Silver-Activated Alkali Halides

Abstract

The emission, excitation, and absorption spectra of silver‐activated alkali halides have been investigated. Three absorption bands due to ionic silver have been observed in NaCl, NaBr, KCl, and KBr, and the growth of these bands with silver concentration has been studied. In each of these crystals the two shorter‐wavelength bands are ascribed to isolated silver ions, while the band of longest wavelength is ascribed to pairs of silver ions. Upon x‐ray irradiation as many as five new absorption bands arise in certain alkali halides in addition to the F band. Excitation into three of these bands (designated as the B, C, and D bands) produces luminescence, the emission spectrum being different for each band. The B band is attributed to a center consisting of an electron trapped at a silver ion adjacent to a halogen‐ion vacancy; the C band to an electron trapped at a complex of two silver ions adjacent to a halogen‐ion vacancy; and the D band to a hole trapped at an alkali‐ion vacancy adjacent to a silver ion.