Optically Stimulated Luminescence Response Research Articles

Influence of aliovalent impurity doping and effect of sensitized luminescence in KCl single crystals for dosimetry applications

Sensitized luminescence properties of various alkali halide single crystals of dosimetric importance doped with aliovalent impurities are studied. Single crystals of KCl co-doped with (Ce,Mn), (Ce,Mg) (Ce,Tb) and (Eu,Tb) are grown using the Czochralski technique. The XRD of grown crystals showed good crystalline nature with face-centred cubic KCl structure. Thermally stimulated luminescence (TSL) and optically stimulated luminescence (OSL) characteristics of grown crystals are investigated after subjecting to gamma dose. TSL response of KCl:Eu,Tb and KCl:Ce,Tb showed an enhancement of 6.5 times and 3.5 times, respectively, compared to singly doped KCl:Tb. Co-doping of the divalent activators such as Mn and Mg did not result in enhanced TSL response with rare earth sensitizers. Notwithstanding the low TSL response, KCl:Ce,Mn showed very high OSL response, six times than that of single-doped KCl:Tb and 3.5 times than that of KCl:Ce,Tb and KCl:Eu,Tb. However, KCl:Ce,Mg did not exhibit noticeable OSL intensity enhancement compared to single doping. The high TSL and OSL response is apparently the conclusive evidence of the energy transfer mechanism between dopants, which is confirmed by photoluminescence studies. The dose–response curve of KCl:Ce,Mn that exhibited very high OSL response showed linearity up to 100 Gy, which indicated the material is a good candidate for dosimetric applications. The growth and characterisation of aliovalent impurity-doped KCl single crystals and mechanism of resonance energy transfer between the dopants are discussed in this paper.

Thermoluminescence, photoluminescence and optically stimulated luminescence characteristics of CaSO4:Eu phosphor: Experimental and density functional theory (DFT) investigations

The CaSO4:Eu phosphor in nanocrystalline form was obtained by chemical method. The sample was annealed at various temperatures and quenched. The structural, electronic and optical properties are studied using various experimental techniques. As synthesized CaSO4:Eu particles have nanorod shapes with diameter of ~15 nm and length of ~250 nm. After annealing (at around 900 °C) a significant increase in their size (~2–4 μm) with phase transformation from hexagonal to orthorhombic was observed. Thermoluminescence (TL) and optically stimulated luminescence (OSL) intensities were found to increase with temperature up to 900 °C and decrease thereafter for 1 Gy of test dose of β-rays from 90Sr-90Yr source. However, the maximum OSL sensitivity was found to be more than that of CaSO4:Eu microcrystalline phosphor (prepared by acid recrystallization method) contrary to the usually found in the literature but much less than that of commercially available α-Al2O3:C phosphor. The activation energy for thermally assisted OSL process was found to be 0.0572 ± 0.0028 eV. The dose ranges of TL and OSL response was found from 0.04 Gy to 100 Gy and 0.02 Gy–100 Gy, respectively. The experimental results are also correlated with computational calculations based on density functional theory (DFT). The crystal structures and electronic structures of both hexagonal and orthorhombic CaSO4 and CaSO4:Eu materials show that they are direct band gap (5.67–5.86 eV) insulators, with Ca2+ substitution by Eu2+ found to introduce donor states in the band gap near Fermi level and the valence band edge of CaSO4 on doping with Eu2+ impurity ions.

Optically stimulated luminescence dosimetry performance of novel MgO–La(OH)3 phosphors

The aim of this work was to study the optically stimulated luminescence (OSL) properties of novel MgO co-doped with different lanthanides and lithium ions as well as to evaluate the feasibility of using the mentioned phosphors as OSL dosimeters. In this context, the OSL efficiency corresponding to different stimulation wavelengths and different filters was analyzed for all the samples. The properties of the most efficient material, namely, MgO–La(OH)3, were further studied. Moreover, the repeatability and linearity of the OSL response, the fading of the OSL signal and the minimum detectable dose were investigated. Finally, feasibility of using these compounds in OSL dosimetry was assessed.

Dosimetric characterization of MgB4O7:Ce,Li as an optically stimulated dosimeter for photon beam radiotherapy

Summary Currently there is a growing interest in the development of optically stimulated luminescence (OSL) dosimeters that may be useful for assessing the neutron flux contribution on the doses in radiotherapy due to neutrons produced in the interaction of megavoltage photon beams. In this work, OSL responses of MgB4O7:Ce,Li with 11B are presented for some photon beams, including 6 MV and 10 MV. For 10 MV, the behavior of the phosphor containing 10B was also evaluated. The material with 10B exhibited an OSL response slightly more intense than that with 11B, indicating a possible application of this new material for dosimetry in photon radiotherapy.

Optical responses of a copper-activated sol-gel silica glass under low-dose and low-dose rate X-ray exposures

Ionic copper-doped silica glasses are attractive materials for radiation detection and dosimetry based on radioluminescence (RL) and optically stimulated luminescence (OSL). We characterized the optical responses, under X-rays, of a Cu+-doped silica glass rod prepared via the sol-gel technique and spliced to transport pure silica optical fibers. Both the low-dose and the low-dose rate regimes were specially investigated at room temperature. RL and photoluminescence (PL) measurements confirmed that the Cu+ ions are the luminescent centers of interest for the targeted applications. RL dose rate response dependence shows a linear behavior from 260 μGy(SiO2)/s up to 23 mGy(SiO2)/s, allowing the monitoring of the dose rate evolutions during an irradiation run. The OSL response also linearly depends on the dose from 42 mGy(SiO2) to 200 Gy(SiO2), enabling a precise dose measurement shortly after the irradiation. The presented results confirm the potentialities of this material to monitor ionizing radiations in harsh environments.

Radiation-induced changes in the optical properties of NaMgF3(Sm): Observation of resettable Sm radio-photoluminescence

Stable radio-photoluminescence (RPL) is observed in NaMgF3(Sm) after X-ray irradiation due to valence conversion of Sm3+ to Sm2+. This valence conversion can be reversed by deep UV (254 nm) illumination. It is likely that this reversible process occurs via defects near some of the Sm3+ sites that act as hole traps. The ratio of the Sm2+/Sm3+ RPL emissions follows an exponential-type curve dependence on X-ray dose where the ratio saturates above ∼500 Gy. Optically stimulated luminescence (OSL) is also observed but only from Sm3+ and primarily from electrons trapped at F-centers. The OSL response is demonstrated to be linear up to 100 Gy. Thus, NaMgF3(Sm) has potential as a dosimeter where individual irradiations can be monitored via OSL and the total cumulative dose via non-destructive RPL readout. The RPL can be optically reset when required.

Evaluation of the thermally and optically stimulated response of an Italian Obsidian irradiated in 60Co beams

From Obsidian silicate, in its natural form, pellets were manufactured adding Teflon to the material in powder. These pellets were exposed to the gamma radiation beams of a 60Co source in a dose interval from 10 Gy to 10 kGy. The Obsidian in powder was investigated in relation to its physical and chemical characteristics, by means of the X-ray diffraction, scanning electronic microscopy and energy-dispersive X-ray spectroscopy techniques. After the irradiation procedure, the signal of the samples was evaluated by means of three techniques: thermoluminescence (TL), optically stimulated luminescence (OSL) and thermally stimulated exoelectron emission (TSEE). The objective of this work was to verify the TL, OSL and TSEE response of the Obsidian+Teflon pellets after exposure to high doses of gamma radiation. Different response characterization tests were performed, as TL and TSEE emission curves, OSL signal decay, reproducibility, dose-response curves, lower detection limits and fading. From these results, it can be observed that the Obsidian+Teflon pellets present good conditions to be used as high dose gamma radiation detectors; the results obtained with the OSL technique were the most adequate in terms of response in function of absorbed dose. The fading of the signals, varying from about 26% (TSEE) to 44% (OSL), in a time interval of 360 h post-irradiation, also showed favorable results for the use of this material as radiation detector, when the measurements are taken after a defined time interval.

Optically stimulated luminescence of CaF2:Ce

Optically Stimulated Luminescence (OSL) is the luminescence emitted from a previously irradiated with ionizing radiation material by exposure to light. The aim of this paper is to evaluate the Blue Stimulation Luminescence (BSL) and Infra-Red Stimulation Luminescence (IRSL) for CaF2:Ce produced by the Solution Combustion Synthesis (SCS) method. The results showed that the OSL response of CaF2:Ce is strongly influenced by post-combustion thermal sintering temperature and dopant concentration. OSL response to dose are of the same order of magnitude of Al2O3:C, indicating the possibility of use of this material for radiation dosimetry.

OSL dosimetric properties and efficiency of Brazilian natural calcium fluoride pellets

Calcium fluoride (CaF2), in both natural and synthetic forms, has been exhaustively studied and explored as thermoluminescent (TL) detector. However its sensitivity to ambient light points to the applicability of CaF2 as OSL (Optically Stimulated Luminescence) detector, increasing the research about its luminescent properties. Although some properties to employ CaF2 detectors with OSL technique have been already demonstrated, there is a lack of some essential information as the OSL response to different types and energy of ionizing radiation. In order to extend the use of Brazilian natural CaF2 with OSL technique, we evaluated the efficiency and dosimetric properties of cold pressed CaF2:NaCl pellets. The CaF2 detectors presented good reproducibility and negligible fading of the signal over one month after irradiation. The dose response using OSL, TL and residual TL showed linear behavior for different radiation beams (protons, photons and alpha and beta particles), being equivalent to the results obtained with BeO and MTS (LiF) detectors through OSL and TL technique respectively. Moreover, differences were observed in OSL efficiency according the beam type and energy; CaF2 detectors presented a higher OSL and TL sensitivities to protons, photons and beta particles than to alpha particles. The energy response to photons obtained using OSL and residual TL intensities present an over response at lower photon energy similar to TL energy response. In addition, differences in the OSL curve shapes were observed according to radiation type and energy, pointing to the possibility of applying this material in mixed radiation fields and to estimate average LET (Linear Energy Transfer).

Luminescence properties of natural muscovite relevant to optical dating of contaminated quartz samples

Muscovite is a mineral commonly found along quartz in sediments, where the latter is the mineral of choice in numerous optically stimulated luminescence (OSL) dating studies. Since muscovite cannot be efficiently eliminated following standard laboratory treatments, it is important to assess its luminescence properties. This study is focused on the investigation of muscovite hand-picked from a quartz sample extracted from loess and of museum specimens of muscovite in order to evaluate their potential implication in the OSL dating of quartz samples contaminated with muscovite grains. The obtained results show that generally applicable luminescence characteristics cannot be described for muscovite. In terms of the thermoluminescence (TL) response, all samples investigated display the same wide peak at 200 °C. The blue light and infrared (IR) sensitivities differ between the samples: 3 out of 5 samples present no or negligible level of OSL and IRSL response, while the other 2 samples are characterised by both blue light (2000–3400 counts in 0.31 s of stimulation for 10 mg of muscovite after irradiation with a dose of 136 Gy) and IR sensitivity (265–320 counts in 0.31 s of stimulation for 10 mg of muscovite after irradiation with a dose of 136 Gy). Based on the samples analysed in this study, aliquots of quartz contaminated with optically (blue light) sensitive muscovite would also be IR sensitive. Hence, potentially problematic aliquots can be identified via the IRSL purity test usually used in the OSL dating of quartz samples for detection of feldspar contamination. The impact of muscovite on dose determination for quartz was also tested and it was concluded that at least in the case of bright quartz, muscovite minerals do not influence the OSL measurements.

OSL dosimetric properties of synthetic topaz

The optically stimulated luminescence (OSL) properties under beta radiation of synthetic topazes produced from three different reactants are reported for the first time. Topazes were synthesized by chemical vapor deposition using sodium hexafluorosilicate (Na2SiF6) compacts as solid precursor and either aluminum oxide, aluminum hydroxide or kaolinite compacts as reactants. The OSL dosimetric characteristics of the most promising composition, namely, topaz synthesized using aluminum oxide, were determined and analyzed. The alumina-derived topaz exhibited a linear response in the dose range from 0.2 up to 20 Gy, a satisfactory repeatability and a fading of approximately 30% in the first hours, after which the OSL response remained constant. These characteristics, together with a minimum detectable dose (MDD) of 0.01 Gy – corresponding to a 3σ background signal – suggest the potential of synthesized topaz as an OSL dosimeter. The OSL mechanism might be explained by at least two trap types, possibly related to topaz shallow traps. A decreasing behavior – featuring a single exponential decrease –, similar to that of OSL signal was observed in ultraviolet and visible light bleaching measurements.

Investigation of Optically Stimulated Luminescence and Signal Fading Properties of Several Materials.

Optically stimulated luminescence (OSL) dosimetry involves the illumination of an irradiated sample on an appropriate material to produce a stimulated emission of light, whose intensity is indicative of the radiation dose. This technique is currently used for personnel dosimetry, environmental dosimetry, and geological dating applications. While a great deal of published research focusing on α-Al2O3:C and natural materials used for geological dating exist, relatively little is known about the OSL properties of thermoluminescent (TL) materials. This paper reports the results of an experiment conducted to characterize the OSL behavior of KBr, CaSO4:Tm, CaSO4:Dy, CaSO4:Dy+P, LiF:Mg,Cu,Na,Si, and LiF:Mg,Cu,Si. The OSL signal responses to seven excitation wavelengths from 625 nm to 455 nm for each material were measured at 12 time periods post-irradiation from 6 h to 120 d. The magnitude and fading characteristics of the OSL response of each material were then analyzed. The data demonstrated that significant OSL responses exist for CaSO4:Tm, LiF:Mg,Cu,Na,Si, and LiF:Mg,Cu,Si. In addition, it was found that the fading rates of OSL signals depend on the excitation wavelength used to elicit the signals and that these fading rates and the corresponding excitation wavelengths correlate well with the material's TL behavior. Thus, the various fading rates with respect to the excitation wavelengths could be used to obtain temporal dose information.

Thermoluminescence and optically stimulated luminescence properties of Dy3+-doped CaO–Al2O3–B2O3-based glasses

We developed Dy3+-doped CaO–Al2O3–B2O3 based glasses with Dy concentrations of 0.5, 1.0, and 2.0mol% using a melt-quenching technique. The as-synthesized glasses were applicable as materials exhibiting thermoluminescence (TL) and optically stimulated luminescence (OSL). The optical and radiation response properties of the glasses were characterized. In the photoluminescence (PL) spectra, two emission bands due to the 4F9/2→6H15/2 and 4F9/2→6H13/2 transitions of Dy3+ were observed at 480 and 580nm. In the OSL spectra, the emission band due to the 4F9/2→6H15/2 transition of Dy3+ was observed. Excellent TL and OSL responses were observed for dose ranges of 0.1–90Gy. In addition, TL fading behavior was better than that of OSL in term of the long-time storage. These results indicate that the Dy3+-doped CaO–Al2O3–B2O3-based glasses are applicable as TL materials.

OSL response bleaching of BeO samples, using fluorescent light and blue LEDs

The optically stimulated luminescence (OSL) is widely used as a dosimetric technique for many applications. In this work, the OSL response bleaching of BeO samples was studied. The samples were irradiated using a beta radiation source (90Sr+90Y); the bleaching treatments (fluorescent light and blue LEDs) were performed, and the results were compared. Various optical treatment time intervals were tested until reaching the complete bleaching of the OSL response. The best combination of the time interval and bleaching type was analyzed.

A novel TL/OSL MCaPO4:Ce (M = Li, k) phosphor for radiation dosimetry

The polycrystaline MCaPO4:Ce (M=Li, K) phosphors were synthesiszed via solid state method. Structural properties of prepared MCaPO4:Ce (M=Li, K) phosphors are confirmed by X-ray diffraction (XRD). The optical properties were characterized by use of photoluminescence (PL), thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques. The XRD pattern of MCaPO4:Ce (M=Li, K) phosphor fully matched with the Internatonal center for diffaction data (ICDD) file with card no 01-079-1396 and 00-033-1002. The PL excitation spectra consists broad band in range 200–350nm and maximum intensity observed at 313nm and emission spectra consist broad in range 325–500nm and maximum intensity observed at 381nm. The TL glow curve of MCaPO4:Ce (M=Li, K) phosphors were consist overlapping peaks in temperature 50–350°C and these peaks were deconvoluted by using peak fit software. The kinetic parameters such as activation energy, frequency factor and order of kinetic were calculated by using peak shape method. Also MCaPO4:Ce (M=Li, K) phosphors show excellent OSL response under β irradiation.

TL and OSL studies on undoped diamond films grown by hot filament chemical vapor deposition

In this work, approximately 0.5µm thick diamond films were grown on a silicon substrate by hot filament chemical vapour deposition (HFCVD) method in a gas mixture of hydrogen and methane. The batch to batch reproducibility of the sample using this technique was found to be very good. The obtained film was characterized by micro laser Raman spectroscopy (MLRS), grazing incidence X-ray diffractometry (GIXRD), scanning electron microscopy (SEM) and atomic force miscroscopy (AFM) techniques. MLRS and GIXRD results confirmed the formation of diamond whereas SEM and AFM analyses indicated uniform morphology of the film with an average grain size of 200nm. The deposited film was studied for ionizing radiation dosimetry applications using the thermoluminescence (TL) and optically stimulated luminescence (OSL) techniques after irradiating the film by a calibrated 5mCi, 90Sr/90Y beta source. In the TL measurement, for a heating rate of 4K/s, broad glow curve was obtained which was deconvoluted into seven TL peaks. The integrated TL counts were found to vary linearly with increasing the radiation dose up to 10kGy. The characteristic TL output seen in the temperature range 200–300°C, may be considered good for thermal stability of the film and it could also avoid TL fading during storage and non-interference of any black body radiation during the measurement. However, in comparison to TL output, the OSL response for 470nm LED stimulation was found to be lesser. The CW–OSL decay curve has shown two components contributing to the OSL signal, having photoionization cross-section 1.5×10−18 and 5.2×10−19cm2 respectively. The studies have revealed the possibility of using diamond film for high dose radiation dosimetry with TL/OSL method.

Optically stimulated luminescence (OSL) from Ag-doped Li2B4O7 crystals

Optically stimulated luminescence (CW-OSL) is observed from Ag-doped lithium tetraborate (Li2B4O7) crystals. Photoluminescence, optical absorption, and electron paramagnetic resonance (EPR) are used to identify the defects participating in the OSL process. As-grown crystals have Ag+ ions substituting for Li+ ions. They also have Ag+ ions occupying interstitial sites. During a room-temperature exposure to ionizing radiation, holes are trapped at the Ag+ ions that replace Li+ ions and electrons are trapped at the interstitial Ag+ ions, i.e., the radiation forms Ag2+ (4d9) ions and Ag0 (4d105s1) atoms. These Ag2+ and Ag0 centers have characteristic EPR spectra. The Ag0 centers also have a broad optical absorption band peaking near 370nm. An OSL response is observed when the stimulation wavelength overlaps this absorption band. Specifically, stimulation with 400nm light produces an intense OSL response when emission is monitored near 270nm. Electrons optically released from the Ag0 centers recombine with holes trapped at Ag2+ ions to produce the ultraviolet emission. The OSL response is progressively smaller as the stimulation light is moved to longer wavelengths (i.e., away from the 370nm peak of the absorption band of the Ag0 electron traps). Oxygen vacancies are also present in the Ag-doped Li2B4O7 crystals, and their role in the OSL process as a secondary relatively short-lived electron trap is described.

Study of the luminescent behavior of Spectrolite + Teflon pellets in 90Sr + 90Y beams

The Spectrolite, from the silicate family, a variety of Labradorite, was already studied in relation to its thermoluminescence (TL) and optically stimulated luminescence (OSL) responses, in high-dose gamma radiation fields; the results indicated their good application as gamma radiation detectors. In the present work, the analyses performed to investigate powdered Spectrolite are presented, by means of the XRD, SEM and EDX techniques. The luminescent behavior of Spectrolite + Teflon samples, in the concentration of 1:1, was studied in beta radiation beams (90Sr + 90Y), using the luminescent phenomena of TL and OSL. The results showed adequate TL and OSL reproducibility of the samples; the dose–response curves for both techniques presented a linear behavior in a range from 0.5 Gy to 1 kGy, and the fading showed that after 150 h there were 46.7% and 31.6% of the remaining signal of samples for TL and OSL responses, respectively. Therefore, the Spectrolite + Teflon pellets may be used in beta radiation dosimetry.

Investigations of OSL properties of LiMgPO4:Tb,B based dosimeters

Lithium magnesium phosphate LiMgPO4 (LMP) doped with Tb and B is one of new materials intended for use in optically stimulated luminescence (OSL) dosimetry. LMP doped with Tb and B luminophors were synthetized at IFJ PAN in Krakow. The investigations were carried out on self-developed dosimeters consisting of a slide with four LMP detectors and a light tight cover. LMP detectors were investigated in regard to their OSL properties using OSL reader named HELIOS adopted to the readouts of dosimetric cards. New LMP detectors showed high sensitivity to the ionizing radiation, good repeatability of OSL signal and good dose response, 25% of fading in the first two weeks after irradiation. Also, the pronounced dependence of OSL response on the energy of the measured radiation requires to apply the compensation filters.

Thermoluminescence and optically stimulated luminescence characteristics of Al2O3:C films annealed at different tempeartures

-Al2O3:C crystal is a high sensitive luminescence dosemeter, and it possesses a high thermoluminescence (TL) sensitivity, approximately 40-60 times greater than LiF: Mg, Ti. However, the crystal growth requires sophisticated laboratories, high temperatures and highly reducing atmosphere. The fluorescence and TL characteristics of -Al2O3:C ceramic are similar to those of -Al2O3:C crystal, however, it shows three TL peaks. In this work, porous alumina membranes are prepared by two-step anodization in 0.5 M/L oxalic acid at 5 ℃. We investigate the influence of annealing temperature ( 600 ℃) on thermoluminescence (TL) and optically stimulated luminescence (OSL) characteristics of Al2O3:C films and discuss the influence mechanism. The scanning electron microscopy measurement reveals that Al2O3:C film possesses highly ordered nanopores with homogeneous dimensions arranged in a closed-packed hexagonal pattern. The energy dispersive X ray spectroscopy and the Fourier transform infrared spectroscopy results indicate that oxalic acid impurity is incorporated into the porous alumina membrane in the synthesis process, after the annealing treatment, the oxalic acid impurity decomposes and C2+ replaces Al3+, which leads to the formation of F+and the C content of samples increasing with elevated annealing temperature. The X-ray diffraction measurement reveals that Al2O3:C films annealed at different temperatures are amorphous. TL measurements show that the dominated peak of Al2O3:C film is centered at around 310 ℃, owing to the number of F+increasing with the annealed temperature increasing, under the same irradiation dose, the sample annealed at 600 ℃ has the greatest TL intensity. With the increase of the irradiation dose, the TL intensity increases and the dominated peak gradually shifts to high temperature, which is consistent with the general order kinetic model. The sample annealed at 600 ℃ has the greatest TL sensitivity and its TL response shows excellent linear characteristic in as dose range of 1-10 Gy, but shows super-linear behavior in a dose range of 10-120 Gy. The OSL measurements show that with the increases of the annealed temperature and the irradiation dose, the OSL initial intensity increases and each of all samples shows a typical exponential decay. Compared with the case of -Al2O3:C crystal, the fast attenuation rate of film is dramatically accelerated. In a dose range of 1-200 Gy, the OSL responses of all samples each show an excellent linear characteristic, the sample annealed at 600 ℃ has the greatest OSL sensitivity. Compared with TL response, OSL response of Al2O3:C film shows a wider range of linear dose response. In this paper we have made a beneficial exploration for Al2O3:C films as OSL dosimerer.