Phototransferred Thermoluminescence Research Articles

A first look at phototransferred thermoluminescence of rose quartz

We report a preliminary study of phototransferred thermoluminescence (PTTL) induced by 470 nm light source in rose quartz. The glow curve corresponding to 1 Gy consists of five peaks at 76, 115, 180, 290 and 423 °C labelled I through V in that order. In the PTTL experiments employing blue light. PTTL was regenerated at peak I following preheating to remove peak I only and at peaks I and II otherwise. The dependence of the PTTL intensity on duration of illumination is analyzed in terms of a system of one acceptor and two donors in both cases. The mechanisms for the PTTL phenomena in the rose quartz are comprehensively discussed in this paper.

A Photo-transfer Thermoluminescence (PTTL) Study of TLD-100 over a Wide Dose Range

Photo-transferred thermoluminescence (PTTL) is defined as the transfer of electrons from deep traps into shallow traps via optical stimulation. The importance of PTTL is that it allows for a second measurement of dose assessments for accuracy in cases such as an erroneous dose evaluation. In this study, the PTTL signal of TLD-100 was investigated in detail for a wide dose range from mGy to Gy. The investigation of PTTL signals in the order of Gy is the main innovation of this study. Based on the results of the low dose measurement (mGy), the PTTL dose-response curve has a significant sublinear characteristic in the order of mGy for the total area condition. Additionally, PTTL signals could not be distinguished from the background signal up to 5mGy. Therefore, the PTTL method can be used by taking into account the sublinear function obtained after 5mGy for the total area. On the other hand, it can be applied to TLD-100 between 0.5mGy and 50mGy using ROI. Based on the high dose measurement results (Gy), the PTTL method can be applied up to 10Gy regardless of the total area and ROI. Therefore, the dose reassessment can be performed with PTTL signal in high dose measurements (Gy) such as in the radiotherapy field. Furthermore, in future studies, heating the dosimeters during UV exposure, predose effect, or subjecting the dosimeters to fast cooling following the annealing process may provide important outputs to obtaining higher PTTL intensity, thus, it may allow measuring lower radiation doses.

Phototransferred thermoluminescence of calcite: Analysis and mechanisms

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.

Radiometric and stimulated luminescent characterization of Amazonian sediments from the Middle Rio Negro, Western Amazon

The sediments were collected from paleodunes, river terraces, islands, and sand bars at Mariuá Archipelago, Rio Negro, Brazil. XRD analysis revealed that quartz is the predominant mineral along with a trace quantity of kaolinite. Neutron activation analysis of the sediments revealed the assembly of rare-earth elements, metals and semi-metals. The values of U and Th were found to be 3–5 ppm in paleodunes and 9–16 ppm in terraces, and K-40 concentration is below detectable limit. The OSL of quartz (dune) is composed of three components with decay times of 0.2, 11.0 and 350 s, respectively. This OSL emission is related to the TL peaks below 380 °C. Also, photo-transferred TL is observed in the temperature range of 190–250 °C for a blue stimulation of 500 s. TL peaks kinetic parameters were calculated and discussed. The lifetimes of TL peaks at 272 and 355 °C are approximately 4.0×104 and 1.5×109 years, respectively. Using the conventional SAR protocol, 11 samples were dated, including two old paleodunes with ages of 124.4 and 169.7 ka, increasing the age interval of the site, the other samples were younger sediments, with ages between 0.39 and 53.9 ka.

Properties of phototransferred thermoluminescence of Al2O3:Cr

Phototransferred thermoluminescence of Al2O3:Cr induced by 470 nm blue light is reported. The glow curve corresponding to irradiation to 162 Gy and heating to 650 °C at 1 °C s−1 has at least seven peaks labelled I onwards. Of these, only peaks III-V stand out under phototransfer. The PTTL is discussed as systems of an acceptor and donors where the number of donors scales with preheating temperature. The PTTL time-response profiles are analysed using various models and the results are consistent with experimental patterns. We put particular attention on PTTL from deep electron traps whose dose response is sublinear but becomes linear if extensive illumination is used for the phototransfer. The intensity of the PTTL corresponding to deep electron traps goes through a maximum with illumination temperature. The initial increase is ascribed to thermal assistance and the subsequent decrease to thermal quenching.

Studies on luminescence properties and photo-thermo transfer phenomena in fluorapatite

This study reports the structure, composition, photoluminescence (PL), thermoluminescence (TL), and optically stimulated luminescence (OSL) properties of the Brazilian natural fluorapatite. Also, the existence of photo-thermo transfer phenomena is investigated from TL/OSL emission mechanisms. X-ray diffraction (XRD) pattern reveals that the sample has a hexagonal system with a crystallite size of about 46 nm calculated using the Scherrer formula. The presence of several elements including the rare earths such as Ce, Nd, and Er are identified using total X-ray fluorescence (TXRF) spectroscopy results. Ce3+ ions are associated with the emission band at 371 nm when excited at 300 nm. Fluorapatite exhibits intense TL and OSL signals when irradiated with beta particles and shows linear dose-response from 1 up to 50 Gy. The TL glow curves are deconvoluted to six peaks centered at 99, 147, 188, 242, 329, and 431 °C using general order kinetic equation. The corresponding activation energies vary between 0.68 and 1.11 eV. An anomalous fading is noticed for the first TL peak, which decays completely in 6 h; the second TL glow peak decays about 59% within 12 h and other high temperature peaks are more stable. Continuous-wave OSL (CW-OSL) is constituted of three components, having decay times (τ) of 0.39, 5, and 64 s. The deconvoluted linearly modulated OSL (LM-OSL) has four peaks, with peak maxima (tm) at 2.85, 7.4, 27, and 130 s. Further, it is noticed the phenomenon of phototransferred TL (PTTL) at 30 °C, due to the optical transfer of electrons related to the traps of 329 and 431 °C peaks to the main peak at 242 °C. The temperature-induced PTTL using thermally assisted OSL (TA-OSL) at 170 °C with 400 s of blue stimulation depicted a transfer of trapped electrons from very deep traps (VDTs), located at temperatures higher than 500 °C, to the main peak. Here, the luminescence intensity increases with the beta dose.

Phototransferred thermoluminescence of CaF2: Principles, analytical methods, and mechanisms

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.

Processes related to phototransfer under blue- and green-light illumination in annealed Al2O3:C,Mg

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.

Using Infra-red stimulated luminescence and phototransferred thermoluminescence to investigate electron trapping and charge transport in feldspars

Previous studies have observed mineral specific variations in the ratios of IRSL signals stimulated at the different discrete wavelengths of lines corresponding to Xe lamp emission lines, which fall within the broad excitation spectrum of IRSL. Meanwhile recent accounts of IRSL have referred to single trapping systems within the excitation band, and modelled excitation spectra as continuous gaussian distributions. A simple single trap model should not result in variations in the ratio of IRSL intensities produced at different wavelengths. In the study reported here 22 different feldspar samples, which have all been characterised by SEM and x-ray analysis, were measured using a portable OSL instrument equipped with 890 nm and 940 nm diode arrays to confirm and extend the previous observations of variations in IRSL intensity ratios. Of the samples investigated the sensitivity varied over 3–4 orders of magnitude. Albite samples in this selection showed consistently high responses. The plagioclase samples show significant variations, and the microcline and K-feldspar samples produced a large range of responses. Excitation ratios of 940 nm–890 nm show mineralogically linked variations which together with the earlier Xe lamp data point to distributions of trapping systems within the variable environments of these minerals. These results do not readily fit simple single trap models for luminescence from feldspars; instead, they suggest multiple traps or a series of similar traps which are significantly perturbed by their local lattice structural environments. Post Stimulation Phosphorescence (PSP) was observed for all samples, and phototransferred thermoluminescence (PTTL) has also been confirmed following IR stimulation suggesting that recombination mechanisms involve charge mobility and interactions with shallow traps in band-tail states rather than primarily being associated with direct quantum tunnelling recombination. The relative proportions of PSP to prior IRSL also varied between the two stimulation wavelengths which further emphasises the physical differentiation between processes influencing different subpopulations of the trapping states associated with IRSL and their local lattice environments.

New correlation between PTTL and POSL components in Al2O3:C

We describe newly found correlations between thermoluminescence (TL), pulsed optically stimulated luminescence (POSL), and phototransfer TL (PTTL) signals in Al2O3:C. A set of Al2O3:C samples were characterized for their TL and OSL curve shapes, as well as TL/POSL integrals and correlated with their PTTL behavior. POSL was used to separate the contribution from fast UV emission (F+ centers) and slow blue emission (F centers) OSL components in Al2O3:C. The results show that samples with high PTTL exhibit TL curve shapes with a peak at higher temperatures and OSL curves that decay slower compared to samples with low PTTL. The ratio of the integral POSL components, the UV/B ratio, was found to inversely correlate with the PTTL. We discuss the possible causes of our observations and outline the limitations of commonly used luminescence models to explain our data. These correlations add yet another piece to the puzzle of the stimulated luminescence mechanisms of Al2O3:C.

Phototransferred thermoluminescence characteristics of microcline (KAlSi3O8) under 470 nm blue- and 870 nm infrared-light illumination

We report phototransferred thermoluminescence (PTTL) induced in microcline by 470 nm blue- and 870 nm infrared-light. A conventional thermoluminescence (TL) glow curve measured from a sample irradiated to 40 Gy produces five composite TL glow peaks P1, P2, P3, P4 and P5 at 90, 123, 166, 298 and 391 °C respectively. The sample produces PTTL peaks also identified as P1, P2, P3 and P4 following illumination by blue or infrared light after irradiation to 40 Gy and preheating to 400 °C. Step-annealing suggests the presence of deep electron traps associated with a signal beyond 500 °C. However, preheating to 500 °C and exposure to blue or infrared light does not produce significant PTTL peaks. For doses between 40 Gy and 100 Gy, the maximum PTTL is emitted within 60 and 150 s of blue light illumination. On the other hand, the same feature under the infrared light illumination occurs within 100–200 s of illumination. PTTL peaks P1, P2, P3 and P4 reproduced under blue light illumination have a linear dose response between 10 Gy and 100 Gy and those reproduced under infrared light illumination have a superlinear dose response between 10 and 100 Gy. In contrast, donor peak P5 in both cases follows sublinear dose response within the same dose range. Fading of PTTL peaks P1, P2, P3 and P4 as well as the donor peak P5 are negligibly small under blue light illumination compared to that of infrared light illumination. PTTL glow curves are also found to be properly reproducible.

Phototransferred thermoluminescence of BeO: Time-response profiles and mechanisms

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±0.07eV 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.

Light-induced inter-electron-trap charge movement in annealed Al2O3:C,Mg

Inter-electron-trap charge movement induced under phototransferred thermoluminescence (PTTL) in Al2O3:C,Mg annealed at 700 and 900 °C is reported. Such annealing modifies the emission spectrum and electron trapping states in Al2O3:C,Mg. The glow curve of Al2O3:C,Mg annealed at 700 °C has eight peaks at 46, 76, 100, 170, 199, 290, 330 and 375 °C respectively. In comparison, that of the sample annealed at 900 °C has nine at 49, 80, 100, 174, 206, 235, 290, 335 and 375 °C. The peaks are labelled I, II, III … in that order. Only peaks I-IV re-appear under phototransfer. The PTTL is analysed qualitatively as well as by computational and phenomenological models as systems of an acceptor and multiple donors. Point defects that likely contribute to emergence of PTTL are discussed and are deduced to lie mostly in the oxygen sub-lattice.

Thermally assisted IRSL and VSL measurements of display glass from mobile phones for retrospective dosimetry

Investigations of retrospective dosimetry have shown that components of mobile phones are suitable as emergency dosimeters in case of radiological incidents. For physical dosimetry, components can be read out using optically stimulated luminescence (OSL), thermoluminescence (TL) and phototransferred thermoluminescence (PTTL) methods to determine the absorbed dose. This paper deals with a feasibility study of display glass from modern mobile phones that are measured by thermally assisted (Ta) optically stimulated luminescence. Violet (VSL, 405 nm) and infrared (IRSL, 850 nm) LEDs were used for optical stimulation and two protocols (Ta-VSL and Ta-IRSL) were tested. The aim was to systematically investigate the luminescence properties, compare the results to blue stimulated Ta-BSL protocol (458 nm) and to develop a robust measurement protocol for the usage as an emergency dosimeter after an incident with ionizing radiation.First, the native signals were measured to calculate the zero dose signal. Next, the reproducibility and dose response of the luminescence signals were analyzed. Finally, the signal stability was tested after the storage of irradiated samples at room temperature. In general, the developed Ta-IRSL and Ta-VSL protocols indicate usability, however, further research is needed to test the potential of a new protocol for physical retrospective dosimetry.

Phototransferred thermoluminescence of tanzanite: A matrix-based analysis of time-response profiles and competition effects

We report the phototransferred thermoluminescence of tanzanite induced by 470 nm blue light. A glow curve measured after irradiation to 120 Gy and heating at 1 °C s−1 shows three nominal peaks at 86 °C (peak I) and two secondary peaks at 160 °C and 320 °C. The latter two peaks are collocated peaks with each one consisting of multiple components. Phototransferred thermoluminescence is only reproduced at peak I. Although this work addresses phototransfer, the system studied is unconventional in that the phototransferred TL is associated with an indeterminate number of donors. A matrix-based method has been used to analyse the time-response profiles of the phototransferred thermoluminescence. Competition effects, where putative donor electron traps act in competition with acceptor electron traps, have been studied using empirical models.

The role of sodium ions in the thermoluminescence peaks of laboratory-irradiated natural quartz

In this study, the role of sodium ions (Na+) in the generation of thermoluminescence (TL) peaks in the 77–680 K region of natural quartz are investigated by combining the TL and phototransferred thermoluminescence (PTTL) spectrally-resolved glow curves. The TL spectrum is characterized by four emission bands at 380, 470, 590, and 620 nm, which are related to four TL peaks at 383, 513, 598, and 648 K, respectively. The dynamic parameters of the TL peaks are evaluated using the initial rise method. PTTL is also studied in the temperature range of 77–330 K. In this region, PTTL curves show four main peaks at 160, 190, 250, and 295 K, in which the intensity of the PTTL peak at 250 K is shown to be relative to the Na+ concentration and the double irradiation process. PTTL measurements were further used to estimate the relationship between the TL peak at 598 K and PTTL peak at 383 K.

Analysis of illumination-time-dependent profiles of phototransferred thermoluminescence of Al2O3:C,Mg

Time-dependent profiles of phototransferred thermoluminescence (PTTL) of Al2O3:C, Mg are presented and analysed. Whereas qualitative discussions consider theoretical predictions, mathematical analysis of the profiles is based on experimental results. The thermoluminescence glow curve of unannealed Al2O3:C, Mg measured at 1 °C/s following irradiation to 2 Gy consists of at least eight peaks. There is a prominent peak at 165 °C and 7 secondary peaks at 43, 73, 195, ~246, 284, ~336 and 374 °C respectively. These are labelled I through VIII in order of appearance. Of these, only peaks I-IV are reproduced under phototransfer. The role of various electron traps as donors was determined using pulse annealing as well as by monitoring the dependence of peak intensity on duration of illumination used in the phototransfer. In particular, this shows that the electron trap for peak III at 165 °C, the main one, is the dominant donor to the electron traps responsible for PTTL at peaks I and II. There is also evidence of deep electron traps and deep hole traps beyond 500 °C which contribute to phototransferred thermoluminescence associated with peak III. The dependence of PTTL intensity on illumination time has been analysed using sets of coupled first order linear differential equations which describe the charge transfer at the electron traps involved. Particular solutions to the family of equations set up have been applied on experimental data successfully as evident in residuals associated with each fit.

The photo-transferred thermoluminescence phenomenon in case of emergency dose assessment

A major disadvantage of dose reconstruction by means of thermoluminescence (TL) is the fact that during readout of any TL material exposed to ionizing radiation (i.e., during measuring the glow curve), the radiation-induced signal gets lost. Application of the photo-transferred thermoluminescence phenomenon (PTTL) may offer a solution to this problem. In PTTL, the residual signal that is not destroyed by conventional TL readout (because it comes from deeper electron traps) can be readout through simultaneous stimulation by UV light and heating, allowing to obtain information about the absorbed dose in a second run. The present paper describes the application of PTTL for emergency dose assessment. For this, MTS-N thermoluminescent detectors (LiF: Mg, Ti) were exposed using a high-energy Clinac 2300 medical linear accelerator to doses of 100 mGy, 300 mGy, 500 mGy, 700 mGy and 1000 mGy. Irradiation with UV radiation allowed the determination of the optimal heating time of 3 h, while the optimal temperature was identified to be 70 °C. The results obtained demonstrated the usefulness of the PTTL method for emergency dose assessment. The efficiency of the PTTL method was determined as 19%. Finally it was found that the detector background after UV exposure should not be underestimated during routine dose measurements.

Quartz optically stimulated luminescence configurational coordinate model

In a recent study using pulsed stimulation we revealed that optically stimulated luminescence (OSL) and photo-transferred thermoluminescence (PTTL) in quartz are characterised by a common pulse response. We interpreted this result as indicating that both emissions are governed by the same detrapping mechanisms. In the present study we develop a common configurational coordinate model to describe the mechanisms. Within our model we identify the energy associated with the thermal assistance effect as the vibrational energy of the ground state of the dimer that represents the trap. Further, we model the OSL stimulation process as an optical transition between a vibrationally-excited ground state level and a dimer excited state. By introducing additional luminescence parameters, we reveal that the processes that underlie thermal quenching and the room temperature OSL response to pulsed stimulation can be represented by competing modes which empty the excited state. In particular, we find that the room temperature pulse response can be modelled in terms of an optical transition from the excited state to a lower antibonding level from which a hole is ejected. In contrast, thermal quenching is explained by excited state vibrational dissociation at large dimer component separations.

PTTL characteristics of glass samples from mobile phones

Phototransferred thermoluminescence (PTTL) of mobile phone display glass (category A) is systematically investigated to develop a robust measurement protocol for its emergency dosimeter usage after an incident with ionizing radiation. First, optimal readout parameters were defined by varying preheat temperature and holding time preceding violet exposure (405 nm). Next, the detection window of the PTTL measurement was adjusted to optimize the ratio between radiation-induced (RIS) and non-radiation-induced signals (nRIS) of the PTTL. Finally, the developed protocol determines PTTL after preheating to 400 °C and holding for 10 s was tested using the detection window centered at 340 nm. Dosimetric properties such as the PTTL reproducibility and dose response were investigated. PTTL signal stability tests showed that the violet PTTL signal originates from deeper and consequently more thermally stable traps. A signal loss of less than 10% after 10.6 days (254 h) storage was observed. Additionally, TL and PTTL spectra were recorded to investigate the luminescence emissions after beta and gamma irradiation and different UV exposures. PTTL emissions are similar to TL emission. Varying UV energy a qualitative comparison demonstrate that the RIS and nRIS PTTL signal intensities increase significantly with decreasing UV stimulation wavelength. In general, the developed PTTL protocol indicates better signal stability and thus some advantages over other techniques, however, further research is needed to test the potential of a new method for physical retrospective dosimetry.