Time-resolved optically stimulated luminescence and spectral emission features of α-Al2O3:C

This report is concerned with the influence of measurement temperature on luminescence lifetime and on the spectral emission features of luminescence from α-Al2O3:C. The lifetimes were determined from time-resolved luminescence spectra. Spectral measurements were done using thermoluminescence and X-ray excited optical luminescence. The emission spectra of α-Al2O3:C studied in this work shows prominent bands at 330, 380 and 420 nm associated with vacancies in the oxygen sub-lattice in α-Al2O3:C and an additional band at 695 nm due to Cr substitution for Al. Emission bands below 500 nm are independent of temperature below 125 °C but widen with temperature. Direct evidence of thermal quenching of the 420 nm emission band is provided. Beyond 200 °C, the 380 and 420 nm bands merge and widen, with the 420 nm emission dominant. Before the onset of thermal quenching, luminescence lifetimes are affected by retrapping both in the shallow- and in the main electron trap. This was deduced from features of time-resolved luminescence spectra measured from samples with and without the shallow trap. Additional measurements with temperature decreasing from 160 to 20 °C, after phototransfer as well as after a considerable delay between irradiation and measurement, suggest that the change in lifetimes could also be related to other factors including slight shifts in emission wavelength for the 380 and 420 nm emissions.