Optical Absorption of KCl Single Crystals in the Spectral Region from 1.1 to 7.0 eV

Abstract

The reflectivity of KCl in the region from 1.1 to 6.2 eV has no structure and increases slightly with photon energy. Moreover, it depends little on the origin of the specimen. The optical density of KCl is small and increases linearly with photon energy in the region up to 5.5 eV. In this region, the optical density is almost independent of the thickness of the specimen and is therefore attributed to absorption at the surface. At 5.5 eV, however, the optical density rises steeply and depends on the thickness. However, the value extrapolated to zero thickness connects smoothly with the optical density below 5.5 eV. In KCl, the surface levels cover the band gap of the bulk. The levels which lie more than 4.0 eV below the vacuum level are occupied by electrons, and there seems to be a continuous and homogeneous distribution of the surface level.