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This paper presents an improved Monte Carlo algorithm for calculating thermoluminescence (TL) curves for complex cluster systems, which contain a large number of localized levels. The new algorithm is based on generation of two random numbers, instead of the many random number generations used in previous approaches. The first random number generation is associated with the choice of which type of energy transition takes place in the model, while the second random number generation is connected with the choice of a cluster group for which this transition occurred. The proposed new algorithm was tested on a new TL model consisting of clusters containing both electron traps and deep competitor traps. The luminescence centers in the model are treated as uniformly distributed defects. Applicability of the Monte Carlo method is demonstrated by simulating for the first time in this type of model the complete TL process, including the excitation, relaxation and heating stages. The new model explains the anomalous heating rate effect of TL, and describes the effect of localized trapping processes within the cluster on the intensity and temperature position of the TL peaks. • Improved Monte Carlo method for calculating TL in cluster system has been proposed. • New cluster TL model with deep electron trap is analyzed by Monte Carlo method. • The excitation and relaxation stages are simulated at first for cluster system. • The anomalous heating rate effect was found in terms of TL model under study. [ABSTRACT FROM AUTHOR]

Abstract New Al 2 O 3 -BeO ceramics were synthesized from alumina nanopowder in BeO crucibles by high-temperature treatment in reducing conditions. It was found that the TL curve of these ceramics is characterized by a dosimetric peak at 520–530 K for a heating rate of 2 K/s. The integrated TL of the peak is not influenced by the heating rate of the samples, unlike that in anion-defective alumina and beryllia crystals. The presence of an energy distribution of the traps which cause dosimetric TL peak is verified by Tm-Tstop and initial rise methods. Linear dependence on dose of the intensity of TL peak at 520–530 K is observed in the 10–300 Gy gamma-dose range. The diversity of TL sensitivity of the ceramic samples synthesized in one cycle does not exceed 10%. The results obtained show that the newly synthesized Al 2 O 3 -BeO ceramics are promising materials for TL dosimetry of high doses of ionizing radiation. Highlights • New Al 2 O 3 -BeO ceramics were synthesized in vacuum in reducing conditions. • Dosimetric TL peak at 520 K is associated with trap depth distribution. • TL thermal quenching is not observed in Al 2 O 3 -BeO samples. • TL dose response in 520 K peak is linear from 10 to 300 Gy. [ABSTRACT FROM AUTHOR]

The influence of high-temperature annealing (900-1700 оС) on the morphological features, luminescent and dosimetric properties of ultrafine α-Al 2 O 3 ceramics obtained from nanopowder by its compaction has been studied. In contrast to previously published papers, for more reliable and unambiguous determining of the relationship between the nanocrystallite size and luminescent properties, the samples were annealed in air without a reducing agent. It has been established that at Т>1500 оС there is a significant increase in the intensity of thermoluminescence (TL) of the peak at 170 оС, which coincides with the temperature range of the most significant increase in the size of nanocrystallite. Another reason for the increase in the TL response may be the formation of luminescence centers during annealing, which is proved by the appearance of a new cathodoluminescence band at 2.2–3.4 eV of unknown nature. The analysis of the dose dependences of TL of nanostructured ceramics irradiated with a high-dose pulsed electron beam (130 keV, 1.5 kGy per pulse) reveals their sublinear nature. Moreover, anomalous TL fading has been found, the magnitude of which increases with a crystallite size. • The effect of annealing in air on TL of ultrafine α-Al 2 O 3 ceramics was studied. • TL intensity increases with the growth of the nanocrystallite size. • TL dose dependences in ceramics irradiated with pulsed electron beam are sublinear. • The anomalous TL fading was found, which increases with a crystallite size. [ABSTRACT FROM AUTHOR]

This paper presents a model of sublinearity of thermoluminescence (TL) dose response, based on the competitive interaction between active electron trapping centers and deep hole centers during excitation and heating of a phosphor. It is shown by analytical and numerical calculations that the sublinear response is observed at low doses, when the trap occupancy is far from saturation. It is found that the linearity index of TL dose response depends on the concentration of the deep hole traps, and on the coefficient of non-radiative electron recombination. The TL dose response is derived in parametric form. A new analytical expression is derived for the threshold doses, at which the TL response changes from a sublinear growth to an almost linear behavior. This phenomenon of a sublinear TL response changing into a linear behavior, is explained by the deep traps filling up to saturation. The dependence of the linearity index on the model parameters is found by numerical methods. [ABSTRACT FROM AUTHOR]

Luminescent properties of monoclinic zirconium oxide, obtained by using compacting microcrystalline powder, were studied. The maximums of bands in the photoluminescence (PL) spectrum, PL excitation spectrum and pulse cathodoluminescence were determined. Thermal quenching of PL in the samples under study was found in the 480 nm band, different methods were used to define its parameters. Peaks at 125 °С and 225 °С as well as thermoluminescence (TL) of shallow traps are observed on the TL glow curve, when the samples are exposed to a pulsed electron beam with the energy of 130 keV. The TL yield of the dominant peak at 125 °С decreases with an increasing heating rate. Analysis of the peak shape, variation of the heating rate,and analysis of isothermal decay were used to define kinetic parameters of the TL of this peak. The parameters were specified by the method of curve fitting, taking into account thermal quenching. [ABSTRACT FROM AUTHOR]

The effect of deep traps filled by a pulse electron beam on the thermoluminescent (TL) properties in Al 2 O 3 :C dosimetric crystals is studied. When the deep traps are filled, the dosimetric peak at 170 °C acquires a double-peak structure not present in the initial samples. The effect of the population of the deep centers having various nature (electron or hole traps) and energy depth on the shape of the dosimetric TL peak structure is analyzed. An assumption is made that in the temperature ranges of 350–500 °C and 650–750 °C, electron traps are emptied, whereas at T = 500–650 °C hole traps are emptied. The possibility of using the TL associated with deep traps in high-dose dosimetry of pulse electron beams is shown. [ABSTRACT FROM AUTHOR]

We studied features of isothermal decay curves of thermoluminescence (TL) in the dosimetric peak at 525 K of Al 2 O 3 –BeO composite ceramics. The temperature ranges were revealed in which an anomalous drop in the TL decay rate was observed with increasing temperature. By using the data obtained with the Tm-Tstop and initial rise methods, we proved that there was a complex activation energy distribution of traps with the energies varying from 0.85 to 1.55 eV. We found that the anomalous decrease with temperature in the isothermal luminescence decay rate can be associated with the superposition of the contributions to the TL from several traps with different energy depth values. It was shown that the analysis of the TL isothermal decay rate change can be used as one of the methods for revealing the complex energy structure of traps in dosimetric phosphors. • Anomalous drop of isothermal TL decay rate is observed with increasing temperature. • Complex energy distribution of traps from 0.85 to 1.55 eV is found in the 525 K peak. • Anomalous decay of TL is due to presence several traps with different energy depth. [ABSTRACT FROM AUTHOR]

TL dose dependences were simulated following the semi-localized transitions (SLT) model and the model with cluster defects which contain TL-active electron traps, luminescence centers and deep hole traps. Monte-Carlo method was used to calculate cluster occupancy at the irradiation and relaxation stages. At the heating stage, TL yield was calculated with Monte-Carlo method and with the proposed analytical approach. This approach expressed TL yield via cluster occupancy after relaxation stage. The results showed that non-monotonic dose dependence emerges in both models when the excited level of TL-active trap is deep enough. The reported effect was demonstrated to be directly related to intracluster non-radiative recombination of electron at the excited level of the trap and hole in the luminescence center. The intracluster competition between hole centers makes dose response less non-monotonic. When the heating rate decreases, TL yield at high doses drops and TL dose dependence becomes more non-monotonic. • TL dose response was simulated in terms of SLT and cluster kinetic models. • Non-monotonic TL dose dependence is due to intracluster transitions. • Influence of deep hole traps on non-monotonic TL dose dependence is studied. [ABSTRACT FROM AUTHOR]

The present report deals with the experimental observations of the thermally stimulated migration of charge carriers from trapping centres responsible for the main thermoluminescence (TL) peak at 450 K to a deep trap and, also, the optically stimulated transport of carriers from the deep trap to the main trap, which gives rise to the phototransferred TL at 450 K, in anion-defective α-Al2O3 crystals. The obtained results provide an experimental proof to the adequacy of the assumptions made in the model of the mutual interaction of the main and deep traps in the crystals under study. [ABSTRACT FROM AUTHOR]

Results of a comparative study on specific features of luminescence of thermochemical and radiation-colored crystals of aluminum oxide have been described. It is shown that crystals containing oxygen vacancies of different origins have identical main optical properties. A vacancy or vacancy-impurity origin of deep traps has been assumed. Some specific features of thermoluminescence (TL), which are common for both types of crystals, such as the dependence of the TL output on the heating rate and the occupancy of deep traps described by the model of interactive trap system, have been established. [Copyright &y& Elsevier]

The luminescent and dosimetric properties of nanostructured aluminum oxide which contains a mixture of metastable transition Θ, δ, and κ-phases were investigated. To vary the phase composition of the samples, they were annealed in air at 850–1200 оС. It was found that annealing the samples at Т = 850–1100 оС in air results in a change in the percentages of κ- and δ-phases with a slight variation in the Θ-phase concentration. Alpha-phase begins to form in the samples at Т = 1100 оС, its concentration reaches 100% at Т = 1200 оС. The PCL spectra featured bands associated with F- and F 2 -type centers, the intensity of which decreased with increasing annealing temperature due to thermal destruction of centers. Kinetic TL parameters of the samples irradiated with a pulsed electron beam (130 keV) were found by deconvoluting TL curves into elementary peaks of general order kinetics. These parameters change insignificantly when the annealing temperature increases up to 1000 оС and they change greatly when the temperature grows further and α-phase is formed in the samples. The presence of sublinear sections of the TL dose response at doses of 1.5–45 kGy shows that the use of nanostructured aluminum oxide which contains transition phases for high-dose TL dosimetry of pulsed electron beams is promising. • The phase transformation in nanostructured Al 2 O 3 during annealing was found. • PCL spectra feature the emission bands of F- and F 2 -type centers. • TL kinetic parameters were determined by glow curve deconvolution. • TL dose dependences after pulsed electron beam irradiation feature sublinear regions. [ABSTRACT FROM AUTHOR]

Abstract: It is studied experimentally how the dosimetric sensitivity in the dosimetric thermoluminescence (TL) peak at 450 К in TLD-500 detectors depends on the occupancy of deep traps by charge carriers of unlike signs. A kinetic model for the TL of F-centers taking into account the nonradiative capture of electrons in deep hole traps is proposed. The model explains the variation dynamics of the dosimetric sensitivity and dependences of the TL output on the heating rate during filling of deep centers. [Copyright &y& Elsevier]

New Al 2 O 3 –BeO ceramics were synthesized by using high-temperature treatment of the initial compacts of nanostructured alumina in BeO crucible. The decomposition of the pulsed cathodoluminescence spectra into Gaussians revealed the luminescence bands related to oxygen vacancies and their aggregates in the ceramics. TL of the synthesized ceramics exposed to high-dose irradiation contained three peaks at 360 (A), 525 (B) and 730 K (C). It was found that optical stimulation at the wavelength of 470 nm causes optical bleaching of the traps responsible for peaks A and B, in contrast to the deep traps of the peak C, and gives rise to OSL. At the same time, there was a shift of the position of peaks A and B to the high-temperature region. This result shows the presence of the energy distribution of the traps responsible for TL peak A. It was found that the range of linearity of the TL dose response after gamma-irradiation is from 0.01 to 1.0 kGy. After irradiation with a pulsed electron beam (130 keV), the linear behavior of the OSL dose response was observed from 3 to 30 kGy. • The synthesis conditions affects the content, TL and PCL of Al 2 O 3 –BeO ceramics. • Emission centers in ceramics are formed by oxygen vacancies and their aggregates. • Irradiation with light at 470 nm causes optical bleaching of traps and OSL. • The traps of TL peak at 525 K are distributed along the energy depth. • TL and OSL of ceramics can be used for high-dose dosimetry (0.01–30 kGy). [ABSTRACT FROM AUTHOR]

The TL dose response was simulated within the framework of a kinetic model with cluster defects which contain electron TL-active traps and deep traps. It was shown that superlinearity of the TL dose dependence arises due to the temperature-dependent competition between the intracluster capture of electrons by deep traps and their thermal release into the conduction band. The regularities of the influence of the main parameters of the model (heating rate, activation energies of the ground and excited levels of TL-active traps) on the TL yield and nonlinearity of the dose dependence were found. • TL dose response was simulated in terms of cluster kinetic model with deep traps. • Superlinearity is due to the temperature-dependent competitive effect of deep traps. • The dependences of the linearity coefficient on the model parameters are studied. [ABSTRACT FROM AUTHOR]

Abstract: The mechanism of nonlinear dose dependence in the thermally stimulated luminescence (TL) of anion-defective single crystals of was studied. Our experiments revealed a new feature: the heating rate of crystals during TL measurements influences the nonlinearity of the dose characteristic. It was found that, along with other features of TL in the material, this phenomenon is described well by a unified mechanism of interactive interference between dosimetric and deep traps. Recommendations were formulated on how to reduce the interval of superlinearity of the dose characteristic in the investigated crystals. [Copyright &y& Elsevier]

The spectra of pulsed cathodoluminescence (PCL) and thermoluminescence (TL) in TLD-500 detectors, which were exposed to a strong beam from a pulsed electron accelerator, have been studied. Additional bands in the PCL spectrum and new peaks in the TL curves, which are due to impurity ions, have been revealed. Luminescence bands of F- and F+-centers cannot be used in the dosimetry of strong electron beams using TLD-500 detectors because of the saturation of dose dependence and the decrease in the TL yield. It is shown that high doses from these beams can be measured by recording TL in the luminescence band of impurity titanium ions. [Copyright &y& Elsevier]

A temperature growth and a decrease in impurity ion concentration result in a sensitivity increase of Al 2 O 3 :Mn ceramics to the ionizing radiation. The highest sensitivity to the ionizing radiation for Mn-doped alumina ceramics is observed for minimum dopant concentration and a maximum of temperature sintering (maximum sintering temperature). A sublinear increase in a thermoluminescence intensity with a growing dose is observed in the range of 1–400 Gy for the peak at 460 K and in the range of 1–100 Gy for the peak at 620 K for the Mn-doped alumina ceramic (1 wt % of Mn in a solution) annealed under vacuum at the temperature of 1700°С for 2 h. • PCL intensity in 678 nm band (Mn4+) is the highest at 1700°С and 10 wt % of Mn at doping. • The sintering temperature growth is result in a sensitivity increase to irradiation. • The highest TL intensity is observed for Al 2 O 3 :Mn ceramics with a minimum Mn content. • A sublinear dose response is observed in the range of 1–400 Gy (β-source) at 460 K peak. [ABSTRACT FROM AUTHOR]