Optically Stimulated Luminescence Decay Curves Research Articles

Short-term fading studies on optically stimulated luminescence in LiMgPO4:Er

The main drawback of LiMgPO4 is high fading. In order to improve the time stability of the optically stimulated luminescence (OSL) signal of LiMgPO4 after irradiation, five preparation processes had been adopted to prepare five kinds of LiMgPO4:Er phosphor. The structure of the prepared samples was analyzed by X-ray diffraction. The OSL decay curves, thermoluminescence (TL) glow curves, OSL sensitivity, minimum detectable dose (MDD) and the fading properties after irradiation for the five kinds of LiMgPO4:Er phosphors were investigated. Considering minimizing fading 24 h after irradiation, the preparation process for samples heated at 900 °C for 10 h is optimal. The OSL fading of LiMgPO4 phosphor is improved significantly by changing the preparation processes. The less than 5% loss of the OSL signal was measured after 24 h of the irradiation for samples heated at 900 °C for 10 h when the integration time is more than 0.5 s, and the sensitivity by taking the total area under the OSL curve of this samples is about half that of TLD-500k. There is a loss of less than or equal to 5% of the OSL signal for samples heated at 900 °C for 10 h when the integration time is greater than or equal to 20 s within 30 days after irradiation. LiMgPO4:Er samples heated at 900 °C for 10 h is the LiMgPO4 phosphor with the lowest fading so far. It is possible to prepare a LiMgPO4 phosphor with a low fading after irradiation and a moderate sensitivity by further investigating the preparation processes.

Correlation between thermoluminescence and optically stimulated luminescence signal in BeO

Beryllium Oxide (BeO) is a promising dosimetric material that is rapidly becoming an essential instrument in Optically Stimulated Luminescence (OSL) dosimetry applications. Despite the potential of BeO as a luminescence dosimeter, gaps remain in understanding how its Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) signals are connected. Our study aimed at examining Residual Thermoluminescence (R-TL) glow curves after various bleaching times to find an association between TL traps and OSL components across a wide range of doses, at 40 mGy and from 10 to 100 Gy. OSL decay curves and intensities of R-TL glow curves were fitted to either pure exponential decay functions or to stretched exponential decay functions, due to optical attenuation, to determine the OSL components and the bleaching decay rates of each TL peak, respectively. A good correlation between the decay rates of the OSL components and bleaching decay rates of each TL peak for both high and low-dose irradiations was found only for the model functions considering optical attenuation in the material. Taken together, this qualitative method helped to identify various traps, and results revealed a more consistent luminescence mechanism between TL and OSL signals than was previously assumed. Further support for the correlation between TL and OSL was derived from thermal stability studies of the OSL signal and from the dose response of the TL peaks and the OSL signal after different thermal pretreatments. Different bleaching models were discussed to define the appropriate one for BeO. These results may enhance our understanding of BeO as a dosimeter.

TSL, OSL and scintillation properties of Tb-doped barium fluoride translucent ceramics

We report on the fabrication of Tb-doped barium fluoride translucent ceramics, and their scintillation and dosimetric characteristics. The Tb-doped barium fluoride ceramics were fabricated by spark plasma sintering. Scintillation derived from the 4f→4f transitions of Tb3+ under X-rays was observed from the Tb-doped barium fluoride ceramics. Their decay times under X-rays were about 10 ms. Further, thermally-stimulated luminescence originating from the transitions was detected, and their dose responses were observed in the range of 0.1–100 mGy. Moreover, the Tb-doped barium fluoride ceramics exhibited optically-stimulated luminescence (OSL), and three exponential decay components were detected in the OSL decay curves.

Investigation of dosimetric properties of CaSO4:Mn phosphor prepared using slow evaporation route

The objective of this work was to investigate the luminescent properties of CaSO4:Mn synthesized by slow evaporation route. The crystalline structure, morphology, thermal and optical properties of the phosphors were characterized by X-ray diffraction analysis (XRD), Scanning electron microscopy (SEM), photoluminescence (PL) and thermogravimetric analysis (TGA). Moreover, using thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques, the dosimetric properties of the phosphors, such as emission spectra, glow curve reproducibility, dose-response linearity, fading of the luminescent signal, variation of the TL intensity with the heating rate, OSL decay curves, correlation between TL and OSL emissions and minimum detectable dose (MDD) were comprehensively investigated. For dosimetric analyses, the samples were irradiated with doses from 169 mGy to 10 Gy. The emission band fits with the characteristic line of the Mn2+ emission features, ascribed to 6A1→4T1 transition. CaSO4:Mn pellets present a TL glow curve with a single typical peak centered around 494 nm, an OSL decay curve with predominance of a fast decay component, and a MDD on the order of mGy. The luminescent signals showed to be linear and reproducible in the studied dose range. The trapping centers located between 0.83 eV and 1.07 eV were revealed for different heating rates in the TL study. The high TL sensitivity of CaSO4:Mn was proven when comparing with commercially available dosimeters. The luminescent signals exhibit a smaller fading than described in the literature for CaSO4:Mn produced by other methods.

New perspectives on traps and radiative recombination centers for optically stimulated luminescence in LiF:Mg,Cu,P

LiF:Mg,Cu,P (MCP) is well-known for its high thermoluminescence (TL) sensitivity and is widely used for TL dosimetry. Following recent studies, highlighting its optically stimulated luminescence (OSL), the properties of MCP have been studied for OSL-based 2D and 3D dosimetry. Here, we have measured the spectrally resolved OSL emission as a function of stimulation time, identifying the peak of the emission band to be at ∼355 nm during the early stimulation period before shifting to peaking at ∼382 nm during the remaining part of the experiment. By assuming the spectra to originate from radiative recombination centers with Gaussian emission bands, we identified two recombination centers with emission centered at ∼355 nm (RC1) and ∼394 nm (RC2), respectively. From the OSL decay curves, we have identified two dominating types of OSL traps (fast and slowly decaying OSL traps). We provide indicative values for the photoexcitation cross section of these OSL traps. The fast-decaying OSL traps were found to predominantly emit OSL through RC1. By depleting the fast-decaying OSL traps before TL measurements, we have identified these traps to be associated with a previously undetected TL peak at ∼87 ° C (1 °C/s heating rate), located between the TL peaks usually denoted as peaks one and two. We further found that the features related to the fast-decaying OSL traps were not observable for powder samples without a heat treatment at ∼560–700 °C. Pellet samples show these features without the heat treatment, but could potentially have undergone a similar treatment during sintering.

Observations of optically and thermally stimulated luminescence from aluminosilicate glasses

Analysis of thermoluminescence (TL) glow curves from aluminosilicate glass reveals that the glow curve in the region ∼400 K–∼600 K can be partly described by thermally excited tunneling from a defect excited state to the recombination center, plus a TL signal caused by thermal excitation directly to the delocalized band from a distribution of trapping states. Mathematical fitting reveals a range of trap depths and frequency factors for the tunneling which depend upon pre-heat temperature in a manner consistent with that expected from a tunneling model. Optical bleaching removes the TL signal from this region of the glow curve while at the same time producing an optically stimulated luminescence (OSL) signal. The OSL decay curve can be described by optically excited tunneling, plus a term consistent with ionization of trapped electrons directly to the delocalized band. Analysis of the dependence of the optical cross-section for tunneling indicates that the excited state resides within the band-tails states for the glass. Fading of the OSL signal is consistent with ground-state tunneling directly to the recombination site, while fading of the TL signal is consistent of ground-state tunneling plus thermal emptying of the shallower parts of the distribution of trapping states.

Novel Sm3+ doped BaZn2(PO4)2 glass-ceramic for optically stimulated luminescence dosimetry

Sm3+ doped glass-ceramic with crystallized BaZn2(PO4)2 was prepared and its structural, optical, and stimulated luminescence dosimetry properties were investigated. The excitation and emission spectra of photoluminescence exhibit Sm3+ associated transitions. The relationship between the doping concentration and the optically stimulated luminescence (OSL) intensity was investigated. The OSL intensity reached a maximum at a Sm3+ concentration of 0.25 mol%, after that, a concentration quenching was observed. The OSL decay curves of BaZn2(PO4)2: 0.25Sm3+ glass-ceramic are deconvoluted by using general order kinetics show the two components that contribute to the OSL signal with photoionization cross sections of 1.693 × 10−17 and 2.443 × 10−18 cm2, respectively. The thermoluminescence curve has two peaks at 393 and 477 K. The linear radiation dose response range is identified as 0.2-500 Gy. These results show that Sm3+ doped BaZn2(PO4)2 glass-ceramic has the potential to be used as a candidate material for radiation dosimetry.

Thermoluminescence and optically stimulated luminescence of Ba-doped Al2O3 produced by a modified sol-gel route

This work features the synthesis and characterization of Al2O3 phosphors doped with different concentrations of barium. The samples are produced by a modified sol-gel route, with glucose used as a chelating agent. The luminescent response of the phosphors is also evaluated through their thermoluminescence (TL) and optically stimulated luminescence (OSL). These optical properties are characterized with pellets obtained from the addition of Teflon to the phosphors. Through the TL analysis carried out with a heating rate of 10 °C/s, the samples reveal two intense TL glow peaks with different glow curve shapes when varying the dopant concentration of all the samples. By means of the TL emission curves of the pellets, activation energies associated with the transfer processes of the materials are determined. The phosphors present typical exponential OSL decay curves with a predominance of fast and medium components, indicating that the traps have a high photoionization cross section for blue light-emitting diodes.

Optically stimulated luminescence dosimetry on tissue equivalent LiF: Mg, Cu, Na, Si phosphor

Lithium fluoride (LiF) is one of the best tissue equivalent materials exhibiting good thermoluminescence (TL) properties, however it shows weak optically stimulated luminescence (OSL) response with blue light (470 nm) stimulation. Several research groups are working on improving the OSL properties of LiF phosphor. In an attempt, a thorough investigation on tissue equivalent LiF: Mg,Cu,Na,Si (MCNS) as a possible OSL material has been done in the current work. As the preparation route and particle size can modify the energy levels and optical transitions, the striking improvement is expected by preparing it in nanocrystalline form. The structural and morphological characterization has been done using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). The OSL emission is observed in continuous wave mode under blue (460 nm) light stimulation. The OSL decay curve exhibits a significant increase in intensity which is ~2 times higher than LiF based commercial phosphor (TLD-100) irradiated with gamma dose of 0.1 Gy. The phosphor shows a linear dose response in the range of 0.1–20 Gy with almost constant decay rate. The phosphor has shown low residual signal which is good for its repetitive use. The OSL decay curve has been analysed and related parameters such as photoionization cross-section and decay constant are determined. ESR study has been done to identify the defect centres and describing the role of point defects and charge compensators involved in the luminescence process. This reveals the existence of Cu in Cu+ or Cu0 state. Good OSL properties suggests MCNS phosphor has a potential as a OSL dosimeter. The current study adds new knowledge and opens a new window to improve the OSL sensitivity of LiF material.

Thermoluminescence and optically stimulated luminescence of colemanite-rich borate mineral

We report structural, chemical composition, thermal decomposition and stimulated luminescence properties of a colemanite-rich borate (Ca2B6O11•5H2O) mineral collected from Kırka, Eskişehir region of Turkey. X-ray diffraction shows that the colemanite phase has a monoclinic crystal structure. Further, Raman spectroscopic analysis reveals that the sample contains 45.83% of B and 17.93% of CaO. Thermogravimetric analysis indicates that there is removal of hydroxyl groups followed by explosive release of water from the sample at temperature below 200 °C. The sample produces thermoluminescence (TL) and optically stimulated luminescence (OSL) following beta irradiation. A TL glow curve measured at 1 °C/s consists of five glow peaks at ∼145, 175, 215, 267 and 322 °C. The activation energy associated with the peaks are ∼0.73, 0.77, 0.83, 0.90 and 1.19 eV respectively and the frequency factors are ∼106 ‒ 108 s−1. The lifetimes of the traps at room temperature are estimated to be ∼1.42 days to 2.33 × 104 years. The peaks at ∼175, 215 and 267 °C show supralinear dose response between 32 and 16000 Gy whereas the ones at ∼145 and 322 °C show supralinearity between 32 and 2048 Gy. Analysis of the OSL decay curve shows that the decay curve has a ‘fast’-, ‘medium’- and a ‘slow’ component. The dose response of the fast component is found to be linear within 2–4096 Gy and that of the medium- and slow components are found to be superlinear between 2 Gy and 4096 Gy.

Comparison of stimulated luminescence properties of various porcelain-based items from Turkey towards prevalent features for retrospective dosimetry

In the present study, different porcelain-based materials including a sugar bowl, an ashtray, a porcelain breaker, an artificial dental implant, an electric fuse and the seal of a porcelain moneybox were investigated via thermally (TL) and optically stimulated luminescence (OSL). For this purpose, luminescence dosimetric properties such as TL and OSL curve shapes, reproducibility, bleachability, along with dose response features such as linearity and lowest detectable dose limits (LDDL) of these materials were compared. A feature that is sample-dependent deals with both quartz and mullite content of each porcelain paste, as it was indicated by XRD analysis. Three dominant peaks in TL glow curves were ubiquitously observed, and OSL decay curves formed in two components (C1 and C2) for all samples. It was determined that the LDDL for only two TL peaks (P1 and P2) seem acceptable for accidental retrospective dosimetry applications (0.9–2.2 Gy). On the other hand, the LDDL values obtained according to OSL analysis yielded more promising results in terms of accidental retrospective dosimetry applications as 0.3–0.4 Gy and 0.75–1.35 Gy for C1 and C2 components, respectively. TL peaks P1 and P2 indicate the majority of prevalent, if not universal, properties of stimulated luminescence. This latter universality could support an argument towards identification of these two TL peaks directly correlated to quartz mineral. On the other hand, TL P3 could be attributed to a contribution of more than one mineral, such as quartz, kaolinite and mullite, due to the lack of prevalence over all stimulated luminescence features.

Optically stimulated luminescence decay and dosimetric properties of cerium-doped potassium sulfate phosphor.

Optically stimulated luminescence (OSL) is used for dating in archaeology and geology, and in dosimetry of ionizing radiation. Some crystalline wide band-gap insulators may be used as OSL radiation detectors. Recently it was found that cerium-doped potassium sulfate crystals have promising luminescence properties. This paper presents some OSL properties of K2 SO4 :Ce crystals that were prepared in the form of pellets. The crystals exhibited a strong luminescence signal, good measurement repeatability, and high sensitivity for ionizing radiation. Best results were obtained after annealing at 1000°C. Dose-dependence characteristics were determined in the range 10 mGy to 11.2 Gy. OSL decay curves consisted of several components. Fast and slow OSL components of the phosphor had different properties. The slow component was quite stable and obeyed power law dependence. It decayed in the 55 days after irradiation. Its luminescence properties depended on sample preparation and the storage time after irradiation.

OSL with chips from US credit cards

Chips from credit cards issued by the major US banks have been tested with optically stimulated luminescence (OSL) as potential materials for use in emergency radiation dosimetry. The following dosimetric properties have been studied: (1) OSL decay curves from both irradiated and unirradiated samples; (2) dose-response characteristics of the OSL and values of minimum detectable doses; (3) fading of the OSL signal with time after irradiation. No OSL was detected in unexposed samples while prominent signals were observed after irradiation. It was found that the shape of the OSL signals can be fitted by a combination of an exponentially decaying function and a power function. The dose-response relationship was linear in the range 0–7 Gy if the OSL signals were measured at the same effective time after irradiation and normalized to the response to a test dose. Dose recovery tests demonstrated that the doses can be reconstructed with an accuracy ±20% if the OSL measurements are conducted within 7 days after exposure and the corresponding OSL doses are corrected for fading.

Uniformity of Thermoluminescence and Optically Stimulated Luminescence Signals Over the Length of Doped LiMgPO4 Crystal Rods Grown by Micro-Pulling-Down Method.

The purpose of this work was to systematically assess the distribution of thermoluminescence (TL) and optically stimulated luminescence (OSL) properties along the length of crystals grown by the micro-pulling-down method, in relation to the microstructure and distribution of activators. We analyzed lithium magnesium phosphate (LiMgPO4; LMP) crystals doped with terbium (Tb; 0.8 mol%) or with a combination of thulium (Tm; 0.8 mol% or 1.2 mol%) and boron (B; 10 mol%). Crystals of several centimeters in length and 3 mm in diameter were cut into 20–40 slices, depending on length. For each sample, TL glow curves and OSL decay curves were examined. Optical microscopy and scanning electron microscopy were used to assess the microstructure and elemental composition of several selected samples. Two-dimensional TL readouts were performed to identify the areas with higher and lower signal emission. Our study showed that there may be significant differences not only in LMP sensitivity along the crystal’s axis but also on the surface of the slice. The distribution of activators varies depending on the type of crystals and strongly affects luminescence properties.

Characterization of optically-stimulated luminescence properties by NaCl:Eu2+ crystal and the thermal response

In this paper, we report optically-stimulated luminescence (OSL) properties of Eu2+-doped NaCl single crystal as a candidate phosphor for use in near real-time radiation measurement and dosimetry. The crystal was grown by the vertical Bridgman–Stockbarger method. The obtained crystal shows a strong photoluminescence (PL) band peaking at 430 nm due to the parity-allowed 5d-4f transitions of Eu2+. After irradiating with X-rays, it demonstrates OSL also at 430 nm due to the Eu2+ ion acting as an emission center while stimulating by light (500 ± 30 nm). Compared with a commercial BaFBr:Eu2+ OSL detector, the sensitivity to X-ray dose is lower by about one order of magnitude. In addition, while the crystal is reused multiple times, the OSL response signal increases despite the same given radiation dose. The OSL decay curve can be decomposed into three exponential decay functions with the lifetimes of 0.6, 6.4, and 120.5 s, and the decomposition analyses revealed that only the intensity of intermediate component increases with the number of reused cycles. Further analyses with thermally-stimulated luminescence (TSL) revealed that the intermediate OSL component is related to a TSL glow signal originated from trapping centers having the activation energies of ~0.93 eV and ~1.27 eV and the frequency factors of ~7.52 × 108 s−1 and ~6.29 × 1011 s−1, respectively.

Thermoluminescence and optically stimulated luminescence properties of ulexite mineral

Although naturally occurring luminescence materials such as quartz and feldspars are generally used for radiation dosimetry and dating, natural borates may also stand as a promising material for dosimetry and dating. We report thermoluminescence (TL) and optically stimulated luminescence (OSL) of one of the most abundant boron minerals in Turkey namely, ulexite (NaCaB5O6(OH)6·5H2O). An X-ray diffraction (XRD) analysis confirmed that the sample has triclinic crystal structure and contains 40.55% of B, 5.92% of Na2O, 12.3% of CaO. A thermogravimetric analysis indicates two stages of dehydration within 60–160 °C, 160–250 °C and dehydroxylation within 260–580 °C. Analysis of TL glow curves using fractional glow and deconvolution reveal that there are four glow peaks at 154, 211, 273 and 327 °C in the glow curve of ulexite. All the glow peaks follow a non-first order kinetics. The activation energies of the traps are estimated from the fractional glow curves as 0.72, 0.93, 1.16 and 1.28 eV and that evaluated from the deconvolution analysis as 0.76, 0.83, 0.96 and 1.27 eV. The lifetimes of these traps are estimated within 1.55 days–3.6 × 104 years. The radiation dose responses of the TL peaks are supra-linear between 8 Gy and 1024 Gy. OSL decay curve of ulexite consists a fast, a medium and a slow component with recombination lifetimes of (0.63 ± 0.08), (7.51 ± 0.71), (93.49 ± 3.62) s respectively. The fast OSL component obeyed first order, whereas medium and slow components obeyed general order of kinetics. The dose response of the medium and slow OSL components showed a sub-linearity from 64 Gy to 4096 Gy whereas the fast component showed linear response between 8 and 4096 Gy.

On the production of the medium component in quartz OSL: Experiments and simulations

Optically stimulated luminescence (OSL) production of the medium component was investigated using a coarse-grained quartz sample from Australia. Analysis of OSL decay curves measured at different stimulation temperatures revealed that there was strong interaction between the initial occupancies of fast and medium OSL components. Preheating experiments showed that the thermal stability of the medium OSL component was almost the same as that of the fast OSL component. These results suggested that both the fast and medium OSL components originate from the same source trap. The production of the medium OSL component was simulated using a kinetic model in which the medium OSL signal was originated from the 325 °C TL trap and the relevant charge is retrapped in the 170 °C TL trap due to the phototransfer effect. A good match between measured and simulated OSL decay curve was achieved.

Ultrafast component effects on quartz single grains dose estimation from Khutagt Uul Mountains, Mongolia

Abstract This study presents single-grain optically stimulated luminescence (OSL) results from pottery and sediments from the archaeological site “The burials in Khutag Uul Mountains (Mongolia)”. A global fitting procedure was used on a selection of single grains from pottery, D0 values obtained were between 16 to 40 Gy and 25 to 82 Gy and the equivalent doses De ranged from ~8 to 12 Gy and from 4.2 ± 0.4 Gy to 37.3 ± 2.5 Gy for pottery and sedimentary quartz, correspondingly. For pottery, the relative spread in CAM De values increases as higher precision constraints are applied and lead to significant increases in the relative standard error from 2.7% to ~7.5%. The number of accepted grains which passed acceptance criteria reduced from 180 to 65. For sedimentary quartz, there is a trend observed that both MAM De and FMM De values increase as higher precision in De is applied, and the number of accepted grains reduces from 146 to 53. The detailed study of the OSL decay curves identified an ultrafast OSL component with the decay rates of 53 ± 1 s–1 in addition to the fast and medium components and its effect on De was examined.

Single-Grain Quartz OSL Characteristics: Testing for Correlations within and between Sites in Asia, Europe and Africa.

We studied the characteristics of the optically stimulated luminescence (OSL) signal of single-grain quartz from three sites in China, Italy, and Libya, including the brightness, decay curve and dose response curve (DRC) shapes, recuperation, and reproducibility. We demonstrate the large variation in OSL behaviors for individual quartz grains of different samples from different regions, and show that recuperation, sensitivity change, and reproducibility are independent of the brightness and decay curve shape of the OSL signals. The single-grain DRCs can be divided into at least eight groups with different characteristic saturation doses (D0), and a standardized growth curve (SGC) can be established for each of the DRC groups. There is no distinctive difference in the shape of OSL decay curves among different DRC groups, but samples from different regions have a difference in the OSL sensitivities and decay shapes for different groups. Many of the quartz grains have low D0 values (30–50 Gy), and more than 99% of the grains have D0 values of <200 Gy. Our results raise caution against the dating of samples with equivalent dose values higher than 100 Gy, if there are many low-D0 and ‘saturated’ grains.

Evidence of Optically Stimulated Luminescence in Lu3Al5O12:Ce

Lutetium aluminum garnet, commonly known as LuAG, is a versatile material finding numerous optical applications, and whose scintillation properties have been widely investigated. In this study, experimental evidences of optically stimulated luminescence (OSL) phenomena occurring in LuAG:Ce crystals are shown. After demonstrating the possibility to optically bleach an electron trap responsible for a thermally stimulated luminescence (TSL) peak at 280 °C (heating rate 1.7 °C s−1) using red light, a direct measurement of the OSL decay curve and of the resulting characteristic Ce3+ 5d‐4f emission spectrum is carried out. The assessment of the bleaching spectrum of the TSL peak at 280 °C reveals that light with wavelength in the 600–650 nm interval is the most efficient in depleting the TSL peak, making He‐Ne lasers suitable sources of optical stimulation. The finding of OSL features in LuAG:Ce paves the way to new application perspectives. In particular, the achievement of a good balance between scintillation and energy storage properties of LuAG.Ce can drive a constructive integration between X‐rays imaging approaches based on photo‐stimulable phosphors and those exploiting scintillating materials.