Investigation on the Relationship Between Carbon Cores and Fluorescence Moieties by Measurement of Fluorescence Anisotro
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doi: 10.1007/s40242-020-9109-2
Article
Investigation on the Relationship Between Carbon Cores and Fluorescence Moieties by Measurement of Fluorescence Anisotropy of CDs with Different Sizes WANG Yijie, WANG Lei and WANG Haiyu* State Key Laboratory of Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012, P. R. China Abstract Carbon dots(CDs) have been considered as a marvellous photoluminescence(PL) material, and their PL mechanism remains debatable. The carbon core, as an essential part of CDs, apparently plays an intricate role in the PL of CDs. However, the influence of the core on the PL and the relationship between the core and fluorescence moiety are still unclear. Here, we investigated the influence of carbon cores with different sizes on the rotational motion of fluorescence moieties to determine the relationship between carbon cores and fluorescence moieties. CDs with different size distributions were synthesized by controlling carbonization time. The core sizes and rotational correlation time(RCT) of the CD samples were measured by transmission electron microscopy(TEM) and fluore scence anisotropy measurement, respectively. And the rotating unit radius were calculated from the RCT. The experimental results show that the rotational motion of the fluorescence moiety is independent of the carbon core sizes and it possesses total rotational freedom. This work is helpful for understanding the connection between the carbon core and fluorescence moiety and its influence on the PL properties of CDs. Keywords Carbon dot; Fluorescence; Anisotropy
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Introduction
Carbon dots(CDs) are an emerging class of photoluminescence(PL) materials. After their first discovery in 2004[1], CDs have attracted extensive attention due to their potential applications in bio-imaging, sensing, catalysis, and lightemitting devices[2]. Compared with the conventional organic dyes and the heavy-metal-based semiconductor quantum dots, CDs have significant advantages, such as low toxicity, easy fabrication, outstanding biocompatibility, high photo-stability and high water-solubility[3—7]. In the past decades, many synthesis methods, such as arc-discharge, laser-ablation, electrochemical exfoliation, chemical oxidation, and hydrothermal graphene oxide reduction have been proposed, and the quantum yield(QY) of CDs has increased to a relatively high level[8,9]. CDs are usually considered to be composed of two parts: a carbon core in the center and functional groups surrounding[10]. CDs synthesized by different ways usually possess similar absorption and fluorescence properties to some extent. Strong optical absorption in the UV region with a tail extending into the visible range is typically observed. Their emission peaks usually cover a broad spectral range with a relatively large Stokes shift[11]. Although lots of efforts have been made to uncover the
origin and mechanism of the PL of CDs[12], the PL mechanism still remains debatable. The proposed explanations can be classified into
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