Synthesis Of Noble-metal Nanoparticles And Research On Localized Surface Plasmon-enhanced Upconversion

In this thesis, hexagonal β-NaYF₄ was used as host material. The up-conversion of β-NaYF₄:Er³⁺,Yb³⁺ and the local field enhancement effect of noble-metal nanoparticles on up-conversion were investigated. The experimental results showed that those materials have potential applications in solar cells, red laser and biological detection. Noble-metal nanoparticles can generate the localized surface plasmon （LSP） under light, which can enhance fluorescence intensity of β-NaYF₄:Er³⁺,Yb³⁺ up-conversion phosphors. The major points of this thesis are listed below:1. Several noble-metal nanoparticles were prepared and the absorption spectra was also studied. Ag nanocubes （NCs） were synthesized by the chemical reduction method, and Ag@SiO₂ nanostructured materials were prepared by the Stober method. The thickness of SiO₂ shell was controlled to be 7.5-33.0 nm via the change of the volume of tetraethyl orthosilicate （TEOS）. The absorption spectra of the samples show that the dipole resonance absorption peak of Ag@SiO₂ has a red-shift, compared with that of Ag NCs. Au nanospheres （NPs） and Au nanorods （NRs） were prepared by seed-mediated growth method, the morphology and absorption characteristics of Au NRs with different addition of seed were also studied.2. The surface plasmon-enhanced upconversion of β-NaYF₄:Er³⁺,Yb³⁺ combined with Ag NCs was researched. The upconversion nanophosphors β-NaYF₄:Er³⁺,Yb³⁺ were prepared by co-precipitation method. The surface plasmon enhanced upconversion luminescence of β-NaYF₄:Er³⁺,Yb³⁺ combined with Ag NCs was observed in oleic acid solution. The influence of doping concentration of Ag NCs to red and green emission was also studied. The upconversion luminescence reached maximum while doping concentration of Ag NCs was 2.0%. The largest enhancement factors of red and green upconversion emission were 1.97 and 1.79, respectively. When the upconversion nanophosphors NaYF₄:Er³⁺,Yb³⁺ doped with Ag NCs/Ag@SiO₂, the surface plasmon enhancement of upconversion of NaYF₄:Er³⁺,Yb³⁺ NPs around single Ag NC/Ag@SiO₂ was studied by the micro-field fluorescent spectra. The enhancement factors of upconversion with single Ag@SiO₂ are 1.5 （green） and 2.7 （red）, while single Ag NC just enhances green upconversion.3. The surface plasmon-enhanced upconversion in P-NaYF₄:Er³⁺,Yb³⁺ doped with Au NPs/NCs were studied. NaYF₄:Er³⁺,Yb³⁺@SiO₂ was prepared and dispersed in water, the surface plasmon enhanced upconversion luminescence of β-NaYF₄:Er³⁺,Yb³⁺@SiO₂ combined with Au NPs/NRs was observed. The influence of doping concentration of Au NPs/NRs to red and green emission was also studied. The upconversion luminescence reached maximum while doping concentration of Au NPs was 0.02%. The largest enhancement fadtors of red and green upconversion emission are 1.61 and 1.25, respectively. While the doping concentration of Au NRs was 0.03%, the upconversion luminescence reached maximum. The largest enhancement factors of upconversion are 1.66 （green） and 2.75 （red）.