Optically and thermally stimulated luminescence characteristics of MgO:Tb3+

In this paper main optically stimulated luminescence (OSL) and thermoluminescence (TL) characteristics are presented of a newly synthesised material MgO doped with terbium (Tb) developed at the Institute of Nuclear Science, Vinca. A thermally stimulated emission spectrum showed the characteristic lines of Tb3+ in a wide range of wavelengths. The TL sensitivity of the main TL glow peak at 315 degrees C is 1.7 times higher than the TL of Al2O3:C. The highest OSL sensitivity was obtained under green lamp (500-570 nm) stimulation. The fast component in the OSL decay curve is 2.4 times faster than Al2O3:C. The OSL signal is linear with dose up to 10 Gy. The lower limit of detection was found to be 100 microGy. These first results show that the newly synthesised material has some promising properties for the application in radiation dosimetry.     

Optically stimulated luminescence in retrospective dosimetry

Since the beginning of the 1990s the exploration of optically stimulated luminescence (OSL) in retrospective accident dosimetry has driven an intensive investigation and development programme at Ris? into measurement facilities and techniques. This paper reviews some of the outcomes of this programme, including the evaluation of the single-aliquot regenerative-dose (SAR) measurement protocol with brick quartz and the determination of dose-depth profiles in building materials as a guide to determining the mean energy of the incident radiation. Investigations into heated materials are most advanced, and a lower detection limit for quartz extracted from Chernobyl bricks was determined to be <10 mGy. The first results from the measurement of doses in unheated building materials such as mortar and concrete are also discussed. Both small-aliquot and single-grain techniques have been used to assess accident doses in these cement based building materials more commonly found in workplaces. Finally some results of a preliminary investigation of the OSL properties of household chemicals are discussed with reference to their potential as accident dosemeters.     

Optical properties of sol–gel derived Sr2SiO4:Dy3+ – Photo and thermally stimulated luminescence

Trivalent dysprosium-doped strontium silicate (Sr₂SiO₄) phosphors were prepared by sol–gel synthesis using tetra ethyl orthosilicate (TEOS) as precursor. The synthesis temperature could be brought down to 600 °C for formation of a single phase sample. The material was characterized by X-ray diffraction (XRD), Scanning electron microscopy (SEM), photoluminescence (PL), and thermally stimulated luminescence (TSL). The luminescence study revealed strong ⁴F_9/2 → ⁶H_13/2 transition at 577 nm (yellow), strong ⁴F_9/2 → ⁶H_15/2 transition at 482 nm (blue) and weak ⁴F_9/2 → ⁶H_11/2 transition at 677 nm (red), when excited by 250 nm (Charge transfer band, CTB) or 352 nm (f–f band). The concentration of the dopant ion and the temperature of annealing were optimized for maximum PL intensity. The critical energy-transfer distance for the Dy³⁺ ions was evaluated based on which, the quenching mechanism was verified to be a multipole–multipole interaction. The thermally stimulated luminescence studies of Sr₂SiO₄:Dy³⁺ sample showed main TSL glow peak at 413 K. The trap parameters namely activation energy (E), order of kinetics (b), and frequency factor (s) for this peak were determined using glow curve shape method.     

Optically stimulated luminescence in an imaging plate using BaFi:Eu

BaFI:Eu phosphors are fabricated using a new method of synthesis: liquid phase synthesis, in which the phosphor particles are formed through the association of Ba2+ ions, F-ions and Eu2+ ions in solution. An intense optically stimulated luminescence (OSL) peak at about 410 nm is observed by stimulating X ray irradiated BaFI:Eu phosphor with about 550-750 nm light. It is found that the peak wavelength of the optically stimulation spectrum is about 690 nm. This result suggests that the semiconductor laser can be used as the stimulating light source. It is also found that the OSL intensity is increased with increasing the X ray dose. The BaFI:Eu phosphor as a photostimulable material for the imaging plate of a computed radiography system provides the following advantages; (1) high X ray absorption coefficient, (2) high monodispersion in size which would contribute to sharp images, (3) high OSL and thus low luminescence mottle and (4) high DQE (detective quantum efficiency).     

Optically stimulated luminescence from Al2O3:C irradiated with relativistic heavy ions.

Optically stimulated luminescence (OSL) from Al2O3:C (ALOC) irradiated with selected heavy ions (4He, 12C, 40Ar, and 56Fe) was examined for discussion on the effectiveness of ALOC for space radiation protection dosimetry. The OSL efficiency on the absorbed dose basis was almost unity for He (LETinfinity x H2O: 2.2 keV x microm(-1)) and decreased with increasing LET for C (14 keV x microm(-1)), Ar (91 keV x microm(-1)), and Fe (198 keV x microm(-1)); a notable reduction greater than 60%, was observed for Fe ions. The linearity in dose response and the angular independence for the heavy ions were fairly good (+/- <15%) Although further experimental studies are clearly necessary, these results suggest that small ALOC chips can be a part of an integrating dosimetry system in future space missions.     

On the quasi-equilibrium problem in thermally stimulated luminescence and conductivity

Strong doubts havc been expressed about the validity of the quasi-equilibrium (QE) assumption used in the derivation of the analytical expressions of thermoluminescence (TL). So far there is no established method available to check if QE actually prevails during the emission of an experimental TL signal. The present study shows that the level of QE changes with a change in the heating rate beta. The change in the level of QE in its turn gets reflected in a change in peak shape when the system turns to a non-QE condition. This property is used as the first ever experimental method to test whether or not the emission of a given glow peak occurs under the QE condition. An essential condition for holding the QE condition is found to be T(R)/taum> or = 10(-3) where T(R) and taum are the glow peak recording duration and the maximum value of the free carrier lifetime, respectively. This relation between T(R) and taum is useful in finding the approximate value of taum. The value of taum being a function of the concentration and cross section of the TL related centres, one may be able to assess these basic parameters from the study of TL glow curves. The theoretical results are discussed in the perspective of LiF (TLD-100).     

Ionisation density dependence of the optically and thermally stimulated luminescence from Al2O3:C

This paper presents an overview of recent results on ionisation density dependence of the thermally stimulated luminescence (TL) and optically stimulated luminescence (OSL) signals from Al2O3:C, with emphasis on the sensitivity, efficiency, shape of the TL/OSL curves and the emission spectrum. High-ionisation densities are created uniformly by accumulated high doses of low-linear energy transfer radiation (gamma, beta, X rays) or non-uniformly in heavy charged particle tracks, even at low fluences, as in the case of space radiation fields. Significant deep trap filling, which occurs at these high-ionisation densities, ultimately results in changes in the concentration of recombination centres (F+-centres) and, consequently, in sensitivity changes and other effects. An OSL emission band at 335 nm has been observed in addition to the main F-centre luminescence band, and the relative intensities of these bands have been observed to be dependent on the ionisation density. The implications of these results and open issues are discussed.     

Photoluminescence,thermally stimulated luminescence and electron paramagnetic resonance studies of U6+ doped BaSO4

U⁶⁺ doped BaSO₄ samples were synthesized by precipitation route. PL, TL and EPR investigations of γ and self α irradiated samples were carried out. PL spectra of these samples give structured broad band peaking around 518 nm with five vibronic bands centred around 498·4, 516·0, 533·7, 554·0 and 575·1 nm, respectively and the average frequency of symmetric stretching of O=U=O in the ground electronic state was found to be 674 cm^?1. Trap level spectroscopic studies of U doped BaSO₄ give glow peaks at 411, 488 and 512 K, respectively and their spectral characteristics are typical of UO \(_{2}^{2+}\) emission. EPR studies of γ-irradiated U⁶⁺:BaSO₄ sample have shown the presence of sulphoxy centred radicals like SO \(_{4}^{-}\) and SO \(_{3}^{-}\) in addition to OH^?, O \(_{3}^{-}\) and SH^2?. TSL peaks at 411 and 488 K were correlated with thermal destruction of SO \(_{4}^{-}\) and SO \(_{3}^{-}\) radicals.     

Performance of CVD diamond as an optically and thermally stimulated luminescence dosemeter

Diamond is a material with extreme physical properties. Its radiation hardness, chemical inertness and tissue equivalence qualify it as an ideal material for radiation dosimetry. In the present work, the optically stimulated luminescence (OSL) and thermoluminescence (TL) characteristics of a 10 microm thick CVD diamond (polycrystalline diamond films prepared by chemical vapor deposition) film were studied in order to test its performance as a beta radiation dosemeter. The TL response is composed of four main TL glow peaks; two of these are in the range of 150-200 degrees C and two additional peaks in the 250-400 degrees C temperature range. The integrated TL as a function of radiation dose is linear up to 100 Gy and increases with increasing dose exposure. The dose dependence of the integrated OSL exhibits a similar behavior. The observed OSL/TL behavior for the CVD diamond film clearly demonstrate its capability for applications in radiation dosimetry with special relevance in medical dosimetry owing to the diamond's intrinsic material properties.     

Tunnelling in afterglow,its coexistence and interweaving with thermally stimulated luminescence

After irradiation of a phosphorescent material, the intensity of the afterglow is usually strongly dependent on the temperature: as lower temperatures are reached, it drops below the noise. But sometimes this intensity stops dropping and becomes stationary. It is seen then to decrease slowly with the time t with (1/t) kinetics. This odd emission is shown to compete with the regular TL or OSL by involving the same traps and centres. It is proposed that in this process the trapped charges recombine with centres without thermal excitation by tunnelling through a potential barrier. The parasitical effect of anomalous fading in radiation dosimetry and dating, with its experimental logarithmic law of loss of stored TL, is shown to be explained by this tunnelling. This effect, together with widening of TL peaks, turns up in samples which have less perfect or disordered crystal lattices.     

Preparation and luminescence characterization of GGAG:Ce3+,B3+ for a white light-emitting diode

We prepared Gd₃Ga₂Al₃O₁₂ (GGAG) co-doped with trivalent cerium and boron ions and investigated its luminescence properties as a function of the B³⁺ concentration. The luminescence intensity was enhanced markedly by adding B³⁺ as a co-dopant. The non-boron-doped GGAG:Ce³⁺ converted less than 10% of the absorbed blue light into luminescence. As the B³⁺ concentration increased, Q increased and reached a maximum of Q = 21% at 1.5 moles in GGAG:Ce³⁺. White light closer to daylight with good color-rendering index properties was generated with the proper combination of yellow emission from GGAG:Ce³⁺,B³⁺ and blue emission from a GaN chip.     

Optically stimulated luminescence dosimetry performance of natural Brazilian topaz exposed to beta radiation

Optically stimulated luminescence (OSL) has become the technique of choice in many areas of dosimetry. Natural materials like topaz are available in large quantities in Brazil and other countries. They have been studied to investigate the possibility of use its thermoluminescence (TL) properties for dosimetric applications. In this work, we investigate the possibility of utilising the OSL properties of natural Brazilian topaz in dosimetry. Bulk topaz samples were exposed to doses up to 100 Gy of beta radiation and the integrated OSL as a function of the dose showed linear behaviour. The fading occurs in the first 20 min after irradiation but it is <6% of the integrated OSL measured shortly after exposure. We conclude that natural colourless topaz is a very suitable phosphor for OSL dosimetry.     

Thermally stimulated luminescence and photoluminescence investigations of Eu3+ and Eu2+ doped SrBPO5

Thermally stimulated luminescence (TSL) investigations of SrBPO₅:Eu^3?+ and SrBPO₅:Eu^2?+ phosphors were carried out in the temperature range of 300–650 K. In order to characterize the phosphors, X-ray diffraction and photoluminescence (PL) techniques were used. The emission spectrum of air heated SrBPO₅:Eu^3?+ phosphor exhibited emission bands at 590, 614, 651 and 702 nm under 248 nm excitation, assigned to transitions of Eu^3?+ ion. In phosphor prepared in reducing (Ar + 8% H₂) atmosphere, a broad emission band due to Eu^2?+ ranging from 350 to 400 nm was observed with 340 nm excitation. EPR studies have confirmed the presence of Eu^2?+ ions in the samples prepared in reducing atmosphere. TSL glow curve of SrBPO₅:Eu^3?+ had shown intense peaks around 397, 510, 547 K and a weak peak around 440 K whereas in case of SrBPO₅:Eu^2?+ system, glow peaks at 414, 478 and weak peak at 516 nm were observed. The shift in TSL glow pattern can be attributed to stabilization of different oxidation states of the dopant ion in the host lattice. Apart from this, TSL trap parameters such as trap depth and frequency factor were determined. Spectral characteristics of TSL emission have shown that Eu^3?+?/Eu^2?+ ion acts as the luminescent centre in the respective phosphors.     

Optically stimulated luminescence of some thermoluminescent detectors as an indicator of absorbed radiation dose

Stimulation spectra of several TLD materials in the short-wave spectral region are measured using the optically stimulated afterglow (OSA) method for determination of absorbed dose. Optical stimulation spectra are studied in the region of wavelengths lower than those of emission spectra. The effective optical stimulation hands have been found for examined materials in the regions of wavelengths which overlap with fluorescence excitation bands. Application of short-wave OSA bands for determination of absorbed dose is analysed.     

Photoluminescence, thermally stimulated luminescence and electron paramagnetic resonance of europium-ion doped strontium pyrophosphate

Europium-ion doped strontium pyrophosphate was prepared via a chemical precipitation method to investigate the fluorescence of europium ions, the phosphate radical ions formed upon gamma-ray irradiation and their role in the thermally stimulated luminescence (TSL) of this compound. Fluorescence spectra revealed that europium ions were present in divalent as well as trivalent oxidation states. The measurements of fluorescence life time indicated that Eu³⁺ ions existed in two different types of environments in the lattice. Gamma irradiated europium-ion doped Sr₂P₂O₇ showed the presence of two thermo-luminescence glow peaks at 465 and 565 K; however, no glow was observed in the undoped sample. Electron paramagnetic resonance (EPR) studies of europium-ion doped samples showed signals from Mn²⁺ ions (present as impurity) prior to and after gamma irradiation. Upon gamma irradiation, signals originating from PO₂²⁻, PO₃²⁻ and O₂⁻ radical ions were observed in the undoped and doped samples. In the gamma irradiated europium-ion doped samples, additional low-field EPR signals, attributed to Eu²⁺ ions, were observed. By correlating the TSL and EPR results on europium-ion doped Sr₂P₂O₇, the mechanism for the glow peak at 565 K was identified.     

VUV–UV luminescence of Ce3+, Tb3+, Eu3+, and Dy3+ doped GdOCl

The vacuum ultraviolet spectroscopic properties of GdOCl:Re³⁺ (Re³⁺ = Ce³⁺, Tb³⁺, Eu³⁺, and Dy³⁺) are investigated in detail for the first time. The host absorption band is determined to be around 179 nm, and the f–d transition bands as well as the charge transfer bands are assigned. Upon 179 nm excitation, Re³⁺ (Re³⁺ = Ce³⁺, Tb³⁺, Eu³⁺, Dy³⁺) ions shown their characteristic emissions. Energy transfers from Gd³⁺ to Re³⁺ ion were observed. A broad band ranging from 350 to 400 nm corresponding to the d–f transition of Ce³⁺ is observed. Eu³⁺ has typical red emission with the strongest peak at 620 nm; Tb³⁺ shows characteristic transition of ⁵D_3,4 → ⁷F_j, and its spin-forbidden and spin-allowed f–d transitions in VUV region are calculated with Dorenbos’ equations, these calculated values agree well with the experimental results. Dy³⁺ presents yellow emission (⁴F_9/2 → ⁶H_13/2) with the strongest peak at 573 nm.     

Synthesis and tunable luminescence of RbCaGd(PO4)2:Ce3+, Mn2+ phosphors

RbCaGd(PO₄)₂ doped with Ce³⁺, Mn²⁺ was synthesized by the sol-gel method. The crystal structure and crystallographic location of Ce³⁺ in RbCaGd(PO₄)₂ were identified by Rietveld refinement. Powder X-ray diffraction (XRD) revealed that the structure of RbCaGd(PO₄)₂:Ce³⁺ compounds is hexagonal structure which is similar to that of hexagonal LnPO₄ with the lattice constant of a = b = 7.005(57) Å, c = 6.352(05) Å, and V (cell volume) = 269.980 Å³. The photoluminescence behavior and emission mechanism were studied systematically by doping activators in the RbCaGd(PO₄)₂ host. The Mn²⁺ incorporated RbCaGd(PO₄)₂:Ce³⁺, Mn²⁺ compounds exhibited blue emission from the parity- and spin-allowed f-d transition of Ce³⁺ and orange-to-red emission from the forbidden ⁴T₁ → ⁶A₁ transition of Mn²⁺. The emission chromaticity coordinates of RbCaGd(PO₄)₂:0.10Ce³⁺, xMn²⁺ (x = 0.16, 0.25) are close to the white region due to an energy transfer process and the energy transfer mechanism from Ce³⁺ to Mn²⁺ in the RbCaGd(PO₄)₂ host was dominated by dipole-dipole interactions.