OSL 信号衰减曲线分解揭示浅电子陷阱对中组分信号的干扰

The intervention of shallow electron traps on the production of the medium component in quartz OSL revealed by decomposition of OSL decay curves

关键词:  光释光  浅电子陷阱  衰减曲线  广义阶动力学

Key words:  optically stimulated luminescence  shallow electron trap  decay curve  general-order kinetic

摘要:

光释光（optically stimulated luminescence，OSL）测年是一种常用的辐射剂量测定技术，已被广泛用于考古和地质年代测定。以澳大利亚粗颗粒石英为研究对象，测量其不同激发温度的OSL信号衰减曲线，运用广义阶动力学（general-order kinetic，GOK）模型对其进行分解，获得快、中组分OSL信号的衰减速率、动力学阶数和信号强度。在此基础上，结合固体能带理论，对石英OSL信号激发过程中快、中组分的耦合过程以及浅电子陷阱对中组分OSL信号的干扰机制进行研究。结果表明：中组分OSL信号衰减速率与动力学阶数随激发温度升高发生显著变化，并且这种变化与浅电子陷阱的发光峰位置密切相关，表明该信号组分的产生受到浅电子陷阱光转移效应的显著影响。研究结果为揭示中组分OSL信号的产生机制提供了物理证据。

Abstract:

Background, aim, and scope Optically stimulated luminescence (OSL) dating is a commonly used radiation dosimetry technology, which has been widely applied in archaeological and geological researches. The medium component OSL signal contained in the initial part of an OSL decay curve can significant influence the OSL dating results. However, the production mechanism of the medium OSL component is unclear, and little is known about the influence of shallow electron traps on the production of the medium OSL component. Here, we reveal the influence of shallow electron traps on the production of the medium OSL component by decomposition of decay curves. Materials and methods OSL decay curves of Australian coarse quartz samples measured at different stimulation temperatures were decomposed using the general-order kinetic (GOK) model to obtain the decay rates, kinetic orders and signal intensities of fast and medium OSL components. The coupling process of fast and medium components during the simulation of quartz OSL signals and the effect of shallow electron trap on the production of the medium component OSL signal are revealed according to the band theory of solids. Results The decay rates, kinetic order, and signal intensities of the medium OSL component demonstrate complex variation patterns as the stimulation temperature increases. Specially, the decay rate increases but kinetic order decreases gradually with the stimulation temperature when the temperature is obviously lower than the peak temperatures of the shallow electron traps (i.e., 110 ℃ and 170 ℃); and the decay rate decreases but kinetic order increases dramatically with the stimulation temperature when the temperature is closely approaching the peak temperatures of the shallow electron traps. Discussion The variations of the characteristic parameters of the medium OSL component with the stimulation temperature are obtained. These results are closely related to the change in competition for electrons within the shallow electron traps as the stimulation temperature increases. The production of the fast OSL component is mainly affected by the depletion of electrons (the cleaning of the trap) while the production of the medium OSL component is affected not only by the cleaning of the trap but also by the retrapping ability of the electron trap (the filling of the trap). The trapping of electrons from the conduction band will strongly affect the OSL stimulation process controlled by the depletion of electrons and the cleaning of the trap. This delays the combination of electrons from the conduction band with holes from the luminescence center. Conclusions (1) The photo-transferred effect of the shallow electron trap can strongly affect the production of the medium OSL component, although its influence on the production of the fast OSL component is negligible. (2) The variation of the kinetic parameters of the medium OSL component is closely related to the competition effects of the shallow electron traps that change with the stimulation temperature. (3) The shallow electron traps (i.e., the 110 ℃ and 170 ℃ TL traps) influence the standard electron transfer routine in which free electrons evicted from the 325 ℃ TL trap are transferred directly from the conduction band to the luminescence center during OSL stimulation. Recommendations and perspectives The GOK model can be applied to reveal complex retrapping processes of electron traps during OSL stimulation. A better understanding on the production mechanism of the medium OSL component helps to improve OSL dating techniques in the near future.