Eu3+and Li+ Co-doped SmCa4O(BO3)3 phosphors: Negative thermal quenching and photoluminescence properties

Abstract

Eu3 +-doped SmCa4O(BO3)3 (SCOB:Eu3+) phosphors, with and without Li+ co-doping, were synthesized via a solgel combustion method and analysed for their structural and photoluminescence (PL) properties. X-ray diffraction and Rietveld refinement confirmed the monoclinic structure of the host lattice, showing that Eu3 + ions preferentially substitute Sm3 + rather than Cat+, as evidenced by negligible lattice parameter variations. Quantitative analysis using the Scherrer and Williamson-Hall methods revealed reductions in crystallite size and increased lattice strain upon doping, with Li+ co-doping stabilizing the lattice and enhancing crystallinity. Li+ co- doping significantly enhances the 611 nm red emission in Eu3 +-doped SCOB by reducing non-radiative losses, improving energy transfer efficiency, and modifying the local crystal field to favor radiative recombination. PL measurements demonstrated intense 611 nm emission (5D0-*7F2 transition) and secondary emission at 823 nm (5D0-*7F6 transition), highlighting the unique capability of the SCOB host to support magnetic dipole transitions. Bidirectional energy transfer between Eu3 + and Sm3 + ions was observed under varying excitation wavelengths, emphasizing the dynamic nature of luminescence. CIE chromaticity analysis confirmed the tunable orange-to-red emission under varying excitation wavelengths, with Li+ co-doping shifting the chromaticity coordinates further into the red region, optimizing the material for warm white LEDs. Temperature-dependent PL measurements demonstrated negative thermal quenching, where emission intensity increased with rising temperatures, showcasing the thermal stability of SCOB:Eu3 +. The critical distance (Ra = 19.30 & Aring;) for energy transfer indicated that energy migration predominantly occurs through electric multipolar interactions. SCOB:Eu3 + phosphor enhanced PL lifetime (1.18 ms), indicating high radiative efficiency and reduced non-radiative losses. These findings highlight the dual role of Li+ co-doping in stabilizing the lattice and enhancing photoluminescence properties, establishing SCOB:Eu3 + and SCOB:Eu3 +,Li+ phosphors as promising candidates for thermally stable, high-efficiency red-emitting devices in solid-state lighting and photonic applications.