Fundamental optical absorption edge and exciton-phonon interaction in Cu6PS5Br superionic ferroelastic

The absorption edge of monocrystalline Cu6PS5Br was studied in the 4.2-505 K temperature range. At low temperatures (T < 180 K), Wannier-Mott s-excitons were detected at the absorption edge as well as in the photoluminescence spectra and, their basic parameters at 77 K were estimated. The mechanisms of exciton-photon interaction resulting in exponential absorption edge and Urbach's tail at temperatures T > 200 K were analyzed and interpreted in the framework of the Dow-Redfield theory. Two types of structural disorder affecting the optical absorption tail were studied. (C) 1998 Elsevier Science S.A. All rights reserved.