Continuous Wave Optically Stimulated Luminescence Research Articles

Study on the thermoluminescence and optically stimulated luminescence of LiMgPO4:Dy phosphors synthesized by different methods

LiMgPO4:Dy phosphors were synthesized by high-temperature solid-state method and sol-gel method. The effects of different synthesis methods on crystal structure, morphology, thermoluminescence (TL) properties, and optically stimulated luminescence (OSL) properties of LiMgPO4:Dy were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), TL glow curve and continuous wave OSL (CW-OSL) curves. XRD patterns showed that the crystal phase of the samples synthesized by the two methods is LiMgPO4. The morphology of the samples synthesized by sol-gel method was better than that synthesized by high-temperature solid-state method. The TL sensitivity of the samples synthesized by sol-gel method was higher than that synthesized by high-temperature solid-state method. The TL strongest glow peak of the LiMgPO4:Dy sample synthesized by high-temperature solid-state method was 363 K, while that the LiMgPO4:Dy sample synthesized by sol-gel method was 380 K. The OSL sensitivity of the samples synthesized by sol-gel method was significantly higher than that synthesized by high-temperature solid-state method. The synthesis method had no effect on the OSL decay of the sample. LiMgPO4:Dy phosphor synthesized by sol-gel method may be a suitable candidate material for radiation dosimetry.

Characterization of indigenous OSL phosphors LiCaAlF6:Eu,Y and α-Al2O3:C for space dosimetry

The possibility of using indigenously synthesized Optically Stimulated Luminescence (OSL) phosphors, α-Al2O3:C and LiCaAlF6:Eu,Y is explored for application in space dosimetry. The dosimeters prepared using these phosphors were irradiated in BARC-TIFR Pelletron Accelerator facility with proton beam (8–20 MeV). The OSL properties with proton beam irradiation were compared with beta irradiation corresponding to 90Sr/90Y. No change in the OSL emission was found for both the phosphors when exposed to with low LET 90Sr/90Y beta (0.2 keV/μm) and high LET proton (2 keV/μm, 20 MeV). It was observed that Continuous Wave (CW) OSL signal decays faster with increasing LET of the proton beam for both types of dosimeters α-Al2O3:C and LCAF. The OSL dose response is linear for the high LET proton beam which is similar to the response obtained using low LET beta and gamma irradiation. The variation of OSL efficiency per unit fluence matches reasonably well with the theoretically calculated values of absorbed dose in water.

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.

TL and OSL characteristics of the fluoroperovskite KMgF3:Eu,Yb, Li for dosimetry applications

The purpose of this work was to investigate the dosimetric and luminescence properties of the novel KMgF3:Eu0.5%,Yb0.1%,Li15% fluoroperovskite synthesized using the sol-gel method. The luminescence signals were characterized using Optically Stimulated Luminescence (OSL) spectra, Linearly-Modulated OSL (LM-OSL), Continuous-Wave OSL (CW-OSL), and Thermoluminescence (TL) techniques. The blue light (470 nm) stimulated OSL associated with Eu2+, and Eu3+ emissions was correlated with the TL peaks up to 300 °C. The photoionization cross-section of each OSL component was evaluated using deconvolution analysis following two different optical stimulation modes, namely LM-OSL and CW-OSL. The activation energy values were evaluated using the Tm-Tstop and CGCD methods. OSL signal fading of 5% and 13% was observed at the end of 24 h and over the next three months, respectively. The results indicate that the OSL from KMgF3:Eu0.5%,Yb0.1%,Li15% fluoroperovskite has suitable properties for dosimetry, including high sensitivity to ionizing radiation and a wide linear dose range (0.1–500 Gy). These results enhance the understanding of the origin of the luminescence properties in this material and this work paves the way toward its utility for dosimetry purposes.

Continuous-wave optically stimulated luminescence properties of Guajillo chilli polyminerals exposed to gamma radiation

In this investigation, the Continuous-Wave Optically Stimulated Luminescence (CW-OSL) properties of polyminerals extracted from Mexican and Peruvian Guajillo chilli were studied using a source of cesium-137 (Cs-137) gamma radiation. The Guajillo chilli polyminerals were stimulated with blue light for 120 s, and their luminescence was detected in the UV region. The General Order Kinetics (GOK) deconvolution analysis of the CW-OSL curves was carried out using three individual components. The CW-OSL dose response from 10 to 5000 Gy was analysed in Guajillo chilli polyminerals. After different storage periods, the polyminerals show an increase in the CW-OSL intensity. A strong and moderate effect of the sunlight (60 min) and artificial (6 h) light is observed on the CW-OSL response. Therefore, the CW-OSL properties of polyminerals could be used in the identification of Mexican and Peruvian Guajillo chilli exposed to Cs-137 gamma radiation.

Carbon doping-induced defect centers in anodized alumina with enhanced optically stimulated luminescence

Anodized aluminum oxide (AAO) in amorphous form is shown to be a prospective phosphor for optically stimulated luminescence (OSL) by implanting 50 keV carbon ions at a fluence of 1 × 1016 ions/cm2 at room temperature. An almost 20-fold enhancement in continuous wave OSL (CW-OSL) sensitivity is obtained in carbon-doped AAO (C:AAO) by exposing to beta radiation, while an almost linear increase in CW-OSL intensity is recorded with increasing dose from 0.3 to 5 Gy. However, cathodoluminescence (CL) suggests an upsurge of oxygen vacancies, especially F+ and F22+ centers, at the cost of F center-related defects in C:AAO. Detailed X-ray photoelectron spectroscopy (XPS) analysis further reveals that the implanted carbon atoms can act as cationic impurities in AAO and stabilize the nearby F+ centers via substitution of Al3+ by C2+. The combined CL and XPS results are also shown to be capable of illustrating the CW-OSL response. This study would, therefore, be a benchmark for understanding the role of carbon in the substitutional sites of AAO for generating OSL active electron traps.

OSL response of α-Al2O3:C, Mg exposed to beta and UVC radiation: A comparative investigation

Continuous wave optically stimulated luminescence (CW-OSL) of an Al2O3:C, Mg single crystal was investigated after irradiation with ultraviolet C radiation (UVC; peak emission at 254 nm) as well as with a beta source under different doses (100 mGy – 3 Gy). Analysis of the OSL decay curves provided experimental evidence that: i) UVC- and beta-irradiated Al2O3:C, Mg single crystal showed similar OSL decay curves, and that ii) a same fast (τ~2.9 s) and a same slow (τ~29 s) components were identified in the OSL decay curves for both types of radiation. On the other hand, analysis of the results suggested that radiation type generated distinct initial concentration of charges trapped at these two traps. The differences in the OSL decay curves were attributed either to differences in the initial population of the traps or to a balance of trapping-detrapping during UV irradiation.

Optically stimulated luminescence of cowrie shells

Characteristics of continuous wave optically stimulated luminescence (CW-OSL) and linear modulation OSL (LM-OSL) from three different types of cowrie shells are presented. Irradiated samples were optically stimulated at 72 mW/cm2 for CW-OSL and linearly ramped from zero to 72 mW/cm2 to obtain LM-OSL. The measured CW-OSL and LM-OSL curves of the shells are each determined to consist of three components namely fast, medium and slow components. The fast, medium and slow LM-OSL components peak at 17.0 ± 0.8, 45.0 ± 1.8 and 140.8 ± 6.7 s respectively for all samples. In addition, peak positions are independent of dose. The photoionization cross-sections of the OSL traps for the three components estimated from CW-OSL are similar to those determined using LM-OSL. The OSL of the three components increases linearly with dose. The coefficient of variation of responses from repeated measurements of same aliquot lies below 2.3%. The shells are thus potential materials for retrospective dosimetry.

Estimation of dose and elapsed time after unrecognized high-dose radiation exposure using the continuous-wave optically stimulated luminescence from Mg2SiO4:Tb

For precisely estimating dose and elapsed time after an unrecognized high-dose radiation exposure in radiological emergency, applicability of the continuous-wave optically stimulated luminescence (CW-OSL) signals from Mg2SiO4:Tb (MSO) was investigated. Small disks of MSO were irradiated with β-rays from a Sr-90 source and their CW-OSL signals were analysed. The CW-OSL curves obtained by stimulation with a blue light (λ = 458 nm) at 5, 10, 20, 50 and 1119 h after irradiation indicated that they have short- and long-life components; each component was empirically deconvoluted to the sum of two exponential functions. Through repetitive regression analyses on those curves, a practical method for estimating the dose and elapsed time after an unrecognized radiation exposure was proposed. Results of blind tests indicated that the accuracy of absorbed dose estimation using this method was satisfactory while the estimated elapsed times were accompanied with considerable uncertainties.

Study of optically stimulated luminescence and calculation of trapping parameters of K2Ca2(SO4)3:Eu nanophosphor

K2Ca2(SO4)3:Eu nanophosphor was synthesized by chemical coprecipitation method and annealed at different temperatures from 400 to 900 °C. The nanophosphor annealed at 600 °C showed cubic structure with crystallite size ~25 nm. TEM shows morphology of K2Ca2(SO4)3:Eu nanophosphor was in the form of nanorods having diameter ~20 nm and length of ~100–200 nm. These samples were irradiated with gamma radiation for the doses varying from 10 mGy to 10 kGy and their Thermoluminescence (TL) and continuous-wave optically stimulated luminescence (CW-OSL) have been studied. CW-OSL response was found to be maximal for the sample annealed at 600 °C. The TL glow curve of the nanophosphor apparently showed a major peak at around 160 °C accompanied by three low intensity peaks at ~75, 215 and 285 °C. The traps responsible for all the TL peaks in K2Ca2(SO4)3:Eu were also found to be OSL sensitive. The qualitative correlation between TL peaks and CW-OSL response suggested that the traps associated with low temperature peaks are responsible for fast decay and the traps associated with the higher temperature peaks are responsible for slow decay of the OSL signal. OSL response showed linear behavior up to 1 kGy and saturated with further increase in the gamma dose. The wide OSL response makes studied K2Ca2(SO4)3:Eu nanophosphor a good candidate for high dose measurement.

Influence of optical bleaching on spectrally resolved thermoluminescence in beta irradiated potassium chloride pellets

Spectrally resolved thermoluminescence (SR-TL) measurements of beta irradiated chemically pure KCl pellets were carried out. Before each SR-TL measurement the pellets were measured using continuous wave optically stimulated luminescence (CW-OSL) with a green stimulation source. It was found that CW-OSL readout significantly affects the SR-TL response with respect to both total intensity and spectral distribution of the luminescence. The results were dependent on the stimulation time, however even after 45 min of optical bleaching a significant number of traps and recombination centers was still populated. After green stimulation additional short wavelength (UV) band appears. The resulting emission spectrum was deconvoluted to four and five emission bands. In both cases the peak positions were stable irrespective of the stimulation time. Theoretical analysis of the dependence of spectral components on the OSL stimulation time was performed. It indicates that at least some of recombination and/or bleaching processes did not involve a delocalized band.

Particle size effect on TL/OSL response of NaMgF3:Tb phosphor

NaMgF3 is a nearly tissue equivalent material with low Zeff = 10.4 and a well-known phosphor for its high sensitivity concerning luminescence. The type of preparation route followed greatly affects the luminescence efficiency of a material. Grinding of NaMgF3:Tb phosphor for a long time induces several lattice defects in the phosphor. In this work, effect of particle size on TL/OSL response of NaMgF3:Tb irradiated by 60Co source of gamma radiations with a dose of 15 Gy has been investigated. NaMgF3:Tb samples has been synthesized by solid state reaction method using different grinding times i.e. 1 h and 5 h. XRD technique confirms its formation and crystallite size is calculated. TL studies show that sample synthesized by 5 h grinding is almost 2 times more intense than the sample obtained by 1 h grinding. Also, a clear enhancement is seen in the shoulder peak of sample grinded for 5 h. This could be due to increase in occupancy of trapped charge carriers in the trap levels. However, the position of main TL glow peak remains same in both the samples. Associated TL kinetic parameters such as order of kinetics, activation energy, frequency factor and trap density have been calculated by deconvoluting the TL glow peaks to understand the TL phenomenon. Continuous-wave optically stimulated luminescence (CW-OSL) decay curves have been obtained under blue LED stimulation for 40 s. Analyzing the CW-OSL decay curves reveal that grinding time significantly affects the OSL intensity of the phosphor as well. The decay constant and photoionization cross-section is determined for the faster and slower components of the total OSL intensity. It could be concluded that the time of grinding taken during preparation of the material has a major role in affecting the concentration of trap levels formed inside the forbidden gap of the phosphor.

On the stochastic uncertainties of thermally and optically stimulated luminescence signals: A Monte Carlo approach

Phenomenological models are frequently used to analyze experimental signals in thermally and optically stimulated luminescence experiments. Typically, these models consist of systems of differential equations describing various electronic transitions. An alternative to the differential equation approach is the use of Monte Carlo (MC) methods, which also allow an estimation of the theoretical stochastic uncertainty of the intensity of the luminescence signal. By running and averaging several MC variants, these stochastic uncertainties are estimated in this paper for various luminescence models.In the case of first-order kinetics processes, the MC results compare well with previously published analytical results for the coefficient of variation (CV) in stochastic linear pure death processes. By contrast, no analytical results are available for the more general one trap one recombination center model (OTOR), and MC is the only method available for estimating the stochastic uncertainties.In this paper the CV coefficients are simulated for three commonly used experimental stimulation modes, namely thermally stimulated luminescence (TL), continuous-wave optically stimulated luminescence (CW-OSL) and linearly modulated OSL (LM-OSL). The results of the simulations show that CW-OSL signals have the smallest CV values among the three stimulation modes, and therefore these signals are least likely to exhibit stochastic variations. The stochastic uncertainties in these phenomenological models are discussed in the context of single grain luminescence experiments and nanodosimetric materials, in which one deals with small numbers of charge carriers.

Component-resolved bleaching correlation between OSL and IRSL signals in various geological materials

The primary aim of the present study includes establishing a qualitative as well as quantitative correlation between OSL and IRSL signals in various materials of geological origin, by investigating the influence of the IR stimulation to the OSL signal. The materials which are the subject of the present study include one K-feldspar belonging to the group of microcline, two different grain size fractions of Durango apatite at the edge of the nano-scale and gypsum. A two-step stimulation protocol was applied, including an exposure of the irradiated sample to infrared stimulation for various time and a subsequent continuous wave OSL using blue light. In the framework of a component-resolved analysis, the IRSL decay curves were fitted using analytical equations describing the localized tunneling recombination model; the subsequent OSL decay curves were also fitted using a linear superposition of analytical expressions describing both delocalized and localized recombination processes. The selection of number and type of components in the latter case is also elaborated, based on the physical meaningfulness of the de-convolution results.

Dosimetric properties of ZrO2 and ZrO2:Sm3+ exposed to beta rays

This work investigates thermoluminescence (TL) and optically stimulated luminescence (OSL) properties of ZrO2 and ZrO2:Sm3+ (1 mol%) synthesized by solution combustion method. XRD measurement suggested that both the samples exhibit monoclinic phase. The average crystallite size measured using scanning electron microscopy is found to be ~ 60 nm. TL glow curve of ZrO2 had a prominent peak at 429 K and a less prominent (or smaller) peak at 510 K. On the other hand, ZrO2:Sm3+ had a broad glow peak at 460 K. TL glow curve intensity of all the peaks is found to increase linearly with beta dose (upto 16.4 Gy) for both samples. TL Trapping parameter are analyzed after deconvolution of TL glow curves using CCDA method. The recombination sites of glow peaks are investigated through TL emission spectrum. The 429 K peak show a band at 500 nm is attributed due to oxygen vacancies. Continuous Wave–OSL measurements (CW-OSL) suggests a linear increase in the intensity with beta dose for both samples. The decay curves are deconvoluted by using general order kinetics. CW–OSL decay curve has shown two components contributing to the OSL signal. The photoionization cross sections of ZrO2 and ZrO2:Sm3+ for two components are found to be 1.187 × 10−16, 6.255 × 10−18 and 1.303 × 10−16, 8.842 × 10−18 cm2 respectively. Linearly Modulated - OSL (LM-OSL) of ZrO2 exhibit broad peak and it is deconvoluted into 4 peaks. These results suggests the possibility of choosing suitable activator for development of new TL dosimeters.

Study of optically stimulated luminescence in K2SO4:Ce

Highly sensitive cerium-doped K2SO4phosphor was synthesized for optically stimulated luminescence (OSL) properties. The present study mainly investigated various kinetic parameters and correlation between the thermoluminescence and OSL (TL-OSL) processes. Continuous wave-OSL sensitivity of the phosphor is four times more than that of Al2O3:C (Landauer). The phosphor exhibits good TL-OSL correlation. Most of the charge carriers in K2SO4:Ce get depleted using optical stimulation which confirms their participation in TL as well as OSL processes. Optical bleaching also affects the order of kinetics for TL. The glow curve of K2SO4:Ce without illumination exactly fits with two components, whereas it is fitted with three components when optically bleached for 60 s. Bleaching also shifted the glow peaks toward higher temperature side indicating non- first-order kinetics.

Dosimetric characterization of highly sensitive OSL phosphor: LiCaAlF6:Eu,Y

The paper presents the dosimetric characterization of lithium calcium aluminum fluoride doped with europium and yttrium (LiCaAlF6:Eu,Y), synthesized by simple melt process. The characterization involved thermoluminescence (TL), optically stimulated luminescence (OSL), photoluminescence (PL) spectra, OSL emission spectra, minimum measurable dose, fading, dose response and photon energy dependence measurements. The OSL sensitivity of this phosphor to ionizing radiation was found to be ∼20 times to that of commercially available Al2O3:C, whereas, the TL sensitivity was ∼2.5 times to that of CaSO4:Dy (0.05 mol%). Photoluminescence (PL) and OSL emission spectra suggest that the Eu2+ ions are responsible for OSL emission. The reusability of OSL discs for 50 cycles for a test dose of 20 mGy has been established. Minimum detectable dose for the phosphor in continuous wave OSL (CW-OSL) mode was found to be 0.5 μGy with negligible fading post 9 days of irradiation. Owing to its excellent dosimetric characteristics the phosphor is a highly sensitive dosimetric grade phosphor and is a serious contender for various radiological applications.

Factors influencing the shape of CW-OSL signal obtained by stimulation of very deep traps in carbon-doped aluminium oxide: An experimental study

The optically stimulated luminescence from carbon-doped aluminium oxide (α-Al2O3:C) displays a peak with time under certain measurement conditions. In this paper, we present factors that influence the peak-like shape of continuous-wave optically stimulated luminescence (CW-OSL) signal. The report is based on the experimental study of OSL signals obtained by stimulation of very deep traps in α-Al2O3:C. Methods exploiting post-irradiation annealing, variable dose and temperature dependent OSL measurements were used in the investigation. It is found that the rising part of the CW-OSL peak is obtained when the rate of retrapping at the most optically active trap (main trap) exceeds the rate of direct radiative recombination following optical release of charges from all optically active traps. This is possible if, during optical stimulation, the primary trap responsible for OSL i.e. the main trap, is substantially unoccupied and the very deep, donor traps are substantially filled up. The rate of charge retrapping itself is deduced to depend on the occupancy of the acceptor traps i.e. shallow, main and secondary traps; concentration of charge carriers in the very deep, donor traps; the post-irradiation annealing temperature and the temperature at which the OSL is measured.

Optically stimulated luminescence of natural NaCl mineral from Dead Sea exposed to gamma radiation

In this work, the continuous wave - optically stimulated luminescence (CW-OSL) emissions of natural salt minerals, collected from Dead Sea in summer of 2015, were studied. The CW-OSL dose response of natural salt showed a linear range between 0.5Gy and 10Gy of gamma radiation of 60Co. Samples exposed at 3Gy exhibited good repeatability with a variation coefficient of 4.6%. The CW-OSL response as function of the preheating temperature (50–250°C) was analyzed. An increase of 15% of the CW-OSL response was observed in NaCl samples during storage period of 336h. The results showed that the natural Dead Sea salt minerals could be applied as natural dosimeter of gamma radiation.

Pure thermal sensitisation and pre-dose effect of OSL in both unfired and annealed quartz samples

The sensitisation of quartz has attracted much attention since its thorough understanding is important in luminescence studies and dating applications. The present investigation examines the influence of pure thermal activation and predose treatments on the sensitisation of different components of linearly modulated optically stimulated luminescence (LM-OSL) measured at room temperature (RT) thereby eliminating undesired thermal quenching effects. Annealed and unfired quartz samples from Nigeria were used. The OSL measurements were carried out using an automated RISØTL/OSL reader (model-TL/OSL–DA–15). A new approach was adopted to match each of the resolved components of the RT-LM-OSL to respective thermoluminescence (TL) peaks that share the same electron trap and recombination centers. Pure thermal activation and pre-dose treatments respectively affect the sensitisation of all the components of the RT-LM-OSL in a similar manner as the one reported for the 110°C TL peak but without thermal quenching contributions. Component C4 in annealed samples that was identified to share the same electron trap and recombination centers with the 110°C TL peak was also proved appropriate for RT-LM-OSL, instead of the initial part of the continuous wave (CW) OSL signal, thus the methods can serve as complementary dating methods.