The Urbach Tail in Cuprous Halides

Abstract

The absorption edge spectra are investigated on CuCl, CuBr and CuCl,Br between 4∼450 K. The observed temperature- and photon energy-dependences are analyzed in terms of the Urbach rule, and the parameters, E₀, σ and K₀, for this rule are determined experimentally. The dynamical properties of excitons in cuprous halides are discussed basing upon the recent theory of the Urbach rule. Discussion is also made on the effect of disordered lattice on the Urbach parameters from the experimental results on CuCl,Br mixed crystals.