Dopant-Controlled Synthesis of Water-Soluble Hexagonal NaYF_(4) Nanorods with Efficient Upconversion Fluorescence for Multicolor Bioimaging

A novel strategy is proposed to directly synthesize water-soluble hexagonal NaYF4 nanorods by doping rare-earth ions with large ionic radius (such as La^(3+), Ce^(3+), Pr^(3+), Nd^(3+), Sm^(3+), Eu^(3+), and Gd^(3+)), 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.

Synthesis of gold/rare-earth-vanadate core/shell nanorods for integrating plasmon resonance and fluorescence

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 Eu^3＋ fluorescence with quantum yield as high as -17%; bright Sm^3＋ and Dy^3＋ 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.

Surface-roughness-adjustable Au nanorods with strong plasmon absorption and abundant hotspots for improved SERS and photothermal performances

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.

Strong tunability of cooperative energy transfer in Mn2＋-doped （Yb3＋, Er3＋）/NaYF4 nanocrystals by coupling with silver nanorod array

Fluorescent rare-earth ions are useful for efficient energy transfer via multi- channels 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.