Absorption of Colloidal Band in Mixed Alkali Halides

Colloidal formation of alkali metals in KCl crystals containing various amount of NaCl was studied by the measurement of optical absorption. The position of the colloidal bands in KCl-NaCl mixed crystals is shorter than that in pure KCl; the position shifts markedly to longer wavelengths with increasing temperature of annealing. At higher temperatures, colloidal bands produced with illumination are not different from those produced in dark, while below 200°C position of the former differs from that of the latter when the time of annealing is short, but approaches to the position of the latter with prolonged treatment. It is concluded that the colloids in the mixed crystal contain much more sodium proportionately than does the host crystal and the change in the position of the colloidal band is principally due to the change in the ratio of Na to K in K-Na alloy colloids.