Preparation And Fluorescence Ag @ SiO ₂ Core-shell Nanoparticle Enhancement

Noble metalic (gold, silver.etc) nanoparticles can produce surface plasmon in an appropriate field excitation, and the fluorescence of light-emitting molecules or ions around the metalic nanoparticles can be enhanced obviously.This effect is called surface enhanced fluorescence(SEF). The effect can be broadly applied in many fields and it is expected to significantly improve the sensitivity of fluorescence detection, bio-tracking, and fluorescence imaging technology. So it darws attention from many scholars all over the world.However, research on this effect is mainly concentrated in the metalic nanoparticles deposited on the film, which is made into a substrate to study the fluorescence enhancement of organic fluorescent molecules, and threre is still no systematic study reported on rare-earth doped fluorescent substance fluorescence emission enhancement effects, So it is urgent to research and explore in-depth and meticulous to design and synthesis such enhancement system.Existing research results show that significant fluorescence enhancement phenomenon can be observed only when the luminescence centers and the surface of the substrate with a suitable distance for surface-enhanced fluorescence phenomenon. Too far away or too close, can not reach the maximum enhancement, and if the distance too close will weaken fluorescence or even quenching it. The size of the noble metal nanoparticles plays a key role in this effect, when other conditions are same, only the appropriate size of nanoparticles can achieve optimum enhancement effect. The rare earth ions are doped into the matrix, so it is significant to prepared metal nanoparticles/rare-earth-doped core-shell structure, to explore the enhancement effect of the system for the study surface enhanced fluorescence effect of rare earth doped nano-system, develop the application of rare earth luminescent materials.In this thesis, I research SEF in four parts:The first part discussed the differences on shape, size dispersion and other characteristics of silver nanoparticles, which are produced in different methods. And the features of different silver nanoparticles which are produced in different ways. We found that silver nanoparticles, which are produced through deoxygenating Silver nitrate with sodium borohydride in a mixture of water and ice, cannot be wrapped by SiO2shell successfully. Silver nanoparticles, which are produced through deoxygenating Silver nitrate with tri-sodium in high temperature, have a poor dispersion, and it’s not easy to control its size and shape. Although it’s easy to adjust the distance between the nanoparticles and the luminescent molecules by covered with SiO2molecules. The thickness of the SiO2is not easy to control, especially the thickness less than5nm of SiO2is not able to achieve. Silver nanoparticles, which are produced through deoxygenating Silver nitrate with ethylene glycol in high temperature, are relatively easy to control its dispersion, size and shape. Which is better than before are they are not only easy to coat SiO2but also can control the thickness of SiO2from2to40nm comfortable.In the second part we have a full discussion in enhanced fluorescence effects of aqueous solution of Acridine Orange, Rhodanmine B, Rhodanmine6G in different concentrations by changing the concentration, which also can change the distance of Ag or Ag@SiO2nanoparticles. What can we find through experiments is that there are no enhancement effects for Ag and Ag@SiO2nanoparticles in different concentrations with Acridine Orange, and there are several certain enhancements for Rhodanmine B, obvious enhancements for Rhodanmine6G.In the third part of this paper, I discussed the effects of luminescence enhancement of Eu3+affected by Ag and Ag@SiO2nanoparticles. The Ag@SiO2nanoparticles are coated with a layer of Y2O3which is doped with Eu3+.In the fourth part of this thesis, I simulated and calculated the physical properties of Ag nanoparticles and Ag@SiO2nanoparticles, discussed the law of electromagnetic field which is surrounding the nanoparticles and the spectral absorption peak’s changing as the changing of the nanoparticles’size and the thickness of SiO2. And I calculated the Fano Resonance Effect of the interference between the bright mode and the dark mode as Nano-dimer symmetry is destroyed. The main purpose of this part’s work is to provide a theoretical basis for that Precious metal nanoparticles can have the Fluorescence Enhancement with light-emitting molecules or ions.