Interaction of Slow Electrons With Insulating Crystals. 2. Comparison of Electron and Photon Absorption Coefficients for KCl and KBr

Abstract

The electron absorption coefficient for pure KCl and additively colored KCl and KBr was measured in the energy range from 0.2 to 12 ev. These data are compared with photon absorption measured in the same crystals in the energy range from 1.2 to 6.5 ev and with published optical and photoemission data above 6.5 ev. Certain imperfection interactions were found at corresponding photon and electron energies. The surface transition layer, even for pure KCl, was observed to contain $F$ and ${V}_{3}$ centers. There was no evidence of direct electron-exciton interactions. The valence band of KCl was observed to be 8.6\ifmmode\pm\else\textpm\fi{}0.2 ev below the vacuum level; this agrees with Eby, Teegarden, and Dutton's measurements. Upon electron bombardment, an optical absorption near the first fundamental band was found to develop. Its characteristics do not coincide with any of the absorption bands previously reported in this energy region.