Quartz as a natural luminescence dosimeter.

Luminescence from quartz is commonly used in retrospective dosimetry, in particular for the dating of archaeological materials and sediments from the Quaternary period. The phenomenon of luminescence is related to the interaction of natural radiation with mineral grains, by the activation of and subsequent trapping of electrons at defects within the quartz lattice. The latent luminescence signal (i.e. the trapped electrons) is released when the grains are exposed to stimulation energy in the form of light or heat. Despite the fact that quartz is most nominally pure SiO2, the mineral forms in several different geological settings, i.e. under different pressure and temperature conditions. The luminescence emitted from quartz is complex and shows a variety of different components with diverse physical properties. This complexity is explained by the variety of defects in quartz that are either intrinsic (e.g., Si and O vacancies) or related to impurity atoms (e.g., Al or Ti). The concentration of impurity-related defects is dependent on the conditions of mineral formation or subsequent alteration. Experimental data have shown that the luminescence properties of quartz are highly variable with geological source and vary even at a grain-to-grain level within a sediment. As a consequence, caution is needed when making any general statements about the luminescence properties of quartz. When using luminescence measurements as a dating technique, it is necessary to adjust the measurement procedures for each geological provenance. Furthermore, some quartz has luminescence properties that make it problematic, or even unsuitable, for certain applications. These problems can arise from low and changing luminescence sensitivity, thermal transfer of trapped electrons, thermal instability of the trapped electrons and low saturation dose. Reviewing the present knowledge reveals that insufficient information is available either to unambiguously link distinctive lattice defects with characteristic luminescence components, or even to explain problems observed in application studies by potential dynamics of the defects within the crystal. This paper gives some ideas on how future research could utilise innovative analytical tools to identify or map the distribution of lattice defects and how practitioners could relate lattice defects to measured luminescence properties of quartz.