【作者】 谢蒂旎；

【导师】 黄世华； 彭洪尚；

【作者基本信息】 北京交通大学 ， 光学工程， 2014， 博士

【摘要】 摘要：长期以来,人们采用表面修饰的方法来削弱表面效应、提升纳米材料的发光效率,而在众多的表面修饰方法中,核壳结构是一种十分有效的方法。壳层的包覆可以提供一个保护层,将发光中心与外界的环境隔绝开来,阻断发光中心与表面猝灭中心的能量传递途径,从而有效的降低表面猝灭的程度,提升材料的发光效率。大量的研究工作围绕着壳层厚度的优化而展开,在这个过程中,人们发现了核壳结构纳米材料中的离子扩散现象。如果核壳结构纳米颗粒中的掺杂离子穿过壳层从纳米颗粒的核心中扩散到了表面,表面效应和表面猝灭将会重现,那么壳层的保护作用将失去意义。因此,离子扩散可能会对核壳结构纳米材料的发光性能造成重大影响。研究并了解核壳结构纳米材料中掺杂离子在多高的温度下能够发生何种程度的扩散,以及这种扩散会对材料的发光性能造成什么样的影响,是非常有必要的。本论文的研究主要包括以下三个部分：(一)采用共沉淀法制备YVO4:Eu3+纳米颗粒和不同壳层厚度的YVO4: Eu3+@YVO4核壳结构纳米颗粒。通过x射线粉末衍射,透射电子显微镜,光谱测试等手段对其形貌、大小以及发光性能进行表征,验证不同壳层厚度对核壳结构纳米颗粒发光性能的影响。(二)在保护条件下对YVO4:Eu3+@YVO4核壳结构纳米颗粒进行热处理,既要确保纳米颗粒之间不发生团聚,又要能够促使核心中的Eu3+向外扩散。然后以发光光谱以及发光衰减的测试和拟合为主要手段,表征出不同热处理阶段下Eu3+的扩散程度。(三)采用Monte Carlo方法对YVO4:Eu3+@YVO4核壳结构纳米颗粒中Eu3+的扩散过程以及发光衰减过程进行计算机模拟,并与实际测试得到的数据进行比对,获取扩散过程中的各项参数。这些研究能够让人们对YVO4:Eu3+@YVO4核壳结构纳米颗粒中Eu3+的扩散有一个比较直观的印象,有助于深化对表面效应和浓度猝灭效应的认识。所获取的数据可以作为其他核壳结构纳米材料的制备和应用的有益参考,也希望能够为高温条件下设计和制备高发光效率的核壳结构纳米材料拓宽思路、提供一些新的选择。如果能够在高温下对核壳结构纳米颗粒进行热处理而又不发生团聚,那么就有可能从三个方面同时实现发光效率的优化：1.高温处理提升材料的结晶度；2.将掺杂离子的扩散控制在内部局部的范围中避免表面猝灭；3.通过核心中掺杂浓度和扩散程度的设计,避免浓度猝灭。这样才能最大限度的提高核壳结构纳米材料的发光性能。更多还原

【Abstract】 ABSTRACT:Core-shell structure has been used to weaken surface effect and raise luminescent efficiency of nano-materials. The shell can provide a protective layer, isolate the emission centers from the outer environment and cut off the energy transfer access between the emission centers and the surface quenching centers, which could reduce the degree of surface quenching and raise luminescent efficiency of nano-materials. A lot of research works revolve around optimizing the thickness of the shell, and then the ions’diffusion in the core-shell nano-materials was discovered. If the doped ions diffuse through the shell from the core of nanoparticles (NPs) to the surface, surface effects and surface quenching will reproduce and the protective effect of the shell would be meaningless. Thus, ions’diffusion might significantly influence the luminescent properties of core-shell nano-materials. It is quite necessary to study and find out the doped ions would diffuse at what temperature to what extent and how it will influence luminescent properties of core-shell nano-materials. My research mainly includes the following three parts:1. Synthesize YVO4:Eu3+NPs and YVO4:Eu3+@YVO4core-shell NPs with different shell thickness by co-precipitation method. Characterize the prepared nano-materials’ phase, morphology, size and luminescent properties by X-ray diffraction, transmission electron microscopy, and photoluminescence spectrum. Verify the influence of shell thickness on luminescent properties of core-shell NPs.2. Heat-treat the YVO4:Eu3+@YVO4core-shell NPs under certain protective conditions. Make sure that the Eu3+diffuse outward without NPs’aggregation. Characterize Eu3+’s diffusion extent of different heat-treatment stages by photoluminescence spectrum, photoluminescence decay and fitting method.3. Simulate the diffusion process and luminescence decay of the YVO4:Eu3+@YVO4core-shell NPs, and compare the simulation result and the actual test data to obtain the parameters of the diffusion process.These studies will give a direct impression of Eu3+diffusion in YVO4: Eu3+@YVO4core-shell NPs and help understanding the surface effect and concentration effect. The acquired data should be reference to preparation and application of other core-shell structure of nano-materials. It also provides new options to design and synthesize high luminescent efficiency core-shell nano-materials at elevated temperatures.If the core-shell NPs can be annealed at high temperature without aggregation, then it is possible to optimize luminescent efficiency from three aspects:1. Improve the crystallinity of nano-materials at elevated temperature;2. Prevent surface quenching by controlling the ions’diffusion in a located range.3. Prevent concentration quenching by delicately design the doping concentration in the core and the diffusion extent.更多还原