Symmetry of the Green Phosphorescence of Heat Pretreated Colored KCl Crystals

On thermal pretreatment in the open air (at 700^∘{}C), the phosphorescence of KCl crystals after x coloring at liquid-air temperature turned from violet to green. While the former phosphorescence showed no anisotropy the green was found to become partially polarized after irradiation with [011] light. The irradiation also induced dichroic absorption at 3650A. Both the polarization in the phosphoresence and the dichroic absorption persisted up to nearly 200^∘{}K.The polarized light bleached the component of the 3650A absorption in parallel to it, but enhanced the green phosphorescence with the main effect on the perpendicular component.It is suggested that oxygen which diffused into the crystal during the heat treatment is responsible for the asymmetric center.