The rational optimization of plasmonic property of metal nanocrystals by manipulating the structure and morphology is crucial for the plasmon-enhanced application and has always been an urgent issue. Herein, Au nanorods with tunable surface roughness are prepared by growing PbS, overgrowing Au, and dissolving PbS nanoparticles on the basis of smooth Au nanorods. The transverse plasmon resonance of Au nanorods is notably improved due to plasmon coupling between Au nanorods and the surface-modified Au nanoparticles, resulting in the strong and full-spectrum light absorption. Numerical simulations demonstrate that the surface-rough Au nanorods have abundant and full-surround hotspots coming from surface particle–particle plasmon coupling between ultrasmall nanogaps, sharp tips, and uneven areas on Au nanorods. With these characters, the surface-roughness-adjustable Au nanorods possess high tunability and enhancement of surface-enhanced Raman scattering (SERS) detection of Rhodamine B and significantly improved photothermal conversion efficiency. Au nanorods with the largest surface roughness have the highest Raman enhancement factor both at 532 and 785 nm laser excitation. Meanwhile, photothermal conversion experiments under near-infrared (808 nm) and simulated sunlight irradiation confirm that the Au nanorods with rough surface have prominent photothermal conversion efficiency and can be regarded as promising candidates for photothermal therapy and solar-driven water evaporation.

Colloidal Au-core/Ag-shell nanorods with an asymmetric transverse cross-section and a strong octupolar plasmon resonance are synthesized by the controlled growth of Ag shells on one side of the Au cores. A largely enhanced second harmonic generation (SHG) from these asymmetric core–shell nanorods is demonstrated for the first time by tuning the dipolar and the octupolar plasmon modes to make them resonant with the fundamental and harmonic frequencies, respectively. The SHG intensity of the Au–Ag nanorods with dual-frequency resonances is enhanced by 21 times compared to that of the bare Au nanorods. The co-existence of the dipolar, quadrupolar, and octupolar radiations in the SHG is revealed. Additionally, the cellular uptake of the Au–Ag nanorods is monitored and the evolution of the membrane bleb is successfully observed by the SHG imaging. Our observations provide a strategy for enhancing the SHG of the colloidal metal nanoparticles and can have applications in chemical process monitoring and biological sensing.

The nanoscale core/shell heterostructure is a particularly efficient motif to combine the promising properties of plasmonic materials and rare-earth compounds; however, there remain significant challenges in the synthetic control due to the large interfacial energy between these two intrinsically unmatched materials. Herein, we report a synthetic route to grow rare-earth-vanadate shells on gold nanorod (AuNR) cores. After modifying the AuNR surface with oleate through a surfactant exchange, well-packaged rare-earth oxide (e.g., Gd₂O₃: Eu) shells are grown on AuNRs as a result of the multiple roles of oleate. Furthermore, the composition of the shell has been altered from oxide to vanadate (GdVO₄: Eu) using an anion exchange method. Owing to the carefully designed strategy, the AuNR cores maintain the morphology during the synthesis process; thus, the final Au/GdVO₄: Eu core/shell NRs exhibit strong absorption bands and high photothermal efficiency. In addition, the Au/GdVO₄: Eu NRs exhibit bright Eu³⁺ fluorescence with quantum yield as high as ~17%; bright Sm³⁺ and Dy³⁺ fluorescence can also be obtained by changing the lanthanide doping in the oxide formation. Owing to the attractive integration of the plasmonic and fluorescence properties, such core/shell heterostructures will find particular applications in a wide array of areas, from biomedicine to energy.

Fluorescent rare-earth ions are useful for efficient energy transfer via multichannels with different properties. Tuning these transfer processes in functional rare-earth materials has attracted considerable attention to satisfy the various demands of diverse practical applications. In this study, strong tunabilities of cooperative energy transfer and nonlinear upconversion emissions are realized using (Yb³⁺, Er³⁺)/NaYF₄ nanocrystals with and without doped Mn²⁺ ions by adopting a plasmonic nanocavity composed of a silver nanorod array. The plasmon nanocavity can not only increase the energy transfer between Mn²⁺ and (Yb³⁺, Er³⁺) but also significantly enhance the radiative emission. This reveals a prominent nonlinear gain in the nanocavity nanosystems. These observations suggest the prospective applications in the design and preparation of rare-earth nanocrystals with excellent tunabilities of multiple functionalities.

A novel strategy is proposed to directly synthesize water-soluble hexagonal NaYF₄ nanorods by doping rare-earth ions with large ionic radius (such as La³⁺, Ce³⁺, Pr³⁺, Nd³⁺, Sm³⁺, Eu³⁺, and Gd³⁺), and the dopant-controlled growth mechanism is studied. Based on the doping effect, we fabricated water-soluble hexagonal NaYF₄: (Yb, Er)/La and NaYF₄: (Yb, Er)/Ce nanorods, which exhibited much brighter upconversion fluorescence than the corresponding cubic forms. The sizes of the nanorods can be adjusted over a broad range by changing the dopant concentration and reaction time. Furthermore, we successfully demonstrated a novel depth-sensitive multicolor bioimaging for in vivo use by employing the as-synthesized NaYF₄: (Yb, Er)/La nanorods as probes.