| Rare-earth doped up-conversion luminescent materials are widely used in lighting display systems,optical agriculture,solar cell spectrum conversion materials,bio-photodynamic therapy,and magnetization because of their long fluorescence lifetime,weak background fluorescence,high crystallinity,low toxicity,and other advantages.Resonance imaging and many other fields.Due to its low phonon energy and good chemical stability,NaYF4 is often used as a matrix material.However,as the ratio of rare earth particles to the surface of the particles increases,defects on the surface of the particles increase,resulting in increased fluorescence-free radiation relaxation and reduced fluorescence emission efficiency;in addition,rare earth doped up-conversion materials primarily prepared by thermal decomposition and solvothermal methods do not Water-soluble,it is difficult to be widely used in biological,chemical and other aspects.Therefore,it is especially important to increase the fluorescence emission efficiency of rare-earth doped up-conversion materials while satisfying the water solubility.In this paper,NaYF4(core)nanocrystal was prepared by hydrothermal method,and the surface of core was coated by inert shell NaGdF4.The growth mechanism of the core-shell particles was discussed.We also studied that the effects of shell thickness and growth time on the luminescence emission spectra of NaYF4:Yb3+/Er3+@NaGdF4.The water-solubility test and bio-imaging experiments of the synthesized core-shell samples were further investigated.The main work includes the following aspects:Preparation of water-soluble NaYF4:Yb3+/Er3+@NaGdF4:the hydrothermal method was used for the first time to synthesize hexagonal phase crystal core-shell particles with water-soluble,magnetic and up-conversion luminescence emission.By sampling and testing samples at different reaction time periods,combined with TEM,XRD and other characterization tests,the epitaxial growth mechanism of the core-shell structure was revealed.Single-particle fluorescence emission study:keeping other experimental conditions unchanged,adjusting the shell thickness by changing the molar amount of the shell precursor,further study the effect of shell thickness and the growth time of the shell on the fluorescence emission spectrum of single-particle core-shell nanocrystal.Bio-imaging research:disperse the synthesized samples into the cell-like growth solutions and perform the water-solubility test.Using water as the blank control group in the vitro Ti-weighted MR imaging experiment.Discuss the significance of this sample in magnetic resonance imaging technology;In addition,the water-soluble crystal particles were injected into the mice to study their UC luminescence image. |
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