Preparation And Properties Of Core-shell Upconversion Nanoparticles

Upconversion nanoparticles?UCNPs?have many applicationsinthe field of biomedical and fluorescence imaging.Compared with traditionalmaterials,fluorescent materials have lots of adventages including lower toxicity,higer chemical stability,light penetration depth in tissue and high sensitivity imaging.Its also have Potential application values on biomarker and biological monitoring.We chose NaYF₄ as the host crystal of upconversion nanoparticles because it was proved the most efficient on fluorescence.But it still has many shortcomings,Such as poor water solubility and biocompatibility,Surface defects and low luminous efficiency.In order to solve these problems,this paper has done the following works.?1?NaYF₄:Yb,Er hydrophobic upconversion nanoparticles was prepared by high temperature thermal decomposition method.It was characterized by XRD,TEM,FTIR,fluorescence and other means.The results showed that the synthesized nanoparticles had good crystallinity,uniform morphology and good luminescence properties.It was found that the fluoride ion concentration had a great influence on the morphology,size and luminescence properties of the nanoparticles.?2?A thin thickness of SiO₂ was coated on the NaYF₄:Yb,Er nanoparticles surface by the areverse micro-emulsion method.We also make the NaYF₄:Yb,Er@SiO₂nanoparticles amination by the areverse micro-emulsion method.It transforms from oil-soluble nanoparticles into water-soluble nanoparticles.The XRD test showed that Compared with the original nanoparticles,the structure of NaYF₄:Yb,Er@SiO₂nanoparticles did not change,but only the characteristic diffraction peaks of amorphous silica were obtained.The fluorescence properties of the test showed that the fluorescence intensity did not change substantially.?3?We use high temperature thermal decomposition method to prepare nanoparticles.NaGdF₄ shells were coated on the surface of?-NaYF₄:Yb,Er UCNPs,Then the surface defects was disappeared.In order to further enhance the fluorescence properties of nanoparticles,we coat a layer of silica on the surface of NaYF₄:Yb,Er@NaGdF₄.The silver nanoparticles were then deposited on the silica surface by reducing the silver ammonia solution with glucose.The fluorescence properties of the composite nanoparticles were tesed and show that the fluorescence intensity was greatly increased,which was mainly due to the plasma resonance effect of silver nanoparticles.?4?TiO₂ nanoparticles were deposited on the surface of?-NaYF₄:Yb,Tm@SiO₂composite nanoparticles by TBOT hydrolysis.The UV-visible absorption spectra show that TiO₂ nanoparticles can absorb the energy from the radiation transition of?-NaYF4:Yb,Tm.In this paper,we have a experiment on photodegraded using?-NaYF₄:Yb,Tm@SiO₂@TiO₂ composite nanoparticles.The result show that new nanoparticles has good photodegradation of organic pollutants RhB.Cyclic experiments show that TiO₂ nanoparticlescan reduce the catalytic activity.