A model for low-temperature luminescence in lithium- and sodium-doped beryllium oxide single crystals

BeO:Li and BeO:Na single crystals have been investigated by thermoluminescence (TL) techniques in the interval 10-300 K. X-irradiated BeO:Na exhibits an intense glow peak at 85 K and a weak one near 46 K. BeO:Li displays intense glow at 72 K. Analyses of the two strong peaks (the weak one was not amenable to analysis) yield the following TL parameters: Tm=72 K, E=0.143 eV, s=1.08×108 sec-1, and l=1.3; Tm=85 K, E=0.197 eV, s=1.05×1010 sec -1, and l=1.2, where E is the thermal activation energy, s is the frequency factor, and l is the order of kinetics. Spectral emission from the two intense glow peaks were similar, characterized by band emission with maxima near 320 and 525 nm. A model consistent with previous TL and magnetic resonance results which adequately describes our data is presented. It is suggested that the main glow peaks are due to holes released at V centers whereby they recombine with F and F+ centers. Recombination at the F center yields 525-nm radiation whereas recombination at the F+ defect produces 320-nm emission. Optical excitation, photobleaching, and phototransfer experiments support this model