On the optical dating signal from quartz

Abstract

A series of experiments were conducted on the optical dating signal from quartz. Results are presented showing the quantitative equivalence of the light sums of the optically stimulated luminescence (OSL) emitted by quartz under exposure to 514.5 nm light and that of the quartz “325°C“ thermoluminescence (TL) peak. Discrepancies observed between the OSL and TL light sums under “typical” measurement conditions (i.e. when OSL is measured at ∼293 K and the 325°C TL peak is measured at ∼600 K, in both cases observing ultraviolet emissions) are attributed to thermal quenching of luminescence at the recombination centres (non-radiative recombination). The bleach response spectrum (using bleaching wavebands ranging from 400.6 Δ 10.1 nm to 899.1 Δ 13.2 nm) of OSL from quartz (514.5 nm stimulation) was measured and found, within experimental errors, to be indistinguishable from that previously measured for the 325°C TL peak of quartz. Also measured was the thermal dependence of the OSL signal under stimulation by various wavebands ranging from 480.9 Δ 6.8 nm to 861.1 Δ 12.5 nm, in the temperature range from ∼ 100 to ∼ 500 K. Strong thermal assistance was found for all wavebands tested, with the magnitude of thermal assistance increasing as stimulation wavelength increased— behaviour not inconsistent with photoionization. Supplementary work showed that OSL production involves a single-photon-absorption untrapping step. It is concluded that the OSL emitted by quartz under exposure to visible light, and the 325°C TL peak of quartz, originate from one and the same trapped electron population. Furthermore, optical untrapping of this trapped charge population, resulting in both the bleaching of the 325°C TL peak and the prompt emission of OSL, proceeds by the same mechanism: single-photon-absorption photoionization direct to the conduction band.