Charge separation of excitons and the radiative recombination process in ${\mathrm{PbBr}}_2$ crystals

The photoluminescence (PL) properties at low temperatures have been investigated in ${\mathrm{PbBr}}_2$ crystals. We find that the blue-green PL band at 2.55 eV (BG band) originates from the intrinsic relaxed state of excitons. The analysis of the decay curve of the BG band reveals that the excitons relax into charge-separated pairs of a self-trapped electron and a self-trapped hole. The relaxation of an exciton results from the repulsive correlation between the electron and hole through acoustic phonons.