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Sci Rep. 2014 Jun 18;4:5294. doi: 10.1038/srep05294.

Formation mechanism and optimization of highly luminescent N-doped graphene quantum dots.

Author information

  • 11] State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Changchun 130033, Jilin, P. R. China [2] University of Chinese Academy of Science, Beijing 100000, P. R. China.
  • 2State Key Laboratory of Luminescence and Applications, Changchun Institute of Optics, Fine Mechanics and Physics, Changchun 130033, Jilin, P. R. China.
  • 3State Key Laboratory of Polymer Physics and Chemistry, Changchun Institute of Applied Chemistry, Changchun 130022, Jilin, P. R. China.
  • 4Center for Micro- Engineering and Materials, Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, NM 87106, United State.
  • 51] Center for Micro- Engineering and Materials, Department of Chemical and Nuclear Engineering, University of New Mexico, Albuquerque, NM 87106, United State [2] Sandia National Laboratories, Advanced Materials Laboratory, Albuquerque, NM 87106, United State.

Abstract

Photoluminescent graphene quantum dots (GQDs) have received enormous attention because of their unique chemical, electronic and optical properties. Here a series of GQDs were synthesized under hydrothermal processes in order to investigate the formation process and optical properties of N-doped GQDs. Citric acid (CA) was used as a carbon precursor and self-assembled into sheet structure in a basic condition and formed N-free GQD graphite framework through intermolecular dehydrolysis reaction. N-doped GQDs were prepared using a series of N-containing bases such as urea. Detailed structural and property studies demonstrated the formation mechanism of N-doped GQDs for tunable optical emissions. Hydrothermal conditions promote formation of amide between -NH₂ and -COOH with the presence of amine in the reaction. The intramoleculur dehydrolysis between neighbour amide and COOH groups led to formation of pyrrolic N in the graphene framework. Further, the pyrrolic N transformed to graphite N under hydrothermal conditions. N-doping results in a great improvement of PL quantum yield (QY) of GQDs. By optimized reaction conditions, the highest PL QY (94%) of N-doped GQDs was obtained using CA as a carbon source and ethylene diamine as a N source. The obtained N-doped GQDs exhibit an excitation-independent blue emission with single exponential lifetime decay.

PMID:
24938871
PMCID:
PMC4061557
DOI:
10.1038/srep05294
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