Synthesis of a novel broadband near-infrared fluoride phosphor with nearly 100% internal quantum efficiency using a cationic substitution strategy†

Broadband near-infrared (NIR) phosphors are essential for assembling portable NIR light sources. However, the development of efficient and stable broadband NIR phosphors remains a major challenge. This work designed an ultra-high efficient NIR-emitting Cs₂KSc_0.83Ga_0.1F₆:0.07Cr³⁺ phosphor by substituting Sc³⁺ with a Ga³⁺ ion. This cationic substitution strategy enables the internal quantum efficiency of NIR emission to reach a staggering high of 98.56%, almost 100%, along with excellent thermal quenching resistance (I_423K = 62.4%). The Ga³⁺ → Sc³⁺ replacement lowers the local site symmetry and overcomes the parity selection rule, rendering the electronic transitions with much larger oscillator strength and thus improved optical properties. The NIR phosphor conversion light emitting diode (pc-LED) based on Cs₂KSc_0.83Ga_0.1F₆:0.07Cr³⁺ demonstrated a premium photoelectric conversion efficiency of 31.46% at 40 mA. The potential of the pc-LED as a light source for night vision and anti-counterfeiting has also been demonstrated. These results highlight the phosphor's performance improvement via a cationic substitution strategy and demonstrate the practical application potential of the broadband Cr³⁺-based NIR phosphor in the design of high-efficiency devices.