Advances in Fe3+-activated luminescent materials for near-infrared light sources

Fe³⁺-activated near-infrared (NIR) luminescent materials have attracted growing research interests for their tunable broadband emission and extensive application potentials in the fields of night vision, biomedical imaging, nondestructive food analysis, etc. Deep insight into the relation between crystal structure and luminescence performance plays a significant role in developing novel efficient NIR functional materials. In this review, after a brief introduction, we first discuss the mechanism of Fe³⁺ luminescence in octahedral and tetrahedral crystal fields based on the Tanabe-Sugano energy level diagram. Next, the research progress of Fe³⁺-doped NIR luminescent materials, including structure, property and potential application, is summarized, followed by the strategies to enhance NIR steady-state luminescence, persistent luminescence and mechanoluminescence performances. Then we conduct a comparison of luminescence efficiency and luminescence thermal stability of Fe³⁺-doped NIR materials. At last, we propose several challenges and outlooks in the research of Fe³⁺-activated NIR luminescent materials. This review is aimed to provide a deeper understanding of not only Fe³⁺ luminescence mechanism but also the current research progress of Fe³⁺-doped materials, so as to provide constructive strategy in the exploitation of efficient Fe³⁺-activated NIR luminescent materials.