Optical Constants and Exciton States in KCl Single Crystals. II. The Spectra of Reflectivity and Absorption Constant

Abstract

The reflectivity between 6 eV and 12 eV and the absorption tails both in the intrinsic region and in the impurity bromine band region of KCl single crystals are studied as a function of temperature in the range 10°K to 573°K. The absorption measurement complements the earlier results reported in 1960 ¹⁾ and 1961 ²⁾ in improving the wavelength scale and in extending the temperature range. The present data allow us to investigate the phonons interacting with \(\varGamma\)-exciton, yielding \(\hbar\omega{=}1.42{\times}10^{-2}\) eV (for (3/2, 1/2-component)) and =1.59×10 ^-2 eV (for (1/2, 1/2)-component)) for phonons effective to the peak shift and \(\hbar\omega{=}1.47{\times}10^{-2}\) eV for phonons taking part in the optical absorption processes in the intrinsic Urbach tail. The temperature dependence is presented on the absorption constant spectra up to 12 eV and dispersion spectra n up to the \(\varGamma\)-exciton region, each being derived by the Kramers and Kronig analysis with the use of the above data. The data of the absorption tail position E (10 ^α ) at A =10 ^α cm ^-1 (α: a constant) and the peak position E ( A _max ) for the (3/2, 1/2)-component are summarized for all the alkali halides investigated in different places up to the present. An analysis of the data indicates that the difference in energy E ( A _max )– E (10 ^α ) is nearly independent on the individual species of alkali halide for the intrinsic Urbach tail at any temperature.