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Future experiments in high energy physics and medical imaging require radiation detectors having properties which are not presently available. The main limitations arise from a lack of suitable scintillation crystals. This dilemma prompts the need for research leading to the discovery of new fast and bright scintillator materials that combine unique properties to fulfil modern experiment requirements without compromises. In this work, single crystals of Cs2MgCl4 and Cs3MgCl5 up to 12 mm in diameter are grown via the vertical Bridgman method. Scintillation properties are reported for the first time, and core valence luminescence is observed for both compounds. X-ray excited radioluminescence emission of Cs2MgCl4 is centered at 295 nm, with a scintillation decay time of 2.25 ± 0.05 ns and relatively high core-valence light yield of 2200 ± 110 ph per MeV. Cs3MgCl5 has two main emission peaks centered at 242 nm and 302 nm, a decay time of 1.46 ± 0.05 ns, and a light yield of 1340 ± 70 ph per MeV. The better coincidence time resolution (CTR) is obtained with Cs2MgCl4, which is measured to be 129 ± 4 ps FWHM. Density functional theory (DFT) calculations are also performed and provide supporting evidence that the observed scintillation originates from core valence luminescence. The combination of speed and brightness of these new scintillators could be useful for fast timing applications in which moderately dense materials are required. [ABSTRACT FROM AUTHOR]

Organic–inorganic and all-inorganic halide perovskites have become leading candidates toward high-performance optoelectronic devices and radiation detectors. In this work, we report novel zero-dimensional Cs4EuX6 (X = Br, I) perovskite single crystals as self-activated scintillators with superior performance for gamma-ray spectroscopy. Both Cs4EuBr6 and Cs4EuI6 single crystals grown by the Bridgman method were determined to have the trigonal crystal structure with the R3̅c space group, and have a melting point of approximately 540 °C. Cs4EuBr6 and Cs4EuI6 exhibit blue emission under UV excitation and high light yields of 78 000 ± 4000 photons per MeV and 53 000 ± 3000 photons per MeV under 137Cs gamma-ray irradiation, respectively. In particular, the former represents the best result achieved for self-activated scintillators thus far. Thermally stimulated luminescence studies and density functional theory calculations elucidate the correlation between halogen vacancies and long-lived emission (afterglow) at room temperature in Cs4EuX6 (X = Br, I) single crystals. Our findings not only demonstrate the high gamma-ray detection efficiency in Cs4EuX6 (X = Br, I), but will further promote the development of 0D metal halide-based novel luminescent and radiation detection materials. [ABSTRACT FROM AUTHOR]

Codoping is an effective approach for precise control of point defects in many advanced materials, and can be used to optimize their function. This paper reports an effort toward tailoring the scintillation properties of metal halides through defect engineering. A study of aliovalent codoping of the KCaI3:Eu2+ single‐crystalline scintillators is performed, through which it is discovered that a simultaneous suppression of X‐ray induced afterglow and improvement of gamma‐ray energy resolution can be successfully achieved via Zr4+ codoping. The afterglow level is reduced by more than twofold with Zr4+ codoping. The energy resolution of a 5 mm cubic KCaI3:Eu2+ sample is improved from 3.25 to 2.7% at 662 keV, and 6.5 to 5.73% at 122 keV upon Zr4+ codoping. Physical explanations for the improvements are revealed from our investigations into both the electronic structure and thermodynamics of the defects by using thermoluminescence techniques and density functional theory calculations. The codoped Zr4+ ions prefer to form interstitials acting as shallow electron traps. The {ZrCa+VCa} complex can co‐exist with Zri interstitials as shallow hole traps under certain condition, which are able to trap holes temporarily. [ABSTRACT FROM AUTHOR]

Lithium codoping has emerged as an effective strategy to enhance the light yield of oxide scintillators for radiation detection applications, but the understanding of the actual role played by Li + remains unclear. In this work, we comprehensively study the effects of Li codoping on optical and scintillation properties of Lu 2 SiO 5 :Ce (LSO:Ce) single crystals and reveal the critical role of site occupancy of Li. High-quality LSO:Ce single crystals codoped with 0.05, 0.1, and 0.3 at. % Li ions were grown by the Czochralski method. The optical absorption spectra confirm nonconversion of stable Ce 3+ to Ce 4+ in Li-codoped LSO:Ce regardless of the Li codoping concentration. The photoluminescence decay kinetics suggest an enhanced ionization of the excited 5d 1 state of Ce 3+ centers in highly codoped samples. A simultaneous improvement of scintillation light yield, decay time, and afterglow is achieved in LSO:Ce codoped with low concentrations of Li. The preferential occupation of Li at interstitial spaces and lutetium sites is proven to rely on its codoping concentration by using the 7 Li nuclear magnetic resonance technique. The concentration-dependent site occupancy of Li alters the defect structures of LSO:Ce, in particular resulting in a distinct change in the number of cerium spatially correlated oxygen vacancies confirmed by thermoluminescence and afterglow measurements.