Characterisation of Sm<sup>2+</sup>-doped CsYbBr<sub>3</sub>, CsYbI<sub>3</sub> and YbCl<sub>2</sub> for near-infrared scintillator application

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Fast energy transfer from Yb2+ to Sm2+ is a requirement when using Yb2+ as a sensitiser for Sm2+ emission for near-infrared scintillator applications. This cannot be achieved through dipole-dipole interactions due to the spin-forbidden nature of the involved Yb2+ transition, making the rate of energy transfer too slow for application. This work explores whether exploiting the exchange interaction by increasing the Yb2+ concentration to 99% is an effective way to increase the rate at which energy is transferred from Yb2+ to Sm2+. The scintillation characteristics of CsYbBr3:1%Sm, CsYbI3:1%Sm and YbCl2:1%Sm single crystals were studied through 137Cs excited pulse height spectra, X-ray excited decay and X-ray excited luminescence spectra. An energy resolution of 7% and a light yield of 30,000 ph/MeV was achieved with CsYbI3:1%Sm. Photoluminescence spectroscopy and decay studies were performed to study the band structure and relaxation dynamics.