Near-Infrared-Plasmonic Energy Upconversion in a Nonmetallic Heterostructure for Efficient H2 Evolution from Ammonia Borane.

Plasmonic metal nanostructures have been widely used to enhance the upconversion efficiency of the near-infrared (NIR) photons into the visible region via the localized surface plasmon resonance (LSPR) effect. However, the direct utilization of low-cost nonmetallic semiconductors to both concentrate and transfer the NIR-plasmonic energy in the upconversion system remains a significant challenge. Here, a fascinating process of NIR-plasmonic energy upconversion in Yb3+/Er3+-doped NaYF4 nanoparticles (NaYF4:Yb-Er NPs)/W18O49 nanowires (NWs) heterostructures, which can selectively enhance the upconversion luminescence by two orders of magnitude, is demonstrated. Combined with theoretical calculations, it is proposed that the NIR-excited LSPR of W18O49 NWs is the primary reason for the enhanced upconversion luminescence of NaYF4:Yb-Er NPs. Meanwhile, this plasmon-enhanced upconversion luminescence can be partly absorbed by the W18O49 NWs to re-excite its higher energy LSPR, thus leading to the selective enhancement of upconversion luminescence for the NaYF4:Yb-Er/W18O49 heterostructures. More importantly, based on this process of plasmonic energy transfer, an NIR-driven catalyst of NaYF4:Yb-Er NPs@W18O49 NWs quasi-core/shell heterostructure, which exhibits a ≈35-fold increase in the catalytic H2 evolution from ammonia borane (BH3NH3) is designed and synthesized. This work provides insight on the development of nonmetallic plasmon-sensitized optical materials that can potentially be applied in photocatalysis, optoelectronic, and photovoltaic devices.