Near-Infrared Emitting of Zero-Dimensional Europium(II) Halide Scintillators: Energy Transfer Engineering via Sm²⁺ Doping

Near-infrared (NIR)-emitting scintillators, coupled with high quantum efficiency silicon-based photodetectors, have emerged as a promising solution for highly efficient radiation detection applications. However, the study of efficient NIR-emitting scintillators and their associated luminescence mechanism is still limited. In this work, we developed NIR-emitting zero-dimensional Cs 4 EuBr 6 halide scintillators via Sm 2+ doping. Single crystals of Cs 4 EuBr 6 with varying Sm 2+ concentrations were grown by the vertical Bridgman method. Under X-ray irradiation, the scintillation emission of highly Sm-doped Cs 4 EuBr 6 single crystals is dominated by the Sm 2+ 5d–4f emission peaking at 831 nm with a weak Eu 2+ 5d–4f emission peaking at 443 nm. The energy transfer processes between Eu 2+ and Sm 2+ were investigated by using photoluminescence (PL) spectra, PL decay kinetics, and soft X-ray excited decay kinetics measurements. Based on the temperature-dependent PL decay results, we constructed a configurational coordinate diagram of Sm 2+ in the Cs 4 EuBr 6 host. Furthermore, we evaluated the gamma spectroscopy response of Cs 4 EuBr 6:Sm single crystals using an avalanche photodiode detector known for its high sensitivity in the NIR wavelength region.