发光碳基纳米材料的超快动力学研究

发布时间：2018-07-29 12:10

【摘要】：碳基纳米材料作为碳家族新成员,引起了人们广泛的研究兴趣。它们具有较强的荧光性质,被广泛应用于生物荧光成像、发光二极管和激光器等领域。碳基纳米材料的荧光具有激发波长依赖和p H响应等特征。尽管人们通过各种技术手段研究碳基纳米材料的荧光性质,但其真正的发光机制还存在较大的分歧。依据不同种类的碳基纳米材料,可以总结影响其荧光发射的原因主要有以下几种:量子限域效应、sp2区域、表面态、边缘态、分子态、交联加强发射作用和巨大红边效应等。本论文以超快时间分辨光谱技术为探测手段,仔细研究了碳基纳米材料的载流子动力学过程变化和荧光机制。首先,利用飞秒激光器自行搭建了瞬态吸收光谱探测系统,并在此装置的基础上,拓展出两套探测系统:超连续瞬态反射系统和超连续瞬态吸收反射系统。还自行搭建了一套时间分辨光克尔荧光光谱探测系统,它可以探测450-700nm的全谱荧光,系统的最小响应时间为500fs。其次,开发了时间分辨信号的数据处理方法,采用矩阵重组和变量投影最小二乘法的方法拟合动力学衰减曲线。通过对比分析发现,这两种不同的算法能够得到全局最优解,且变量投影最小二乘法的计算方式所耗用时间缩短了将近10倍。对于瞬态吸收光谱数据的分析开发几种不同的处理和分析方法,如:组分个数的判断,确定初始非线性参量和二维相关光谱等。通过瞬态吸收光谱研究不同酸碱环境下的碳量子点,发现其表面态主要是由碳基骨架边缘碳原子与含氧官能团(环氧基、羰基和羧基)组成。通过全局拟合分析发现碳量子点在不同的pH水溶液环境中经历了四个弛豫通道:电子-电子的散射和表面态的捕获;光学声子散射;声学声子散射;电子-空穴再复合。在碱性环境下,羧基的去质子化作用改变了碳基骨架与表面态之间π电子云的分布,导致其在1 ps时间内较易被表面态捕获。通过时间分辨光克尔荧光的探测方法研究了碳量子点在强酸性、中性和强碱性水溶液环境下的荧光光谱的动力学变化和其相应的发光机制。在强酸性、中性和强碱性环境中的溶剂化平均动力学寿命分别为:11.9 ps、7.39 ps和2.6 ps。溶剂化动力学过程引起碳量子点荧光光谱的峰值移动。在强酸性的环境下,羧基所形成表面态的跃迁偶极矩较大需要较长的溶剂化时间。随羧基官能团的进一步电离,在强碱性的条件下碳量子点的跃迁偶极矩相应减小,从而导致溶剂化时间降低。全局拟合分析发现,碳量子点存在三个荧光组分。在强碱性的水溶液环境下,碳量子点羧基官能团的去质子化作用加速了第一个寿命过程内载流子向不发光表面态的迁移。合成了具有双光子荧光性质的近红外碳点,其最优发光位置在710nm,荧光量子产率为26.28%。通过飞秒瞬态吸收实验探测近红外碳点的载流子动力学变化过程和相应的发光机制,实验结果表明碳点中碳核和表面态协同决定其荧光发射。通过相应的表征分析手段说明羧基碳和石墨氮在近红外碳点的红光发射中起着决定性的作用。通过双光子荧光实验证明了近红外碳点的双光子荧光性质,并且通过构建相应的分子模型计算其双光子吸收截面,分析双光子荧光的来源。
[Abstract]:Carbon based nanomaterials, as new members of the carbon family, have aroused wide interest in research. They have strong fluorescence properties and are widely used in the fields of bioluminescence imaging, light-emitting diodes and lasers. The fluorescence of carbon based nanomaterials has the characteristics of excitation wavelength dependence and P H response. Although people have passed various technical means The fluorescence properties of carbon based nanomaterials are studied, but there are still great differences in their real luminescence mechanisms. According to different kinds of carbon based nanomaterials, the main reasons that affect the fluorescence emission of carbon based nanomaterials are as follows: quantum confinement effect, SP2 region, surface state, edge state, molecular state, crosslinking enhanced emission and huge red edge effect. In this paper, we studied the carrier dynamics process and fluorescence mechanism of carbon based nanomaterials with ultrafast time resolved spectroscopy. First, a transient absorption spectrum detection system was built by femtosecond laser, and on the basis of this device, two sets of detection systems were expanded: supercontinuous transient reflection. The system and the supercontinuous transient absorption reflection system have also built a set of time resolved light Kerr fluorescence detection system. It can detect the full spectral fluorescence of 450-700nm. The minimum response time of the system is next to 500fs.. The data processing method of time resolved signal is developed, and the square method of matrix recombination and the variable projection least square method are used. It is found that the two different algorithms can get the global optimal solution by comparison and analysis, and the time-consuming time of the calculation method of the variable projection least square method is nearly 10 times shorter. The initial nonlinear parameters and two-dimensional correlation spectra are determined. The carbon quantum dots in different acid and alkali environments are studied by transient absorption spectra. It is found that the surface state is mainly composed of carbon based skeleton edges carbon atoms and oxygen containing functional groups (epoxy, carbonyl and carboxyl groups). Through global fitting analysis, the carbon quantum dots are found in different pH aqueous solutions. There are four relaxation channels: electron electron scattering and surface state capture; optical phonon scattering; acoustic phonon scattering; electron hole recombination. In alkaline environment, the deprotonation of carboxyl changes the distribution of the pion cloud between the carbon matrix and the surface state, resulting in its easier capture in the surface state within 1 ps time. The time resolved optical Kerr fluorescence detection method studied the kinetic changes of the fluorescence spectra of carbon quantum dots in strong acidic, neutral and strong alkaline aqueous solutions and their corresponding luminescence mechanisms. The mean kinetic lifetime of the solvent in strong acidic, neutral and strong alkaline environments was divided into 11.9 PS, 7.39 PS and 2.6 PS. solvent kinetics. The process causes the peak shift of the fluorescence spectra of carbon quantum dots. In the strong acidic environment, the transition dipole moment of the surface state of the carboxyl group needs a longer solvation time. With the further ionization of the carboxyl functional groups, the transition dipole moment of the carbon quantum dots should be reduced under the strong alkaline condition, which leads to the reduction of the time of the solvent. It is found that there are three fluorescent components in the carbon quantum dots. In the strong alkaline water environment, the deprotonation of carboxyl functional groups of the carbon quantum dots accelerates the migration of the carrier to the non luminous surface state in the first life process. The near infrared carbon point with two photon fluorescence properties is synthesized, and the optimal luminescence position is at 710nm, The fluorescence quantum yield is 26.28%. through the femtosecond transient absorption experiment to detect the change process of the carrier dynamics and the corresponding luminescence mechanism of the near infrared carbon point. The experimental results show that the carbon nucleus and the surface state determine the fluorescence emission in synergy. The red light of the carboxyl carbon and graphite nitrogen in the near infrared carbon point is explained by the corresponding characterization analysis. The two-photon fluorescence properties of the near infrared carbon point are proved by the two-photon fluorescence experiment, and the two photon absorption cross section is calculated by constructing the corresponding molecular model, and the source of the two-photon fluorescence is analyzed.
【学位授予单位】：吉林大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB383.1

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