Achieving Thermally Stable YAl_3–<i>x</i>Ga_<i>x</i>(BO₃)₄:Cr³⁺ Near-Infrared Emitting Phosphors via Chemical Substitution for Plant Growth LEDs

Indoor plant cultivation has been receiving increased attention due to concerns about sustainable agricultural production. Phosphor-converted light-emitting diodes (pc-LEDs) offer substantial promise as lighting solutions for regulating plant growth. However, the quest for high-performance phosphors with precise responsiveness to far-red phytochromes poses a challenge. Our study proposes a chemical substitution strategy to develop near-infrared (NIR) phosphors, YAl_3-<i>x</i>Ga_<i>x</i>(BO₃)₄:Cr³⁺. Benefiting from Ga³⁺ replacement of Al³⁺, a red shift in the NIR emission of YAl_3-<i>x</i>Ga_<i>x</i>(BO₃)₄:Cr³⁺ is realized to attain a good alignment with far-red phytochrome absorption centering at 730 nm. The optimized YAl_2.5Ga_0.5(BO₃)₄:Cr³⁺ exhibits a favorable quantum yield of 71.8% and robust thermal stability of 101.0%@423 K, owing to local structural distortion and thermal repopulation caused by Ga³⁺ incorporation. The fabricated pc-LED combined with the phosphor yields an NIR output power of 40.9 mW and a photoelectric conversion efficiency of 15.4% at 100 mA. Plant growth experiments demonstrate that under NIR illumination from the devices, the average lengths of pea roots and stems gain 127 and 225% promotion, respectively, further highlighting the potential of YAl_2.5Ga_0.5(BO₃)₄:Cr³⁺ phosphors for applications in plant cultivation.