Liu Xingchen, Yu Jingyan, Tan Yonggen, Zhang Wengao, Zhu Lingquan, Ye Shenglin, Feng Jun
Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, Guangdong, China.
Department of Materials Science and Engineering, Southern University of Science and Technology, Shenzhen 518055, Guangdong, China; Guangdong Provincial Key Laboratory of Functional Oxide Materials and Devices, Southern University of Science and Technology, Shenzhen 518055, Guangdong, China.
J Colloid Interface Sci. 2025 May 15;686:951-959. doi: 10.1016/j.jcis.2025.02.024. Epub 2025 Feb 5.
Nitrogen doping is a widely used method for enhancing the performance of carbon quantum dots (CQD). However, the precise relationship between nitrogen content and emission spectra remains unclear when preparing high-performance nitrogen-doped CQD (N-CQD). This study systematically investigates the effects of nitrogen content on the crystalline structure, optical properties, and electronic band structure of N-CQD. Citric acid was used as the carbon source, and ethylenediamine monohydrate was used as the nitrogen source, with their ratio controlled to hydrothermal synthesized N-CQD with N/C ratios ranging from 0 to 0.4. Notably, when the N/C ratio increases from 0 to 0.2, the N-CQD exhibits redshifted emission with excitation dependence. However, when the N/C ratio rises from 0.2 to 0.4, the N-CQD shows blueshifted emission with excitation-independence. We define it as the dual-phase emission behavior of N-CQD attributed to the transition of doping sites from graphitic nitrogen to pyridine nitrogen with increased nitrogen content. DFT calculations indicate that different doping sites influence electron transfer in N-CQD, resulting in distinct optical behaviors. Importantly, this work comprehensively explains the relationship between nitrogen content and the emission behavior of N-CQD for the first time, providing crucial insights for refining the theoretical framework of N-CQD.
氮掺杂是一种广泛用于提高碳量子点（CQD）性能的方法。然而，在制备高性能氮掺杂碳量子点（N-CQD）时，氮含量与发射光谱之间的确切关系仍不明确。本研究系统地研究了氮含量对N-CQD的晶体结构、光学性质和电子能带结构的影响。以柠檬酸为碳源，以乙二胺一水合物为氮源，控制它们的比例，通过水热法合成了N/C比范围为0至0.4的N-CQD。值得注意的是，当N/C比从0增加到0.2时，N-CQD表现出与激发相关的红移发射。然而，当N/C比从0.2增加到0.4时，N-CQD表现出与激发无关的蓝移发射。我们将其定义为N-CQD的双相发射行为，这归因于随着氮含量增加，掺杂位点从石墨氮转变为吡啶氮。密度泛函理论（DFT）计算表明，不同的掺杂位点会影响N-CQD中的电子转移，从而导致不同的光学行为。重要的是，这项工作首次全面解释了氮含量与N-CQD发射行为之间的关系，为完善N-CQD的理论框架提供了关键见解。
