Energy transfer–driven orange–red emission in Sm ³⁺ /Pr ³⁺ co-activated Sr ₉ MgK(PO ₄ ) ₇ phosphors

Sm3+ and Pr3+ co-activated Sr9MgK(PO4)7 phosphors (with doping concentrations in the range of 0.5 to 2.5 mol %) were synthesized using a wet chemical method and systematically investigated for their structural and photoluminescence properties. X-ray diffraction and Rietveld refinement confirmed the formation of a single-phase trigonal structure with R3c symmetry, indicating successful incorporation of rare-earth ions without altering the host lattice. FTIR analysis verified the presence of characteristic phosphate groups. Photoluminescence studies revealed intense orange–red emissions originating from the 4G5/2 → 6HJ transitions of Sm3+ and the 1D2 → 3H4 transition of Pr3+ ions. Concentration-dependent emission behavior indicated the occurrence of concentration quenching, governed predominantly by multipolar interactions as confirmed by critical transfer distance calculations. Spectral overlap and co-doped emission analysis demonstrated efficient energy transfer from Sm³+ to Pr³+ ions, resulting in a broad orange–red emission. The calculated CIE chromaticity coordinates exhibited high color purity, suggesting the suitability of the developed phosphors for orange–red emitting solid-state lighting applications.