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Scintillators are materials that convert ionizing radiation in the form of particles or photons into low-energy photons in the ultraviolet to near-infrared spectral range. This work reviews efforts to use colloidal nanocrystals as scintillator materials. To date, research on colloidal nanocrystals as scintillators has focused on doped phosphor systems, quantum dots and related structures, and perovskite-based nanocrystals. Among various material classes and forms, colloidal semiconductor nanocrystals stand out thanks to their appealing fluorescence properties, yet understanding of their radioluminescence and cathodoluminescence is incomplete. This review discusses fundamental limits and material design challenges toward achieving high brightness, fast speed, and durable scintillator performance with nanocrystal scintillators. First, this review describes the basic principles and efficiency limitations of scintillation, particularly the large influence of multiple exciton generation in many nanocrystal species, as well as performance metrics. Second, methods for measurement are described. Third, we review the results of the main classes of nanocrystal scintillators, including quantum dots and related particles, perovskites, and doped-phosphor particles. Fourth, scintillation imaging is discussed in terms of the relevant performance metrics and results obtained using nanocrystal materials. Finally, we note the strengths and weaknesses of nanocrystal scintillators and discuss potential areas of further development. [ABSTRACT FROM AUTHOR]

Bright and fast scintillators are highly crucial for high-speed X-ray imaging in the medical diagnostic radiology including angiography and cardiac computed tomography. The CsPbBr3 nanocrystal scintillator featuring a nanosecond radioluminescence decay time is a promising candidate. However, it suffers from a substantial photon self-absorption limiting the light output, and being bright and fast simultaneously is difficult. Here we design and in-situ synthesize multi-site ZnS(Ag)-CsPbBr3 heterostructures to modulate the bright and fast features of scintillators. We find external energy from ZnS(Ag) can effectively transfer to CsPbBr3 based on the non-radiative Förster resonance energy transfer, resulting in a light yield of 40,000 photons MeV−1. By combing a radioluminescence decay time of 36 ns and a spatial resolution of 30 lp mm−1, the scintillator enables high-speed X-ray imaging at 200 frames per second. This study showcases the structure design is significant for obtaining bright and fast perovskite scintillators for the real-time X-ray imaging. Yang et al. report in-situ growth of ZnS(Ag)-CsPbBr3 heterostructures through all solid-phase synthesis for X-ray scintillators. The multiple contact sites promote light yield via efficient energy transfer from ZnS(Ag) into CsPbBr3 and enable fast decay for high-speed X-ray imaging at 200 fps. [ABSTRACT FROM AUTHOR]

Metal halide perovskites are revolutionizing X‐ray detection through a combination of low cost, solution processing, favorable optoelectronic properties, and high stopping power for high‐energy ionizing radiation. While perovskite single crystals and polycrystalline wafers are considered direct X‐ray converters, most medical X‐ray applications are based on scintillators that shift high‐energy radiation into the visible. Several materials are on the market, but demonstrations based on CsPbBr3 nanocrystals, possibly embedded in a matrix material or combined with organic molecules as luminescent species, highlight their competitiveness with established scintillators in terms of radioluminescence yield and transient behavior. Major hurdles that perovskite nanocrystal scintillators must overcome are environmental stability and toxicity. While there are still few examples of high‐performance lead‐free perovskite nanocrystal scintillators, microcrystalline perovskites are emerging with promising properties, reduced toxicity, and significant Stokes shifts to avoid reabsorption of emission in thick films. Thus, the near future of perovskite nanocrystal scintillator materials will primarily be the adoption of recipes for materials with proven properties in microcrystalline form. The nanocrystal colloidal solutions will facilitate the large‐scale printing of homogeneous and scattering‐free films to obtain high contrast and spatial resolution X‐ray images by scintillation. [ABSTRACT FROM AUTHOR]

Organic scintillators, pivotal in security and medical applications, face challenges due to limited X‐ray absorption and exciton utilization. Herein, a novel class of organic scintillators is introduced, named guest‐induced thermally activated delayed fluorescence (TADF) within supramolecular macrocycles via host‐guest through‐space charge transfer (TSCT). Four co‐crystals are obtained through orthogonal crystallizations involving calix[3]acridan (C[3]A) and calix[3]phenothiazine (C[3]P) macrocycles as hosts, along with 1,2‐dicyanobenzene (DCB) and 4‐bromo‐1,2‐benzenedicarbonitrile (BrDCB) as guests. Interestingly, DCB@C[3]A and BrDCB@C[3]A co‐crystals exhibit strong host‐guest TSCT with reduced single‐triplet energy gap for efficient TADF emission, which leads to enhanced exciton utilization and X‐ray absorption, yielding radioluminescence intensities over 29 and 25 times higher than C[3]A. Similarly, substituting C[3]A with C[3]P, the obtained TADF co‐crystals also outperform C[3]P in scintillation performance. Additionally, the scintillation color of co‐crystals can be adjusted by varying the electron‐donating abilities of macrocycles and the electron‐accepting abilities of guests, offering a simpler color‐tuning mechanism than covalent‐bonded scintillators. Furthermore, the flexible film based on DCB@C[3]A exhibits promising application in X‐ray radiography, showcasing a high spatial resolution of 20 lp mm−1 @MTF = 0.77. The innovative strategy of fabricating organic scintillators via reversible non‐covalent interactions presents a novel solution for designing color‐tunable and high‐performance scintillators. [ABSTRACT FROM AUTHOR]

Highly sensitive stimuli‐responsive luminescent materials are crucial for applications in optical sensing, security, and anticounterfeiting. Here, we report two zero‐dimensional (0D) copper(I) halides, (TEP)2Cu2Br4, (TEP)2Cu4Br6, and 1D (TEP)3Ag6Br9, which are comprised of isolated [Cu2Br4]2−, [Cu4Br6]2−, and [Ag6Br9]3− polyanions, respectively, separated by TEP+ (tetraethylphosphonium [TEP]) cations. (TEP)2Cu2Br4 and (TEP)2Cu4Br6 demonstrate greenish‐white and orange‐red emissions, respectively, with near unity photoluminescence quantum yields, while (TEP)3Ag6Br9 is a poor light emitter. Optical spectroscopy measurements and density‐functional theory calculations reveal that photoemissions of these compounds originate from self‐trapped excitons due to the excited‐state distortions in the copper(I) halide units. Crystals of Cu(I) halides are radioluminescence active at room temperature under both X‐ and γ‐rays exposure. The light yields up to 15,800 ph/MeV under 662 keV γ‐rays of 137Cs suggesting their potential for scintillation applications. Remarkably, (TEP)2Cu2Br4 and (TEP)2Cu4Br6 are interconvertible through chemical stimuli or reverse crystallization. In addition, both compounds demonstrate luminescence on‐off switching upon thermal stimuli. The sensitivity of (TEP)2Cu2Br4 and (TEP)2Cu4Br6 to the chemical and thermal stimuli coupled with their ultrabright emission allows their consideration for applications such as solid‐state lighting, sensing, information storage, and anticounterfeiting. [ABSTRACT FROM AUTHOR]

Zero‐dimensional (0D) hybrid manganese halides have gained wide attention for the various crystal structures, excellent optical performance and scintillation properties compared with 3D lead halide perovskite nanocrystals. In this work, a new family of 0D hybrid manganese halides of A2MnBr4 (A = BzTPP, Br‐BzTPP, and F‐BzTPP) based on discrete [MnBr4]2− tetrahedral units is reported as highly efficient lead‐free scintillators. Excited by UV or blue light, these hybrids emit bright green light originating from the d–d transition of Mn2+ with near‐unity PLQY (99.5%). Significantly, high PLQY and low self‐absorption render extraordinary radioluminescence properties with the highest light yield of 80,100 photons MeV−1, which reached the climax of present hybrid manganese halides and surpassed most commercial scintillators. The radioluminescence intensity features a linear response to X‐ray doses with a detection limit of 30 nGyair s−1, far lower than the requirement of medical diagnostic (5.5 µGyair s−1). X‐ray imaging demonstrates ultrahigh spatial resolution of 14.06 lp mm−1 and short afterglow of 0.3 ms showcasing promising application prospects in radiography. Overall, we demonstrated new hybrid manganese halides as promising scintillators for advanced applications in X‐ray imaging with multiple superiorities of nontoxicity, facile‐assembly process, high irradiation light yield, excellent resolution, and stability. [ABSTRACT FROM AUTHOR]

A new one-dimensional hybrid [APCHA]Cu2I4 was designed and applied as an X-ray scintillator. It exhibits broad-band green emission with a high PLQY of 74.80% and excellent stability. It demonstrates radioluminescence property with a light yield of 28 336 photons MeV−1, detection limit of 41 nGyair s−1, and high spatial limit of 13.95 lp mm−1 in X-ray imaging. [ABSTRACT FROM AUTHOR]

Inorganic scintillators play a pivotal role in diverse fields like medical imaging, nondestructive detection, homeland security, and high‐energy physics. However, traditional inorganic scintillators encounter challenges such as high fabrication costs and low light yield. Recently, low‐dimensional metal halide scintillators (LDMHS) have witnessed rapid progress, owing to their distinctive crystal structure and superior radioluminescence performance. Herein, an overview of recent advancements and proposed instructive pathways for achieving high‐performance LDMHS is provided. First, the scintillation physical mechanism and emphasis on the essential requirements of scintillators for diverse applications are elucidated. Furthermore, LDMHS are classified according to B‐site cations, and their respective characteristics and recent advancements are introduced. This encompasses the understanding of structure‐property relationships and the routes and rules for optimizing scintillation performance. Finally, the persisting challenges in this burgeoning field and proposed potential research directions for future exploration are discussed. [ABSTRACT FROM AUTHOR]

Radiation detection is being revolutionized by integrating photonic elements into scintillators. In this study, a scalable and cost‐effective method is proposed to achieve tuneable emission enhancement across the visible spectrum by colloidal self‐assembly of photonic crystals on scintillator surfaces. This concept is demonstrated for Eu3+/Tb3+‐doped Gd and Ta oxides. Widely available and affordable colloidal nanospheres of SiO2 or polymethyl methacrylate are self‐assembled on these scintillators. The size of the nanospheres is carefully optimized to match the desired emission lines of Eu3+/Tb3+. The result is homogeneous and closely‐packed structures with clear photonic bandgap in the visible range. Under X‐ray excitation, the scintillators covered with the photonic layers exhibit enhanced light extraction in the direction perpendicular to the surface, compared to isotropic emission in the bare scintillator. Such scintillation directionality, when optically matched with a proper detector, will result in higher efficiency of the overall detection system. Moreover, X‐ray imaging demonstrates an enhancement of 25% in system resolution of the scintillator supplemented with the photonic layer compared to unmodified scintillators. The proposed method is scintillator‐ and nanosphere‐agnostic, thus offering a promising versatile approach for directing the scintillation light toward a photodetector and increasing detection system performance, including high‐resolution imaging applications. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Organic 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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

Lanthanide nanoparticle (LnNP) scintillators exhibit huge potential in achieving radionuclide‐activated luminescence (radioluminescence, RL). However, their structure–activity relationship remains largely unexplored. Herein, progressive optimization of LnNP scintillators is presented to unveil their structure‐dependent RL property and enhance their RL output efficiency. Benefiting from the favorable host matrix and the luminescence‐protective effect of core–shell engineering, NaGdF4 : 15 %Eu@NaLuF4 nanoparticle scintillators with tailored structures emerged as the top candidates. Living imaging experiments based on optimal LnNP scintillators validated the feasibility of laser‐free continuous RL activated by clinical radiopharmaceuticals for tumor multiplex visualization. This research provides unprecedented insights into the rational design of LnNP scintillators, which would enable efficient energy conversion from Cerenkov luminescence, γ‐radiation, and β‐electrons into visible photon signals, thus establishing a robust nanotechnology‐aided approach for tumor‐directed radio‐phototheranostics. [ABSTRACT FROM AUTHOR]

Lanthanide nanoparticle (LnNP) scintillators exhibit huge potential in achieving radionuclide‐activated luminescence (radioluminescence, RL). However, their structure–activity relationship remains largely unexplored. Herein, progressive optimization of LnNP scintillators is presented to unveil their structure‐dependent RL property and enhance their RL output efficiency. Benefiting from the favorable host matrix and the luminescence‐protective effect of core–shell engineering, NaGdF4 : 15 %Eu@NaLuF4 nanoparticle scintillators with tailored structures emerged as the top candidates. Living imaging experiments based on optimal LnNP scintillators validated the feasibility of laser‐free continuous RL activated by clinical radiopharmaceuticals for tumor multiplex visualization. This research provides unprecedented insights into the rational design of LnNP scintillators, which would enable efficient energy conversion from Cerenkov luminescence, γ‐radiation, and β‐electrons into visible photon signals, thus establishing a robust nanotechnology‐aided approach for tumor‐directed radio‐phototheranostics. [ABSTRACT FROM AUTHOR]

Copper halides, a new class of attractive and potential scintillators, have attracted tremendous attention in X‐ray imaging. However, the ambiguity surrounding their exciton properties and the unclear effect of crystal structure on their photophysical performance hinder an in‐depth understanding of their luminescence mechanism and their further application in the X‐ray imaging field. Herein, copper halide scintillators Cs3Cu2X5 (X = I, Br, and Cl) with a 0D crystal structure is prepared, and their photophysical properties and luminescence mechanism are revealed using both theoretical calculation and experimental verification. The small exciton Bohr diameter together with the high exciton binding energy can cause Cs3Cu2X5 to hold strongly confined excitons and lack quantum‐size effects. The 0D Cs3Cu2X5 materials exhibit a structural framework with a soft crystal lattice and Frenkel excitons with strong confinement effects, further resulting in a luminescence mechanism with self‐trapped excitons. In particular, Cs3Cu2I5 is demonstrated as an efficient scintillator with high radioluminescence efficiency and high spatial resolution of ≈106 µm in radiography, which is primarily attributed to strongly confined excitons to improve the radiative recombination probability of electron‐hole pairs. Overall, this work provides a pathway for developing 0D scintillators with strongly confined excitons to improve X‐ray imaging performance. [ABSTRACT FROM AUTHOR]

Long‐lasting radioluminescence scintillators have recently attracted substantial attention from both research and industrial communities, primarily due to their distinctive capabilities of converting and storing X‐ray energy. However, determination of energy‐conversion kinetics in these nanocrystals remains unexplored. Here we present a strategy to probe and unveil energy‐funneling kinetics in NaLuF4:Mn2+/Gd3+ nanocrystal sublattices through Gd3+‐driven microenvironment engineering and Mn2+‐mediated radioluminescence profiling. Our photophysical studies reveal effective control of energy‐funneling kinetics and demonstrate the tunability of electron trap depth ranging from 0.66 to 0.96 eV, with the corresponding trap density varying between 2.38×105 and 1.34×107 cm−3. This enables controlled release of captured electrons over durations spanning from seconds to 30 days. It allows tailorable emission wavelength within the range of 520–580 nm and fine‐tuning of thermally‐stimulated temperature between 313–403 K. We further utilize these scintillators to fabricate high‐density, large‐area scintillation screens that exhibit a 6‐fold improvement in X‐ray sensitivity, 22 lp/mm high‐resolution X‐ray imaging, and a 30‐day‐long optical memory. This enables high‐contrast imaging of injured mice through fast thermally‐stimulated radioluminescence readout. These findings offer new insights into the correlation of radioluminescence dynamics with energy‐funneling kinetics, thereby contributing to the advancement of high‐energy nanophotonic applications. [ABSTRACT FROM AUTHOR]

Long‐lasting radioluminescence scintillators have recently attracted substantial attention from both research and industrial communities, primarily due to their distinctive capabilities of converting and storing X‐ray energy. However, determination of energy‐conversion kinetics in these nanocrystals remains unexplored. Here we present a strategy to probe and unveil energy‐funneling kinetics in NaLuF4:Mn2+/Gd3+ nanocrystal sublattices through Gd3+‐driven microenvironment engineering and Mn2+‐mediated radioluminescence profiling. Our photophysical studies reveal effective control of energy‐funneling kinetics and demonstrate the tunability of electron trap depth ranging from 0.66 to 0.96 eV, with the corresponding trap density varying between 2.38×105 and 1.34×107 cm−3. This enables controlled release of captured electrons over durations spanning from seconds to 30 days. It allows tailorable emission wavelength within the range of 520–580 nm and fine‐tuning of thermally‐stimulated temperature between 313–403 K. We further utilize these scintillators to fabricate high‐density, large‐area scintillation screens that exhibit a 6‐fold improvement in X‐ray sensitivity, 22 lp/mm high‐resolution X‐ray imaging, and a 30‐day‐long optical memory. This enables high‐contrast imaging of injured mice through fast thermally‐stimulated radioluminescence readout. These findings offer new insights into the correlation of radioluminescence dynamics with energy‐funneling kinetics, thereby contributing to the advancement of high‐energy nanophotonic applications. [ABSTRACT FROM AUTHOR]

In the efforts to generate a less toxic X‐Ray bioimaging contrast agent, a fully organic, radioluminescent nanoparticle system that emits in the near‐infrared (NIR) region when excited with an X‐Ray source is synthesized using a two‐step process. First, red‐emitting nanoparticles are fabricated by the emulsion copolymerization of styrene and propargyl acrylate with anthracene, naphthalimide, and rhodamine B methyl methacrylate derivatives. Subsequently, the nanoparticles are modified with silicon phthalocyanine and indocyanine green derivatives via a copper(I)‐catalyzed azide/alkyne cycloaddition "click" reaction. By coupling an organic scintillator with four Förster resonance energy transfer‐pairing dyes, X‐Ray‐induced, multiple, sequential energy transfer is exploited to convert ionizing radiation from an X‐Ray source into NIR light, which is optimal for biomedical imaging. Proof‐of‐concept imaging studies show that the X‐Ray‐induced indocyanine green fluorescence from the particulate system can be visualized through porcine tissue. Additionally, toxicity studies in human embryonic kidney cells indicate that the particles are nontoxic and applicable in vivo. [ABSTRACT FROM AUTHOR]

Organic scintillators have recently gained considerable attentions in X‐ray detection for their potential applications in biomedical radiograph and security inspection. However, the weak X‐ray absorption and/or inefficient exciton utilization have limited the development and commercialization of organic scintillators. Currently, high‐performance X‐ray organic scintillators are scarce and organic scintillators with dual triplet‐harvesting channels have not been explored before. Here, we develop several proof‐of‐concept sulfone‐based organic molecules, C1–C7, using different alkoxy chains to manipulate molecular packing mode. These materials exhibit dual triplet‐harvesting channels of thermally activated delayed fluorescence (TADF) and room‐temperature phosphorescence (RTP) in aggregated state. Inspiringly, these molecules display distinct radioluminescence under the X‐ray stimulation. Among them, C6 behaves the highest light yield of 16,558 photons MeV−1. Moreover, clear X‐ray images are demonstrated in both aggregated state and single‐molecule level. High spatial resolutions of 15.0 and 10.6 line pairs per millimeter (lp mm−1) are achieved for rigid and flexible scintillator screens, exceeding most reported organic and conventional inorganic scintillators. These results highlight the great potential of organic molecules with TADF and RTP nature for efficient X‐ray scintillation and imaging. [ABSTRACT FROM AUTHOR]

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In recent years, the development of new scintillation materials with red and near-infrared light emission has had significant advantages based on the development of an avalanche photodiode with high quantum yield. This study used a hydrothermal method to synthesize rare-earth-doped Cs2NaScCl6 crystals, in which a red emission of Cs2NaScCl6:Sm was investigated with high X-ray sensitivity and low detection limit. In addition, a tunable wavelength range of radioluminescence can be achieved, in which a near-white light emission can be generated by precisely controlling the proportion of Sm3+ and Tb3+ doping concentrations. Meanwhile, a Cs2NaScCl6:7%Sm scintillation film has been successfully prepared by direct coating with a thickness of 150 μm, which achieves a spatial resolution of 11.9 lp mm−1 based on X-ray imaging experiments. Therefore, this perovskite material has shown potential application as an eco-friendly multifunctional imaging material. [ABSTRACT FROM AUTHOR]

Doping Mn2+ in newly emerged lead‐free metal halides to access versatile optoelectronic applications is highly desired. However, understanding the chemical pathway of Mn2+ doping and precisely controlling it remains challenging. Here, the crucial role of the initial surface adsorption of Mn2+ in doping kinetics is demonstrated, and the adsorption step is effectively optimized by a moderate Lewis base ligand. The results show that not only the doping concentration of Mn2+ in Cs3Cu2I5 is modulated flexibly but also the produced Cs3Cu2I5:Mn2+ microcrystals exhibit tuned photoluminescence/radioluminescence properties, indicating their applicability in anti‐counterfeiting and X‐ray imaging. Systematic experimental and theoretical outcomes reveal that the moderate Lewis base ligand dually links Mn2+ (hard acid) and Cu+ (soft acid) on the matrix surface, which improves the initial surface adsorption of the dopant and further promotes the doping step. This study contributes a simple strategy for simply controlling Mn2+ doping in Cu(I)‐based halides and also opens a new avenue for understanding the fundamentals of doping dynamics in metal halide systems. [ABSTRACT FROM AUTHOR]

Inorganic scintillation crystals have been widely used in applications of high-energy physics, nuclear medical imaging, industrial nondestructive inspection, etc. In this work, a single crystal Ba3Y(PO4)3 (BYP) with 1.0 at% Ce3+-doping concentration was first grown by the Czochralski method, and the electronic structure was calculated using first principles based on density functional theory. In addition, a series of Ce3+-doped BYP phosphors were synthesized, and the fluorescence emission under UV excitation was measured through low-temperature spectroscopy, containing double-peaked emission from 5d–4f transition and self-trapped exciton recombination. A comparison of the UV and X-ray-excited fluorescence spectra reveals the existence of oxygen vacancies as well as F+ centers in the crystal. The air annealing of the crystal effectively reduces the thermoluminescence defects but reduces the emission intensity under UV or X-ray excitation. The BYP:Ce crystal shows a fast decay lifetime of 15.5 ns, and the fast component is as short as 8 ns. The results show that the Ce3+-doped BYP crystal has potential as a kind of scintillator with fast decay properties. [ABSTRACT FROM AUTHOR]

Organic scintillators have recently attracted growing attention for X‐ray detection in industrial and medical applications. However, these materials still face critical obstacles of low attenuation efficiency and/or inefficient triplet exciton utilization. Here we developed a new category of organogold(III) complexes, Tp‐Au‐1 and Tp‐Au‐2, through adopting a through‐space interaction motif to realize high X‐ray attenuation efficiency and efficient harvesting of triplet excitons for emission. Thanks to the efficient through‐space charge transfer process, this panel of complexes achieved higher photoluminescence quantum yield and shorter radiative lifetimes compared with the through‐bond reference complexes. Inspiringly, these organogold(III) complexes exhibited polarity‐dependent emission origins: thermally activated delayed fluorescence and/or phosphorescence. Under X‐ray irradiation, Tp‐Au‐2 manifested intense radioluminescence together with a record‐high scintillation light yield of 77,600 photons MeV−1 for organic scintillators. The resulting scintillator screens demonstrated high‐quality X‐ray imaging with >16.0 line pairs mm−1 spatial resolution, outstripping most organic and inorganic scintillators. This finding provides a feasible strategy for the design of superior organic X‐ray scintillators. [ABSTRACT FROM AUTHOR]

Organic scintillators have recently attracted growing attention for X‐ray detection in industrial and medical applications. However, these materials still face critical obstacles of low attenuation efficiency and/or inefficient triplet exciton utilization. Here we developed a new category of organogold(III) complexes, Tp‐Au‐1 and Tp‐Au‐2, through adopting a through‐space interaction motif to realize high X‐ray attenuation efficiency and efficient harvesting of triplet excitons for emission. Thanks to the efficient through‐space charge transfer process, this panel of complexes achieved higher photoluminescence quantum yield and shorter radiative lifetimes compared with the through‐bond reference complexes. Inspiringly, these organogold(III) complexes exhibited polarity‐dependent emission origins: thermally activated delayed fluorescence and/or phosphorescence. Under X‐ray irradiation, Tp‐Au‐2 manifested intense radioluminescence together with a record‐high scintillation light yield of 77,600 photons MeV−1 for organic scintillators. The resulting scintillator screens demonstrated high‐quality X‐ray imaging with >16.0 line pairs mm−1 spatial resolution, outstripping most organic and inorganic scintillators. This finding provides a feasible strategy for the design of superior organic X‐ray scintillators. [ABSTRACT FROM AUTHOR]

The influence of scavengers of the primary water radiolysis products and the H atom on the spectra and intensity of radioluminescence and photoluminescence of the Tb3+ ion in aqueous solutions of TbCl3 and Tb(NO3)3 is considered. The effect of activation of Tb3+ radioluminescence in the presence of H scavengers has been revealed, indicating the presence of a specific (Tb3+)* quenching reaction by this radiolysis product, which is inhibited by its scavengers. Enhancement in the activation has been revealed in the joint presence of H and scavengers in the solution, with a similar effect of activation of Tb3+ radioluminescence being previously established for scavengers. [ABSTRACT FROM AUTHOR]

Thermally activated delayed fluorescence (TADF) materials have numerous applications in energy conversion and luminescent imaging. However, they are typically achieved as metal‐organic complexes or pure organic molecules. Herein, we report the largest Au‐Ag‐oxo nanoclusters to date, Au18Ag26(R1COO)12(R2C≡C)24(μ4‐O)2(μ3‐O)2 (Au18Ag26, where R1 = CH3‐, Ph‐, CHOPh‐ or CF3Ph‐; R2 = Ph‐ or FPh‐). These nanoclusters exhibit exceptional TADF properties, including a small S1‐T1 energy gap of 55.5 meV, a high absolute photoluminescence quantum yield of 86.7%, and a microseconds TADF decay time of 1.6 μs at ambient temperature. Meanwhile, Au18Ag26 shows outstanding stability against oxygen quenching and ambient conditions. Atomic level analysis reveals the strong π⋯π and C‐H⋯π interactions from the aromatic alkynyl ligands and the enhancement of metal‐oxygen‐metal interactions by centrally coordinated O2−. Modeling of the electronic structure shows spatially separated highest occupied molecular orbital and lowest unoccupied molecular orbital, which promote charge transfer from the ligand shell, predominantly carboxylate ligands, to O2−‐embedded metal core. Furthermore, TADF Au‐Ag‐oxo nanoclusters exhibit promising radioluminescence properties, which we demonstrate for X‐ray imaging. Our work paves the way for the design of TADF materials based on large metal nanoclusters for light‐emission and radioluminescence applications. [ABSTRACT FROM AUTHOR]

Flat-panel x-ray scintillators with a high spatial resolution at a low radiation dose rate are desirable for efficient imaging applications in medical diagnostics, security inspection, and nondestructive inspection. To promote the progress of x-ray imaging technologies, it is of great interest to explore transparent scintillators with reduced light scattering, high light yields, and uniform radioluminescence. Herein, we design and prepare a novel lead-free (C12H28N)2Cu2I4 metal halide featuring a high luminescent efficiency and white emission benefiting from the double self-trapped exciton mechanism, which enable to not only match the response of semiconductor-based sensors but also enhance light yields and decrease exposed doses to objects. Furthermore, transparent, and flexible scintillators with large areas of 20.25 cm2 demonstrate an outstanding scintillation performance including a high spatial resolution of 19.8 lp mm−1 and an ultralow detection limit of 28.39 nGyair s−1, which are ∼4 times higher and 194 times lower than typical values for medical imaging, respectively. This work provides not only a new route to explore promising alternatives with broadband emission but also a novel opportunity to develop flexible x-ray imaging technology. [ABSTRACT FROM AUTHOR]

In recent years, hybrid manganese(II) halides (HMHs) have attracted wide attention due to their impressive optical properties, low toxicity, and facile synthetic processibility. Being effective reabsorption-free phosphors, these compounds demonstrate the potential to be used as low-cost solution-processable scintillators. However, most of the HMHs studied to date contain bulk organic cations and, as a result, are characterized by low density and low X-ray stopping power. For this reason, we studied manganese(II) bromides with compact organic cations such as formamidinium (FA+) and acetamidinium (AcA+). In particular, we synthesized four new phases, two of which are characterized by octahedral coordination of manganese ions ((FA)MnBr3 and (AcA)MnBr3) and red emission, whereas the other two have tetrahedrally coordinated Mn2+ ions ((FA)3MnBr5 and (AcA)2MnBr4) and green emission. Photoluminescence (PL) and radioluminescence measurements demonstrated high PL quantum yields and reasonable scintillation light yields of acetamidinium-based compounds. In addition, unlike most known HMH-based scintillators, the discovered materials have a relatively high density due to the small fraction of the volume occupied by organic cations, so their X-ray attenuation coefficients are comparable to the well-known oxide scintillators. [ABSTRACT FROM AUTHOR]

X‐ray radiography, playing a crucial role in the daily life of humans, extends the application landscapes of perovskites. Lead halide perovskites remain superior candidates because of strong X‐ray absorption and effective conversion of X‐ray to visible photons. Unfortunately, the perovskites exhibiting efficient band‐edge emission (3D, quasi‐2D or 2D) usually suffer from severe self‐absorption, while the perovskites showing broadband emission with large Stokes shift (0D, 1D or 2D) usually have low quantum yield, long afterglow or poor solution‐processability. Halide‐intercalated perovskites, with incorporated halides in organic layers, exhibit attractive optoelectronic properties due to reduced confinement of excitons, but their development falls far behind due to limited molecular design strategies and wet‐chemistry methods. Here, the use of universal‐wet‐chemistry‐synthesized novel halide‐intercalated perovskites as an efficient X‐ray scintillator for X‐ray imaging is reported. These novel perovskites exhibit superior luminescence by exploiting both free and self‐trapped excitons via halide intercalation. Accordingly, such perovskite scintillators present higher radioluminescence performance compared with conventional perovskite scintillators through enhanced radiative recombination and suppressed self‐absorption simultaneously. With such a scintillator screen, high‐performance X‐ray imaging is demonstrated. The results not only represent a universal synthesis route for the development of perovskites, but also provide valuable guidance for high‐performance X‐ray radiography. [ABSTRACT FROM AUTHOR]

The dosimetry performances of a nitrogen‐doped core (diameter of 8 μm) optical fiber, before and after 100 kV X‐Ray preirradiation treatments, up to cumulated dose of 1 MGy(SiO2), to highlight their effects on the radiation‐induced luminescence (RIL), are investigated. The RIL reproducibility versus dose rate calibration curves (in the 0.17–50 Gy s−1 range) are evaluated using four sets of ten different probes: three sets using preirradiated samples at 80 kGy, 280 kGy, 1 MGy, respectively, and one set with pristine samples. The RIL kinetics during ≈60 h long preirradiations at constant dose rate are also studied, showing a non‐negligible bright burn effect. The main outcome is that the preirradiation improves the fiber dosimetry properties since it: 1) enhances fiber radiation detection sensitivity, 2) improves the linearity of the RIL dose rate dependence, and 3) suppresses the observed afterglow postirradiation effect. However, after preirradiation, larger dispersion between the different probes is noted, from 4% (non‐irradiated samples) to 10% for the 1 MGy preirradiated samples. The possible physical explanations are discussed on the basis of the preirradiation filling deep traps that, competing with the RIL centers for the trapping of electrons released by ionization, influence the RIL efficiency. [ABSTRACT FROM AUTHOR]

The PEA2PbBr4 scintillator exhibits varied performance in photoluminescence (PL) and radioluminescence (RL) profiles. PL in the reflectivity mode shows emission peaks at 414 and 434 nm, whereas PL and RL in the transmission mode exhibit only one peak at 434 nm. Temperature-dependent PL spectra measurements confirm that self-absorption contributes to this difference. PEA2PbBr4 displays decay times of 1.3 ns (90%) and 4.4 ns (10%) for PL and 11.5 ns (89%) and 47 ns (11%) for RL. To explain the distinct decay times, we construct two models for simulating laser and radiation excitation and investigate carrier dynamics using non-adiabatic molecular dynamics. Our findings suggest that the relatively long radiative recombination process of carriers contributes to the slow RL decay time. [ABSTRACT FROM AUTHOR]

The photoluminescence and radioluminescence properties of Y3(Al0.99TM0.01)5O12 (TM = Ti, V, Mn, and Cu) single crystals were investigated. Single crystalline rods of approximately 5 mm diameter were grown by the optical floating zone method. The photoluminescence quantum yields of the obtained single crystals were 1.3-3.8%. Both the intrinsic luminescence of Y3Al5O12 (YAG) and the extrinsic luminescence due to each dopant were observed in the radioluminescence spectra. The radioluminescence decay times of YAG doped with either Ti, V, Mn, or Cu were in the range from 6.9 µs to 10.2 ms. [ABSTRACT FROM AUTHOR]

Ce-doped 20CsCl-20SrCl2-60ZnCl2 glasses were investigated for their optical and scintillation properties. Under X-ray irradiation, a broad emission peak at approximately 350 nm with a shoulder peak at 375 nm was observed, and its origin was attributed to Ce3+. In the pulse height spectrum under 241Am a-ray, the glass doped with 0.05% Ce exhibited the highest light yield (LY) of 25 ph/MeV (138 ph/5.5MeV-a) among zinc-halide-based glasses. The afterglow levels of the samples were superior to that of commercial CsI:Tl. [ABSTRACT FROM AUTHOR]

In the framework of the project RemoteALPHA, several radioluminescence scanning systems were developed to establish the metrological basis for the optical detection of alpha-emitting radionuclides. This work demonstrates an application of the ultraviolet imaging system for the characterization of low-activity alpha sources: contaminated environmental samples, and nuclear materials featuring depleted uranium. The measurements were performed at a reference distance of 2 m from the source. The weakest samples were measured in a chamber with an N2 + NO gas atmosphere. Using the scanning method, the total surface activity was calculated for analyzed samples, with the lowest reported value of just 51 Bq. [ABSTRACT FROM AUTHOR]

Time-resolved radioluminescence (TRRL) properties of the Cu(I) cluster Cu4I62− upon pulsed X-ray, β-ray or α-particle excitation are described. The longer (>2 μs) TRRL component displays exponential decay comparable to pulsed UV excitation; however, temporal behaviour at shorter times indicates that high local excited state density provides an alternative decay channel. [ABSTRACT FROM AUTHOR]

Despite the extraordinary X‐ray scintillation performance of three‐dimensional (3D) lead perovskite nanocrystals (PNCs), the serious biotoxicity of Pb2+ and luminescent instability in water remain insurmountable obstacles for their applications in medical imaging. To address these drawbacks, herein, the study demonstrates one new lead‐free zero‐dimensional (0D) hybrid cuprous halide of single‐crystalline [BzTPP]2Cu2I4 (BzTPP = Benzyltriphenylphosphonium) as a satisfactory X‐ray scintillator. [BzTPP]2Cu2I4 displays broadband yellowish‐green light emission with a high photoluminescent quantum yield (PLQY) of 44.2% and large Stokes shift of 167 nm upon UV light excitation. High PLQY and negligible self‐absorption enable [BzTPP]2Cu2I4 to display impressive scintillation performance excited by X‐ray with a light yield of 27 706 photons MeV‐1 and low detection limit of 0.352 µGy s−1, surpassing typical 3D PNCs. More importantly, [BzTPP]2Cu2I4 represents extraordinary structural and luminescent stability in water for at least one month. The excellent and stable radioluminescence performance as well as solution growth method ensure a [BzTPP]2Cu2I4‐based screen for fine‐resolution X‐ray imaging with potential in radiography and inspection. This work highlights the multiple merits of low‐toxicity and cost, high light yield, and long‐term water‐stability of 0D hybrid cuprous halides as highly desirable X‐ray scintillators. [ABSTRACT FROM AUTHOR]

The aim of this work is to highlight the correlation between treatment conditions, composition, and structure of reduced zinc oxide (ZnO:Zn) with optical and radioluminescence properties for the production of high yield scintillating powders. Purchased zinc oxide (ZnO) powders (≈0.35 ± 0.15 μm) were thermally reduced in Ar/H2 (3%) atmosphere at temperatures ranging between 600 (≈0.40 ± 0.17 μm) and 1000 °C (≈6.4 ± 1.6 μm), obtaining ZnO:Zn powders. The reduction degree, evaluated through energy dispersive spectroscopy, showed a linear increase from 0% up to 20% (800 °C sample), reaching a plateau condition at about 25% for the highest treatment temperatures (1000 °C sample). Structural analysis highlighted the existence of a threshold temperature, previously reported in the literature, around 800 °C, beyond which (i) the grain size remarkably increases, (ii) the shape changes from hexagonal to round-shaped, and (iii) the intensity of electron spin resonance (ESR)-active defects at g = 1.9596 decreases for a new resonance at g = 2.0105. Additionally, a substantial variation, from 5.63 ± 0.02 down to 5.2 ± 0.1 g/cm3, of the skeletal density and a slight contraction of the optical bandgap are observed. Unlike the structural properties, PL and x-ray radioluminescence showed a continuous increase of the green emission intensity, associated with ESR-active ionized oxygen vacancies and ESR non-active recombination centers, and of the PL defective lifetimes (33 ns < τfast < 88 ns, 395 ns < τslow < 930 ns). [ABSTRACT FROM AUTHOR]

The search for efficient, re-absorption-free scintillators has recently focused the attention on antimony-based halides, which exhibit largely Stokes shifted luminescence due to radiative recombination of excitons self-trapped (STE) in strongly Jahn-Teller distorted Sb3+ color centers. Here, the synthesis of a hybrid structure is reported with chemical formula (C13H14N3)3SbCl6 consisting of spatially isolated [SbCl6]3- octahedra separated by organic N, N'-diphenylguanidinium (Gua) molecules. The optical properties of this material are mainly determined by the inorganic component and are characterized by a pronounced Stokes shift of "1.3 eV and a room-temperature photoluminescence (PL) efficiency of up to 85%. Remarkably, highly efficient radioluminescence (RL) is observed with scintillation light yields of "2000 ph MeV-1 using both soft X-rays and a 124 keV gamma source. Temperature-dependent PL and RL measurements confirm the minor role of non-radiative channels, which are completely suppressed below 100 K. Thermally stimulated luminescence measurements suggest that the traps in Gua3SbCl6 crystals have a significantly large energy depth distribution below the absorbing state. [ABSTRACT FROM AUTHOR]

Ternary copper halide pseudo‐perovskites are in the forefront of research as potential active materials in light emission applications. The optoelectronic properties of these compounds can be fine‐tuned by the preparation of mixed‐halide compositions. After irradiation, self‐trapped excitonic states are formed in these materials. However, the emission from these self‐trapped states is not yet fully understood. In this work, mixed‐halide Cs3Cu2X5 films (where X: I and/or Br) are prepared by a simple spray‐coating method. Using ultraviolet photoelectron spectroscopy, the changes in optoelectronic properties are linked to the electronic structure of these materials. It is revealed that the incorporation of bromide into the lattice makes the emission process of these materials more vulnerable to trap states. By combining the different spectroscopic characterization techniques, the exact band structure of these compounds is determined, and the different processes are translated to the absolute energy scale. As an alternative excitation mechanism of self‐trapped states, α‐particles are used to induce radioluminescence response. The Cs3Cu2X5 films exhibit composite decay patterns, most likely attributed to a multitude of different trap state‐mediated recombination processes. [ABSTRACT FROM AUTHOR]

In this study, a new Cs4SrI6:Yb2+,Sm2+ near‐infrared (NIR) emitting scintillator was developed using sensitization strategy. It was found that Yb2+ sensitization significantly enhances the NIR radioluminescence (RL) of Sm2+, providing a new approach of designing highly emissive sensitized NIR scintillators. By studying the optical spectra and decay kinetics of Cs4SrI6:Yb2+,Sm2+, it was revealed that the energy transfer pathways involve both radiative and nonradiative processes. The gamma spectroscopy performance of Cs4SrI6:Yb2+,Sm2+ single crystals was studied by using the high‐quantum‐efficiency avalanche photodiode (APD) as the readout. Our results highlight the importance of using sensitization strategy of achieving NIR emitting scintillators and demonstrate the significant potential for radiation detection applications. [ABSTRACT FROM AUTHOR]

Scintillators, which can convert high‐energy ionizing radiation (e.g., X‐ or γ‐rays) into ultraviolet‐visible light, have been widely applied in medical and industrial fields. Developing new scintillation materials with high performance and low cost is very desirable in order to address the growing application demands. Among them, single‐crystal scintillators of organic‐inorganic hybrid metal halides (OIMHs) have attracted much attention because of their excellent optical transparency, suppressed light scattering, and facile solution preparation methods. Herein, three new centimeter‐sized (2‐DMAP)2MnX4 (2‐DMAP+ = 2‐dimethylaminopyridinium, X = Cl, Br, I) single crystals with high crystal quality are synthesized via the solvent evaporation method. Benefiting from the high optical transparency and remarkable luminescence property, (2‐DMAP)2MnBr4 delivers a high X‐ray light yield of 22 000 photons MeV−1, a low limit of detection of 9.50 nGy s−1, and an excellent X‐ray imaging spatial resolution of 20–25 lp mm−1. Moreover, the regulation of single‐crystal thickness from 0.31 mm to 3.03 mm can be easily achieved via a simple solution post‐treatment method, which has a significant influence on the transmittance, spatial imaging resolution, and detection limit. This work demonstrates a promising single‐crystal scintillator for the application of high‐resolution X‐ray imaging with low preparation cost and tunable thickness. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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Organic hybrid halide perovskite, which has excellent characteristics of low cost, nontoxicity, and high recognition, has attracted extensive attention in optical anticounterfeiting applications. In this paper, (TEA)2ZrCl6 (TEA = tetraethylammonium) single crystals (SCs) are synthesized by an easy‐to‐operate hydrothermal method, which exhibits excitation wavelength‐dependent emission at 254 and 365 nm, respectively. Moreover, the photoluminescence quantum yield of (TEA)2ZrCl6 SCs achieves 84.7%, with the introduction of Sb3+ ions. (TEA)2ZrCl6 and doped (TEA)2ZrCl6 patterns can be recognized with excitation by different wavelengths. In addition, as‐prepared (TEA)2ZrCl6 crystals show interesting radioluminescence for another anticounterfeiting model with the light yield of 17 709 photons per MeV. The experimental results indicate the novel (TEA)2ZrCl6 SCs have a huge potential for X‐ray imaging and anticounterfeiting. [ABSTRACT FROM AUTHOR]

X‐ray photography plays an important role in the fields of medical treatment, security inspection, and non‐destructive testing. The high image quality depends on X‐ray detectors with excellent properties. To meet the future demand for high‐performance scintillation screens, adding a new luminescent center in Cs3Cu2I5 by doping is considered. The successful incorporation of Mn brought a new luminescence peak at 565 nm. Different excitation modalities such as ultraviolet and X‐rays have the ability to tune luminescence. X‐ray can promote the energy transfer efficiency of self‐trapped excitons and non‐radiative intermediate trap states to doping Mn2+ ions. This results in a higher radioluminescence intensity of a radioluminescence light yield of 65 000 Photons MeV−1. Subsequently, a Cs3Cu2I5: Mn scintillation screen is prepared by anodized aluminum oxide (AAO) template. The array channel structure of the AAO template strongly suppresses the internal scintillation light scattering, allowing more scintillation photons to be emitted efficiently. Under the combined effect of Mn‐enhanced radioluminescence properties and AAO template suppressed light scattering, it obtains the lowest detection limit of 49 nGyair s−1. High X‐ray imaging quality has been achieved for circuit boards, beetles, and ball‐point pens and reached a high X‐ray imaging resolution of 11.8 lp mm−1. [ABSTRACT FROM AUTHOR]

Nanocrystals 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. [ABSTRACT FROM AUTHOR]

Phosphorescent octahedral metal cluster complexes are highly attractive in terms of biomedical applications, particularly in the area of luminescent diagnostics and photodynamic therapy (PDT). The ability of clusters to be excited by x-radiation followed by red/near infrared emission makes them a new promising class of photosensitizers for deep-PDT. This work demonstrates a direct observation of x-ray-excited optical luminescence of hexanuclear clusters, by example of rhenium cluster complex Na4[{Re6Se8}(CN)6], in a true aqueous solution. The article also describes point-by-point the details and pitfalls of studying cluster radioluminescence in aqueous solution. [ABSTRACT FROM AUTHOR]

For the first time, hafnia (HfO2) nanoparticles have been produced by photochemical synthesis. The photochemical route has been proven to be scalable, affordable, and straightforward to create monoclinic HfO2 nanoparticles with a size of tens of nanometers. The exploitation of this route offers a chance to create large amounts of dense nanoparticles with reduced costs and time of production for future creation of large area composite scintillators for fast timing techniques. Specific annealing treatments from 450 °C to 1000 °C have been targeted to tune the structural and morphological properties and optimize the luminescence of the nanoparticles. Hafnia nanoparticles annealed at low temperature display an amorphous structure. After thermal treatment at 1000 °C, HfO2 nanoparticles crystallize into a monoclinic phase, as evidenced by thermal analyses and X-ray diffraction. Radioluminescence and photoluminescence of HfO2 have been investigated at room temperature and 77 K. The emission band of hafnia covers a range from 300 to 600 nm and it can be attributed to defects within the matrix. In particular, the highest radioluminescence intensity appears in the crystalline sample annealed at 1000 °C, thanks to the higher crystallinity degree and the reduction of non-radiative channels and quenching defects. Photoluminescence and scintillation decay have evidenced the presence of the fast decay in the nanosecond time range. Thus, due to their size, density, and spectroscopic and timing features, monoclinic hafnia nanoparticles obtained by photochemical synthesis are attractive for potential creation of large area scintillating composites. [ABSTRACT FROM AUTHOR]