β-Phase CsAgCl ₂ Single Crystals with Self-Trapped Exciton Emission for Gamma Spectroscopy

Low-dimensional metal halides with negligible self-absorption and efficient radioluminescence have attracted considerable attention in the field of radiation detection materials in recent years. In this work, β-phase CsAgCl2 single crystals were grown by the vertical Bridgman method, and the capability of serving as gamma spectroscopy scintillators is demonstrated. The CsAgCl2 has a solid phase transition occurring at 122 °C. The β-phase CsAgCl2 exhibits yellow emission peaking at 612 nm with a large Stokes shift of 2.43 eV associated with self-trapped exciton emission. Based on temperature-dependent photoluminescence spectral and decay results, the luminescence mechanism in β-phase CsAgCl2 single crystals is proposed. Under 137Cs gamma-ray irradiation, the β-phase CsAgCl2 single crystal has a decent light yield of 10,600 ± 2000 photons/MeV with an energy resolution of 10.5 ± 0.3% at 662 keV. These results demonstrate the potential of silver-based low-dimensional halides for gamma-ray detection applications.