A comprehensive model of nitrogen-free ordered carbon quantum dots.
A comprehensive model of nitrogen-free ordered carbon quantum dots.
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DOI：
10.1186/s11671-023-03773-0
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发表时间：
2023-01-31
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--
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我们提出并演示了一系列新颖的模型，以准确确定具有有序石墨烯层状结构的无氮碳量子点（CQD）的光学特性。我们根据对文献的广泛回顾获得的 CQD 的全方位实验结果确认了我们的模型结果。该模型同样适用于不同尺寸和石墨烯片基面氧含量不同的 CQD。我们证明，实验观察到的无氮 CQD 的蓝色荧光发射可能与石墨烯片外围的小氧化区域有关，或者与限制在氧化石墨烯片中心的高度对称性的亚纳米非功能化 sp2 杂化碳岛有关。功能化石墨烯片中心较大和/或不太对称的非功能化区域被发现是无氮 CQD 发出绿色甚至红色荧光的来源。我们还演示了一种通过用等效应变多环芳烃替代来简化所讨论的 sp2 岛建模的方法。此外，我们表明 CQD 的带隙（和光致发光）不依赖于石墨烯片的面外波纹或 sp2 岛之间的间距。有利的是，我们提出的模型表明，不需要涉及接枝到颗粒外围的具有任意结构的发光多环芳香族分子（纳米石墨烯）来解释在整个实验工作中观察到的 CQD 的大量光学现象。
We propose and demonstrate a novel range of models to accurately determine the optical properties of nitrogen-free carbon quantum dots (CQDs) with ordered graphene layered structures. We confirm the results of our models against the full range of experimental results for CQDs available from an extensive review of the literature. The models can be equally applied to CQDs with varied sizes and with different oxygen contents in the basal planes of the constituent graphenic sheets. We demonstrate that the experimentally observed blue fluorescent emission of nitrogen-free CQDs can be associated with either small oxidised areas on the periphery of the graphenic sheets, or with sub-nanometre non-functionalised islands of sp2-hybridised carbon with high symmetry confined in the centres of oxidised graphene sheets. Larger and/or less symmetric non-functionalised regions in the centre of functionalised graphene sheet are found to be sources of green and even red fluorescent emission from nitrogen-free CQDs. We also demonstrate an approach to simplify the modelling of the discussed sp2-islands by substitution with equivalent strained polycyclic aromatic hydrocarbons. Additionally, we show that the bandgaps (and photoluminescence) of CQDs are not dependent on either out-of-plane corrugation of the graphene sheet or the spacing between sp2-islands. Advantageously, our proposed models show that there is no need to involve light-emitting polycyclic aromatic molecules (nanographenes) with arbitrary structures grafted to the particle periphery to explain the plethora of optical phenomena observed for CQDs across the full range of experimental works.
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