Thermally stimulated depolarization measurements on NaF:02-, NaCI:S2-.and KC1:S2-

In NaCl:S^2-, KC1:S² and NaF:0^2-(i) optical absorption and emission spectra and (ii) electric conductivity measurements show that after suitable heat treatment the bivalent anion impurities are paired with anion vacancies. Conventional dielectric absorption measurements and sensitive measurements of thermally stimulated depolarizing (t. s. d.) currents (ionic thermocurrent) have failed to detect the presence of bivalent anion-anion vacancy dipoles in these crystals. We suggest that derealization or sharing of the electron of the bivalent impurity ion, possibly with the vacancy, considerably reduces the dipole moment.