Investigation of Heavy Atom Effect on Fluorescence of Carbon Dots: NCDs and S,N-CDs
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ORIGINAL ARTICLE
Investigation of Heavy Atom Effect on Fluorescence of Carbon Dots: NCDs and S,N-CDs A. O. Aswathy 1 & S. Madanan Anju 1 & J. Jayakrishna 1 & N. S. Vijila 1 & J. S. Anjali Devi 1 & B. Anjitha 1 & Sony George 1 Received: 8 July 2020 / Accepted: 11 August 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract The present work is an attempt to investigate the heavy atom effect imparted by halide ions, especially iodide (I−) ions on the fluorescence behavior of carbon dots (CDs). Here two different types of CDs viz. nitrogen doped carbon dots (NCDs) from Citric Acid (CA) & Urea and Sulfur and nitrogen co-doped carbon dots (S,N-CDs) from CA & L-Cysteine were synthesized and the fluorescence of both CDs were quenched by heavy atom effect on adding potassium iodide (KI). The large difference in average lifetime was obtained in time-correlated single-photon counting (TCSPC) analysis suggests the dynamic quenching and heavy atom effect. Keywords Static quenching . Dynamic quenching . Anions . Fluorescence lifetime
Introduction Carbon dots (CDs) are one of the star members in luminescent quantum dots. The stardom of CDs was more celebrated after its accidental discovery in 2004 mainly because of its unique optical properties [1]. CDs offer many fascinating properties such as good biocompatibility, very high aqueous stability and non-toxicity were attract them as a perfect platform for various applications [2]. The most promising feature of CDs is their fluorescent property [2, 3]. But the origin of fluorescence in carbon dots is still behind the screen. One of the strong beliefs regarding the emergence of fluorescence was attributed to quantum size effect and surface defects [4]. Interestingly, the fluorescence properties of CDs can be tuned by the modulation of surface functional groups and the size of CDs. The two main strategies for enhancing the fluorescence of CDs are doping and surface functionalization of pristine CDs [5]. Common dopants used are N, S, and Be. Among this N is Electronic supplementary material The online version of this article (https://doi.org/10.1007/s10895-020-02607-x) contains supplementary material, which is available to authorized users. * Sony George [email protected] 1
Department of Chemistry, School of Physical and Mathematical Sciences, Research Centre, University of Kerala, Kariavattom Campus, Thiruvananthapuram, Kerala 695581, India
most studied dopant and acts as an n-type impurity. To achieve desired properties more effectively sometimes single element doping was replaced by co-doping [4, 6]. Co-doping involves the combination of elements like B, P, S with N as dopants. S is the most explored co-dopant of N [7]. One of the widely used compounds for co-doping is L-cysteine which can serve as a source of both S and N. Moreover it can easily bind with carbon precursor giving CDs with excellent fluorescence properties [8, 9]. The quenching of fluorescence and fluorescence recovery was widely explored in developing fluorescence sensors [10,
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