Linearly Modulated Optically Stimulated Luminescence Research Articles

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.

Linearly Modulated OSL in K\(_{3}\)Na(SO\(_{4}\))\(_{2}\):Eu\(^{3+}\) Phosphor Irradiated With 48 MeV Li\(^{3+}\) and 85 MeV C\(^{6+}\) Swift Heavy Ions Beam

K\({}_{3}\)Na(SO\({}_{4}\))\({}_{2}\):Eu\({}^{3+}\) shows OSL when irradiated with swift heavy ion beams of Li\({}^{3+}\) and C\({}^{6+}\) at different fluences. The micro sample is prepared through solid state diffusion method along with its counter parts of ball milled (7 days) nanophosphor and co-precipitated nanophosphor samples. The material was characterized by XRD to confirm its formation in a single phase. Comparison of the experimental data with that of the data available in the literature (JCPDS data file \#74 0398) shows formation of a single hexagonal phase, with the space group P3 m1. Study on the particle size effect shows that particle size in the 75--106 \(\mu\)m rangeis more suitable for the linearly modulated-optically stimulated luminescence (LM-OSL) dosimetry in micro form. Dosimetric properties of the phosphor material using LM-OSL technique for blue light stimulation (\(\lambda=470\) nm and \(t=120$\) seconds) show that it is highly sensitive in the linear dose range. Here in this paper, we tried to find a relationship between detrapping probabilities and photoionization cross section using curve fitting (deconvolution) method. We also calculated and converted the fluence into doses using SRIM software. Data are presented indicating that the LM-OSL peak is composed of three overlapping components originating from populated traps with optical cross sections of 10\({}^{-17}\)-10\({}^{-18}\) cm\({}^{2}\). It was found that micro and ball milled nanophosphor Carbon ion beam irradiated samples dominates the photoionization cross section as compared with lithium ion irradiated samples, but co-precipitated sample is dominant in lithium irradiated samples. Which infers about the different trapping level formation and also recombination processes involved during the preparation and in readouts of samples.

Electron trap filling and emptying through simulations: Studying the shift of the maximum intensity position in Thermoluminescence and Linearly Modulated Optically Stimulated Luminescence curves

In the present work, the response of peak positions in Linearly Modulated Optically Stimulated Luminescence (LM-OSL) curves as a function of physical and technical parameters were investigated and compared theoretically; specifically, the time or temperature values (tm,Tm) of their maximum intensity (Im). The stimulation modes of Thermoluminescence (TL) and LM-OSL differ slightly in terms of peak resemblance (geometrical structure) but differ greatly as physical phenomena, so it could be ideal to study the effects responsible for electron trap filling or trap emptying. These simulations could also extend our knowledge in Stimulated Luminescence phenomena regarding expected experimental outcomes. In the present study, four simulation experiments were conducted based on the One Trap – One Recombination center (OTOR) model for the case of equal re-trapping and recombination probabilities signifying second order kinetics. The first experiment defines the Tm shifting for various heating and optical stimulation rates. The second depicts an electron trap filling process, in which dose progresses from a low value until the saturation state. In the third experiment, a trap emptying procedure was simulated via thermal bleaching (Isothermal Decay), whereas in the final one, the same trap emptying procedure was conducted via optical bleaching (Continuous wave optically stimulated luminescence) for different time spans. Generally the tm,Tm shifting in trap emptying processes, is proven, according to simulations, to follow a similar behavior to the tm,Tm shift as a function of heating or optical stimulation rate. Regarding trap filling, tm and Tm shift to lower values as the dose increases.

New analytical expressions derived from the localized transition model for luminescence stimulation modes of TL and LM-OSL and their applications in computerized curve deconvolution

Localized transitions within the forbidden energy band have been used to describe a variety of luminescence behaviors for a wide range of materials. In this work, transformed analytical expressions based on the localized one trap one recombination-center (OTOR) model are derived to describe thermoluminescence (TL) glow peaks and linearly-modulated optically stimulated luminescence (LM-OSL) components. These expressions contain two geometric parameters describing the location of a peak/component that can be estimated directly from the curve. The deviations of activation energies determined using the TL expression are within 1% for peaks of various kinetic orders and the deviations of decay rates determined using the LM-OSL expression are within 4% for components with systematic factors smaller than 0.6. It demonstrates that these expressions can precisely fit measured TL/LM-OSL curves consisting of seriously overlapped peaks/components. The implications on application of the computerized curve deconvolution (CCD) method were discussed.

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.

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.

Component resolved bleaching study in natural calcium fluoride using CW-OSL, LM-OSL and residual TL glow curves after bleaching

Natural calcium fluoride has been commonly used as thermoluminescence (TL) dosimeter due to its high luminescence intensity. The aim of this work includes attempting a correlation between specific TL glow curves after bleaching and components of linearly modulated optically stimulated luminescence (LM-OSL) as well as continuous wave OSL (CW-OSL). A component resolved analysis was applied to both integrated intensity of the RTL glow curves and all OSL decay curves, by using a Computerized Glow-Curve De-convolution (CGCD) procedure. All CW-OSL and LM-OSL components are correlated to the decay components of the integrated RTL signal, apart from two RTL components which cannot be directly correlated with either LM-OSL or CW-OSL component. The unique, stringent criterion for this correlation deals with the value of the decay constant λ of each bleaching component. There is only one, unique bleaching component present in all three luminescence entities which were the subject of the present study, indicating that each TL trap yields at least three different bleaching components; different TL traps can indicate bleaching components with similar values. According to the data of the present work each RTL bleaching component receives electrons from at least two peaks. The results of the present study strongly suggest that the traps that contribute to TL and OSL are the same.

Using LM‐OSL of quartz to distinguish sediments derived from surface‐soil and channel erosion

AbstractThis study describes the use of linearly modulated optically stimulated luminescence (LM‐OSL) to distinguish surface‐soil derived sediments from those derived from channel bank erosion. LM‐OSL signals from quartz extracted from 15 surface‐soil and five channel bank samples were analysed and compared to signals from samples collected from two downstream river sites. Discriminant analysis showed that the detrapping probabilities of fast, first slow and second slow components of the LM‐OSL signal can be used to differentiate between the samples collected from the channel bank and surface‐soil sources. We show that for each of these source end members these components are all normally distributed. These distributions are then used to estimate the relative contribution of surface‐soil derived and channel bank derived sediment to the river bed sediments. The results indicate that channel bank derived sediments dominate the sediment sources at both sites, with 90.1 ± 3% and 91.9 ± 1.9% contributions. These results are in agreement with a previous study which used measurements of137Cs and210Pbexfallout radionuclides to estimate the relative contribution from these two sources. This result shows that LM‐OSL may be a useful method, at least in the studied catchment, to estimate the relative contribution of surface soil and channel erosion to river sediments. However, further research in different settings is required to test the difference of OSL signals in distinguishing these sediment sources. And if generally acceptable, this technique may provide an alternative to the use of fallout radionuclides for source tracing. Copyright © 2015 John Wiley & Sons, Ltd.

Monte Carlo simulations of luminescence processes under quasi-equilibrium (QE) conditions

Previous researchers have carried out Monte Carlo simulations of thermoluminescence (TL) phenomena by considering the allowed transitions of charge carriers between the conduction band, electron traps and recombination centers. Such simulations have demonstrated successfully the effect of trap clustering on the kinetics of charge carriers in a solid, and showed that trap clustering can significantly change the observed luminescence properties. While such Monte Carlo simulations have been carried out for TL, there has been no such trap clustering studies for optically stimulated luminescence phenomena (OSL). This paper presents a simplified method of carrying out Monte Carlo simulations for TL and linearly modulated optically stimulated luminescence (LM-OSL) phenomena, based on the General One Trap (GOT) model, which is a special case of the one trap one recombination center model (OTOR) when quasi-equilibrium conditions (QE) hold. The simulated results show that the presence of small clusters consisting of a few traps in a solid can lead to multiple peaks in both the TL and LM-OSL signals. The effects of retrapping and degree of trap filling are simulated for such multi-peak luminescence signals, and insight is obtained into the mechanism producing these peaks. The method presented in this paper can be easily generalized for other types of luminescence solids in which the recombination probability varies with time.

Analytical solutions for stimulated luminescence emission from tunneling recombination in random distributions of defects

Recently a new kinetic model was presented in the literature, which describes localized electronic recombination in donor–acceptor pairs of luminescent materials. Within this model, recombination is assumed to take place via the excited state of the donor, and nearest-neighbor recombinations take place within a random distribution of centers. Two versions of the model were presented which were found to be in good agreement with each other, namely an exact model that evolves both in space and in time, and an approximate semi-analytical model evolving only in time. The model simulated successfully both thermally stimulated luminescence (TL) and optically stimulated luminescence (OSL), and also demonstrated the power law behavior for simulated OSL signals. This paper shows that the system of simultaneous differential equations in the semi-analytical model can be approximated to an excellent precision by a single differential equation. Furthermore, analytical solutions are obtained for this single differential equation, and for four different experimental modes of stimulation: TL, OSL, linearly modulated OSL (LM-OSL) and isothermal TL processes. The exact form of the power law for the model is found in analytical form for both OSL and isothermal TL processes. The analytical equations are tested by successfully fitting typical infrared stimulated luminescence (IRSL) signals, as well as experimental TL glow curves from feldspar samples. The dimensionless number density of acceptors in the model is estimated from fitting the experimental IRSL and TL data. The analytical expressions derived in this paper apply also to stimulated emission via the excited state of the donor–acceptor system. However, the same analytical expression, with different numerical values for its constants, can also be applied in the case of ground state tunneling, with important implications for luminescence dating.

Radiation dose response correlation between thermoluminescence and optically stimulated luminescence in quartz

The fast, linearly modulated optically stimulated luminescence (LM-OSL) component in quartz is the main dosimetric signal used for the dating applications of this material. Since the blue light stimulation (470nm, 40mWcm −2) time needed to obtain the fast LM-OSL component is less than 50s the electron trapping levels responsible for it are still highly populated. In this way an active radiation history is created which could play an important role in the dosimetric characteristics of the fast OSL signal. In the present work the dose response behavior of the fast OSL signal is investigated in quartz samples with an annealed radiation history and quartz samples possessing an artificial radiation history. A computerized curve de-convolution analysis of the LM-OSL curves for 50s stimulation time showed that it consists of three individual OSL components. The faster component C1 with peak maximum time around 5s has a linear dose response in virgin samples, which turns to a slight superlinearity as a function of the artificial radiation history. On the other hand the component C2 with peak maximum time at 12s is slightly superlinear which turns into strong superlinearity as a function of artificial radiation history. Finally, component C3 with peak maximum time at about 45s is strongly superlinear for both virgin samples and as a function of artificial radiation history. The implications to practical application are discussed.

TL–OSL correlation studies of LiMgPO4:Tb,B dosimetric phosphor

The recently synthesized LiMgPO4:Tb,B (LMP) is a highly sensitive Optically Stimulated Luminescence (OSL) phosphor for dosimetric applications. Studies were carried out to assess the correlation between thermoluminescence (TL) and OSL of this phosphor. Measurements like Residual TL (R-TL), Continuous Wave OSL (CW-OSL) and Linearly Modulated OSL (LM-OSL) of LMP were carried out and various curves thus obtained were de-convolved using Computerized Curve Deconvolution (CCD) program. The deconvolution of CW-OSL and LM-OSL curves showed five different first order components in LMP. It was observed that OSL signal of LMP has its origin from five traps having different photo-ionization cross-sections. Same traps were found to be responsible for both TL and OSL in this phosphor. Bleaching decay rates were calculated for each R-TL glow peaks and compared with the decay rates of individual OSL components. The value of decay rates of R-TL and OSL matches well. Experimental verification of presence of individual OSL components using tbleach–tmax method was carried out.

On the initial-occupancy dependence of some luminescence phenomena under the one-trap-one-recombination-center (OTOR) model

We discuss the expected dependence of the maximum signal of a number of luminescence phenomena, used in dosimetry and archaeological and geological dating, on the initial occupancy of the relevant traps, n 0 , within the OTOR (also called General One Trap (GOT)) model. This, in turn, has important bearing on the dose dependence of these phenomena. We discuss the dependence of the linearly-modulated optically-stimulated-luminescence (LM-OSL) as well as the non-linear optical stimulation (NL-OSL) on the initial concentration n 0 of trapped carriers. We also consider the behavior of CW-OSL and phosphorescence in a transformed form, as well as TL measured under hyperbolic and linear heating rates. Using an appropriate presentation, the maximum of the signal is seen to depend nearly linearly on n 0 , which in many cases means nearly linear dependence on the dose, a property important for dosimetry and dating.

The correlation of fast OSL component with the TL peak at [formula omitted] in quartz of various origins

The fast component of the optically stimulated luminescence (OSL) signal in quartz is the basic tool for the optical dating. Its relation with the thermoluminescence (TL) glow-peak at about 325 ∘ C is well established for naturally irradiated quartz. This relationship is also an important part of a general model for quartz on which many theoretical simulations of various OSL experimental results have been based. In the present work this relationship is systematically investigated in nine quartz samples of different origin. The linearly modulated OSL (LM-OSL) curves of all quartz samples for stimulation time less than 50 s consists of two components discriminated easily by a computerized curve deconvolution (CCD) analysis. By comparing the un-bleached to the respective bleached TL glow-curve, it is found that the system of these two fast OSL components is directly related with only a small portion of the electron traps responsible for the TL glow-peaks in the temperature region 200 – 400 ∘ C . By increasing the stimulation times, besides the two fast components, the medium and the slow components are also obtained. The medium and slow components are clearly related with the main body of the electron traps responsible for TL glow-peaks in the same temperature region 200 – 400 ∘ C . Despite their different origin all quartz samples show an appreciable homogeneity concerning the number and time position of the individual components, whereas, the relative TL/OSL intensities vary strongly from sample to sample with the integrated TL intensity being generally much less than the integrated OSL intensity.

LM-OSL thermal activation curves of quartz: Relevance to the thermal activation of the 110 °C TL glow-peak

The thermally activated characteristics (TAC) of the linearly modulated optically stimulated luminescence (LM-OSL) signals of seven quartz samples from different origin were studied relative to the TAC of their respective thermoluminescence (TL) glow-peaks at 110 °C. Within the framework of the study the TAC behavior of the LM-OSL was investigated by measuring the OSL signal at room temperature (RT) with the 110 °C glow-peak present during OSL measurements, as well as, at 125 °C without the glow-peak at 110 °C removed by a cut-heat at 180 °C prior to OSL measurement. The LM-OSL curves were analyzed into individual components using a computerized deconvolution procedure. It was found that all individual LM-OSL components of each kind of quartz follow the TAC behavior of the respective TL glow-peak at 110 °C. The fourth component of the LM-OSL curve, centered at about t m = 400 s , appeared when the OSL measurements were performed at RT, whereas it was absent when the OSL measurement were performed at 180 °C. It is suggested that this component is closely related with the TL glow-peak at 110 °C.

Component resolved OSL dose response and sensitization of various sedimentary quartz samples

The structure of the linearly modulated optically stimulated luminescence (LM-OSL) signal was studied for four sedimentary quartz samples, collected from different sites around Istanbul, Turkey. Applying a computerized deconvolution analysis to the LM-OSL curves, at least six individual components of first-order kinetics were identified and photoionization cross-section of each component was evaluated. The OSL dose–response curve of each component for each quartz sample was obtained, showing a remarkable differentiation from component to component. The behavior of a highly dosed sample to successive LM-OSL measurements was also studied showing a stable recuperation signal in the position of the “slow” and “medium” components and high resistance to OSL bleaching of the “slow” component. The individual sensitivity of each component as a function of the activation temperature was obtained. The sensitivity of each component was normalized over the respective sensitivity of the glow-peak at 110 °C of quartz in order to investigate the ability of the 110 °C glow-peak to act as a correction factor for all components of the LM-OSL curves examined.

Dose measurement using the fast component of LM-OSL signals from quartz

A method is described for equivalent dose determination using the linearly modulated optically stimulated luminescence (LM-OSL) signal from quartz. After analysis of the LM-OSL curves, only the fast component from quartz is used for equivalent dose calculation. The results of applying the method to purified quartz and to grains without mineral separation are presented.

Linearly modulated photoconductivity and linearly modulated optically stimulated luminescence measurements on Al2O3:C

A measurement technique is introduced which involves linearly modulating the power of the stimulation light while measuring the photoconductivity in Al2O3:C. This produces peaks in the measured photoconductivity instead of the typical exponential decay seen when using a constant power stimulation light. The technique, called linearly modulated photoconductivity (LM-PC), is the conductivity equivalent of linearly modulated optically stimulated luminescence (LM-OSL). Two peaks are seen in the LM-PC measurements that correspond to the same charge residing in the 450 and 600 K thermally stimulated conductivity peaks, respectively. Simultaneous measurements on both the LM-PC and LM-OSL reveal that the second peak in the LM-PC is not present in the LM-OSL. Deconvolutions are performed on the LM-OSL to determine the underlying components that make up the detected OSL emissions.

LM-OSL from single grains of quartz: a preliminary study

The recently developed single grain attachment for the Risø TL-OSL reader has been modified to achieve linearly modulated optically stimulated luminescence (LM-OSL). Three different types of luminescence behaviour were observed in 81 quartz grains measured. These types are those showing only the easy-to-bleach component, those with only the hard-to-bleach component, and those exhibiting all components. The results of this preliminary study show that LM-OSL experiments carried out at the single grain level may give important insights into the luminescence properties observed when viewing samples consisting of multiple grains.