Ya-Fang Zhang

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 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.

Unusual and Tunable One-Photon Nonlinearity in Gold-Dye Plexcitonic Fano Systems

Recent studies of the coupling between the plasmonic excitations of metallic nanostructures with the excitonic excitations of molecular species have revealed a rich variety of emergent phenomena known as plexcitonics. Here, we use a combined experimental and theoretical approach to demonstrate new and intriguing aspects in the ultrafast nonlinear responses of strongly coupled hybrid Fano systems consisting of gold nanorods decorated with near-infrared dye molecules. We show that the severely suppressed linear absorption around the Fano dip significantly enhances the unidirectional energy transfer from the plasmons to the excitons and further allows one-photon nonlinearity to be drastically and reversibly tuned. These striking observations are interpreted within a microscopic model stressing on two competing processes: saturated plasmonic absorption and weakened destructive Fano interference from the bleached excitonic absorption. The unusually strong one-photon nonlinearity revealed here provides a promising strategy in fabricating nanoplasmonic devices with both pronounced nonlinearities and good figures of merit.

Review on nanomaterials synthesized by vapor transport method: growth and their related applications

Nanostructures with different dimensions, including bulk crystals, thin films, nanowires, nanobelts and nanorods, have received considerable attention due to their novel functionalities and outstanding applications in various areas, such as optics, electricity, thermoelectricity, photovoltaic fields and sensing devices. In recent years, remarkable progresses and modifications have been made upon the fabrication of nanomaterials by vapor transport method. In this review, we introduce various representative nanostructures prepared by vapor transport method and focus on the discussion of their growth, physical properties, and potential applications. Meanwhile, the essential growth mechanisms of nanostructures also have been extensively reviewed, for example, the different growth modes depending upon the specific sample growth. Finally, we conclude this review by providing our perspectives to the future vapor transport method, and indicating some key existing problems. Vapor transport process offers great opportunities for the low-cost preparation of novel single crystals with different doping level and the realization of integrating such nano/micro single crystals into spintronic and electronic devices.

Size-dependent plasmon relaxation dynamics and saturable absorption in gold nanorods

The surface plasmon resonances of metallic nanoparticles are highly dependent on size and shape, which leads to high tunability of both linear and nonlinear optical responses. Here, we investigate the plasmon resonance and saturable absorption of gold nanorods (AuNRs) with different lengths and reveal the size dependence of electron relaxation dynamics. The strong plasmon absorption leads to ground-state bleaching and saturable absorption (SA) in AuNRs, Z-scan measurements demonstrate that the saturation threshold decreases as the length of AuNRs increases. The time-resolved differential transmittance reveals that the longer AuNRs have large relaxation times for hot electrons, which accounts for the decrease of the SA threshold.

Facile synthesis of flower-shaped Au/GdVO4:Eu core/shell nanoparticles by using citrate as stabilizer and complexing agent

Metal/rare-earth core/shell hetero-nanostructures combine the optical properties of metal cores and rare-earth shells, which are widely reported and expected to be used in multitask applications. However, there is still no facile and efficient strategy to directly prepare such materials. Herein, we present a facile hydrothermal method for directly coating rare-earth vanadate shells onto the Au nanoparticle (AuNP) cores. Citrate plays a fascinating and critical role in the whole synthesis process, and not only acts as the capping agent to stabilize the as-prepared AuNP cores and the final products but also serves as the complexing agent to assist the nucleation and growth of rare-earth vanadate shells. Interestingly, the grown Au/GdVO4:Eu core/shell NPs have a flower-like shape with tunable plasmon resonance and bright fluorescence. The morphology and crystallinity as well as the growth mechanism and tunable optical properties of the Au/GdVO4:Eu are investigated. The method developed here could be extended for preparing other metal/rare-earth hybrids and the multifunctional products with specific morphology have the potential in the photocatalytic and biomedical application.

Synthesis of gold nanorod/neodymium oxide yolk/shell composite with plasmon-enhanced near-infrared luminescence

A yolk/shell composite consisting of an AuNR core and an Nd2O3 shell with a 19 nm gap is synthesized by a multi-step over-growth method. The near-infrared luminescence of AuNR@Nd2O3 is up to 4.6 times higher than that of Nd2O3 hollow nanoparticles. The underlying mechanism of plasmon-induced luminescence enhancement is further investigated.

Plasmon-Enhanced Fluorescence of Rare Earth Nanocrystals

Rare earth (RE) nanocrystals (NCs) exhibit featured fluorescence properties and are widely used in many applications of biomedical labeling, display, sensing, light-emitting devices, etc. Plasmon-enhanced and -manipulated fluorescence of RE NCs usually shows different behaviors compared with organic dye molecules and semiconductor NCs. In this Chapter, we firstly present the enhanced upconversion fluorescence of RE fluoride NCs by the dopant-controlled synthesis. Then the preparation of plasmon/RE core/shell NCs by wet-chemical growth method is introduced. Finally, we demonstrate the plasmon-enhanced upconversion fluorescence of a single RE NC and by plasmonic array nanostructures.