Impurity core–valence luminescence in Rb 1− xCs xCl mixed crystals

Abstract

Core–valence luminescence, caused by radiative recombination of holes of the upper core band with valence electrons, has been studied in Rb 1− x Cs x Cl ( x=0.02–1) crystals using X-ray and VUV synchrotron excitation in the temperature range from 7 to 300 K. The luminescence excitation spectra exhibit thresholds of 14.2 and 14.5 eV at 300 and 7 K, respectively, and clearly resolved structures in the range of creation of 5pCs and 4pRb core excitons. Light yields of the mixed crystals turn out to be larger than that of pure CsCl under excitation by 15.1 eV photons, i.e. at the maximum of the excitation spectrum. It is revealed that the low energy core excitons (5pCs, j= 3 2 →Γ 12 ) can also be involved in excitation of core-valence luminescence at high temperature. Creation of [CsCl 8] clusters in heavy-doped crystals ( x>0.36) is suggested. The clusters are responsible for the additional emission band (5.1 eV) in Rb 1− x Cs x Cl.