Linear and nonlinear optical properties of modified graphene-based materials
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Introduction Graphene, as a two-dimensional nanoscale sheet with an extended sp2 carbon network, has attracted much recent attention for both fundamental investigations and potential technological applications.1–7 The optical properties of graphene and related carbon nanomaterials and nanocomposites have also been widely explored.8–14 Graphene sheets are generally produced either topdown by exfoliation of graphite,12,15–17 including an indirect route through oxidation into exfoliated graphene oxides (GOs) followed by reduction,12,17 or bottom-up by techniques such as vapor deposition.18,19 Pristine graphene is a zero-bandgap material, but to manipulate and control its optical and electronic properties, researchers have devoted much effort to producing nonzero bandgaps.20–23 Various approaches for opening energy gaps have been used in graphene materials by creating either defects or isolated nanoscale islands of graphene-like material.9,22,24–31 These approaches can be separated into two categories, depending on whether this modification is achieved by manipulating the π-electronic network to form sp2 domains in a graphene sample or breaking large graphene sheets into nanoscale pieces. Linear and nonlinear optical properties of graphene-based materials offer the potential for highly attractive applications in photonics and optoelectrionics.9,10,14,32,33 For example, photoluminescence associated with induced bandgaps in graphene has been pursued as an alternative to fluorescent quantum dots
(QDs). In addition, because of its extended π network, graphene exhibits an excellent nonlinear optical reponse.34–36 Among the various nonlinear optical properties of graphene materials, one of the most widely pursued has been optical limiting, which is important in a number of technologies, from passive manipulation of optical beams35,37–39 to protection against intense laser pulses.38 In this article, the optical absorption characteristics and photoluminescence properties due to various induced energy gaps and, in some cases, the creation of graphene quantum dots (GQDs) in graphene-based materials are highlighted. Nonlinear optical properties of these materials are reviewed with an emphasis on optical limiting through both nonlinear absorption and scattering mechanisms.
Absorption Graphene sheets with sp2-hybridized carbon atoms and associated π networks exhibit optical absorption over a broad spectral range from the ultraviolet to the near-infrared, although their insolubility has made solution-phase studies of optical absorption difficult.17,22,28,40–42 As with other carbon nanomaterials, including carbon nanotubes and even carbon nanoparticles,43–47 π-plasmon absorption plays a major role in photon harvesting by graphene-based materials.9,48,49 Graphene oxides (GOs) are graphene “derivatives” in which a substantial fraction of the sp2-hybridized carbons are
Li Cao, Department of Chemistry, Clemson University; [email protected] Sushant Sahu, Department of Chemistry, Clemson University; [email protected] Parambath Anilkumar, De
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