Optical and Thermal Electron Transfer in KCl: Tl+ Crystals

Abstract

Abstract The absorption spectra of Tl2+ in KCl crystals have been measured from 77 to 300 K. Tl2+ gives rise to five absorption bands peaking at 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 Tl0 bands. Thermal excitation of a crystal containing only Tl2 + and Tl++ results in the simultaneous decay of Tl2 + and Tl++. It is concluded that electrons released from Tl2 + by optical or thermal excitation are trapped at Tl+ and Tl++. A discussion is given on Tl2 +++: A Tl2 +++ which has an absorption band at 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.