Breaking the Absorption-Efficiency Paradigm: 270% EQE Gain in Cr3+-Doped Phosphors via Crystal Field Engineering

Near-infrared (NIR) phosphor-converted LEDs (pc-LEDs) are critical for smart agriculture and night vision, but their efficiency is limited by low external quantum efficiency (EQE) of phosphors. Herein, the introduction of Al 3+ ions via chemical substitution increased the EQE of the GdGa 2.85 (BO 3 ) 4 :0.15Cr 3+ NIR phosphor from 8.3% to 30.7% (a relative increase of 270%). Importantly, an “absorption-efficiency decoupling” paradigm is identified: while the Al 3+ substitution reduces the absorbance, confirmed by Density Functional Theory, diffuse reflectance spectra, and X-ray photoelectron spectroscopy, the quantum efficiency is significantly increased. Theoretical analyses and spectroscopic evidence suggest that the superior EQE gain stems from Al 3+ -induced crystal field enhancement and subsequent energy level remodeling. This remodeling optimizes the Cr 3+ excited state dynamics by suppressing the non-radiative transitions pathway and increasing the radiative transitions, thus overcoming the detrimental effects of absorption reduction. The optimized phosphor, combined with a blue LED chip, produced an NIR pc-LED achieving 41.7 mW output power and 15.7% photoelectric efficiency at 100 mA. The device successfully demonstrated potential for precision agriculture and night vision. This work provides novel insight into “absorption-efficiency decoupling” and offers a new design strategy for efficient Cr 3+ -doped NIR phosphors.