Lanthanide-doped nanocrystals that convert near-infrared (NIR) irradiation into shorter wavelength emission (ultraviolet-C) offer many exciting opportunities for biomedicine, bioimaging, and environmental catalysis. However, developing lanthanide-doped nanocrystals with high UVC brightness for efficient photocatalysis is a formidable challenge due to the complexity of the multiphoton process. Here, we report a series of heterogeneous core-multishell structures based on a co-sensitization strategy with multi-band enhanced emission profiles under 980 nm excitation. Interestingly, the multiphoton processes involving two to six-photon upconversion are highly promoted via a co-sensitization strategy. More importantly, through growth layers of TiO2 and CdS photocatalysts, these lanthanide nanocomposites with efficient multi-upconverted emission show efficient photocatalytic activity. This study provides a new perspective for mechanistic understanding of multiphoton processes in heterostructures and also offers exciting opportunities for highly efficient photocatalytic applications.