Inter- and intraconfigurational luminescence of Pr3+ in Ca6Ba(PO4)4O

The photoluminescence properties of Pr3+ -doped Ca6Ba(PO4)4O are reported and analyzed for the first time. The phosphors were synthesized via a conventional solid-state method with Pr3+ concentrations ranging from 0.5 to 2.0 mol% and Li+ co-doping for charge compensation. X-ray diffraction confirmed the formation of a single-phase monoclinic structure (C2/m) for all compositions. Photoluminescence studies showed both interconfigurational 4f5d → 4f 2 and intraconfigurational 4f 2 → 4f 2 transitions of Pr3+, producing UV and visible emissions. The dominant red emission originates from the 1D2 → 3H4 transition, indicating efficient nonradiative relaxation from the 4f 5d states in the phosphate host. Maximum emission intensity was achieved at 0.5 mol% Pr3+, with concentration quenching observed at higher dopant levels. Timeresolved measurements revealed nanosecond 4f5d lifetimes and microsecond 1D2 lifetimes. These findings enhance the understanding of luminescence mechanisms in phosphatebased materials and confirm Ca6Ba(PO4)4O as a stable and efficient host for Pr3+ -activated phosphors.