Study Of The Coupling Between Localized Surface Plasmon And Exciton

Surface plasmon resonance (SPR), which makes it possible to investigate the interaction between light and matter beyond the diffraction limit, is a phenomenon that arises from the collective oscillation driven by the electromagnetic field of light. The study on the interaction between SPR and exciton is theoretically and practically important, which will not only deepen and broaden the understanding of light and matter interaction, but also contribute to its application in light-emitting diode, solar cells, nonlinear optical devices, ultrafast optical switch, biomedical detection, low-threshold lasing and quantum information processing and so on.Depending on the coupling strength, the interaction between SPR and exciton can be divided into two principal regimes:the weak coupling and the strong coupling regime. In the weak coupling regime, this work focuses on localized surface plasmon (LSP)-enhanced fluorescence, LSP-enhanced photocatalytic degradation, LSP-controlled Fdrster resonance energy transfer (FRET) as well as LSP-enhanced Raman scattering (SERS). In the strong coupling regime, in photoluminescence (PL) spectra, we report on the direct observation of strong coupling between LSP and exciton of quantum dots (QDs). Stimulated emission can be realized both in the weak and strong regime, and both LSP-controlled incoherent and coherent stimulated emission are achieved in this work. The primary achievement of this work is described as follow:(1) LSP-enhanced fluorescence is achieved utilizing Au@SiO2/QDs core-shell nanostructure. The distance dependence of LSP coupled FRET of QDs is experimentally investigated using Au@SiO2/QDs system composed of donor and acceptor QDs and the optimized FRET efficiency and rate are obtained.(2) Flower-like silver nanostructures with controlled morphology and composition were prepared through wet-chemical synthesis. The reaction rate is simply manipulated by the amount of ammonia added which is the key point to determine the ratio of hexagonal close-packed (HCP) to face-centered cubic (FCC) phase in silver nanostructures. The existence of formic acid that is the oxidation product of aldehyde group is demonstrated to play a crucial role in achieving the metastable HCP crystal structures. Utilizing flower-like silver nanostructures as SERS substrates, Raman signal of Rhodamine 6G or 4-aminothiophenol with concentration as low as 10-7 M was detected.(3) One-pot solution-based chemical precipitation method was developed to synthesize leaf-like CuO nanostructures. The morphology and size of the leaf-like CuO nanostructures can be simply manipulated by controlling the type and concentration of precursors. Porous CuO/Ag microspheres could also be prepared. These two structures could serve as effective photocatalyst for the degradation of Rhodamine B under visible light irradiation in the presence of hydrogen peroxide. Moreover, compared to pure CuO nanostructures, the photodecomposition activity of CuO/Ag microspheres increases by 42.9% due to plasmon-enhanced light absorption.(4) Incoherent and coherent random lasing is obtained in Ag(or Au)@(SiO2+Gain) nanostructures. Stimulated emission has also been achieved in (void Ag nanoshells+R6G) system, and the cavity mode is responsible for the stimulated emission which is demonstrated through FDTD simulation.(5) Under UV-light irradiation, Ag@ZnO core-shell nanostructures were prepared through wet-chemical synthesis. By optimizing the parameters, the emission intensity of ZnO in the UV region is enhanced, meanwhile the defect emission is suppressed. These Ag@ZnO nanostructures could be a potential candidate for the realization of surface plasmon amplification by stimulated emission of radiation (SPASER).(6) In photoluminescence spectra, Rabi splitting of approximately 160 meV as an indication of strong coupling between excited states of CdSe/ZnS QDs and LSP modes of silver nanoshells is directly observed under nanosecond pulsed laser excitation. The strong coupling manifests itself as an anticrossing-like behavior. Further analysis substantiates the essentiality of high pump energy and collective strong coupling of many QDs with the radiative dipole mode of the metallic nanoparticles for the realization of strong coupling. Moreover, comparing the strong coupling behavior of Ag nanoshells and Ag (or Au) nanospheres, the threshold of strong coupling related factors are discussed and the advantages of Ag nanoshells in the realization of strong coupling are demonstrated.