Thermoluminescence Emission Spectra Research Articles

Correlated ESR, PL and TL studies on K 3Na(SO 4) 2 : Eu thermoluminescence dosimetry phosphor

Strong thermoluminescence (TL) was observed in K 3Na(SO 4) 2 : Eu phosphor in the Eu doped K 2SO 4–Na 2SO 4 system. The defect centres formed in this TL phosphor are studied using the technique of electron spin resonance. Two glow peaks at 423 and 475 K are observed in K 3Na(SO 4) 2 : Eu phosphor prepared by the melt method. The peak 475 K is shown to be at least thrice as sensitive as the conventional CaSO 4 : Dy phosphor used in the TL dosimetry of ionizing radiations. Two centres, assigned to SO 4 − and SO 3 −, are observed at room temperature in the melt prepared phosphor. Step annealing measurements showed a connection between these centres and the observed TL glow peaks. Three TL glow peaks at 360, 423 and 453 K are observed in the K 3Na(SO 4) 2 : Eu phosphor prepared by the evaporation method. A SO 4 − centre and two different SO 4 − centres are observed in this phosphor. TL and photoluminescence emission spectra indicate that the europium ion is in the divalent state in K 3Na(SO 4) 2 : Eu phosphor.

A study of thermoluminescence emission spectra and optical stimulation spectra of quartz from different provenances

The present study examines (1) variability in the thermoluminescence (TL) emission spectrum and optical stimulation (OSL) spectrum of quartz from different provenances and, (2) possible correlations between spectral features and the nature of the complex growth curves (ranging from saturating exponential to those described by a cubic polynomial function), so as to determine the validity of the currently used experimental protocols. The results suggest that commonly used UV emission for dating constitutes only a minor component of the total quartz emission and in view of this a dose-dependent contribution from blue/blue–green emission peak to the UV detection is likely. The OSL stimulation spectrum shows a definite change in stimulation response between 500–520 nm, hence implying that stimulation in this window may contribute as an additional source of scatter in multi-grain samples.

Thermoluminescence from within large defect complexes

Thermoluminescence was originally modelled in terms of highly localised point defects with independent trapping and recombination sites. Neither concept is now throught to be appropriate and data are presented which indicate the scale of defect complexes, within which thermoluminescence occurs where long range interactions are often evident. The present views are strongly supported by data from thermoluminescence emission spectra. For example, the glow peak temperatures of emission from different rare earth ions depend on the dopant, implying that the trap and recombination centre are spatially linked. In LaF3 there are examples of peak shifts of up to 18 K which depend directly on the ionic radii of the rare earth ions. Similar data from other systems are noted, all of which underpin models of thermoluminescence generated by internal charge transfer within very large defect complexes.

Extended Defect Models for Thermoluminescence

Thermoluminescence modelling started with very simple models of highly localised point defects, and separation of trapping and recombination centres. Whilst these ideas still dominate the discussions, current research indicates that most defects are far more complex, with localised transitions, and defect interactions extending over many lattice. sites. Multi-ion defect sites have been clearly established for LiF dosemeters and, similarly, models to account for charge compensation and lattice distortion of rare earth dopant ions (e.g. in CaF 2 , CaSO 4 etc.) all include the possibility of large complex recombination sites. Data obtained from thermoluminescence emission spectra indicate that ions can interact directly by coupling between the trapping and recombination sites Further, the thermoluminescence dosimetry must originate within different parts of the same large complex. Many examples support models of large complexes with internal transitions, including glow peak temperatures which differ with changes in rare earth ion dopants, where the peak shifts are determined by the ionic radii of the rare earth ions. Examples are presented which emphasise that thermoluminescence is often generated by internal charge transfer within very large defect complexes.

Basic Thermoluminescence Properties of Sr3(PO4)2:Eu2+

The thermoluminescence investigation is reported of Sr 3 (PO 4 ) 2 :Eu 2+ , which is a commercially available X ray phosphor. Its TL emission spectrum is dominated by a single emission band centred at 420 nm, which is characteristic of Eu 2+ . The glow curve of the Eu 2+ band has two well separated peaks, a feature which rarely occurs in dosimetric materials. Owing to the above properties, Sr 3 (PO 4 ) 2 :Eu 2+ seems to be the best choice for studying thermoluminescence (TL) kinetics and the relation between radioluminescence (RL) and TL. The first results of such investigations are reported.

The Use of Albite as a Dosemeter in Accident Dose Reconstruction

In retrospective accident dosimetry different minerals can be used as dosemeters. In this communication some characteristic features of the thermoluminescence (TL) signal from sodium rich feldspars (albite) are studied. The TL emission spectra from albite (NaAlSi 3 O 8 ) shows two characteristic bands peaked at 290 and 390 nm. At these bands, different glow curves presenting rather broad glow peaks are detected. The glow curves at these two wavelengths can be simultaneously recorded during the same readout by a simple device developed in this laboratory. The natural accrued dose is only observed in the high temperature side of the glow curve at 390 nm while the 290 nm glow curve, peaked at lower temperatures, only contains the contribution of young events. From the study and characterisation of the thermal stability of the 290 nm TL curve, it has been possible to obtain accurate dose values, even several months after the accidental irradiation. This determination is made directly from TL measurements without the necessity of subtracting any indirectly estimated dose.

Thermoluminescence of KI:Eu2+ Stimulated by Ultraviolet Irradiation at Different Temperatures

The thermoluminescence (TL) of KI:Eu2+ after ultraviolet (254 nm) irradiation at different temperatures from -40(C to +40(C has been studied. Two main glow peaks and some minor features have been identified on the thermoluminescence glow curves. Irradiating at low temperature gives a strong peak at ~5(C and a less pronounced one at 230(C. The TL glow peak emission spectra were analysed as consisting of the addition of several Gaussian shaped emission bands. The position of the Gaussian peaks, and their widths, are coincident with divalent europium emission at different sites of the KI:Eu2+ system. A new emission band centred at 3.05 eV, 0.16 eV FWHM for Eu2+ has been observed from the TL emission spectra. The changes in the spectral distribution of the TL emission with irradiation temperature are discussed.

Spectra Thermoluminescence Emissions and Continuous Trap Distribution of a Cross-Hatch Twinned Low Microcline

Thermoluminescence (TL) emission spectra have been obtained from a well-characterised cross-batch low microcline using a high sensitivity spectrometer. Tests of thermal stability at different temperatures show a continuous trap distribution with progressive changes in the glow curve shape, intensity and temperature position of the maximum peak. The results suggest that the characteristic 340 nm emission band of microcline is associated with the presence of cross-hatch twinning. The present contribution speculates that both the 340 nm and 380 nm spectra bands could be linked by thermal alkali self-diffusion through the twinning interfaces.

Thermoluminescence Emission Spectra of Gamma Irradiated Topaz [Al2SiO4 (F,OH)2

To characterise the thermoluminescence (TL) of Brazilian topaz, TL emission spectra of as-received samples and gamma irradiated samples (with 100 Gy, 1 kGy, and 106 Gy) submitted or not to a previous annealing procedure are presented. All the samples show a broad emission band between 300 and 600 nm for all the glow peaks between 50 and 400(C. In some gamma irradiated samples a narrow emission band between 200 and 350 nm was also observed. Effects of annealing temperature and of irradiation dose are discussed.

Glow curves and emission spectra of burnt flints

The thermoluminescence (TL) behaviour of a group of burnt flints from a prehistoric site in North Italy has been studied. Due to incomplete burning or non-reproducible results only three samples could be reliably dated. The flints have been studied through electron microscopy with microprobe, X-ray diffraction and TL, also wavelength resolved. A new type of preparation using a hydraulic press avoids modifications of the natural TL signal. The effects of acid etching were also studied. All the samples turned out to be composed of microquartz and megaquartz. The glow-curves gave indication of incomplete burning through the appearance of a peak at about 450°C (heating rate 8°C s -1), contrary to the well-annealed samples that presented a composite peak in the 280–380°C region. Encouraging results have been obtained in the analysis of the TL emission spectra. Three emission regions have been detected: 260–330 nm, 350–500 nm and 580–640 nm. While only the middle one is usually detected by conventional 2D instrumentation, also the UV region could be probably proposed for dating burnt flint.

The MgO-P2O5 glasses as thermoluminescent gamma dosimeters

The effect of gamma irradiation on thermoluminescence (TL) of the MgO-P2O5 glass system (10–60mol% MgO) has been studied in the dose range from 2.5–120 Gy. The resulting TL emission spectra are characterized by a double peak at temperatures of about 90°C and 300°C depending on the MgO content and the gamma dose value. The intensity of the glow peaks was found to be dependent on gamma dose and MgO concentration. The prepared glass system was found to be insensitive to visible light and has thermally stable glow peaks which grew almost linear with the absorbed gamma dose up to a value of 120 Gy. The enhancement of TL intensity was found to be obtained at both low and high MgO concentration, but the high MgO content (i.e. ≥ 50 mol% MgO) is preferable for better glass-stability conditions. Results are discussed within the framework of gamma interaction with glass specimens.

Thermoluminescence characterisation of Sr3(PO4)2:Eu2+

The present paper reports on the first results of a comprehensive thermoluminescence (TL) investigation of a commercially available X-ray phosphor, Sr3(PO4)2:Eu2+. Its TL emission spectrum is dominated by a single emission band centered at 420nm, which is characteristic of Eu2+. The glow curve has two distinct peaks at 100 and 260°C respectively (measured at a heating rate of 1°C/s). There is a much weaker emission around 570nm, which is localised in a completely different single glow peak around 140°C. Based on the glow curve characteristics discussed in the paper, Sr3(PO4)2:Eu2+ seems to be not only a promising TL dosimeter material, but it is an interesting model system for studying thermoluminescence kinetics.

Thermoluminescence from CO-doped solid Ar

Cameron bands luminescence from a new thermoluminescence (TL) system - CO-doped solid Ar - has been investigated using selective excitation by synchrotron radiation and thermally stimulated luminescence methods. The photoexcitation and TL emission spectra of the Cameron bands are measured. The activation energies and the frequency factors of charge traps are determined by numerical fitting of the TL emission spectrum.

Crystal field effects on the thermoluminescence of manganese in carbonate lattices

Thermoluminescence emission spectra are reported for a wide range of carbonates. All the samples show Mn luminescence centres and the spectra variously include narrow and features, when the Mn is in low concentration, or broad emission bands at high concentrations. The form of the spectra change with temperature, and for some Mn concentrations, alter from broad to narrow band spectra with increasing temperature. In calcite there is concentration quenching of the luminescence when the Mn impurity levels exceed ∼ 1000 ppm which varies with glow peak temperature. The emission wavelengths of the Mn show monotonic dependencies, in both rhombohedral and orthorhombic lattices, as a function of the length of the metal to oxygen bonds in the various minerals, and the presence of Mn in alternative sites is revealed for dolomite. The detailed line spectra can be related to the Mn ion energy level diagram, as perturbed by the crystal field term, which for emission in rhombohedral calcite has a value of ∼ 1000 cm −1, but for orthorhombic sites in aragonite is ∼ 1200 cm −1.

Luminescence Spectra of Alkali Feldspars: Some Relationships Between Structural Features and Luminescence Emission

Thermoluminescence (TL) emission spectra have been obtained from alkali feldspars ranging from monoclinic and triclinic potassium-rich feldspars to triclinic sodium-rich feldspars, as well from a synthetic gel of KAlSi 3 O 8 composition. Emissions were detected in the wavelength range 200-800 nm using a high sensitivity spectrometer. The results suggest that the 290 nm emission band in TL is associated either with the presence of crystalline phases of NaAlSi 3 O 8 or with Na/K exsolution interfaces.

Thermoluminescence Emission, Excitation and Stimulation Spectra of CaSO4:Dy and CaSO4:Tm

The results of thermoluminescence (TL) emission and excitation spectra for CaSO 4 :Dy and CaSO 4 :Tm are presented. TL emission as a function of temperature verifies that the lattice defect and Dy 3+ (Tm 3+ ) emissions possess the same peak temperature. Excitation spectra establish the presence of a 'spectral overlap' between Dy 3+ (Tm 3 ) absorption and lattice defect emission in the 340-360 nm range. The excitation spectrum is observed initially to increase and then decay over the temperature range corresponding to the production of TL. Over this same temperature range, a lattice-related- broad-band structure emerges corresponding to the creation of centres which are capable of transferring energy to Dy 3+ (Tm 3+ ) ions. Laser stimulation at 266 and 532 nm produces optically stimulated luminescence (OSL) in CaSO 4 :Dy. The production of OSL by 266 and 532 nm stimulation is shown to cause a reduction in the TL glow curve.

Radioluminescence Properties of Alpha-Al2O3 TL Dosemeters

The radioluminescence characteristics of different types of α-Al 2 O 3 thermoluminescence dosemeter materials (Al 2 O 3 :C, Al 2 O 3 :Mg,Y), induced by 4 MeV linear accelerator electrons are reported. The main emission peak of these materials occurs at 410-420 nm, which closely matches their thermoluminescence emission spectra. The half-lives of this emission are in the ms range. However, in Al 2 O 3 :C another emission peak can be observed at 520 nm, which decays much faster, with a half-life of 28 μs. The intensity of this peak is low in unirradiated samples, and increases monotonously with dose.

Estimation of Ultraviolet Radiation Dose Using CaF2:Tb Phosphor

To observe and estimate the dose of ultraviolet (UV) radiation in sunlight, the available thermoluminescence (TL) materials were studied. Several kinds of lanthanide elements were doped in pure CaF2 powdered crystals and the properties of the TL for UV were observed. The TL intensity from CaF2Tb was the highest among the samples doped with various lanthanide elements, and from the TL emission spectra (380-540 nm) the TL is estimated to be due to inner transition of Tb3+. The peak wavelength of the TL excitation light was located approximately at 235 nm and light of a longer wavelength than 320 nm was unable to excite the TL. The ultraviolet response of CaF2:Tb depended on its sintering temperature. Even without ? ray pre-irradiation the CaF2:Tb sample with 1 h exposure to sunlight has enough sensitivity to estimate the change of UV. Seasonal change of UV intensity in sunlight was measured with this TLD during four months in 1993. The results agreed with that of other institutes in Japan.

Interpretation of Rare Earth Thermoluminescence Spectra

Thermoluminescence emission spectra of rare earth dopants provide evidence on the site symmetry and interactions with many neighbouring atoms which show that there are changes associated with temperature, dopant concentration and other impurities, as well as the host lattice. Such factors require us to reassess the models of the defect sites and the mechanism of thermoluminescence. Results from recent spectral data lead to the conclusions that the trapping and recombination sites may not be independent; that the rare earth ions are always in the trivalent state; that energy transfer between sites is significant, and that the so called point defects sites are in fact complexes of many ions.

Effects of type of radiation on glow curve and thermoluminescence emission spectrum of CaF 2:Tm

Thermoluminescence emission spectra of CaF 2:Tm (TLD-300) samples irradiated with 48 keV X-rays 60Co gamma rays, 4.5 MeV alpha particles and 15 MeV neutrons were measured in the 300–650 K temperature region. Seven emission bands were observed of which the one in the infrared (at 803 nm) is very intense. The emission bands can be assigned to 1D, 1G, 3F and 3H levels characteristic for Tm 3+ de-excitation in a cubic field. All observed lines in the spectrum are due to 4f-4f transitions. The spectra undergo remarkable changes in intensity when the temperature is raised from room temperature up to 350°C, while the number of the emission bands remains constant. The glow curve structure is both dependent on emission wavelength and the type of radiation. Evidence has been found that the trapping structures responsible for glow peaks 2 and 3 alter under the influence of high LET (α) radiation. For glow peaks 4–6 the filling of the traps alters with the type of radiation. The observations can be explained assuming a TL process involving several hole trapping centres but with only one luminescent centre (Tm 3+) active at all temperatures.