Factors controlling the shape of the OSL decay curve in quartz

The effects of stimulation temperature on the shape of the quartz OSL decay curve have been investigated using a green light stimulation source and a quartz sample from the Kimberley region of Western Australia. The relationship between the initial OSL (first 0.4 s), the OSL at the end of a 100 s stimulation period, and the full OSL integral, is presented as a function of stimulation temperature (25-500 degrees C). It is deduced that a single trap/luminescence centre combination is responsible for the majority of the OSL at stimulation temperatures between 150 and 275 degrees C, and thus that traps giving rise to TL peaks in this temperature range cannot contribute significantly to the OSL signal, either directly or indirectly. Comparison of the initial and integral OSL values in this temperature range permits the effects of thermal assistance and thermal quenching to be separated and the activation energies for each process to be calculated. Below 150 degrees C the relationship changes markedly; this change cannot be explained in terms of only thermal assistance and thermal quenching. After 100 s of stimulation, the contribution to the OSL from deeper traps (> 330 degrees C) is deduced to be only about 1.7% of the average OSL over 100 st All of this luminescence from deep traps appears to be thermally quenched, and it is concluded that the 375 degrees C TL trap in particular does not contribute measurably to the slowly decaying component of the OSL from this material. Furthermore, shallow traps below about 150 degrees C do not contribute a large fraction of the OSL signal by direct stimulation. However, we show that competition for charge by the 110 degrees C trap may be significant during stimulation, and some limits are estimated for this process. The possible implications of our findings' for dating procedures are also considered. (C) 1998 Commonwealth Scientific and Industrial Research Organization. Published by Elsevier Science Ltd.