Toward high-efficiency photoluminescence emission by fluorination of graphene oxide: Investigations from excitation to emission evolution

Graphene oxide (GO) alters zero bandgap of graphene to achieve photoluminescence (PL), while the low quantum yield (generally: PLQY < 1%) seriously restricts its further development in practical applications. Here we employ two-step fluorination strategy to controllably modify GO, achieving island structure of aromatic regions in continuous phase of fluorine regions. The fluorinated product (FGO) presents a high PLQY of 66%, far exceeding the largest value (21.2%) reported for modifications of GO. We systematically and meticulously investigate fluorine effect of FGO during whole PL evolution. In excitation process, the coexistence of fluorine and aromatic regions in FGO is responsible for new electronic bandgap structure then multitudinous excited electrons produce, thus providing foundation for strong PL. In emission process, Raman measurements show that the weaker electron-phonon interactions in FGO result in slower nonradiative decay. It is attributed to that FGO possesses larger rigidity, as demonstrated by temperature-dependent fluorescence spectra, broadband dielectric measurements, density functional theory calculations and infrared spectra. Interestingly, different types of fluorine-related groups in FGO play different roles. That is, unoriented CF2 and CF3 groups realize passivation of defects, and C-F bonds perpendicular to graphene plane contribute to weakening interlayer interactions, both greatly enhancing PL. (c) 2020 Elsevier Ltd. All rights reserved.