Are lanthanide-doped upconversion materials good candidates for photocatalysis?

The inability to harvest the broad spectrum of solar irradiation has constrained the practical applications of photocatalysis in the environmental and energy sectors. Although the importance of largely improving visible photon utilization is well recognized, the opinion on photon capture in the near-infrared (NIR) region of the solar spectrum is somewhat controversial due to the low energy of NIR photons and relatively more photon absorption by water in this range with respect to the visible regime. In addition, the viability of enhancing the utilization of NIR light for photocatalysis via lanthanide-doped upconversion (UC) particles is also under debate because of their low UC quantum yield and preference for lasers with specific, limited wavelengths as excitation sources, etc. Facing these challenges, several groups have made efforts toward the investigation of NIR-light photocatalysis enabled by UC particles. The achieved great advances in enhancing the light absorption of UC particles by coupling them with plasmonic metals render this emerging area, UC-enhanced photocatalysis, quite promising. Herein, we review the most recent advances of UC particles from the perspective of synthetic methods, luminescence enhancement strategies and their applications in photocatalysis. In particular, we intend to draw attention to the recent progress in designing efficient and broadband photocatalysts by integrating traditional semiconductor photocatalysts and/or recently emerging plasmon-semiconductor photocatalysts with lanthanide-doped UC materials. We would like to highlight that the involvement of plasmonic nanomaterials opens up a new avenue for the use of UC nanomaterials in photocatalysis. The current challenges in and perspectives toward this dynamic field are also provided.