Erbium-doped tungsten selenide nanosheets with near-infrared II emission and photothermal conversion

Two-dimensional transition metal dichalcogenides (2D TMDs) have drawn considerable attention due to their promising applications in biomedical and optoelectronic areas. However, the emission of 2D TMDs materials and devices is mostly limited from visible to the edge of near-infrared (NIR), which restricts their wide applications. Herein, we develop Er doped WSe 2 nanosheets through cation exchange and ultrasonication-assisted liquid-phase exfoliation. Thanks to the Er ions, the luminescence of 2D nanosheets can be extended to NIR II window. The emission at NIR II range can effectively penetrate several centimeters thick biological tissue. Furthermore, a series of photothermal experiments is also performed with 808 nm laser. The photothermal conversion efficiency of as-produced nanosheets is determined to be as high as 35.2%, which is greatly higher than many previous reports. It suggests that as-prepared nanosheets combining NIR II emission and highly effective photothermal conversion property may be promising as a bifunctional agent for bioimaging and photothermal therapy.