N掺杂碳量子点的荧光增强机制及其在电致发光器件中的应用研究

Owing to the unique energy gap tunable properties and the fluorescent stability, carbon quantum dots (CQDs) have shown great potential for development and application prospects in the field of photoelectric display. However, the low quantum yield (QY) of CQDs still restrict its development. The doping of N element can effectively improve the QYs of CQDs, but the influencing mechanism of N element on the CQDs' luminescence are still unclear. Therefore, the intensive research on the CQDs' fluorescence enhancement technique as well as the mechanism has important scientific significance. In this project, the combination of N-doping technique and an effective method for the preparation of CQDs via gel microspheres will be employed toward fabricating CQDs with higher QYs (>80%). The effect of N-doping on the CQDs' photoluminescence will be explored and some key parameters such as the concentration, doped valence state and the structure of N elements will be determined. In addition, based on the relationship of N doping key parameters and the variation of CQDs' surface chemical and inner band gap structure, the regulation mechanism of N doping on CQDs' luminescence will be thoroughly illustrated. Finally, the electroluminescent devices with high quantum efficiency will be constructed by taking advantages of the high fluorescence of N-CQDs. During the property analysis of the device, the regulation mechanism of the N doping on the band gap structure of CQDs will be further verified according to the physical structure changes of CQDs emitting layer. By this project, new knowledge about regulation and control mechanisms of N doping on the CQDs' fluorescence will be acquired. In addition, this study will provide practical guidance for the optoelectronic properties of carbon quantum dots.

碳量子点（CQDs）以其独特的能隙可调及光学稳定等优势，在光电显示领域展示出巨大的发展潜力，然而较低的量子产率仍然是目前限制其应用的主要瓶颈。N掺杂技术可有效提高CQDs的量子产率，但是掺杂过程中N元素对CQDs荧光增强的作用机制仍不明确。对此，本项目利用原位N掺杂凝胶微球合成高效N-CQDs的制备方法，获得量子产率>80%的N-CQDs；研究可有效提高CQDs量子产率的N掺杂关键技术参数，并基于N掺杂与CQDs荧光增强的构效关系探索N掺杂对CQDs边缘化学结构和内部碳核能带结构的调控规律，揭示N掺杂对CQDs的荧光增强机制；利用N-CQDs构建高效的电致发光器件，并根据相同注入势垒下CQDs与N-CQDs器件界面结构的对比分析，阐明N掺杂对CQDs发光层物理结构的调控机制。本研究不仅对深入理解碳量子点的发光机理具有重要意义，而且为碳量子点在光电领域中的应用提供理论依据。

本项目首先通过乳液聚合法制备胶体微球，基于对微球碳源内部的官能团调控，实现高性能荧光碳量子点（CQDs）的合成；分析CQDs量子产率与其内部官能团种类的对应关系，得出CQDs量子产率的变化关系为：含酰胺基团>环氧基团>吡咯基团>铵盐。所制备的CQDs可发射蓝光、橙光及暖白色荧光，量子产率最高可达约89%。此外，采用日常绿色原料为碳源，所制备的CQDs量子产率可提高5.6倍。. 系统分析CQDs荧光量子产率与N元素掺杂含量的对应关系，研究CQDs光学性能有效提高的调控规律及关键技术参数，结果表明：CQDs的量子产率随N元素掺杂含量的增加先增长后降低，N掺杂存在最佳浓度。对应于N元素掺杂/化学基团改变与CQD内部化学与能带结构模型的变化关系，说明CQDs的荧光发射来源于内部缺陷态激子的辐射复合，适当的N掺杂可有效促进CQDs内纳米限域中的电子转移，促进CQDs荧光性能的提高。. 以所制备的高性能CQDs为荧光粉构筑在LED器件中，实现了不同光发射LED器件的制备；通过将微透镜阵列引入至WOLED中，有效促进了器件的光束整形及亮度增强。此外，实验表明，所制备的荧光CQDs还可以作为荧光墨水应用在防伪打印以及成骨细胞的荧光成像中。. 项目目前在国内外重要学术刊物上已发表SCI收录期刊论文8篇，所取得的研究进展可用于指导高性能荧光量子点的制备与生产，并为其在光学、电学及生物领域中的应用打下基础。