Unlocking Advanced Near‐Infrared Luminescence Activated by Iron Ions for Versatile Applications toward a Treasure Trove of Garnet‐type Structures

The development of highly efficient and compact near‐infrared (NIR) light source technology has unlocked new prospects for miniaturization and portability in advanced NIR photonic applications, and the growing diversity of application requirements has driven the exploration and development of novel NIR materials. Here, a novel rigid garnet‐based Fe3+‐activated NIR‐emitting material Ca3Sn2Ga2GeO12 (CSGG): Fe3+ is reported. The material can produce a robust NIR emission peaking at 760 nm over a broad range of 600 to 1100 nm, and the impressive luminescence efficiency (IQE = 54.1%, EQE = 40%) and thermal stability (72%@423 K) are superior to the majority of the previously reported Fe3+‐activated systems. First‐principles calculations uncover that the efficient NIR luminescence mechanism from tetrahedra Fe3+ is possibly attributed to the lower concentrations of iron occupation at octahedral sites and the quenching of luminescence from octahedral Fe3+ by 2T2 intermediate energy level. Finally, the multifunctional application potential of the developed materials in advanced NIR photonic was also demonstrated. These findings not only deepen the understanding of the photophysical processes in the Fe3+‐activated system, but also reveal the effectiveness of Fe3+ as an NIR‐emitter ion, providing valuable insights for the design of new NIR materials and the advancement of smart applications.