Transformation of Phonon Mode Behaviour in the AgCl_xBr_1−x System

Abstract

Systematic studies of far infrared reflection spectra and photoluminescence spectra of free excitons have been performed in AgCl_xBr_1−x mixed crystals at low temperatures in the composition range x=0 to 1 and between x=0.10 and 0.39, respectively. Reflection spectra exhibit the existence of two TO-phonon modes for 0.03≤x≤0.50, whereas only one TO-phonon mode is recognized for x>0.87. Variation of reflection bands with the composition x indicates the transformation of phonon mode behaviour from the two-mode type to the one-mode type with increasing x. Photoluminescence spectra also exhibit the existence of two LO-phonon modes in AgBr-rich crystals, 0.12≤x≤0.27.