Sensitisation and stability of quartz OSL: Implications for interpretation of dose-response curves

Recent developments in our understanding of the relative importance of temperature-dependent charge transfer and luminescence recombination probability in quartz have shown the latter to be the dominant effect in experiments using a heat treatment (preheat) before optically stimulated luminescence (OSL) measurement. This has enabled us to develop new ways of measuring doses in quartz, using only a single sample. The origins of the OSL signal are first discussed, and it is argued that stimulation at elevated temperature (125 degrees C) increases the rate of decay of the luminescence, and simplifies the interpretation of the signal by avoiding the involvement of the 110 degrees C TL trap in the stimulation process. This is supported by the observation that a single trap/recombination centre combination is responsible for almost all the luminescence when preheats of between 160 and 300 degrees C (for 10 s) are used. Experiments are also discussed which quantify the activation energies for thermal quenching and thermal assistance of the OSL. By measuring directly the luminescence recombination probability during OSL measurement, the effects of sensitivity change (both during burial and during laboratory procedures) have been investigated, and a simple model derived which combines luminescence sensitivity change and thermal depopulation of electron traps. Predictions based on this model confirm that the main criterion for selecting a preheat procedure should be that the laboratory dosed samples be measured with the same probability of luminescence as the naturally dosed samples. Finally, a new single-aliquot regenerative-dose protocol is discussed, which is insensitive to preheat procedure, and which has provided further compelling evidence that thermal transfer is not a significant factor in the measurement of the burial dose in sedimentary or heated quartz.