The synergy of structural constraints and lattice engineering endows Ba _2.80 Sr _0.20 Sc(BO ₂ ) ₉ : Eu ³⁺ phosphor with a concentration‐free quenching effect and far‐red emission

Abstract Eu 3+ ‐activated red phosphors are popular for their classic 5 D 0 → 7 F J ( J = 0, 1, 2, 3, 4) emission characteristics. However, the weak emission of the 5 D 0 → 7 F 4 transition and the concentration quenching caused by energy migration have become the main obstacles to achieving strong far‐red emission. Herein, we report a novel Ba 3 Sc 1‐ x (BO 2 ) 9 : x Eu 3+ phosphor that simultaneously enhances 5 D 0 → 7 F 4 emission and suppresses quenching through size confinement and low phonon energy. A Sr 2+ → Ba 2+ substitution strategy optimizes luminescence, achieving 1.56‐fold intensity enhancement and improved quantum efficiency (IQE: 83% → 92%; EQE: 38% → 40%). The improvement mechanism was revealed through the local coordination distortion of Eu 3+ and the change of the band gap when Sr and Ba coexist. Structural analysis reveals enhanced thermal stability (423 K: 86% → 97%; 483 K: 78% → 95%) originates from increased lattice rigidity. Abnormal thermal quenching (303–363 K) is white light‐emitting diodes (WLEDs) device prepared based on Ba 2.80 Sr 0.20 Eu(BO 2 ) 9 phosphor shows a color temperature of 4532 K and a color rendering index of 91.6. This article also explores three applications of plant growth, latent fingerprint visualization, and anti‐ counterfeiting QR code. This finding provides a reference for further exploring the design of high concentration quenching and efficient far‐red emitting phosphors.