Adjustment And Control Of Microstructure And Upconversion Emission Properties Of Alkaline Earth-rare Earth Fluoride Synthesized With Solvothermal Method

Due to their unique luminescent and magnetic properties, upercopnversionluminescent nanomaterials doped with rare-earth have a lot of potential applications inthe fileds of luminescence, laser anti-counterfeit, display, detection of biologicalmacromolecules, biological fluorescence imaging and bioseparation and magneticresonance imaging. Therefore, seeking new photoluminescent materials anddeveloping new ways to realize the controlled synthesis of the nanomaterial are veryimportant to meet various requirements of their applications. According to the phasediagram of alkaline earth-rare earth fluoride systems, there exisit aboundance phasesat high temperature in these systems. However, up to date, the systematic work on thephase consititions and the controlled synthesis of these systems at low temperature islacking. Therefore, in the thesis, several typical alkaline earth-rare earth fluorideswere synthesized using solvothermal method at low temperature. The influences of Lncontent and reaction conditons on the phase structure, grain size and morphology ofthe products were studied systematicly, and the upconversion emission properties ofthe synthesized ultra-fine monodisperse nanocrystals were also investigated. The maincontents and results are as follows:1. The study on the effects of the reaction conditions on the phase consitutions,grain size and morphology of the reaction products in SrF₂-LaF₃system by usingsolvothermal method, and the multicolor upconversion emission behaviors of thenanosized SrF₂-LaF₃products. It is found that, the phase consititutions of the reactionproducts of Sr_1-xLa_xF_2+xobtained by solvothermal method are strongly dependent onthe fluorides, the cubic phase, mixtures of cubic and hexagonal phases, and hexagonalphase can be obtained in Sr_1-xLa_xF_2+xas its composition is in the range of0≤x<0.35,0.35≤x≤0.9, and0.9<x≤1, respectively. By adding of NaOH into the SrF₂-LaF₃solvothermal system, the NaLaF4nano-particles doped can be produced dure thepresence of Sr2+. Moreover, with the La content increasing, the average grain size ofpure cubic Sr_1-xLa_xF_2+x（x<0.35） nanocrystals （NCs） decreases, and ultrafinemonodisperse nanocrystals can be obtained through the additon of NaOH in thereaction systems. By doping with a proper amount of the lanthanide ions （Yb3+, Er3+,and Tm3+）, the intense blue, yellow, and white-color upconversion （UC） emission canbe realized in the Sr0.67La0.33F2.67NCs under the excitation of a980nm laser. Inaddition, intense near-infrared UC can also be obtained in the Yb/Tm codoped NCs. 2. The study on the effects of the reaction conditions on the phase consitutions,grain size and morphology of the reaction products in BaF₂-LuF₃system by usingsolvothermal method, the multicolor upconversion emission behaviors of thenanosized BaF₂-LuF₃products. By using NH₄F as fluorine source in the solvothermalreaction sytem of BaF₂-LuF₃, the products containing cubic BaF2and Ba_1-xLu_xF_2+xphases, monoclinic BaLu2F8and cubic NH₄Lu2F8phases were succefully synthesized.However, to obtain the Ba_1-xLu_xF_2+xwith pure cubic structure, the compostion of theflorides should be controlled around x＝0.40. By addiing NaOH into the reactionsystems, the products containing cubic BaF2and Ba_1-xLu_xF_2+xphases, monoclinicBaLu4F14phase, and hexagonal Ba7F12Cl2and NaLuF4phase can be obtained, and thecompostion of the fluorides to obtain pure cubic Ba_1-xLu_xF_2+xphase is expended to bein the range of0.30<x<0.55. By optimizing conditions, the ultrafine pure Ba_1-xLu_xF_2+x（x=0.33） phase with cubic structure and average grain size less than10nm can besynthesized, and the multicolor UC emission can be realized through a proper amountof lanthanide ion （Yb3+, Er3+, and Tm3+） doping.3. The study on the effects of the reaction conditions on the phase consitutions,grain size and morphology of the reaction products in SrF₂-LuF₃system by usingsolvothermal method, the multicolor upconversion emission behaviors of thenanosized SrF₂-LuF₃products, and surface modifaction of the products. By usingsolvothermal method under low temperature in the SrF₂-LuF₃reaction systemswithout NaOH containing, the products of Sr_1-xLu_xF_2+xcontain the mixtures of cubicSrF2and Sr_1-xLu_xF_2+xphases, the pure cubic Sr_1-xLu_xF_2+xphase, and the mixtures ofcubic Sr_1-xLu_xF_2+xand orthogonal LuF3phase as its composition is in the range of0<x<0.2,0.2≤x≤0.45, and0.5≤x<1, respectively. Under the same synthesis conditions,the average grain size of the pure Sr_1-xLu_xF_2+x（0.2≤x≤0.45） phase with cubic structuregradually decreases with the increase of Lu content, and which can be further reducedby adding NaOH in the reaction system. By doping with a proper amount of rare-earth（Yb3+, Er3+, and Tm3+）, the Sr_1-xLu_xF_2+xnanocrystals can emit the multicolorupconversion fluorescence. Moreover, by using the inverse emulsion method, theultrasmall monodisperse Sr_1-xLa_xF_2+xnanocrystals coated with a thin SiO₂layer can beobtained, which exhibit hydrophilicity and enhanced luminescent properties.4. The study on the nucleation and growth mechanism of the ultrasmllmonodisperse alkaline earth-rare earth fluoride nanocrystals in BaF₂-GdF₃system. Byusing solvothermal method, the products of Ba_1-xGd_xF_2+xwith pure cubic structure canbe synthesized at190C as its composition is in the range of0.5≤x≤0.8, and the grain size of the products is less than10nm. Under the same conditions, the Ba_1-xGd_xF_2+xproducts with the composiotn in the range of0.5≤x≤0.8show a grain size far smallerthan that of pure phase BaF2and GdF3. It is found that GdF3has an extremely lowsolubility product constant in H2O solution in comparison with BaF2and there exist alarge amount of defects in cubic Ba_1-xGd_xF_2+xnon-stoichiometric phase, which may beresponsible for the ultrafine grain size of Ba_1-xGd_xF_2+x.