石墨烯量子点的制备、表征及发光机理研究
发布时间：2019-03-21 20:09
【摘要】：近几年,作为一种新型纳米碳材料石墨烯量子点,由于良好的水溶性、生物低毒性、稳定而明亮的荧光等特点,而被广泛关注和研究。大量的制备方法不断被提出用来合成石墨烯量子点,并被应用于生物成像、光电子器件、传感器、药物传输和光催化剂等领域。然而,石墨烯量子点的发光机理仍存存着很大的争议,特别是本征态发光与缺陷态发光的竞争或合作机制,使得石墨烯量子点随着不同制备方法而展现出不同的发光机理。基于此,我们就如何制备获得高晶格质量、高量子产率的石墨烯量子点的合成方法进行探索研究。此外,我们还对所制备的石墨烯量子点的发光起源进行了深入研究。本文中,我们的主要研究成果如下:1.高质量的石墨烯量子点的制备以葡萄糖、浓硫酸、去离子水为反应物,在温度200 oC下水热法加热3小时,获得具有良好晶格质量和量子产率为14.3%的蓝色荧光石墨烯量子点。结构表征结果表明制备获得的石墨烯量子点平均尺寸大小为3.35 nm和平均厚度为1 nm,是1~3层石墨烯层的盘状结构。光学表征结果表明该石墨烯量子点可发出几乎独立于激发波长的紫色和蓝色荧光。2.石墨烯量子点的合成机理调控实验中浓硫酸的使用量,发现合成的产物从无定形的低量子产率的绿色荧光碳点向晶化良好的高量子产率的石墨烯量子点转变。通过调控反应温度、反应时间和葡萄糖量来优化实验条件参数,获得更高质量的石墨烯量子点。分析并阐述石墨烯量子点合成机理,即葡萄糖先成碳核,反应环境提供足够能量使得碳核继续生长并去除含氧官能团,获得尺寸更大、质量更高的石墨烯量子点。3.石墨烯量子点的发光机理基于深入分析分析吸收谱、光致发光光谱和光致发光激发谱,认为石墨烯量子点的紫外荧光和蓝色荧光分别来源于C=C键的局域电子空穴对的复合和sp2碳域的电子跃迁。变温光致发光光谱也进一步证明上述结论,同时表明出石墨烯量子点中存在着强电子-电子散射和强电子-声子耦合,与半导体量子点相类似的温度特性。4.石墨烯量子点薄膜的良好导电性在抛光硅片上制备了石墨烯量子点薄膜,并测试了薄膜的暗电导和光电导。石墨烯量子点薄膜的暗电导约为9?S,表明石墨烯量子点之间存在着很强的电子耦合和薄膜具有良好的导电性;光电导比暗电导明显增大了50%,意味着石墨烯量子点有望应用在光电探测上。以上研究工作获得了国家自然科学基金项目(11304197,61370042,11474201和61234005)的资助,特此感谢。
[Abstract]:In recent years, graphene quantum dots (QDs), as a new nano-carbon material, have been widely studied because of their good water solubility, low toxicity, stable and bright fluorescence and so on. A large number of preparation methods have been proposed for the synthesis of graphene quantum dots and have been used in the fields of bio-imaging, optoelectronic devices, sensors, drug transport and photocatalysts. However, the luminescence mechanism of graphene quantum dots is still controversial, especially the competition or cooperation mechanism between intrinsic state luminescence and defective state luminescence, which makes graphene quantum dots show different luminescence mechanism with different preparation methods. Based on this, we explore how to prepare graphene quantum dots with high lattice quality and high quantum yield. In addition, the origin of the photoluminescence of graphene quantum dots has been studied deeply. In this paper, our main research results are as follows: 1. High quality graphene quantum dots were prepared with glucose, concentrated sulfuric acid and deionized water as reactants, heated by hydrothermal method at 200 oC for 3 hours. Blue fluorescence graphene quantum dots with good lattice quality and 14.3% quantum yield were obtained. The results of structural characterization show that the average size and thickness of graphene quantum dots are 3.35 nm and 1 nm, respectively. They are disk-like structures with 1 / 3 layers of graphene. The optical characterization results show that the graphene quantum dot can emit purple and blue fluorescence almost independent of the excitation wavelength. 2. The synthesis mechanism of graphene quantum dots regulates the usage of concentrated sulfuric acid. It is found that the synthesized products change from amorphous green fluorescent carbon dots with low quantum yield to well crystallized graphene quantum dots with high quantum yield. Higher quality graphene quantum dots were obtained by adjusting the reaction temperature, reaction time and glucose content to optimize the experimental parameters. The synthesis mechanism of graphene quantum dots is analyzed and expounded, that is, glucose is first formed into carbon nucleus, and the reaction environment provides sufficient energy for the carbon nucleus to continue to grow and remove oxygen-containing functional groups to obtain larger size and higher quality graphene quantum dots. 3. The luminescence mechanism of graphene quantum dots is based on in-depth analysis of absorption spectra, photoluminescence spectra and photoluminescence excitation spectra. It is considered that the UV fluorescence and blue fluorescence of graphene quantum dots are derived from the recombination of local electron hole pairs of C _ (C) bond and the electron transition of sp2 carbon domain, respectively. The temperature-varying photoluminescence spectra further prove the above conclusions, and it is shown that there are strong electron-electron scattering and strong electron-phonon coupling in graphene quantum dots, which are similar to semiconductor quantum dots in temperature. 4. The results show that there are strong electron-electron scattering and strong electron-phonon coupling in graphene quantum dots. Graphene quantum dot thin films were prepared on polished silicon wafers by good conductivity of graphene quantum dot films. Dark conductivity and photoconductivity of graphene quantum dot thin films were measured. The dark conductivity of graphene quantum dot films is about 9 S, which indicates that there is strong electron coupling and good conductivity between graphene quantum dots. The apparent increase of the dark conductance by 50% means that graphene quantum dots are expected to be used in photoelectric detection. The research received funding from the National Natural Science Foundation of China (11304197,61370042, 11474201 and 61234005).
【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O471.1;O482.31
本文编号：2445277
[Abstract]:In recent years, graphene quantum dots (QDs), as a new nano-carbon material, have been widely studied because of their good water solubility, low toxicity, stable and bright fluorescence and so on. A large number of preparation methods have been proposed for the synthesis of graphene quantum dots and have been used in the fields of bio-imaging, optoelectronic devices, sensors, drug transport and photocatalysts. However, the luminescence mechanism of graphene quantum dots is still controversial, especially the competition or cooperation mechanism between intrinsic state luminescence and defective state luminescence, which makes graphene quantum dots show different luminescence mechanism with different preparation methods. Based on this, we explore how to prepare graphene quantum dots with high lattice quality and high quantum yield. In addition, the origin of the photoluminescence of graphene quantum dots has been studied deeply. In this paper, our main research results are as follows: 1. High quality graphene quantum dots were prepared with glucose, concentrated sulfuric acid and deionized water as reactants, heated by hydrothermal method at 200 oC for 3 hours. Blue fluorescence graphene quantum dots with good lattice quality and 14.3% quantum yield were obtained. The results of structural characterization show that the average size and thickness of graphene quantum dots are 3.35 nm and 1 nm, respectively. They are disk-like structures with 1 / 3 layers of graphene. The optical characterization results show that the graphene quantum dot can emit purple and blue fluorescence almost independent of the excitation wavelength. 2. The synthesis mechanism of graphene quantum dots regulates the usage of concentrated sulfuric acid. It is found that the synthesized products change from amorphous green fluorescent carbon dots with low quantum yield to well crystallized graphene quantum dots with high quantum yield. Higher quality graphene quantum dots were obtained by adjusting the reaction temperature, reaction time and glucose content to optimize the experimental parameters. The synthesis mechanism of graphene quantum dots is analyzed and expounded, that is, glucose is first formed into carbon nucleus, and the reaction environment provides sufficient energy for the carbon nucleus to continue to grow and remove oxygen-containing functional groups to obtain larger size and higher quality graphene quantum dots. 3. The luminescence mechanism of graphene quantum dots is based on in-depth analysis of absorption spectra, photoluminescence spectra and photoluminescence excitation spectra. It is considered that the UV fluorescence and blue fluorescence of graphene quantum dots are derived from the recombination of local electron hole pairs of C _ (C) bond and the electron transition of sp2 carbon domain, respectively. The temperature-varying photoluminescence spectra further prove the above conclusions, and it is shown that there are strong electron-electron scattering and strong electron-phonon coupling in graphene quantum dots, which are similar to semiconductor quantum dots in temperature. 4. The results show that there are strong electron-electron scattering and strong electron-phonon coupling in graphene quantum dots. Graphene quantum dot thin films were prepared on polished silicon wafers by good conductivity of graphene quantum dot films. Dark conductivity and photoconductivity of graphene quantum dot thin films were measured. The dark conductivity of graphene quantum dot films is about 9 S, which indicates that there is strong electron coupling and good conductivity between graphene quantum dots. The apparent increase of the dark conductance by 50% means that graphene quantum dots are expected to be used in photoelectric detection. The research received funding from the National Natural Science Foundation of China (11304197,61370042, 11474201 and 61234005).
【学位授予单位】：上海交通大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：O471.1;O482.31
【参考文献】
相关期刊论文 前1条
1 何小芳;罗四海;曹新鑫;;纳米金刚石的应用及表面处理技术研究进展[J];硅酸盐通报;2013年05期
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