Radioluminescence Research Articles

Plasmonically‐Enhanced Radioluminescence Induced by Energy Transfer in Colloidal CsPbBr3 Nanocrystals via Hybridization of Silver Nanoparticles

AbstractNanocrystals of CsPbBr3, a colloidal perovskite, are hybridized with silver nanoparticles (Ag NPs) and organic molecules (2,5‐diphenyloxazole, PPO) to improve X‐ray radioluminescence (RL). It is known that charge transfer from the PPO molecules to the CsPbBr3 nanocrystals enhances the RL efficiency of the CsPbBr3 nanocrystals. In this study, Ag NPs are introduced to further enhance the RL efficiency. The plasmonic process of the Ag NPs is activated by the PPO molecules, which contain X‐ray‐induced high‐energy charges. Subsequently, electric fields induced by the plasmonic process of the Ag NPs accelerate the charge transfer from the PPO molecules to the CsPbBr3 nanocrystals. The plasmonic effect of the Ag NPs is demonstrated by the full‐width half maximum (FWHM): the photoluminescence FWHM of the hybridized CsPbBr3 nanocrystals is reduced, whereas the RL FWHM remains unchanged. The Ag‐NP‐induced plasmonic effect improves the RL efficiency of the PPO‐decorated CsPbBr3 nanocrystals by ≈10%. The obtained results demonstrate that a plasmonic process can strengthen the RL of X‐ray scintillators for X‐ray detection and imaging.

Real-time in vivo dose measurement using ruby-based fibre optic dosimetry during internal radiation therapy

In vivo dosimetry (IVD) in a commonly used liver cancer treatment of selective internal radiation therapy (SIRT) has been done based on the post-treatment image-based dosimetry approach. Real-time IVD is necessary to verify the dose delivery and detect errors during the treatment for better patient outcomes. This study aims to develop a fibre optic dosimeter (FOD) for in vivo real-time dose rate measurement during internal beta radiation therapy, e.g., SIRT. A ruby fibre optic probe was prepared and studied the radioluminescence (RL) characteristics, including its major challenge of stem effect arising from Cherenkov radiation and luminescence from the irradiated fibre. The stem signal was suppressed adequately using the stem removal technique of optical filtering, and only 2.3 ± 1.1% stem signal was contributed to the measured RL signal. A linear dose rate response was observed during the exposure of the ruby probe to varying dose rates using a 6 MeV electron beam and a positron-emitting radionuclide fluorine-18. The ruby exhibited a temporally non-constant RL signal, which increased the RL signal by 0.84 ± 0.29 counts/sec2 during the irradiation of the maximum dose rate used in this study of 9 Gy/min for 2 min. The ability of ruby FOD to measure the absolute dose rate with sufficient stem effect suppression and the linear RL dose rate response indicates its suitability for real-time IVD during internal beta radiation therapy. Future work will investigate the time-dependent RL characteristic of ruby and validate post-treatment image-based dosimetry using ruby-based FOD.

Flow synthesized LiBaF3 nanocubes as a promising optically stimulated luminescence phosphor

Integrating dosimeters are used in fields like personal dosimetry and radiotherapy quality assurance. Nanoparticles of LiBaF3 have been synthesized using a low-cost, high-throughput flow-synthesis setup and are found to be crystallographically phase-pure. Their radioluminescence (RL) emission shows three peaks corresponding to core-valence-band luminescence, self-trapped-exciton luminescence, and possibly impurity-related violet emission. Optically- and thermally stimulated luminescence (OSL and TL, respectively) overlap spectrally and show only the low-energy violet band, indicating a common luminescence pathway. The rapidly read-out OSL signal is linear in dose up to ∼1 kGy. The main TL glow peak, found around 120∘C, is depleted by optical stimulation, and similarly the OSL signal disappears following a TL readout. The thermal trap depth is found by the peak position method to be ∼1 eV. The high OSL light yield and reasonable fading of the nanoparticles qualifies them as an excellent candidate for OSL dosimetry.

The energy response of LiF:Mg,Ti radioluminescent detector: A Monte Carlo simulation and experimental tests

It has been reported that LiF as commonly used thermoluminescent dosimeter (TLD) has a flat energy response, yet the energy dependence as radioluminescent (RL) detector has not been reported up to now. LiF is a near-tissue-equivalent material with a low effective atomic number, leading to its intrinsic virtue of flat energy response, theoretically. In this paper, Super-MC software was employed to simulate the energy deposition of LiF, the energy response of which was compared with NaI, and then the influence of the size of the detector on energy response was also investigated. Finally, the experimental verification of RL energy response was performed based on an in-house developed detector coupled LiF:Mg,Ti crystal with SiPM. The experimental energy responses (with respect to 137Cs) of three volume detector show good agreement (within ±30% in the range of 33 keV–1.25 MeV) with MC simulation results, which proved that LiF:Mg,Ti has a flat energy response, and it is feasible to obtain real-time dose-rate from count-rate collection without traditional method of hardware compensation or energy spectrum acquisition. In conclusion, this scheme can be a promising candidate for the rapid and accurate real-time dosimetry in the future, simplifying detector structure and measurement algorithm.

Thermoluminescence and optically stimulated luminescence properties of NaMgF3:Dy,Eu synthesized by hydrothermal method and DFT calculations for the bandgap

This study indicates Thermoluminescence (TL) and Optically Stimulated Luminescence (OSL) radiation dosimetry characteristics for NaMgF3:Dy1%,Eu0.1% fluoroperovskite. Nanocrystalline NaMgF3:Dy1%,Eu0.1% material was synthesized by hydrothermal technique. The structure and optical properties were investigated by X-ray powder diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG), derivative thermogravimetry (DTG), radioluminescence (RL) and photoluminescence (PL) techniques. The bands on RL spectrum at 365, 488 and 477 nm might be attributed to Eu,2+ Eu3+ and Dy3+ ion emissions, respectively. The experimentally obtained TL glow curve was analyzed by the computerized glow curve deconvolution (CGCD) and various heating rate (VHR) methods and the order of kinetics (b), activation energy (E), and frequency factor (s) were determined for the appeared four peaks of the TL glow curve with 2°C /s heating rate. The energy bandgaps were calculated and the dependence of bandgap on composition was reported through the Density Functional Theory (DFT) computation.

Organic Chain Length Effect on Trap States of Lead Halide Perovskite Scintillators

Scintillators fabricated from organic–inorganic layered perovskites have attracted wide attention due to their excellent properties, including fast decay times, superior light yield, and high exciton binding energy. In relation to their optoelectronic properties, hybrid organic–inorganic perovskites are known for their tunability, which could be manipulated by modifying the organic cations. In this study, we investigate the optical and scintillation properties of lead halide perovskites A2PbBr4, where A vary from amylammonium (AA), hexylammonium (HA), octylammonium (OA), and benzylammonium (BZA) organic ligands. Photoluminescence (PL) spectra display dual peaks due to surface and bulk trap states contributions, while fast average decay times from time-resolved photoluminescence (TRPL) for all samples are within the range of 0.69 ± 0.11–0.99 ± 0.13 ns. The optical band gap of these hybrid perovskites is within ∼3 eV range, which fulfill the criteria of promising scintillators. Radioluminescence (RL) spectra show negative thermal quenching behavior (NTQ) in all samples, with the AA2PbBr4 peak intensity appearing at relatively lower temperature compared to other samples. Thermoluminescence (TL) measurement reveals trap-free states in AA2PbBr4, while other samples possess shallow traps (<40 meV) as well as low trap density, which is beneficial for fast-decay scintillators, X-ray detection and energy conversion for solar cells. Overall, our results demonstrate that the extension of linear organic chains in lead-based perovskite is a deterministic strategy for a fast response hybrid-based scintillator to date.

Effects of Measurement Temperature on Radioluminescence Processes in Cerium-Activated Silica Glasses for Dosimetry Applications.

Cerium-doped-silica glasses are widely used as ionizing radiation sensing materials. However, their response needs to be characterized as a function of measurement temperature for application in various environments, such as in vivo dosimetry, space and particle accelerators. In this paper, the temperature effect on the radioluminescence (RL) response of Cerium-doped glassy rods was investigated in the 193-353 K range under different X-ray dose rates. The doped silica rods were prepared using the sol-gel technique and spliced into an optical fiber to guide the RL signal to a detector. Then, the experimental RL levels and kinetics measurements during and after irradiation were compared with their simulation counterparts. This simulation is based on a standard system of coupled non-linear differential equations to describe the processes of electron-hole pairs generation, trapping-detrapping and recombination in order to shed light on the temperature effect on the RL signal dynamics and intensity.

High temperature and water stable CaF2:Eu2+ glass ceramic for high resolution X-ray detection

The rising requirement for radiation detection materials for practical applications has inspired to burgeoning investigation of scintillator materials. High performance X-ray detection require high spatial resolution and long-term stability, particularly for targeted objects at extreme conditions. Here, the CaF2:Eu2+ glass ceramic (GC), in which the CaF2:Eu2+ nanoparticles are wrapped by the glassy matrix, is successfully obtained the melting method. The as-obtained CaF2:Eu2+ GC manifests bright blue radioluminescence (RL) emission peaked at 470 nm thanks to the effective 5d-4f transition of Eu2+ ions. In addition, the as-obtained CaF2:Eu2+ GC presents high transmittance of 84.2% and visible light, contributing an excellent spatial resolution of 15 lp/mm at room temperature. Importantly, the as-obtained CaF2:Eu2+ GC exhibits high robustness at water conditions and high thermal stability with X-ray resolution of 12.1 lp/mm at 473 K. Our work demonstrates that CaF2:Eu2+ GC scintillators provide an excellent visualization tool for high-resolution scintillators X-ray images in harsh conditions.

Ge-Doped Optical Fibers for Passive and Active Radiation Detection Modes

Silica-based optical fibers made by Modified Chemical Vapor Deposition (MCVD) technique have been doped with different concentrations of germanium (Ge). After characterization of the thermoluminescence (TL) process in each of these fibers, their real-time responses were studied by radioluminescence (RL) under X-rays. First, the same counterintuitive trend was observed for the intensity of the two phenomena as a function of the Ge content, namely the decrease in TL and RL signals with increasing Ge content. This behavior was explained by the existence of thermally disconnected traps. Then, the RL response as a function of the dose-rate of the fiber doped with 1% Ge was judiciously chosen and investigated in detail. The results show that up to Total Ionizing Dose (TID) of 1.9 kGy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> ), this response is not only insensitive to the accumulated dose effect but also exhibits an afterglow decay at the end of the radiation much faster than that of a Ce-doped fiber, a very useful feature where irradiations are repetitive as in the medical field of flash-therapy. In addition to the medical field where the Ge-doped fiber seems to be quite suitable, slightly larger core diameters would also allow this same fiber to meet the challenge of high sensitivity in the environmental radiation monitoring around nuclear power plants or radioactive waste storage areas.

Mirror-Assisted Radioluminescent Optical Fibers for X-Ray Beam Monitoring

In the framework of the current development of optical fiber sensors for dosimetry or beam monitoring applications based on radioluminescence (RL), we propose a method to enhance their radiation-induced light collection efficiency. This method consists in the deposition of a thin metallic layer, acting as a mirror, at the free output extremity of a radioluminescent optical fiber. Emitted visible photons guided in both directions along the optical fiber core can be collected by a single-ended detection system such as a photomultiplier tube. We characterize the impact of depositing two different types of metallic mirrors (Al and Au) on the performances of a RL based dosimeter, constituted by a Nitrogen-doped multimode optical fiber: its sensitivity has been calibrated with 40 keV X-rays at room temperature for dose rates from 0.05 to ~4 Gy(SiO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> )/s. Also, investigation about the total ionizing dose effects on the mirror has been carried out to understand the evolution of the reflectance of the mirror under radiation exposure. This architecture of sensors appears as very promising, especially for the monitoring of low photon flux.

Luminescence and scintillation properties of Gd3(Al5-xScx)O12:Ce garnet crystals grown by floating zone method

The luminescence and scintillation properties of Ce3+-doped Gd3(Al5-xScx)O12 (x = 1, 1.5, 2, 2.5, 3) garnet crystals grown by the floating zone method were investigated. With increasing Sc content, the Ce3+ 5d1 → 4f luminescence was blue shifted due to a decrease in 5d1-5d2 crystal field splitting (Δ12) of the 5de doublet state. The Sc content showed a strong influence on purity of garnet phase in the Gd3(Al5-xScx)O12:Ce crystals. The presence of secondary phase (perovskite and/or α-Al2O3) results to a poor transparency and a lower light yield (LY) value. The Gd3Al3Sc2O12:Ce crystal exhibited pure garnet phase, highest quantum yield (∼76 %) and transmittance (∼80 %), and highest LY value (6,850 photons/MeV at 662 keV γ rays) among the studied samples. Above RT, a decrease of radioluminescence (RL) yield occurs for all samples due to the thermal ionization process. A decrease of the RL yield at low temperature observed in correlation with the intense thermoluminescence peaks can be explained by the localization of electrons at intrinsic shallow traps.

The Role of Er3+ Content in the Luminescence Properties of Y3Al5O12 Single Crystals: Incorporation into the Lattice and Defect State Creation

Erbium-doped Y3Al5O12 (YAG) single crystals grown using the micro-pulling-down technique were investigated. Three Er concentrations were chosen: 0.1, 0.3 and 1 at%. Er3+ electron paramagnetic resonance (EPR) spectra were measured in the ground and first excited states. The corresponding g tensors and 167Er hyperfine interaction were changing upon Er content indicating moderation of the Er-O bond length and/or Er local surrounding. Photoluminescence (PL) and radioluminescence (RL) spectra were complex, consisting of strongly overlapped typical Er3+ transitions. In addition, there were other broad PL band (3.1 eV) and RL band (3.95 eV) attributed to the F+ center and yttrium substituting for aluminum (YAl), respectively. The X-ray excited decay kinetics exhibited a decrease of the decay time of the YAl from hundreds of nanoseconds to nanoseconds upon Er doping level. This is discussed and explained considering EPR data.

Highly Efficient, Low‐Dose, and Ultrafast Carbazole X‐Ray Scintillators

AbstractOrganic fluorescence scintillators, owing to the ultrafast response time, versatile chemical structures, low processing temperature, and low cost, are considered as one of the promising materials for medical diagnostics, radiation detection, and X‐ray astronomy. However, the low radioluminescence (RL) intensity and low sensitivity hinder their practical applications. In this work, a highly efficient organic fluorescent scintillator, 4,4′‐bis(9‐carbazolyl)biphenyl (CBP), is presented, exhibiting a high X‐ray RL intensity, narrow full width at half‐maximum of 49 nm, and ultrafast decay time of 1.15 ns. More importantly, it has a low detection limit of 25.5 nGy s−1, which is only 1/215 dose rate compared with the commercial X‐ray diagnostics. Such an excellent scintillation performance is mainly attributed to its high photoluminescence quantum yield (PLQY = 61.92%) and good carrier transport (average hole mobility of 0.094 cm2 V−1 s−1). By mixing the CBP into polydimethylsiloxane, the fabricated large area flexible film can be applied in X‐ray radiography, which exhibits a high spatial resolution of 14.3 lp mm−1 at MTF &gt; 0.2. This work paves a way for the implementation of organic fluorescence dyes with high PLQY, high carrier mobility in efficient X‐ray scintillation and imaging.

Gd-doped silica fiber fabricated using surface plasmachemical deposition with view to radiation sensor applications

A Gd3+-doped-silica optical fiber free of other codopants in the core was fabricated with the help of surface plasma chemical vapor deposition (SPCVD) for the first time. The SPCVD-process parameters are described as well as the fiber properties in the as-drawn state (absorption and photoluminescence (PL) spectra upon excimer-laser excitation at λ = 276 and 193 nm and PL decay kinetics) and during γ-irradiation at 1–3.5 Gy/s up to 0.5–1.4 kGy (radiation-induced absorption (RIA) and radioluminescence (RL)). The 315-nm RL band is argued to be suitable for real time dose-rate monitoring, although RIA and persistent luminescence can influence the RL intensity. The possibility to suppress RIA on completion of irradiation by thermal annealing at 500 °C during 15 min was demonstrated.

Mn2+‐Activated Cs3Cu2I5 Nano‐Scintillators for Ultra‐High Resolution Flexible X‐Ray Imaging

AbstractZero‐dimensional (0D) copper‐based perovskite‐derivative nano‐scintillators (NSs), as a promising non‐toxic alternative to lead‐based halide perovskite, have shown great potential in flexible X‐ray detection and imaging. However, their practical applications are still impeded by low X‐ray imaging resolution associated with inadequate radioluminescence (RL) and poor environmental stability. Herein, for the first time a simple but valid Mn2+‐activation strategy is proposed to highly enhance the RL and stability of 0D Cs3Cu2I5 NSs, where the Mn2+ ions are embedded into the highly localized [Cu2I5]3− units by utilizing a modified hot‐injection method. As such, a newly emerged emission band of Mn2+ ion centered at ≈562 nm coupled with much improved intrinsic self‐trapped excitons (STE) emission of the 0D Cs3Cu2I5 host peaking at ≈445 nm can be achieved in these resultant Mn2+‐activated 0D Cs3Cu2I5 NSs, thereby delivering a light yield of 71 000 photons MeV−1 that is much superior to their lead‐based perovskite counterparts and commercial scintillators. As a consequence, X‐ray detectors made of these Mn2+‐activated NSs implement an ultrahigh X‐ray imaging resolution of 16.2 line pairs mm−1 and an ultra‐low detection limit of 127.5 nGyair s−1, highlighting their potential as promising candidates for flexible X‐ray detection and imaging.

Chirality–Racemization Strategy Toward Copper (I) Iodide Hybrid Single‐Crystalline Scintillators for X‐Ray Detection and Imaging Applications

AbstractOrganic–inorganic hybrid copper(I)‐based halides have attracted great interest in the field of optoelectronics due to their low cost, non‐toxicity, large Stokes shift, and high photoluminescence quantum yields (PLQYs). Here, bulk zero‐dimensional (0D) organic‐inorganic hybrid copper(I)‐based (R,S‐2‐mpip)2Cu2I6 (mpip = methylpiperazinium, C5H14N22+) single crystals have been grown with equal stoichiometric ratios of R‐ and S‐2‐mpip ligands by chirality–racemization strategy for the first time. Interestingly, (R,S‐2‐mpip)2Cu2I6 single crystals exhibit strong blue–green photoluminescence (PL) located at 520 nm with large Stokes shift of about 230 nm and high PLQY of about 65.96%, which originates from self‐trapped excitons (STEs). More importantly, (R,S‐2‐mpip)2Cu2I6 single crystals also exhibit the strong radioluminescence (RL) at 520 nm, the fast X‐ray scintillation response with a light yield of about 47 000 photon MeV−1 and low detection limit of 6.48 nGyairs−1 when exposed to X‐ray irradiation condition, which is superior to that of other copper(I) iodide‐based hybrids. Based on the excellent characteristics, X‐ray imaging systems based on (R,S‐2‐mpip)2Cu2I6 single crystals exhibit the clear images of “QFNU” logo and crystal symbol pattern. This work not only deepens the understandings of material design and fundamental properties of these racemate systems, but also provides guidance for the further applications in the multi‐functional optoelectronics.

Influence of Eu3+ dopant on lithium barium gadolinium phosphate glass properties for orange-reddish photonic devices

The Eu3+-doped lithium barium gadolinium phosphate glasses were prepared using the conventional melt-quenching method with different concentrations of Eu2O3 and Gd2O3. The physical characteristics were determined by refractive index, density, molar volume, oxygen packing volume, and oxidation states. Moreover, the optical characteristics were investigated via photoluminescence spectroscopy (PL), UV-vis spectroscopy, Radioluminescence (RL), and decay time. It was found that the Gd2O3 concentration of 12 mol% was the optimum composition for further investigations of the Eu2O3 doping concentration optimization. The emission spectra of PL and RL showed the strongest intensity of orange-reddish emission (λEx = 394 nm) when the Eu2O3 concentration was at 0.3 mol% corresponding to energy transition from 5D0→7F0,1,2,3,4. The oxidation state of Eu3+ ions due to the formation of non-bridging oxygens (NBO) in the glass network was confirmed by using X-ray Absorption Near Edge Spectroscopy (XANE). Furthermore, the high transparency and fast decay time in the range of 2.4–2.8 ms displayed the potential to improve laser and radiation detector performances.

X‐Ray‐Excited Luminescence of High‐Quality Doped GaN Single Crystals

X‐Ray‐induced luminescence behavior of Si/Ge‐doped GaN single crystals is observed and analyzed in combination with undoped GaN. Similarities between radioluminescence (RL) and photoluminescence (PL) indicate an analogous physical process. Under X‐Ray irradiation, the gallium nitride (GaN) single crystals doped with Si/Ge elements intensely emit tunable visible light ranging from 1.8 to 2.2 eV, and an ultraviolet (UV) emission of ≈3.3 eV is aroused by the intrinsic direct band‐edge transition of GaN. Due to the difference in the physical properties of excitation source and the self‐absorption effect, the UV signal in RL has a dramatic reduction (especially for undoped GaN) and redshift, which is also considered to be the obvious difference between the two spectra. RL results obtained herein along with PL demonstrate that the visible luminescence of Si/Ge‐doped GaN is mainly attributed to DAP or/and e‐A recombination, which is supported by density functional theory (DFT) calculations.

Investigation of the photoluminescent properties, scintillation behaviour and toxicological profile of various magnesium tungstate nanoscale motifs.

We have synthesized several morphologies and crystal structures of MgWO4 using a one-pot hydrothermal method, producing not only monoclinic stars and large nanoparticles but also triclinic wool balls and sub-10 nm nanoparticles. Herein we describe the importance of reaction parameters in demonstrating morphology control of as-prepared MgWO4. Moreover, we correlate structure and composition with the resulting photoluminescence and radioluminescence properties. Specifically, triclinic-phase samples yielded a photoluminescence emission of 421 nm, whereas monoclinic-phase materials gave rise to an emission maximum of 515 nm. The corresponding radioluminescence data were characterized by a broad emission peak, located at 500 nm for all samples. Annealing the wool balls and sub-10 nm particles to transform the crystal structure from a triclinic to a monoclinic phase yielded a radioluminescence (RL) emission signal that was two orders of magnitude greater than that of their unannealed counterparts. Finally, to confirm the practical utility of these materials for biomedical applications, a series of sub-10 nm particles, including as-prepared and annealed samples, were functionalized with biocompatible PEG molecules, and subsequently were found to be readily taken up by various cell lines as well as primary cultured hippocampal neurons with low levels of toxicity, thereby highlighting for the first time the potential of this particular class of metal oxides as viable and readily generated platforms for a range of biomedical applications.

Characterisation and Quenching Correction for an Al2O3:C Optical Fibre Real Time System in Therapeutic Proton, Helium, and Carbon-Charged Beams.

Real time radioluminescence fibre-based detectors were investigated for application in proton, helium, and carbon therapy dosimetry. The Al2O3:C probes are made of one single crystal (1 mm) and two droplets of micro powder in two sizes (38 μm and 4 μm) mixed with a water-equivalent binder. The fibres were irradiated behind different thicknesses of solid slabs, and the Bragg curves presented a quenching effect attributed to the nonlinear response of the radioluminescence (RL) signal as a function of linear energy transfer (LET). Experimental data and Monte Carlo simulations were utilised to acquire a quenching correction method, adapted from Birks' formulation, to restore the linear dose-response for particle therapy beams. The method for quenching correction was applied and yielded the best results for the '4 μm' optical fibre probe, with an agreement at the Bragg peak of 1.4% (160 MeV), and 1.5% (230 MeV) for proton-charged particles; 2.4% (150 MeV/u) for helium-charged particles and of 4.8% (290 MeV/u) and 2.9% (400 MeV/u) for the carbon-charged particles. The most substantial deviations for the '4 μm' optical fibre probe were found at the falloff regions, with ~3% (protons), ~5% (helium) and 6% (carbon).