Electronic States and Optical Absorption Spectra ofHCenters in Potassium Halide Crystals

Abstract

Irradiation of undoped KI single crystals with a KrCl excimer laser ( h ν=5.58 eV) near liquid helium temperature results in the production of α, β, F , F ′ and H centers. The H centers, i.e., I 4 3- molecular ions in KI, give rise to two prominent optical absorption bands peaking at 2.23 and 2.77 eV. The theoretical results for the (halogen) 4 3- molecular ion, which are obtained by using the semiempirical self-consistent field method, show that the 2.23- and 2.77-eV bands are ascribed to the transitions of the ground 2 Σ u 1/2 + state to the excited 2 Π g 1/2 and 2 Σ g 1/2 + states, respectively. The same assignments are made for two distinct absorption bands arising from H centers in KCl and KBr crystals. The relative intensities of the two distinct bands for KCl, KBr and KI crystals depend on the magnitude of the spin-orbit interaction in halogen atoms. The peak energies and intensities of absorption bands caused by H centers in the potassium halide crystals are discussed in comparison between experi...