Investigation of the optically stimulated luminescence dating method ...

– CHAPTER 2 –
OSL FROM QUARTZ
Quartz is the dosimeter that has been used throughout this work. This mineral was chosen
because of its abundance in the sediments to be investigated, and because it has certain
advantages with regard to microdosimetry and anomalous fading. Furthermore, over the
last seven years or so, considerable progress has been made in the understanding of its
luminescence properties, through which it nowadays has become the preferred mineral for
dating purposes. In this chapter, the key features of the quartz OSL signal are discussed.
2.1. Stimulation of quartz
A stimulation spectrum yields information on the efficiency by which a certain
wavelength is able to stimulate a certain mineral. For instance, Hütt et al. (1988)
discovered in this manner that infrared light could be used for stimulating feldspars, but
not for quartz. Knowledge of the stimulation spectra is however not only important
because it allows the selection of a specific mineral, but also for optimising the
stimulation wavelength to obtain a maximum light output.
Bøtter-Jensen et al. (1994) investigated the stimulation efficiency of quartz at different
wavelengths. They found an increase in signal intensity (I) with decreasing stimulation
wavelength (increasing energy), as is shown in Figure 2.1. Stimulation spectra were also
published by Ditlefsen and Huntley (1994; further elaborated by Huntley et al., 1996) and
Kuhn et al. (2000), with no significant differences. It can be seen in Figure 2.1 that there
is a slight change in response at around 500-520 nm. The reason for this “knee” is still
poorly understood. The same observation was made by Kuhn et al. (2000) who,
consequently, recommended avoiding stimulation with wavelengths in this region to
minimize additional scatter in the luminescence output from identical samples.
The stimulation spectrum also shows that practically no luminescent signal is to be
expected when quartz is stimulated with infrared light. Spooner (1994b) also found that
wavelengths greater than 690 nm are inefficient for stimulating a luminescence signal