Anomalous Behaviors of Visible Luminescence from Graphene Quantum Dots: Interplay between Size and Shape

Kim, Sungeun; Hwang, Sung Won; Kim, Minkook; Shin, Dong Yeol; Kim, Chang Oh; Yang, Seung Bum; Park, Jae Hee; Hwang, E. H.; Choi, Suk Ho; Ko, Gang Jee; Sim, Sunghyun; Sone, Cheolsoo; Choi, Hyoung Joon; Bae, Sukang; Hong, Byung Hee

doi:10.1021/nn302878r

Cited by 561 publications

(383 citation statements)

References 33 publications

(65 reference statements)

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“…Graphene quantum dots (GQDs) have been synthesized or fabricated from various carbon-based materials including fullerene 13 , glucose 14 , graphite or graphene oxides [15][16][17][18][19][20][21][22][23] , carbon nanotubes 24 and carbon fibres 25 . Physical approaches such as lithography 26 , which etch the size of graphene to B20 nm in width, are expensive and are impractical for the production of bulk quantities of material.…”

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confidence: 99%

Coal as an abundant source of graphene quantum dots

et al. 2013

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Coal is the most abundant and readily combustible energy resource being used worldwide. However, its structural characteristic creates a perception that coal is only useful for producing energy via burning. Here we report a facile approach to synthesize tunable graphene quantum dots from various types of coal, and establish that the unique coal structure has an advantage over pure sp 2 -carbon allotropes for producing quantum dots. The crystalline carbon within the coal structure is easier to oxidatively displace than when pure sp 2 -carbon structures are used, resulting in nanometre-sized graphene quantum dots with amorphous carbon addends on the edges. The synthesized graphene quantum dots, produced in up to 20% isolated yield from coal, are soluble and fluorescent in aqueous solution, providing promise for applications in areas such as bioimaging, biomedicine, photovoltaics and optoelectronics, in addition to being inexpensive additives for structural composites.

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confidence: 99%

Coal as an abundant source of graphene quantum dots

et al. 2013

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“…Other morphologies apart from nanotriangles should yield similar high levels of nonlinear response, particularly when their edges are predominantly armchair. Graphene nanoislands with sizes comparable to those considered here have already been fabricated using various methods [36][37][38] , although they lack precise control over size and shape, which limits their applicability to nonlinear photonic technologies. Alternatively, a bottom-up approach based upon chemical self-asembly of molecular precursors provides better degree of control over the sizes and edge configurations [39][40][41] .…”

Section: Discussionmentioning

confidence: 99%

Electrically tunable nonlinear plasmonics in graphene nanoislands

2014

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Nonlinear optical processes rely on the intrinsically weak interactions between photons enabled by their coupling with matter. Unfortunately, many applications in nonlinear optics are severely hindered by the small response of conventional materials. Metallic nanostructures partially alleviate this situation, as the large light enhancement associated with their localized plasmons amplifies their nonlinear response to record high levels. Graphene hosts long-lived, electrically tunable plasmons that also interact strongly with light. Here we show that the nonlinear polarizabilities of graphene nanoislands can be electrically tuned to surpass by several orders of magnitude those of metal nanoparticles of similar size. This extraordinary behaviour extends over the visible and near-infrared spectrum for islands consisting of hundreds of carbon atoms doped with moderate carrier densities. Our quantummechanical simulations of the plasmon-enhanced optical response of nanographene reveal this material as an ideal platform for the development of electrically tunable nonlinear optical nanodevices. T he well established field of nonlinear photonics hosts a vast number of applications, including spatial and spectral control of laser light, all-optical signal processing, ultrafast switching and sensing 1,2 . Because the efficiencies of nonlinear optical processes are generally poor, considerable effort has been devoted towards seeking materials that can display nonlinear effects at low light intensities and ultrafast response times [2][3][4] . For this purpose, plasmonic nanostructures have been particularly attractive due to their ability to generate high local intensity enhancements through strong confinement of electromagnetic fields 3,5,6 , leading to second-harmonic polarizabilities as high as B10 À 27 esu (electrostatic units) per atom, as measured for noble metal nanoparticles 3 , and even beating the best molecular chromophores 3,7,8 . However, although localized plasmons can be customized through the size, shape and surrounding environment of the metal nanostructures 5 , they suffer from low lifetimes and lack post-fabrication tunability 9 .Doped graphene has recently attracted much attention as an alternative plasmonic material capable of sustaining electrically tunable optical excitations with long lifetimes [9][10][11][12][13][14][15][16][17][18] . The existence of gate-tunable plasmons in graphene has been confirmed by THz 13,14 and mid-infrared 15,16 spectroscopies, while optical nearfield microscopy has been used to image them in real space 17,18 . Efforts to extend the plasmonic response of graphene to the visible and near-infrared regimes are currently underway 12 . In addition, graphene has been predicted to display intense nonlinearity due to its anharmonic charge-carrier dispersion relation 19 . Recent four-wave mixing 20 , Kerr effect 21 , and thirdharmonic generation (THG) 22 experiments already confirm a large third-order response in this material in the undoped, plasmon-free state. Graphene plasmons co...

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“…GQDs have many advantages over conventional organic photosensitizers, such as chemical inertness, high water solubility, photo-stability, interplay between optoelectronic features and shape/size, good donors in the fluorescence resonance energy transfer process, high stability in physiological conditions, specific accumulation at the target site and facile surface functionalization. These features therefore make GQDs promising candidates in novel delivery systems for target-specific photosensitization [18 ** -21] due to their photoluminescence (PL) properties [22,23] , quantum confinement and edge effects [24] .…”

Section: Introductionmentioning

confidence: 99%

“…Considerable efforts are being made to understand the interplay of features such as size and shape, in concert with the type and quantity of additional functional groups, for the generation of PL, as well as capacity to act as energy donors for conventional photosensitizers [16,[22][23][24] . The energy transfer between GQDs and cell molecules, such as triplet oxygen, could potentially induce the generation of reactive oxygen species, thus provoking cellular apoptosis.…”

Section: Introductionmentioning

confidence: 99%