Far-Ultraviolet Reflectance Spectra of Ionic Crystals

Abstract

Synchrotron radiation has been used to measure the reflectance spectra of KCl, KBr, RbCl, CsCl, CsBr, Ca${\mathrm{F}}_2$, Sr${\mathrm{F}}_2$, and Ba${\mathrm{F}}_2$ for photon energies $6<\mathrm{}\hslash \omega <36\mathrm{}$ eV at temperatures $90<T<\mathrm{}400\mathrm{}$ K. Excitations of both valence and core electrons show sharp structure and strong $T$ dependence. Analysis of the data in terms of excitonic and interband transitions from core states is made with regard to $T$ dependence, crystal structure, and chemical composition.