Modification of Nitrogen Doped Carbon Quantum Dots Emissive States Using Plasma-Induced Non-Equilibrium Electrochemistry

Highly luminescent nanomaterials with ambient stability, environmental friendliness, low-cost and abundance are in demand for various applications in biological sensing, imaging and optoelectronics [1-6]. Many of the photoluminescent nanomaterials are semiconductors and usually contain toxic elements, heavy and expensive metals which have limited their applications. Carbon nanoparticles are a promising alternative to semiconductor nanocrystals as next generation green nanomaterials due to excellent biocompatibility, low cytotoxicity and solution processability which results in ease of production and incorporation in devices [7]. In the current work, nitrogen doped carbon quantum dots (N-CQDs) are synthesized by plasma-induced non-equilibrium electrochemistry utilizing a direct-current atmospheric pressure microplasma. The direct current microplasmas used in this work serve as a reliable and highly reproducible synthesis method for tuning the optical properties of carbon-based quantum dots. The outcome of precursors and discharge current affecting the surface chemistry and optical properties are studied using various characterization techniques, which have contributed to determine the mechanisms leading to QD formation from the plasma-induced reactions at the interface. The synthesized N-CQDs are crystalline with graphitic core doped with nitrogen and functionalized surface. The luminescence which originates from the combined effect of core and surface states can be finely controlled by changing synthesis conditions. These N-CQDs have potential to be used as an active material in next-generation solar cells or even as down-converters for high energy photons to be absorbed by a lower bandgap transporter [8]. The particularly high photoluminescence quantum yield (33% to 68%) can be exploited for optoelectronic applications. References: [1] Zhenhui Kang and Shuit-Tong Lee, Carbon dots: advances in nanocarbon applications, Nanoscale, 11 (2019) 19214–19224. [2] S. Zhu, Q. Meng, L. Wang, J. Zhang, Y. Song, H. Jin, K. Zhang, H. Sun, H. Wang, B. Yang, Highly photoluminescent carbon dots for multicolor patterning, sensors, and bioimaging, Angew. Chemie - Int. Ed. 125 (2013) 4045–4049. [3] S.K. Bhunia, A. Saha, A.R. Maity, S.C. Ray, N.R. Jana, Carbon nanoparticle-based fluorescent bioimaging probes, Sci. Rep. 3 (2013) 1473. [4] X. Michalet, F.F. Pinaud, L.A. Bentolila, J.M. Tsay, S. Doose, J.J. Li, G. Sundaresan, A.M. Wu, S.S. Gambhir, S. Weiss, Quantum Dots for Live Cells, in Vivo Imaging and Diagnostics, Science (80-. ). 307 (2005) 538–545. [5] Y.-P. Sun, B. Zhou, Y. Lin, W. Wang, K.A.S. Fernando, P. Pathak, M.J. Meziani, B.A. Harruff, X. Wang, H. Wang, P.G. Luo, H. Yang, M.E. Kose, B. Chen, L.M. Veca, S.-Y. Xie, Quantum-Sized Carbon Dots for Bright and Colorful Photoluminescence, J. Am. Chem. Soc. 128 (2006) 7756–7757. [6] S.C. Ray, A. Saha, N.R. Jana, R. Sarkar, Fluorescent carbon nanoparticles: Synthesis, characterization, and bioimaging application, J. Phys. Chem. C. 113 (2009) 18546–18551. [7] L. Lin, M. Rong, F. Luo, D. Chen, Y. Wang, X. Chen, Luminescent graphene quantum dots as new fluorescent materials for environmental and biological applications, TrAC - Trends Anal. Chem. 54 (2014) 83–102. [8] Conor Rocks, Vladimir Svrcek, Tamilselvan Velusamy, Manuel Macias-Montero, Paul Maguire, Davide Mariotti, Type-I alignment in MAPbI3 based solar devices with doped-silicon nanocrystals, Nano Energy 50 (2018) 245–255. Figure 1