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 Ba3Lu2(1-x)Eu2xB6O15 was completely suppressed even at 70 mol % Eu3+ doping (x = 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 Ba3Lu0.6Eu1.4B6O15 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.