Photoconductivity in Colored Potassium Chloride

The photoconductive sensitivity, during the course of bleaching $F$ centers in KCl, was found to vary in much the same way for excitation in the $M$ and $N$ bands as for excitation in the $F$ band, from which it appears that the major effect of bleaching is to decrease the lifetime of photoelectrons. The lifetime of photo-electrons giving rise to the secondary photocurrent was approximately linear with the sensitivity. From the second-order decay of photocurrent, the trapping cross section of $\ensuremath{\alpha}$ centers at room temperature was found to be about ${10}^{\ensuremath{-}13}$ ${\mathrm{cm}}^{2}$. Shallow traps were investigated by means of current glow and isothermal untrapping. Two sets were identified, with depths of about 0.60 and 0.68 eV; the concentration and characteristics vary somewhat between samples.