High-performance multifunctional NIR phosphor K2NaAlF6:Mn4+,Cr3+ for pc-LED and X-ray imaging via efficient energy transfer

The development of efficient and thermally stable near-infrared (NIR) phosphors is crucial for advancing next-generation smart NIR lighting sources, yet remains a formidable challenge. Herein, we report a high-performance K 2 NaAlF 6 :Mn 4+ ,Cr 3+ phosphor engineered via an efficient energy transfer strategy. The optimized phosphor exhibits a dominant NIR emission peak at 725 nm and achieves an exceptional energy transfer efficiency of 87.5 % from Mn 4+ to Cr 3+ . This efficient energy transfer, combined with the enhanced Cr 3+ absorption, contributes to a 91 % enhancement in NIR emission intensity and an increase in internal quantum efficiency from 74.0 % to 82.7 %. Meanwhile, the thermal stability is also significantly improved, with the co-doping sample retaining 83.4 % of its emission intensity at 425 K compared with 73.6 % for the singly Cr 3+ -doped counterpart, which is attributed to the enhanced lattice rigidity and the energy transfer process induced by Mn 4+ doping. A NIR phosphor-converted light-emitting diode (NIR pc-LED) fabricated with this phosphor and a blue chip demonstrates outstanding performance in applications of bioimaging, non-destructive testing and night vision imaging. Furthermore, its outstanding scintillation properties also enable high-resolution X-ray imaging. This work establishes a feasible design strategy for developing advanced multifunctional NIR luminescent materials that simultaneously achieve high efficiency and excellent thermal stability.