ABSTRACT Ionizing radiation in organic scintillators generates a high fraction of triplet excitons that often act as loss channels, limiting light yield and temporal response. Here, we report a linker‐engineering strategy for all‐organic crystalline thermally activated delayed fluorescence (TADF) emitters and scintillators based on the introduction of moderate heavy atoms in the ortho position relative to the donor. Incorporation of phenylsulfanyl groups into the benchmark PXZ‐TRZ framework affords PXZ‐dSP‐TRZ, in which the singlet–triplet energy gap is reduced and spin–orbit coupling is enhanced, promoting selective reverse intersystem crossing (rISC). Single‐crystal analysis shows that sulfur substitution preserves the strongly twisted donor–acceptor geometry, flattens the donor fragment, and changes crystal packing from mixed donor···donor/acceptor···acceptor interactions to predominantly acceptor···acceptor stacking. Consequently, PXZ‐dSP‐TRZ exhibits markedly improved TADF performance, including a photoluminescence quantum yield of up to 90%, a delayed fluorescence lifetime of 0.9 µs, and a high rISC rate of 6 × 10 6 s −1 , enabled by an exceptionally low rISC activation energy of 6.2 meV. Radioluminescence and scintillation measurements under x‐ray and γ‐ray excitation confirm efficient triplet harvesting under ionizing radiation. These results identify sulfur linker modification as a promising route toward fast organic scintillators.

Effects of Lu3+ admixture on photo-and radioluminescence, as well as on scintillation characteristics, were investigated in Gd3-xLuxAl3Ga2O12:Ce,Mg (x = 0.5, 1, 1.5, 2) scintillation ceramics fabricated via chemical co-precipitation and a combination of oxygen sintering, HIP post-treatment and annealing. The Ce3+ 5d1 -> 4f emission in photo-and radioluminescence bands was gradually blue shifted with increasing Lu content due to a decrease in the crystal field splitting of the 5d levels. Furthermore, the thermal ionization activation energy, determined from the temperature-dependent PL decay kinetics, increased with increasing Lu content, leading to higher thermal stability of the Ce3+ centers and increase of light yield value. The onset temperature at 362 K for luminescence quenching was determined from the temperature-dependent photoluminescence kinetics. The GdLu2Al3Ga2O12:Ce,Mg ceramic exhibited the highest light yield value of 11,400 photons/MeV at 662 keV gamma rays along with fast scintillation decay times of 26.5 ns (59%) + 58.2 ns (41%), and good time resolution of 249 ps.

Scintillator performance is inherently governed by a trade-off between scintillation yield and time response, where accelerating carrier recombination often reduces light output. Rational control over this balance remains a central challenge in the engineering of scintillator materials. Here, we report deliberate kinetic tailoring in Bridgman-grown SrCl2 single crystals through controlled Ce3+ incorporation. Optical absorption measurements yield a band gap of about 5.2 eV for pure SrCl2. Scintillation time profile analysis reveals a systematic acceleration of the effective decay time from over 800 ns (pure) to ca. 60 ns (3.5 mol% Ce), corresponding to a 13-fold reduction. This kinetic acceleration is accompanied by a decrease in light yield from over 13 000 to about 6000 ph/MeV, evidencing a controllable speed-efficiency trade-off. Radioluminescence and thermoluminescence data indicate that trap distributions remain primarily host-derived, while increasing cerium concentration promotes the dominant Ce3+ d-f emission and faster recombination pathways. These results establish SrCl2:Ce as a tunable scintillation platform in which recombination kinetics can be engineered in a predictable manner, enabling application-driven optimization between light yield and response speed.

In this paper we present the results of our recent studies performed on undoped and Si-doped beta beta-(Al beta-(Alx beta-(AlxGa beta-(AlxGa1-beta-(AlxGa1-x beta-(AlxGa1-x) beta-(AlxGa1-x)2 beta-(AlxGa1-x)2O beta-(AlxGa1-x)2O3 crystals grown by the Czochralski method at Leibniz-Institut f & uuml;r Kristallz & uuml;chtung in Berlin. The research, including pulse height spectra (with determination of light yield and energy resolution), scintillation time profiles, low-temperature thermoluminescence, and X-ray excited emission spectra recorded as a function of temperature, has been aimed to assess the influence of partial replacing gallium with aluminum on the scintillation properties.

Thermally activated delayed fluorescence (TADF) offers a powerful route for harvesting triplet excitons in organic scintillators, yet achieving simultaneously small singlet–triplet gaps and efficient spin–orbit coupling (SOC) in rigid molecular crystals remains a fundamental challenge. Here we demonstrate that targeted halogen substitution can activate vibrationally assisted spin-flip channels that dramatically enhance triplet harvesting in crystalline donor-acceptor emitters, tailoring them for scintillators with higher light yield and faster response times. Using DMAC-TRZ derivatives bearing fluorine or chlorine substituents, we combine single-crystal structural analysis, temperature-resolved photoluminescence, radioluminescence spectroscopy, and quantum-chemical calculations to reveal how subtle changes in halogen chemistry control excited-state dynamics. While fluorination reduces sharply the singlet-triplet energy gap, chlorine additionally introduces dynamic SOC enhancement mediated by the vibrations of Cl atoms within the crystal lattice. As a result, the chlorinated crystal exhibits an exceptionally small activation energy (Ea = 3.9 meV), (sub)microsecond-scale delayed fluorescence, and a scintillation yield of 26 000 photons MeV-1. These results reveal a powerful, atom-economical approach to achieving near S1-T1 degeneracy combined with vibrationally activated heavy-atom effects, enabling high-performance TADF scintillators in organic crystals.

Thermally activated delayed fluorescence (TADF) offers a powerful route for harvesting triplet excitons in organic scintillators, yet achieving simultaneously small singlet-triplet gaps and efficient spin-orbit coupling (SOC) in rigid molecular crystals remains a fundamental challenge. Here we demonstrate that targeted halogen substitution can activate vibrationally assisted spin-flip channels that dramatically enhance triplet harvesting in crystalline donor-acceptor emitters, tailoring them for scintillators with higher light yield and faster response times. Using DMAC-TRZ derivatives bearing fluorine or chlorine substituents, we combine single-crystal structural analysis, temperature-resolved photoluminescence, radioluminescence spectroscopy, and quantum-chemical calculations to reveal how subtle changes in halogen chemistry control excited-state dynamics. Fluorination lowers the rISC activation barrier to 7.1 meV, consistent with an almost degenerate emissive singlet-triplet manifold, whereas chlorine additionally introduces dynamic SOC enhancement mediated by Cl-atom vibrations within the crystal lattice. As a result, the chlorinated crystal exhibits an exceptionally small Ea of 3.9 meV, (sub)microsecond-scale delayed fluorescence, and a scintillation yield of 26 000 photons MeV-1. These results reveal a powerful, targeted approach to achieving near S1-T1 degeneracy combined with vibrationally activated heavy-atom effects, enabling high-performance TADF scintillators in organic crystals.

Controlled melt nonstoichiometry was investigated as a processing parameter governing secondary-phase formation and functional properties of Ce3+-doped (Tb,Y)3Al5O12 single crystals grown by micropulling-down. Crystals were grown from melts with 0, 3, 6, 9, and 11 mol % Y2O3 deficiency. X-ray diffraction, electron probe microanalysis, and Raman spectroscopy revealed phase-pure garnet up to 3 mol % deficiency, rim-localized α-Al2O3 inclusions at 6 and 9 mol %, and core-localized perovskite-type inclusions at 11 mol %. Secondary-phase formation modified Tb/Y partitioning in the garnet matrix, affecting Ce3+ emission kinetics, Tb3+↔Ce3+ energy transfer, trap depth, and scintillation properties. The 11 mol % deficient crystal showed the highest thermal stability, with the Ce3+ thermal-quenching onset shifting from 375 to 425 K. The 9 mol % deficient crystal reached a luminous efficacy of 158 lm/W and a scintillation light yield of 33,600 photons/MeV. X-ray radiography using the 9 mol % Y2O3-deficient crystal showed clear images of an SD card. These results indicate that melt nonstoichiometry can tune the balance between photoconversion and scintillation performance in rare-earth garnets.

Using OSL in dosimetry requires determining its thermal stability. It is a challenge when one cannot correlate OSL with a specific TL peak due to the complex material TL. Combining the Pulse annealing (PA) method with the variable heating rate (VHR) method allows for determining the OSL trap parameters in such cases. The presented measurement results for YAG:Ce and YAG:Ce,Mg samples and simulations of PA-VHR measurements for various competition scenarios between OSL traps and other traps in the material prove that this method allows for determining the OSL trap depth with perfect accuracy for models with two or three competing traps. The frequency factor value can be determined with an order of magnitude accuracy, which allows for similar estimates of the lifetime of OSL traps. That is satisfactory for dosimetry. The condition for obtaining correct trap parameters is measuring a single OSL component in the PA-VHR protocol. Determining trap parameters responsible for the OSL signal used in dosimetry is necessary to estimate this signal’s thermal stability. In the case of a complex TL curve or strong thermal quenching effects, it is difficult to identify the TL peak associated with the OSL trap. One of the methods used in this case is pulse annealing (PA), where the OSL remaining after annealing to successively higher temperatures is measured and plotted as a function of temperature. A promising possibility is using the different heating rate technique in these measurements. However, when the TL of the material tested is complex, the competition from electron traps shallower or deeper than the tested OSL trap may interfere with the results. Simulations for many competition scenarios of the traps emptied in the same temperature range show that for the vast majority of scenarios, the determined trap parameters are consistent with those in the model.

The controllable doping of hybrid organic-inorganic perovskites (HOIPs) has fueled strong interest in their utilization as scintillating materials. In terms of cation engineering, tin mixed-halide perovskites (TMHPs) are considered a stronger contender than their conventional hybrid perovskite counterparts. However, their inability to undergo physicochemical alteration via simultaneous A-site and X-site substitution remains unresolved to date. In this work, we tailor the organic ligand and halide mixture of TMHPs to shed some light on their optical and scintillation properties. By introducing three organic ligands, we synthesize phenylmethylammonium (PMA), phenethylammonium (PEA) and phenylpropylammonium (PPA) and retain the Br : I ratio at 3 : 1. In terms of structural order, we show that the interlayer spacing between the inorganic layers is gradually extended from 9.88 & Aring; for (PMA)2SnBr3I and 10.29 & Aring; (PEA)2SnBr3I to 10.06 & Aring; for (PPA)2SnBr3I. Based on geometrical order, organic chain penetration and octahedral distortion angles, we propose a rational design to modulate the absorption, photoluminescence (PL), optical bandgap, and thermal quenching of TMHPs. (PMA)2SnBr3I exhibits the fastest decay time (tau avg = 1.1 ns) compared to (PEA)2SnBr3I (tau avg = 2.51 ns) and (PPA)2SnBr3I (tau avg = 3.54 ns), indicating that TMHPs are promising candidates for scintillator applications. This finding is corroborated by density functional theory, which outlines the weakened antibonding interaction between I 5p and Sn 5s orbitals upon tailoring the organic ligand of the perovskite. Our results demonstrate the importance of cation engineering in leveraging innovative hybrid perovskites with novel responses via a rational design.

A next-generation class of dual-phase, multifunctional photoconversion and thermal sensing materials has been developed using Ce3+-doped YAG-YAP eutectic crystals, synthesized via directional solidification at variable rates (0.1-0.9 mm/min) to precisely tailor phase morphology and dopant distribution. Structural and compositional analyses revealed a lamellar microstructure comprising alternating garnet (Y3Al5O12, YAG) and perovskite (YAlO3, YAP) domains, with Ce3+ ions preferentially partitioned into the garnet phase at elevated solidification rates. Systematic control of domain sizes was achieved by modulating the growth rate. Slower growth resulted in larger domains that enabled near-complete transmission of blue light through YAP, whereas faster growth produced finer structures that led to increased scattering and absorption of blue light. This morphology-driven optical tunability enabled dynamic control over the correlated color temperature (CCT), ranging from cool to warm white emissions. Beyond structural engineering, the eutectics demonstrated dual-mode thermal sensing via ratiometric luminescence thermometry under both photoluminescence (PL) and X-ray-induced scintillation excitation. Excitation modality significantly affected thermal sensitivity due to distinct charge transport and energy transfer dynamics. Under PL, the relative sensitivity reached 0.47% K-1, while scintillation-based excitation achieved an enhanced sensitivity up to 1.1% K-1. Crucially, the scintillation mode permits passive, remote temperature monitoring without external optical excitation, activated solely by ambient ionizing radiation. These capabilities position Ce3+-doped YAG-YAP eutectics as promising candidates for advanced thermal sensing in extreme environments, including nuclear reactors, aerospace systems, and high-energy particle detectors.

Scintillators convert high-energy radiation into detectable photons and play a crucial role in medical imaging and security applications. The enhancement of scintillator performance through nanophotonics and nanoplasmonics, specifically using the Purcell effect, has shown promise but has so far been limited to ultrathin scintillator films because of the localized nature of this effect. This study introduces a method to expand the application of nanoplasmonic scintillators to the bulk regime. By integrating 100-nm-sized plasmonic spheroid and cuboid nanoparticles with perovskite scintillator nanocrystals, nanoplasmonic scintillators are enabled to function effectively within bulk-scale devices. Power and decay rate enhancements of up to (3.20 ± 0.20) and (4.20 ± 0.31) folds are experimentally demonstrated for plasmonic spheroid and cuboid nanoparticles, respectively, in a 5-mm thick CsPbBr3 nanocrystal-polymer scintillator at RT. Theoretical modeling also predicts similar enhancements of up to (2.26 ± 0.31) and (3.02 ± 0.69) folds for the same nanoparticle shapes and dimensions. Moreover, a (2.07 ± 0.39) fold increase in light yield under 241Am γ-excitation is demonstrated. These findings provide a viable pathway for utilizing nanoplasmonics to enhance bulk scintillator devices, advancing radiation detection technology.

CsCu2I3 CsCu2I3 lead-free nanocrystals (NCs) have recently garnered significant interest for their outstanding optical and scintillation characteristics, particularly for X-ray imaging applications. In this study, CsCu2I3 NCs are mixed with polydimethylsiloxane (PDMS) resin in the form of a pellet to protect against environmental factors such as moisture. The resulting sample exhibits a light yield of up to 2 ph keV(-1) and an excellent energy resolution of 13% for gamma-ray excitation at 662 keV at room temperature. Additionally, the CsCu2I3 NCs-PDMS resin shows no afterglow and has a negligible trap density. Herein, high stability at low irradiation intensities and reasonable stability at higher intensities are demonstrated. Moreover, the sample features a fast component scintillation decay times of 3.55 ns, which is slightly faster than that of (BZA)(2)PbBr4. This outcome possesses promising combination in designing lightweight and flexible hybrid PDMS-based hybrid materials scintillators. These scintillation properties of CsCu2I3 NCs-PDMS can be a promising candidate for affordable and flexible screens for X- and gamma-ray photon-counting computed tomography.

In this paper we present a broader characterization of two different Gd-based ceramics, mostly from the point of view of their potential scintillator applications. The Gd2O2S (GOS) ceramics were doubly activated with Ce (0.003 at%) and Pr (0.1 at%) ions, whereas the GYAGG ceramics with Ce ions only, forming two compositions: Ce0.006Gd1.996Y0.998(Y0.02Ga0.98)2GaAl2O12 and Ce0.006Gd1.996Y0.998(Y0.04Ga0.96)2GaAl2O12. The following studies were performed: pulse height spectra, scintillation time profiles, radioluminescence as a function of temperature, and low temperature thermoluminescence. We show that the GOS:Pr,Ce ceramics display reasonably high scintillation yields close to 30000 ph/MeV, but with moderately slower decay (a few mu s). The GYAGG:Ce ceramics offer somewhat lower yields compared to GOS:Pr,Ce, but with faster decay. Both ceramics have sufficiently good scintillation properties and could replace single crystals in some applications related to radiation detection.

Inorganic ion doping has emerged as a promising approach to enhance the scintillation properties of twodimensional (2D) organic-inorganic hybrid perovskite (OIHP) crystals, particularly by increasing mass density and effective atomic number (Z). In this study, we investigate the effects of cesium (Cs) doping on (PEA)2PbBr4. Our findings indicate that Cs-doping in (PEA)2PbBr4, especially above 5 %, results in the formation of local quasi2D domains within the grown crystal and even bulk domains at higher concentrations. This leads to an overall narrowed band gap, reduced by as much as 0.2 eV compared to the undoped material. Cs-doping also broadens photoluminescence (PL) spectra and significantly accelerates PL decay times, achieving fast as (1.1 +/- 0.1) ns, with an average decay time reduction of 81 % compared to undoped crystals. Furthermore, the inclusion of Cs ions shortens scintillation decay times, reaching as fast as (51.6 +/- 5.7) ns, with an average decrease of 10 %. Notably, Cs-doping at a threshold concentration of 5 % leads to a 30 % improvement in light yields (LYs). These results demonstrate that Cs-doping significantly enhances the performance of (PEA)2PbBr4 crystals, making them particularly well-suited for high LYs and fast timing applications, such as photon counting and positron emission tomography. This study underscores the potential of Cs-doped OIHP crystals in advancing the capabilities of scintillation-based radiation detection technologies.

To date, hybrid organic-inorganic halide perovskites still attract significant attention due to their intrinsic versatility in optoelectronic devices and scintillation applications. This study aims to investigate the effect of Rb and Li doping on the structural, optical, and luminescence properties of methylammonium lead bromide (MAPbBr3) single crystals (SCs), with particular emphasis on enhancing their cryogenic scintillation performance. Raman, X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS) analyses confirmed minimal structural changes upon doping. Photoluminescence (PL) spectra showed that Li-doped 0.4M-tetrahydrofuran (THF) SC exhibits intense surface emission intensity and a long decay time (100 ns) compared to that of Li-doped control 1M-THF SC, while Rb-doped 0.4M-THF SC has a short decay time compared to that of Rb-doped control 1M-THF SC (17.5 ns). Radioluminescence (RL) analysis displayed strong excitonic luminescence, reduced thermal quenching, and improved thermal stability with dopant incorporation in the orthorhombic phase below 50 K. Furthermore, for both dopants 0.4M-THF SCs exhibit a remarkable RL light yield, surpassing the control crystal of 1M-SCs by more than 2-fold. 0.4M-THF samples consistently outperformed control 1M-THF samples in thermal stability and emission efficiency, with Li-doped SCs showing slightly better scintillation performance than Rb-doped ones, making them highly suitable for cryogenic scintillation applications.

Low-dimensional bismuth-based hybrid organic-inorganic halide perovskites (Bi-HOIPs) are intriguing scintillating materials due to their anisotropic nature. However, a systematic investigation on Bi-HOIP frameworks for X-ray detection imaging remains lacking. In this work, we present the diverse X-ray detection responses in a series of Bi-HOIPs that are incorporated into a polydimethylsiloxane (PDMS) matrix utilizing ionic liquids (ILs) as organic ligands, namely, 1-butyl-1-methyl-pyrrolidinium (BMP), 1-(3-aminopropyl)imidazole (API), and 1-butyl-3-methyl-imidazolium (BMI). The as-synthesized Bi-HOIPs in this series exhibited a modest light yield of similar to 1000 photons per keV at room temperature. Interestingly, the incorporation of tin (Sn), instead of bismuth, resulted in radioluminescence intensity enhancement at low temperatures. An abrupt thermal quenching occurred in the case of APISnBiBr5 and APISn2Br10, leading to an absence of light yield at RT. Interestingly, thermoluminescence (TL) measurements showed that the glow curve was absent in BMIBiBr4 and APIBiBr5, demonstrating the weak contribution of a defect within the crystal lattices. On the contrary, BMPBiBr4, APISnBiBr5 and APISn2Br10 displayed glow curves at temperatures above 100 K. We believe that controlling the number of defects promoted tunable modest distribution traps, manifesting their light yield profile. In terms of the decay profile, BMIBiBr4 exhibited a fast decay component of 4 ns, while APIBiBr5 and BMPBiBr4 yielded a fast decay of 6 ns. A distinct constituent within the ILs could serve as a tuning factor, thereby generating different optical responses and scintillation features. We postulate that this can be attributed to the band gap and polaron signature in BMIBiBr4, which manifested a faster quenching rate than BMPBiBr4 and APIBiBr5. This work sheds new insights on how the population of direct manipulation traps in IL-based bismuth halide perovskites can be driven by regulating the number of halogens at the X-sites of the targeted compounds.

Substituting Sc 3+ for Al 3+ in Pr 3+ -doped Lu 1.5 Y 1.5 Al 5− x Sc x O 12 crystals enhances the Pr 3+ emission across the UV-Vis-NIR spectral range. This enhancement is attributed to an efficient Sc 3+ → Pr 3+ energy transfer and increased structural disorder.

The remarkable brightness and rapid scintillation observed in perovskite single crystals (SCs) become even more striking when they are operated at cryogenic temperatures. In this study, we present advancements in enhancing the scintillation properties of methylammonium lead bromide (MAPbBr3) SCs by optimizing the synthesis process. We successfully synthesized millimeter-sized MAPbBr3 SCs with bright green luminescence under UV light. However, both MAPbBr3 (Control-1M and THF-0.4M) SCs display notable radioluminescence exclusively at low temperatures due to their phase transitions. Notably, the THF-0.4M SCs exhibit a remarkable improvement in radioluminescence light yield, surpassing Control-1M SCs more than 2-fold. Further, THF-0.4M SCs demonstrate an ultrafast decay component of 0.52 ns (82.2%) and a slower component of 1.80 ns (17.8%), contributing to a rapid scintillation response at low temperatures. Therefore, the amalgamation of ultrafast decay components and improved radioluminescence light yield equips THF-0.4M SCs to emerge as a top choice for perovskite scintillators for X-ray timing applications.