Isothermal Luminescence Research Articles

Thermoluminescence and kinetic parameters of Dy3+-doped LiYF4

This work reports the kinetics of charge carriers in Dy3+-doped LiYF4 by means of thermoluminescence (TL) and isothermal luminescence decay (ITL) analyses, where the activation energy for all traps was calculated. LiYF4:Dy was synthesized by a microwave-assisted hydrothermal method. The crystalline structure was studied by X-ray diffraction, refined using Rietveld method. We have investigated TL emission as function of both temperature and wavelength. The influence of heating rate on peak position (temperature of maximum TL intensity), the dose-response curve, and activation energy obtained from the fitting of glow curves and isothermal decay. The results demonstrate that the Dy3+ ion should act as a stable trap at room temperature. TL glow curve was registered after irradiating the samples with doses from 0.1 Gy to 100 Gy using a beta 90Sr/90Y source. From the results, it was possible to identify a first-order kinetic mechanism, with linear dose response of the maximum intensity of the main peak. On the other hand, the total area under TL curves presented sub-linear response for doses higher than 5.0 Gy, which points out to the presence of shallow traps in the material.

Isothermal decay of thermoluminescence and energy distribution of traps in Al2O3–BeO ceramics

We studied features of isothermal decay curves of thermoluminescence (TL) in the dosimetric peak at 525 K of Al2O3–BeO composite ceramics. The temperature ranges were revealed in which an anomalous drop in the TL decay rate was observed with increasing temperature. By using the data obtained with the Tm-Tstop and initial rise methods, we proved that there was a complex activation energy distribution of traps with the energies varying from 0.85 to 1.55 eV. We found that the anomalous decrease with temperature in the isothermal luminescence decay rate can be associated with the superposition of the contributions to the TL from several traps with different energy depth values. It was shown that the analysis of the TL isothermal decay rate change can be used as one of the methods for revealing the complex energy structure of traps in dosimetric phosphors.

Standardizing the computerized analysis and modeling of luminescence phenomena: New open-access codes in R and Python

In this paper we describe a new initiative for the development of open-access codes in R and Python, to be used for computerized analysis and modeling of luminescence phenomena. The purpose of this broad initiative is to help in the classification, organization and standardization of the computerized analysis and modeling of a wide range of luminescence phenomena. Although a very significant number of such open access codes is already available in the literature, there is a lack of common standardization and homogeneity in the nomenclature and in the codes, which we hope to address. New open-access codes are developed for thermoluminescence (TL), isothermal luminescence (ITL), optically stimulated luminescence (OSL), infrared stimulated luminescence (IRSL), dose response (DR) and time-resolved (TR) signals. In each of these categories, computer codes are currently being developed based on (a) delocalized transitions involving the conduction/valence bands and (b) localized transitions based on proximal interactions between traps and centers. Whenever applicable, additional codes are developed for semi-localized transition models, which are based on a combination of localized and delocalized transitions. While many previously published codes are based on the empirical general order kinetics and on first order kinetics, several of the new codes in R and Python are based on physically meaningful kinetics described by the Lambert W function. During the past decade, the Lambert W function has been shown to describe both thermally and optically stimulated phenomena, as well as the nonlinear dose response of TL/OSL/ESR in dosimetric materials. The paper demonstrates the proposed classification and organization of the codes, which it is hoped will be a useful tool, especially for newcomers to the field of luminescence dosimetry.

Comprehensive analysis of thermoluminescence signals in MgB4O7:Dy,Na dosimeter

Magnesium borate (MgB4O7) is a material of interest for thermoluminescence (TL) dosimetry of ionizing radiation, due to its low photon energy dependence and the possibility of developing neutron dosimeters, and its potential as a temperature sensor in passive temperature sensing applications. Recent experimental and modeling work has shown that TL glow curves and isothermal luminescence signals in MgB4O7:Dy,Na can be analyzed using a radiative tunneling model, based on localized recombination processes. This paper presents a comprehensive analysis of TL signals in MgB4O7:Dy,Na dosimeters, based on a recently published model which incorporates simultaneous irradiation and tunneling processes. Four different types of TL data are presented and analyzed using the proposed model: (a) TL glow curves at different irradiation doses, (b) TL signals after sample irradiation at different temperatures, (c) TL after isothermal heating for 500 s at various temperatures, and (d) TL after room temperature irradiation, followed by heating to a temperature Tstop. We also present an alternative fast and efficient Monte Carlo method of analyzing the data, which is very useful for quick analysis of experimental data. The experimental data and modeling results show that the shape of the TL glow peaks remains essentially the same in all four experimental protocols, while the height and temperature of maximum TL intensity depends on the irradiation and preheating conditions.

On the half-life of luminescence signals in dosimetric applications: A unified presentation

Luminescence signals from natural and man-made materials are widely used in dosimetric and dating applications. In general, there are two types of half-lives of luminescence signals which are of importance to experimental and modeling work in this research area. The first type of half-life is the time required for the population of the trapped charge in a single trap to decay to half its initial value. The second type of half-life is the time required for the luminescence intensity to drop to half of its initial value. While there a handful of analytical expressions available in the literature for the first type of half-life, there are no corresponding analytical expressions for the second type.In this work new analytical expressions are derived for the half-life of luminescence signals during continuous wave optical stimulation luminescence (CW-OSL) or isothermal luminescence (ITL) experiments. The analytical expressions are derived for several commonly used luminescence models which are based on delocalized transitions involving the conduction band: first and second order kinetics, empirical general order kinetics (GOK), mixed order kinetics (MOK) and the one-trap one-recombination center (OTOR) model. In addition, half-life expressions are derived for a different type of luminescence model, which is based on localized transitions in a random distribution of charges. The new half-life expressions contain two parts. The first part is inversely proportional to the thermal or optical excitation rate, and depends on the experimental conditions and on the cross section of the relevant luminescence process. The second part is characteristic of the optical and/or thermal properties of the material, as expressed by the parameters in the model.A new simple and quick method for analyzing luminescence signals is developed, and examples are given of applying the new method to a variety of dosimetric materials. The new test allows quick determination of whether a set of experimentally measured luminescence signals originate in a single trap, or in multiple traps.

ATP‐Releasing Nucleotides: Linking DNA Synthesis to Luciferase Signaling

AbstractA new strategy is reported for the production of luminescence signals from DNA synthesis through the use of chimeric nucleoside tetraphosphate dimers in which ATP, rather than pyrophosphate, is the leaving group. ATP‐releasing nucleotides (ARNs) were synthesized as derivatives of the four canonical nucleotides. All four derivatives are good substrates for DNA polymerase, with Km values averaging 13‐fold higher than those of natural dNTPs, and kcat values within 1.5‐fold of those of native nucleotides. Importantly, ARNs were found to yield very little background signal with luciferase. DNA synthesis experiments show that the ATP byproduct can be harnessed to elicit a chemiluminescence signal in the presence of luciferase. When using a polymerase together with the chimeric nucleotides, target DNAs/RNAs trigger the release of stoichiometrically large quantities of ATP, thereby allowing sensitive isothermal luminescence detection of nucleic acids as diverse as phage DNAs and short miRNAs.

ATP-Releasing Nucleotides: Linking DNA Synthesis to Luciferase Signaling.

A new strategy is reported for the production of luminescence signals from DNA synthesis through the use of chimeric nucleoside tetraphosphate dimers in which ATP, rather than pyrophosphate, is the leaving group. ATP-releasing nucleotides (ARNs) were synthesized as derivatives of the four canonical nucleotides. All four derivatives are good substrates for DNA polymerase, with Km values averaging 13-fold higher than those of natural dNTPs, and kcat values within 1.5-fold of those of native nucleotides. Importantly, ARNs were found to yield very little background signal with luciferase. DNA synthesis experiments show that the ATP byproduct can be harnessed to elicit a chemiluminescence signal in the presence of luciferase. When using a polymerase together with the chimeric nucleotides, target DNAs/RNAs trigger the release of stoichiometrically large quantities of ATP, thereby allowing sensitive isothermal luminescence detection of nucleic acids as diverse as phage DNAs and short miRNAs.

Determination of the kinetic parameters of BeO using isothermal decay method

Most of the existing methods for obtaining the frequency factors make use of the trap depth (activation energy) making some assumptions about the order of the kinetics. This causes inconsistencies in the reported values of trapping parameters due that the values of the activation energy obtained by different methods differ appreciably among them. Then, it is necessary to use a method independent of the trap depth making use of the isothermal luminescence decay (ILD) method.The trapping parameters associated with the prominent glow peak of BeO (280°C) are reported using ILD method. As a check, the trap parameters are also calculated by glow curve shape (Chen's) method after isolating the prominent glow peak by thermal cleaning technique. Our results show a very good agreement between the trapping parameters calculated by the two methods. ILD method was used for determining the trapping parameters of BeO. Results obtained applying this method are in good agreement with those obtained using other methods, except in the value of the frequency factor.

Thermally stimulated luminescence glow curve structure of β-irradiated CaB4O7:Dy.

Thermally stimulated luminescence glow curves of CaB4O7:Dy samples after β-irradiation showed glow peaks at ~335, 530 and 675 K, with a heating rate of 2 K/s. The main peak at 530 K was analyzed using the Tmax-Tstop method and was found to be composed of at least five overlapping glow peaks. A curve-fitting program was used to perform computerized glow curve deconvolution (CGCD) analysis of the complex peak of the dosimetric material of interest. The kinetic parameters, namely activation energy (E) and frequency factor (s), associated with the main glow peak of CaB4O7:Dy at 520 K were evaluated using peak shape (PS) and isothermal luminescence decay (ILD) methods. In addition, the kinetics was determined to be first order (b =1) by applying the additive dose method. The activation energies and frequency factors obtained using PS and ILD methods are calculated to be 0.72 and 0.72 eV and 8.76 × 10(5) and 1.44 × 10(6) /s, respectively.

Evaluation of kinetics parameters in the X-irradiated TSL studies of RE3+-doped (RE=Eu, Tb) ZnO nanorods for dosimetric applications

This paper reports the detail description of the structural and thermoluminescence of the RE3+-doped (RE=Eu, Tb) ZnO nanorods prepared by adopting co-precipitation method. Formation of as synthesized ZnO nanorods were confirmed by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The XRD pattern showed monophasic nature of the as prepared ZnO doped with Eu3+ and Tb3+ ions. The SEM image elaborates the nanorod morphology of RE3+ doped ZnO with diameter ranging between 60–90nm and length between 600–900nm. The thermoluminescence spectra of the X-ray irradiated ZnO:Eu3+ and ZnO:Tb3+ show the prominent peak for the broad glow curve peaked at 365°C and 350°C, respectively, which have been generated via the recombination of the released electrons from the traps upon thermal stimulation. The peaks are found to obey first order kinetics and the activation energy for the ZnO:Eu3+ and ZnO:Tb3+ samples, estimated via isothermal luminescence glow peak decay method, are found to be 0.8eV and 0.9eV respectively. Furthermore, the TL dose response and reproducibility were also studied in details, which could be very useful to establish the potentiality of the present phosphors in the field of radiation dosimetry.

Surface segregation in blends of miscible amorphous polymers

The isothermal luminescence decay kinetics in near-surface nanolayers of plasma-activated bulk samples of amorphous polystyrene (PS) and poly(2,6-dimethyl-1,4-phenylene oxide) (PPO) and their miscible blends with weight ratios PS/PPO of 75/25 and 50/50 has been studied at 77 K. The intensities of isothermal luminescence (I) of homopolymer and blend surfaces have been compared. It has been found that the ratio between the luminescence intensities for PS and PPO (I(PS)/I(PPO)) may be as high as 50, while the luminescence intensities for the PS–PPO blends are close to I(PPO). The results obtained indicate that the PPO concentration in the surface layers of the blends is higher than that in the bulk.

Simulations of isothermal processes in the semilocalized transition (SLT) model of thermoluminescence (TL)

Semilocalized transition (SLT) kinetic models for thermoluminescence (TL) contain characteristics of both a localized transition (LT) and of a single trap model. TL glow curves within SLT models typically contain contain two TL peaks; the first peak corresponds to the intra-pair luminescence due to LTs and the second TL peak corresponds to delocalized transitions involving the conduction band (CB). The latter delocalized TL peak has also been found to exhibit non-typical double-peak structure, in which the main TL peak is accompanied by a smaller peak called the displacement peak. This paper describes the simulation of isothermal luminescence signals using a previously published SLT model. It is found that these simulated isothermal signals exhibit several unusual time characteristics. Isothermal signals associated with the LTs follow first order kinetics and are therefore described by single decaying exponentials. However, isothermal signals associated with delocalized transitions show a non-typical complex structure characterized by several time regions with different decay characteristics. For certain values of the parameters in the SLT model the isothermal signals can also exhibit non-monotonic behaviour as a function of time. Another notable result from the simulations is that isothermal currents (which are proportional to the concentration of electrons in the CB) can persist for very long periods of time, even after the apparent termination of the isothermal luminescence signals. It is concluded that isothermal processes described by the SLT model depend strongly on the presence of SLTs, in contrast to previous studies using Monte Carlo simulations, which showed a weak interdependence of these phenomena. The simulations in this paper suggest that isothermal experiments offer a sensitive method for detecting the presence of SLTs in a dosimetric material.

Calculation for the trapping parameters of K 3Na(SO 4) 2 phosphor by isothermal luminescence decay method

In this paper thermally stimulated luminescence (TSL) studies of K 3Na(SO 4) 2 phosphor are reported. A polycrystalline sample of K 3Na(SO 4) 2 was prepared by the solid state diffusion method. Formation of compound was checked by use of XRD and Fourier-transform infrared (FTIR) spectroscopy. The TSL glow curves of X-irradiated K 3Na(SO 4) 2 sample show one glow peak at temperature 170 °C indicating that only one set of traps is being activated within the particular temperature range each with its own value of activation energy ( E) and frequency factor ( s). The trapping parameters associated with the prominent glow peak of K 3Na(SO 4) 2 are calculated by using isothermal decay method. The release of hole/electron from defect centers at the characteristic trap site initiates the luminescence process in these materials. The intensity of the TL glow peaks increases with increase of the X-ray dose to the sample.

Study of kinetic parameters of K 2Ca 2(SO 4)3 thermoluminescence dosimeter

The dosimetry study of thermoluminescence materials is based on a good knowledge of its kinetics para-meters. A polycrystalline sample of K 2Ca 2(SO 4)3 was prepared by the solid-state diffusion method. Formation of the compound was checked by using X-ray diffraction and Fourier-transform infrared spectroscopy. Thermally stimulated luminescence (TSL) glow curves of X-ray-irradiated K 2Ca 2(SO 4)3 phosphor exhibit one glow peak at 195 °C and a shoulder at around 120 °C, indicating that two different sets of traps are being activated within the particular temperature range, each with its own value of activation energy (E) and frequency factor (s). The kinetic parameters associated with the prominent glow peak of K 2Ca 2(SO 4)3 were calculated using the isothermal luminescence decay method. The electron spin resonance study of the prepared compound exhibits the presence of and radical ions that are responsible for the observed TSL glow peaks. The release of hole/electron from trap centres at the characteristic trap site initiates the luminescence process in these materials.

Structural analysis, TSL studies and evaluation of trapping parameters of Cu 2+ activated CaSO 4

The XRD and SEM and TSL studies of the as prepared pure, Cu and Mn doped CaSO 4 have been carried out. From the comparative TSL studies it has been seen that the 137 °C glow peak of CaSO 4:Cu is superior to undoped and Mn doped CaSO 4 compounds as well as other Cu doped alkaline earth sulphates. Evaluation of trapping parameters of the most intensive glow peak Cu (0.5 mol%) doped CaSO 4 is accomplished by a technique named isothermal luminescence decay method and comparison of these parameters with the previously calculated trapping parameters by glow curve shape method (Chen’s method) have been done. It is observed that the most intensive glow peak of Cu doped CaSO 4 is found to obey second order kinetics, because of availability of vacant traps for retrapping to take place. Moreover the effect of various doping concentration of Cu on the TSL glow curve and reproducibility of Cu doped CaSO 4 has also studied.

Determination of trapping parameters from thermally stimulated luminescence glow curves of Mn-doped Li2B4O7 phosphor

The determination of trapping parameters such as order of kinetics, activation energy and frequency factor is one of the most important studies in the field of thermally stimulated luminescence (TSL). A polycrystalline sample of Mn-doped Li2B4O7 was prepared by melting method. The formation of the doped compound was checked by Fourier transform infrared study. The TSL study of the Mn-doped lithium tetraborate sample shows two glow peaks at 190 °C and 310 °C, of which the intensity of the 310 °C glow peak is the maximum. In this paper, the trapping parameters associated with the prominent glow peak of Mn-doped lithium tetraborate were reported using the isothermal luminescence decay and glow curve shape (Chen's) methods. Our results show a very good agreement between the trapping parameters calculated by the two methods.

Ionic and excited species in irradiated poly(vinyl chloride) doped with aromatic admixtures: low temperature studies

The influence of temperature (77–290 K) on the fate of dopant radical ions and respective excited states in irradiated poly(vinyl chloride) (PVC) matrix, doped with pyrene, (Py) and tris(2-ethylhexyl) trimellitate (TOTM) is described. At 77 K dopant radical ions start to recombinevia tunneling charge transfer, leading to weak isothermal luminescence (ITL). The wavelength-selected radiothermoluminescence (WS RTL) broad maxima observed for doped PVC in the temperature range 95–110 K have a similar origin, i.e., recombination of dopant radical ionsvia tunneling. Apart from the peaks representing the absorption of dopant radical ions the absorption maximum at 411 nm found for the PVC−Py system is attributed to Py−Cl adduct generated in Py•++Cl− reaction. The mechanisms involved in these processes are discussed.

A peak structure in isothermal luminescence signals in quartz: Origin and implications

Isothermal heating is commonly used in luminescence dosimetry and trap parameter studies. It is often observed that the isothermal luminescence signal has a peak shape instead of a monotonous decay form. We provide here evidence that this peak shape in quartz may equally result from a ‘thermal lag’ problem in contrast to the earlier propositions of non first-order kinetics. Temperature modelling suggests that the peak-shaped signal contains elements of both the ramped — and isothermal — thermoluminescence (TL). The modelled changes in the peak movement as a function of isothermal temperature and the ramp-rate show an excellent agreement with those obtained experimentally. This understanding of thermal lag is extended to optically stimulated luminescence (OSL) measurements for which the effects of isothermal TL contamination and changing thermal assistance during thermal equilibration are discussed. Appropriate methods are suggested to identify thermal lag on the basis of the peak structure, and to circumvent this effect in isothermal methods.

Isothermal thermoluminescence signals from quartz

Dating sediment older than ∼ 150 ka still remains difficult because of a lack of suitable chronological tools. Here we report on studies to determine whether measurements of quartz thermoluminescence made at constant temperature (isothermal luminescence) can be used to extend the dose limit in sediment dating. The origins and dosimetric characteristics of the quartz isothermal signal at 310 ∘ C are investigated. It is shown that, in general, application of a single aliquot regenerative (SAR) dose protocol with this signal overestimates the expected equivalent doses in sedimentary samples, from a variety of environments and locations. This anomaly originates from a change of luminescence sensitivity, during or after the initial thermal measurement. A single aliquot regenerated and added dose (SARA) protocol suggested as the only approach known to compensate for this initial change of sensitivity was unsuccessful.

Testing heated flint palaeodose protocols using dose recovery procedures

Thermoluminescence (TL) dating of materials from archaeological contexts has been shown to be an accurate method when comparisons are made with other chronometric dating methods; however, little has been published on the verification of the measurement protocols used to determine the equivalent dose (palaeodose). Instead of testing TL dating protocols for heated flint using archaeological material with unknown thermal and radiation history, dose recovery tests for three samples of different geological origin are presented. These samples exhibit TL emission in the UV, blue and orange–red wavelengths. In addition to the two multiple aliquot protocols (standard additive-regeneration and normalization) generally used to determine the palaeodose, the single-aliquot-regenerative-dose (SAR) TL and OSL procedure, a ‘short’ SAR–TL and isothermal luminescence (IT) decay procedures are applied using detection windows limited to these emissions. Accurate dose recovery is obtained for the standard and normalization protocols in the commonly employed detection window (UV-blue), the ‘short’ SAR in the orange–red window and some IT measurements. While the standard techniques give the most accurate and precise results, detection of the TL and IT orange–red emission in connection with a ‘short’ SAR protocol also gave accurate and precise results. Such procedures are especially suitable for samples too small for standard multiple aliquot techniques, which require large samples.