Decoding Balanced High-Performance in Fe ³⁺ NIR Phosphors via Site-Selectivity for Versatile Applications

The development of efficient and stable near-infrared (NIR) phosphor-converted LEDs has significantly advanced NIR photonics. However, widely reported Cr 3+ -activated NIR luminescent materials remain limited in performance and fail to satisfy the increasing demands of diverse applications. Herein, a Cr-free alternative utilizing a rigid garnet host is proposed. Through the design and synthesis of a novel Fe 3+ -activated phosphor, Ca 3 Sn 2 Ga 2 SiO 12:Fe 3+ (CSGS: Fe 3+ ), efficient broadband NIR emission centered at 770 nm and spanning 600–1100 nm is successfully realized. This material achieves an internal quantum efficiency (IQE) of 62.38% and an external quantum efficiency (EQE) of 46.56%, while maintaining 62% of its emission intensity at 423 K. Its overall balanced performance exceeds that of most reported Fe 3+ -based systems. Supported by first-principles calculations, this study systematically clarifies the electronic structure, mechanical properties, site preference, and valence stability of Fe 3+, elucidates the excited-state transition behavior, and proposes a crystal-field-induced site-selective luminescence mechanism. This work not only presents a high-performance Fe 3+ -activated NIR phosphor, but also provides theoretical insights and practical guidance for material design and optimization in solid-state lighting, nondestructive testing, and spectral analysis.