High Temperature Thermoluminescence Research Articles

Optical properties of pure and Sn-doped β-Ga2O3 single crystals grown by optical float zone technique

High-quality single crystals of both pure and Sn:β-Ga2O3 single crystals weregrown using the optical floating zone technique and a comprehensive study of its luminescence and scintillation properties was carried out. The pure and Sn:β-Ga2O3 grown crystals were oriented along (100) by Laue diffraction pattern and its monoclinic structure was confirmed using a single crystal XRD. X-ray induced luminescence spectrum shows a maximum emission peak at 365 nm. The cut off wavelength was observed around 258 nm and the optical band gap was calculated to be 4.64 eV from UV–Vis-NIR transmission spectroscopy. The room temperature Raman spectra were recorded and the various vibration modes were investigated. Low temperature (10 to 300 K) and high temperature (325 to 675 K) TL measurements were carried out on X-ray irradiated crystals and its TL kinetic parameters such as activation energy (eV) and frequency factor (S) were calculated. Scintillation decay time profiles were measured for both pure and Sn-doped crystals under 137Cs γ-ray excitation. The calculated scintillation light output is 2300 Ph/5.5 Mev for Sn:β-Ga2O3 crystal under α-particle excitation from 241Am radiation source.

Study of the centers responsible for the TL emission by EPR and PL analysis of Eu-doped CaSiO3 phosphors synthesized by the devitrification method

CaSiO3 doped at different ppm of Eu were synthesized by the devitrification method. Polycrystals exhibit a prominent high-temperature TL peak that increases in intensity and shifts toward higher temperatures with increasing amounts of dopant. TL emission spectrum of CaSiO3: Eu displays two very broad bands centered at 400 and 440 nm corresponding to the temperatures of 229.5 and 373.5 °C, respectively. PL measurements indicate the presence of Eu2+ and Eu3+ ions. EPR spectrum arises from two defect centers. One of the centers with principal g-values 2.016, 2.0091, and 2.0051 is attributed to O− ion and the center correlates with the TL peak at 236 °C. Center II with an isotropic g-value of 2.0018 is attributed to an F+ center and the center relates to the TL peak at 120 °C. Center III is also tentatively identified as the F+ center which is associated with the TL peak at 365 °C.

Etioplasts are more susceptible to salinity stress than chloroplasts and photosynthetically active etio-chloroplasts of wheat (Triticum aestivum L.).

High soil salinity is a global problem in agriculture that directly affects seed germination and the development of the seedlings sown deep in the soil. To study how salinity affected plastid ultrastructure, leaf segments of 11-day-old light- and dark-grown (etiolated) wheat (Triticum aestivum L. cv. Mv Béres) seedlings were floated on Hoagland solution, 600 mM KCl:NaCl (1:1) salt or isosmotic polyethylene glycol solution for 4 h in the dark. Light-grown seedlings were also treated in the light. The same treatments were also performed on etio-chloroplasts of etiolated seedlings greened for different time periods. Salt stress induced slight to strong changes in the relative chlorophyll content, photosynthetic activity, and organization of thylakoid complexes. Measurements of malondialdehyde contents and high-temperature thermoluminescence indicated significantly increased oxidative stress and lipid peroxidation under salt treatment, except for light-grown leaves treated in the dark. In chloroplasts of leaf segments treated in the light, slight shrinkage of grana (determined by transmission electron microscopy and small-angle neutron scattering) was observed, while a swelling of the (pro)thylakoid lumen was observed in etioplasts. Salt-induced swelling disappeared after the onset of photosynthesis after 4 h of greening. Osmotic stress caused no significant alterations in plastid structure and only mild changes in their activities, indicating that the swelling of the (pro)thylakoid lumen and the physiological effects of salinity are rather associated with the ionic component of salt stress. Our data indicate that etioplasts of dark-germinated wheat seedlings are the most sensitive to salt stress, especially at the early stages of their greening.

Synthesis and thermoluminescence of Ce-doped CaF2 phosphor: Study of defect centers responsible for the TL emission by EPR analysis

We present here the thermoluminescence (TL) properties of Ce-doped CaF2 (CaF2:Ce) phosphor synthesized by combustion of the precipitate formed from the addition of NH4F to (Ca(NO3)2)⋅4H2O. The structure analysis of the synthesized sample was carried out by X-ray diffraction (XRD) technique. The CaF2:Ce phosphor shows an intense peak at about 120 °C and a low-intensity peak at 280 °C. Both peaks' thermoluminescence (TL) intensity was observed to increase with γ-dose. The kinetic parameters of TL peaks were calculated for CaF2:Ce phosphor using the Tm-Tstop and deconvolution methods. Electron paramagnetic resonance (EPR) is utilized to identify the defect centers formed in γ-irradiated CaF2:Ce phosphor and also to infer the defect centers involved in the TL process. The presence of two defect centers is inferred and center I has a g-value equal to 2.018 and is identified as an O− ion. The O− ion correlates with the TL peak at 120 °C. Center II with a g-value of 2.0057 is ascribed to a radiation-induced Fe3+ ion and is observed to relate to the high-temperature TL peak at 280 °C. The UV–Vis optical absorption of pure CaF2 and Ce-doped phosphors was investigated.

Zinc silicate phosphor: Insights of X-ray induced and temperature enabled luminescence.

The present investigation deals with the effect of calcination temperature on the structural and thermoluminescent (TL) properties of Zn2 SiO4 materials. For this study, Zn2 SiO4 was prepared via a simple hydrothermal route and calcinated at temperatures from 700°C to 1100°C in an air atmosphere. TL data of all Zn2 SiO4 samples showed two peaks at around 240°C and 330°C due to the formation of the luminescence centre during X-ray irradiation. More interestingly, the Zn2 SiO4 sample calcinated at 900°C exhibited a shift in the TL peak (282°C and 354°C) with an optimal TL intensity attributed to its good crystallinity with a well-defined hexagonal plate-like morphology. X-ray-irradiated Zn2 SiO4 samples calcinated at 900°C exhibited a high-temperature TL glow curve peak, suggesting that the present material could be used for high-temperature dosimetry applications.

Size-Dependent Persistent Luminescence of YAGG:Cr3+ Nanophosphors.

In the current work, YAGG:Cr3+ nanophosphors were synthesized by the Pechini method and then annealed at different temperatures in the range 800–1300 °C. The structure and morphology of the samples were characterized by X-ray Powder Diffraction (XRPD). The lattice parameters and average crystalline sizes as site occupation by Al3+ and Ga3+ ions were calculated from the Rietveld refinement data. To investigate the effect of crystalline size of the materials on their optical properties: excitation and emission spectra were recorded and analyzed. Finally, the effect of crystalline size on the probability of carrier recombination leading to PersL was determined experimentally with thermoluminescence analyses. The Tmax-Tstop method was applied to determine the trap type and particle size (calcination temperature) effect on their redistribution. A correlation between structural changes and trap redistribution was found. In particular, the extinction of high-temperature TL maximum with increasing annealing temperatures is observed, while low-temperature TL maximum increases and reaches a maximum when the lattice parameter reaches saturation.

Recombination pathways in a BeO yielding two main dosimetric TL peaks

Apart 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.

TL and EPR characteristics of SrAl2O4 phosphor prepared by solid‐state reaction method

SrAl2O4 phosphor was prepared by solid-state reaction method and characterized using X-ray diffraction (XRD), thermoluminescence (TL) and electron paramagnetic resonance (EPR) spectroscopy. TL glow curve of irradiated phosphor shows three peaks at 135, 260 and 350 °C. The order of kinetics of the three TL peaks is second order with an activation energy of 1.05, 1.60 and 1.93 eV, respectively. EPR studies have been carried out to identify the defect centers induced by gamma irradiation and also to identify the defect centers involved in the TL process in SrAl2O4. Two distinct centers contribute to the observed spectrum at room temperature. Center I exhibiting a four-line hyperfine splitting is identified as an O− ion. O− ion is associated with the high temperature TL peaks at 260 and 350 °C. An eight-line spectrum with a g-value of 2.0068 is attributed to a F+ center (singly ionized oxygen vacancy). This center relates to the 135 °C TL peak.

Use of infrared light-emitting diodes to determine dosimetric characteristics of MgO:Tb,Gd,Li via the optically stimulated luminescence technique

In this study, the temperature dependence of Infrared Stimulated Luminescence (IRSL) in MgO:Tb,Gd, Li samples were investigated and the basic dosimetric properties were examined for the radiation dosimetry. Terbium, gadolinium, and lithium doped MgO were synthesized using the solution combustion synthesis method, and the characterization of the material was performed by X-ray diffraction (XRD) and scanning electron microscope (SEM) techniques. The effects of the dopants were investigated by specifying the radioluminescence (RL), thermoluminescence (TL), and optically stimulated luminescence (OSL-blue stimulation/IRSL-infrared stimulation) curves of the MgO:Tb,Gd, Li phosphor. Decay curves of the light flash vs. time showed that the MgO:Tb,Gd, Li was most readily discharged by infrared stimulation. The temperature dependence of the IRSL samples was investigated between 50 and 230 °C. The optimized readout temperature was determined as 120 °C achieving the maximum IRSL intensity. It was shown that there are traps responsible for TL peaks below 200 °C which could be suggested as the source of the IRSL signals for the studied MgO:Tb,Gd, Li samples. The high-temperature TL peak nearly at 400 °C was not affected by infrared stimulation and did not contribute to the obtained IRSL signals. The dosimetric properties such as reusability, multi-readability, dose-response, and fading were examined for applicability to radiation dosimetry. The thermal stability of the sample was investigated using the isothermal annealing technique and activation energy and frequency factor of the traps responsible for IRSL signal were estimated as 0.62 eV and 106 Hz, respectively. The MgO:Tb,Gd, Li luminescent has several properties in its favor. It has been shown that the IRSL signals of the Tb, Gd, and Li doped MgO sample can be investigated and examined as a radiation dosimeter.

Luminescence Characteristics of Intraplate-Derived Olivines

Abstract Olivine has so far attracted limited attention as a potential luminescence dosimeter. In particular, there is a dearth of information concerning the luminescence properties of geochemically characterised, pure olivine samples. Six well-characterised olivine samples from four intraplate settings are investigated in this study, including emission wavelengths and intensities, growth of signal with absorbed dose, signal stability and recovery of a given dose with a single aliquot regeneration (SAR) protocol. All tested olivines share a low-temperature (90–100°C) UV/blue thermoluminescence (TL) peak, and five of six samples also produce a low-temperature red/yellow emission. Higher temperature TL peaks, which would be thermally stable over geological timescales and could be used for dating, are rarely observed at low doses (c. 46 Gy), but detectable though dim at significantly higher doses (c. 460 Gy). Photostimulated luminescence (PSL) emissions are very dim, but reliably detected emissions are stimulated by blue, yellow and infrared (IR) light. PSL yielded generally successful dose recovery results; however, all tested signals are prone to significant anomalous fading and complex thermal transfer between unbleachable and bleachable traps. These characteristics must be addressed if olivine is to be used as a natural dosimeter for luminescence dating. Given the variety of luminescence responses, it appears that olivine samples in future dating work may need to be individually characterised prior to measurement.

Neutron-gamma mixed field dosimetry using a 6LiF:Mg,Cu,P thermoluminescent dosimeter

Satisfactory discrimination between the neutron and gamma components in a mixed neutron-gamma field is one of the most important objectives of neutron dosimetry. One of the common techniques for estimating gamma and neutron dose components in mixed neutron-gamma fields is the two peak method. This method has been applied using dosimeters such as LiF:Mg,Ti, but in the present work, a 6LiF:Mg,Cu,P dosimeter has been used, whose thermoluminescence sensitivity is much higher than the LiF:Mg,Ti dosimeter, and therefore, if appropriate results are achieved, it can drastically reduce the dose estimation threshold. Applicability of 6LiF:Mg,Cu,P for estimation of the gamma dose using the two peak method in a mixed thermal neutron-gamma radiation field was studied. The ratio of the area underneath the high temperature thermoluminescence glow peak to dosimetry peak of this phosphor in an Am-Be neutron field is 0.127, while this ratio in a pure gamma ray field of 137Cs is 0.039. The calibration curves were obtained by separately irradiating 6LiF:Mg,Cu,P chips with known gamma and neutron doses. Results show that 6LiF:Mg,Cu,P can be used to estimate the contributions of neutron and gamma doses in a mixed neutron-gamma field by using the two peak method.

Component-Resolved Analysis Towards Correlation between Thermoluminescence and Optically Stimulated Luminescence in Commercial Magnesium Oxide

Abstract The present study aimed at quantifying the relationship between TL and either CW-OSL or LM-OSL using commercially available magnesium oxide. The samples were bleached at two different temperatures, and a component-resolved analysis on the integrated signals was performed. According to the data of the present study, each one among the five observed LM-OSL component receives electrons from at least two different TL peaks. Two different fast OSL components were resolved in the LM-OSL curves, both accumulating electrons from all TL glow peaks with Tmax>150°C. Component C3 is very well correlated with the TL peaks at 102, 135 and 194°C, while components C4 and C5 are related to the TL glow peaks of 292°C, 353°C and 464°C. We note that for CW-OSL the resolution is good when two or more components differ in intensity by an order of magnitude. Blue stimulation depletes substantially the first two TL peaks but not the third peak. Substantial depletion of the high-temperature TL peaks is achieved only by using the LM-OSL configuration. The results of the present study suggest that the traps that contribute to TL and OSL are the same, despite using different recombination pathways.

Surface paleothermometry using low-temperature thermoluminescence of feldspar

Abstract. Thermoluminescence (TL) of feldspar is investigated for its potential to extract temperature histories experienced by rocks exposed at Earth's surface. TL signals from feldspar observed in the laboratory arise from the release of trapped electrons from a continuous distribution of trapping energies that have a range of thermal stabilities. The distribution of trapping energies, or thermal stabilities, is such that the lifetime of trapped electrons at room temperature ranges from less than a year to several billion years. Shorter lifetimes are associated with low-temperature TL signals, or peaks, and longer lifetimes are associated with high temperature TL signals. Here we show that trapping energies associated with shorter lifetimes, or lower-temperature TL signals (i.e. between 200 and 250 ∘C), are sensitive to temperature fluctuations occurring at Earth's surface over geological timescales. Furthermore, we show that it is possible to reconstruct past surface temperature histories in terrestrial settings by exploiting the continuous distribution of trapping energies. The potential of this method is first tested through theoretical experiments, in which a periodic temperature history is applied to a kinetic model that encapsulates the kinetic characteristics of TL thermometry. We then use a Bayesian approach to invert TL measurements into temperature histories of rocks, assuming that past temperature variations follow climate variations observed in the δ18O records. Finally, we test the approach on two samples collected at the Mer de Glace (Mont Blanc massif, European Alps) and find similar temperature histories for both samples. Our results show that the TL of feldspar may be used as a paleothermometer.

Investigation of luminescence properties of BeO ceramics doped with metals for medical dosimetry

Abstract The objective of this work was to investigate the luminescence properties of metal-doped BeO optical ceramics that were efficiently synthesized by the co-precipitation method in the presence of air. BeO nanophosphors individually doped with metal elements: Al, Ca, Mg, Na, Li, K, B, Si, Zn, Sr, In, and Cu in different dopant concentrations (0.1, 0.5, 1 and 5%). The phase formation and morphology of the samples were studied using x-ray diffraction (XRD) and scanning electron microscopy (SEM) analyses. The formation of the hexagonal wurtzite phase of BeO was confirmed by XRD data and SEM images showed that BeO ceramics exhibit different surface morphologies and have a narrow size distribution. Similar broad UV emission bands between 200 nm and 450 nm were observed in radioluminescence (RL) analyses of the single-metal doped BeO ceramics. The effect of metal doping on thermoluminescence (TL) and optically stimulated luminescence (OSL) signals were investigated to achieve a promising BeO dosimeter for medical dosimetry applications. While Al, Na, K, B, and Zn dopants increased the intensities of sensitivities of TL peaks responsible for traps settled up to 300 °C, Ca, Mg, K, B and In dopants significantly increased the intensities of higher-temperature TL peaks located between 300 and 650 °C. There was, in addition, an increase in OSL signal intensity of undoped BeO material with Na, Li, K, and Cu dopants by 47%, 37%, 18%, and 28%, respectively. To investigate the feasibility of the dosimetric utility of the studied BeO materials, dose-response, reusability, and fading properties of the promising ceramic dosimeters were investigated in medical applications.

Thermoluminescence response of various dosimeters as a function of irradiation temperature

The behavior of various TL dosimeters following two different thermal treatments with temperature ranging between 50 and 230 °C, was investigated in this particular study. The thermal treatment consists of two different protocols, including a simultaneous irradiation-heating and a post irradiation heating. The dosimeters that are the subject of the present study include two different families of lithium fluorides, namely the Harhsaw LiF family (TLD-600, TLD-700), LiF of the Krakow university (MTS-600, MTS-700), BeO and the commonly used CaSO4 samples with two different impurities (Dy and Tm). According to the analysis, it seems that the TLDs and MTS-600 are identical with regard to their characteristics, while MTS-700 is different. The treatment showed that the intensities of peak 5 of all LiF samples increases up to 20–30% at 110 °C which is followed by a decrease, while the high temperature peaks of LiF showed a high dependence on the treatment temperatures. As for the case of BeO, one peak has a minor increase of 10% at 80–90 °C and a decrease up to 230%, while the other is stable. CaSO4 samples show no increase and there is a decrease starting at 150 °C. Also, this work studied the kinetic parameters of all peaks for these samples via the computerized glow curve deconvolution method. In the end, there is a categorization of the LiF samples based on their properties and their glow curves. Lastly, the results indicate that the lack of strong increase of the TL response with increasing irradiation temperature for the majority of the TL peaks of these aforementioned phosphors does not support strong competition effects. A notable exception is observed for the high temperature TL peaks in all LiF samples regardless of whether these were purchased from Harshaw or from Poland.

Effect of thermal treatment on luminescence properties of long persistent CaAl2O4:Eu2+,Dy3+ synthesized by combustion method

We report on the effect of thermal treatments on photoluminescence, thermoluminescence and afterglow of CaAl2O4:Eu2+,Dy3+ synthesized by combustion method and annealed under a carbon atmosphere at 1423 K for 6 h. As synthetized phosphor exhibit a typical Eu2+ emission with a maximum at 438 nm corresponding to the allowed transition from 4f65d to 4f7 levels of Eu2+ ion. The TL glow curves recorded after beta irradiation consist of at least three overlapped TL peaks with maxima at about 340, 410, and 480 K and a high temperature TL with a peak maximum higher than 680 K. Immediately after beta irradiation, intense AG is observed demonstrating the possibility to emit lightfor hours at a level exceeding background signal. The decay curves exhibit two components, fast and slow, due to the liberation of electrons from traps responsible for the 340 and 410 TL peaks with characteristic duration times of about ten seconds and a couple of hours, respectively.The synthesized phosphor was subjected to additional thermal treatments (TTs) in an air atmosphere at 883 and 1183 K for 1h. The TTs lead to a pronounced increase the narrow excitation and emission bands attributable to f – f transitions of the Eu3+ ions and slight changes of the excitation and emission bands corresponding to Eu2+ ions. The effect the TTs on the TL reveals itself in the decrease of the 410 and 480 K TL peaks. On the other hand, the 340 K TL peak does not change under the TTs. The study of TT effects on luminescent properties of calcium aluminate codoped with rare earth is important for understanding the mechanism of trapping and detrapping processes in this phosphor.

The Effect of Cr3+ and Mg2+ Impurities on Thermoluminescence and Deep Traps in β-Ga2O3 Crystals

Thermally stimulated luminescence (TSL) of β-Ga2O3 single crystals doped with Cr3+ and Mg2+ impurities was investigated. Based on the correlation between the Cr3+ concentration and light sum accumulated in the thermoluminescence (TL) glow peak at 285 K, it was concluded that doping of β-Ga2O3 with Cr3+ ions leads to the formation of electron traps manifested in this peak. The activation energy of peak at 285 K is equal to Ec-0.55 eV and close to E1. Thus the Cr3+e− centers can be a candidate for E1. The high-temperature TL glow peak at 385 K (Ec-0.94 eV) is related to oxygen vacancies which are created in gallium oxide doped by Mg2+ ions to compensate for the negative charge formed by the substitution of gallium sites by magnesium ions.The co-doping of β-Ga2O3 crystals with Cr3+ and Mg2+ impurities leads to the appearance of a new TL glow peak at 320 K with an energy close to E*2 (Ec-0.7). It is suggested that this peak is formed by defect complex, in particular, oxygen vacancies with Cr3+ or Fe3+ ions.

RELIABILITY OF REUSING THE SENSITIZED LIF THERMOLUMINESCENCE DOSIMETERS

The reliability of reusing the sensitized thermoluminescence (TL) for LiF (TLD-100) dosimeters have been investigated. It has been found that reusing the same sensitized LiF dosimeters may influence the sensitivity of the dosimeters even under the same experimental conditions when the temperature readout range does not include the high-temperature TL signal at T > 505K. But, if the high-temperature TL signal is included in the temperature readout range, it has been found that the ultra-high temperature TL signal significantly increases with increasing the number of reusing the dosimeters. After almost 7 times of reusing the sensitized dosimeters, the total area under the glow-curve becomes stable and independent of the number of reusing the dosimeters. It has been also found that the TL signal located between the low-temperature TL signal and the ultra-hightemperature TL signal was almost stable over all the number of reusing the dosimeters. For all the lowtemperature peaks, the kinetics parameters of the sensitized LiF dosimeters have not to be influenced by reusing the same dosimeters. However, the activation energy of peak 5 which lies at temperature range (460-500K) has been influenced by the readout temperature range and reusing the dosimeters. The typical value for this glowpeak has been obtained in the case which the high-temperature TL signal has been included in the temperature readout.

A component resolved study on the stable signal of Merck α-quartz: Tentative correlation among TL peaks, OSL components and EPR signals

In the present work, pre-dosed α-quartz is investigated towards its effective applications in retrospective dosimetry and dating as a reference material. The purpose of the study is to find tentative correlations between Thermoluminescence (TL) (high temperature TL (HTTL) peaks), Optically Stimulated Luminescence (OSL) (both continuous wave (CW) and linear modulated (LM)) and Electron Paramagnetic Resonance (EPR). The present work indicates a triple correlation between the fast CW-OSL component and certain peaks of LM-OSL and TL signals, while all these luminescence entities are attributed to the EPR signal with g-value (Landé splitting factor) at 1.9975 called C2EPR. The present study provides experimental evidence that (i) one TL peak might be the source for more than two LM-OSL components and (ii) even two different TL peaks can contribute to the same OSL component. Furthermore, on the EPR signal, besides the well established Ge center, another un-identified component has been resolved.

Manganese agglomeration and radiation damage in doped Li2B4O7

Manganese clustering effects were studied in Li2B4O7 (LTB) ceramics. The samples LTB:Me + Mn (Me = Sn, Cu, Mn, Zn, Be) were prepared by a two-stage doping method (except for LTB doped with Mn solely). EPR, pulsed cathodoluminescence, thermoluminescence (TL) were measured. Mn clustering causes supralinearity of the material response to the radiation dose, reversible shift of the dosimetric TL peak, and irreversible radiation damage. Radiation damage of the LTB crystal lattice is accompanied with the formation of a peroxide bridge instead of a single oxygen at the common vertex of two BO4 tetrahedra. Repelled by an excessive positive charge of a Mn cluster, holes are localized around at traps including the peroxide bridges where they are stable up to 630 K. The extent of the radiation damage can be estimated by the intensity of the high-temperature TL at 630 K, when the released holes recombine with the electrons near regular Mn2+. The most stable against the radiation damage and also suitable for TL dosimetry is LTB:Sn + Mn.