Photoluminescence (PL) and excitation spectra have been measured at temperatures between 5 and 250K single crystals of As 2 Se 3 , As 2 S 3 and the mixed system As 2 Se 3-x S x , (0<x<1.5). Broad PL bands are observed near half the band-gap energy. The quantum efficiency is near unity at 5K but decreases rapidly with increasing temperature with well defined activation energies and from this behaviour an energy level scheme is proposed. A model is considered to explain the spectral linewidth by strong electron-phonon interactions and the variation of the optical band gap with composition is discussed.
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Street et al. (1974) studied this question.
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