Synergetic Contributions of High Quenching Concentration and Tuned Square Antiprism Geometry Boosting Far-Red Emission of Eu³⁺ with Near-Unit Efficiency

Far-red phosphors have emerged as a desirable research hotspot owing to their critical role in promoting plant growth. Especially, Eu³⁺ ions typically present the ⁵D₀→⁷F_J (J = 0, 1, 2, 3, 4) transitions, which overlap with the far-red light required for plant photosynthesis. However, achieving high-efficiency far-red emission of Eu³⁺ remains challenging due to weak ⁵D₀→⁷F₄ transition and concentration quenching. The study constructs two anomalously efficient far-red garnet phosphors A₃Sc₂C₃O₁₂ (A = Y³⁺, Gd³⁺. C = Al³⁺, Ga³⁺):Eu³⁺. A high-resolution STEM measurement equipped with an aberration corrector provides the direct proofs for both the [EuO₈] configuration-dependent strong ⁵D₀→⁷F₄ and the origin of high quenching concentration. Excitedly, a two-component substitution (replacing Y³⁺-Al³⁺ with Gd³⁺-Ga³⁺) triggers a near-unity internal quantum efficiency (IQE = 99.01%) and high external quantum efficiency (EQE = 38.73%) in Gd₃Sc₂Ga₃O₁₂:60%Eu³⁺, resulting from the effective modulation of ⁵D₀→⁷F₄/⁷F₂ transitions. A far-red LEDs device based on Gd₃Sc₂Ga₃O₁₂:60%Eu³⁺ exhibits an output power of 113 mW at 300 mA. Subsequently, practical applications for promoting plant growth underscore the significance of these findings. This work opens a new path for the development of highly efficient far-red phosphors via the synergistic effect of Eu³⁺ square antiprism configuration and high quenching concentration.