Thermal stability and quantum efficiency improvement of Cr3+-activated garnet phosphors via regulating A/B sites for near-infrared LED applications

The discovery of phosphors with highly efficient broadband near-infrared emission is urgent for constructing NIR sources for various applications. Herein, we synthesized a series of near-infrared emitting garnet-type (A₃B₂C₃O₁₂) Lu_2-xCaAl_3.99Cr_0.01SiO₁₂:xGd/La and Lu₂CaAl_3.99-yCr_0.01SiO₁₂:ySc/Ga phosphors and systematically investigated the effect of A/B-site substitution on the crystal structure and luminescence properties. Structural and optical analyses revealed that the A/B-site substitution weakened the crystal field strength, further enhancing the broadband emission of the allowed ⁴T₂ → ⁴A₂transition and diminishing the narrow-peak emission of the forbidden ²E → ⁴A₂ transition. As expected, NIR phosphors, exemplified by Lu_1.7CaAl_3.99Cr_0.01SiO₁₂:0.3Gd and Lu₂CaAl_3.49Cr_0.01SiO₁₂:0.5Sc, showed outstanding thermal stabilities at 423 K (150 °C) registering values of 103.02% and 94.91%, with high quantum efficiencies of 80.48% and 85.01%, respectively. In addition, pc-LEDs with broadband NIR output and good optoelectronic properties have been realized, demonstrating the great potential of broadband NIR pc-LEDs for applications. This work not only provides a series of high-efficiency phosphors for NIR pc-LED applications, but also provides a systematic idea and an efficient method to improve the luminescence performance of garnet-type phosphors.