Coating a N-doped TiO2 shell on dually sensitized upconversion nanocrystals to provide NIR-enhanced photocatalysts for efficient utilization of upconverted emissions

Development of TiO2-based photocatalysts capable of utilizing NIR light is very important for practical applications using the solar spectrum. The combination of upconversion nanocrystals (UCNs) with TiO2 is a promising route for activation of photocatalysts under NIR irradiation. Here we propose integration of dually sensitized UCNs with N-doped TiO2 with a core-shell-shell structure. In such composite photocatalysts, the core-shell UCNs exhibit enhanced UC emissions in response to two NIR bands and all the UC emissions can be utilized by the N-TiO2 shell. The doping manner of the UCN cores and the N-doping level of the TiO2 shell both have a significant effect on the photocatalytic activity. Our results suggest that rational design of the configuration of the component materials is a feasible way to improve the photocatalytic activity of such UCN/TiO2 nanocomposites.