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Phototransferred thermoluminescence (PTTL) induced from natural calcite using 470, 525, and 405 nm illumination is reported. We consider the measurement and analysis of time-response profiles, the dependence of PTTL intensity on the sample temperature during illumination to induce phototransfer, the role of deep electron traps, and discuss mechanisms for phototransfer in calcite. The conventional TL glow curve is a complex collection of closely overlapping glow peaks, but there are three stand-out ones near 90, 210, and 330 °C, denoted as I–III. These are reproduced under phototransfer. The dependence of PTTL intensity on illumination can be properly described by systems of acceptors and donors, where the number of the latter depends on the preheating temperature. The systems have been analyzed by phenomenological and kinetics models. The intensity of the PTTL is influenced by the illumination temperature, and the attendant thermal assistance and thermal quenching have been quantified. Electronic processes relevant to the PTTL of calcite are thought to involve the relaxation of (CO3)2− and Mn2+ ions. An anomalous increase in PTTL induced from deep electron traps has been deduced to be a possible result of quantum tunneling of charge between (CO3)3− stabilized close to Mn3+ cations. [ABSTRACT FROM AUTHOR]

Phototransferred thermoluminescence (PTTL) of natural fluorite induced by 470 nm blue-, 525 nm green-, and 870 nm infrared light is reported. Although its conventional thermoluminescence (TL) glow curve measured during heating to 600 °C has six peaks, only five are reproduced under phototransfer. One of them corresponds to a hole trap. The sixth peak counterintuitively increases in intensity with illumination in a change suggestive of competition effects involving deep electron traps. The dependence of PTTL intensity on duration of illumination for each PTTL peak is analyzed using phenomenological and kinetic models as systems of acceptors and donors with the number of the latter informed by experiment. The intensity of PTTL increases with the temperature of illumination with an activation energy of thermal assistance of 0.14 ± 0.01 eV and decreases at elevated temperatures with an activation energy of thermal quenching of 1.1 ± 0.3 eV. The long-term behavior of time-response profiles and the interaction of holes with stimulated electrons as studied by stability theory show unstable critical points. Supplementary tests show that exposing CaF2 to UV illumination achieves the same effect as beta irradiation, and any resultant peaks relate to conventional TL rather than phototransfer. [ABSTRACT FROM AUTHOR]

We report the existence of a hole trap in α-Al2O3:C,Mg as determined using thermoluminescence (TL) and optically stimulated luminescence (OSL). The associated experiments are based on the hypotheses that if a TL glow peak is associated with a hole trap in the glow curve of α-Al2O3:C,Mg, that hole trap will not participate in any light-induced electron-transfer process and its removal will not cause the OSL intensity to decrease. To examine the first hypothesis, a TL glow curve was recorded at 1 °C/s to establish the position of glow peaks. There is a high intensity peak at 184 °C (labeled as peak IV) and eight secondary peaks at 48, 80, 108, 228, 288, 320, 386, and 426 °C (peaks I, II, III, and V–IX). The light-induced charge transfer between various electron traps associated with the peaks was studied. This study reveals that all peaks except the one at 228 °C (peak V) participate in the charge-transfer process. A test of the second hypothesis shows that peak V is also not reproduced by illumination (phototransfer), and the depletion of this peak does not influence the charge-transfer process. An additional study on the effect of temperature on the TL and OSL intensity was carried out to further assess the nature of the charge traps associated with the peaks. The depletion of peak V does not affect the OSL intensity. The results from both experiments are clear evidence consistent with the hypothesis that the charge trap associated with peak V is a hole trap. [ABSTRACT FROM AUTHOR]

Phototransferred thermoluminescence (PTTL) of Al2O3:C,Mg induced by 470 nm blue, 525 nm green, and 870 nm infrared light is reported. Although its conventional TL glow curve measured during heating to 600 °C has seven peaks (labeled I–VII), only peak II is reproduced under phototransfer, except when the sample is preheated to 180 °C when peak IV also re-appears. The dependence of PTTL intensity on the duration of illumination for both PTTL peaks is analyzed using phenomenological and kinetic models as systems of acceptor and donors, with the number of the latter determined by experiment. The intensity of PTTL increases with the temperature of illumination with an activation energy of thermal assistance of either 0.015 ± 0.002 or 0.047 ± 0.002 eV when either 470 or 525 nm light is used but decreases at elevated temperatures with an activation energy of thermal quenching equal to 0.51 ± 0.02 eV independent of illumination wavelength. The long term behavior of time-response profiles for a system of one acceptor and a single donor, as an exemplar, as studied by stability theory, shows an unstable critical point. Mechanisms for the PTTL are discussed and the emission is ascribed to electron centers in the oxygen sub-lattice. [ABSTRACT FROM AUTHOR]

Phototransferred thermoluminescence (PTTL) from BeO is reported. The conventional TL glow curve has five peaks, I–V, at 50, 182, 283, 437, and 535 °C when measured at 1 °C s−1 The dominant one is peak II. Only the first three reappear under phototransfer. Electron traps for peaks IV and V weakly contribute to the PTTL. The PTTL at peak III, supposedly associated with these weak donors, is counterintuitively intense. All PTTL peaks are affected by light-induced fading, thermal quenching, and all but peak II by thermal fading. The activation energy for thermal quenching was found as 0.56 ± 0.02 , 0.53 ± 0.05 , and 0.94 ± 0.07 eV using peaks I, II, and III, respectively. Electronic processes relevant in the PTTL of BeO are discussed. PTTL time-response profiles are analyzed using systems of coupled linear differential equations as well as by theoretical modeling. [ABSTRACT FROM AUTHOR]

Pr3+ impurity transitions in monoclinic and cubic phases of ZrO2 have been investigated by photoluminescence and thermoluminescence (TL). Zr(1− x)Pr x O2 (0 ⩽ x ⩽ 0.015) samples were prepared by the combustion method. Rietveld refined x-ray diffraction results confirm that undoped ZrO2 has a monoclinic structure, whereas Pr doped ZrO2 samples are in mixed phase consisting of monoclinic and cubic structures. ZrO2 shows a broad defect-related emission peak centered at 500 nm under an excitation wavelength of 300 nm. A series of Pr3+-related emissions are observed at 512, 584, 612–640 nm due to 3P0 → 3H4, 3P1 + 1I6 → 3H5, 1D2 → 3H4 transitions and between 719 and 740 nm due to 1D2 → 3H5 transitions when excited with 454 nm. The PL decay lifetime of Zr0.996Pr0.004O2 is 1.55 μ s for fixed λ ex = 300 nm and λ em = 612 nm. The TL glow curve of Zr0.99Pr0.01O2 shows a prominent peak at 695 K and secondary peaks at 508 K and 570 K, which are not observed in undoped ZrO2. The TL emission measured at 695 K confirms that Pr3+ replaces Zr4+ in cubic lattice sites of ZrO2. This work shows the relationship between the luminescence properties and different structures of ZrO2 and that supports the design of new materials for possible applications. [ABSTRACT FROM AUTHOR]

Thermoluminescence (TL) and fluorescence studies of aluminium oxide (Al2O3) implanted with 80 keV argon ions at fluences in the range 1 × 1014–1011 × 1016 ions/cm2 are presented. Thermoluminescence measurements were made at 1°C/s subsequent to irradiation to 20 Gy. The glow curve consists of a prominent peak centred at 170°C, the subject of this study, and three secondary peaks of weaker intensity centred at 242, 306, and 450°C. It is observed that the TL sensitivity of the main peak decreases with fluence of implantation. This suggests that ion implantation reduces the concentration of trapping centres responsible for the thermoluminescence. Kinetic analysis carried out by means of the variable heating rate, whole glow peak and curve fitting methods shows that the activation energy of the main peak is about 1.00 eV and the frequency factor of the order of 1010 s−1 irrespective of ion fluence. Fluorescence studies show emission bands at around 436, 676, 695 and 754 nm. These emission bands may be attributed to -centres or Cr3+ impurities substituting for aluminium. Scanning electron microscopy images taken from the samples indicate that their surface morphology remains the same irrespective of the implantation fluence. [ABSTRACT FROM AUTHOR]

Sr4Al14O25:Eu2+,Dy3+ is a commercially available green light emitting persistent luminescent phosphor. Owing to its complex crystalline structure and induced point defects, it shows fascinating luminescence that persists to typically up to 18 hrs after excitation. We report a trap-spectroscopic analysis of Sr4Al14O25:Eu2+,Dy3+ using thermoluminescence (TL). A TL glow curve measured at 1 °C/s following irradiation to 2 Gy at 20 °C shows two maxima at ~64 (labelled as P1) and 252 °C (P2). The variation of integrated TL intensity as a function of heating rate shows competition between radiative and non-radiative recombination processes. Beyond 1 °C/s heating rate, the non-radiative recombination process dominates and the luminescence efficiency drops sharply beyond 100 °C. The activation energy for thermal quenching is estimated to be W = 0.69 ± 0.07 eV. The peak maxima of P1 and P2 after correction for thermal quenching are found at ~70 and 275 °C. In addition, a secondary peak appears on the high temperature side of P1. Both the peaks show a gradual shift in their peak position Tm towards high temperature with preheating temperature Tstop. Moreover, the peaks also show a similar shift in Tm towards high temperature with increase in irradiation temperature Tirr. This suggests that peaks P1 and P2 are combinations of several closely spaced overlapping components. The activation energy of the component peaks comprising P1 is estimated to be ~0.63 - 0.68 eV whereas that of the component peaks comprising P2 is ~1.22 - 1.65 eV. An analysis of the fractional area between a pair of glow curves measured from the sample irradiated at different temperatures (Tirr) shows that the trap distribution associated with peak P1 is non-Gaussian whereas that associated with peak P2 follows Gaussian distribution. [ABSTRACT FROM AUTHOR]

Calcite, as do all carbonates, derives from the (CO3)2- anion. Calcite produces intense thermoluminescence (TL) which is mostly attributed to presence of Mn2+ anions. The emission spectra of calcite [1] and carbonatite [2] consist of broadband features at lower temperatures and line structures at high temperatures. These wavelength multiplexed differences are attributed to the solubility of Mn within calcite [1]. Although there has been considerable progress in understanding mechanisms of TL in calcite, corresponding advance related to optical stimulation has been halting. In this study we combine the utility of optical stimulation with the facility of thermal stimulation to study the phototransferred thermoluminescence (PTTL) of calcite induced by 470 nm blue-, 525 nm green- and 405 nm illumination. The conventional glow curve measured during heating to 600oC has an indeterminate number of glow peaks only three of which stand out and are regenerated under phototransfer. These are the ones studied. PTTL time-response profiles, that is, the dependence of PTTL intensity on the duration of illumination, are analysed using three methods, namely, a matrix- based analytical model, by use of vector fields and by theoretical modelling. We also address attendant effects such as backscattering to donor traps and competition effects, where supposed donor electron traps suppress electron trapping at acceptor electron traps. The time-response profiles corresponding to blue and UV light illumination displays the archetype increase through a maximum whereas that induced by green light is drawn out and, in some cases, tends to saturation. Surprisingly, the PTTL induced from deep electron traps by 405 nm illumination counterintuitively increases monotonically. We consider the extent to which this behaviour reflects the influence of slow bleaching components at the higher end of the corresponding PTTL peak or the effect of emission over a range of excited states as predicted by the modified Orgel (1955) diagram rather than the principle 4P(4T1g) relevant here. The intensity of PTTL induced from deep electron traps increases with temperature of illumination with an activation energy of thermal assistance of 0.052 ± 0.002 eV and decreases at elevated temperatures with an activation energy of thermal quenching of 0.75 ± 0.06 eV. The long term behaviour of the PTTL as studied by stability theory shows unstable critical points. The dosimetric characteristics of the latter including pre-dose effects are described. [ABSTRACT FROM AUTHOR]

The intention of this study is to explore the thermoluminescence properties of beta-irradiated Li–Zn fluoroborate glass. The glow-curve corresponding to 10 Gy shows two peaks when measured at 1°C/s. The dose response of the glass to beta irradiation was investigated. The trapping level parameters such as activation energy, frequency factor and order of kinetics associated with the observed glow-peak were determined using different methods. The thermoluminescence is affected by thermal quenching. A possible mechanism for the thermoluminescence is described. [ABSTRACT FROM AUTHOR]

Conventional and phototransferred thermoluminescence of crystalline synthetic quartz implanted with 70 keV Ar ions at fluences in the range 1 × 1014–5 × 1015 ions/cm2is reported. The glow curves, recorded at 5°C/s from beta-irradiated samples of similar mass, show a prominent peak between 100°C and 120°C. The thermoluminescence intensity of all implanted samples was greater than that of the unimplanted one. The increase in sensitivity is attributed to a corresponding increase in the concentration of point defects, as a result of the implantation, which act as electron traps or recombination centres. Kinetic analysis carried out using the peak shape, whole glow-peak and curve-fitting methods produced values of the activation energy, frequency factor and order of kinetics that are generally independent of implantation fluence. This result suggests that implantation did not necessarily affect the nature of the electron traps. With respect to phototransferred thermoluminescence, it was observed that it only appeared in the sample implanted at the highest fluence of 5 × 1015 ions/cm2. This may be so because the concentration of deep traps produced as a result of implantation at low fluence is too low to give rise to phototransferred thermoluminescence. The intensity of the phototransferred thermoluminescence goes through a peak with illumination time. We attribute this behaviour to the relative concentration of holes at recombination centres and phototransferred electrons at shallow traps. [ABSTRACT FROM PUBLISHER]

The experimental separation of overlapping peaks is a common practical concern in thermoluminescence experiments. In this regard, we have investigated the use of isothermal heating as a method for separating closely collocated peaks for kinetic analysis. The method has been developed and applied on a sample of synthetic quartz in which the thermoluminescence intensity is not reproducible in successive measurements on the same aliquot. Preparatory experiments performed to establish a suitable combination of temperature and heating time are described in detail. A comparative analysis of results from conventional thermal cleaning with those from isothermal cleaning, done as a means to assess the effectiveness of the latter, has shown isothermal heating to be a reliable method of separating closely collocated glow-peaks. The method is conveniently applied in combination with a new technique for kinetic analysis based on the use of the temperature-dependence of the area under an isothermal decay-curve. Isothermal heating was also applied to separate collocated peaks in europium-doped orthosilicate (Sr2SiO4:Eu2+), a luminophor, and in carbon-doped aluminium oxide (α-Al2O3:C), a dosemeter. The set studied in Sr2SiO4:Eu2+, unlike in the quartz, consists of peaks where the intensity of the lower-temperature one is greater than subsequent ones at higher temperature. On the other hand, the example investigated in α-Al2O3:C is similar except that the dominant peak subsumes the lower intensity secondary peak to the extent that they appear as one. [ABSTRACT FROM AUTHOR]

Thermoluminescence (TL) from beta irradiated ultra-high molecular weight polyethylene has been studied for measurements between 30 and 200 °C. An aliquot studied in this work produced TL glow curves consisting of two peaks, the main peak at 88 °C and a weaker intensity peak at 148 °C for heating at 1 °Cs-1 following an excitation dose of 215 Gy. The position of the main peak is poorly reproducible for heating rates of 0.2 and 0.6°Cs-1 investigated with the peak position decreasing when the sample is freshly irradiated and the TL re-measured. The said change in peak position is however less of an effect for measurements made at 1 °Cs-1 with the peak position being fairly reproducible in this case. Further measurements of the dosimetric properties of ultra-high molecular weight polyethylene showed that its dose response is linear from 26 Gy to about 161 Gy but exhibits slower growth in intensity with dose from about 860 Gy after regions of sub- and supra-linearity in between. If the TL is not measured immediately after irradiation, the signal fades with the delay approximately exponentially. In addition, a number of tests including phosphorescence analysis showed the possibility that the order of kinetics might not be unique but sensitive to several factors including measurement temperature. Thus for instance, the dependence of the peak position on the stop temperature in the partial heating procedure Tm - Tstop implied first-order kinetics but analysis of the geometrical factor µg for the same set of data gave µg = 0.46 ± 0.03 a value corresponding to characteristics somewhat intermediate between first and second order. In comparison, the results of analysis of the phosphorescence recorded at several temperatures on the rising edge of the main peak were only in agreement for measurements at 40 ?C with general-order analysis suggesting second-order kinetics apply as did TL-like transformation of the monotonic phosphorescence decay. Both results were also consistent with an additional finding that the time dependence of the isothermal decay at 40 ?C was consistent with second-order kinetics. Analysis of the TL for the activation energy using the initial rise method, variable heating rate procedure, TL-like transformation of phosphorescence and the peak shape estimates, produced a self-consistent set of values equal to 0.76 ±0.05 eV, 0.66±0.03 eV, 0.77±0.06 eV and values of the order of 0.8 eV, respectively. The kinetic parameters found in this study compare favourably with literature values. [ABSTRACT FROM AUTHOR]

The influence of irradiation dose on luminescence lifetimes has been studied in suites of natural quartz from Brazil, Nigeria and South Korea. The lifetimes were evaluated from time-resolved luminescence spectra measured from quartz pulse-stimulated at 470 nm and detected between 360 and 380 nm. The effect of irradiation varied between materials, decreasing with dose in the Brazilian quartz, independent of dose in the samples from South Korea, and increasing with dose in the quartz from Nigeria. The dose-related effects are accounted for with reference to an energy band scheme for quartz in which the luminescence lifetime is associated with a primary radiative recombination centre at which most capture of holes produced during irradiation and associated hole re-trapping takes place. The measurements on the effect of irradiation dose on luminescence lifetimes were augmented by investigations concerned with the influence of measurement temperature between 20 and 200°C on luminescence lifetimes in the same materials. It was observed that the luminescence lifetimes decrease continuously with temperature of stimulation and in a manner suggestive of increased thermal quenching of the corresponding luminescence. However, better consistency with the Mott-Seitz configurational coordinate model of thermal quenching is only apparent at temperatures greater than 120°C. The discrepancy is attributed to the model used to derive the formulae for luminescence lifetimes in which any re-trapping of stimulated charge is assumed negligible. However, it is argued that if re-trapping were in fact not negligible then the decrease of luminescence lifetimes with measurement temperature would be evidence of the progressive reduction of the re-trapping as the measurement temperature were increased with the overall effect being the monotonic decrease in luminescence lifetimes as observed. [ABSTRACT FROM AUTHOR]

We discuss an approach by which the initial rise (IR) method can be extended to evaluate the frequency factor (s) of a glow peak, in addition to activation energy (E) that is usually obtainable from it. The approach requires that the phosphor be irradiated to a dose near or equal to the saturation dose of the glow peak to be analyzed. By plotting ln(I) against 1/T for the thermoluminescence glow peak, one obtains a straight line whose gradient is - E/k and intercept is ln(n0s/β) from which E and s are determined respectively. The approach was used to analyze two numerically generated glow peaks and reproduce with reasonably good accuracy the E and s values used to generate the glow peaks. It is also shown that when it becomes necessary to include intensities above 10% of the maximum glow peak intensity, the error introduced into the calculated frequency factor by the assumption n≅ n0 is always negligible when the analysis is done by plotting ln(I/n) against 1/T. In this case the frequency factor is obtained from ln(s/β) which is now the intercept. Two experimental glow peaks were also analyzed using the new IR method approach and peak shape method. Good agreement, which again shows the validity and reliability of the present approach was observed between the values of E and s obtained by the two methods. [ABSTRACT FROM AUTHOR]

We present a method for the estimation of defect (trap) physical parameters from thermoluminescence (TL) glow peaks. In this method, the order of kinetics b is determined using two values of TL intensity each of which corresponds to the same temperature ( T 1 ) on two separate glow peaks of a phosphor. The two glow peaks are obtained from two aliquots of the phosphor irradiated to same dose but read out at different heating rates. The proposed method requires a minimum of only two data points in contrast to standard peak shape (PS) methods that require three points corresponding to three different temperatures on the same glow peak. Once the order of kinetics b is determined, the activation energy E is calculated by taking a second point ( T 2 ) on any one of the two glow peaks. The values of b and E thus obtained are used to evaluate the frequency factor S ′′ and the number of trapped electrons before the heating begins n o . The validity of the method was checked using two numerically generated glow peaks. For the two cases, the method reproduced the input values reasonably well. The method was also used to analyse two experimental glow peaks. The results obtained provide a reasonably good fit to the experimental data. The kinetic parameters calculated using the present technique are comparable to those calculated using PS and initial rise methods. Initial guesses can easily be obtained for E and S ′′ using the present technique when a glow curve is to be deconvoluted with a model consisting of many unknown parameters with E and S ″ inclusive. [ABSTRACT FROM AUTHOR]

Thermoluminescence characteristics of two subsidiary glow peaks, one below 100°C and the other above 300°C, have been studied for measurements between 30°C and 500°C in α-Al2O3:C. The thermoluminescence intensity of the lower temperature peak decreased with storage with a half-life of about 150 s. In contrast, the intensity of the higher temperature peak increased with storage towards some maximum. The peak-temperature of each of the secondary glow peaks was essentially constant with dose, whereas that of the main peak decreased with irradiation. The dose response for the three peaks was similar except for sublinear growth in the higher temperature peak at low dose values. These effects are discussed in terms of changes in the concentration of F+ luminescence precursors brought about by competitive electron re-trapping at deep electron-traps or hole-traps. This work refines the physics and application of α-Al2O3:C luminescence in radiation dosimetry. [ABSTRACT FROM AUTHOR]

Polycrystalline CaTa2O6:Pr3+ phosphor is prepared by calcination of a stoichiometric mixture of Ta2O5 and CaCO3 plus a 0.5 mol% PrCl3 dopant level (1200 °C, 4 h). [ABSTRACT FROM AUTHOR]