Absorption of Light by Colloids in Alkali Halide Crystals

Abstract

The thermal transformation of $F$ centers into colloid has been observed in NaCl. The transformation occurs with constant integrated absorption cross section. The shape of the band depends upon the temperature at which the colloid is formed. A theory of the colloid band based upon the free electron model of the alkali metal and Mie's theory of the absorption of light by conducting spheres is presented. The theory makes assertions concerning the integrated absorption, maximum absorption, band width, and band position which are compared with experiment.