Optically Stimulated Luminescence Emission Research Articles

Optically stimulated luminescence properties of In-doped CsBr transparent ceramics

0.01, 0.1, 0.5, and 1% In-doped CsBr transparent ceramics were synthesized by the spark plasma sintering method. Their photoluminescence and optically stimulated luminescence (OSL) properties were evaluated. All the samples showed transparency with transmittances of 40–60%. Luminescence due to 3P1–1S0 transitions of In + appeared at 500 nm. OSL emission peaks were confirmed at 500 nm upon constant stimulation light at 630 nm. A 0.1% In-doped sample showed the highest OSL intensities in prepared samples and the dose-response relationship was linear from 0.01 to 1000 mGy. The spatial resolution of X-ray images was confirmed from 5.00 LP/mm by using OSL of a 0.1% In-doped sample.

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.

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.

Thermoluminescence investigations and kinetic analysis of highly sensitive LiCaAlF6: Eu,Y phosphor for dosimetric applications

The paper presents detailed thermoluminescence characterization and kinetic analysis of highly sensitive and dosimetric grade lithium calcium aluminum fluoride doped with europium and co-doped with yttrium (LiCaAlF6:Eu,Y). It is synthesized by melt processing technique. The thermoluminescence (TL) and optically stimulated luminescence (OSL) correlation was systematically studied. The study reveals that the OSL signal is attributed to the observed TL peaks in this material. Thus, same defects are responsible for TL and OSL in LiCaAlF6:Eu,Y. Further characterization involved measurement of TL emission spectrum, OSL emission spectrum, steady state photoluminescence (PL) spectra, phosphorescence, sensitivity, fading, dose response etc. The TL sensitivity of this phosphor was observed to be ∼5 times and ∼3 times to that of CaSO4:Dy and commercially available Al2O3:C respectively. PL, TL and OSL emission spectra suggest that Eu2+ ion acts as a luminescence center in this material. Minimum measureable dose for the phosphor in TL mode was found to be 0.3 μGy with negligible fading post 10 days of irradiation. The fading of TL signal in this material is similar to the one observed for OSL signal. The thermal stability and hygroscopic nature of LiCaAlF6:Eu, Y were studied using thermogravimetric and differential scanning calorimetry techniques. Owing to the attributes like high sensitivity, wide dynamic dose range it stands as a viable and excellent phosphor material for various radiological and dosimetric applications.

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.

Optically stimulated luminescence in state-of-the-art LYSO:Ce scintillators enables high spatial resolution 3D dose imaging

In this contribution, we study the optically stimulated luminescence (OSL) exhibited by commercial hbox {Lu}_{(2-x)}hbox {Y}_xhbox {SiO}_5:Ce crystals. This photon emission mechanism, complementary to scintillation, can trap a fraction of radiation energy deposited in the material and provides sufficient signal to develop a novel post-irradiation 3D dose readout. We characterize the OSL emission through spectrally and temporally resolved measurements and monitor the dose linearity response over a broad range. The measurements show that the hbox {Ce}^{3+} centers responsible for scintillation also function as recombination centers for the OSL mechanism. The capture to OSL-active traps competes with scintillation originating from the direct non-radiative energy transfer to the luminescent centers. An OSL response on the order of 100 ph/MeV is estimated. We demonstrate the imaging capabilities provided by such an OSL photon yield using a proof-of-concept optical readout method. A 0.1 hbox {mm}^3 spatial resolution for doses as low as 0.5 Gy is projected using a cubic crystal to image volumetric dose profiles. While OSL degrades the intrinsic scintillating performance by reducing the number of scintillation photons emitted following the passage of ionizing radiation, it can encode highly resolved spatial information of the interaction point of the particle. This feature combines ionizing radiation spectroscopy and 3D reusable dose imaging in a single material.

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.

Influence of lanthanide (Gd, Tb or Ce) and silver doping on the luminescence lifetimes of calcium borate investigated by pulsed optically stimulated luminescence

The objective of this work is to evaluate the optically stimulated luminescence (OSL) lifetimes of different polycrystalline CaB6O10:Ln, Agx (Ln = Gd, Tb and Ce; x: % molar concentration) compounds. For the determination of the luminescence lifetimes, time-tagged time-resolved (TTTR) data of the OSL under pulsed stimulation were analyzed. In addition, OSL emission spectra of the samples were recorded to correlate the emission bands with the estimated lifetimes. Whereas single Ce-doped compound presented a fast dominant component (τ < 0.41 μs, ∼63% of the signal), single Gd-doped compound exhibited a slow dominant component (τ = 2.3 ms, ∼67% of the signal). All Ag-codoped compounds (except for the Ce–Ag-codoped compound) presented a common dominant component with a ∼43 μs lifetime, which is ascribed to a broad emission centered at ∼330 nm. Both lifetimes and OSL emission spectra for the Gd-Ag-codoped compounds suggest that two luminescent centers compete for the radiative recombinations, confirming previous reported results. The relative Gd and Ag molar concentrations also had a strong influence in the estimated luminescence lifetimes of the slow component, probably due to the introduction of shallow trapping centers by silver doping. Furthermore, the temperature dependence of the common luminescence in Ag-codoped compounds appeared to be in agreement with the Mott-Seitz model for luminescence quenching. This work provides a better understanding of the physical processes and dynamics behind the radiative recombinations linked to OSL in borate compounds.

Signal requirements for 3D optically stimulated luminescence dosimetry

For 3D optically stimulated luminescence (OSL) based dosimeters to be clinically applicable, certain standards must be met. Among these are low detectable doses with high accuracy and precision, ideally comparable with those of point-like detectors. By investigating a model of the central part of an OSL readout-system, we present an estimate of as the minimum required signal from OSL active materials embedded in a transparent matrix to allow measuring doses of 0.1 Gy with an accuracy and precision of 2 %. Further, 2D spatially resolved measurements of OSL emission from commercially available LiF:Mg, Cu, P pellets are presented and discussed.

Development of wavelength-resolved 3D-inegrated TL and OSL reader system

A new wavelength-resolved thermo luminescence (TL) cum optically stimulated luminescence (OSL) reader system has been designed and developed. This reader system uses the compact Seya-Namioka optical layout based monochromator, PMT, and resistive heating method to acquire TL glow curve emissions spectrum. The phosphor samples heated from room temperature to 400 °C, either linearly with a programmable heating rate of 0.01 to 30 K s−1 or alternative constant step temperature profiles. The TL glow curve emission spectrum has been resolved by rotating the grating attached to a monochromator covering the wavelength from 200 to 900 nm. The wavelength scanning is linear with respect to time and the scan rate can be selected from 0.1 to 8 n m s−1. A broad spectral response of the PMT detection module has been used to record the emitted TL spectrum. The blue (465 nm) reference LED light source is provided for a spectrum calibration of the monochromator. The isometric 3D TL emission spectra of LiCaAlF6:Eu,Y, α-Al2O3:C, and CaSO4:Dy have been successfully recorded using this reader system. In order to record the OSL emission spectrum, 470 nm blue LEDs have been provided as a separate stimulation module.

Variation of luminescence sensitivity, characteristic dose and trap parameters of quartz from rocks and sediments

We investigated the optically stimulated luminescence (OSL) and thermoluminescence (TL) characteristics of quartz from sediments and parent rocks across South America. OSL and TL sensitivities were compared with the characteristic dose of dose response curves. Additionally, we estimated electron trap parameters of quartz from sediments with contrasting OSL sensitivities. Our results show that the natural sensitivities of quartz OSL (initial 0.8 s) and TL (110 °C peak) are positively correlated and range over six and four orders of magnitude respectively. The corresponding characteristic doses range from around 30 Gy–3000 Gy for dose response curves described by a single exponential function. Quartz from igneous and metamorphic rocks and Andean short-transported sediments report low-sensitivity OSL and high characteristic dose. The studied initial OSL signal has significant contribution of medium and slow components in quartz from rocks and Andean short-transported sediments, while in quartz from Brazilian long-transported sediments, the initial OSL signal is dominated by the fast component. The trend of sensitivity increase and characteristic dose decrease is attributed to the relative contribution of medium and low components to the initial OSL emission. Regarding the electron trap parameters, high, medium and low sensitivity quartz has statistically similar values of the activation energy and the frequency factor, but both parameters have larger variations in medium and low sensitivity quartz.

A systematic study on luminescence characterization of lanthanide-doped BeO ceramic dosimeters

This work aimed to investigate the luminescent characteristics of lanthanide and alkali metal ion-doped BeO ceramic pellets prepared using the co-precipitation synthesis technique for Optically Stimulated Luminescence (OSL) dosimetry applications. In this study, BeO nano phosphor was doped with lanthanides (Ln3+) Eu3+, Ce3+, Nd3+, Yb3+, Er3+, Gd3+, Tb3+, Tm3+, Sm3+, Pr3+, and Dy3+ and co-doped with Na+, and characterized using radioluminescence (RL), thermoluminescence (TL) and OSL techniques. Lanthanides introduced as dopants not only affected the luminescence centers but also changed the luminescence mechanisms. The RL spectra of lanthanide-doped BeO samples showed that they mostly possess dominant emissions in the narrow bands (between 200 and 450 nm) in the UV region. OSL emission bands were found to be located between ~250 and ~390 nm. The results have demonstrated that the incorporation of appropriate Ln3+ and alkali metal ion dopants and their optimum concentrations enhanced the luminescence intensity of undoped BeO. The studied BeO:Na5%,Ce0.01%,Er0.01%, BeO:Na5%,Ce0.005%,Tb0.05%, and BeO:Na5%,Ce0.01%,Dy0.01% ceramics can be regarded as highly sensitive controllable luminescence dosimeters. The range of sensitivity of those samples is such that their most probable use in clinical therapy dosimetry rather than in health physics.

Enhanced optical cross-section of radiation induced defect centers under plasmon resonance conditions: Shifting stimulation wavelength of optically stimulated luminescence dosimeters

Plasmon-enhanced luminescence is an important tool for development of advanced sensing technologies but the mechanisms originating these enhancements are still in debate. In this work, we investigate plasmon-enhanced luminescence mechanisms using the Optically Stimulated Luminescence (OSL) from defect centers in X-ray irradiated sodium chloride nanocrystals deposited on silver nanoparticle (AgNP) films with varying plasmon properties upon blue, green, and red OSL stimulation. Although the absolute OSL intensity for NaCl crystals is higher upon blue stimulation, under plasmon resonance conditions, higher absolute OSL intensity occurs upon green stimulation and the largest OSL enhancements are observed by employing red stimulation. These results suggest that, as long as the OSL stimulation wavelength is well tuned with the film plasmon band, plasmonic coupling does not depend on the trap depth and that the largest luminescence enhancements are achieved in spectral regions where the optical cross-sections of the defect centers are smaller. In terms of radiation dosimetry applications, this result allows to shift the stimulation wavelength farther from the OSL emission window, improving the signal to noise ratio and the dose assessment sensitivity and accuracy.

Synthesis, RL and OSL characterization of thulium doped NaMgF3 neighborite

The aim of this work is to study the dosimetric properties of tissue-equivalent thulium doped NaMgF3 neighborites and to determine their possible application as dosimeters in personal dosimetry. In this aspect, radioluminescence (RL) and optically stimulated luminescence (OSL) dosimetric properties of undoped and Tm3+ -doped NaMgF3 have been investigated for the first time. Samples were synthesized by solid state reaction and by considering a stoichiometric mixture of pure NaF and MgF2 reagents. Two emission peaks centered at 460 and 360 nm have been found in the RL emission spectrum of the doped samples, which can be ascribed to the 1D2 – 3F4 and 1D2 – 3H6 transitions of Tm3+ cations, respectively. Maximum OSL emission under blue light stimulation has been found for samples doped with 0.2 mol % of thulium. Furthermore, the OSL signal of this compound depends linearly on dose within the range 0.05–100 Gy. Besides, its OSL signal features satisfactory repeatability and a minimum detectable dose of 0.04 Gy. Finally, it has been found a low fading of the OSL signal of approximately 13% after the first 60 h, after which the OSL response remains constant. The obtained results suggest the feasibility of using this compound as an OSL detector in personal dosimetry.

Optical characterization of LiF:Mg,Cu,P – Towards 3D optically stimulated luminescence dosimetry

The introduction of radiotherapy beam delivery with high spatial modulation, including spot-scanning proton therapy, calls for development of 3D dosimeters for patient-specific treatment verifications. Inherently reusable methods like optically stimulated luminescence (OSL) pose a potential way to introduce a clinically viable 3D-dosimetry solution. Here we present a characterization of the OSL properties of the well-known thermoluminescence material LiF:Mg,Cu,P (MCP). The characterization was performed by monitoring the wavelength-dispersed emission of continuous-wave stimulated MCP pellets. We show that OSL emission is observed under blue (460 nm) and green (532 nm) laser stimulation, while no OSL signal is seen in MCP under red (664 nm) laser stimulation. Long-wavelength fluorescence including accumulating radiophotoluminescence is very intense under blue stimulation and must be suppressed for continuous use of a future 3D-dosimetry system. An evaluation of the number of emitted photons is used to estimate a measurable dose range of 0.1–10 Gy, which prompts further research in the use of MCP for 3D OSL-based dosimetry.

Effects of microwave-assisted hydrothermal treatment and beta particles irradiation on the thermoluminescence and optically stimulated luminescence of SrMoO4 powders

SrMoO4 powders, produced by co-precipitation, are investigated employing thermoluminescence (TL) and optically stimulated luminescence (OSL). The effects of microwave-assisted hydrothermal (MAH) treatment, beta particle irradiation, and thermal treatment are studied to understand their role on defect density and location in the band-gap. The powder X-ray diffraction showed that the SrMoO4 powders crystallize in a tetragonal structure. The raman studies confirmed the presence of active vibration modes characteristic of molybdates, whereas the Fourier Transformed Infrared (FTIR) data exhibit the symmetric and asymmetric stretch vibrations. The trapping depth energies, determined from TL glow curves, range from 0.9 eV to 1.95 eV. The TL data show that the MAH treatment decreases the defect density and favors the formation of defects with lower activation energies. The residual TL signal shows the formation of shallower traps with a glow peak occurring at lower temperatures. The OSL emission only taken place for samples submitted to heating cycles and depends on the heating rate. These results indicate that shallow traps induced by thermal treatment are responsible for the OSL signal. The shape and intensity of the OSL curve depend on the number of heating cycles and on the heating rate, revealing that thermal treatment has a profound influence on this emission. The OSL signal for MAH-treated SrMoO4 samples subjected to thermal treatment increases linearly with beta irradiation dose. The results give insight that SrMoO4 phosphors may have potential applications in the design of a radiation sensor.

The Role of the Cu on OSL Emission in Gamma-LiAlO2:Cu Crystal

A large optically stimulated luminescence (OSL) response has been found from copper doped lithium aluminate (LiAlO2, LAO) which can be applicable in OSL dosimetry. After an irradiation at room temperature with x-rays, an optical absorption band peaking at 277 nm and a luminescence band near 354 nm appear which are assigned to Cu+ ions which occupy the Li+ sites. Based on the experimental study, we construct two models to study the optical spectra of Cu+ occupying the Li+ ion. One is an isolated defect in which Cu+ ions occupy the Li+ ions and present isolated CuLi. The other one is a CuLi bond with a neighboring lithium vacancy (CuLi-VLi). In this work, all calculations are based on density functionals theory (DFT). Advanced hybrid functionals is adopted to relieve the problem of DFT underestimating the band gap. We obtain the optical spectra containing electron‒phonon coupling, and the results are in good agreement with the experimental results. Furthermore, the optical properties of CuLi-VLi are investigated. We find the absorption and luminescence peak are located at 273 nm and 353 nm, which are assigned to the isolated CuLi, and the absorption band near 379 nm is assigned to the CuLi-VLi. To compare the relative stability of the two defects, we present the defect formation energies as a function of Fermi energy under Li-rich and Li-poor conditions, to demonstrate the isolated CuLi is more stable than CuLi-VLi for the Fermi level in the entire range of band gap under Li-rich condition.

Optically-stimulated luminescence properties of Eu-doped Cs(Cl, Br) translucent ceramics

We have developed Eu-doped Cs(Clx, Br1-x) (x = 0, 0.25, 0.5, 0.75, 1) translucent ceramics by the spark plasma sintering technique and evaluated their optical and optically-stimulated luminescence (OSL) properties. As the optical properties, the transmittances of all the samples were 20–60% in the visible range, and the absorption bands around 260 and 350 nm due to 4f-5d transitions of Eu2+ were confirmed. After X-ray irradiation, all the samples showed the new absorption band around 600–700 nm. When increasing x, the generated absorption peak position shifted to shorter wavelength. Regarding the OSL properties, all the samples showed a broad OSL emission peak around 440 nm, and the origin was 5d-4f transitions of Eu2+. The peak positions of the OSL stimulation spectra shifted to shorter wavelength with increasing x. The dose sensitivities using OSL were confirmed to be as low as 0.01 mGy in all the samples.

TL, OSL and RL emission spectra of RE-doped LiMgPO4 crystals

In this work the spectral properties of emission of differently doped lithium magnesium phosphate (LiMgPO4, LMP) compound were investigated by thermoluminescence (TL), optically stimulated luminescence (OSL) and radio-luminescence (RL) methods. The samples were prepared in the form of crystals, which were grown from the melt by micro-pulling-down technique. Different rare-earth (RE) dopants have been studied regarding the influence on luminescence properties. It was found that the presence of boron ions together with the RE dopant seems to have an impact mainly on the TL emission spectra of the studied LMP crystals. TL, OSL, RL and after-glow emission spectra are comparable for the LMP crystals of the same dopants concentrations. The OSL emission spectra were obtained over a whole available wavelength range by the measurements of the after-glow spectra after the sample stimulation has ended. The obtained results tend to suggest that the investigated RE-doped LMP crystals exhibit promising luminescent properties and could be considered as appropriate candidates for real-time detectors.

Luminescent properties of MgB4O7:Ce,Li to be applied in radiation dosimetry

MgB4O7 is a promising matrix host for use in radiation dosimetry due to its low effective atomic number (Zeff = 8.2). The present work aims to investigate dosimetric and luminescent properties of the MgB4O7:Ce0,5%,Li0.5%, produced through solid-state synthesis, using the optically stimulated luminescence (OSL) technique. The first part of this work discusses the luminescent aspects of this phosphor, such as thermoluminescent emission spectra, photoluminescence emission, lifetime of emission centers and the effect of different lithium concentrations as co-dopant. In the second part, the basic OSL properties were evaluated, including dose-response curve, minimum detectable dose (MDD), step annealing, and best bleaching set-up for reuse of MgB4O7:Ce0,5%Li0.5% composites. The photoluminescence and thermoluminescence emission spectra of the composites present an emission peak at UV-VIS range centered around 370 nm, which is the most suitable for OSL dosimetry; this emission is related to Ce3+ electronic transitions and has a luminescence center lifetime of 0.003 ms. From the step-annealing analyses, it can be seen that the OSL emission is related to different depth trap centers in the band gap. The OSL dose-response curve is linear from 0.1 Gy to 100 Gy, with a MDD around 1 mGy. These properties make this material a strong candidate for different applications in radiation dosimetry field.