Core- and Valence-Exciton Effects on Spectra of Soft-X-Ray Radiation from Valence Band to Core Level in Wide-Gap Insulators

Abstract

The core- and valence-exciton effects on the soft-X-ray radiation spectra are theoretically studied. A three band system, composed of a dispersionless core band, a valence band and a conduction band, is employed as a typical example for a wide-gap insulator. Intra-site Coulombic interactions between a core hole and a conduction electron, and also a valence hole and the conduction electron are taken into account as the origin of the core- and valence-excitons. A core-hole phonon interaction is also taken as an origin of a dissipation of a core-hole momentum. Under this model, the radiation spectra are calculated by a quantum mechanical second order optical process. In the case of low-energy off-resonance, a sharp peak of the valence-exciton appears in the spectra, whereas in the case of on-resonance with the conduction band, this peak becomes very small. In the case of on-resonance with the core-exciton, an integrated intensity of the spectrum is very much enhanced, and a prominent peak appears in the spectrum due to an efficient optical conversion from the core-exciton to the valence-exciton.