Ionic Liquid-Based Synthesis, Characterization, And Property Study Of Rare Earth Fluorescent Nanomaterials

This thesis is devoted to the synthesis of complex metal/rare earth fluorides, rare earth oxides, and rare earth oxyfluorides in ionic liquids (ILs). The crystal phase, size, and shape of the as-obtained materials were investigated by various characterization methods. The probably growth mechanisms for the nanocrystals and the relationship between the fluorescent properties and structures of the Ln3+ doped fluorescent materials were studied in detail. Specific research contents and results are summarized as follows:(1) Preparation of ILsThree ILs (1-butyl-3-methylimidazolium bis(trifluoruomethylsulfonyl)imide ([BMIM][Tf2N]), 1-hexadecyl-3-methylimidazolium bromide ([BMIM]Br), and 1-hexadecyl-3-methylimidazolium bis(trifluoruomethylsulfonyl)imide ([C16MIM][Tf2N])) were synthesized through the two-step method. The compositions and structures of the ILs were characterized by elemental analysis, mass spectroscopy, and nuclear magnetic resonance spectroscopy. The results indicate that the as-obtained products are the target ILs.(2) ILs-based Synthesis of Rare Earth Upconversion Nanocrystals with the Assistance of Microwave Radiation and Study of their Fluorescent PropertiesCubic NaYF4 nanoclusters were successfully synthesized in [BMIM]BF4 with the assistance of a microwave accelerated reaction system. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and selected area electron diffraction (SAED) were used to characterize the obtained products. Interestingly, these spherical NaYF4 nanoclusters are formed by the self-assembly of small nanoparticles. The diameters of the nanoclusters could be easily tuned just by changing the amounts of the precursors. By conducting the control experiments with different ILs or precursors, it is proven that the ILs have played key roles, such as the solvents for the reaction, the absorbents of microwave irradiation, and the major fluorine sources for the formation of the NaYF4 nanocrystals. And the final morphologies of the nanocrystals are strongly affected by the viscosities of the ILs.The upconversion properties of NaYF4:Yb,Er and NaYF4:Yb,Tm synthesized in different ILs were compared. The influences of different Ln3+ doping concentrations, different average diameters of the nanoclusters, and different synthetic methods on the fluorescent properties of NaYF4:Yb,Er and NaYF4:Yb,Tm were investigated. The experimental results indicate that the nanoclusters obtained in BmimBF4 could serve as excellent host matrix for upconversion phosphors. Since this ILs-based and microwave-accelerated procedure is efficient and environmentally benign, we believe that this method may have some potential applications in the synthesis of other nanomaterials. (3) Synthesis of Rare Earth Oxides and Oxyfluorides via Solvothermal Method and Study of their Fluorescent PropertiesCubic Y2O3 was synthesized in [C16MIM][Tf2N] through the ionothermal method. XRD, SEM, and TEM were used to characterize the obtained products. The influences of different reaction temperature and time on the morphology and the fluorescent property of Y2O3:Eu were investigated. The experimental results show that the coaxal three-blade structure of Y2O3:Eu could be obtained at 220℃and 24 h, and the fluorescent property of the as-synthesized Y2O3:Eu is better than that of the samples obtained in other conditions.Additionally, a series of cubic rare earth oxyfluorides (REOF) was synthesized through the solvothermal method, and the characterization results by SEM and TEM show that what we obtained are REOF nanotubes. The fluorescent properties of YOF:Eu and YOF:Tb were studied. The results indicate that the as-synthesized REOF could also serve as excellent host materials.