CsPbCl3:Yb3+ nanocrystals: Adverse effects of colloidally stable ytterbium-rich reaction by-products on luminescent down-conversion performance

The development of near infra-red (NIR) emitting down-converters is a promising route for improving photovoltaic output through efficient light management. Quantum-cutting Yb 3+ -doped CsPbCl 3 nanocrystals (NCs) are interesting for this application due to their high photoluminescence quantum yields (PLQY >100 %) and attractive NIR spectral properties which include high absorption cross section and minimal overlap between absorption and emission spectra. In this work, we fabricated CsPbCl 3 :Yb 3+ NCs with the hot-injection method and studied them using structural/optical characterization methods such as x-ray diffraction, scanning transmission electron microscopy, energy-dispersive x-ray spectroscopy, fluorescence lifetime and quantum yield measurements. We found that the hot-injection method is susceptible to the formation of colloidally stable Yb-rich reaction by-products. After separating these by-products from the NCs, NIR PLQY increased by a relative 46 %. Although the PLQY values recorded in this study are 4–7 times lower than in other studies, these findings may explain some discrepancies in photoluminescence efficiency reported with this material. • NIR photoluminescence quantum yields are inconsistent across CsPbCl 3 :Yb 3+ nanocrystal reports. • Alloy-like quantities in rare-earth doping reactions result in colloidally stable by-products. • Colloidally stable by-products limit down-conversion performance of CsPbCl 3 :Yb 3+ nanocrystals. • Reaction and measurement conditions need more meticulous descriptions for higher reproducibility.