Theoretical investigations of localized, semi-localized and unified models of thermally stimulated luminescence: a review (original) (raw)
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The two-level version of semi-localized transitions (SLT) model for thermoluminescence dosimeter
Radiation Measurements, 2019
Mandowski (2005) has developed the semi-localized transitions (SLT) model which is the combination of both simple trap model (STM) and localized transition (LT) model. This model explained anomalous behaviours such as displacement peaks, double peaks, etc. The SLT allows trapped charge carriers to be excited to the conduction band. Calculated TL glow curves of the SLT model show two peaks that are related to transition of the charge carrier between trap and excited state. This additional peak named displacement peak was shown in several TL studies. The researchers have shown that, the main peak of LiF:Mg,Ti, consists of three overlapping glow peaks in which the peak 5a is believed to be related to LTs, while the peak 5 relates to carriers that escaped from the T-RC pair system. In this study, SLT model is simulated using Matlab code and numerical results are presented. Also, the two level version of SLT model is presented including all possible transitions. In new version of SLT model two excited states are considered. Recombination of trapped charge careers occur via two localized and one delocalized transitions simultaneously. Using the two-level version of SLT model, it is shown that existence of more peaks is possible in glow curve.
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2013
As reported in the literature, both in experimental results and in simulated glow curves, in a series of TL peaks associated with a series of trapping states and a single recombination center, the peaks tend to be of first order. In the present work we show theoretically and demonstrate by examples of numerical simulations that the last peak in a series obtained by a model of a single recombination center and multiple traps may be of second order whereas the lower-temperature peaks are usually of first order. This is the case even when retrapping is significantly faster than recombination. In some cases, the last peak has a long tail, longer than that of second-order peaks, which has to do with a different mechanism that has been discussed in a recent paper. Similar simulations of a more complex and more realistic situation of a model with multiple trapping states and multiple recombination centers have been performed. The prevalence of first-order appearance of both the curves of free electrons, associated with thermally stimulated conductivity (TSC) and of TL, evaluated for randomly chosen sets of trapping parameters, is shown by histograms. The occurrence of a small number of very high values of the symmetry factor is also discussed.
A two-stage thermally-assisted optically stimulated luminescence (TA-OSL)
International Journal of Science and Research Archive
A two-stage thermally-assisted optically stimulated luminescence model is studied. Electrons are thermally and optically raised from the ground state to an excited state and there after they are thermally raised from the excited state to the conduction band. A set of simultaneous differential equations generated from the model was solved numerically using ode 15s MATLAB solver. Three assumed conditions are applied to the model and results from the analytical expressions obtained based on the assumptions were compared with the numerical simulation results. The assumed conditions are : (1) the probability of electron moving from the excited state to ground state ( ) is far greater than thermal excitation of electron from the excited state to conduction band ( ) also stimulation light intensity ( ) is far greater than thermal excitation of electron from the ground state to the excited state ( ), (2) also (3) also . For the first condition, the effective activation energy (Eeff) tends t...
Thermally-Optically-Thermally Stimulated Luminescence
IJRDO-Journal of Applied Science
A three-stage energy band model was studied. The model consists of electrons thermally stimulated from the ground state to the first excited state, after which they were optically stimulated into the second excited state and they were finally stimulated thermally into the conduction band. A set of simultaneous differential equations was generated from the models and three assumed conditions were applied to this model, which they were solved analytically and analytical expressions were obtained. The same set of simultaneous equations were solved numerically using ode 15s MATLAB solver. When considering first-order peaks, the kinetic parameters obtained were found to be in good agreement with the analytical expressions. But when considering non first-order peaks, the kinetic parameters obtained numerically were not in good agreement with the analytical expressions and explanations had been given. Second-order peaks could not be obtained despite careful selection of the kinetic paramet...
Journal of Luminescence, 2014
Localized electronic recombination processes in donor-acceptor pairs of luminescent materials have been recently modeled using a new kinetic model based on tunneling. Within this model, recombination is assumed to take place via the excited state of the donor, and nearest-neighbor recombinations take place within a random distribution of centers. An approximate semi-analytical version of the model has been shown to simulate successfully thermally and optically stimulated luminescence (TL and OSL), linearly modulated OSL (LM-OSL) and isothermal TL processes. This paper presents a detailed analysis of the geometrical properties of the TL glow curves obtained within three different published versions of the model. The dependence of the shape of the TL glow curves on the kinetic parameters of the model is examined by allowing simultaneous random variations of the parameters, within wide ranges of physically reasonable values covering several orders of magnitude. It is found that the TL glow curves can be characterized according to their shape factors μ g , as commonly done in TL theory of delocalized transitions. The values of the shape factor are found to depend rather weakly on the activation energy E and the frequency factor s, but they have a strong dependence on the parameter ρ 0 which characterizes the concentration of acceptors in the model. It is also shown by simulation that both the variable heating rate and initial rise methods are applicable in this type of model and can yield the correct value of the activation energy E. However, the initial rise method of analysis for the semianalytical version of the model fails to yield the correct E value, since it underestimates the low temperature part of the TL glow curves. Two analytical expressions are given for the TL intensity, which can be used on an empirical basis for computerized glow curve deconvolution analysis (CGCD).
Non-monotonic dose dependence of thermoluminescence
Radiation Protection Dosimetry, 2006
The thermoluminescence (TL) intensity in different materials is usually a monotonic increasing function of the dose, which quite often reaches a saturation value. In several materials, however, non-monotonic dose dependence has been observed. The TL intensity reached a maximum at a certain dose and decreased at higher ones. Some authors refer to this effect as 'radiation damage'. In the present work, we show that the non-monotonic dependence can easily be demonstrated to result from competition between transitions model with two trapping states and two kinds of recombination centres. Two kinds of competition are considered. One in which competition during excitation dominates, the filling of the active luminescence centre is non-monotonic, and the resulting TL is non-monotonic. In the other, the filling of traps and centres is monotonically increasing, but the competition during heating causes TL intensity to reach a maximum and decline at higher doses.
Radiation Effects and Defects in Solids, 1998
Thermally stimulated luminescence and conductivity measurements have been performed in natural and synthetic semiconducting diamonds, in the temperature range 12-350 K, after excitation, near liquid-helium or liquid-nitrogen temperatures, with uv light, x-ray, 150-keV, and 0;5-MeV electrons. The glow curves observed in synthetic diamonds are similar to the glow curves obtained previously in natural diamonds. Two of the peaks which are reported have only been previously observed in types-I and-IIa diamonds. Conductivity measurements exhibit stages at 160, 230, and 340 K which correlate with thermoluminescence peaks. An additional stage at 50 K is observed after 0.5-MeV electron irradiation. The concentrations of.the traps in these different stages have been deduced. The stage at 50 K is shown to be associated with a donor level situated at 0.02 eV below the conduction band.