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Photoluminescence Quantum Yields of Luminescent Nanocrystals and Particles in the UV/vis/NIR/SWIR
(2023)
The rational design of functional luminescent materials such as semiconductor quantum dots and lanthanide-based upconversion nanoparticles, all photophysical and mechanistic studies, and the comparison of different emitters require accurate and quantitative photoluminescence measurements. Particularly the reliable determination of the key performance parameter photoluminescence quantum yield (f), the number of emitted per absorbed photons, and the brightness are of special importance for luminescence applications in the life and material sciences and nano(bio)photonics.[1] In this context, examples for absolute measurements of the photoluminescence quantum yields of UV/vis/NIR/SWIR emissive semiconductor quantum dots and rods, made from different materials, and spectrally shifting lanthanide upconversion nanocrystals with different surface chemistries in transparent matrices are presented including excitation wavelength and power density dependent studies utilizing integration sphere spectroscopy.[2,3] In addition, procedures for the absolute determination of the photoluminescence quantum yields of scattering dispersions of larger size quantum rods and differently sized inorganic particles have been developed as well as procedures for the characterization of solid luminescent nanomaterials such as different perovskites and YAG:Cer converter materials.[4] Thereby, challenges and pitfalls of f measurements in different wavelength regions including the SWIR and material-specific effects related to certain emitter classes are addressed, achievable uncertainties are quantified, and relative and absolute measurements of photoluminescence quantum yield measurements are compared to underline limitations of the former approach. Finally, a set of novel UV/vis/NIR quantum yield standards is presented including their certification with a complete uncertainty budget.[5]
Eu2+ is used to replace toxic Pb2+ in metal halide perovskite nanocrystals (NCs). The synthesis implies injection of cesium oleate into a solution of europium (II) bromide at an experimentally determined optimum temperature of 130 ○C and a reaction time of 60 s. Structural analysis indicates the formation of spherical CsEuBr3 nanoparticles with a mean size of 43 ± 7 nm. Using EuI2 instead of EuBr2 leads to the formation of 18-nm CsI nanoparticles, while EuCl2 does not show any reaction with cesium oleate forming 80-nm EuCl2 nanoparticles.
The obtained CsEuBr3 NCs exhibit bright blue emission at 413 nm (FWHM 30 nm) with a room temperature photoluminescence quantum yield of 39%. The emission originates from the Laporte-allowed 4f7–4f65d1 transition of Eu2+ and shows a PL decay time of 263 ns.
The long-term stability of the optical properties is observed, making inorganic lead-free CsEuBr3 NCs promising deep blue emitters for optoelectronics.