A Mixed-Anion Design Approach for High-Efficiency X-ray Scintillators: A Study of KLn(SO

High-quality single crystals of mixed anion rare earth sulfate fluorides KLn(SO4)F2 (Ln = Eu, Gd, Tb, Dy, Ho, and Tm), monoclinic space group P21/m, were obtained using an HF-free mild hydrothermal synthesis. Thermal, magnetic, and optical properties of these materials were investigated after determining their crystal structures and their chemical compositions using a combination of single-crystal and powder X-ray diffraction. Notably, the photoluminescence and radioluminescence behavior of KEuSO4F2 and KTbSO4F2 were studied for the first time, featuring the intense green radioluminescence of KTbSO4F2, which is comparable to the integrated intensity of the commercial bismuth germanium oxide (Bi4Ge3O12) scintillator, while KEuSO4F2 scintillates in red with an integrated intensity of 49% of Bi4Ge3O12. The experimental results indicate that doping with appropriate amounts of Tb3+ significantly improves the luminescence performance of KEuSO4F2.