Exciton transfer between localized states in CdS1- xSex alloys: Time-resolved photoluminescence and theoretical models

Abstract

Luminescence decay curves as well as time-resolved and time-integrated spectra obtained with selective excitation in the localized exciton band of CdS 1- x Se x are fitted using two theoretical models. In the first one, exciton transfer to lower energy states occurs through tunnel effect assisted by acoustical phonons. From the energy dependence of the lifetime measured with quasi-resonant excitation in the localized exciton band, we determine the characteristic energy of the tail density of states: E 0 = 2.2 meV. The radiative lifetime is set equal to 1.5 ns. We show that both piezoelectric and deformation potential coupling have to be taken into account to describe exciton transfer. The second model is phenomenological and was used to describe exciton transfer in GaAs 1- x P x alloys. We obtain a good agreement with experimental results using parameters close to the previous ones. We demonstrate that, for selective excitation in the low energy side of the luminescence band, not only the transfer process but also luminescence assisted by acoustical phonons must be taken into account in order to explain time-resolved luminescence results.