Lifetimes of Parity Forbidden Transitions of the Cu+ Center in the Alkali Iodides

Abstract

AbstractThe ultraviolet photoluminescence spectra and excited state lifetime measurements of the Cu+ center in the alkali iodides are reported from 5 to 300 °K. The long lifetimes (greater than 10 μs for all temperatures) obtained indicate that a forbidden transition is involved. The strong temperature dependence of the emission lifetime for LiI:Cu and NaI:Cu is explained on the basis of a linear electron–phonon interaction coupling even and odd parity states, whereas the weak temperature dependence and shorter lifetimes observed for KI:Cu and RbI:Cu are explained on the basis of an off‐center position for the Cu+ excited ion. The oscillator strength determination for the Cu+ absorption in RbI:Cu and the temperature dependence of the absorption for LiI:Cu are reported. These measurements and similar measurements by other authors on NaI:Cu and KI:Cu are compared with the lifetime data. The absence of a correlation between lifetime and absorption measurements indicates that the levels involved in the emission process are different from those of the absorption process.