ON THE OPTICAL DATING SIGNAL FROM QUARTZ

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 simulated luminescence (OSL) emitted by quartz under exposure to 514.5 nm light and that of the quartz ''325 degrees C'' thermoluminescence (TL) peak. Discrepancies observed between the OSL and TL light sums under ''typical'' measurement conditions (i.e. when OSL is measured at similar to 600 K, in both bases observing ultraviolet emissions) are attributed to thermal quenching of luminescence at the recombination centres (non-radiative recombination). The bleach responses spectrum (using bleaching wavebands ranging from 400.6 Delta 10.1 nm to 899.1 Delta 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 degrees C TL peak of quartz. Also measured was the thermal dependence of the OSL signal under stimulation by various wavebands ranging from 480.9 Delta 6.8 nm to 861.1 Delta 12.5 nm, in the temperature range from similar to 100 to similar to 500 K. Strong thermal assistance was found for all wavebands tested, with the magnitude of thermal assistance increasing as stimulation wavelength increased-behavior not inconsistent with photoionization. Supplementary work showed that OSL production involves a single-photon-absorption untrapping step. It is concluded that OSL emitted by quartz under exposure to visible light, and the 325 degrees 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 degrees C TL peak and the prompt emission of OSL, proceeds by the same mechanism single-photon-absorption photoionization direct to the conduction band.