The Temperature Dependence of the Photoluminescence of CsPbBr₃ Nanocrystals Reveals Phase Transitions and Homogeneous Linewidths

Semiconductor perovskites are known to be strongly coupled to a dynamically disordered lattice. Two key phenomena to consider are phase transitions and phonon contributions to homogeneous linewidths. Each of these parameters will be highly dependent on material parameters and would benefit from a simple measure. Here, we perform temperature-dependent photoluminescence spectroscopy on bulk CsPbBr₃ perovskite nanocrystals. The data reveals a discontinuity in the energy gap, suggesting a phase transition between orthorhombic and cubic phases. The temperature dependence of the linewidth reveals negligible coupling to the ligands but strong coupling to polar optical phonons via the Fröhlich coupling. This temperature dependence suggests that homogeneous line broadening dominates the observed linewidths.