Synthesis Of Silver Nanostructures And The Interaction With Quantum Dots

Surface plasmons polaritons (SPPs) are electromagnetic waves bounded on a metal-dielectric interface. The capabilities of SPPs, such as the enhanced local electromagnetic field and confining the light far below the diffraction limit, make them ideal candidates to realize nanoscale optical manipulation and nanoscale integrated optical circuits. The researches on SPPs are not only of fundamental importance for light-matter interactions but also of abundant applications, like quantum circuits, plasmonic waveguide and nanolaser. Recently, SPPs have been developed rapidly and are also significant to interdiscipline composed of material science, information science and photoelectronics.Along with the development of nanotechnology, including the physical and chemical preparation, more and more noble metal nanostructures have been prepared, which greatly promoted the development of SPPs. Chemically synthesized noble metal nanostructures possess smooth surface and lower losses, which make them ideal candidates to enhance the light-matter interaction. Plasmon-based fluorescence modulation has led to important advances in various fields and has paved the way toward promising scientific research aimed at enabling new applications. A variety of theoretical and experimental investigations have shown that noble metal nanostructures placed in close proximity to fluorescent particles can result in considerably modified fluorescence properties, including fluorescence intensity, lifetime,polarization and radiation patterns. Ag nanowire (NW) have proven to be key elements in subwavelength optical and its local surface plasmons(LSPs) and Fabry-Perot (FP) cavity modes can be launched by both the incident excitation beam and the excitation energy of the quantum dots(QDs), which provides abundant physical parameters to control the fluorescence.In this thesis, our study mainly focuses on the preparation of silver nanostructures with different morphologies, the build of fluorescence intensity and lifetime scanning microscope, and the control of two-photon fluorescence of QDs by Ag NW. The research works and conclusions present as follows:1. We report a facile biomolecule-assisted hydrothermal strategy for controlled synthesis of Ag NWs with baseball-like tips, where biomolecule rutin is used as both capping and reducing agents and the molar ratio of rutin to AgNO3 is a key factor to form the Ag NWs. We have also successfully synthesized silver nanorings using a new method,as well as nanoplates by changing the molar ratio of reactants. We believe that this work is significant for the understanding of biomolecule-assisted synthesis and design of novel nanostructures.2. We do lots of experiments to prepare Ag NWs and have a more profound understanding in how to improve the yield and control the aspect ratio of the Ag NWs. We successfully produce the hybrid NWs(HNW) consisting of Ag NW core and dense CdSe/ZnS QDs layers separated by SiO2 spacer. During the synthesis, we avoid the byproduct SiO2 nanospheres and the corrosion of Ag NWs.3. We build a fluorescence intensity and lifetime scanning microscope, which allows us to reconstruct the 2-dimension or 3-dimension fluorescence intensity and decay rate mappings. We solve several key technical problems, such as the quality of laser spot, the stable output of the transistor transistor logic (TTL) signal from the piezoelectric transition stage, the dark counts of time correlated single photon counting (TCSPC) system and the offset of the Ag NWs relative to the laser spot. This part is of great reference value to the researcher who builds the similar system.4. We raster scan the HNW and obtain the two-photon fluorescence(TPF) mappings of the intensity and decay rate. We find that the spatial distributions of the intensity and decay rate strongly depend on both the Fabry-Perot cavity modes of SPPs and the LSPs mode launched by the incident laser and the excitation energy of the QDs. The relaxation process of the TPF shows a double exponential decay process, in which the slow and fast components are attributed to the energy transfer between the QDs and the propagating SPP and LSPs modes, respectively.The experimental results are explained using finite difference time domain (FDTD) method and the simulation results have a great agreement with the experimental results. The incident polarization and position dependence of the intensity and decay rate of the TPF presents a very convenient way to control the TPF. Thus, other SPP cavities can also be designed to modulate the fluorescence properties and the energy transfer process between QDs or fluorescent molecules and SPP cavity modes. This method has promising applications in many fields, such as plasmonic devices, plasmon rulers and highly sensitive sensors.