Optical Properties of Alkaline-Earth Chalcogenides. II. Vacuum Ultraviolet Reflection Spectra in the Synchrotron Radiation Region of 4–40 eV

The reflectivity spectra have been measured on single crystals of CaO, CaS, SrO, SrS, SrSe, BaO, BaS and BaSe in the syncrotron radiation region of 440 eV. In order to prevent surface deterioration effect, all measurements have been made at 77 K on the fresh (100) surfaces cleaved within a high vacuum. From a chemical trend of the spectra, the observed spectral features are classified into two groups, the interband and band-exciton transitions in the lower energy region, and the core-excitons in the higher energy region. The structures of the former group are interpreted in terms of a band-structure model which predicts the smallest direct gap at the X-point. For the features of the latter group, the ligand-field model by Satoko and Sugano gives a successful account of the observed core-exciton multiplets.