Radioluminescence Research Articles

Nonlinear scintillation effects in the intrinsic luminescence from Sc1.318Y0.655Si1.013O4.987 crystal excited by electrons and γ-quanta

The spectral and kinetic properties of intrinsic luminescence from (Y2Sc1)0.(3)(Sc)[Si]O5 crystal are studied. The emission is excited by electrons and γ-quanta. The composition (Y2Sc1)0.(3)(Sc)[Si]O5 is the congruent one for Sc2SiO5-Y2SiO5 solid solutions. It is found, that the crystal emits fairly bright intrinsic cathodololuminescence (CL) and radioluminescence (RL) at room temperature. In particular, the light yield of scintillation excited by γ-quanta with the energies of 661.7 keV is of 12000 photons/MeV. An increase in the beam flux by ∼20 times leads to the shift in the maximal CL energy spectral density from 315 to 340 nm and to the decrease in the CL decay time at 415 nm from 1377 ± 3 ns to 1165 ± 1 ns. Simultaneously, the decay time of RL excited by a photoelectron with the energy of 644.7 keV is of 1310 ± 10 ns while a Compton electron with the energy of 477 keV excites RL with the decay time of 1050 ± 10 ns. Also, we observed differences in the CL yield dependencies on the volume-averaged density of electronic excitations (EEs) at different wavelengths. An explanation of the results is given considering the nonlinear scintillation phenomena induced by an interaction between EEs. It is based on a conception that an increase in EE volume density leads to an increase in EEs nonradiative quenching due to these interactions.

Improvement of BGO ceramic scintillators through hot‐pressing sintering methodology

AbstractIn the present work, the sintering of bismuth germanate through hot pressing and the improvement of scintillator performance were investigated. The linear shrinkage, crystalline structure, microstructure, transparency degree, and radioluminescence (RL) were studied as functions of the sintering pressure. X‐ray diffraction revealed that the samples were predominantly composed of the Bi4Ge3O12 phase, accompanied by small amounts of Bi12GeO20, with concentrations varying according to the sintering parameters. These concentrations were quantified through Rietveld refinement, which also indicated a tendency for the cell parameters to shrink as the sintering pressure increased. The microstructure of the ceramic pellets produced under varying hot‐pressing parameters was investigated using scanning electron microscopy (SEM), revealing that while the grain size was preserved, the porosity and grain boundary thickness were reduced by the hot pressing, forming a quasicontinuum in some areas of the sample. The RL of all the samples exhibited a green color, with a maximum at 540 nm, ascribed to the transitions from the 3P0,1,21P1 excited states to the fundamental 1S0 state of the Bi3+ ions. For samples sintered under a pressure of .18 MPa, the enhancement in the optical transmittance, accompanied by a 61.36% increase in light output at the maximum wavelength, was observed.

A custom-made integrated system for thermoluminescence and radioluminescence spectroscopy

Thermoluminescence (TL) and Radioluminescence (RL) are widely used in dosimetry applications. We present a custom-built integrated system, designated LUMI22, for measuring TL, TL spectroscopy, RL, and RL as a function of temperature. LUMI22 includes a heating system based on Kanthal® A1 alloy (FeCrAl), a microcontroller to regulate the temperature ramps (e.g. 1–5 °C/s). To irradiate samples an X-ray tube (Moxtek 50 kV, 50 μA) is powered, controlled, and monitored by an FTC-200 standard controller. The dose rate at the sample position is 0.43 Gy/min. Light collection includes a Photomultiplier Tube (PMT, Hamamatsu H10493-012:HA, 185–850 nm). Additionally, a miniature fiber optic spectrometer (Ocean Optics, QE65000, range 200–1100 nm) coupled with a 1000 μm diameter fiber optic (QP1000- 2-UV-VIS) was employed for TL and RL spectroscopy measurements. To assess the functionality of the system, it was used to measure TL and RL from Al2O3:C,Mg, Al2O3:C and TLD-100 phosphors which have been previously well investigated. The measured TL and RL data were well compared to the published ones, confirming the functionality of the system.

Effect of Ga/Al ratio on the luminescent properties of inorganic scintillating GGAG:(4 mol%)Ce ceramic powder

Gadolinium gallium aluminum garnet doped with cerium (GGAG:Ce), a promising ceramic scintillator material, is being excessively explored for its high quality optical properties by the bandgap engineering with different Ga/Al ratio. In this study, GGAG:Ce powders were synthesized using a solvothermal method and sintered at 1300 °C to investigate the impact of the gallium-to-aluminum (Ga/Al) ratio on optical characteristics. The results revealed that a decrease in the Ga/Al ratio led to a decrease in particle size. This observation can be attributed to the different reactivity and growth kinetics of gallium and aluminum precursors during the solvothermal process. Perturbations from the optimized Ga/Al ratio of 1.5–1.77 and 1.27 resulted in substantially enhanced photoluminescence (PL) and radioluminescence (RL) spectra intensities. PL lifetime measurements of various Ga/Al ratio exhibit average PL lifetime between 48 and 57 ns. Specifically, the deviations to 1.77 and 1.27 ratios yielded approximately 125 % and 106 %, respectively, in observed luminescent measurements compared to other ratios. This enhancement in PL and RL intensity suggests that the Ga/Al ratio plays a critical role in modulating the optical properties of GGAG:Ce ceramic powders. The results of this study also highlight the importance of the Ga/Al ratio in tailoring the optical or luminescence characteristics of GGAG:Ce powders.

Enhanced OSL emission from α- Al2O3 produced in the presence of halloysite nanocrystals

Aluminum oxide (Al2O3) compounds are extensively used in ionizing radiation dosimetry due to their high sensitivity when doped with carbon. However, their production is difficult and expensive, leading to much research on alternative ways to increase its sensitivity. This paper proposes a seed-mediated synthesis of α-Al2O3 by the combustion method with halloysite nanocrystals as seeds, which also have the ability to scavenge heavy metal ions. The dosimetric features were studied by radioluminescence (RL), thermoluminescence (TL), and optically stimulated luminescence (OSL). Scanning electron microscopy images and X-ray diffraction patterns pointed to the halloysite nanotubes (HNT) acting as heterogeneous nucleation seeds, and as adsorber centers for the chromium ions (Cr3+), as evidenced by the decreased crystallite size and Cr3+ RL emission. Decreased TL intensity upon increasing HNT content in addition to the RL data suggested that the Cr3+ ions strongly participate in the TL emission process as a luminescent center. Remarkable 6-fold enhanced OSL area intensity and 69-fold OSL initial intensity enhancement were registered from the samples seed-mediated by HNT, revealing that, by scavenging Cr3+, the HNT eliminated a luminescent center that competes with the OSL emission. Therefore, HNTs are promising nanomaterials to enhance the sensitivity of Al2O3 dosimeters with potential application in medical physics, where a decrease in the density of concurrent luminescent centers and an increase in OSL intensity were evidenced by the presence of HNT in Al2O3.

Long-Range Imaging of Alpha Emitters Using Radioluminescence in Open Environments: Daytime and Night-Time Applications.

Alpha emitters like plutonium pose severe health risks when ingested, damaging DNA and potentially causing cancer. Traditional detection methods require proximity within millimeters of the contamination source, presenting safety risks and operational inefficiencies. Long-range detection through alpha radioluminescence (RL) offers a promising alternative. However, most of the previous experiments have been carried out under controlled conditions that preclude the overwhelming effect of ambient light. This study demonstrates the successful detection of a 3 MBq alpha emitter in an open environment using a compact alpha camera. This camera incorporates a deep-cooled CCD and a low f-number lens system designed to minimize the blue shift effects of filters. Night-time imaging was achieved with a dual-filter system using a sandwich filter assembly centered at 337 nm and 343 nm for capturing alpha RL and subtracting background light, respectively. At night, the alpha source was detected from 1 m away within one minute, and the lowest detection limit can be calculated as 75 kBq. The system was also evaluated under simulated urban lighting conditions. For daytime imaging, a stack of tilted 276 nm short pass filters minimized sunlight interference, enabling the detection of the alpha source at 70 cm within 10 min under indirect sunlight. This research highlights the viability of long-range optical detection of alpha emitters for environmental monitoring in real-world settings.

X-ray spectrum estimation from the transmission method using the radioluminescence of an Al2O3:C crystal

The X-ray spectrum of X-ray tube is crucial for radiation dose calculations. Due to the high photon flux, it is difficult to directly measure the primary spectrum of X-ray tube. Transmission measurement is one of indirect method used to determine the primary spectrum of X-ray tube. Although the method is experimentally simple, X-ray spectrum estimation from transmission method is a seriously ill-conditioned problem. In this paper, a new transmission measurement instrument with an the Al2O3:C crystal detector is proposed. Real-time dose rate attenuation data from transmission method are collected by using the radioluminescence(RL) of the Al2O3:C crystal. The expectation-maximization (EM) method is applied for X-ray spectrum estimation from transmission method. The method is demonstrated on typical simulated spectra of 80,100,120,140 and 160 kV from X-ray tubes. The X-ray spectra are simulated with the Monte Carlo code Geant4. The EM method is successfully applied to seriously ill-conditioned and under determined estimation problems. The results showed that the X-ray spectrum estimation method is a robust technique for estimating the primary spectrum of X-ray tube, and that the new instrument for transmission measurements can be used to accurately estimate X-ray spectrum.

Radioluminescence Dosimetry in Modern Radiation Therapy

Accurate and precise measurement of radiation energy delivered to and absorbed by the patient's tissue is of great importance in radiation therapy (RT) quality assurance. Radioluminescence (RL) dosimetry has shown great potential for high spatiotemporal resolution dose measurement of RT fields. Implementation of efficient RL dosimetry in RT requires multidisciplinary effort and skills in optics, medical physics, radiation physics, electronics, and imaging science. In this review, a wide overview of fundamentals and applications of RL properties of media for RT dosimetry with emphasis on their potential use for multidimensional, small‐field, and ultra‐high dose rate RT dosimetry is provided.

Impact of sample preparation temperature on Li and Ce co-doped MgB4O7 dosimetry performance: A plausible scenario for controlling defect clustering

MgB4O7 co-doped with Ce and Li has been recognized as a promising dosimetric material for spatially-resolved optically stimulated luminescence (OSL) measurements. Nevertheless, conflicting information exists in the literature regarding its dosimetric characteristics. These include discrepancies in fading, the proportion of shallow traps, the range of linear dose response, and a notable absence of direct sensitivity comparisons. These discrepancies are likely attributed to variations in the synthesis methods utilized to produce this material. As part of our research initiative aiming at elucidating the influence of synthesis on the luminescence properties, we are examining in this contribution a single parameter – specifically, the sample preparation temperature – and assessing its impact on the luminescence properties. For the first time, we identified a correlation between the width of the thermoluminescence (TL) glow curves, the TL, optically stimulated luminescence (OSL), and radioluminescence (RL) intensities, as well as the fading characteristics over time and annealing temperature. We show that annealing at higher temperature leads to narrowing of the main TL peak (c.a. 240 °C at 5 °C/s heating rate) compared with samples prepared at lower temperatures, which in turn leads to a decrease in the integrated TL intensity of that peak. Despite exhibiting lower intensity, samples prepared at temperatures above 800 °C show less than 10 % TL/OSL fading over 60 days. Our measurements suggest an involvement of clustered defects for the samples prepared at 600 °C, with a shift towards a scenario of delocalized transitions in samples prepared at higher temperatures.

Luminescence properties of cerium-doped Li2O–Gd2O3 –ZrO2–P2O5 glasses for scintillator application

In this study, we developed the phosphate glass doped with CeF3 for scintillator applications. The phosphate glasses, 20Li2O−5Gd2O3–2ZrO2−(73-x) P2O5−xCeF3 were synthesized at different CeF3 concentrations by using the conventional melt-quenching technique. The density, molar volume, transmittance, photoluminescence (PL) and radioluminescence (RL) properties were investigated and quantified. The study found a positive correlation between the concentration of CeF3 with the density values and refractive index of the glass samples. The transmission spectra exhibited a red shift as the level of CeF3 increased. The emission spectra revealed a wide range of wavelengths resulting from the transition between the 5d and 4f transitions of the Ce3+ ion. The maximum intensity of emission for both PL and RL were observed at a concentration of 0.50 mol% CeF3. Moreover, the results of the emission spectra measured under Gd3+ excitation and the PL decay curves of Gd3+ in glass samples showed clearly evidence energy transfer (ET) from Gd3+ to Ce3+. The XPS spectra revealed the existence of phosphorus oxidation states. The XANES analysis revealed the existence of Ce3+ and Ce4+ in all glass samples, as evidenced by the appearance of peaks at approximately 5.728 keV for Ce3+, 5.732 keV and 5.739 keV for Ce4+. The scintillation efficiency of CeF3-doped phosphate glass with a concentration of 0.50 mol% was found to be 60.63% when compared to BGO crystal. Additionally, the decay time is extremely fast, varying from 17.52 to 25.93 ns, which is a critical attribute in the development of radiation detectors. In addition, X-ray imaging was conducted to investigate its potential efficacy in scintillator applications for X-ray imaging. The X-ray imaging investigation had a spatial resolution of 10 lp/mm with an MTF of 0.25. The results suggest that CeF3-doped phosphate glass has the potential to serve as a scintillator in X-ray imaging systems.

Study on structural and optical properties of Tb3+ co-doped Au glasses for green optical application

This report investigates the structure and optical properties of Tb3+ co-doped Au glasses, with a focus on their applicability in green luminescent optical behavior. The study of Tb3+ co-doping in the presence of Au nanoparticles (AuNPs) within glass matrices. The starting materials include SiO2, Al2O3, B2O3, CaO, Sb2O3, Na2O, K2O, SnO2, SeO2, Tb2O3, and AuNPs. Glass fabrication employs the conventional melt quenching technique, followed by comprehensive characterization of physical, optical, luminescence, and structural properties. The density values reported for the glass, ranged from 2.8269 to 2.8359 g/cm3, molar volume was 26.3382 to 26.2591 cm3/mol, and refractive index was 1.5438–1.5526. The absorption spectra consist of three absorption bands that are located at 524, 1894, and 2178 nm and are assigned to 7F6 → 5D4, 7F6 → 7F0,1,2, and 7F6 → 7F3, respectively. Photoluminescence (PL) and radioluminescence (RL) show similar trend and the optical properties are scrutinized using a spectrofluorometer. Size of the nanoparticle was evaluated and show around 8–16 nm and interplanar distance showing 2.1 Å. This study underscores the potential of Tb3+ and Au co-doped materials as promising for green optical applications.

Two-dimensional real-time dosimetry system using micro-and nano-(C44H38P2)MnCl4 radioluminescence coatings

This study investigates the impact of particle size on the radioluminescence (RL) response of (C44H38P2)MnCl4 coatings, which have been made with five crystal size fractions ranging from ≈200 nm to 75 μm. These coatings underwent testing using a bespoke 2D real time prototype system, comprising a camera affixed to the head of a linear accelerator and oriented towards the flexible RL coatings positioned at the beams' isocentre. Upon irradiation, a consistent RL peak at 525 nm was observed across all particle size fractions, albeit with varying light intensities. Minimum detectable dose-rate values were determined to be 0.05 Gy/min, and even for the coating exhibiting the lowest light intensity (Nano-01), individual pulses could be discerned, yielding a minimum detectable dose of 0.28 mGy. Basic dosimetric tests were conducted to characterize these coatings, evaluating their response with respect to dose-rate, dose, and small field relative responses. Subsequently, the coating demonstrating the most favorable dosimetric properties underwent further analysis to assess its suitability for machine quality assurance (QA). These tests included the standard alternating leaves, chair, and pyramid checks routinely employed for QA purposes.

Optimization of Eu0.6Gd(0.4-x)TbxBO3 phosphor with Tb3+ concentration for X-ray screen material application

In this study, Eu0.6Gd(0.4-x)TbxBO3 (0.000 ≤ x ≤ 0.015) phosphors doped with varying concentrations of Tb3+ were synthesized using the solid-state reaction technique at a temperature of 900 °C for 18 h. X-ray diffraction (XRD) was employed to analyze the crystal structures of the Triclinic and Hexagonal phases corresponding to EuBO3 (ICSD No 01-089-7888) and EuBO3 (ICDD No 00-013-0485), respectively. The optical properties were analyzed through absorption excitation and emission spectra obtained via photoluminescence (PL) and radioluminescence (RL) techniques. The CIE chromaticity coordinates indicate a reddish-orange. The sample with x = 0.010 exhibited good optical efficiency under both PL (λex = 394) and RL. Furthermore, the radioluminescence performance of the x = 0.010 phosphor was 9.4% higher than that of the undoped phosphor. Samples responding to X-rays can be presented radiography, appearing brighter and clearer. This indicates that the samples exhibit favorable characteristics for application as an X-ray screen.

A comprehensive study on the structural, radioluminescence and thermoluminescence properties of scheelite and wolframite type tungstates

In this study, the structural and spectroscopic properties of AWO4 (A = Ca, Sr, Ba, Mg, Zn and Cu) ceramics synthesized by conventional solid-state reaction technique were investigated. The local structure around the W and accessible various metal cations have been investigated using X-ray absorption spectroscopy (XAS). Local structural changes have been observed in scheelite-type structures and wolframite type structures. β-irradiated thermoluminescence (TL) glow curve for all samples were recorded and analyzed to obtain the trapping parameters, such as activation energy (E), order of kinetics (b) and frequency factor (s). The scheelite-type tungstates exhibited a distinct TL peak of second order kinetics indicating the presence of deeper traps, whereas wolframite-type tungstates did not exhibit such peak. Apart from BaWO4, and CuWO4, all the other samples demonstrated broad radioluminescence (RL) in the range 400 nm–700 nm when subjected to X-ray excitation. The RL and TL properties of the AWO4 ceramics are correlated with their respective crystallographic structure.

Luminescence properties of SrB6O10:Ce,Gd phosphor for applications in OSL dosimetry and lighting

Strontium hexaborate (SrB6O10) doped with different metals and/or lanthanides has been studied widely as the thermoluminescence (TL) dosimeter. However, there is almost no dosimetry study concerning the utility of Optically Stimulated Luminescence (OSL) on SrB6O10. This preliminary study aims to examine the luminescence properties of SrB6O10 phosphor for their application in the areas of dosimetry and lighting technologies. Undoped and doped material to get an OSL dosimeter were synthesized by incorporating the dopants Ce3+, in the range of 0.1–0.7 % wt, and Gd3+, in the range of 0.1–1 % wt into the SrB6O10 structure using the solution combustion (SCS) method. The structural and morphological characterizations were performed using X-ray diffraction (XRD) and Scanning Electron Microscope (SEM) methods, respectively. Two TL peaks of SrB6O10:Ce0.1%,Gd0.5% occurred at 70 °C and 182 °C after 1 Gy exposure to beta rays with a heating rate of 2 °C/s. The step annealing measurements were carried out to determine the traps responsible for the OSL signal. Various properties of the luminophore including dose-response and reusability were investigated using blue light stimulation. The phosphor showed a little variation of response up to 20 cycles within 2 % deviation (STD) from the first OSL readout. The OSL output within the range of 2–20 Gy was determined as linear. Radioluminescence (RL) measurement was investigated by emission in the range λem = 200–1000 nm. The parent compound displayed UV emission subdivided into UVA (315–400 nm), and UVB (280–315 nm) emissions at room temperature. The Chromaticity Coordinates (CIE) of SrB6O10:Ce0.1%,Gd0.5% were calculated as x = 0.2165, y = 0.1767. These remarkable characteristics show that, if developed, SrB6O10 could be used as an OSL dosimeter.

Insights into luminescence and energy transfer processes in Ce3+- and Tb3+ co-doped (Gd, Y)3Al2Ga3O12 garnet single crystals

Driven by the pursuit of optimizing the luminescent properties of garnet-based single crystals for X-ray imaging applications, this work reports on the successful synthesis and in-depth characterization of GYAGG crystals doped with Ce³⁺ or Tb³⁺ ions, and doubly-doped with both of them. Micro-pulling down synthesis yielded crystals with a single cubic phase confirmed by X-ray diffraction. Photoluminescence (PL) and radioluminescence (RL) measurements on Ce³⁺,Tb³⁺ co-doped GYAGG revealed bidirectional energy transfer processes. Characteristic broadband 5d1→4f emission of Ce³⁺ centers peaking at 530 nm and narrow 4f→4f emission lines of Tb³⁺ ions starting from 5D4 level within 480–630 nm were observed. At higher doping levels, cross-relaxation in Tb³⁺ pairs resulted depleted 5D3 state and only the emission from 5D4 one was observed in the spectra. Analysis of PL decay characteristics corroborated the spectral observations, confirming progressively decreasing Ce³⁺ decay time (down to 40 ns at 15 % Tb3+) due to enhanced Ce³⁺→Tb³⁺ energy transfer. Similarly, the Tb³⁺ decay time accelerated by more than 60 % after the Ce³⁺ co-doping. Notably, co-doping with 0.5 % Ce³⁺ and 10–15 % Tb³⁺ doubled the luminescence intensity of RL spectra compared to 0.5 % Ce³⁺-doping alone, attributed to the increased density of emitting centers.

Effect of Dual-Organic Cations on the Structure and Properties of 2D Hybrid Perovskites as Scintillators.

Two-dimensional (2D) hybrid organic-inorganic perovskite (HOIP) crystals show promise as scintillating materials for wide-energy radiation detection, outperforming their three-dimensional counterparts. In this study, we synthesized single crystals of (PEA2-xBZAx)PbBr4 (x ranging from 0.1 to 2), utilizing phenethylammonium (C6H5CH2CH2NH3+) and benzylammonium (C6H5CH2NH3+) cations. These materials exhibit favorable optical and scintillation properties, rendering them suitable for high light yield (LY) and fast-response scintillators. Our investigation, employing various techniques such as X-ray diffraction (XRD), photoluminescence (PL), time-resolved (TR) PL, Raman spectroscopy, radioluminescence (RL), thermoluminescence (TL), and scintillation measurements, unveiled lattice strain induced by dual-organic cations in powder X-ray diffraction. Density functional theory analysis demonstrated a maximal 0.13 eV increase in the band gap with the addition of BZA cation addition. Notably, the largest Stokes shift of 0.06 eV was observed in (BZA)2PbBr4. The dual-organic cation crystals displayed >80% fast component scintillation decay time, which is advantageous for the scintillating process. Furthermore, we observed a dual-organic cations-induced enhancement of electron-hole transfer efficiency by up to 60%, with a contribution of >70% to the fast component of scintillation decay. The crystal with the lowest BZA concentration, (PEA1.9BZA0.1)PbBr4, demonstrated the highest LYs of 14.9 ± 1.5 ph/keV at room temperature. Despite a 55-70% decrease in LY for BZA concentrations >5%, simultaneous reductions in scintillation decay time (12-32%) may work for time-of-flight positron emission tomography and photon-counting computed tomography. Our work underscores the crucial role of dual-organic cations in advancing our understanding of 2D-HOIP crystals for materials science and radiation detection applications.

Thermally Activated Delayed Fluorescent Ag(I) Complexes for Highly Efficient Scintillation and High‐Resolution X‐Ray Imaging

AbstractOrganic thermally activated delayed fluorescent (TADF) scintillators hold promising potential for applications in medical radiography and security detection, but the poor X‐ray absorption ability and inferior radioluminescence (RL) hampered their progression. Herein, the study has pioneered the development of high‐performance TADF Ag(I)‐based scintillators from M2X2(dppb)2 (M = Ag, Cu; X = Cl, Br, I) complexes with 1,2‐Bis(diphenylphosphino)benzene (dppb) ligand. In comparison with Cu(I) complexes, the Ag(I) series generally exhibited superior scintillation performance. Notably, Ag2Cl2(dppb)2 (Ag1) stands out with exceptionally high RL intensity (≈125% higher than that of CsI:Tl) and a low detection limit of 59.8 nGy s−1. The outstanding scintillation performance of Ag1 is primarily attributed to the synergistic effect of the high exciton utilization efficiency origin from a small singlet‐triplet energy gap, enhanced X‐ray absorption capacity by heavy atoms, and the high photoluminescence quantum yield (76.47% in ambient atmosphere). By fabricating a flexible film constructed with Ag1 submicron crystalline powders, a high spatial resolution of 25.0 lp mm−1 for X‐ray imaging is obtained. It offers new opportunities for utilizing TADF metal–organic complexes for highly efficient X‐ray scintillation and imaging.

Silica-based scintillators: basic properties of radioluminescence kinetics.

Radioluminescent silica-based fiber dosimeters offer great advantages for designing miniaturized realtime sensors for high dose-rate dosimetry. Rise and fall kinetics of their response must be properly understood to better assess their performances in terms of measurement speed and repeatability. A standard model of radioluminescence (RL) has already been quantitatively validated for doped silica glasses, but beyond conclusive comparisons with specific experiments, a comprehensive understanding of the processes and parameters determining transient and equilibrium kinetics of RL is still lacking. We analyze in detail the kinetics inherent in the standard RL model. Several asymptotical regimes in the RL growth are demonstrated in the case of a pristine sample (succesive quadratic, linear and power-law time dependencies before the plateau is reached). We show how this situation is modified when a pre-irradiation partly fills traps beforehand. RL growth is then greatly accelerated because of the pre-formation of recombination centers (RCs) from dopant ions, but not due to pre-filling of trapping levels. In all cases, the RL intensity eventually tends to a constant level equal to the pair generation rate, long before all carrier densities themselves reach equilibrium. This occurs late under irradiation, when deep traps get to saturation. The fraction of dopants converted into RCs is then 'frozen' at a lower level the smaller the density of deep traps. Controlling RL kinetics through the engineering of material traps is not an option. Pre-irradiation appears to be the simplest way to obtain accelerated and repeatable kinetics.

Synthesis of cerium-doped gadolinium gallium aluminum garnet (GGAG:Ce) scintillating powder via solvothermal method

The powder material Gd3Ga3Al2O12:Ce (GGAG doped with Cerium) has garnered significant attention in radiation detection due to its high light yield and rapid decay time. Despite its potential, the synthesis of high-quality and reproducible GGAG:Ce scintillating powder remains a considerable challenge. In this study, we present a solvothermal approach with an annealing temperature of 1300 °C for producing cerium-doped GGAG powder with varying concentrations (4, 2, and 0.5 mol%). The structural and luminescent characteristics were meticulously examined using X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), photoluminescence (PL), radioluminescence (RL) spectroscopy, and X-ray photoelectron spectroscopy (XPS). XRD analysis confirmed the single-cubic phase garnet structure of the synthesized powder. By comparing the intermediate solvothermal products synthesized at different sintering temperatures (900 °C for 3 h and 1300 °C for 1 and 3 h), a direct correlation between solvothermal conditions and the structure/property relationships of the product was established. FESEM images revealed an ellipsoidal to irregular morphology of the as-synthesized GGAG:Ce microparticles, ranging from 0.1 to 0.3 μm, regardless of the Ce concentration. PL spectra demonstrated a strong emission peak at approximately 550 nm, characteristic of Ce3+ ions. RL data confirmed the peak luminescence at around 550 nm, with an almost twofold increase in intensity as the concentration of Ce3+ increased from 0.5 mol% to 4 mol%. XPS data disclosed the Ce3+/Ce4+ ratio in solvothermally synthesized GGAG:Ce, wherein Ce loading of 4 mol% demonstrated the increase in Ce3+ concentration to 95%, whereas the concentration of Ce4+ decreased to 5%. Notably, the highest luminescence efficiency was achieved with GGAG:Ce at a 4 mol% concentration. Thus, the solvothermal method employed in GGAG:Ce synthesis presents a straightforward approach, yielding rapid results with precise control over particle morphology and size.