Concentration-Quenching-Suppressed Eu³⁺-Activated Ba₃Lu₂B₆O₁₅ Orange-Red-Emitting Phosphors via One-Dimensional Structural Confinement for Thermally Stable White LEDs

Conventional Eu³⁺-activated phosphors often suffer from severe concentration quenching at high doping levels, significantly limiting their achievable brightness and efficiency. Furthermore, achieving both high color purity and strong emission intensity in the orange-red region remains challenging. In this context, we report the successful synthesis of Eu³⁺-activated Ba₃Lu₂B₆O₁₅ phosphors via a multistep solid-state reaction under ambient conditions, exhibiting intense reddish-orange emission. Upon near-ultraviolet excitation at 398 nm, the phosphors exhibited dominant emission at 593 nm with a long decay time (about 4.1 ms), attributed to the magnetic dipole-allowed ⁵D₀ → ⁷F₁ transition of Eu³⁺ ions occupying inversion-symmetric Lu³⁺ lattice sites. Remarkably, concentration quenching of Eu³⁺ luminescence in Ba₃Lu_{2(1-<i>x</i>)}Eu_2<i>x</i>B₆O₁₅ was completely suppressed even at 70 mol % Eu³⁺ doping (<i>x</i> = 0.70), which can be understood from the unique one-dimensional chain-like architecture of the host lattice that restricts inter-Eu³⁺-ion energy migration to defect states. The as-synthesized Ba₃Lu_0.6Eu_1.4B₆O₁₅ composition demonstrated an internal quantum efficiency of ∼53%, coupled with superior color purity (97.5%) as evidenced by CIE coordinates of (0.605, 0.387). Furthermore, the material displayed outstanding thermal stability, retaining ∼98% of its room-temperature emission intensity at 450 K. These combined attributes position Ba₃Lu₂B₆O₁₅:Eu³⁺ as a promising phosphor for next-generation warm-white LEDs.