Absorption Spectra of Excitons in Alkali Halides in the Vacuum-Ultraviolet Region

Abstract

On the basis of the localized excitation model, characteristic absorption spectra of excitons in alkali halides in the range of photon energy around 20 eV corresponding to the n p 6 → n p 5 n ' s and n p 6 → n p 5 n d excitations of alkali ions are theoretically treated by using methods developed in the ligand field theory. By assuming reasonable values of Slater integrals, the spin-orbit interaction constant and the ligand-field strength, the observed positions including their chemical shifts and the relative intensities of five absorption peaks called A , B , C , D and E in RbX(X=F, Cl, Br, I) are explained satisfactorily. In constant to the case of the band picture, the excited d -orbital responsible for the absorption of RbX is shown to be mainly of the d γ character, although mixing of the p 5 s , p 5 d e and p 5 d γ configurations is appreciable.