Phototransferred thermoluminescence of α-Al2O3:C: Experimental results and empirical models

Abstract

The thermoluminescence glow curve of α-Al2O3:C consists of a prominent apparently-single peak and a number of weaker intensity secondary peaks. Phototransferred thermoluminescence (PTTL) from secondary glow peaks in α-Al2O3:C is reported. For completeness and to aid discussion, complementary results for the main peak are included. The problem studied is one of phototransferred thermoluminescence for a system of multiple acceptors and multiple donors. A TL glow curve recorded at 5 °C/s following irradiation to 0.5 Gy shows the main peak (labelled II) at 240 °C and two secondary peaks at 86 °C (peak I) and 360 °C (peak III). Peak I is reproduced under phototransfer after any preheating between 100 and 500 °C. Peak II is also reproduced as a PTTL peak after preheating to any temperature up to 800 °C. For the latter, the duration of preheating matters because if the sample is preheated at 800 °C for say, 6 min, PTTL is obtained but not when this is extended to say, 15 min. No PTTL was observed from peak III at all. A study of the time dependence of the PTTL intensity from peak III, following preheating that removes peaks I and II, shows that its electron trap acts as an acceptor when the duration of illumination to stimulate electrons from deep traps is brief but that when the illumination time is extended, the electron trap for peak III loses some of its trapped electrons to the shallower traps thus acting as a donor trap. Kinetic analysis of PTTL peak I shows that its activation energy is ∼0.70 eV and its frequency factor, of the order of 1010 s−1, the same as for the corresponding conventional TL peak. It is shown, for the first time, that this secondary peak (I) can be used to study thermal quenching in α-Al2O3:C. The PTTL peak was found to be affected by thermal quenching with an activation energy for thermal quenching of 1.03±0.08 eV. Thermal quenching is also adduced to be responsible for lack of any PTTL for peak III. Phenomenological mathematical models have been developed to explain the time-dependence of PTTL from peaks I and II corresponding to various preheating temperatures.