High‐Temperature Negative‐Thermal‐Quenching in Broadband NIR Light‐Emitting ScF₃:Cr³⁺ Phosphors

Abstract Broadband near‐infrared (NIR) phosphors with superior thermal stability are critical enablers of high‐power NIR pc‐LEDs, emerging as essential light sources for NIR spectroscopy applications. In this work, an unprecedented high‐temperature negative thermal quenching (NTQ) phenomenon persisting up to 500 K is reported in Cr 3+ ‐activated ScF 3 phosphors, which emit broadband NIR emission in the 700–1200 nm (λ em = 850 nm, FWHM = 132 nm). The theoretical calculations employing the Exchange‐Charge Model (EMC) for crystal field parameters of Cr 3+ ions in [ScF 6 ] octahedral sites remain in perfect agreement with the experimental results. Critically, Yb 3+ ‐codoping enables efficient Cr 3+ → Yb 3+ energy transfer, achieving substantial spectral broadening (FWHM = 254 nm) and significantly enhanced thermal stability. The temperature‐dependent X‐ray diffraction (XRD) and theoretical calculations reveal that anisotropic F‐atom vibrations drive negative thermal expansion (NTE) in cubic ScF 3 , distorting [ScF 6 ] octahedra. It is demonstrated that synergistic electron‐phonon coupling and NTE‐driven structural dynamics underpin the superior thermal stability of NIR emission. These findings establish a design paradigm for new broadband NIR phosphors with outstanding thermal stability for next‐generation high‐power NIR pc‐LED applications.