【作者】 刘国聪；

【导师】 段学臣；

【作者基本信息】 中南大学 ， 材料物理与化学， 2010， 博士

【摘要】 稀土掺杂的金属氧化物微/纳米材料在纳米器件、光电器件、微传感器、催化、气敏以及磁性等领域有着广泛的应用前景。发展新的合成方法,获取特定尺寸、形貌、维度、单分散性的微/纳米材料并探索其形成机制,对深入系统研究微/纳米结构与性能的关系,构建新型稀土掺杂金属氧化物微/纳米结构体系,最终实现材料的工业应用具有重要意义。本论文对Eu3+、Dy3+、Sm3+等稀土离子掺杂CeO2、Ga2O3、LaVO4和YBO3等基质的微/纳米材料的液相调控合成及其荧光性质进行了详细研究,并对微/纳米材料的形貌、形成机制和晶粒尺寸等因素与荧光性能之间的相关性进行了探索。通过大量的实验与分析,取得了一些创新性成果。发展了一种高分子表面活性剂(聚乙烯吡咯烷酮,PVP)辅助的水热法合成稻草状CeO2:Sm3+微米晶的水热-分解路线。通过改变初始浓度,反应时间及温度,PVP含量等参数有效地控制了CeO2:Sm3+的形貌。实验结果表明稻草状CeO2:Sm3+(5.0at.%)微米晶表现出最好的荧光强度,并且升高退火温度可以提高其黄光和蓝光的发射强度。提出了一种乙醇-水混合体系合成单分散纳米晶的溶剂热路线。以Ce(NO3)3、Eu(NO3)3和NH3·H2O为原料,控制醇-水体系pH为9,180℃下反应12h获得晶粒尺寸小于100nm的单晶结构的立方萤石型CeO2:Eu3+纳米晶。样品表现出良好的紫外吸收性能,能将吸收的能量有效传输给Eu3+,在593、612、632nm处发射较高强度的橙红光。采用CTAB辅助的水热合成技术,控制CTAB含量为0.6g,初始pH为9,160℃水热反应24h能够获得晶化程度高且单分散性好的方片状Ga2O3:Dy3+纳米晶。通过考察初始溶液pH值,CTAB含量,反应温度和反应时间等参数对Ga2O3:Dy3+样品的形貌和物相结构的影响,提出了方片状样品的形成机制。试验发现Dy3+的掺杂提高了Ga2O3基质与Dy3+之间的能量传递和发光效率。掺杂6at.%Dy3+的方片状样品具有最强的蓝光发射。通过简单的水热反应,以Ga2O3、Eu2O3、HCl和NaOH为基本原料,控制pH为6,140℃下反应10h获得GaOOH：Eu3+棒状前驱体,再热分解可得形貌保持的Ga2O3:Eu3+纳米棒。通过控制母液pH能很好地调节产品的纵横比,进而控制样品的形貌。棒状α-Ga2O3:Eu3+和β-Ga2O3:Eu3+能吸收波长小于275nm的紫外光,其能带隙分别为4.40 eV和4.30 eV。样品的形貌和物相结构对其色纯度、荧光强度有较大影响,其中棒状β-Ga2O3:Eu3+比α-Ga2O3:Eu3+具有更好的发光强度和较大的红橙比(R/O)。建立了一种pH调控水热合成新颖多面体LaVO4:Dy3+纳米晶的新方法。通过调节初始pH、反应时间以及煅烧温度等参数,实现了对LaVO4:Dy3+多面体的晶粒尺寸、物相结构、形貌以及化学组成的有效调控。多面体LaVO4:Dy3+纳米晶的最佳水热合成工艺条件为：初始溶液pH为9,水热温度为160℃,反应时间≥24h。LaVO4:Dy3+多面体具有较强的黄光发射和较高的色纯度。升高退火温度能不同程度地强化多面体的蓝光和黄光发射,而且其蓝光强度增大速率远大于其黄光。建立了EDTA络合-水热合成LaVO4:Sm3+纳米棒的新方法。考察了EDTA浓度、前驱体溶液pH、反应时间、反应温度以及不同反应底物等因素对产物的晶相、尺寸和形貌的影响,发觉络合剂(EDTA)所扮演的鳌合物基体和诱导试剂的双重作用是样品从单斜独居石型结构向四方锆石型结构转变和晶体一维生长机制的重要因素。荧光结果说明棒状t-LaVO4:Sm3+比m-LaVO4:Sm3+晶体具有更优越的红光发射,相比其它形貌,棒状晶体中的Sm3+含量较高,表现出较强的三个特征发射峰,并且在4G5/2→6H5/2处发射峰强度的增加速率高于4G5/2→6H9/2处的发射峰。另外,t-LaVO4:Sm3+纳米棒的4G5/2→6G7/2的跃迁可望实现红色激光输出。设计了一条简单的、环境友好的乙醇-水混合溶剂热法合成新颖鱼骨状LaVO4:Eu3+微/纳米晶体的合成路线。系统考察了各反应参数对样品形貌和物相结构的影响,提出了鱼骨状晶体的生长机制。初始pH=9,乙醇含量20 ml,Eu掺杂浓度为4.0 at.%,水热温度160℃反应24h时所得的样品是规整形貌的鱼骨状LaVO4:Eu3+纳米晶并表现出最强的红光发射。鱼骨样品的Eu3+的5D1-7F2跃迁发射的衰减曲线遵循指数衰减规律,其荧光寿命稍长于棒状样品,是一种颇具前途的红色荧光粉。建立了乙二醇-水混合溶剂热法以及表面活性剂(PVP)辅助的水热法,通过控制乙二醇浓度及PVP含量,分别获得了新颖花瓣扇形和夹心薄饼状的YBO3:Eu3+微/纳米晶。研究了晶体结构、颗粒形貌、荧光性能与生长行为的相关性。详细考察了不同形貌样品的紫外吸收性能和荧光特性。实验结果显示,花瓣扇形样品具有优异的红光发射,是彩色等离子平板显示器(PDP)用红色荧光粉的理想材料。更多还原

【Abstract】 Metal oxide micro-/nanomaterials doped with rare earth ions have enormous potential applications in photoelectric devices, nanodevices, sensors, catalysis and magnetism due to its special physical and chemical properties. Preparation of micro/nanomaterials with well-defined size, morphology dimensionality and diversity through novel synthesis approaches and investigation of their formation mechanism should be a key precodition to reveal the relation between the structures and properties, fabricate a novel micro/nano-structure system for metal oxides doped by rare earth ions and pave the way to real applications. New solution-based manipulated synthetic strategies and fluorescent properties of CeO2, Ga2O3, LaVO4 and YBO3 micro/nanomaterials doped by Eu3+, Dy3+ and Sm3+, respectively, have been detailedly investigated in this dissertation. The valuable explorations have been carried out on the relationship between fluorescence and size/morphology of the prepared micro/nanomaterials. Some new and interesting results were achieved and listed as follows.A new hydrothermal-decomposition method was developed to prepare straw-like CeO2:Sm3+ microcrystals in water solution assisted by macromolecule surfactant (PVP). Herein, the morphologies could be well-controlled through the changes of original concentration, reaction time and temperature as well as the content of PVP. Straw-like CeO2:Sm3+(5.0 at.%) microcrystals prepared exhibited the best fluoresence intensity in comparation with other shapes, and high annealing temperature was helpful to enhance intensities of yellow and blue emission. Besides, a simple solovthermal route was proposed to synthesize monodispersed nanocrystals in ethanol-water mixed solution. Employing Ce(NO3)3, Eu(NO3)3 and NH3·H2O as reaction materials, cubic fluorite CeO2:Eu3+ with single crystal structure, the diameter of which was shorter than 100 nm, could be prepared in the solution with the pH value of 9 at 180℃for 12 h. CeO2:Eu3+ nanocrystal possessed a good ultraviolet absorption and effectively transmited the absorbed energy to Eu3+, resulting in high strength emissions at 593,612, and 632 nm, respectively. The hydrothermal/ solvothermal methods are availed to controlled synthesize polymorphological CeO2:Ln3+ micro-/nanocrystals.When the content of CTAB was 0.6 g, and the pH value of solution was 9, as well as the reaction was carried out at 160℃for 24 h, monodispersed squarelike Ga2O3:Dy3+ particles with well-crystallization could easily synthesized via hydrothermal route assisted by CTAB. The effects of pH, the content of CTAB, reaction time and temperature on the morphology and structure of the sample were detailedly discussed. The formation mechanism of squarelike Ga2O3:Dy3+ nanocrystals was proposed. It was found that the doping of Dy3+ enhanced the efficiency of energy transfer between Ga2O3 and Dy3+ and improved its luminescence, and squarelike Ga2O3:Dy3+ nanocrystal with doped Dy3+of 6 at.% showed the highest blue emisssion. With Ga2O3, EU2O3, HCl and NaOH as original materials, a simple hydrothermal method was applied to prepare rodlike GaOOH in water solution with the pH value of 6 at 140℃for 10 h. The as-prepared GaOOH could be decomposed thermally into Ga2O3:Eu3+ nanorod. It was found that the aspect ratios and morphologies of the samples could be well-controlled by adjusting pH values of the solutions. Both a-Ga2O3:Eu3+and p-Ga2O3:Eu3+ could absorb ultraviolet radiation (≤275 nm), and the energy bands of which were 4.40 and 4.30eV, respectively. The morphologies and crystal structures of the obtained samples showed significant influences on color purity, fluorescene intensity of the samples. Rodlikeβ-Ga2O3:Eu3+ had better luminous intensity and a larger ratio of red emission to orange emission than rodlikeα-Ga2O3:Eu3+.A simple hydrothermal method was adopted to synthesize a novel polyhedron LaVO4:Dy3+ nanocrystal. For LaVO4:Dy3+polyhedrons, the crystal size, crystal structure, shapes and chemistry constituent of the samples could be controlled by adjusting the parameters of pH, reaction time and temperature, which have been synthesized in the solution with the pH value of 9 at 160℃for more than 24 h. It was found that the as-prepared polyhedron showed higher color purity and stronger yellow emission. Higher annealing temperatures for the samples enhanced the intensities of blue and yellow emission, and the increasing rate of intensity from blue emisssion was more larger than yellow emission. Furthermore, a novel complexing-hydrothermal method assisted by EDTA was also proposed to synthesize LaVO4:Sm3+ nanorods. The effects of concentration of EDTA, pH values, reaction time and temerature on crystal structure, size and morphology of the samples were discussed. It was found that double reactions of mating reaction and induction behavior from EDTA played important roles for LaVO4:Sm3+ to accomplete the transformation from monoclinic (m-) structure to tetragonal (t-) phase and to facilely form nanorods. Rodlike t-LaVO4:Sm3+ showed higher red emisssion than m-LaVO4:Sm3+ nanorod. The content of Sm3+ of nanorod was more than the sample with other shapes, taking on three stronger characteristic emisssions. Increasing rate of emission intensity from 4G5/2→6H5/2 was higher than that of emission from 4G5/2→6H9/2. Besides,4G5/2→6G7/2 transition of t-LaVO4:Sm3+ nanorod could be used as red laser output.A simple and environmentally friendly solvothermal strategy was designed to fabricate a novel fishbonelike LaVO4:Eu3+micro-/nanocrystals in mixed ethanol-water solution. The formation mechanism for fishbonelike LaVO4:Eu3+ crystal has been investigated in detail after the effects of experimental parameters on the structure and morphology of the samples were disscussed. A great deal of fishbonelike LaVO4:Eu3+ crystals with stronger red emission could be facilitatedly synthesized when the content of ethanol was 20 ml, the concentration of Eu3+ was 4.0 at.% and the pH value of solution was 9, as well as the reaction was carried out at 160℃for 24h. The delay curve from 5D1-7F2 transition of Eu3+ in the as-prepared crystals accorded to exponential delay rule. The fluorescence lifetime of 5D1-7F2 transition of Eu3+ for fishbonelike LaVO4:Eu3+ crystal was a little longer than rod-like sample. As a red phosphor, fishbone-like LaVO4:Eu3+did possess the undoubted advantages.YBO3:Eu3+ micro/nanocrystals with novel morphologies of petal sector and sandwich cake were synthesized by surfactant-assisted hydrothermal/solvothermal methods. The studies on the crystal growth revealed the relationship among the crystal Structures, the morphology and fluorscence.The experimental results from ultraviolet light absorbancy and fluorescence properties presented by YBO3:Eu3+ crystals with various morphologies indicated that petal sector-like YBO3:Eu3+ possessed some red emission advantages than the others, becoming a promising candidate of PDP red phosphor.更多还原