Light Scattering in ``Pure'' and Impurity-Doped Potassium Chloride

Abstract

The angular dependence of the light scattering in samples of KCl:Pb and KCl:BO2 is strongly dependent on crystal orientation. The scattering units in these systems are shown to have the form of cylinders, length 50 000 Å, diameter <400 Å, lying parallel to the cubic crystal axes and composed of different scattering centers in the two systems, but both characterized by an anisotropic polarizability ellipsoid which has a specific orientation relative to the cylinder axis. Plausible estimates of the magnitude of the effective polarizabilities of the two types of centers are obtained and compared with theory. Samples of KCl:pure, KCl:Ca, and KCl:Sr did not show any orientation dependence of the scattering. The primary scattering units in KCl:pure are identified as small spherical voids. For KCl:Ca the units are spherical impurity precipitates and voids, radius∼800 Å. In KCl:Sr the scattering is almost entirely caused by spherical precipitates characterized by a randomly oriented anisotropic polarizability tensor having two of its principal values equal. The effects of heat treatment on the scattering by the systems KCl:BO2, KCl:pure, and KCl:Sr are consistent with the identifications of the scattering units and also provide corroboration of previous work on orientation-dependent samples.