31 research outputs found
Thermoluminescence and optically stimulated luminescence properties of natural barytes
No full textGeorge S. Polymeris is indebted to TUBITAK (The Scientific and Technological Research Council of Turkey) for financial support.Heavy, baryte-loaded, concrete is commonly used as radiation shielding material around high energy particle accelerators. Concrete samples received from a shielding block located at CERN cite contain many crystalline inclusions which were identified as barytes by X-ray diffraction analysis and separated by their color, classified as white, orange and green. Basic properties of thermoluminescence (TL) and optically stimulated luminescence (OSL) signals of these barytes samples such as thermal and optical stability, repeatability and mainly the linearity of both their luminescence responses were investigated as a function of beta dose These results are also discussed regarding detailed investigation on the correlation between TL and OSL signals and their implications for retrospective dosimetryTürkiye Bilimsel ve Teknolojik Araştırma Kurumu (TÜBİTAK)Publisher's Versio
On the half-life of luminescence signals in dosimetric applications: A unified presentation
No full textEffect of Sm(3+)and Mn2+ incorporation on the structure and luminescence characteristics of Zn2SiO4 phosphor
No full textTo evaluate the dopant effect precisely, X-ray diffraction (XRD) for structural, scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS) analysis for morphological, photoluminescence (PL) and thermoluminescence (TL) characteristics of un-doped, 2.0 mol% Sm3+ doped and 2.0 mol% Sm3+;x mol% Mn2+ (x = 0.5, 1.0, 2.0, 4.0) doped Zn2SiO4 phosphors were tested. PL mechanisms of excitation and emission were discussed together with data on the structure and morphology of the samples. The beta doses from 0.1 to 500 Gy with various steps were applied to observe the glow curve readouts after 200 degrees C preheat at a linear heating rate of 2 degrees C/s from RT to 500 degrees C. Zn2SiO4:2.0%Sm3+;0.5%Mn2+ was chosen for further analysis due to having both the most PL and TL peak area. Various heating rate method was used to determine the kinetic parameters as well as initial rise with T-M-T-stop analysis and computerized glow curve deconvolution methods.Research Fund of Cukurova University, Turkey [FBA2019-11318, FAY-2015-435]All authors thank Dr. M. Ayvacikli and Prof. Dr. N. Can for their support on XRD and PL evaluations. Z.G. Portakal-Ucar would like to thank Dr. J.M. Kalita and Dr. G.S. Polymeris for the valuable discussions on the TL results. The current study is financially supported by the Research Fund of Cukurova University, Turkey (Project Numbers: FBA2019-11318 and FAY-2015-435)
Thermally-assisted optically stimulated luminescence from deep electron traps in α-Al2O3: C, Mg
No full textWe report thermally-assisted optically stimulated luminescence (TA-OSL) in α-Al2O3:C,Mg. The OSL was measured at elevated temperatures between 50 and 240 °C from a sample preheated to 500 °C after irradiation to 100 Gy. That OSL could be measured even after the preheating is direct evidence of the existence of deep electron traps in α-Al2O3:C,Mg. The TA-OSL intensity goes through a peak with measurement temperature. The initial increase is ascribed to thermal assistance to optical stimulation whereas the subsequent decrease in intensity is deduced to reflect increasing incidences of non-radiative recombination, that is, thermal quenching. The activation energy for thermal assistance corresponding to a deep electron trap was estimated as 0.667 ± 0.006 eV whereas the activation energy for thermal quenching was calculated as 0.90 ± 0.04 eV. The intensity of the TA-OSL was also found to increase with irradiation dose. The dose response is sublinear from 25 to 150 Gy but saturates with further increase of dose. The TA-OSL dose response has been discussed by considering the competition for charges at the deep traps. This study incidentally shows that TA-OSL can be effectively used in dosimetry involving large doses
Prompt isothermal decay properties of the Sr4Al14O25 co-doped with Eu2+ and Dy3+ persistent luminescent phosphor
No full textThermoluminescence (TL) techniques are very useful in the research of the persistent Luminescence (PL) phosphors research. It gives information about the existence of energy levels within the forbidden band, its activation energy, kinetic order, lifetime etc. The TL glow curve of Sr4Al14O25:Eu2+,Dy3+ persistent phosphor, consists of two well separated glow peaks. The TL techniques used to evaluate activation energy were the initial rise, prompt isothermal decay (PID) of TL of each peak at elevated temperatures and the glow – curve fitting. The behavior of the PID curves of the two peak is very different. According to the results of the PID procedure and the subsequent data analysis it is suggested that the mechanism behind the low temperature peak is a delocalized transition. On the other hand the mechanism behind the high temperature peak is localized transition involving a tunneling recombination between electron trap and luminescence center. © 2018 Elsevier B.V
Recombination pathways in a BeO yielding two main dosimetric TL peaks
No full textApart from the commercially used Thermalox, BeOR is a new type of Beryllium Oxide fabricated by a different company in Turkey. As it is shown by other groups, this dosimeter yields two overlapping main dosimetric TL peaks in the temperature region of 100–300 °C and one peak at 350 °C. The aim of the present study is the calculation of the activation energies of these two peaks with the use of specific protocols, including the Fractional Glow Technique (FGT), an Isothermal Decay signal (PID) and the Peak Shape Methods (PSM). Also, these experimental procedures were conducted in two different readers, namely the Harshaw and the Risø reader, for better repeatability and in order to minimize the error of the calculations. Moreover, another goal is to correlate the activation energy values with the recombination pathways that are present in the BeOR and its corresponding peaks. Specifically, both peaks have activation energies around 1–1.3 eV in most cases, although there are some kinds of indications for a difference in the pathways, as the high-temperature region TL main peak seems to follow the localized recombination via tunneling, in contrast with the low-temperature region TL main peak which sticks to the delocalized model with the passing via the conduction band. © 2022 Elsevier Lt
Experimental and modeling evidence for the reduction of thermal conductivity in Mg 2 Si by fine tuning the nano & micro-structural features
No full textElectron trap filling and emptying through simulations: Studying the shift of the maximum intensity position in Thermoluminescence and Linearly Modulated Optically Stimulated Luminescence curves
No full textIn the present work, the response of peak positions in Linearly Modulated Optically Stimulated Luminescence (LM-OSL) curves as a function of physical and technical parameters were investigated and compared theoretically; specifically, the time or temperature values (tm,Tm) of their maximum intensity (Im). The stimulation modes of Thermoluminescence (TL) and LM-OSL differ slightly in terms of peak resemblance (geometrical structure) but differ greatly as physical phenomena, so it could be ideal to study the effects responsible for electron trap filling or trap emptying. These simulations could also extend our knowledge in Stimulated Luminescence phenomena regarding expected experimental outcomes. In the present study, four simulation experiments were conducted based on the One Trap – One Recombination center (OTOR) model for the case of equal re-trapping and recombination probabilities signifying second order kinetics. The first experiment defines the Tm shifting for various heating and optical stimulation rates. The second depicts an electron trap filling process, in which dose progresses from a low value until the saturation state. In the third experiment, a trap emptying procedure was simulated via thermal bleaching (Isothermal Decay), whereas in the final one, the same trap emptying procedure was conducted via optical bleaching (Continuous wave optically stimulated luminescence) for different time spans. Generally the tm,Tm shifting in trap emptying processes, is proven, according to simulations, to follow a similar behavior to the tm,Tm shift as a function of heating or optical stimulation rate. Regarding trap filling, tm and Tm shift to lower values as the dose increases. © 2022 Elsevier Lt
Properties of quartz TA – OSL signal with a peculiar decay shape for SAR TA – OSL applications
No full textEvaluation of thermoluminescence trapping parameters in Li2B4O7 co-doped with Ag+ and Gd3+ using various experimental techniques
No full textThe aim of this study is to determine the thermoluminescence (TL) kinetic parameters, including the activation energy (E), frequency factor (s) and order of kinetics (b), for the traps of silver and gadolinium co-doped lithium tetraborate (Li2B4O7:Ag,Gd) phosphor. Four different experimental techniques were applied, including Fractional Glow Technique (FGT), Computerized Glow Curve Deconvolution (CGCD), as well as both Isothermal TL (ITL) and Optically Stimulated Luminescence (OSL) measurements at various stimulation temperatures. The TL glow curve of the phosphor was determined to be composed of two single peaks with delocalization temperatures around 80 °C and 360 °C with a heating rate of 2 °C/s after 10 Gy beta dose. Moreover, a composite TL signal is observed within the temperature region between 110 °C and 320 °C. Both the deconvolution analysis as well as the FGT partially indicates that this composite signal consists of two overlapping TL glow peaks along with a satellite TL peak of suppressed intensity. The reusability of the phosphor was studied up to 20 experimental cycles using beta dose values of 0.5, 5 and 10 Gy to support the FGT procedure. The plot of activation energy vs measured temperature yielded a smooth continuum, with the presence of three not so prominent plateau regions. On the contrary, the CGCD analysis indicated the presence of five TL peaks with increasing activation energy values ranging between 0.63 and 1.56 eV. The ITL results indicate that for the constituents of the composite TL signal within 110 °C and 320 °C, the activation energy is less than 0.5 eV, while the corresponding OSL results of the same signal indicate an activation energy value of 0.83 eV. Based on the results of the present study, (a) the continuum shape of the E vs Tfin plot of the FGT analysis and (b) the behavior of the normalized ITL decay curves provide adequate arguments for the existence of a tunneling recombination pathway in the phosphor. The argumentation is also supported by recent related literature. © 2019 Elsevier B.V.Firat University Scientific Research Projects Management Unit: FDK-2017-6833This research was supported by the Cukurova University Rectorate , Scientific Research Projects Coordination Unit under contract numbers FDK-2017-6833 . The authors gratefully acknowledge this support
