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Abstract
Thermoluminescence (TL) of α-A12O3 samples has been studied in the temperature range 100–480K. The crystals were previously submitted to X-ray and UV irradiation at an average temperature T a ≈ 170K. The TL signal is characterized by four bands detected at wavelengths 300, 418, 696 and 750 nm revealing the respective emission of F+-centres, F-centres, chromium ionic impurities and titanium ionic impurities. A profile change of trap levels is proposed to explain the difference of TL response after exposure of the sapphire crystal to X and UV radiation. From the TL results of α-Al2O3 submitted to Uv illumination (4·8 eV), we conclude that the energy level of the ground state of the F-centre lies in the bandgap at around 4·5eV above the top of the valence band, while the F+-centre presents a fundamental level lower than that of the F-centre by roughly 2eV.