Influence of Li+-Induced Lattice Distortion on Luminescence Properties and Thermometric Sensitivity in Sm3+-Doped Sodium Barium Bismuth phosphate: A Judd–Ofelt Analysis
摘要
Developing high-efficiency orange-red light emitting phosphors is vital for progress in solid-state lighting and optical sensing applications. In this work, Sm3+-doped and Li+ co-doped NaBaBi2(PO4)3 (NBBP) phosphors were synthesized via solid-state reaction and evaluated for structural, morphological, luminescent, and thermometric properties. XRD confirmed a pure cubic phase (I-43d) with no secondary impurities, while bandgap values increased slightly from 4.11 eV (undoped) to 4.14 eV (Sm3+) and 4.15 eV (Li⁺ co-doped). Photoluminescence spectra revealed intense orange–red emission, dominated by the hypersensitive transition at 598 nm. Judd–Ofelt analysis yielded intensity parameters (Ω2, Ω4, Ω6), reflecting strong asymmetry and moderate covalency around the Sm3+ ions, which favoured an enhanced electric dipole transition. Li⁺ incorporation improved emission intensity due to the local field distortion but resulted in reduced lifetimes (1.754 ms) and decreased thermal stability (84% → 79% emission retention at 423 K). The concentration quenching mechanism was identified as dipole-dipole interaction, with a critical distance of 23.45 Å. The chromaticity analysis placed the CIE coordinates close to the orange–red region, demonstrating high color purity and suitability for warm-light applications. The optical thermometry confirmed reproducible multi-modal sensitivity: FIR-based relative sensitivity reached 10.8 × 10− 2% K− 1 (Sm3+) and 21.0 × 10− 2% K− 1 (Li⁺ co-doped) at 483 K; FWHM-based sensitivity values decreased to 7.6 × 10− 2% K− 1 (Sm3+) and 5.2 × 10− 2% K− 1 at 483 K; while lifetime-based sensitivities were 1.2 × 10− 2% K− 1 (Sm3+) and 0.61 × 10− 2% K− 1 (Li⁺ co-doped) at 303 K. These results highlight the NBBP host as a robust platform for advanced pc-WLEDs and luminescent thermometry.