Preparation And Upconversion Emissions Properties And PEG Modification Of Nanocrystalline With Core-shell Structure

Rare-earth doped luminescent upconvertion nanocrystal has great potentialapplications in many areas, such as solar cells, display devices, laseranti-counterfeiting material and biomedicine. Particularly, rare earth up-convertingluminescent nanocrystal has been more and more comprehensive concerned, due totheir unique superiorities in bio-fluorescence labeling and bioimaging. But the lowup-convertion luminescent efficiency and weak water-solubility of nanocrystalhave limited its actual applications. So the methods of modifying the nanocrystalto improving the up-convertion luminescent efficiency and water solubility havegreat significance in theoretical and practical aspects. The main research contentsof this thesis are the synthesis of core-shell fluoride nanocrystalline, water solublemodified and up-conversion fluorescence properties.The synthesis process of core-shell nanocrystal has been studied. The rare earthsalts are used as precursor. The synthesis methods have been developed to makecontrollable morphology NaYF₄:Yb³⁺/Tm³⁺nanocrystalline. Using solvothermalmethod through controlling the proportion of surfactant, growth time andtemperature to get small, uniform and monodispersive of NaYF₄:Yb³⁺/Tm³⁺nanocrystalline particles of hexagonal phasehave been prepared. Thenanocrystalline has been covered by homogeneous insert shell （NaYF₄） and activeshell （NaYbF₄）. The as-synthesized bare core nanocrystalline and core-shellstructure nanocrystalline have been characterized by XRD and TEM and etc.The up-convertion luminescence properties of core-shell structurenanocrystalline have been studied. Through the measurement of the up-convertingluminescence spectrum and upconvertion time-resolved spectrum has been foundthat the cladding can enhance upconversion luminescence in nanocrystals,upconversion luminescence enhanced with thicker shell. And active shell is moreconducive to enhanced upconversion luminescence than the inert shell.Nanocrystalline upconversion luminescence mechanism has been analyzed byluminescence intensity and pump power.The modification of fluoride nanocrystalline to enhance its water solublility hasbeen studied by coating nanocrystalline with PEG. Material proportion used incoating nanocrystalline with PEG has been optimized. Different PEG has beenused to modify nanocrystalline to compare their efficiency of improving solubility.Monodispersion has been improved by coating nanocrystals with PEG by TEMimages. Fourier transform infrared absorption spectra showed that the different kinds of PEG coated on the nanocrystalline have different coating rate.Upconversion luminescence spectroscopy results showed that the coating of PEGon the nanocrystalline upconversion luminescence does not have an negativeimpact on upconverting efficiency.