Thermally and optically stimulated luminescence of natural red and blue corundum (Al2O3)

We report the thermoluminescence (TL) and optically stimulated luminescence (OSL) of natural corundum (Al2O3) of two varieties; one red and the other blue. X-ray fluorescence spectroscopy of the samples show that the concentration of Al2O3 in the red corundum is 43.05% and 46.87% in the blue corundum. TL measurements carried out on un-annealed samples and samples annealed at 700 °C, 900 °C and 1200 °C show that the TL sensitivity increases with annealing. The sensitivity of the red corundum reaches a maximum after annealing at 900 °C whereas that of the blue corundum increases with annealing up to the maximum annealing temperature of 1200 °C used in this study. Both samples have a complex glow curve between 30 °C and 500 °C. The composite nature of the glow curves is deduced to be due to a continuum in the trap distribution in the crystal. The activation energy of the traps vary between 0.70 eV and 1.15 eV. The dose response of the red corundum under TL is linear within 100‒1000 Gy whereas that of the blue corundum is superlinear for the same dose range. The TL of both samples is reproducible but the signal fades with time between irradiation and measurement. Both samples produce OSL under 470 nm blue light stimulation. The dose response of the OSL is superlinear within 100‒1000 Gy. It is found that the samples also produce thermally-assisted OSL (TA-OSL) at elevated temperature. The TA-OSL intensity of the red corundum increases with dose up to 400 Gy and saturates thereafter. On the other hand, the intensity of the blue corundum increases consistently with dose from 100 Gy to 1000 Gy.