Energy Storage and Luminescence in KI:Tl at Low Temperatures

Abstract

X irradiation of KI:Tl at 78°K results in storage of energy which can later be released as light by thermal or by optical means. Observation of stimulation spectra, absorption spectra, and emission spectra together with light sum and bleaching experiments indicate that the storage centers are I₂⁻ and Tl^{+ +} trapped holes and Tl⁰ trapped electrons. The first thermal glow results from the mobility of I₂⁻ holes, while the second thermal glow and stimulated emission result from the release of electrons from Tl⁰ centers. Three distinct emission modes correspond to the three recombination processes. Stimulated electrons returning to I₂⁻ centers produce emission bands at 302 and 370 mμ. Electrons recombine with Tl^{+ +} holes to give a 425‐mμ emission identical with that from uv excited fluorescence. I₂⁻ holes migrating to Tl⁰ centers produce a broader emission at 425 mμ. This material is compared to other alkali halide phosphors and also to phosphors in general.