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Roles of Nitrogen Functionalities in Enhancing the Excitation-Independent Green-Color Photoluminescence of Graphene Oxide Dots

Abstract

Fluorescent graphene oxide dots (GODs) are an environmentally friendly and biocompatible material for photoluminescence (PL) applications. Our study employs annealing and hydrothermal ammonia treatments at 500 and 140 C, respectively, to introduce nitrogen functionalities on GODs for enhancing their green-color PL emissions. The hydrothermal treatment preferentially produces pyridinic and amino groups, whereas the annealing treatment produces pyrrolic and amide groups. The hydrothermally treated GODs (A-GODs) present a high conjugation of the nitrogen nonbonding electrons in pyridinic and amino groups with the aromatic π orbital. The conjugation introduces a nitrogen nonbonding (nN2p) state 0.3 eV above the oxygen nonbonding state (nO2p state; the valence band maximum of the GODs). The GODs exhibit excitation-independent green-PL emissions at 530 nm with a maximum quantum yield (QY) of 12% at 470 nm excitation, whereas the A-GODs exhibit a maximum QY of 63%. The transformation of the solvent relaxation-governed π*→nO2p transition in the GODs to the direct π*→nN2p transition in the A-GODs possibly accounts for the substantial QY enhancement in PL emissions. This paper elucidates the role of nitrogen functionalities in the PL emissions of graphitic materials and proposes a strategy for electronic structure design to promote PL performance.

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Publication details

The article was received on 12 Feb 2017, accepted on 15 May 2017 and first published on 16 May 2017


Article type: Paper
DOI: 10.1039/C7NR01037K
Citation: Nanoscale, 2017, Accepted Manuscript
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    Roles of Nitrogen Functionalities in Enhancing the Excitation-Independent Green-Color Photoluminescence of Graphene Oxide Dots

    C. Teng, B. Nguyen, T. Yeh, Y. Lee, S. Chen and H. Teng, Nanoscale, 2017, Accepted Manuscript , DOI: 10.1039/C7NR01037K

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