Core Exciton of Alkali and Alkali-Earth Halides

Abstract

Low energy electron loss spectra (LEELS) of alkali halides LiF, NaCl, KCl, KBr, KI, RbBr and CsCl, and alkali-earth halides CaF₂ and CaCl₂ are measured for primary energies 30 to 900 eV. For K and Ca-halides, there are four loss peaks in the core exciton regions, some of which have not been observed in optical measurements and high energy electron loss spectra. The intensities of these loss peaks are primary energy dependent and decrease with the increase of incident energy. The primary energy dependency is largest for K and Ca-halides and decreases for Rb and Cs, and is almost not observed for Li and Na-halides. These loss peaks are thought to be caused by intra-atomic transitions between localized p-core and d-conduction bands in metal ions.