NIR-II luminescence and X-ray induced UV luminescence from Ce3+, Nd3+ co-doped NaLuF4 phosphors

Owning to exceptional optical and physicochemical properties, lanthanide-doped inorganic dual-mode luminescence materials are regarded as promising platform for multifunctional applications. Herein, a facile hydrothermal method is used to integrate Ce3+ and Nd3+ ions co-doped NaLuF4 phosphors, achieving dual-mode with ultraviolet (UV) and the second near-infrared (NIR-II) luminescence from single particles under two excitation sources. Higher NaF/LnCl3 ratio can not only promote the crystal phase transformation from cubic to hexagonal and the shape evolution from nanoparticles to microprisms, but also promote the UV and NIR-II luminescence properties of NaLuF4:Ce3+, Nd3+ phosphors. Upon irradiation with X-ray, Ce3+ and Nd3+ ions co-doped NaLuF4 phosphors exhibit strong broad band UV emission due to 5d→4f transition emission of Ce3+. Under 808 nm NIR excitation, the phosphors give NIR-II emission with two peaks at around 1060 nm and 1340 nm, which are attributed to the 4F3/2→4I11/2 and 4F3/2→4I13/2 electron transitions of Nd3+ ions respectively. Furthermore, the possible emission and energy transfer mechanism between Ce3+ and Nd3+ under the excitation of X-ray and 808 nm laser are discussed in details. The above results not only pave the way for future research of dual-mode luminescent materials, but also endow such materials with potential bio-applications for deep tissue bioimaging and therapy.