Enhancing External Quantum Efficiency of Blue-Emitting Phosphor Ba(K)-β-Al₂O₃:Eu²⁺ by Lattice Site Engineering for Full-Spectrum Lighting

Abstract

The discovery of violet-excitable blue-emitting phosphor is a significant breakthrough for the development of phosphor-converted full-spectrum white light-emitting diodes (WLEDs). However, the application of most known violet-excitable blue-emitting phosphors is limited by their low external quantum efficiency (EQE). In this work, we reported on how the EQE values of Eu²⁺-doped Ba(K)-β-Al₂O₃ blue-emitting phosphor can be significantly improved through lattice site engineering. By partially substituting K⁺ for Ba²⁺, the Eu²⁺-occupied crystallographic site changes and the coordination polyhedron of Eu²⁺ shrinks, leading to the increase of crystal field splitting. Consequently, the excitation spectrum exhibits a continuous red shift to match the violet excitation, which enhances the PL intensity of solid solution phosphor (Ba_0.4K_1.6)_0.84Al₂₂O_35-α:0.32Eu²⁺ ((B_0.4K_1.6)_0.84AO:Eu) by 1.42 times compared to that of the end-member Ba_1.68Al₂₂O_35-α:0.32Eu²⁺ (B_1.68AO:Eu) phosphor. Correspondingly, under the 400 nm violet light excitation, the EQE of optimal blue-emitting (B_0.4K_1.6)_0.84AO:Eu phosphor is up to 53%. Additionally, the phosphor also shows excellent resistance to luminescence thermal quenching (95% at 150 °C). Finally, the WLED fabricated based on (B_0.4K_1.6)_0.84AO:Eu and commercial green and red phosphors exhibited an ultra-high color rending index with Ra = 95.5 and R1-R15 >90. This work offers guidance for tuning the spectral properties of phosphors through lattice site engineering.