Upconverting CeO2: Yb3+/Tm3+ hollow nanospheres for photo-thermal sterilization and deep-tissue imaging in the first biological window

The up-conversion emissions falling within the first biological window (NIR-I, 650-1000 nm) are very important in deep tissue imaging due to their large penetration depths. Herein, the hollow-structured CeO2: Yb3+/Tm3+ nanospheres with red and near-infrared (NIR) two-channel up-conversion emissions were prepared via the urea-assisted co-precipitation method without any templates. The Yb3+ and Tm3+ concentration-dependent up-conversion luminescence and photo-thermal effects of hollow CeO2: Yb3+/Tm3+ nano-spheres were investigrated under the excitation of 980 nm laser. The red-NIR up-conversion emissions (650-900 nm) of Tm3+ were accomplished through the Tm3+ -> Yb3+ energy back transfer (EBT) process, and the potential applications of the present sample in photo-thermal sterilization and deep-tissue imaging were also assessed.