Super Broadband Near‐Infrared Solid Solution Phosphors with Adjustable Peak Wavelengths from 1165 to 875 nm for NIR Spectroscopy Applications

Abstract Cr³⁺‐activated near‐infrared (NIR) phosphors have attracted wide attention owing to applications in phosphor‐converted light‐emitting diodes (pc‐LED) for spectroscopy. Because a broader spectrum covers more information to detect, the width of the spectrum is an important parameter to consider. Here, the blue LED excitable ultra‐broadband Cr³⁺‐activated LiInGeO₄ phosphors, which exhibit unprecedented long‐wavelength NIR emission with a wide full‐width at half maximum (FWHM) of 305 nm, are developed. The overall emission tuning from 1165 to 875 nm with broadened FWHM from 305 to 508 nm is realized through designing continuous solid solution hosts of LiIn_1−zSc_zGeO₄/(LiIn)_1−yMg_2yGeO₄ and finite solid solution hosts of (LiIn)_1−yZn_2yGeO₄:Cr³⁺. The observation of such long‐wavelength NIR from Cr³⁺ not Cr⁴⁺ is studied and confirmed by electron paramagnetic resonance, X‐ray absorption near‐edge structure, and steady‐/transient‐state photoluminescence. The formation of finite solid solutions induces the change in the local structure of Cr³⁺ that ultimately leads to the observation of super broadband (FWHM = 508 nm) luminescence. The luminescence mechanism is discussed in this study. Finally, this study demonstrates that the as‐synthesized phosphors with tunable NIR luminescence can be well used in NIR pc‐LEDs for spectroscopy detection.