Optical and Thermal Electron Transfer in KCl: T l+ Crystals

The absorption spectra of Tl2+ in KCl crystals have been measured from 77 to 300 K. Tl2+ gives rise to five absorption bands peaking a t 1760, 860, 680, 460 and 233 nm. These oscillator strengths have been calculated. Optical excitation in the 460 nm band destroys the Tl2+ and Tl++ bands and produces the Tl° bands. Thermal excitation of a crystal containing only Tl2+ and T1++ results in the simultaneous decay of Tl2+ and Tl++. I t is concluded th a t electrons released from Tl2+ by optical or thermal excitation are trapped a t T1+ and T1++. A discussion is given on Tl2+++: A Tl2+++ which has an absorption band a t 1075 nm is formed when a (Tl+)2 traps a positive hole of a nearby Cl2~, whereas it is deformed when a Tl2+++ traps an electron released from a Tl2+ by optical excitation in the 460 nm band.