Thermal stability and quantum efficiency improvement of Cr 3+ -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 (A 3 B 2 C 3 O 12 ) Lu 2- x CaAl 3.99 Cr 0.01 SiO 12 : x Gd/La and Lu 2 CaAl 3.99- y Cr 0.01 SiO 12 : y Sc/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 4 T 2 → 4 A 2 transition and diminishing the narrow-peak emission of the forbidden 2 E → 4 A 2 transition. As expected, NIR phosphors, exemplified by Lu 1.7 CaAl 3.99 Cr 0.01 SiO 12 :0.3Gd and Lu 2 CaAl 3.49 Cr 0.01 SiO 12 :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.