Synthesis And Fluorescence Quenching Effect Of Nanoparticles Modified By Na Nanoparticles Modified By NaYF4 + / Sup> 3 + @SiO <2> Complex Nanostructures

The rare earth doped luminescent materials have many unique characterics, which include stable photochemical properties, long fluorescence lifetime, high quantum yield, narrow emission spectra, large stokes shift and so on. It was widely applied in biological imaging, solid laser, lighting, solar cells, and many other aspects. In current work, two kinds of rare-earth doped nanomaterials are produced by hydrothermal method, which are NaYF4:Yb3+/Er3+and NaYF4:Eu3+nanoparticles. The first one has excellent up-conversion luminescence properties, and the second one has good down-conversion luminescence performance. For NaYF4:Yb3+/Er3+nanoparticles, we mainly studied the influence of reaction condition on the sample morphology, size and fluorescence experimentally. For gold nanoparticle modified NaYF4:Ln3+@SiO2composite nanometer system, the fluorescence effects of metal nanoparticles to the rare-earth doped luminescence materials are explored. The results showed that the nanosystem of the NaYF4:Ln3+(Ln=Yb, Er, Eu) attached with Au nanoparticles, presented more significant fluorescence quenching. When the distance between the Au NPs and rare-earth doped nanoparticles is5nm, and the excitation and emission spectrum of NaYF4:Ln3+nanosystem is overlaped with the absorption spectrum of Au NPs, Au nanoparticles can absorb the energy of the excitation light and fluorescence. This made the fluorescence emission intensity of NaYF4:Ln3+@SiO2@Au nanocomposite system reduced obviously.The thesis mainly consist three aspects:In the first part, we studied the morphology, size and fluorescence emission of NaYF4:Yb3+/Er3+nanoparticles under different preparation conditions (reaction temperature and reaction time). The result showed that, with the extension of the reaction temperature and time, the sample will implement the phase shift from cubic to hexagonal, its size increases gradually, and fluorescence intensity enhanced accordingly.In the second part, the method of hydrothermal synthesis was used to prepare the Au nanoparticle modified NaYF4:Yb3+/Er3+@SiO2composite nanosystem, and the SiO2 layer control the space distance between Au nanoparticles and NaYF4:Yb3+/Er3+, and acted as an isolation layer. Under the980nm laser excitation, the interaction of Au surface plasmon with NaYF4:Yb3+/Er3+control the fluorescence emission effectively. The results showed that the system of NaYF4:Yb3+,Er3+@SiO2@Au nanocomposite produced fluorescence quenching. At suitable space distance, the overlap of fluorescence emission band of Er3+ions with the resonance absorption band of the gold surface plamon can cause fluorescence resonance energy transfer between rare earth ions and Au nanoparticles.In the third part, we took the Au nanoparticle modified NaYF4:Eu3+@SiO2composite nanosystem as the research object. The fluorescent effect of the Au nanoparticles on to the composite system of NaYF4:Eu3+@SiO2is studied under532nm excitation. The stronger quenching effect was observed. From the overlap degree of the excitation and emission with the absorption of the gold surface plasmon, a corresponding analysis and discussion for the quenching phenomenon was carried out. The result showed that the wavelength of the excitation light and the Eu3+ion emission peak overlaped with the absorption band of Au nanoparticles in the nanosystem. When the rare earth nanoparticle with Au nanoparticles has a suitable distance such as5nm, Au nanoparticles absorb the energy of the excitation light and the fluorescence emission, which caused the decrease of emission intensity of the NaYF4:Eu3+@SiO2@Au composite nanosystems.