On the dose-dependence of luminescence lifetimes in natural quartz

The influence of irradiation dose on luminescence lifetimes has been studied in suites of natural quartz from Brazil, Nigeria and South Korea. The lifetimes were evaluated from time-resolved luminescence spectra measured from quartz pulse-stimulated at 470nm and detected between 360 and 380nm. The effect of irradiation varied between materials, decreasing with dose in the Brazilian quartz, independent of dose in the samples from South Korea, and increasing with dose in the quartz from Nigeria. The dose-related effects are accounted for with reference to an energy band scheme for quartz in which the luminescence lifetime is associated with a primary radiative recombination centre at which most capture of holes produced during irradiation and associated hole re-trapping takes place. The measurements on the effect of irradiation dose on luminescence lifetimes were augmented by investigations concerned with the influence of measurement temperature between 20 and 200C on luminescence lifetimes in the same materials. It was observed that the luminescence lifetimes decrease continuously with temperature of stimulation and in a manner suggestive of increased thermal quenching of the corresponding luminescence. However, better consistency with the Mott-Seitz configurational coordinate model of thermal quenching is only apparent at temperatures greater than 120C. The discrepancy is attributed to the model used to derive the formulae for luminescence lifetimes in which any re-trapping of stimulated charge is assumed negligible. However, it is argued that if re-trapping were in fact not negligible then the decrease of luminescence lifetimes with measurement temperature would be evidence of the progressive reduction of the re-trapping as the measurement temperature were increased with the overall effect being the monotonic decrease in luminescence lifetimes as observed.