Controlling Eu2+ Substitution towards a Narrow-Band Green-Emitting Borate Phosphor NaBaB9O15:Eu2+

Highly efficient, thermally stable, narrow-band phosphors that can be excited by a blue LED chip are crucial for energy-efficient light bulbs and display lighting. Here, a rare narrow-band, green-emitting phosphor based on the compound NaBaB₉O₁₅:Eu²⁺ is demonstrated. The emission peak is centered at 515 nm with a full-width at half-maximum (fwhm) of 61 nm (2294 cm⁻¹), and a photoluminescence quantum yield of >80% using blue or near-UV LED excitation. This borate’s remarkable green emission stems from Eu²⁺ substituting on the smaller [NaO₆] polyhedron instead of the larger and more favorable [BaO₉] polyhedron. The phosphor also exhibits negligible thermal quenching up to 650 K owing to the wide band gap, high connectivity of the rigid NaBaB₉O₁₅ crystal structure, and the depopulation of trap-states. This combination of optical properties and its straightforward synthesis conditions makes NaBaB₉O₁₅:Eu²⁺ an ideal green phosphor for next-generation LED-based lighting or display systems.