Multiplication mechanisms of electronic excitations in KBr and KBr:Tl crystals

The reflection spectrum and excitation spectra of self-trapped exciton emissions have been measured in the spectral region from 6.5 to 30 eV for a freshly cleaved KBr crystal at liquid-helium temperature. The following mechanisms of multiplication of electronic excitations have been distinguished by using luminescence methods: (i) formation of secondary excitons by hot photoelectrons; (ii) formation of secondary electron-hole pairs by hot photoelectrons; (iii) formation of electron-hole pairs due to nonradiative Auger decay of cation electronic excitations. The analysis of the spectrum of the intensity ratio of {π} and {σ} emissions of self-trapped excitons allowed us to obtain quantitative data on exciton formation by photoelectrons. The excitation spectra for the T and X Jahn-Teller components of Tl⁺-center emission have been measured in a KBr:Tl crystal at liquid-helium temperature in the region from 6.5 to 30 eV. A sharp maximum at 15 eV in the intensity ratio of T and X emissions is connected with the excitation of Tl⁺ centers by hot photoelectrons.