On the Interpretation of Luminescence of Lead Halide Crystals

Abstract

Emission and excitation spectra, and the luminescence decay kinetics have been studied for PbCl 2 crystals at the temperatures 0.45-100 K. It has been found that even at the lowest temperatures, where the non-radiative decay of exciton states in PbCl 2 does not take place, the decay times of both the ultraviolet (UV) and the blue (B) exciton emission are by a few orders of magnitude shorter than the decay times of the emission arising from the triplet relaxed excited state of Pb 2- centres in lead-doped ionic crystals. A conclusion has been drawn that the luminescence of lead halides cannot be connected with single Pb 2+ ions. It is proposed that the radiative decay of the self-trapped excitons of the type of [(Pb 2 ) 3+ + hole} is responsible for the UV and the B emission of PbCl 2 crystals, while the lowest-energy (BG) emission arises from the tunnelling recombinations between the (Pb 2 ) 3+ -type self-trapped electrons and V K -type self-trapped holes.