Investigation of the optically stimulated luminescence dating method ...

OSL from quartz 21
confirmed however, if the OSL emission wavelength also increases with increasing
temperature.
Temperature (°C) Wavelength (nm)
22 365
95-110 376
150-180 392
200-220 410
305-325 430
Table 2.1: Emission wavelengths of the “family” of TL peaks at ~100, 180, 220 and 305°C (Franklin et al.,
1995). The emission peak at room temperature is for OSL, and was obtained by Huntley et al. (1991; see
Figure 2.2).
The probable luminescence centre giving rise to the OSL emission has been identified by
Yang and McKeever (1990a, b) as the [H3O4]° centre (these are silicon vacancies,
occupied by 3 hydrogen atoms and a trapped hole, the latter being denoted by the
superscript °). Using ESR (electron spin resonance) and TL, they were able to show that
two point defects are responsible for the TL signal at ~100°C, namely [AlO4]° and
[H3O4]°. However, only the [H3O4]° centre yields emission at 380 nm, comparable to the
OSL emission (Figure 2.2 and Table 2.1), from which is deduced that it is the most likely
recombination centre.
2.3. Measuring the OSL from quartz
To avoid detecting the stimulation light without a significant attenuation of the 365 nm
luminescence to be measured, the wavelengths must be sufficiently separated from each
other. Also, the stimulation wavelength must be longer than the one from the desired
luminescence, to avoid the use of signals originating from traps that are not relevant to
dating (Aitken, 1998; see also Chapter 1). On the other hand, the stimulating light must
remain sufficiently energetic for the stimulation to be efficient.