Spectral study of radioluminescence in carbon-doped aluminium oxide

The spectral emission study of the radioluminescence (RL) measured from carbon-doped aluminium oxide (alpha-Al2O3:C) at various temperatures between 30 and 300 degrees C is reported. The energy-resolved RL emission spectra measured at room temperature show seven gaussian emission bands centred at 1.75, 1.79, 1.85, 2.22, 2.96, 3.72 and 4.44 eV. The 2.96-eV emission, associated with F-centres, is the primary RL emission whereas the narrow (R-line) emission centred at 1.79 eV, associated with Cr3+ impurity ions, is the most intense secondary emission. However, the intensity of 1.79-eV emission decreases with repeated RL measurements. The central emission energy for F-centres is constant throughout the temperature range of investigation. The full width at half maximum (FWHM) for the F-centre emission band increases with temperature whereas the F-centre peak intensity exhibits thermal quenching behaviour at temperatures above 160 degrees C. On the other hand, the emission energy for the R-line emission of Cr3+ is constant for temperatures between 30 and 160 degrees C, whereas its peak intensity generally decreases with temperature. F-centres experience strong-coupling in their crystallographic sites with estimated electron-lattice coupling parameters of S = 5.0 +/- 0.9, E-p = 0.079 +/- 0.008 eV and nu = 1.91 x 10(13) Hz where S, E-p and v are the Huang-Rhys factor, the phonon energy and the phonon frequency, respectively. The RL spectra recorded while ramping the temperature of a sample at a constant rate have been compared against conventional TL spectra.