Mixed-order kinetic analysis of the glow curve characteristics of single crystal LiF:Mg,Ti as a function of Ti concentration

The glow curve characteristics of single crystal LiF:Mg,Ti, grown by the Bridgman method, were studied as a function of Ti concentration (3-14 ppm Ti). The glow curves were deconvoluted into component glow peaks using mixed-order (MO) model kinetics. The thermoluminescence (TL) sensitivities of all the low temperature peaks (peaks 2-5) increase with increasing Ti concentration, reaching a maximum at 12-13 ppm Ti. The increase of peak 5 sensitivity is especially dramatic, a factor 10 higher at concentrations above 10 ppm compared to the lower sensitivity over the range of Ti concentrations from 3-6 ppm. In glow curves Without a post-irradiation anneal, the activation energies of peaks 2 and 3 are constant as a function of Ti concentration, 1.3 +/- 0.1 and 1.15 +/- 0.1 eV respectively. The activation energy of peak 4, however, increases, with a correlated decrease in the activation energy of peak 5. In glow curves following a 165 degrees C/15 min anneal to remove peaks 2-4, the activation energy of peak 5 was observed to increase from 1.65 +/- 0.1 eV at the lowest Ti concentrations to 1.9 +/- 0.1 eV from 8-14 ppm Ti concentration. The unique behaviour of peak 5 is interpreted as additional evidence indicating that peak 5 arises from a complex TC/LC spatially correlated defect structure, Mg trimers coupled to Ti, and that the Ti ions perturb the TC, thereby leading to a change in the activation energy. (C) 1998 Elsevier Science Ltd. All rights reserved.