Highly efficient and water-resistant BaGa₄S₇:Eu²⁺ phosphor prepared by a self-reduction method

The development of eco-friendly luminescent materials is imperative for the advancement of phosphor-based technologies. This study corroborates the self-reduction of Eu³⁺ to Eu²⁺ through analyses utilizing photoluminescence (PL), excitation spectroscopy (PLE), and X-ray photoelectron spectroscopy (XPS). Density functional theory (DFT) calculations demonstrate that Eu²⁺ ions can efficaciously substitute Ba²⁺ ions within the BaGa₄S₇ lattice, preserving its structural integrity. Upon blue light excitation, BaGa₄S₇:Eu²⁺ manifests a robust green emission attributed to Eu²⁺ ions, showcasing a peak wavelength near 526 nm. The quantum yield (QY) of BaGa₄S₇:Eu²⁺ is remarkably high, registering at 74.8 %. Moreover, the temperature-dependent luminescence properties of BaGa₄S₇:Eu²⁺ phosphor were subjected to thorough investigation. Water resistance assays indicate that the sample preserves 76 % of its initial luminous intensity following 40 days of aqueous immersion. Additionally, BaGa₄S₇:Eu²⁺ based phosphor-converted white light-emitting diodes (WLEDs) demonstrate emission of high-quality white light. This unique water-resistant green emission sulfide phosphor is expected to have potential applications in lighting fields.