X-Ray Spectroscopic Studies of CaF2, CaO and CaS

The Kα emission and Kβ emission spectra in the fluorescence of Ca 2+ in CaF 2 , CaO and CaS are measured with a two-crystal vacuum spectrometer. Chemical shifts are observed for the Ca 2+ Kα 1,2 , Kβ 1,3 and Kβ 5 emission peaks. The measured Kβ 5 emission bands are presented along with the ultraviolet photoelectron spectrum of the F - 2p valence band of CaF 2 , the X-ray photoelectron spectrum of the O 2- 2p valence band of CaO, the S 2- Kβ emission spectrum of CaS and the Ca 2+ K absorption spectra of these compounds, reported previously. By using these spectra, the first small peak at the Ca 2+ 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 CaF 2 , CaO and CaS, respectively.