Characteristics of luminescence lifetimes in natural quartz from Brazil and South Korea

Abstract

Time-resolved optically stimulated luminescence has been used to investigate the influence of annealing temperature as well as irradiation dose on luminescence lifetimes in samples of sedimentary natural quartz from Brazil and South Korea. The luminescence was stimulated at a pulse width of 11 μ s using 470 nm blue light and detected in the wavelength region between 340 and 380 nm. Measurements were made on samples annealed between 500 and 900°C as well as on un-annealed subsets. The luminescence was excited by beta irradiation covering the dose range within 7 and 344 Gy. It was observed that in both samples, luminescence lifetimes increase with annealing temperature to a maximum at around 600°C and decrease again thereafter. As regards the effect of irradiation dose on luminescence lifetimes, it was found that the lifetimes are independent of irradiation in un-annealed samples from South Korea but decrease with irradiation in un-annealed samples from Brazil. When the quartz samples were then annealed at 800°C, that is, beyond the first phase inversion temperature (570°C) of quartz, it was found that lifetimes increased with dose in samples from South Korea but were independent of dose in the samples from Brazil. These effects of annealing temperature and irradiation dose on luminescence lifetimes have been explained using an energy band model for quartz. Results from the present work and those in the literature on natural quartz samples from some other origins showed that quartz samples have two regions of temperature, where lifetimes have distinct characteristics as a function of either annealing temperature or irradiation dose. Specifically, lifetimes go through either a peak or a minimum as a function of annealing temperature and the dependence of lifetimes on dose also depends on annealing temperature. This means that dependence luminescence lifetimes on irradiation dose or annealing temperature can be used as an indicator for the presence of phase transition.