X-Ray Spectroscopic Studies of CaF2, CaO and CaS

Abstract

The Kα emission and Kβ emission spectra in the fluorescence of Ca2+ in CaF2, CaO and CaS are measured with a two-crystal vacuum spectrometer. Chemical shifts are observed for the Ca2+ Kα1,2, Kβ1,3 and Kβ5 emission peaks. The measured Kβ5 emission bands are presented along with the ultraviolet photoelectron spectrum of the F- 2p valence band of CaF2, the X-ray photoelectron spectrum of the O2- 2p valence band of CaO, the S2- Kβ emission spectrum of CaS and the Ca2+ K absorption spectra of these compounds, reported previously. By using these spectra, the first small peak at the Ca2+ K absorption threshold of each compound is identified as being due to a core exciton, the energy level of which is formed below the bottom of the conduction band. The binding energies of the excitons are estimated to be 3.6 (±0.4), 2.5 (±0.5) and 0.6 (±0.5) eV for CaF2, CaO and CaS, respectively.