Optical and thermal studies of deep levels in anion deficient aluminum oxide:carbon

Various optically and thermally stimulated luminescence and conductivity studies were undertaken to understand the role of deep level defect centers on the F-center emission of Al₂O₃:C. These studies consisted of thermoluminescence (TL), thermally stimulated conductivity (TSC), optically stimulated luminescence (OSL) and photoconductivity (PC). Studies of the F center emission when stimulated with 6 eV light indicate a temperature dependence of the F center lifetime. As the temperature is increased, the lifetime of the F center decreases. This was attributed to thermal quenching. From studies of the stimulation energy dependence of OSL and PC, several different trapping centers were found at threshold optical depths of ∼1.7–2.5 eV, ∼3.0–3.8 eV, and ∼4.0–4.9 eV. Using a non-negative least squares algorithm, deconvolution of the data was presented which indicates that these centers are not discrete but are distributed in energy. Linearly modulated photoconductivity (Im-PQ and linearly modulated optically stimulated luminescence (Im-OSL) measurements were undertaken at stimulation energies of 2.41, 2.71, and 3.50 eV. At least two different trapping centers were found to contribute to the lm.-PC, but only one was found to contribute to the Im-OSL. A model for first and general order kinetic lm-OSL and 1m-PC was examined. It was found that first order lm-PC/1m-OSL kinetics could be indistinguishable from higher order kinetics for a given stimulation energy. The conclusion was that lm-OSL/lm-PC measurements should be taken using more than one stimulation energy in order to be certain of the kinetic order.