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

Abstract Far‐red phosphors have emerged as a desirable research hotspot owing to their critical role in promoting plant growth. Especially, Eu 3+ ions typically present the 5 D 0 → 7 F 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 Eu 3+ remains challenging due to weak 5 D 0 → 7 F 4 transition and concentration quenching. The study constructs two anomalously efficient far‐red garnet phosphors A 3 Sc 2 C 3 O 12 (A = Y 3+ , Gd 3+ . C = Al 3+ , Ga 3+ ):Eu 3+ . A high‐resolution STEM measurement equipped with an aberration corrector provides the direct proofs for both the [EuO 8 ] configuration‐dependent strong 5 D 0 → 7 F 4 and the origin of high quenching concentration. Excitedly, a two‐component substitution (replacing Y 3+ ‐Al 3+ with Gd 3+ ‐Ga 3+ ) triggers a near‐unity internal quantum efficiency (IQE = 99.01%) and high external quantum efficiency (EQE = 38.73%) in Gd 3 Sc 2 Ga 3 O 12 :60%Eu 3+ , resulting from the effective modulation of 5 D 0 → 7 F 4 / 7 F 2 transitions. A far‐red LEDs device based on Gd 3 Sc 2 Ga 3 O 12 :60%Eu 3+ 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 Eu 3+ square antiprism configuration and high quenching concentration.