Thermostimulated Luminescence Peaks Research Articles

Influence of composition on luminescence properties of Cd1-xZnxWO4 solid solutions

A set of single-phase Cd1-xZnxWO4 (x = 0–1) solid solutions synthesized by spontaneous crystallization technique was studied by the methods of luminescence and electron paramagnetic resonance (EPR) spectroscopy. Luminescence spectra of all studied solutions are characterised by a single emission band related to the intrinsic emission of self-trapped excitons. The dependence of luminescence spectra and thermostimulated luminescence (TSL) curves on solution composition was investigated, and the origin of TSL peaks was analysed on the basis of the EPR data. It is shown that the values of optical bandgap and activation energy of luminescence thermal quenching gradually change with solution composition. Several phenomena are observed in solid solutions predominantly at intermediate concentrations of Cd and Zn cations that can be connected with the structural disorder of the solid solutions. In particular, the deviation of lattice parameters from the Vegard's law, the redshift and broadening of the emission band, the suppression of low-temperature (T < 80 K) TSL peaks related to self-trapped holes and the broadening of high-temperature (100–200 K) TSL peaks related to structural defects. The structural disorder arises due to the non-homogeneous distribution of substitutional atoms in cation lattice sites, pronounced because of the mismatch in ionic radii of substitutional cations, which reaches 28.3 % for Cd2+ and Zn2+.

Shallow and deep trap levels in X-ray irradiated β-Ga2O3: Mg

The results of the investigation of thermostimulated luminescence (TSL) and photoconductivity (PC) of the X-ray irradiated undoped and Mg2+ doped β-Ga2O3 single crystals are presented. Three low-temperature peaks at 116 K, 147 K and 165 K are observed on the TSL glow curves of undoped crystals. The high-temperature TSL peaks at 354 K and 385 K are dominant in Mg2+ doped crystals. The correlation between doping with Mg2+ ions and the local energy levels of the intrinsic structural defects of β-Ga2O3, which are responsible for the TSL peaks and PC, is established. The nature of TSL peaks and the appropriate photoconductivity excitation bands are discussed.

Recombination luminescence of Cu and/or Ag doped lithium tetraborate single crystals

Complex investigations of thermostimulated luminescence (TSL) and radioluminescence properties of Li2B4O7 (LTB), LTB:Cu, LTB:Ag and LTB:Cu, Ag crystals suitable for tissue equivalent dosimeters were carried out in the temperature range 4.2–700K. TSL, cathodoluminescence and X-ray excited luminescence spectra are compared to those measured under photoexcitation. The emission band at 4.6eV in LTB:Ag is reliably related to Ag+ ions based on the comparison of the results of optical spectroscopy studies and first principle calculations. Energy transfer from the relaxed exited state of the Ag+ ion to the Cu+ ion in double-doped LTB:Cu, Ag crystals is demonstrated. Thermostimulated recombination of charge carriers in irradiated crystals is seen to take place mainly at oxygen sites at low temperatures and at impurity sites at high temperatures. For the first time, the appearance of the low-temperature TSL peak at 90K is assigned to ionic processes in LTB crystals. The appearance of pyroelectric flashes due to the lattice relaxation in the temperature region 90–240K is demonstrated and their surface-related nature clarified. In accordance with EPR studies the dosimetric TSL peaks in copper and silver doped LTB crystals are attributed to thermally released electrons recombining with Cu2+ and Ag2+ centres.

Effect of annealing on natural calcitic crystals—A thermostimulated luminescence (TSL) study

The quality crystals (Calcitic limestone) were selected using the UV–visible methylene blue adsorption method. The thermostimulated luminescence (TSL) glow curve characteristics of six well crystallized limestone samples were analyzed. The glow curves of unannealed sample show only one peak in the range 320–330 °C. The sample irradiated with a gamma dose of 100 Gy shows two additional peaks in the range of 113–125 °C and 242–260 °C when recorded with linear heating rate of 10 °C/s. The annealed sample also shows the same trend as that of irradiated sample. Annealing treatment above 250 °C increases the sensitivity of all TSL peaks except 320 °C. On the other hand, annealing at 750 °C caused a collapse in the TSL sensitivity. The enhancement in TSL sensitivity was found to depend on the annealing temperature and time. Annealing treatment at 650 °C for 4 h followed by quenching in air is the optimum condition for TSL sensitization. The response to gamma irradiation is linear in the range from 0.5 Gy to 10 4 Gy. The emission spectra of all the samples show an emission at around 610 nm but with different intensities for each TSL peak. With reference to earlier work, it may be assumed that the recombination site always involves Mn 2+ ions. The observation made through infra-red (IR) and X-ray diffraction (XRD) studies with thermal treatment shows the structural changes of calcite from D 3h to C s symmetry at 750 °C. The Thermogravimetric-Differential Thermal Analysis (TG-DTA) analysis shows the calcite gets disordered at 760 °C. Hence, the collapse in the TSL sensitivity at 750 °C is due to structural change or structural disorderedness.

Thermo-stimulated luminescence of ion-irradiated yttria-stabilized zirconia

Yttria-stabilized zirconia (ZrO2:Y3 + )single crystals (with 9.5 mol% Y2O3) were irradiated with ions (from 1 MeV He to 2.6 GeV U). Electronparamagnetic resonance (EPR) data show that two kinds of colour centres (F + -typeand T centres) are produced. Thermo-stimulated luminescence (TSL) data exhibit a quite strong peakat ∼ 500–550 K in the glow curves of all irradiated samples regardless of the ion species and energy. Moreover,the 3D-TSL measurements reveal that this peak is correlated with a light emission at a wavelength of ∼ 620 nm(i.e. photon energy ∼ 2 eV). The TSL peak maximum temperatures are consistent with characteristic temperaturesof about 500 K of annealing stages of colour centres. However, the trap-depthenergies (ranging between 0.7 and 1.4 eV) deduced from the initial rise of partiallycleaned TSL peaks, or from a rough approximation using Urbach’s formula, arerather larger than the activation energies for defect recovery, ranging between 0.3and 0.7 eV, as deduced from the EPR data. The processes involved in TSL arediscussed in relation to available photoluminescence and defect energy-level data.

A comparison between neodymium doped alumina samples obtained by Pechini and sol–gel methods using thermo-stimulated luminescence and SEM

Neodymium doped and undoped aluminum oxide samples were obtained using two different techniques: Pechini and sol–gel. Fine grained powders were produced using both procedures, which were analyzed using Scanning Electron Microscopy (SEM) and Thermo-Stimulated Luminescence (TSL). Results showed that neodymium ions incorporation is responsible for the creation of two new TSL peaks (125 and 265 °C) and, also, for the enhancement of the intrinsic TSL peak at 190 °C. An explanation was proposed for these observations. SEM gave the dimensions of the clusters produced by each method, showing that those obtained by Pechini are smaller than the ones produced by sol–gel; it can also explain the higher emission supplied by the first one.

Applicability and performance of an imaging plate at subzero temperatures

The performance of imaging plates (IPs) has not been studied at temperatures lower than 0 degrees C. In the present study, an IP was irradiated with gamma rays emitted from the mineral monazite at temperatures between -80 and 30 degrees C to determine its fundamental properties. The IP response as a function of irradiation time was found to be linear, suggesting that the IP works properly at low temperatures. Fading, an effect which should be considered at temperatures of more than 0 degrees C, was not observed at -30 and -80 degrees C. Furthermore, the fading-corrected PSL value of the IP irradiated at -80 degrees C was lower than at other temperatures (30, 5 and -30 degrees C). This can be explained by thermostimulated luminescence (TSL). Since the only intensive TSL peak in the temperature range from -80 to 30 degrees C is present at about -43 degrees C, some of the electrons trapped at F centers recombine with holes through the process of TSL before the stored radiation image is read out at room temperature. This finding suggests that the apparent sensitivity of the IP is lower at -80 degrees C although it is similar to sensitivities between -30 and 30 degrees C. This low sensitivity should be corrected to perform quantitative measurements.

Thermostimulated luminescence characteristics of dolomitic rocks and their use as a gamma ray dosimeter

The thermostimulated luminescence (TSL) glow curve characteristics of ten dolomitic crystals of Salem and Namakkal districts of Tamilnadu are analysed. The natural thermoluminescence (NTL) measurements were carried out for all the samples and show two peaks at 270 °C and 335 °C. The sample irradiated with a gamma dose of 200 Gy shows an additional peak at 180 °C, when recorded with linear heating rate of 10 °Cs −1. At the same time, the NTL peak at 270 °C is shifted to 260 °C while increasing in intensity and there is no change in the peak position of 335 °C. The annealed sample also shows the same trend. The sample was annealed in air at the temperatures ranging from 200 to 950 °C, at an interval of 50 °C, for 1 h duration. Annealing treatment above 250 °C increases the sensitivity of all three TSL peaks. On the other hand, annealing at 800 °C caused a collapse in the TSL sensitivity. The enhancement in TSL sensitivity was found to depend on the annealing temperature and time. Annealing treatment at 700 °C for 4 h followed by quenching in air is the optimum condition for TSL sensitization. The response to gamma irradiation is linear in the range from 0.5 to 10 4 Gy. The number of glow peaks was identified through partial heating method. Using peak shape and initial rise method the kinetic parameters (activation energy (E), frequency factor (S) and order of kinetics (b)) were evaluated. The investigations show that the trapping centers are not affected by the annealing procedure. The emission spectra of all the samples show an emission at around 608 nm but with different intensities for each sample. With reference to earlier work, it may be assumed that the recombination site always involves Mn 2+ ions.

Cr-related centers in Gd 3Ga 5O 12 polycrystals

The luminescence excitation spectra, emission spectra under photo- and X-ray excitation, luminescence decay kinetics and thermostimulated luminescence (TSL) of Gd 3Ga 5O 12 garnet (GGG) polycrystalline samples have been investigated. It was established that the spectrum of Cr 3+ ion emission were present in all TSL peaks. The activation energies of traps that are responsible for appearance of TSL in the region 295–600 K were estimated. It is shown that delocalization of electrons from the Cr 3+e traps leads to the appearance of thermoluminescence (TL) glow peak at 390 K. The nature of other TSL peaks is discussed. The influence of visible light on the TSL intensity of the preliminary X-ray-irradiated samples is shown.

Thermo- and photostimulated luminescence in LiF : Mg, Ti single crystals irradiated by ions and VUV light

A coordinated study of the relaxation of optical absorption induced by vacuum ultraviolet radiation, x-rays, and α -particles, as well as of photo- and thermostimulated luminescence (TSL) of LiF : Mg,Ti crystals (TLD-100) in the 295-750-K interval, has revealed that TSL regions characterized by activation energies E a = 2.2-2.4 eV and anomalously high frequency factors p 0 = 10 21 -10 22 s -1 alternate with regions where E a = 1.5 eV and p 0 = 10 12 -10 14 s -1 . The relative intensities of the TSL peaks produced by UV illumination (10-17 eV) differ strongly under the conditions of selective photon-induced generation of anion excitons, free electrons and holes, or near-impurity electronic excitations. The latter are responsible for the high efficiency of tunneling radi- ative (involving titanium centers) or nonradiative (involving hydroxyl ions) recombination. The analysis of TSL peaks of LiF : Mg,Ti and LiF took into account two-step processes, namely, thermal dissociation of three-fluo- rine molecules and recombination of the products of their decay ( V K and V F centers, H interstices).

Thermostimulated luminescence and electron spin resonance in X-ray- and photon-irradiated oxygen-deficient silica

Influences of oxygen-deficiency on radiation properties of high-purity, low-OH fused silica were studied. It is found that thermostimulated luminescence (TSL) peaks are different for photo (7.7 eV) and X-ray excitation at 77 K. X-ray excitation produces TSL peaks at 125 and 170 K corresponding to the anneal temperatures of two types of self-trapped holes centers STH 2 and STH 1, respectively, detected by electron spin resonance (ESR). Oxygen-deficiency apparently increases the number of electron traps, stabilizing a larger number of STHs in the continuous defect-free silica network than is observed in similarly X-irradiated stoichiometric silica glasses. Photoexcitation of oxygen-deficient glass at 7.7 eV produces TSL peaks at 105 and 200 K, presently attributed to STHs at perturbed sites in the immediate vicinity of oxygen-deficiency centers (ODCs). High temperature TSL peaks at 240 and 400 K are produced by both types of irradiations and are followed by ESR detection of E′ centers only. All observed TSL and ESR signals were proportional to the level of oxygen-deficiency. The main spectral band in TSL near 2.7 eV is a triplet–singlet transition, ascribable to the twofold-coordinated silicon center (ODC(II)) modified by its nearest structure. It is proposed that this recombination process results when a thermally detrapped STH encounters an electron trapped at the site of ODC(I), and is transmuted into a modified ODC(II):e −. In principle, any such ODC:e − defect should be paramagnetic. However, no trapped-electron centers were detected by ESR in the present experiments. Based on the recent work of others, the E α ′ centers that were observed are believed to be trapped hole centers. Thus, for reasons unknown, the postulated ODC(II):e − centers, which may be the primary electron traps in oxygen-deficient silicas, appear to be ESR-silent.

Energy transfer and charge carrier capture processes in wide‐band‐gap scintillators

AbstractElectron and hole trapping phenomena below room temperature were studied by simultaneous use of electron paramagnetic resonance (EPR) and thermostimulated luminescence (TSL) experiments in Ce‐doped YAlO3, Y3Al5O12 and Lu3Al5O12 single crystals. Charge‐carrier trapping associated with O– centers and antisite Y(Lu)Al defects in perovskite and garnet structures, respectively, was evidenced by EPR and associated with the dominant TSL peaks. Existence of F+ centers was proved by EPR in YAlO3. A Ce3+ ion at the Al site and spatially correlated CeLu and LuAl centers were evidenced in Lu3Al5O12 by the same method. Spatial correlation of the latter two centers is further supported by the associated tunneling‐driven radiative recombination process evidenced by phosphorescence decay. (© 2007 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Dependence of accumulated luminosity of thermostimulated luminescence on type of the electron–hole center distribution in a crystal

The thermostimulated luminescence (TSL) was modeled by the method of the cellular automation within the temperature range 77–400 K. The TSL modeling was performed under the initial distribution of electrons and holes on a surface of multifractal and chaotic types, differing in homogeneity, level of orderliness and value of the informational entropy. Dependence of the entropy on the temperature at which the sample is heated to, shows that at the temperature corresponding to the TSL peak, the informational entropy of the system does not change. This fact proves that the multifractal structure has a great stability factor. As it was revealed that in addition to the crystal–chemical, physical–chemical and geological factors, the structure factor, characterized by the type of the electron–hole center distribution in a crystal, exerts an influence on the thermostimulated luminescence process.

Thermostimulated luminescence properties of CaSO4:Dy and CaSO4:Tm phosphors annealed at high temperatures

AbstractPre‐irradiation annealing at temperatures ≥800 °C in air drastically reduces the 230 °C dosimetric thermostimulated luminescence (TSL) peak in CaSO4:Dy/Tm and simultaneously the 60 °C and 120 °C peaks are strongly enhanced. In samples sintered at 1000 °C, the dosimetric peak vanished totally while the low temperature peaks exhibit a high TSL sensitivity. Moreover, the PL intensities decrease drastically on high temperature sintering; a reduction by as much as 75% is seen at 1000 °C. Photo‐transfer studies indicate that the 60 °C peak might originate from electron release while the 120 °C peak from hole release. These two low temperature TSL peaks could have potential applications for photostimulation. (© 2005 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)

Thermally and optically stimulated radiative processes in LiBaF3 crystals

In LiBaF3 crystals both valence–core transitions (5.4–6.5eV) and so-called self-trapped exciton luminescence (about 4.3eV) are important for practical application. Here, we present a study of 4.3eV luminescence under photo- and thermostimulation after X-irradiation of undoped LiBaF3 crystals at various temperatures. Optically stimulated luminescence as a result of electron recombination with both self-trapped holes and holes localized at some defects, were observed after X-irradiation below 130K and that of electron recombination with defect-localized holes was observed after X-irradiation above 130K. The spectra of thermo-stimulated luminescence (TSL) contain a broad band about 4eV related to the electron (high-energy side) or hole (low-energy side) recombination depending on TSL peak temperature.

Behaviour of F and Fz Centres Under Thermal Stimulation in KCl:Eu2☎ Irradiated with Ionizing and UV Radiation

The optical absorption (OA) of F and Fz, centres in beta-and UV-irradiated KCl: Eu2☎ have been studied. The spectra measured at room temperature and during the subsequent heatings up to 600 K, were analyzed by a deconvolution procedure. The OA bands of the F and Fz centres are well described respectively by asymmetric and symmetric gaussiane with parameters that are linearly dependent on the temperature. The thermal stability of the Fz centres correlates with the low-temperature thermostimulated luminescence (TL) peaks. The stability of the F centres is determined at least by two processes. Part of the F centres is destroyed together with the Fz centres. The remaining ones are destroyed during further heating up to 470 K, correlating with the TL peak at 425 K (at heating rate of 0.1 K/s).

Influence of (group IIB) codopants on the thermostimulated luminescencesensitivity of CaSO4:Dy/Tm

Thermostimulated luminescence (TSL) phosphors based onCaSO4:Dy, Zn and CaSO4:Tm, Cd have been studied. These phosphors show anincrease in the 220 °C TSL peak intensity by a factor of about 50%compared to CaSO4:Dy, as there is no change in the position of the peaktemperature. Their dose response characteristics to 60Co gamma radiationis similar to that of CaSO4:Dy. However, there are very minor changes intheir photoluminescence intensity and excitation spectra compared with thoseof CaSO4:Dy.

Thermostimulated luminescence, photoluminescence and X-ray-induced luminescence in CaSO 4 : Ce; CaSO 4 : Ce, Na; CaSO 4 : Ce, Mn and CaSO 4 : Ce, Mn, Na phosphors

Thermostimulated luminescence (TSL) and photoluminescence (PL) studies were carried out on CaSO 4 : Ce; CaSO 4 : Ce, Na; CaSO 4 : Ce, Mn and CaSO 4 : Ce, Mn, Na phosphors with the aim of studying their PL and TSL processes as well as the energy transfer and the effect of charge compensation. Following γ-irradiation, a drastic reduction in Ce 3+ fluorescence was observed in all these samples. To explain the peculiar nature of the TSL glow curve of CaSO 4 : Ce, the γ-ray-induced oxidation of Ce 3+ ions (i.e., Ce 3+→Ce 4++e −) is proposed as a viable mechanism of hole trap production. Post-irradiation thermal annealing and optical bleaching data shows a coincidence between one of the recovery steps of Ce 3+ fluorescence and the 400°C TSL peak readout. However, dramatically opposing trends were witnessed in the PL and TSL efficiencies of CaSO 4 : Ce 3+ with the co-doping of Na + charge compensator. The presence of Ce 3+ emission in the Mn 2+ induced 92°C peak as well as the differences in the emission spectra of Mn 2+ in the TSL glow peaks and in the PL spectra of Mn 2+ excited via Ce 3+ in CaSO 4 : Ce, Mn indicate the absence of energy transfer from one activator ion to another during TSL. The glow peak temperature-dependent spectral emission of CaSO 4 : Ce, Mn as well as the X-ray-induced luminescence spectral data are however consistent with the energy transfer model proposed by Morgan and Stoebe. Unlike the results reported in literature, the TSL sensitivity of 400°C peak in CaSO 4 : Ce, Mn is found to be less than that in CaSO 4 : Ce.

Thermostimulated Luminescence of PbWO4, Bi2WO6, and Y2WO6 Ceramics

Thermostimulated luminescence (TSL) of PbWO4, Bi2WO6, and Y2WO6 ceramics on x-ray excitation is investigated. The spectral luminosity of the thermostimulated luminescence is analyzed. The thermal activation energies conforming to the corresponding thermostimulated luminescence peaks are determined. It is established that on emptying trapping centers radiative recombination occurs at the intrinsic-luminescence centers associated with tungsten-oxygen complexes WO42−.

Thermostimulated Luminescence, Exoelectron Emission and X-Ray Induced Luminescence Studies in CaSO4 : Eu and CaSO4: Eu, Na

X- and UV radiation induced thermostimulated luminescence (TSL), thermostimulated exoelectron emission (TSEE) and X-ray induced luminescence (XIL) studies in CaSO4 : Eu and CaSO4 : Eu, Na reveal that the X-ray induced TSL peaks exhibit Eu2+ (blue) and Eu3+ (red) emissions — but their relative ratio varies with the peak. In contrast, UV induced TSL peaks exhibit only Eu3+ emission. Even in the CaSO4 : Eu sample, which contains both Eu2+ as well as Eu3+, no Eu2+ emission is seen in all the TSL peaks produced by UV irradiation. These results confirm that the X-ray induced TSL in these phosphors is best explained by the energy transfer model while UV induced TSL is best explained by the charge transfer model. In CaSO4 : Eu, the X-ray induced TSEE peak coincides exactly with the 400 K TSL peak whereas the UV induced TSEE is negligible. This indicates an Auger-like decay of electrons following the self-absorption of 400 nm Eu2+ emission due to the 400 K TSL peak. Intense XIL in CaSO4 : Eu occurs mainly due to Eu2+ emission which decreases with increasing irradiation temperature from 100 K perhaps due to thermal quenching. But the significant variation in XIL intensity in the temperature interval 350 to 450 K is attributed to Eu2+ → Eu3+ oxidation. XIL in CaSO4: Eu increases with X-ray intensity but is nearly independent of X-ray exposure time. These results suggest that XIL emission is probably caused by metastable Eu2+ centers formed during X-irradiation.