Terbium-doped Gadolinium Oxysulfide Research Articles

Controlled Synthesis of Terbium-Doped Colloidal Gd2O2S Nanoplatelets Enables High-Performance X-ray Scintillators.

Terbium-doped gadolinium oxysulfide (Gd2O2S:Tb3+), commonly referred to as Gadox, is a widely used scintillator material due to its exceptional X-ray attenuation efficiency and high light yield. However, Gadox-based scintillators suffer from low X-ray spatial resolution due to their large particle size, which causes significant light scattering. To address this limitation, we report the synthesis of terbium-doped colloidal Gadox nanoplatelets (NPLs) with near-unity photoluminescence quantum yield (PLQY) and high radioluminescence light yield (LY). In particular, our investigation reveals a strong correlation between PLQY, LY, particle size, and Tb3+concentration. Our synthetic approach allows precise control over the lateral size and thickness of the Gadox NPLs, resulting in a LY of 50,000 photons/MeV. Flexible scintillating screens fabricated with the solution-processable Gadox NPLs exhibited a 20 lp/mm X-ray spatial resolution, surpassing commercial Gadox scintillators. These high-performance and flexible Gadox NPL-based scintillators enable enhanced X-ray imaging capabilities in medicine and security. Our work provides a framework for designing nanomaterial scintillators with superior spatial resolution and efficiency through precise control of dimensions and dopant concentration.

A-Si EPID Modeling in GATE for Monte Carlo Investigation on the Optical Properties of Gd<sub>2</sub>O<sub>2</sub>S:Tb and Lu<sub>2</sub>SiO<sub>5</sub>:Ce Scintillators

A detailed a-Si Electronic Portal Imaging Device (EPID) was implemented in GATE (Geant4 application for tomographic emission) toolkit for Monte Carlo simulations, employing the standard electromagnetic processes and optical photon processes. The composition of the scintillating material is varied using the conventional terbium-doped gadolinium oxysulfide phosphor (Gd2O2S:Tb) and cerium-doped lutetium oxyorthosilicate (Lu2SiO5:Ce) which is widely used in Positron Emission Tomography (PET) detectors due to its supremacy in aiding the detection of low-energy photons. It was found that the number of optical photons produced is higher when using the Lu2SiO5:Ce scintillator resulting in a slightly better signal-to-noise ratio (SNR). The scattering within the EPID components was also investigated where the majority of the detected secondary particles were created in the scintillator. The results also show that the copper plate layer of the EPID contributes to additional Compton electrons and bremsstrahlung and annihilation photons to the measurements in the scintillator and photodiode layer. The glass substrate, graphite plates, electronic components, and aluminum bottom cover are also found to contribute a huge fraction of backscattered particles to the measurements at the photodiode layer.

Demonstrating the high sensitivity of MoS2 monolayers in direct x-ray detectors

Two-dimensional transition metal dichalcogenides (TMDCs) are demonstrated to be appealing semiconductors for optoelectronic applications, thanks to their remarkable properties in the ultraviolet-visible spectral range. Interestingly, TMDCs have not yet been characterized when exposed to x rays, although they would be ideal candidates for optoelectronic applications in this spectral range. They benefit from the high cross section of the constituent heavy atoms, while keeping the absorption very low, due to the ultrathin structure of the film. This encourages the development of photodetectors based on TMDCs for several applications dealing with x rays, such as radioprotection, medical treatments, and diagnosis. Given the atomic thickness of TMDCs, they can be expected to perform well at low dose measurements with minimal perturbation of the radiation beam, which is required for in vivo applications. In this paper, the use of TMDCs as active materials for direct x-ray detection is demonstrated, using a photodetector based on a MoS2 monolayer (1L-MoS2). The detector shows a response to x rays in the range of 101–102 keV, at dose rates as low as fractions of mGy/s. The sensitivity of 1L-MoS2 reaches values in the range of 108–109µC Gy−1 cm−3, overcoming the values reported for most of the organic and inorganic materials. To improve the x-ray photoresponse even further, the 1L-MoS2 was coupled with a polymeric film integrating a scintillator based on terbium-doped gadolinium oxysulfide (Gd2O2S:Tb). The resulting signal was three times larger, enabled by the indirect x ray to visible photoconversion mechanism. This paper might pave the way toward the production of ultrathin real-time dosimeters for in vivo applications.

Water Phantom Characterization of a Novel Optical Fiber Sensor for LDR Brachytherapy

This work considers the feasibility of using a novel optical fiber-based sensor, employing a terbium-doped gadolinium oxysulfide (Gd2O2S:Tb) inorganic scintillator, as a real-time in vivo dosimetry solution for applications in low-dose-rate (LDR) prostate brachytherapy (BT). This study specifically considers the influence of scintillator geometry (hemisphere tip versus cylindrical cavity), polymethyl methacrylate (PMMA) fiber core diameter (0.5 versus 1.0 mm), and sensor housing material (stainless steel versus plastic) on the measured scintillation signal. Characterization measurements were performed using a silicon photon-multiplier (SiPM) detector and a commercial water phantom system, integrated with custom 3-D printed components to allow for precise positioning of the LDR BT radiation source with respect to the optical fiber sensor (OFS). Significant differences in the rate of fall-off in the scintillation signal, with distance from the source, were observed between the different scintillator geometries considered. The hemisphere tip geometry was shown to be the most accurate, tracking with the expected fall-off in dose-rate, within measurement uncertainty. Reducing the fiber core diameter from 1.0 to 0.5 mm resulted in a sixfold reduction in the detected scintillation signal. A further 57% reduction was observed when housing the 0.5-mm fiber within a stainless steel LDR BT needle applicator. Initial results demonstrate the feasibility of employing an OFS, for applications in LDR BT, given the excellent agreement of measurements with theoretical expectations. Furthermore, a calibration process has been described for converting the detected scintillation signal into absorbed dose/dose rate, using our water phantom-based experimental setup.

Spectral response tuning of organic photodetectors using strong microcavity effects for medical X-ray detector application

An X-ray detector system was fabricated with an organic small molecule photodetector and a terbium-doped gadolinium oxysulfide (Gd2O2S:Tb) scintillating screen. Though the microsphere cluster structure of the Gd2O2S film had advantage in low material cost, wavelength matching to the proper photodetector is challenging due to its scintillating performance property in the relatively narrow emission spectrum range. To tune the absorption spectrum of the organic photodetector to that of the emission spectrum of the Gd2O2S, a microcavity effect was applied by controlling the thickness of the C60 layer. The peak wavelength of the absorption spectrum was tuned over a broad region of wavelengths, from 461 nm to 776 nm. The fabricated X-ray detector system was demonstrated in a medical X-ray radiography system.

Frequency-dependent optimal weighting approach for megavoltage multilayer imagers

Multi-layer imaging (MLI) devices improve the detective quantum efficiency (DQE) while maintaining the spatial resolution of conventional mega-voltage (MV) x-ray detectors for applications in radiotherapy. To date, only MLIs with identical detector layers have been explored. However, it may be possible to instead use different scintillation materials in each layer to improve the final image quality. To this end, we developed and validated a method for optimally combining the individual images from each layer of MLI devices that are built with heterogeneous layers. Two configurations were modeled within the GATE Monte Carlo package by stacking different layers of a terbium doped gadolinium oxysulfide Gd2O2S:Tb (GOS) phosphor and a LKH-5 glass scintillator. Detector response was characterized in terms of the modulation transfer function (MTF), normalized noise power spectrum (NNPS) and DQE. Spatial frequency-dependent weighting factors were then analytically derived for each layer such that the total DQE of the summed combination image would be maximized across all spatial modes. The final image is obtained as the weighted sum of the sub-images from each layer. Optimal weighting factors that maximize the DQE were found to be the quotient of MTF and NNPS of each layer in the heterogeneous MLI detector. Results validated the improvement of the DQE across the entire frequency domain. For the LKH-5 slab configuration, DQE(0) increases between 2%–3% (absolute), while the corresponding improvement for the LKH-5 pixelated configuration was 7%. The performance of the weighting method was quantitatively evaluated with respect to spatial resolution, contrast-to-noise ratio (CNR) and signal-to-noise ratio (SNR) of simulated planar images of phantoms at 2.5 and 6 MV. The line pair phantom acquisition exhibited a twofold increase in CNR and SNR, however MTF was degraded at spatial frequencies greater than 0.2 lp mm−1. For the Las Vegas phantom, the weighting improved the CNR by around 30% depending on the contrast region while the SNR values are higher by a factor of 2.5. These results indicate that the imaging performance of MLI systems can be enhanced using the proposed frequency-dependent weighting scheme. The CNR and SNR of the weighted combined image are improved across all spatial scales independent of the detector combination or photon beam energy.

Fabrication and properties of Gd2O2S:Tb scintillation ceramics for the high-resolution neutron imaging

Terbium doped gadolinium oxysulfide (GOS:Tb) ceramics were successfully fabricated by pre-sintering in vacuum and HIP post-treatment in Ar atmosphere. Ceramic densification in vacuum and HIP was discussed in the detail mainly by relative density and FESEM characterizations. The fabricated GOS:Tb ceramics were translucent with 0.5 mm thickness after HIP post-treatment. Optical and scintillation properties of GOS:Tb ceramics were also investigated. Temperature-dependent X-ray excited spectra were recorded using a homemade XEL spectrometer. Neutron scintillation light output was also measured in China Spallation Neutron Source (CSNS). The light output was measured to be about 284 photons per neutron with different thicknesses of GOS:Tb ceramics.

EVALUATION OF DIGITAL DETECTOR ARRAYS SYSTEMS FOR INDUSTRIAL RADIOGRAPHY

Digital Detector Arrays (DDA) or Flat Panel Detector (FPD) is a highly efficient technique that is used in nondestructive testing of internal features of an object. The evaluation of DDA systems for industrial radiography is important to ensure the image quality and to enables long-term stability of this system. This evaluation is specified by ASTM E2737–10, which describes the fundamental parameters of DDA systems to be measured. The tests require the usage of either the five-groove wedge or the duplex plate phantom with separate Image Quality Indicators (IQIs). The purpose of this work was evaluate the radiographic performance achieved using both techniques in two DDA systems manufactured by GEIT: DXR250P and DXR250V, which have thallium-doped cesium iodide (CsI:Tl) and terbium-doped gadolinium oxysulfide (Gd2O2S:Tb - GOS) scintillators, respectively. For this purpose, it was used an X-ray equipment as radiation source. The image quality parameters analyzed were Image Lag (IL), Offset Level (OL), Bad Pixel distribution, Burn In (BI), Spatial Resolution (SR), Material Thickness Range (MTR), Contrast Sensitivity (CS), Signal Level (SL) and Signal-to-Noise Ratio (SNR). As result of this study, has been observed that the use of the five-groove wedge phantom made the measurements to become easier to execute. Regarding the DDA system, the DXR250P presented more IL and BI, but produced images with better CS and SNR and needed a dose almost twice smaller than the DXR250V to achieve a similar SL.

Light Yield Enhancement of 157-Gadolinium Oxysulfide Scintillator Screens for the High-Resolution Neutron Imaging

This paper reports on light yield enhancement of terbium-doped gadolinium oxysulfide based scintillator screens achieved by coating their substrates with thin layers of a high density and high atomic number material. For this purpose, iridium was chosen and layers of various thicknesses were applied by atomic layer deposition (ALD). We assessed newly developed scintillator screens for neutron absorption, light yield and spatial resolution and compared them to previously used non-iridium-coated scintillator screens. The addition of the iridium layer resulted in 65 % light yield enhancement in comparison to uncoated scintillator screens while the spatial resolution and absorption power remained unchanged.Highlights•65 % light yield enhancement of the scintillator light output with preservation of the spatial resolution•Use of atomic layer deposition for nanoengineering of the neutron sensitive scintillator screens

Multi-point gamma-ray monitoring at radioprotection levels with image devices

A multi-point system for the simultaneous interrogation of several extrinsic polymer optical fiber-based gamma-ray sensors is demonstrated. As a proof of concept, four different sensing heads have been measured, all of them based on a chemically etched fiber tip plus an inorganic scintillator powder. Two inorganic scintillators have been tested, namely Terbium doped Gadolinium Oxysulfide (Tb:GADOX) and Cerium doped Yttrium-Aluminum garnet (YAG:Ce). These sensing heads are interrogated with a commercial image device (CMOS camera). Such device does not need any cooling stage, optical filters or image intensifier elements. The response for each individual transducer is inside a 2D grid-shape array image, which provides a multiplexing method scalable with the number of the desired interrogation points. The interrogation procedure takes advantage of well-stablished digital image processing techniques, which include the selection of the regions of interest (ROIs) associated to the response of each individual sensing-head, plus the suitable RGB channel selection to improve the signal to noise ratio in the final measurement. Thus, only the Green channel has been found to render useful signal for gamma ray monitoring. Furthermore, the selection of the exposure time in the CMOS camera also permits to adjust the radiation levels to be detected.All tests were run under gamma irradiation from a calibrated 137Cs source, the reference isotope for environmental protection. The obtained results show the feasibility of simultaneously interrogating several gamma ray sensors, which can provide reliable measurements to quickly detect the presence of hazardous radioactive materials in large accidental leakage scenarios.

High-Performance Next-Generation Perovskite Nanocrystal Scintillator for Nondestructive X-Ray Imaging.

Readily commercializable and cost-effective next-generation CsPbBr3 perovskite nanocrystals (PNCs) based X-ray detectors are demonstrated. The PNCs-based X-ray detector exhibits higher spatial resolution (9.8 lp mm-1 at modulation transfer function (MTF) = 0.2 and 12.5-8.9 lp mm-1 for a linear line chart), faster response time (≈200 ns), and comparable stability (>40 Gyair s-1 of X-ray exposure) compared with the commercialized terbium-doped gadolinium oxysulfide (GOS)-based detectors (spatial resolution = 6.2 lp mm-1 at MTF = 0.2 and 6.3 lp mm-1 for a linear line chart, response time =≈1200 ns) because the PNCs-based scintillator has ≈5.6-fold faster average photoluminescence lifetime and stronger emission than the GOS-based one.

Effect of Tb3+ concentration in the visible emission of terbium-doped gadolinium oxysulfide microspheres

Experimental data obtained from optical characterization of Gd2O2S:Tb3+ microspheres were compared with a rate-equation model in order to understand and simulate the emission intensity and color tonality as a function of Tb3+ concentration. The microparticles were prepared by hydrothermal synthesis and characterized by TEM and XRD to confirm spherical microparticles with a hexagonal lattice. Furthermore, fluorescent spectroscopy and rate equation model revealed that the direct energy transfer between Gd3+→Tb3+ ions and the migration of the excitation energy between Tb3+ play an important role in the luminescence intensity, while the color tonality is mainly governed by the non-radiative relaxation processes between Tb3+ at low concentrations. Finally, our results suggest that the rate equation model provides an efficient alternative to estimate theoretically the maximum doping concentration in oxysulfides before they present quenching of luminescence.

Dynamic gamma-ray monitoring at radioprotection levels with extrinsic polymer optical fiber sensors

The dynamic performance of extrinsic gamma-ray sensors at radioprotection levels is studied. The sensors have been fabricated with chemically etched polymer optical fibers covered with an inorganic scintillator powder (Terbium doped Gadolinium Oxysulfide). This scintillator shows a maximum emission peak at 543 nm, therefore only the signal amplitude at this wavelength has been measured with a commercial grade CCD spectrometer. The transducers have been done at the end of both short (1 m) and large fiber patchcords (27 m). Short patchcords are further mechanically spliced to a fiber link 25 m length through an industrial grade connector-less mating sleeve, and therefore can be easily replaced if needed.All tests were run under gamma irradiation from a 137Cs source, the reference isotope for environmental protection. The measured response of the devices is very repeatable and stable, with a percentage standard deviation below 2% when the air kerma rate is above 1 Gy/h. This deviation increases for lower rates. A Limit of Detection of 0.2 Gy/h, with an integration time at the detection stage of 10 s, has been achieved for transducers done in the 1 m length patchcords spliced to the 25 m length fiber link. This integration time can be further reduced when no splice is included between transducer and detection unit. The behavior of the devices is linear with the delivered air kerma rate, and can provide reliable measurements under repeated radiation exposures. This behavior makes the sensors useful to quickly detect the presence of hazardous radioactive materials in accidental leakage scenarios.

Highly Sensitive Extrinsic X-Ray Polymer Optical Fiber Sensors Based on Fiber Tip Modification

An extrinsic X-ray fiber sensor with improved sensitivity is presented. The developed device is based on an inorganic scintillator (terbium-doped gadolinium oxysulfide) attached to a polymer fiber tip. Sensitivity improvement has been accomplished by modifying the fiber tip in two ways: by thermomechanical tapering and by chemical etching. Thus, the useful surface in contact with the scintillator increases, and so the fluorescence light gathering capability. All the fabricated devices have been tested under X-ray irradiation from a Linac at a dose rate of 300 monitor units/min, with a readout every 100 ms. The obtained results shown a signal improvement of up to 43 times when compared with previous reported proposals using inorganic scintillators and polymer fibers. Moreover, the recorded signal under the same measurement conditions can be further improved if the inorganic scintillator is used in powder format instead into an epoxy matrix.

Embedded structure fiber-optic radiation dosimeter for radiotherapy applications

An investigation into a novel in-vivo PMMA (polymethyl methacrylate) plastic fiber-optic dosimeter for monitoring low doses of ionizing radiotherapy radiation in real time and for integrating measurements is presented. The fabricated optical fiber tip possessed an embedded structure. A scintillation material, terbium-doped gadolinium oxysulfide (Gd2O2S:Tb), capable of emitting visible light at around 545 nm which is ideal for transmission through the PMMA when exposed to ionizing radiation was embedded in the PMMA plastic fiber. The dose rate of incident ionizing radiation is measured by analyzing the signal intensity emitted from the scintillation material which propagates through the fiber to a distal MPPC (multi-pixel photon counter). The dosimeter exhibits good repeatability with an excellent linear relationship between the fiber-optic dosimeter output and the absorbed radiation dose with an outstanding isotropic response in its radial angular dependence.

Toxicity evaluation of high-fluorescent rare-earth metal nanoparticles for bioimaging applications.

Research on nanometer-sized luminescent semiconductors and their biological applications in detectors and contrasting agents is an emergent field in nanotechnology. When new nanosize technologies are developed for human health applications, their interaction with biological systems should be studied in depth. Rare-earth elements are used in medical and industrial applications, but their toxic effects are not known. In this work, the biological interaction between terbium-doped gadolinium oxysulfide nanoparticles (GOSNPs) with human peripheral blood mononuclear cells (PBMC), human-derived macrophages (THP-1), and human cervical carcinoma cell (HeLa) were evaluated. The GOSNPs were synthetized using a hydrothermal method to obtain monodisperse nanoparticles with an average size of 91 ± 9 nm. Characterization techniques showed the hexagonal phase of the Gd2 O2 S:Tb3+ free of impurities, and a strong green emission at λemi = 544 nm produced by Tb3+ was observed. Toxic effects of GOSNPs were evaluated using cell viability, apoptosis, cell-cycle progression, and immunological response techniques. In addition, an Artemia model was used to assess the toxicity in vivo. Results indicated cell apoptosis in both types of cells with less sensitivity for PBMC cells compared to HeLa cells. In addition, no toxic effects were observed in the in vivo model of Artemia. Moreover, GOSNPs significantly reduced the activation and cell-cycle progression of PBMC and HeLa cells, respectively. Interestingly, an increase in proinflammatory cytokines was not observed. Our data suggest that fluorescence applications of GOSNPs for biolabeling are not toxic in primary immune cells and they may have an immunomodulatory effect. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 605-615, 2017.

X-ray imaging with scintillator-sensitized hybrid organic photodetectors

Medical X-ray imaging requires cost-effective and high-resolution flat-panel detectors for the energy range between 20 and 120 keV. Solution-processed photodetectors provide the opportunity to fabricate detectors with a large active area at low cost. Here, we present a disruptive approach that improves the resolution of such detectors by incorporating terbium-doped gadolinium oxysulfide scintillator particles into an organic photodetector matrix. The X-ray induced light emission from the scintillators is absorbed within hundreds of nanometres, which is negligible compared with the pixel size. Hence, optical crosstalk, a limiting factor in the resolution of scintillator-based X-ray detectors, is minimized. The concept is validated with a 256 × 256 pixel detector with a resolution of 4.75 lp mm−1 at a MTF = 0.2, significantly better than previous stacked scintillator-based flat-panel detectors. We achieved a resolution that proves the feasibility of solution-based detectors in medical applications. Time-resolved electrical characterization showed enhanced charge carrier mobility with increased scintillator filling, which is explained by morphological changes.

Photovoltaic cells energy performance enhancement with down-converting photoluminescence phosphors

Summary Phosphors, synthesized by the urea homo-precipitation method, were examined as ultraviolet-spectral down conversion materials for improving the light absorption and electrical characteristics of commercial single-junction silicon solar cells. The photovoltaic (PV) cells were coated with erbium and terbium doped gadolinium oxysulfide phosphors encapsulated in ethyl vinyl-acetate binder using blade screen printing technique, and the optimum concentration of phosphor in the composite resulted in the largest light conversion, and superior electrical output and energy transfer efficiency. Moreover, the results demonstrated that the composition of dispersed phosphors has a strong influence on the amount of ultraviolet-light converted and electron transition capacity of PV cells. The experimental results showed in an optimized PV cell, an enhancement of 0.54% (from 12.11% to 12.65%) in the energy conversion of a Si-based PV cell was achieved. Copyright © 2015 John Wiley & Sons, Ltd.

Photovoltaic cells energy performance enhancement with down-converting photoluminescence phosphors

Phosphors, synthesized by the urea homo-precipitation method, were examined as ultraviolet-spectral down conversion materials for improving the light absorption and electrical characteristics of commercial single-junction silicon solar cells. The photovoltaic (PV) cells were coated with erbium and terbium doped gadolinium oxysulfide phosphors encapsulated in ethyl vinyl-acetate binder using blade screen printing technique, and the optimum concentration of phosphor in the composite resulted in the largest light conversion, and superior electrical output and energy transfer efficiency. Moreover, the results demonstrated that the composition of dispersed phosphors has a strong influence on the amount of ultraviolet-light converted and electron transition capacity of PV cells. The experimental results showed in an optimized PV cell, an enhancement of 0.54% (from 12.11% to 12.65%) in the energy conversion of a Si-based PV cell was achieved. Copyright © 2015 John Wiley & Sons, Ltd.

Evaluation of the modulation transfer function of megavoltage X-rays

The modulation transfer function (MTF) must be measured against the requirements of the specific digital imaging application under consideration in order to evaluate the performance of detector equipment and to further develop the detector by performing quality-assurance (QA) procedures. The purpose of this study was to measure the MTF in digital megavoltage images (DMVs) for radiation therapy (RT) by using an edge block. We used 6 megavolts (MVs) of energy for the pre-sampling MTF, along with a photo-stimulating phosphor-based computed radiography (CR) system and a hexalon lead screen that contained a terbium-doped gadolinium oxysulfide granular phosphor (Gd2O2S:Tb). The DMV MTF was measured at both low and high resolutions according to changes in the dose in monitor units (MUs) by using four different detector combinations: CR-IP (image plate: photo-stimulable phosphor screen), CR-IP-Lead (image plate + lead screen), CR-IP-Regular (fast front screen + image plate + fast front screen) and CR-IP-Fast (fast back screen + image plate + fast front screen). At a low resolution, the MTF 50% and the MTF 10% when using the CR-IP detector increased by about 30% and 46%, in proportion to the increase in the dose from 1 to 20 MU, respectively. At a high resolution, the CR-IP and the CR-IP-Lead detectors showed increases in the MTF of about 8% or 10% when the dose increased from 1 to 20 MU. The present study, therefore, evaluates how edge methods can be helpful in taking MTF measurements during QA tests of a megavoltage imaging (MVI) system.