【作者】 龚伦军；

【导师】 林建国；

【作者基本信息】 湘潭大学 ， 材料科学与工程， 2013， 博士

【摘要】 稀土掺杂纳米材料具有独特的发光和磁性质，在发光、颜色显示、防伪、生物大分子检测、生物荧光成像、生物分离和磁共振成像等方面应用前景广阔。寻找新的发光基质材料并研究其可控合成，得到满足各种应用需求的稀土掺杂纳米材料具有重要的学术价值和现实意义。碱土-稀土氟化物在高温下具有丰富的相组成，但对其低温相组成和纳米晶的可控合成还缺乏系统研究。本文以几种典型的碱土-稀土氟化物为研究对象，系统研究了在低温溶剂热合成时，稀土元素含量、反应条件对产物相结构、晶粒尺寸及形貌的影响，并对所获得的纳米晶的发光性能进行了研究。主要研究内容及结论如下:1.低温溶剂热合成条件对SrF₂-LaF₃体系反应产物的相组成、晶粒尺寸及形貌的影响，纳米晶发光性能的调控。研究结果表明:采用低温溶剂热合成法制备的产物的相组成取决于SrF₂-LaF₃体系的成分，名义成分为Sr_1-xLa_xF_2+x（原子百分数，at.%，以下相同）的产物，在0≤x<0.35、0.35≤x≤0.9和0.9<x≤1的范围分别由纯立方相、立方相和六方相的混合物以及纯六方相组成;在反应体系中加入NaOH，会由于Sr2+的存在而生成Sr掺杂的NaLaF4相;立方相Sr_1-xLa_xF_2+x（x<0.35）纳米晶的平均晶粒尺寸随着La含量的增加而减小，在反应体系中加入NaOH后，可进一步降低其晶粒尺寸，并得到超细单分散的纳米晶;通过稀土（Yb、Er和Tm）掺杂，Sr_1-xLa_xF_2+x（x＝0.33）立方相纳米晶可以实现蓝色、黄色和白色上转换发光，其中Yb/Tm共掺的纳米晶还具有较强的红外上转换发光。2.低温溶剂热合成条件对BaF₂-LuF₃体系反应产物的相组成、晶粒尺寸及形貌的影响，纳米晶发光性能的调控。研究结果表明：以NH₄F为氟源时，可得立方相的BaF2和Ba_1-xLu_xF_2+x、单斜相的BaLu2F8和立方相NH₄Lu2F8，其中得到纯立方Ba_1-xLu_xF_2+x相的体系成分范围很窄，在x＝0.40左右;当反应体系中加入NaOH后，反应产物包括立方相的BaF2和Ba_1-xLu_xF_2+x、单斜相的BaLu4F14、六方相的Ba7F12Cl2和NaLuF4，其中获得纯立方相Ba_1-xLu_xF_2+x的体系成分范围扩大，在0.30<x<0.55均可得到纯立方相。通过优化合成条件，纯立方相Ba_1-xLu_xF_2+x（x=0.33）的晶粒尺寸可以控制在10nm以下，并通过适当的稀土（Yb、Er和Tm）掺杂，该纳米晶可以实现多色上转换发光。3.低温溶剂热合成条件对SrF₂-LuF₃体系反应产物的相组成、晶粒尺寸及形貌的影响，纳米晶发光性能的调控及其表面改性。研究结果表明：以HF为氟源、不加NaOH时，名义组成为Sr_1-xLa_xF_2+x的产物在0<x<0.2、0.2≤x≤0.45和0.2≤x≤0.45范围内，其相组成分别为SrF2和Sr_1-xLa_xF_2+x立方相共存、纯Sr_1-xLa_xF_2+x立方相以及Sr_1-xLa_xF_2+x立方相和LuF3正交相共存;立方相Sr1-xLuxF2+x（0.2≤x≤0.45）纳米晶的平均晶粒尺寸随着Lu含量的增加而减小，通过在反应体系中加入NaOH，可使得其晶粒尺寸进一步降低，从而得到超细单分散的纳米晶，通过适当的稀土（Yb、Er和Tm）掺杂，Sr_1-xLu_xF_2+x立方相纳米晶可以实现多色上转换发光；在此基础上，采用反相乳液法，在Sr_1-xLu_xF_2+x纳米晶表面包覆一层SiO₂后，可得到亲水性的纳米晶，该纳米晶表现出更高的上转换发光强度。4. BaF₂-GdF₃体系超细单分散碱土-稀土氟化物纳米晶的成核生长机制研究。研究结果表明：采用低温溶剂热合成法，可制备出名义为Ba_1-xGd_xF_2+x的纳米晶，该纳米晶在0.5≤x≤0.8成分范围内具有纯立方相结构，并通过优化合成条件，其晶粒尺寸可以控制在10nm以下；由于在溶剂热反应体系中，GdF3的溶度积常数极低，导致含有Gd的Ba_1-xGd_xF_2+x在结晶过程中更易均匀形核，同时，Ba_1-xGd_xF_2+x固溶体中还存在大量缺陷能阻碍晶粒生长，因而Ba_1-xGd_xF_2+x在溶剂热合成时更易获得超细单分散的纳米晶。更多还原

【Abstract】 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.更多还原