Fundamental Optical Absorption and Valence Bands in Alkali Silver Halide Crystals

Anisotropic fundamental optical absorption bands have been found at 4.4 eV in K 2 AgI 3 and Rb 2 AgI 3 , and at 4.9 eV in Rb 2 AgBr 3 . The X-ray photoelectron spectrum of Rb 2 AgI 3 indicates that the uppermost valence band is the p-band of halogen. Optical absorption spectra are interpreted in terms of transitions of the charge transfer type from the halogen to the silver ion. The photo-excitation in the fundamental absorption region have been observed to induce luminescence and a radiation damage effect at low temperature.