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.