Changes in luminescence colour images from quartz slices with thermal annealing treatments

Abstract

Changes in the thermoluminescence (TL) glow curves of quartz grains after thermal annealing have been investigated. For the grain samples from Madagascar crystal rocks, intrinsic blue-TL (BTL) sensitivity in the higher glow curve temperature regions is enhanced linearly with the annealing temperature beyond 700°C, while at the same time red-TL (RTL) was newly induced and increased steeply beyond 800°C. Both peaks from BTL and RTL glow curves tend to move towards higher temperatures with annealing temperatures. These results suggest correlations to β-quartz/tridymite phase inversion temperature at 870°C. For Z-cut quartz slices from the Madagascar rock crystal, two-dimensional luminescence images of TL and after glow (AG) have been semi-quantitatively analyzed using a colour image analyzer with particular concern for luminescence property changes accompanied by thermal annealing treatment at 1000°C. Every luminescence image showed interesting stripe or zonal patterns resulting from the crystal formation conditions. A prominent colour change from the originally weak BTL into RTL and RAG (red-AG) has unexpectedly occurred on the quartz slices, while the original BTL has transferred into more intense BTL after the annealing treatment. These changes in the TL colour image (TLCI) patterns were also correlated with the aluminium concentrations using images from an electron probe microanalyzer (EPMA). From these results, it was verified that the BTL on the original slice is inversely proportional to aluminium and sodium contents whereas both TLCI and AGCI patterns on the annealed slice offered positive correlation with aluminium concentrations along the crystal growth direction.