Cubic CsPbBr3 with Li passivation: robust room temperature photoluminescence

We investigate the room-temperature optical properties of CsPbBr3 nanocrystals (NCs) embedded in a Cs2PbBr6 matrix and their Li-doped analogues. X-ray diffraction (XRD) confirms a cubic phase for all samples and NC sizes of approximately 20–40 nm. Based on the Goldschmidt tolerance factor, Li+ is too small to occupy the perovskite A- or B-sites; accordingly, the lattice remains essentially unchanged, and Li most likely passivates surface dangling bonds and defect states. Room-temperature upconversion photoluminescence (PL) is robust across a wide excitation range and, in Li-doped samples, is up to an order of magnitude stronger than in undoped NCs. We attribute this enhancement to reduced nonradiative recombination via Li-induced passivation, consistent with the XRD/Goldschmidt analysis. These findings highlight the structural and optical stability of this composite platform and motivate its use in ambient optoelectronic applications