Research On The Controllable Synthesis And Fluorescent Application Of Rare Earth Based Nanomaterials

In recent years,rare earth based nanomaterials have attracted more and more attention due to their outstanding fluorescence properties.In general,the rare earth based nanomaterials can be divided into downconversion and upconversion based on the luminescence mechanism.For the downconversion nanomaterials,lanthanide(Ln³⁺)-doped rare earth vanadates were synthesized via simple and quick methods by improving the synthesis conditions.The fluorescence properties were studied in detail,and a series of related applications were developed.Due to the special fluorescence properties of upconversion nanomaterials,they have great advantages in biomedicine.In our works,we tried to synthesize good rare-earth based upconversion fluorescent nanomaterials with small size,excellent fluorescence and multi-functionality for multi-modal bioimaging.In the first chapter,the concepts,research methods,history and current advances of rare earth based nanomaterials are introduced.At the end of this chapter,the importance of the project is demonstrated.In the second chapter,we synthesized highly water-soluble Ln³⁺-doped tetragonal phase（t-）LaVO₄ nanoparticles（NPs）via a simple,fast and green microwave-assisted hydrothermal method.The average size of t-LaVO₄ NPs was about 43 nm.The aqueous solutions of Ln³⁺-doped t-La VO₄ exhibited excellent fluorescence properties under UV excitation（t-LaVO₄:10%Eu was bright red and t-LaVO₄:0.5%Dy was close to white）.Some superb anti-fake fluorescent patterns were printed using Ln³⁺-doped t-LaVO₄ aqueous solution as ink,which indicates the as-prepared Ln³⁺-doped t-LaVO₄ NPs as fluorescent ink can meet the various anti-fake requirements.Notably,the designed convenient anti-fake fluorescent codes with improved security could be directly scanned and decoded by a smart phone.What’s more,the as-prepared NPs can be used for the development of latent fingermark on various substrates and the second-level detail information can be clearly obtained from the magnification of a fingermark.In the third chapter,monodisperse and water-soluble Ln³⁺-doped Y（Gd）VO₄ NPs have been successfully synthesized through a fast,facile,and environmentally friendly microwave-assisted route with polyacrylic acid as the surfactant.The Y（Gd）VO₄:Ln（Ln=Eu,Dy,Sm）NPs have the unique fluorescence properties.GdVO₄ NPs can act as the contrast agent for CT and MR bioimaging due to the magnetic and X-ray absorption properties.The results indicate that the obtained Y（Gd）VO₄ NPs can be potential candidates for multi-modal optical/MR/CT bio-imaging.To improve the synthetic methods of rare earth vanadates,we synthesized highly water-soluble YVO₄:Eu NPs with uniform size and shape via co-precipitation at room temperature.The strong red emission from YVO₄:Eu NPs could be selectively quenched by Cu²⁺ions with limit of detection of as low as 0.57μM.In the forth chapter,monodisperse,water-dispersible Ln³⁺-doped BaYF₅ NPs were synthesized through microwave-assisted modified polyol process with polyethyleneimine as the surfactant.The TEM images illustrate the sphere-like and flower-like morphologies of the obtained NPs.Intense multicolor downconversion luminescence is also achieved in Ce³⁺/Ln³⁺（Ln=Tb,Dy）doped BaYF₅ NPs.Then,upon excitation at 980 nm,upconversion fluorescence properties of BaYF₅:Yb/Ln（Ln=Er,Tm,Ho）NPs and energy transfer between Yb³⁺and Ln³⁺are systematically surveyed.Furthermore,a layer of SiO₂ is coated on the surface of the NPs and MTT assays are performed to test the cytotoxicity of BaYF₅:Ln NPs.Due to the X-ray absorption property of Ba element,a proof-of-concept CT imaging with BaYF₅:Ln NPs is conducted.These results indicate that the obtained NPs have great potential as optical/CT bioprobe.In the fifth chapter,sub-10 nm core-shell NPs,which selected Sr₂LuF₇:Yb/Er as core,Sr₂Gd F₇ as middle shell and SrF₂ as outerest shell,were synthesized by a seed-mediated growth process.The NPs possess good crystallinity,morphology and upconversion fluorescence property.After modification by PEI,in vitro cell upconversion imaging with low auto-fluorescence was realized.Due to the presence of Gd³⁺ions,in vivo MR imaging was also achieved with these designed NPs.More significantly,these special core-shell NPs exhibited high contrast in in-vivo CT imaging because of their good X-ray absorption ability.These results indicate that the core-shell upconversion NPs can serve as promising contrast agents for upconversion fluorescence/MR/CT tri-modal bioimaging.The last chapter is the summary of the research project.This thesis illustrates a comprehensive investigation of rare earth based nanomaterials from controllable synthesis to related application,especially multi-modal bioimaging.