New electron-excess color centers in KCl: Effect of O 2- and SO 2-4 ions

Two new absorption bands, along with the T bands previously reported by Ring and Grossweiner, have been observed in additively colored KCl. The bands are developed by bleaching F centers at high temperature in relatively pure KCl, but may be produced rapidly at room temperature in colored KCl crystals containing O ^2-, or in sulfate-doped KCl which has been additively colored. It is proposed that the development of these bands is accelerated by the presence of negative ion vacancies introduced as charge compensation for the divalent anions, and that the new centers are aggregates containing one or more F centers with a vacancy pair. The segregation coefficient of K ₂SO ₄ in KCl, between crystal and melt, was found to be 1.0 × 10 ^-3.