Thermally transferred luminescence in fine-grained quartz from Chinese loess: Basic observations

Abstract

Results of a series of experiments designed to investigate the properties of thermally transferred optically stimulated luminescence (TT-OSL) in fine-grained quartz from Chinese loess are reported. This signal is confirmed as having two sources, recuperation and basic transfer, as proposed by earlier workers. The combined TT-OSL signal is shown to be due to electrons being ejected from electron traps that are very similar to the main OSL traps, and may indeed be identical to them. However, the dose dependences of the main OSL signal and the recuperated TT-OSL signal behave in a different way, with the TT-OSL signal showing slower onset of saturation. This behavior is interpreted in terms of the OSL production being limited by the number of available luminescence centres, rather than electron traps. This opens up the possibility of a new OSL dating procedure capable of extending the age range by almost an order of magnitude. The thermal and optical stabilities of the two sources of electrons that give rise to the TT-OSL signal are investigated. The basic TT-OSL signal is the result of the direct thermal transfer of electrons from a trap that is thermally deeper than the main OSL trap and which is optically insensitive. The recuperated TT-OSL is directly derived from an optically insensitive refuge trap which trapped electrons during the initial optical stimulation following irradiation. These two signals can be separated easily by a sequence of repeated thermal and optical treatments (or a single isothermal treatment). It is found that the recuperated TT-OSL signal is the major contributor to the TT-OSL signal when these procedures are carried out at 260 ∘ C for the fine-grained quartz studied here.