荧光碳纳米点全色发光机制的时间分辨光谱研究

As a kind of environment-friendly nanomaterials, fluorescent carbon nanodots (C-dots) possess bright perspective in various optoelectronic functional fields, such display and illumination. It has been one of the important sources for developing the novel concept of carbon light-emitting diodes——(CLEDs). Since C-dots not only consist of organic carbon structures similar to small molecules, but also are strongly influenced by the quantum confinement effect in theory, this leads to the diversity of emission states (even prepared from the same carbon sources, the fluorescence of C-dots can cover the range of blue, green and red lights) and multi-source problem (there could be several possible origins for each emission band in C-dots, namely, single C-dot may have multi-chromophoric centers), which have been the major obstacle to design and optimize the CLED device structure and performance. In this project, based on the applicant’s previous research in the related fields, we are planning to deep insight into the photophysics of phenylenediamine-based C-dots with full-color light-emissions by the combination of single-molecule/particle fluorescence lifetime measurement and ensemble averaged time-resolved spectroscopies. We will systemically investigate the excited-state dynamics processes in C-dots’ emission states and quantum confined states, and explore the possible molecular structures of emission centers. In addition, we will discuss the inside relations between the C-dots’ emission centers and surrounding carbon environments in such a small nanoscale. This project will lay the solid foundation and guidelines for improving the fluorescence quantum yield of C-dots in the red-emitting range, establishing full-color light-emission models on the basis of the molecule origins of C-dots’ emissions, and fabricating the novel carbon-based devices using full-color light-emission C-dots from the photophysics point of view.

荧光碳纳米点（简称碳点）作为一种绿色环保纳米材料在显示、照明等光电功能领域有着光明的应用前景，是发展新型发光概念器件——碳基光发射二极管（CLEDs）的基石之一。由于碳点既兼具类似小分子的有机结构，又理论上受量子限域效应的显著影响，这使得其发光多样性（即使由相同碳源制备的碳点，其发光范围也可以覆盖蓝绿红三色波段）和多源性（各发光波段的物理来源有多种，即单一碳点可能同时具有多个发光中心）问题成为设计、优化CLED器件结构与性能的主要障碍。本课题拟在申请者前期良好的工作基础上，通过将单点荧光寿命测量和系综平均的时间分辨光谱测量有机结合的方式，系统研究苯二胺基全色发光碳点中发光态与量子限域态的激发态动力学过程，揭示其发光中心的分子构成及与周围碳纳米环境的可能关联，为提高碳点在红光波段的发光效率，建立阐述其全色发光机制的分子起源模型，构造全色发光的碳基纳光子学器件提供坚实的物理依据和原理性指导。

在有机发光二极管（OLED）技术已经商品化的今天，发展下一代具有更低功耗且绿色环保的显示技术的需求促使人们不断寻找新型发光材料。除了目前正在朝大规模商品化发展、期望在几年后与OLED一较高下的量子点发光二极管（QLED），石墨烯氧化物、石墨烯量子点、碳纳米点等荧光碳纳米材料以及近年来出现的各种新颖的二维半导体材料（典型代表为过渡族金属硫族化合物中的MoS2单层），在光伏、LED及激光等领域展现了巨大的应用潜力。由于它们不仅可以向下与OLED技术兼容，而且还有可能直接取代目前比较成熟的有机光电材料、发展成本更低、超薄且柔性、以及性能更优异的碳基/二维半导体光电器件，因此，对碳基纳米材料与二维半导体材料的研究分别是目前国际研究热点之一。本项目的主要研究内容是利用超快光谱手段探索碳纳米发光材料，包括碳纳米点、石墨烯、石墨烯氧化物的光物理特性，通过调控碳纳米材料的组成成分（还原程度）、形貌（纳米点和纳米片形态），及其与二维半导体材料接触，来系统研究碳纳米点的发光机制及电荷转移过程，最终掌握了高效红色发光碳纳米点的合成方法，搭建了可测得准零维碳纳米点、二维半导体、三维钙钛矿微晶的微区荧光寿命测量系统。尤其是，我们从超快光谱研究的角度，详细阐述了石墨烯/MoS2单层异质结中的电荷转移过程，为深入理解相关二维器件的光物理图像和工作机制提供了原理性的解释（该工作发表在Nature Communications）；并且揭示了石墨烯氧化物的在不同氧含量下的绝缘-半导体-半金属转变特性。此外，我们对钙钛矿量子点与电子/空穴淬灭剂接触以及钙钛矿微晶的自发放大辐射过程进行了对照研究，为研究荧光碳纳米点的荧光淬灭机制有启发作用，对将来探索荧光碳纳米点的激射现象具有借鉴意义。项目研究期间，共发表SCI论文7篇，包括Nature Communications（1篇）、Nanoscale（1篇）、Journal of Physical Chemistry C（1篇）、Physical Chemistry Chemical Physics（2篇）、Optical Materials Express（2篇）。相关论文总被他引72次。