Investigation of the optically stimulated luminescence dating method ...

OSL from quartz 39
Figure 2.12: Glow curves for some individual quartz grains, illustrating the wide variability (modified
from Huntley et al., 1993). The quartz grains were extracted from an Australian dune sand. The inset
shows the distribution of photon counts for 100 grains and demonstrates the presence of a small fraction
of super-bright grains (indicated by the arrows).
Using single-grain luminescence equipment, Duller et al. (2000) measured the OSL from
a large number of individual quartz grains from seven samples. Their results are shown in
Figure 2.13, from which it is clear that in reality each sample consists of a heterogeneous
collection of grains. For a sample in which all the grains would emit the same
luminescence, a straight diagonal line would be found. The study demonstrated
furthermore that the proportion of the grains from which a significant OSL signal can be
observed varies from one sample to another, and that in extreme cases, 95% of the total
light-sum emitted can originate from only about 5% of all the grains measured. Jacobs et
al. (2003a) recently investigated the variability in signal intensity for single quartz grains
extracted from three coastal sand dunes from South Africa. For all three samples they
found that only 10% of the grains gave rise to 90-95% of the total light-sum. It is perhaps
worth mentioning that recent investigations by Duller et al. (2003) indicate that feldspars
seem to be more uniform in their luminescence intensity than quartz.
The above clearly illustrates the extreme non-uniformity in luminescence brightness
exhibited by different quartz grains. As only very few grains contribute to the measured
luminescence, it can consequently be expected that some of this variability will also be