Luminescent Lifetimes and Decay Processes of Hetero-Nuclear Relaxed Excitons [ClI^-(V_K)+e] in KCl:I and RbCl:I

Abstract

Lifetimes, emission yields, and their temperature dependence of the BG emission from localized excitons with the configuration of [ClI - +e] are investigated in KCl:I and RbCl:I from 1.9 K to 30 K. Below 4 K, the emission in KCl:I decays with two exponential components: τ s ∼8.0 ms and τ f ∼120 µs. In raising temperature, τ s decreases rapidly to approach a constant value ∼170 µs, while τ f remains constant up to ∼9 K where this component vanishes abruptly and is replaced by an appearance of a delayed `build-up'. Similar results are obtained in RbCl:I. Analysis is made in terms of phonon-induced transitions among zero-field-split triplet sub-levels. Concerning the spin-lattice relaxation mechanism, importance of ralaxation process of Orbach type is suggested in place of the one-phonon direct process which has been successful for the π-emission in KI.