Fundamental Optical Absorption and Valence Bands in Alkali Silver Halide Crystals

Anisotropic fundamental optical absorption bands have been found at 4.4 eV in K2AgI3 and Rb2AgI3, and at 4.9 eV in Rb2AgBr3. The X-ray photoelectron spectrum of Rb2AgI3 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.