RbSrSc 2 (PO 4 ) 3 :Pr 3+ : A Langbeinite-Type Structure with Blue-to-UVC Upconversion Properties

A new phosphate, RbSrSc 2 (PO 4 ) 3, was synthesized via a conventional solid-state route and characterized by X-ray powder diffraction. Rietveld refinement of undoped and Pr 3+ -doped samples confirmed a langbeinite-type cubic structure (space group P 2 1 3), comprising corner-sharing [ScO 6 ] octahedra and [PO 4 ] tetrahedra, with [Sr,Rb] ions occupying distorted 9- and 12-coordinate cavities. Photoluminescence studies show that RbSrSc 2 (PO 4 ) 3:1% Pr 3+ exhibits visible Stokes emission (orange 1 D 2 → 3 H 4 transition) and ultraviolet anti-Stokes upconversion emission in the 235–315 nm spectral range under 3 P 2 excitation. The upconversion intensity significantly exceeds that of the reference material YPO 4:1% Pr 3+, highlighting the potential of langbeinite-type phosphates for germicidal and photonic cancer therapy applications. Power-dependent and lifetime measurements indicate that the ultraviolet upconversion under visible excitation occurs via excited-state absorption (ESA). Additional characterization includes SEM imaging, FT-IR spectroscopy, thermal analysis, and luminescence studies under synchrotron radiation.