Creating a Green-Emitting Phosphor through Selective Rare-Earth Site Preference in NaBaB 9 O 15 :Eu 2+

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 Eu 2+ -substituted green-emitting borate phosphors is demonstrated. The green emission in NaBaB 9 O 15:Eu 2+ stems from Eu 2+ occupying the smaller [NaO 6 ] polyhedron instead of the larger [BaO 9 ] 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% (λ ex = 430 nm). This phosphor also exhibits negligible thermal quenching up to 650 K due to the wide bandgap, high connectivity of the rigid NaBaB 9 O 15 crystal structure, and the depopulation of trap states stemming from the aliovalent rare-earth substitution. Fabricating two blue light pumped LED prototypes with NaBaB 9 O 15:Eu 2+ 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 NaBaB 9 O 15:Eu 2+ in next-generation LED-based lighting or display systems.