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

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