Thermoluminescence and optical stimulated luminescence trap parameters of LiMgPO4: Tm, Tb

Abstract

In recent years, the preparation and luminescent properties of LiMgPO4 as a matrix have received much attention, but most of the studies are limited to the trap parameters of thermoluminescence (TL), which do not involve the trap parameters of optical stimulated luminescence (OSL). In this paper, LiMgPO4:Tm, Tb powder samples are synthesized by solid-state reaction at high temperature. All the experiments reported here are measured by Riso TL/OSL-15-B/C reader after being irradiated by beta-rays. The TL glow curves obtained show that the high temperature peak at 300℃ belongs to the first-order kinetic peak because the peak temperature does not change as irradiation dose increases. Based on the first-order kinetics, the TL trap depth E = 1.72 eV and the frequency factor s= 3.97 1014 are determined by the methods of various heating rates.However, LiMgPO4:Tm, Tb is also an OSL material, the analysis of its OSL trap kinetic parameters would help to understand the OSL mechanism and to know the relationship between TL and OSL traps. The pulse annealing method is suitable for OSL trap parameter analysis. For low sensitivity samples, the fluctuation of the pulse annealing method is relatively large. And this method only records the OSL signal of fast decay component, which is suitable for measuring the samples with high sensitivity and fast fading OSL signals. In order to study the OSL signal of slow decay component, the multiple annealing method is proposed based on the pulse annealing method. The multiple annealing procedure is as follows. Firstly, the sample is annealed from room temperature to 500℃ which lasts 30 s. The heating rate is 5℃/s. Secondly, the sample is irradiated with 90Sr beta radiation doses of 1 Gy. Thirdly, the sample is preheated to 150℃ with a heating rate of 0.2 ℃/s. And then OSL measurement lasts 500 s after cooling to room temperature. The above steps are repeated in preheating temperature steps of 10℃. Four repetitive measurements are made for each preheating rate. The preheating rates are 0.2, 0.5, 1, and 2℃/s.Finally, the OSL trap parameters E = 1.69 eV and s = 1.05 1014 are determined by the multiple annealing method. The correlation between TL and OSL trap parameters shows that the TL and OSL signals are likely to come from the same traps. Besides, the trap depth of the main peak of the phosphor shows that the sample has better thermal stability than those of the other phosphors of LiMgPO4 as the matrix.