Localized and self-trapped exciton states in PbI2-PbBr2 mixed crystals

Abstract

Time-integrated luminescence spectra and time behaviour of the luminescence have been measured in PbI2(1-x)Br2x mixed crystals in order to elucidate the relaxation processes of free, localized and self-trapped excitons. The luminescence spectra for values of the composition ratio x below 0.05 exhibit recombination lines due to free and bound exciton states. Above x = 0.07, the luminescence coming from the localized exciton states which we denote as L states, becomes dominant. The observed decay time of this L band luminescence at the lowest energy is 100 ps. This rather short decay time is explained as due to the transition of the localized exciton state to lower energy excited states including a self-trapped exciton.