Tunable Orange-Red Emission and Judd-Ofelt Parameterization of Sm³⁺-Doped NaCaBi₂(PO₄)₃: A Multifunctional Phosphor...

A series of Sm³⁺- doped NaCaBi₂(PO₄)₃ (NCBP: xSm³⁺, x = 0.02-0.14 mol) phosphors were synthesized via a conventional solid-state method. Phase purity, morphology and elemental composition were confirmed through PXRD data, FESEM images and EDAX analysis respectively. The Rietveld refinement analysis was performed and crystal structure was modelled using VESTA software. The optical energy band gap values were estimated from DRS measurements. Photoluminescence studies under 403 nm excitation revealed characteristic Sm³⁺ emissions at 563, 600, 647, and 707 nm (⁴G_5/2 → ⁶H_J).The emission intensity increased with Sm³⁺ concentration up to x = 0.08 mol, beyond which concentration quenching occurred due to non-radiative energy transfer predominantly through dipole-dipole interactions among Sm³⁺ ions. Lifetime measurements for the 600 nm emission revealed a systematic decrease in decay lifetime with increasing Sm³⁺ doping, supporting the observed quenching mechanism.The optimized composition (x = 0.08 mol) exhibited good thermal stability. The temperature dependent luminescence lifetime of the NCBP:0.08Sm³⁺ phosphor was measured under excitation at 403 nm and emission at 600 nm showed that the relative sensitivity is increasing from 0.21% °C^- 1 at 30 °C to 0.35% °C^- 1 at 210 °C. The CIE coordinates (0.590, 0.408) and low CCT (1647 K) confirmed efficient orange-red emission of the prepared sample. The internal quantum efficiency of the optimum phosphor was measured to be 33.32%. The calculated Judd-Ofelt intensity parameters confirm the low local symmetry and high covalency of the environment within the lattice, resulting in efficient radiative transitions. These results highlight the potential of NCBP: Sm³⁺ as a multifunctional phosphor for warm white solid-state lighting and temperature-sensing applications.