Efficient Blue‐Violet‐Light‐Excitable Near‐Infrared Luminescence in Fe 3+ Activated Phosphors With High Internal Quantum Efficiency and Superior Thermal Stability

ABSTRACT Trivalent iron (Fe 3+ ) has attracted extensive attention as an environmentally friendly and cost‐effective near‐infrared (NIR) emitting activator ion. However, its weak absorption in the blue‐violet light region and relatively low internal quantum efficiency (IQE) have long constrained its practical applications. In this study, a series of Ca 3 Ga 2‐x Sn 2 GeO 12 : xFe 3+ NIR phosphors with a cubic garnet structure was successfully synthesized via a high‐temperature solid‐state reaction method. Efficient NIR luminescence under long‐wave ultraviolet (LWUV) chip excitation was observed, exhibiting broadband NIR emission centered at 740 nm. Remarkably, the phosphor achieves an internal quantum efficiency (IQE) as high as 82.3%, representing the highest efficiency reported to date for Fe 3+ ‐doped NIR phosphors under blue‐violet light excitation. Temperature‐dependent luminescence analysis reveals excellent thermal stability: the integrated emission intensity at 423 K retains 67.06% of its initial value at room temperature. A prototype NIR phosphor‐converted LED (pc‐LED) device fabricated with the studied phosphor and a commercial chip (400–410 nm) exhibits stable electroluminescence performance and good output power conversion. In summary, the Ca 3 Ga 2‐x Sn 2 GeO 12 : xFe 3+ phosphor, with its efficient luminescence under blue‐violet light excitation, outstanding thermal stability, and temperature‐independent emission peak position, demonstrates significant application potential in the field of high‐efficiency and high‐stability NIR light sources.