Oxygen-mediated structural optimization in SrGa2S4:Eu2+: a dual enhancement of thermal stability and luminescent intensity
The Eu 2+ -activated sulfide green phosphor SrGa 2 S 4 :Eu 2+ has attracted significant attention for its narrow emission band, high color purity, and strong emission intensity, making it a promising candidate to replace β -SiAlON:Eu 2+ in white light-emitting diode (LED) backlights for ultra-wide-color-gamut liquid crystal displays. However, the practical application of SrGa 2 S 4 :Eu 2+ is limited by its poor thermal stability, which results in diminished luminescence at high temperatures. This study proposes a host structure optimization strategy through partial O-S substitution to enhance the thermal stability. Density functional theory (DFT) analysis reveals that oxygen doping stabilizes the Eu 2+ centers and increases the bandgap of the SrGa 2 S 4 host. A series of Sr 1– x Ga 2 S 4– y O y :Eu 2+ phosphors were synthesized via a high-temperature solid-state reaction method. The effects of O-S substitution on crystal structure and luminescent properties were systematically investigated through fluorescence decay curves, diffuse reflectance spectra, and polyhedral distortion analysis. Structural refinement demonstrates that O doping increases the distortion of Ga-S 4 tetrahedra, amplifying the repulsion between Eu 2+ luminescent centers and anions, thereby widening the bandgap and improving thermal stability. With the increasing of O content, the thermal stability progressively enhances. The luminescence intensity of Sr 0.95 Ga 2 S 3.5 O 0.5 :0.05Eu 2+ at 150 °C improves from 55.4% to 76.5% compared to Sr 0.95 Ga 2 S 4 :0.05Eu 2+ . The optimized phosphor exhibits a green emission peak at 535 nm under 460 nm excitation, with a full width at half maximum (FWHM) of 48 nm, and 140% of the room-temperature emission intensity of commercial β -SiAlON:Eu 2+ . This work provides a feasible new strategy to enhance the thermal stability of sulfide-based green phosphors for advanced optoelectronic applications.
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