Metal/semiconductor hybrids show potential application in fields of surface-enhanced Raman spectroscopy (SERS) and photocatalysis due to their excellent light absorption, electric field, and charge-transfer properties. Herein, a WO 3 -Au metal/semiconductor hybrid, which was a WO 3 nanobrick decorated with Au nanoparticles, was prepared via a facile hydrothermal method. The WO 3 -Au hybrids show excellent visible light absorption, strong plasmon coupling, high-performance SERS, and good photocatalytic activity. In particular, on sensing rhodamine B (RhB) under 532 nm excitation, bare WO 3 nanobricks have a Raman enhancement factor of 2.0 × 10 6 and a limit of detection of 10 −8 M due to the chargertransfer property and abundant oxygen vacancies. WO 3 -Au metal/ semiconductor hybrids display a largely improved Raman enhancement factor compared to pure Au and WO 3 components owing to the synergistic effect of electromagnetic enhancement and charge transfer. The Raman enhancement factor and limit of detection are further improved, reaching 5.3 × 10 8 and 10 −12 M, respectively, on increasing the content of Au to 2.1 wt %, owing to the strong plasmon coupling between the Au nanoparticles. Additionally, the WO 3 -Au hybrids also exhibit excellent photocatalytic activity toward degradation of RhB under visible light irradiation. WO 3 -Au (2.1 wt %) possesses the fastest photocatalytic rate, which is 6.1 and 2.0 times that of pure WO 3 nanobricks and commercial P25, respectively. The enhanced photocatalytic activity is attributed to the strong plasmon coupling and the efficient charge transfer between Au and WO 3 nanobricks. The as-prepared materials show great potential in detecting and degrading pollutants in environmental treatment.

The regulation of near-field enhancement of plasmonic nanostructures is very important for plasmon-enhanced spectroscopy. Herein, structure-adjustable Au nanodumbbells (NDs) are prepared via a wet-chemistry method and applied for plasmon-enhanced surface-enhanced Raman scattering (SERS) and second-harmonic generation (SHG). The as-prepared Au NDs show much stronger visible-light absorption and near-field enhancements owing to the enlarged ends. Therefore, Au NDs exhibit much higher SERS response than Au nanorods (9.7-fold enhancement) on detecting Rhodamine B excited by a 532 nm laser. Subsequently, Au NDs are transferred to an ultrasmooth Au film to form particle-on-film systems, which display two kinds of plasmonic nanocavities due to the wrapped surfactant and two raised ends. The Au ND-involved particle-on-film systems show further improved SERS performances. This is because the near-field enhancement around the end region of Au NDs can be further improved by the strong plasmon coupling between Au NDs and the film. Meanwhile, the other nanocavity around the middle surface of Au NDs can also generate strong near-field enhancement for amplifying Raman signals. Most interestingly, by precisely adjusting the end size of Au NDs, the extinction cross section and nearfield enhancements at the fundamental and double frequencies of Au NDs simultaneously reach the maximum. As a result, the Au NDs exhibit double-resonantly improved SHG, which has a 10.3-fold enhancement compared with Au nanorods.