Energy Transfer Engineering Enables Efficient Near‐Infrared Luminescence and Zero‐Thermal‐Quenching in GAGG: Fe 3+ , Yb 3+ Phosphors

In recent years, Fe 3+ ‐activated near‐infrared (NIR) phosphors have made significant progress, but achieving broadband emission with high efficiency and high thermal stability remains a daunting challenge. A series of novel garnet‐type Gd 3 Al 4 GaO 12 (GAGG) phosphors with Fe 3+ single‐doped and Fe 3+ /Yb 3 + co‐doped were synthesized by the high‐temperature solid‐state method. Among them, GAGG: 0.01Fe 3+ exhibits intense broadband emission centered at 786 nm (650–1000 nm), lying predominantly in the NIR‐I region, upon 254 nm excitation, achieving a photoluminescence quantum yield (PLQY) as high as 82.6% and retaining 89% of its room‐temperature intensity at 420 K. Notably, introducing Yb 3+ establishes an efficient energy‐transfer pathway that extends the overall emission response into the NIR‐II region, with measurable emission reaching approximately 1150 nm, while boosting the PLQY to 90.1%. Leveraging the Stark level splitting and thermal population effects of Yb 3+ , the anomalous emission enhancement in the 900–1010 nm region compensates for Fe 3+ thermal quenching, enabling the GAGG: 0.01Fe 3+ , 0.15Yb 3+ phosphor to achieve zero thermal quenching with 100.1% intensity retention at 420 K. The results show that energy transfer engineering provides an effective strategy for developing high‐performance Fe 3+ ‐activated NIR materials with zero thermal quenching, offering promising applications in anti‐counterfeiting, night‐vision illumination, and non‐destructive testing.