Manifestation of the Urbach Rule in the FundamentalElectronic Absorption Spectra of Halide Salt Melts:I. Tails of the Absorption Edge of Alkali Metal Halide Melts

摘要

The long-wavelength tails of the fundamental electronic absorption spectra of alkali metal halide melts have been investigated. The obtained values of the absorption characteristics of the alkali metal halide melts have confirmed the assumption that, over a wide temperature range (600-900°C), the exponential tail of the absorption coefficient of these disordered systems is associated with the presence of the spectrum of fluctuating electronic levels extended to the band gap in the melts under investigation. The fulfillment of the Urbach rule is the limiting case of the general exponential dependence of the optical absorption coefficient in the ultraviolet region of the fundamental absorption edge. in the studied series of melts of alkali metal halide salts, the absorption coefficient in the region of tails of the spectral curves of the halide systems decreases from LiCl to CsCl and from LiCl to Lil. An analysis of the results obtained from the investigation of alkali metal halides has revealed an interrelation between the main parameters of the Urbach rule and between these parameters and the temperature coefficient of the band gap.