photoluminescence of these different emitters in the vis/NIR/IR and as function of excitation power density and underline the impact of such measurements on a profound mechanistic understanding of the nonradiative deactivation pathways in semiconductor and upconversion nanocrystals of different size and particle architecture in different environments.