TL Curves Research Articles

Comparative analysis of predose effects on TL and OSL signals in BeO dosimeters

This study investigates in detail the effects of predose on TL and OSL signals for BeO dosimeters. The TL and OSL signals were deconvoluted to each peak and component. As a result of deconvolution, the variations in the kinetic parameters (E, Tmax, b) for the TL signals and the lifetime values of the OSL signals were investigated. In addition, sensitivity changes according to predose were monitored for each peak and component. Finally, dose response curves were studied using the dose linearity index (f(D)) for each peak and component. Accordingly, the peak structures and kinetic parameters did not change according to the predose for the TL signal, whereas variations in the lifetime values for the OSL signal were observed, especially at the initial dose values (0.1 and 0.2 Gy). There was no change in sensitivity according to the predose for the total area condition although each peak and component exhibited independent behavior. Therefore, TL and OSL signals should be evaluated based on the total area in predose applications. The TL and OSL dose response curves exhibited different behaviors according to predose. TL dose response curves were not affected by the predose except for 1000 Gy, while the OSL dose response curves were affected by the predose considering the total area condition. The possible reason for the differences between the TL and OSL dose response curves is the significant transfer effect in the OSL signal at low doses, which results in greater changes at low doses compared to the TL signal. Also, thermal quenching effects may have resulted in lower intensity in the case of the TL signal. In future studies, preheating tests and thermal quenching corrections on TL peaks at high predoses may increase our understanding of deep trap interactions in BeO dosimeters.

Investigation on thermally assisted optically stimulated luminescence signal in natural CaF2

In this work, thermally assisted OSL (TA-OSL) of natural fluorite was investigated, aiming to understand better the role of traps in both TL and OSL. TA-OSL is the luminescence simultaneously stimulated by light and heat; from this combination it is possible to access deeper traps in the analyzed material, that, in general, need more energy to be accessed. Irradiations were performed at room temperature using the Sr-90/Y-90 source incorporated in the TL/OSL reader at a dose rate of about 10 mGy/s. The optical stimulus was blue light at 470 nm. The dosimeters were also irradiated with X and gamma-rays of various energies (from 20 keV to 1.25 MeV) for comparing the energy dependence of the OSL and the TA-OSL signals. Residual TL curves were acquired after OSL readouts for checking trap participation in OSL emission. The OSL measurements were done at temperatures from 25 °C to 400 °C. For readout temperatures from 25 to ∼185 °C, decay curves were observed, and they were modeled by one stretched-exponential function, giving rise to a good fit to the experimental data. The dependence of the fitting parameter (β) on the photon energy was studied, and it was observed that β increases with the X-ray beam effective energy. The energy dependence of OSL signal is 1.5 times larger than that of TA-OSL signal, pointing to the reduction in energy dependence with the combination of thermal and optical stimuli. The total light emitted (TA-OSL + residual TL) is highly increased by the simultaneous stimulation by light and heat, indicating that light promotes charges to thermally active traps (phototransfer), and heat promotes charges to optically active traps, facilitating their release during illumination.

Spectroscopic studies of metastable tetragonal ZrO2 nanocrystals

This study delves into an examination of the structural and luminescent properties of zirconium dioxide (ZrO2) synthesized via the solid-state combustion method. Nitrates are harnessed as the oxidizing agent, while glycine serves as the fuel. Two distinct compositions are explored: a stoichiometric 1:1 ratio and a fuel-enriched 1:2 ratio. The structural analysis, employing X-ray diffraction and Raman spectroscopy, predominantly manifests a tetragonal structural phase in both samples; however, a minor monoclinic phase has also been observed in the former sample. The band gap was found to be 4.50 eV and 4.28 eV for ZrO2 synthesized in stoichiometric ratio and a fuel-enriched ratio respectively. The samples also show defects assisted photoluminescence in both the samples. The thermoluminescence of samples were investigated after irradiating the samples with UV and gamma rays for different doses. The TL curves manifest a shift towards lower temperatures at higher doses. . Significantly, the sample prepared with a 1:1 nitrate-fuel ratio exhibits a more pronounced overall TL intensity. In conclusion, our findings imply that the formation of the tetragonal phase may be influenced by strain energy, rather than being solely ascribed to size effects and oxygen vacancies within the lattice.

Optically stimulated luminescence of K2SO4:Ce and its relationship with TL glow-curves

K2SO4:Ce was investigated with respect to its OSL and TL properties. Due to the doping with Ce3+ ions, the material shows strong emission in the range of 300–400 nm with a maximum of approx. 330 nm. The spectrum of OSL stimulation is wide and enables stimulation with visible light and infrared. When comparing the 550 nm and 900 nm stimulation, differences in the initial intensity, decay rate and total counts can be seen. The higher total counts are obtained for 550 nm green light, with the initial intensity being higher for 900 nm infrared. The OSL signal, for both stimulations, is sensitive to preheat, however, this relationship is different in both cases. The study of the mutual correlation of the TL and OSL signal showed that only a part of the peaks in the TL curve are bleached by optical stimulation. The result indicates that there are both optically active and non-optically active traps in the material. The OSL-TL correlation study involves the deconvolution of the TL curves and the estimation of the bleaching of two main TL peaks and one minor peak. At least three traps are optically active but are emptied to varying degrees by different stimulations.

Multicolor and multimode luminescence regulation and anti-counterfeiting application of lanthanide ions doped Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> phosphors

Multicolor and multimode luminescence materials have important applications in the field of information security encryption. However, the design and synthesis of multicolor multimode luminescent materials is still a challenge, and only several materials have been reported. In this paper, a series of single doped and double doped Li<sub>1–<i>x</i></sub>K<sub><i>x</i></sub>NbO<sub>3</sub>:Pr<sup>3+</sup>/Er<sup>3+</sup>/Tm<sup>3+</sup> phosphors are prepared by high temperature solid state method. The structure, morphology, optical properties and thermoluminescence (TL) spectra are characterized by X-ray diffractometer (XRD), scanning electron microscope (SEM), luminescence spectrometer and self-made heating device. Firstly, the effects of different values of K<sup>+</sup> content on the luminescence and trap distribution of LiNbO<sub>3</sub> materials are studied. The results show that the ionic lattice is distorted when a small quantity of K<sup>+</sup> ions replace Li<sup>+</sup>. With the addition of K<sup>+</sup>, the photoluminescence excitation (PLE) spectra monitored emission of 620 nm shows that the ratios of the absorption peaks from matrix (200–310 nm) to absorption peaks from the intrinsic transition of Pr<sup>3+</sup> ions 4f→5d (310–430 nm) change significantly, showing a double-peak characteristic. When the concentration of K<sup>+</sup> ions is 0.5, the absorption peak from the matrix disappears, which may be due to the phase transition of the matrix lattice caused by excessive K<sup>+</sup> ions or the introduction of a large number of defect energy levels into the matrix lattice. Moreover, K<sup>+</sup> ion doping can regulate the density and distribution of traps. TL curves show that a small quantity of K<sup>+</sup> doping increases the trap density of shallow traps. When a large quantity of K<sup>+</sup> is doped, the phase changes of matrix lattice and the defect density decrease. Secondly, the doping of Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> matrix by different luminescent centers (Pr<sup>3+</sup>/Er<sup>3+</sup>/Tm<sup>3+</sup>) is studied. The results show that the multicolor luminescence emission in red, blue and green bands and the tunable multimode luminescence (up/down conversion luminescence, afterglow luminescence and photo-stimulated luminescence) are realized by the selective excitation. According to the multicolor and multimode characteristics of the phosphors, a butterfly-shaped anti-counterfeiting pattern is designed. Owing to the different energy level positions of the luminescence centers, dynamic multicolor photoluminescence is realized by selective excitation at different wavelengths. Based on the upconversion luminescence characteristics of Er<sup>3+</sup> and the excellent afterglow characteristics of Pr<sup>3+</sup> in Li<sub>0.9</sub>K<sub>0.1</sub>NbO<sub>3</sub> material, the designed anti-counterfeiting pattern shows the dynamic color change and multicolor, multimode high-order anti-counterfeiting application.

Effects of Mg2+ on enhancing luminescence efficiency for a red long persistent phosphor γ-Zn3(PO4)2: Mn2+

A red long persistent phosphor of γ-Zn3(PO4)2: Mn2+, Mg2+ was prepared through a homogeneous co-precipitation and conventional solid-state calcining method. The crystalline structures and properties of samples were confirmed utilizing X-ray diffractions, scanning electron microscopes, X-ray photoelectron spectroscopies, photoluminescence spectra, decay curves and thermoluminescence spectra. The XRD results reveal that the dopant of Mg2+ will be responsible for the phase transition of Zn3(PO4)2: Mn2+ from α to γ as well as the improvement of the crystallinity of phosphors. The photoluminescence emission spectrum of the red γ-Zn3(PO4)2: Mn2+, Mg2+ phosphor exhibits a prominent peak at 620 nm attributed to the 4T1g-6A1g transition of Mn2+ ion. The luminescence properties of γ-Zn3(PO4)2: Mn2+ can be effectively enhanced by the dopant of Mg2+. The TL curves are employed for the discussion of intrinsic defects. The working mechanism of the persistent luminescence is proposed.

Comparing the monochromatic TL response of a high sensitivity natural quartz irradiated with β and γ rays

This study investigates the effect of the dose-rate in the thermoluminescent glow curves of a single crystal of quartz. The samples were sensitized by the γ radiation combined with the heat-treatments. The glow curves were registered in zeroed (unsensitized) and sensitized conditions using an optical filter centered in violet spectral region. Tens mGy test doses were administered with one β (90Sr/90Y) source and two γ radiation sources (60Co and 137Cs). The TL curves were deconvoluted using a first-order kinetic model. Differences in the glow curves and trapping parameters were observed between zeroed and sensitized samples. Differences were found in the TL curves comparing the three radiation sources. The principal variation is the remarkable increase in the TL signal above 350 °C, which is observed only in sensitized samples with the minor dose-rate source (137Cs). This signal seems to be associated with deep trapping states. The intensities of the components defining the first peak and the high temperature signal show a dependence on the dose-rate. The dose-rate dependence of the first-peak components is explained by the competing effects that may take place during the excitation stage. The components that fitted the sensitized peak (260 oC) do not exhibit a clear dependence on the dose-rate of radiation source.

Thermoluminescence characteristics of GaSe and Ga2Se3 single crystals

GaSe and Ga2Se3 are semiconducting compounds formed from same constituent elements. These compounds have been attractive due to their optoelectronic and photovoltaic applications. Defects take remarkable attention since they affect quality of semiconductor devices. In the present paper, deep defect centers in GaSe and Ga2Se3 single crystals grown by Bridgman method were reported from the analyses of thermoluminescence measurements performed in the 350–675 K range. Experimental TL curves of GaSe and Ga2Se3 single crystals presented one and two overlapped peaks, respectively. The applied curve fitting and initial rise techniques were in good agreement about trap activation energies of 0.83 eV for GaSe, 0.96 and 1.24 eV for Ga2Se3 crystals. Crystalline structural properties of the grown single crystals were also investigated by x-ray diffraction measurements. The peaks observed in XRD patterns of the GaSe and Ga2Se3 crystals were well-consistent with hexagonal and zinc blende structures, respectively.

Theoretical study by analytical equations of optical properties of the phosphors Zn2SnO4 codoped with Cr3+ and (Al3+ or Eu3+) via the crystal field control

The phenomenon of persistent luminescence in the phosphors Zn2SnO4 doped by Cr3+ and codoped by Al3+ or Eu3+ is related to the energy levels of the doping transition ions Cr3+ and rare earth ions Eu3+, the concentration of Al3+ substituting Zn and Sn, the intrinsic defects and the energy bands of the Zn2SnO4 matrix. To fully understand the procedure of persistent luminescence in these phosphors, we firstly determine the role of the Cr3+ ions in this process. For this reason, a crystal-field theory, using the Racah tensor algebra method, of the optical region associated to the transitions between the Stark levels of Cr3+ in these phosphors was performed. We examine then the influence by codoping with Al3+ and Eu3+ on the persistent luminescence process. In the second step, we analyze the role of the traps after discussing some of these properties. Finally, we propose an energy transfer mechanism from PLE, PL spectra and TL curves.

High temperature persistent luminescence in Tb3+ doped CaSr2Al2O6 phosphor

A novel green-emitting long persistent luminescence (LPL) phosphor CaSr2Al2O6:Tb3+ (CSA:Tb3+) has been developed by traditional solid-state reaction. The crystal structure, luminescence properties, decay curves and TL curves of CSA: Tb3+ are studied in this paper. The distribution of Ca, Sr, Al, O and Tb in phosphors was shown by elemental mapping and photoluminescence under fluorescence microscope. CSA: 0.05Tb shows the strongest luminescence, while CSA: 0.0075Tb exhibits the best LPL of 57 min. In order to study the mechanism of afterglow, the trap depth and distribution was analyzed by measuring the TL curves. By measuring the afterglow at high temperature, it is found that the afterglow also presents a high intensity at 464 K, indicating that CSA: 0.0075Tb3+ can be potentially applied above the room temperature.

Impact of Supine Radiographs to Assess Curve Flexibility in the Treatment of Adolescent Idiopathic Scoliosis.

Study Design:Retrospective cohort study.Objectives:The purpose of the study is to evaluate the role of supine radiographs in determining flexibility of thoracic and thoracolumbar curves.Methods:Ninety operative AIS patients with 2-year follow-up from a single institution were queried and classified into MT structural and TL structural groups. Equations were derived using linear regression to compute cut-off values for MT and TL curves. Thresholds were externally validated in a separate database of 60 AIS patients, and positive and negative predictive values were determined for each curve.Results:MT supine values were highly predictive of MT side-bending values (TL group: 0.63, P < 0.001; MT group: 0.66, P = 0.006). Similarly, TL supine values were highly predictive of TL side-bending values (TL group: 0.56, P = 0.001 MT group: 0.68, P = 0.001). From our derived equations, MT and TL curves were considered structural on supine films if they were ≥ 30° and 35°, respectively. Contingency table analysis of external validity sample showed that supine films were highly predictive of structurality of MT curve (Sensitivity = 0.91, PPV = 0.95, NPV = 0.81) and TL curve (Sensitivity = 0.77, PPV = 0.81, NPV = 0.94). ROC analysis revealed that the area under curve for MT structurality from supine films was 0.931 (SEM: 0.03, CI: 0.86-0.99, P < 0.001) and TL structurality from supine films was 0.922 (SEM: 0.03, CI- 0.84-0.98, P < 0.001).Conclusions:A single preoperative supine radiograph is highly predictive of side-bending radiographs to assess curve flexibility in AIS. A cut-off of ≥ 30° for MT and ≥ 35° for TL curves in supine radiographs can determine curve structurality.

Correlation study between OSL, TL and PL emissions of yellow calcite

The present study shows morphological characterization, experimental results, theoretical fittings of TL and OSL curves of yellow calcite and the correlation between these emissions.The OSL of the sample raises with dose and was theoretically decomposed into three components with a lifetime span of 0.5, 10, and 28 s. TL peaks at 90 and 126 °C were observed in UV region and they could be correlated with OSL emission; these peaks were deconvoluted using general order kinetic theory (GOK) they supplied an activation energy (E) values of 0.7 and 1.0 eV and kinetic order (b) of 1.2 and 2.0 respectively. Both peaks presented good response with beta irradiation in the range between 5 and 41 Gy. TL glow curve recorded at VIS-UV region showed 4 peaks, after deconvolution applying GOK, the peaks temperatures were determined at 92.9, 118.9, 155 and 452 °C; with E equal 0.7, 0.8, 1.3, and 1.05 eV, and b equal 1.01, 1.30, 2.00, and 1.70, respectively.In addition, photoluminescence (PL) spectra were carried out with excitation at 350 nm and the calcite exhibited four broad bands at 413, 440, 470, and 486 nm, and a small one at 390 nm, which can be associated with oxygen vacancies and Me–O defects. The PL results was converted to CIE (Commission International deI'Eclairage) and the coordinates color of the phosphors were determined, values x = 0.14959, y = 0.11,775 (blue) for non-irradiated sample, and x = 0.14593, y = 0.05921 (purplish blue) to irradiated one.

Luminescent and dosimetric properties of transition phases of nanostructured aluminum oxide

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 F2-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.

Energy transfer of wide band long persistent phosphors of Sm3+-Doped ZrSiO4

The long persistent phosphors Zr(1-x)SiO4:Sm3+x were synthesized via solid-state reaction in a reducing atmosphere. The X-ray powder diffractometer (XRD) was utilized to analyze the structure of ZrSiO4:Sm3+. The electron cloud density and their shifts around the ions were explored by the X-ray photoelectron spectrometry (XPS). The luminescence properties and possible mechanism of the long persistent phosphors were studied by excitation and emission spectra, decay curves and TL curves of the samples. The observed main emission peaking at 466 nm was attributed to the d-d transition of Zr4+ and several other emission peaks were contributed by the Sm3+ transitions of 6H5/2-4G5/2 (567 nm), 6H7/2-4G5/2 (603 and 615 nm) and 6H9/2-4G5/2 (650 and 660 nm). ZrSiO4:Sm3+ exhibited a turquoise persistent luminescence after UV excitation and a pale red light under the exposure of 365 nm UV. Many means of analysis were used to explore the mechanism of which several factors were responsible for the improvement of luminescence properties.

Electron life time (τ) in trap levels of Dy3+ activated calcium aluminate: Implications in TL dosimetry

RE3+ (Rare Earth) activated calcium aluminates (CaAl2O4) form an excellent class of phosphors for various applications. The multi-functionality of this class of phosphor is tailored by optimising the relative concentration of the trap-levels within the large band gap (Eg=7.4eV). In this paper we determine the trap-levels in Dy3+ activated nanocrystalline calcium aluminate (CaAl2O4: Dy3+) phosphor by rigorous analysis of the complex TL curves by computerised-glow-curve-deconvolution (CGCD) technique. We assume the kinetics to be the general order kinetic (1≤ b ≤ 2). Six trap levels have been identified with a lifetime ranging from 8 hours to 108 years at room temperature. The ones with τ300 = 6.46×1005 years, 1.02×1007 years and 9.02×1008 years in principle can be the candidates for TL dosimetric application.

Temperature lag effect on TL glow peaks: Corrections on kinetic parameters

Analyses on TL glow curves recorded with various heating rates for some ternary and quaternary crystals were accomplished using peak maximum temperatures (Tmax) which are experimentally obtained and corrected according to temperature lag effect proposed by Kitis and Tuyn. Curve fitting, initial rise, peak shape and variable heating rate methods were applied to experimental and corrected TL peaks. In spite of the fact that heating rate does not affect activation energy of a TL peak, analyses performed on the experimentally obtained TL curves resulted in an increment of the activation energy with increasing heating rate. However, as the corrected TL data were used for the analyses, the activation energy values of each TL peak recorded with different heating rate were in good agreement with each other. The detailed analyses on studied samples were given in the present paper.

Determination of Trapping Parameters of Tl2In2S3Se Layered Single Crystal by Thermoluminescence

AbstractThermoluminescence (TL) measurements are performed to evaluate the trap states in Tl2In2S3Se layered single crystals. TL experiments are conducted with varying temperature from 10 to 300 K and warming rates from 0.2 to 1.0 K s−1. From the analysis of both initial rise and curve fitting methods, the activation energy of the traps is obtained as 23 meV. The Chen's method is also used to find activation energy. By means of this technique, the activation energy of the TL glow curve is calculated as 25 meV. From both Chen's method and curve fitting method, the existence of mixed order of kinetics in Tl2In2S3Se crystal is found. The cross section to capture of the trap center is found out from the results of curve fitting method. The trap distribution of the crystals is investigated with different temperatures of illumination at a constant warming rate of 0.8 K s−1. The temperatures of illumination change from 10 to 22 K. As a result of the increase in temperatures of illumination, the peak maximum values move to higher temperatures and intensity of the TL curves decreases. This behavior shows us that quasicontinuous traps distribution is present in Tl2In2S3Se layered single crystals.

Comparative studies on thermoluminescence glow curves of calcium oxide nanophosphor irradiated with various ionizing radiations

Combustion synthesized nanocrystalline calcium oxide is irradiated with gamma rays, beta rays and swift heavy ions. TL glow curves of γ-irradiated samples show a prominent peak at 654 K with shoulder at 411 K. Whereas, β-irradiated samples exhibits two TL glows with peaks at 535 K and 570 K. TL glow peak intensity of β-irradiated samples increases linearly with increase in dose and position of glow peak temperature remains constant. TL of 120 MeV Au9+ ion irradiated sample show similar glow curve structure to that of gamma irradiated one. However, TL mechanism of ion irradiated sample differs from gamma irradiated one and it is discussed in the text. The TL curves are deconvoluted to calculate kinetic parameters. Activation energy and frequency factor are in the range 0.70 eV to 1.40 eV and 4.49 × 107 to 2.85 × 109 s−1 respectively.

On the Urbach's formula for evaluation of electron trapping parameter: The case of persistent luminescent materials

Urbach's formula for evaluation of electron trapping parameter that happens to be the earliest has emerged as a popular method amongst researchers of persistent luminescence. In this study, we analysed the thermoluminescence curves of glow-in-the-dark phosphors. Those included some curves recorded by us and others that solely used the Urbach's formula. Using the parameter obtained by rigorous analysis by fitting the whole TL curves, we presented a comprehensive picture of the potentialities and limitations of the simple Urbach's relation E=Tm/500, where E is the trap-depth and Tm the peak temperature in absolute scale, first proposed by Urbach in 1930. Some simple thumb rules on the use of the formula were presented for beginners as well as non-specialists so that entry of physically unrealistic data into the literature was prevented.

Systematic comparison of saturation effects and afterglow properties of Sr4Al14O25:Eu, Dy phosphor excited by alpha and beta ionizing sources and UV light

This study reports on the radioactive- and photo-charging effects related afterglow properties of the long-afterglow Sr4Al14O25:Eu, Dy phosphor (SAED). Saturation and oversaturation behavior, trapping and de-trapping sequences, decay profiles and resistivity of SAED to alpha, beta and UV excitations are detailed. Thermoluminescence and afterglow measurements were performed on SAED subjected to different irradiation dose/time. In order to determine the saturation point of SAED, phosphors were charged by 0.5–800 Gy dose using radioactive alpha and beta sources and for 0.02–900 min by near UV light. By radioactive excitations only a saturation tendency was observed, whereas clear indication of oversaturation was found for photo-charging. Different saturation tendencies were also observed as a function of average SAED particle size due to the different penetration depth and efficiency of the excitation radiations. A uniform de-trapping sequence, but an opposite trapping sequence was found for ionizing radiation and for UV charging due to secondary excitation effects of high-energy irradiation. After the saturation point, a slight reduction of charge carrier concentration and PL intensity were observed. This was evidenced by the shifting dominant components of the modeled afterglow and TL curves. Repeated charging by ionizing radiation does not effected the afterglow properties of SAED adversely. On the other hand, thermal exposure up to 350 °C reduced photoluminescence intensity even in inert atmosphere.