Trivalent chromium ion-activated broadband near-infrared (NIR) luminescence materials have shown great application prospects as next-generation NIR light sources, but improvement of the luminescence efficiency remains a challenge. Herein, novel K2LiScF6:Cr3+ and K2LiScF6:Cr3+/Mn4+ broadband fluoride NIR phosphors are designed and prepared by a combination of hydrothermal and cation exchange methods for the first time. The crystal structure and photoluminescence (PL) properties of K2LiScF6:Cr3+ are studied in detail, which shows strong absorption in the blue light region (λex = 432 nm) and broadband NIR emission (λem = 770 nm) with a PL quantum efficiency of 77.6%. More importantly, the NIR emission of Cr3+ can be enhanced by co-doping with Mn4+, which may provide an alternative way for improving the PL intensity of Cr3+-activated broadband NIR phosphors. Finally, a NIR phosphor-converted LED (pc-LED) device is fabricated using the as-prepared NIR phosphor and its application in bio-imaging and night vision has been evaluated.