Junfeng Chen

Optimized surface polishing effectively reduces surface damage and defects in CsPbBr ₃ single crystals, suppressing leakage current and electronic noise and thereby significantly enhancing γ-ray energy resolution.

Halide perovskites are promising for applications in light‐emitting diodes, multilevel anti‐counterfeiting, and radiation detection due to their excellent luminescence properties. Mn ²⁺ doping can further tailor the optical properties of perovskites, yet its microscopic mechanism remains insufficiently understood. Here, we report a gradient orbital coupling‐enhanced red emission with a nearly tenfold increase in photoluminescence quantum yield by doping 0.12% Mn ^{2 +} into 1D NH ₄ CdCl ₃ perovskite, constructing asymmetric Cd‐Cl‐Mn functional units. First‐principles calculations indicate that orbital hybridization among Cd(5s, 4d), Cl(3p), and Mn(3d) orbitals in these asymmetric Cd‐Cl‐Mn units creates a stepped carrier‐transport pathway via the formation of coupled gradient orbitals. Transition dipole moment analysis and partial charge mapping reveal that electrons transiently occupy the conduction‐band‐coupled Mn 3d orbitals before relaxing to the conduction band minimum, while most of the holes are localized at Cd sites. This carrier redistribution enhances radiative recombination, thereby optimizing emission efficiency. The as‐prepared semitransparent scintillator films incorporating NH ₄ CdCl ₃ : Mn deliver strong 630 nm emission under x‐ray excitation for high‐resolution imaging. Our findings demonstrate that gradient orbital coupling serves as an effective strategy for enhancing luminescence, paving the way for high‐efficiency perovskite‐based optoelectronic materials and devices.

Barium fluoride (BaF2) crystal is an ultrafast scintillator known for a sub-nanosecond fast component. Recent studies have shown that yttrium (Y) doping effectively suppresses the slow scintillation component. In this study, we comprehensively investigate the impact of Y doping by growing BaF₂ crystals with nominal Y concentrations in the range of 0 to 20 at%. The actual Y concentration in BaF₂:Y crystal samples was determined by inductively coupled plasma atomic emission spectroscopy (ICP-AES), and the optical transmittance (OT), radioluminescence (RL), fast/slow component ratio (F/S) of light output (LO), energy resolution (ER), and decay time (DT) were systematically measured. It was found that Y doping influences not only the LO and F/S but also the DT of BaF₂ crystals. As the doping concentration increased from 0% to 20 at%, the LO intensity of the slow component decreased to 6% of that of undoped crystal, while that of the fast component reduced to 60% of undoped crystal. Consequently, the F/S increased from 0.13 to 1.36, whereas ER@511keV degraded from 12.1% to 38.7%. The LOs of slow and fast components showed distinct trends: the slow component decreased rapidly below 1 at% Y and then decayed with an offset-exponential trend, while the fast component remained up to 2 at% before declining linearly. The slow component in Y-doped BaF₂ crystals consists of two distinct decay processes: the slower one that decreases from 755 ns to 381 ns, and the faster one that declines from 199 ns to 41 ns upon doping with Y.

Bismuth silicate (Bi₄Si₃O₁₂) crystal, due to their high stopping power, fast decay and low raw material cost, are expected to be applied in future high-energy physics (HEP) experiments. However, the high-quality and large crystal growth has restricted its practical HEP applications as a cost-effective scintillator. In this study, BSO crystals with dimensions up to 22.6 mm × 22.6 mm × 369 mm (SIC-BSO-369) and 18.6 mm × 18.6 mm × 259 mm (SIC-BSO-259) were successfully grown in Shanghai Institute of Ceramics, Chinese Academy of Sciences. These are the longest BSO single crystals reported to date. Their scintillation properties were measured, including transmittance, photoluminescence, X-ray excited emission, energy resolution, and light response uniformity. The results show that the SIC-BSO-259 crystal exhibits a high longitudinal transmittance (78.32%@480 nm) close to the theoretical limit value, demonstrating excellent optical quality. Due to internal scattering, the longitudinal transmittance of the SIC-BSO-369 crystal is 45.27% at 480 nm. The average energy resolution of the SIC-BSO-259 and SIC-BSO-369 for 662 keV gamma rays are 27.2% and 29.0%, respectively. And their average absolute light output is 776 and 735 ph/MeV, respectively. The optimal light response uniformity (δ value) of SIC-BSO-259 is (-0.52 ± 0.5) % with a combination of all polished surfaces and ESR as high-reflector material, while for SIC-BSO-369 is (1.41±1.8) % with Tyvek wrapped.

The solar composition problem has puzzled astrophysicists for more than 20 years. Recent measurements of carbon-nitrogen-oxygen (CNO) neutrinos by the Borexino experiment show a ∼2σ tension with the "low-metallicity" determinations. ^{14}N(p,γ)^{15}O, the slowest reaction in the CNO cycle, plays a crucial role in the standard solar model (SSM) calculations of CNO neutrino fluxes. Here we report a direct measurement of the ^{14}N(p,γ)^{15}O reaction, in which S-factors for all transitions were simultaneously determined in the energy range of E_{p}=110-260 keV for the first time. Our results resolve previous discrepancies in the ground-state transition, yielding a zero-energy S-factor S_{114}(0)=1.93±0.10 keV b, which is 15% higher than the 1.68±0.14 keV b recommended in Solar Fusion III (SF-III). With our S_{114} values, the SSM B23-MB22p, and the latest global analysis of solar neutrino measurements, the C and N photospheric abundance determined by the Borexino experiment is updated to N_{CN}=(4.42_{-0.63}^{+0.70})×10^{-4}. This new N_{CN} value agrees well with latest "high-metallicity" composition; however, it is also consistent with the "low-metallicity" determination within ∼1σ CL, indicating that the solar metallicity problem remains an open question. In addition, the significant reduction in the uncertainty of S_{114} paves the way for the precise determination of the CN abundance in future large-volume solar neutrino measurements.

An as-grown 1-inch-diameter Cs ₂ ZnCl ₄ crystal boule in a quartz ampoule (a), a polished Cs ₂ ZnCl ₄ crystal with dimensions of 10 × 10 × 11 mm ³ , and a diagram illustrating the crystal growth process (c).