Electronic States of F-Centers in Alkali Halide Crystals

Abstract

The electronic states of F-centers in alkali halides with NaCl-type structure have been investigated using the discrete variational (DV) Xα cluster method. The electronic transition accompanied by optical absorption is examined on the basis of Slater's transition state concept. The photo-absorption energies of F-centers computed for the compounds with relatively small anions agree well with experimental data, but those for iodides and bromides exhibit much lower values than the observed values. We have also investigated the change in the absorption energy by the atom displacement. By the inward displacement of 1st neighbor cations, the absorption energies are decreased to approach the experimental values. The relaxation of the 1st neighbors estimated from the computation exhibits fairly small values in fluorides, while large values in iodides and bromides. The effect of lattice relaxation around an F-center is discussed in connection with the bonding nature of the F-center level.