Ultrabroad Short-Wave Infrared Emission Enabled by Chemical Unit Cosubstitution of Ni²⁺ in Fluoride K₂LiCrF₆:Ni²⁺ for Infrared Spectroscopy Applications

Short-wave infrared (SWIR) light sources have received widespread attention for their reduced scattering effects, enhanced signal-to-noise ratios, and better substance absorption characteristics. However, the lack of broadband SWIR materials suitable for blue LED excitation hinders applications such as infrared spectroscopy quantitative analysis. Herein, K2LiCrF6:Ni2+ with chemical unit cosubstitution (2Ni2+ → Li+ + Cr3+) exhibits ultrabroadband SWIR emission at ∼1615 nm with a full width at half-maximum (fwhm) of ∼400 nm upon blue-light excitation. The compact Cr3+–Ni2+ distance (∼4 Å) enables an ultrahigh confinement energy transfer (ET) efficiency of >90%. Additionally, Cr3+ can serve as a sensitizer for rare-earth activators (Yb3+, Nd3+, Ho3+, Er3+) in this host lattice to achieve specific SWIR emissions. A phosphor film fabricated from K2LiCrF6:Ni2+ and an inorganic binder demonstrates superior spectral properties and low working temperatures. The combination of this film and blue LED yields a broadband SWIR LED with potential applications in the real-time monitoring of H2O/D2O mixture concentrations.