Near-Infrared CsBa₂I₅ (:Eu, Sm) Crystals and Scintillation Performance Enhancement via CsI-Atmosphere Annealing

摘要: The spectral match between near-infrared (NIR)–emitting scintillators and silicon photodetectors offers a route to detectors with intrinsically higher energy resolution, but in Eu/Sm co-doped halides additional Eu→Sm transfer steps and photon losses often limit performance. Here, we grow crack-free CsBa₂I₅ and CsBa₂I₅:Eu,Sm single crystals by the vertical Bridgman method, identify BaI₂ as a Ba-rich secondary phase that degrades light transport, and show that post-growth annealing in a CsI vapor atmosphere effectively removes these inclusions. Eliminating BaI₂ reduces exciton trapping and scattering, increases optical transmittance, particularly at the shorter wavelengths that mediate Eu→Sm transfer, and strengthens the NIR Sm²⁺ emission. As a result, CsBa₂I₅:Eu,Sm achieves an energy-resolution improvement from 5.50 % to 4.83 % at 662 keV when read out with a silicon avalanche photodiode (APD). This secondary-phase management strategy provides a simple and broadly applicable route to enhancing scintillation efficiency and expand the application potential of NIR-emitting halide scintillators for high-resolution radiation detection.