High‐Efficiency FWHM‐Variable NIR II Phosphor Mg ₄ Al _4.5 Ga _2.45 B _1.05 O ₁₆ : Cr ³⁺ with Excellent Thermal Stability

Abstract A series of high‐performance NIR phosphors Mg ₄ Al _4.5 Ga _2.45 B _1.05 O ₁₆ : xCr ³⁺ (MAGBO: xCr ³⁺ ) with high internal quantum efficiency (IQE, 95.7%), excellent thermal stability (87.5% at 373 K and 73% at 423 K), and various, especially large FWHM (250 nm) are designed for wireless communication as excited by near‐ultraviolet LEDs. The emission is adjusted from 600–950 to 670–1370 nm with a peak at 703–878 nm and a narrow band (FWHM = 49 nm) to an ultra‐broadband (FWHM = 250 nm) as the Cr ³⁺ ions increase. The variations in FWHM and emissions at low temperatures verify three emission centers. Notably, the energy transfer from the high‐energy Cr ³⁺ center to the low‐energy Cr ³⁺ ions in MAGBO is systematically investigated using the temperature‐dependent emission and the decay curves. An NIR pc‐LED device combined with the MAGBO:0.15Cr ³⁺ phosphor with a 395 nm chip demonstrates stable NIR emission under different driving currents. The photoelectric conversion efficiency is 15.8% at 20 mA, and an output power of 120 mW is achieved at 500 mA. The fabricated pc‐LED device is successfully applied for rapid imaging of hand and fist veins, night vision of objects, and encrypted information reading, especially in wireless communication.