Achieving Near‐Infrared II Emission Through Energy Transfer From Cr 3+ to Ni 2+ in Gd 3 Ga 5 O 12 Host

ABSTRACT The Ni 2+ ‐activated phosphors typically show the second window of near‐infrared (NIR‐II) emission. Their quantum efficiency is insufficient due to poor absorption in the blue light region. Here, the Cr 3+ and Ni 2+ co‐activated near‐infrared Gd 3 Ga 5 O 12 (GGG) garnet phosphors were synthesized, and they show dual‐emission in the NIR‐I and NIR‐II regions within the range of 700–1700 nm. Under 460‐nm excitation, the GGG: Cr 3+ , Ni 2+ phosphor exhibits an improved NIR‐II emission peak at 1440 nm due to effective energy transfer (ET) from Cr 3+ to Ni 2+ , with a full width at half maximum (FWHM) of 270 nm at the maximum emission peak. The internal quantum efficiency of the GGG: Cr 3+ , Ni 2+ phosphor in the NIR‐I and II region (700–1700 nm) is 23.4%, while maintaining good overall thermal stability (46.15% at 423 K). Finally, by combining the GGG: Cr 3+ , Ni 2+ phosphor with a 465‐nm blue chip, a NIR pc‐LED was fabricated, demonstrating the potential applications of NIR‐II light sources in night vision and penetration. The co‐doping of Cr 3+ and Ni 2+ addresses the issue of ineffective excitation of Ni 2+ luminescence by blue light, providing a design approach for developing numerous ultra‐broadband NIR‐II pc‐LEDs based on blue LED chips.