TSL Peak Research Articles

Anomalous thermal stability of the [GeO4]- Electron Paramagnetic Resonance signal and the 110 °C Thermally Stimulated Luminescence peak in natural and synthetic quartz

In this work we studied the thermal stability of the 110 °C TSL peak of quartz in both natural and synthetic samples. We compared it with the thermal stability of the [GeO4]- paramagnetic signal with EPR. Our findings show that both these signals decay at the same rate, however, the rate is significantly different between samples. In particular, a couple of samples, a pegmatitic one and a fired synthetic one, showed a drastically increased decay time of both the TSL peak and the EPR signal well beyond the expected experimental fluctuations. The decay time of these two samples differs by almost by a factor two with respect to the average value of all the other samples.

The Effect of Pre-irradiation Defects on the Recombination Luminescence in Activated Crystals K2SO4

The recombinational luminescence of crystals of K2SO4-Mn2+ and K2SO4-Ni2+ is studied in the article. It is established that impurity ions form the radiation induced centers. The cause of changes of the distribution of lightsum on TSL peaks of a matrix is established. It is proposed that it is related to pre-radiation defeсts in crystals. It is established from this effect that ions of Mn2+ and Ni2+ selectively replace cations in a crystal lattice of potassium sulfate.

TSL and fractional glow study of Ge-doped α-quartz

Crystalline α-quartz doped with 0.1wt% and 0.9wt% germanium was studied using TSL and FGT equipment. Sample was chosen because previously it is known that Ge in quartz is efficient trap for electrons, therefore it could be used for detection of hypothetic self-trapped hole in α-quartz. However previous investigations of ODMR and TSL shows that in α-quartz the hole is still mobile and trapping occurs only on defect states. The activation energies for both TSL peaks are found by fractional glow and Hoogenstraaten method. The TSL distribution changes depending on Ge concentration and also on irradiation type. The TSL peaks below 70K in quartz doped with Ge could belong to hole trapped on Ge.

Radioluminescence of synthetic and natural quartz

Abstract The effect of X-ray irradiation and thermal treatments on the radio-luminescence emission spectrum of both a natural pegmatitic quartz and a synthetic one was investigated. All the emission spectra could be deconvolved into the same set of five Gaussian components. Among the identified RL bands, a blue emission at 2.53 eV (480 nm) is enhanced under X-ray irradiation. A strong correlation with the sensitization of the so called “110 °C” TSL peak (in our measurements seen at lower temperature due to the lower heating rate) was proved, suggesting that the recombination centers associated with the 2.53 eV band are produced under X-ray irradiation and are involved in both RL and TSL luminescence mechanisms. When each irradiation was followed by heating up to 500 °C a strong sensitization of the RL band emitting at 3.44 eV and of the 110 °C TSL peak were observed. A perfect correlation between the RL and TSL emissions suggests that the recombination centers involved in the RL and TSL emissions are the same.

Defect states in Pr3+ doped lutetium pyrosilicate

We study defect states in Pr3+-doped Lu2Si2O7 crystal by wavelength resolved thermally stimulated luminescence both below and above room temperature. We identify the TSL peaks, analyze them by the initial rise technique and calculate the characteristic parameters of the corresponding traps. The role of tunnelling of charge carriers between traps and recombination centers up to RT is observed and discussed. The TSL spectra show that the charge carrier recombination predominantly occurs at Pr3+ centers. We also provide some comparison with the LPS:Ce3+ crystal prepared by the same method.

Luminescence and point defects in cerium-doped lutetium scandium orthoborate crystals

Cerium-doped lutetium scandium orthoborate single crystals as potential scintillation materials were grown by the floating zone (FZ) method for the first time and the Czochralski (Cz) grown crystal was used for comparison. In this paper, the representative composition Lu0.5Sc0.5BO3:0.5at%Ce (abbreviated as LSBO:Ce) was selected as the research target. The phase structure of FZ-grown LSBO:Ce crystal was characterized by X-ray diffraction and its optical properties were investigated using photoluminescence emission (PL), excitation (PLE), radioluminescence (RL) spectra. The defect properties of LSBO:Ce crystals were studied by thermoluminescence (TL) as a function of temperature (300–600 K). The glow curve of FZ-grown LSBO:Ce crystal shows three TSL peaks, at 350, 400, 552 K, corresponding to a trap depth of 0.99, 1.14 and 1.50 eV, respectively. Based on UV-irradiation TL measurements and air-annealing experiments, the former two kinds of traps could be ascribed to the radiation-induced defects and the third kind originated from the oxygen vacancies formed during crystal growth. These defects also existed in the Cz-grown LSBO:Ce crystal.

Peculiarities of Radiation Effects in MgO:Mn<sup>2+</sup> Crystals

The thermally stimulated luminescence and IR absorption spectra of MgO:Mn2+ crystals irradiated in different reactors have been studied. It has been shown that dependence of TSL peaks (450 and 550 K) and optical absorption bands (3290, 3720 and 1600 cm-1) on neutron fluence correlate. The trend of these changes in the same fluence range (1014-1017 n/cm2) depends both on the initial state of the crystal and on the irradiation source, which may be explained by the “small dose effect”.

Recombination processes and luminescence in Li6GdxY1−x(BO3)3-Eu crystals

The results of investigation of thermally stimulated recombination processes and luminescence in Li6GdxY1−x(BO3)3-Eu crystals are presented. The steady-state luminescence spectra under X-ray excitation (XRL), the temperature dependence of steady-state luminescence intensity and the thermally stimulated luminescence curves (TSL) were measured at 90–500 K. In the steady-state X-ray luminescence spectra the band at 312 nm related to 6PJ→8S7/2 transitions in gadolinium ion and bands group at 580–700 nm associated with 5D0→7FJ transitions (J = 0…4) in Eu3+ ion were found to be dominant. The intensity of steady-state XRL of these bands in undoped crystal is increased by 15 times as the temperature changes from 100 to 400 K. The probable mechanisms of temperature dependence of steady-state luminescence intensity and their association with energy transfer of electronic excitations in these crystals are discussed. The investigations have shown the principle complex TSL peak with maximum at 150 K and a number of weaker peaks. The thermal activation parameters (activation energy, pre-exponential factor, kinetic order) for all intense TSL peak have been determined. The origin of small trapping centres caused TSL below room temperature and their association with defects in lithium cation sublattice is discussed.

Defect states in Lu 3Ga xAl 5−xO 12 crystals and powders

We study defect states in undoped and Eu 3+-doped Lu 3Ga x Al 5− x O 12 ( x = 0–5) garnet crystals by wavelength resolved thermally stimulated luminescence above room temperature. Eu 3+ ions act not only as recombination centres but also as high temperature traps, as testified by the presence of a TSL peak at 450 °C correlated with Eu 3+-doping. With increasing gallium content all glow peaks are shifted to lower temperatures. This trend is confirmed also for powder samples prepared by sol–gel technique. The observed low temperature shift of the glow peaks can be considered as a consequence of the band gap reduction following the increase of Ga 3+ concentration. The comparison with the glow curve of a Ce 3+-doped crystal is also shown.

Luminescence Properties and Their Temperature Dependence of ${\rm Lu}_{2}{\rm Si}_{2}{\rm O}_{7}:{\rm Ce}$ Scintillation Crystals

Cerium-doped lutetium pyrosilicate (LPS:Ce) crystal with dimension of Φ 10 × 40 mm was grown successfully by Czochralski method. Its crystal structure was determined to be monoclinic with space group of C2/m. The optical transmission, UV and X-ray excited emission spectra, as well as decay curves were measured from 77 K to 500 K. Two emission peaks, 380 nm and 403 nm result from the transition of electrons from 5d1 to two ground levels (2F5/2 and 2F7/2) of Cerium ions (Ce3+) in the LPS:Ce crystals. The decay time of the fluorescence is weakly increasing from 77 K to 400 K and then decreases sharply. The light output of LPS:Ce can be improved greatly by annealing at 1400°C in air. TSL peak at 543 K in LPS:Ce is suggested to be related to oxygen vacancies which are one of the reasons of the poor light output.

Characterization, photoluminescence and correlation between thermoluminescence and ESR of combustion synthesized [formula omitted] material

Samarium-doped monoclinic CaAl 2 O 4 phosphor was prepared at furnace temperatures as low as 500 °C in a short time of 5 min by using the combustion route. Powder X-ray diffraction and scanning electron microscopy studies were used to characterize the prepared combustion powder. Photoluminescence spectra revealed that samarium ions are present in trivalent oxidation states. The CaAl 2 O 4 :Sm exhibits two thermoluminescence glow curves at around 135 and 325 °C. The defect centres formed in the phosphor are studied using the technique of electron spin resonance (ESR). Irradiated CaAl 2 O 4 :Sm shows ESR lines due to a radiation induced Fe 3 + ion and a defect centre. The defect centre is characterized by an isotropic g -value 2.0036 and is assigned to an F + centre. The radiation induced Fe 3 + ion appears to correlate with the main TSL peak at 325 °C.

Carriers trapping and radiative recombination in Ce, Eu and Pr-doped [formula omitted] crystals

The optical properties of as-grown and X-ray irradiated Ce, Eu and Pr-doped LiLuF 4 crystals, prospective for lasers, display panels, fluorescent lamps and scintillation application, are presented. The luminescence of Ce 3 + -doped crystal exhibits the fast radiative spin-allowed df transitions in the UV region, whereas Pr 3 + containing sample shows the UV df and visible ff emissions. LiLuF 4 : Eu reveals the line emission spectrum of Eu 3 + ions and the band peculiar to Eu 2 + ion as well. It was found that the X-ray induced absorption bands and the TSL peak positions are independent of the type of RE 3 + impurity due to intrinsic nature of radiation defects. The total radiation damage and TSL spectra are specific for each dopant. The distinctive features of the energy storage in RE-doped LiLuF 4 crystals are discussed with respect to redox reaction and level positions of RE ion within the gap.

Luminescence and decay of excitons in lead tungstate crystals

A brief review of recent results obtained at systematic study of the luminescence and photo-thermally stimulated defect creation processes in various undoped and doped PbWO 4 crystals is presented. Origin of the blue—B and two green—G(I) and G(II) emissions is clarified. Various localized exciton states are identified and their decay into defects is found. Origin of the defects, created at the decay of self-trapped and localized exciton states and MoO 4 2 - -related states, is studied both by TSL and ESR methods. The origin of the TSL peaks and the mechanisms of defect creation and recombination processes are discussed.

X‐irradiation induced photo‐ and thermostimulated luminescence of CsCdF 3 :Mn crystals

Photo- and thermostimulated luminescence (PSL and TSL respectively) of previously X-irradiated CsCdF3 crystal doped with Mn were investigated. After X-irradiation of CsCdF3 crystal at 8 K PSL bands at about 300 nm and 550 nm appear. Several stimulation bands can be revealed for luminescence at 300 nm and 550 nm. The stimulation band at 340 nm is related to an F-type centre absorption band in accordance with the Mollwo-Ivey relation for halide crystals. Subsequent heating of the crystal after X-irradiation at 8 K shows TSL peaks in the temperature regions 8 K – 90 K and 200 K – 300 K. The spectral composition of the TSL involves both bands at 300 nm and 550 nm. Experiments performed allow us to suggest that the PSL band at 300 nm should be the result of electron recombination with self-trapped holes (STH), but the luminescence at 550 nm is related to Mn ions. The mechanisms of radiative recombinations as well as the thermal stability of both STH and Mn ions are discussed. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Thermostimulated recombination processes in LiBaF3 crystals

The creation of radiation defects in LiBaF3 crystals at 10K and the processes of their thermostimulated recombination are investigated. The methods of optical absorption, thermal bleaching of color centers, thermostimulated luminescence and fractional glow technique are used. The radiation defects anneal in a multi-stage process accompanied with thermo-luminescence at 20, 46, 105, 130, 170, 210 and 270K. Differences in the optical absorption spectra measured before and after the TSL peaks are obtained and recombination parameters are determined. The TSL peak at 20K arises from the delocalization of H-centers. The presence of two TSL peaks related to VK-centers at 105 and 130K indicates that 60° and 90° migration hops occur.

Electron traps related to oxygen vacancies inPbWO4

Four types of electron traps in ${\mathrm{PbWO}}_{4},$ based on regular W sites perturbed by oxygen vacancies, are identified by electron spin resonance (ESR). The analysis of the ESR spectra parameters $(g$-factor values and principal-axes orientations) shows that the revealed centers are $({\mathrm{WO}}_{3}{)}^{\ensuremath{-}}$ vacancy-containing complex anions associated with a defect in the Pb sublattice: $({\mathrm{WO}}_{3}{)}^{\ensuremath{-}}\ensuremath{-}{A}_{\mathrm{Pb}}$ complexes. Two of the centers $({\mathrm{W}}_{1}$ and ${\mathrm{W}}_{2})$ are thermally stable up to 350--370 K, while the other two $({\mathrm{W}}_{3}$ and ${\mathrm{W}}_{4})$ are stable only up to 270--290 K. Above these temperatures the trapped electrons become free and recombine with localized holes, giving rise to a composite TSL glow peak at $T\ensuremath{\approx}323\mathrm{K}$ (characterized by a trap depth of 0.9 eV evaluated by the initial rise method) and to a weaker TSL structure at $T\ensuremath{\approx}365\mathrm{K}.$ The correspondence between $({\mathrm{WO}}_{3}{)}^{\ensuremath{-}}\ensuremath{-}{A}_{\mathrm{Pb}}$ centers and TSL peaks is supported by their similar room temperature time decays, and by the similar dependences of ESR and TSL signals upon annealing treatments. A scheme of local electronic levels in the band gap of ${\mathrm{PbWO}}_{4}$ is proposed.

Preparation, dosimetric characterisation and investigation of related TSL defect centres in Li3Po4:Mg,Cu phosphor.

L3PO4:Mg,Cu, a low effective atomic number and high sensitivity TSL phosphor, has been prepared. Its TSL glow curve shows a major peak around 360 degrees C with minor peaks around 110 degrees C and 230 degrees C. The optimum concentrations of the dopants are found to be 200 ppm each. Its gamma sensitivity is 1.2 times as compared to CaSO4:Dy (0.1 mol%). The optimum preirradiation annealing treatment is found to be 650 degrees C, 15 min. Its PL emission shows a band at 370 nm with excitation band at 250 nm. Dose to TSL response shows that its response is linear up to the gamma dose of 100 Gy for irradiations carried out at RT. An irradiated sample shows a distinct new ESR signal, which is tentatively assigned to an electron/hole localised on one of the oxygen(s) of the phosphate group. Step annealing experiments show decay of the defect centre around 340 degrees C. This correlates well with the TSL peak around 360 degrees C.

New thermostimulated luminescence phosphors based on CaSO 4 : Ag, RE

Ag co-dopant in CaSO 4 : RE phosphors shifts its major TSL peak from 200°C to ∼375–400°C. Similar to the case of CaSO 4 : RE phosphors, the emission spectra of CaSO 4 : Ag, RE is, however, characteristic of the RE 3+ ion. Tm and Dy are the two RE dopants in CaSO 4 : Ag, RE which give the highest TSL sensitivity to gamma radiation. Their sensitivities are comparable to those of CaSO 4 : Tm/Dy. The TSL response of CaSO 4 : Ag, Tm/Dy was found to be linear with γ-dose and irradiation temperature independent up to 280°C.

Characterisation and Modelling of the 450 K TSL Peak of Alpha Alumina by the Simultaneous Analysis of TSL, TSC and TSEE

The TSL peak D' (450 K) of α-alumina is commonly used for ionising radiation dosimetry. Generally, it is simultaneously accompanied by TSC and TSEE peaks. In this work, peaks D' are characterised by using a previously described model in which the defect associated with peak D' is considered as an electron trap and the TSEE resulting from the thermionic effect. The comparison with experimental data does not invalidate these basic hypotheses.

Point defects related to 260 K thermostimulated luminescence in α-Al2O3

Thermo- and photostimulated processes are studied in reduced hydrogen containing α-Al 2 O 3 excited by UV light. It is found that UV excitation in F absorption band at 90 K results in a ionization of the F-centers and capture of released electrons at defects thus producing an anisotropy absorption band at 4.2 eV and the dominant thermoluminescence (TL) peak at 260 K. The 260 K TSL peak is accompanied by complete bleaching of the 4.2 eV absorption band and vice versa-by light stimulation in the region of the 4.2 eV band the 260 K TSL peak disappear and released electrons recombine with F + -centers. Both the effect of the preliminary high-temperature thermal treatment of samples on formation of 4.2 eV-centers and the observed dichroism characteristics allows to conclude that corresponding complex defect contains hydrogen and can involve vacancy pair.