Silver-Based Composite Nanomaterials And Their Optical Properties

Silver nanomaterials have attracted tremendous attention owing to their unique optical properties. Mass production of nanomaterials in a simple and low-cost way is the essential prerequisite for their industrial application. Although various morphologies of silver nanostructures have been successfully prepared in laboratories, the quite low utilization of raw materials (less than 1%) greatly increases the expense of bulk production and hinders the popularization of their application.As a tendency of medical treatment, visualization needs sufficiently strong signal and multimodal output. Unfortunately, traditional one-photon dyes are easy to quench because of their small Stokes shift. Besides, the fluorescence intensity of single molecule is very weak and has only one fluorescence utput. Two-photon fluorescence has much enhanced penetration depth, and significantly reduced auto-fluorescence background and photodamage. However, the possibility of two-photon excitation is quite low, usually orders of magnitude weaker than the single-photon excitation. Noble metal nanostructures, which provide the surface plasmon resonance (SPR), can be utilized to enhance the fluorescence and Raman scattering. They also can be used to obtain the production of light at half wavelength of the excitation laser (SHG). Thus, we proposed the core/shell nanostructures with noble metal as cores and fluorescent dye as shells to utilize the superiority of noble metal and combine the advantages of above two materials simultaneously. In all, this work is discussed as follows.1) The mass production of Ag NWs. Here we systematically investigated the heterogeneous nucleation progress, by using aqueous method-preparation of Ag NWs as a model. The yield of Ag NWs should be higher than 95% to evaluate the feasibility of the synthesis. The linear relationship between [Ag+] (AgNO3) and [Cl-] (NaCl) depended on the intrinsic behavior of AgCl precipitation. The size of AgCl-seeds remained unchanged at a certain concentration range of [Cl-]. The efficient heterogeneous nucleation sites lied on the overall surface area of AgCl seeds and the concentration of Ag+ in aqueous system was finally raised 20 times higher than that of traditional method. This assumption could also be applied to polyol system, in which the linear relationship was also proved effectively. As a result, a production of 5 g Ag NWs in one pot was achieved and the yield of Ag NWs was demonstrated 5 times higher in polyol method than that of previous work. In such polyol method, it was found that the diameters and lengths of final products could be adjusted by the sizes of the AgX-seeds (X= Cl-, Br-, I- and SO42-) and the basic mechanism could be used to help controllable synthesis of other metal nanoparticles. We prepared the TCFs by Meyer-rod coating the Ag NWs (four types mentioned above) inks. It was found that the TCFs prepared by longer Ag NWs had better transparency and higher conductivity, which gave direction to the future development of Ag NWs applications.2) An in situ chemical reaction route was used to prepare the monodisperse Ag@rubrene core-shell nanostructures, in which silver nanoparticles acting as core materials and rubrene acting as shell materials. The shell thickness of rubrene can be well controlled from 2 to 16 nm by adjusting the adding amount of rubrene’+. We investigated the fluorescence intensity of the Ag@rubrene nanostructures with different shell thickness of rubrene and found that the composites with the shell thickness of 8 nm could achieve the highest enhanced-fluorescence intensity. We synthesized a series of Ag@rubrene composites with different SPR bands of Ag nanostructures to verify the effect of SPR and confirmed that the SPR coupling could produce the biggest enhancement factor. Based on this core-shell nanostructure, we achieved bifunctional optical signal output, namely fluorescence and Raman signals. The enhancement factor of fluorescence intensity could reach 29, and the enhancement factor of Raman signal could reach 103.3) We had prepared core/shell nanostructures with Ag nanoparticles as cores and BCPEB as shells by a simple heating process. BCPEB has aggregation-induced emission property and also shows two-photon fluorescence signals. The shell thickness of BCPEB could be well controlled from 2 to 10 nm by adjusting the molecular ratio between BCPEB and silver nanoparticles. The fluorescence intensity of composites became stronger with the increasing of shell thickness of BCPEB. The composites achieved the biggest enhancement factor and could reach 12 folds, when the thickness of BCPEB was up to 10 nm. We synthesized a series of Ag@BCPEB composites with different sizes of Ag cores to verify the coupling effect of SPR and confirmed that the match between SPR and the absorption of BCPEB could produce the biggest enhancement factor. We investigated the wavelength-dependent two-photon intensity of composites and found that the second harmonic generation from Ag nanoparticles could significantly enhance two-photon fluorescence. The enhanced behavior was determined by the match between second harmonic generation and the absorption of BCPEB. The maximum enhancement factor of two-photon fluorescence could reach 17.