Ba2+ co-doping enhances phase purity and enables narrow–band green emission in a Sr5/6Li17/6Al7/6O4:Eu2+ phosphor for backlight display applications

Abstract

Alkaline earth lithoaluminates with the UCr₄C₄-type structure have demonstrated considerable potential in achieving narrow-band emissions from Eu²⁺. However, obtaining single-phase powder samples with green-emitting phosphor characteristics remains challenging. In this study, we address this issue by co-doping Ba²⁺ into the novel UCr₄C₄-type system Sr_5/6−x−yBa_xLi_17/6Al_7/6O₄:yEu²⁺, which significantly enhances phase purity and structural homogeneity. This approach not only reduces the emission bandwidth from 66 nm (2241 cm⁻¹) to 51 nm (1830 cm⁻¹) but also induces a blue shift to 529 nm, fine-tuning the emission into the desired deep green region. Through detailed mechanistic studies—including low-temperature spectroscopy and luminescence decay analysis—we identify the presence of multiple Eu²⁺ emission centers associated with distinct Sr²⁺ sites. Ba²⁺ doping is shown to promote dominant Eu²⁺ emission in the green spectral region, thereby facilitating spectral narrowing. The optimized phosphor achieves a high absorption efficiency of 64.6% and an external quantum yield of 22.2%. When integrated into a white LED prototype, it enables a color gamut covering 97.6% of the NTSC (National Television System Committee) standard, outperforming a commercial β-SiAlON:Eu²⁺-based device. This study provides an effective cationic co-doping strategy for designing high-performance narrow-band oxide phosphors and highlights a promising candidate for next-generation display technologies.