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 Yb³⁺-doped CsPbCl₃ 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 CsPbCl₃:Yb³⁺ 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.