CdTe量子点激发态弛豫特性研究

发布时间：2018-05-13 04:18

本文选题：自组装纳米材料 + 飞秒时间分辨光谱　；参考：《吉林大学》2015年硕士论文

【摘要】：伴随着制备技术的进步，纳米材料科学的发展从单纯的制备不同形态的纳米材料，拓展到对材料体系的物理特性研究上，重在明晰微观尺度材料的相关物理机制。同时，人们努力将微观尺度下丰富多彩的量子局限效应拓展到介观甚至宏观领域。现在，通过化学手段，在超晶格或超分子体系中，这种期待得到实现，相关的材料研究逐步兴起。本文正是基于纳米科学发展的这两个重要方面，在微观尺度研究纳米材料物性与量子局限关系的同时，将量子局限效应通过化学组装的方法拓展到宏观，并对拓展之后的材料整合特性进行了研究。具体内容如下：本论文所使用的材料体系为巯基乙酸(thioglycolic acid)钝化的CdTe(TGA-CdTe)量子点。在强偶极相互作用下，CdTe量子点通过层级自组装形成超分支纳米结构，其结构的构建单元为原始CdTe量子点。研究表明：超分支纳米结构形态受熟化时间、环境pH值以及辅助剂比例的影响；组装后的结构同时具备介观尺度和量子局限性两个特点，同时表现出光学特性上的整合性能，特别是分枝状结构已被实验验证可具有更好的电荷分离效果，因此该种结构在光伏转换和传感等领域有着重要的潜在应用价值。主要研究成果如下：第一部分，通过对合成量子点方法优缺点的对比，我们选择相对环保，实验条件温和的水热法成功制备高质量的TGA-CdTe量子点，并对其形貌和稳态光学性质进行了表征。随后利用瞬态吸收和荧光上转换技术对合成后的TGA-CdTe量子点进行激发态弛豫动力学的探测。我们发现量子局限效应对激发态弛豫过程有强烈的影响。第二部分，通过CdTe量子点自组装的方式，构建了层级型纳米超分支结构，并对超分支结构进行了形貌与光学特性的表征。实验结果表明，CdTe在超分支结构上，原始量子点单元被保存下来，即超分支纳米结构继承了原始TGA-CdTe量子点的量子局限效应。同时，因为与溶液中单分散的量子点相比，量子点与量子点之间的间隔缩小了很多，因此量子点之间形成比较完善的网络连接性，时间分辨实验证明其有利于载流子的扩散传输。第三部分，我们构造了CdTe量子点-Au纳米粒子组成的激子-等离子体系，利用时间分辨光谱手段，研究了Au粒子的引入对CdTe量子点体系的激子复合过程的影响，我们发现随着Au纳米粒子掺杂比例的增加，体系荧光淬灭效果越明显。时间分辨实验清楚的显示了局域场效应是引起这种淬灭的原因。本论文利用超快时间分辨光谱技术对合成的TGA-CdTe量子点的激发态弛豫过程进行了深入的研究，发现量子局限效应对激发态弛豫有强烈的影响，这对改善光电器件的光电转换效率有一定的理论参考价值。另外，我们制备的超分支结构，，比量子点具有更好的电荷分离效果；同时，超分支状结构能够提高对太阳光的收集效率，因此该种结构在光伏转换和传感等领域有着重要的潜在应用价值。最后，我们利用时间分辨光谱手段对CdTe量子点-Au纳米粒子的二元体系荧光淬灭现象做了分析解释，为探索二元体系能量转移机理提供实验依据。
[Abstract]:With the progress of preparation technology, the development of nanomaterial science has developed from simple preparation of different forms of nanomaterials to the physical properties of the material system, and the physical mechanism of microscale materials is clarifying. At the same time, people strive to extend the rich and colorful quantum confinement effect at microscale to mesoscopic and even macro. Now, this expectation is realized by chemical means in superlattice or supramolecular system, and the related material research is rising gradually. This article is based on the two important aspects of the development of nanoscience. At the same time, the quantum confinement effect is assembled by chemical assembly while studying the relationship between the physical property and the quantum confinement of nanomaterials. The method is extended to the macro level, and the characteristics of material integration after expansion are studied.
The material system used in this paper is a CdTe (TGA-CdTe) quantum dot passivated by mercapto (thioglycolic acid). Under the strong dipole interaction, the CdTe quantum dots pass through the hierarchical self-assembly to form a super branched nanostructure. The structure of the structure is a primitive CdTe quantum dot. The study shows that the morphology of the super branched nanostructure is subjected to the ripening time and the ring. The influence of the pH value and the proportion of the auxiliary agent; the assembled structure has two characteristics of mesoscopic scale and quantum limitation, and also shows the integration performance of optical properties, especially the branching structure has been experimentally verified to have a better charge separation effect. Therefore, the structure has the emphasis in the fields of photovoltaic conversion and sensing. The potential application value.
The main research results are as follows:
In the first part, by comparing the advantages and disadvantages of the synthetic quantum dots, we choose a relatively environmentally friendly and mild hydrothermal method to prepare the high quality TGA-CdTe quantum dots, and characterize their morphology and steady state optical properties. Then the TGA-CdTe quantum dots are made by transient absorption and fluorescence upconversion technology. We find that the quantum confinement effect has a strong effect on the relaxation process of excited states.
In the second part, a hierarchical nano superbranch structure is constructed by means of CdTe quantum dots self-assembly, and the morphology and optical properties of the superbranched structure are characterized. The experimental results show that the original CdTe is preserved in the superbranching structure, that is, the superbranch nanostructures inherit the quantum dots of the original TGA-CdTe quantum dots. At the same time, as compared with the monodisperse quantum dots in the solution, the interval between quantum dots and quantum dots is reduced a lot, so a more perfect network connectivity is formed between the quantum dots, and the time resolution experiment proves that it is beneficial to the carrier diffusion.
In the third part, we constructed the exciton plasma system composed of CdTe quantum dots -Au nanoparticles. Using time resolved spectroscopy, we studied the effect of the introduction of Au particles on the exciton recombination process of the CdTe quantum dots system. We found that the fluorescence quenching effect of the system was more obvious with the increase of the proportion of Au nanoparticles. Time resolution was found. The experiment clearly shows that the local field effect is the cause of this quenching.
In this paper, the excited state relaxation process of the synthesized TGA-CdTe quantum dots is deeply studied by using the ultrafast time resolved spectroscopy. It is found that the quantum confinement effect has a strong influence on the excited state relaxation. This has some theoretical value for improving the photoelectric conversion efficiency of the photoelectric devices. In addition, we have prepared the super branching structure. At the same time, the super branching structure can improve the collection efficiency of the sun light, so the structure has an important potential application value in the field of photovoltaic conversion and sensing. Finally, we use the time resolved spectroscopy to quench the two element system of the CdTe quantum dots -Au nanoparticles. The phenomenon is analyzed and explained to provide experimental evidence for exploring the mechanism of energy transfer in the two element system.

【学位授予单位】：吉林大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O471.1

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