Thermally stimulated luminescence, optical absorption and EPR studies on kyanite crystals

The natural mineral blue kyanite (Al2SiO5) crystals were investigated in terms of thermally stimulated luminescence, optical absorption and electron paramagnetic resonance measurements. The glow curves for natural samples present two glow peaks at 155°C and 220°C. Pre-annealed and subsequently irradiated samples give rise to four glow peaks at 160°C, 210°C, 285°C and 360°C. The observed EPR spectra revealed the presence of Fe3+ ions in the crystalline matrix and a change in its valence state is predicted on irradiation. Also E1′ centers and hole type centers are induced on irradiation. A mechanism for the observed thermoluminescence is suggested.