DEPENDENCE OF TL-PROPERTY CHANGES OF NATURAL QUARTZES ON ALUMINUM CONTENTS ACCOMPANIED BY THERMAL ANNEALING TREATMENT

The TL properties were investigated using both an IPDA (Intensified Photo-Diode Array) spectrometric system and a TLCI (Thermoluminescence Colour Image) method after thermal annealing treatment at several temperatures. An apparent colour change from original blue-(BTL) to red-TL(RTL) has unexpectedly occurred in a Z-cut slice of Madagascar quartz, after an annealing treatment around 1000 degrees C. From the TL-colour change studies of Z-cut slice, it was confirmed that original BTL intensities are inversely proportional to the AL contents; the TLCI-patterns of the original or annealed Z-cut slice gave stripe patterns corresponding to Al impurity contents along the crystal growth direction particularly yielding an intense appearance of RTL on higher Al contents after the annealing treatment. This changeability of TL-colour towards RTL after thermal annealing treatment was found to be intimately correlated with the square of Al concentrations, although BTL clearly changed as linearly proportional to Al impurity contents. Finally, the cleavage of Al-O-Al bonds or some sites in the vicinity of Al-O-Al bonds were plausibly considered to play an important role for the formation of RTL colour centres in natural quartzes as a result of the operation of high temperature effects.