Creating a Green-Emitting Phosphor through Selective Rare-Earth Site Preference in NaBaB₉O₁₅:Eu²⁺

Abstract

Highly efficient, thermally stable phosphors excited by blue LEDs are crucial for energy-efficient light bulbs and modern display applications. These materials are a central component in these devices, and here one of the first Eu2+-substituted green-emitting borate phosphors is demonstrated. The green emission in NaBaB9O15:Eu2+ stems from Eu2+ occupying the smaller [NaO6] polyhedron instead of the larger [BaO9] polyhedron. This preferential substitution is identified by using quantum mechanical calculations and supported by high-resolution synchrotron X-ray powder diffraction and photoluminescence data. The resulting green emission peak is centered at 515 nm with a quantum yield of >80% (λex = 430 nm). This phosphor also exhibits negligible thermal quenching up to 650 K due to the wide bandgap, high connectivity of the rigid NaBaB9O15 crystal structure, and the depopulation of trap states stemming from the aliovalent rare-earth substitution. Fabricating two blue light pumped LED prototypes with NaBaB9O15:Eu2+ as the green component and a second red-emitting phosphor demonstrates this novel material’s capabilities in both display and warm white lighting formats. Alongside the outstanding optical properties, the accessible synthetic conditions and cost-effective starting materials suggest the remarkable potential of NaBaB9O15:Eu2+ in next-generation LED-based lighting or display systems.