Electron paramagnetic resonance and the thermoluminescence emission mechanism of the 280 °C peak in natural andalusite crystal

Samples of natural andalusite (Al2SiO5) crystal have been investigated in terms of thermoluminescence (TL) and electron paramagnetic resonance (EPR) measurements. The TL glow curves of samples previously annealed at 600 °C for 30 min and subsequently gamma-irradiated gave rise to four glow peaks at 150, 210, 280 and 350 °C. The EPR spectra of natural samples heat-treated at 600 °C for 30 min show signals at g=5.94 and 2.014 that do not change after gamma irradiation and thermal treatments. However, it was observed that the appearance of a paramagnetic center at g=1.882 for the samples annealed at 600 °C for 30 min followed gamma irradiation. This line was attributed to Ti3+ centers. The EPR signals observed at g=5.94 and 2.014 are due to Fe3+. Correlations between EPR and TL results of these crystals show that the EPR line at g=1.882 and the TL peak at 280 °C can be attributed to the same defect center.