Structural Rigidity Control via Non-Primary Lattice Substitution toward Thermally Stable Cr³⁺-Doped Near-Infrared Phosphors for pc-LED Applications

The performance of near-infrared phosphor-converted light-emitting diodes (NIR pc-LEDs) is dependent on the performance of the phosphor applied to the LED surface; however, the challenges of low external quantum efficiency (EQE) and insufficient thermal stability of NIR phosphors remain. Herein, we propose a novel nonprimary lattice substitution strategy (Y³⁺ → Gd³⁺) to enhance the structural rigidity of Gd_1-<i>y</i>Al_3-<i>x</i>(BO₃)₄:<i>x</i>Cr³⁺,<i>y</i>Y³⁺ phosphor. Unlike conventional host-site substitutions, this approach induces compressive strain on the [Al/CrO₆] octahedron via a Gd³⁺/Y³⁺ size mismatch, thereby increasing bond energy and suppressing electron-phonon coupling. The optimized phosphor emits NIR light in the range of 650-1000 nm under 430 nm excitation, with the thermal stability (@423 K) improving from 73.8% to 92.5%, and the EQE is effectively improved. A prototype NIR pc-LEDs fabricated with a 450 nm chip delivers 40.4 mW output power at 100 mA with 14.7% photoelectric efficiency, demonstrating ultralow quenching rate (<6% intensity loss after 30 days operation). The NIR pc-LEDs was used in butter lettuce cultivation experiments, and the results showed that the growth pattern of butter lettuce changed significantly and the biomass increased significantly (28.9%). In addition, the potential for application in organic detection was demonstrated. This work provides a lattice engineering route to design stable NIR phosphors for multifunctional photovoltaic applications.