Absorption Edge in Solid Solutions of Alkali Halides

Abstract

Temperature dependence of the absorption coefficient in the long wavelength tail of the first exciton band and of the position of its absorption maximum are studied in the solid solutions of alkali halides, KI doped with NaI, with RbI, and with KCl. Absorption measurement are carried out between 80°K and about 700°K. In every solid solution, Urbach’s rule is found to hold in the exciton absorption tail, and the peak energy of exciton absorption band is found to vary linearly with the change in temperature. From the measurements of temperature dependence of so called “steepness parameter” in every solid, the effective frequency of lattice vibration related to the tail part of the absorption band is estimated.