Localized Excitons in CdS_1−<i>x</i>Se_<i>x</i> Solid Solutions

Abstract

Abstract The emission spectra of CdS 1–x Se x solid solutions ( x ≦ 0.3) at helium temperatures are studied under monochromatic excitation in different regions of the absorption spectrum. In all samples very intense luminescence due to excitons localized by composition fluctuations is observed. High intensity of luminescence and complete absence of free exciton emission indicate a high probability of exciton localization. A model for exciton localization is proposed. It is assumed that only the hole component of the exciton is localized by the potential fluctuations. The electron is bound to this hole by Coulomb attraction. The energy migration between the localized states is discussed. Three different regions can be distinguished in the excitation spectrum of localized excitons. The first region corresponds to the excitation of free excitons which are trapped to localization sites in the process of energy migration. There is no energy migration in the third spectral region and all the emission is caused by directly photo‐excited states. In the intermediate region II a limited energy transfer between the localized states takes place via phonon assisted tunneling.