Excitonic Photoluminescence from Nanodisc States in Graphene Oxides

Kozawa, Daichi; Zhu, Xi; Miyauchi, Yuhei; Mouri, Shinichiro; Ichida, Masao; Su, Haibin; Matsuda, Kazunari

doi:10.1021/jz500516u

Cited by 55 publications

(67 citation statements)

References 43 publications

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“…Unreduced GO produced a broad PL band at ~650 nm due to the π−π* transition, corresponding well with literature report 7,12 . As photoreduction progressed, PL was progressively redshifted and weakened.…”

Section: Effects Of Photoreduction On Optical and Magnetic Propertiessupporting

confidence: 91%

“…Compared with GO, rGO has increased visible absorption, which has been attributed to restoration of the π network 7,9 or increased charge carrier concentration 10,11 . GO displays photoluminescence (PL) bands in the range of 500-800 nm, where PL in this range can originate from ensemble emission from sp 2 nanodomains of various sizes 7,12 . In contrast, thermally or photothermally reduced rGO shows fluorescence between 350 and 500 nm 13,14 .…”

Section: Introductionmentioning

confidence: 99%

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Correlated Optical and Magnetic Properties in Photoreduced Graphene Oxide

et al. 2014

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Optical and magnetic properties of graphene oxide (GO) have been intensively investigated because of the promising applications of GO-related materials in various technical fields. So far, the optical and magnetic properties of GO have been discussed independently. However, localized electronic states in reduced GO may simultaneously add optical transitions and spin moments in sp 2 nanodomains in GO nanosheets. In the present study, the structural, optical, and magnetic properties of graphene oxide (GO) photoreduced in an aqueous solution are correlated on the basis of experimental and theoretical investigations. Experimental observations show that photoreduction leads to enhancement of visible absorption, quenching of photoluminescence, and emergence of magnetism. Detailed spectroscopic and microscopic characterizations indicate the presence of photoreduction-produced basal plane C-H bonding and carbon vacancies. Ab initio calculations suggest that the presence of these defects in sp 2 nanodomains results in singly occupied molecular orbital levels in the π-π* gap to afford enhanced visible to near infrared (NIR) absorption and emergence of magnetism, which is consistent with the experimentally observed change in the optical and magnetic properties of GO by photoreduction. Enhancement of NIR emissions observed in shortly photoreduced GO and their extinction found in longer photoreduced GO are explained with integrating the theoretical calculations and time-resolved fluorescence measurements. The correlation among structural, optical, and magnetic properties, highlighted for the first time, could help accelerate the development of open-shell nanographene devices with concurrently tunable electrical, optical, magnetic, and electrochemical properties.

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Section: Effects Of Photoreduction On Optical and Magnetic Propertiessupporting

confidence: 91%

Section: Introductionmentioning

confidence: 99%

Correlated Optical and Magnetic Properties in Photoreduced Graphene Oxide

et al. 2014

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“…the types of oxygen-containing functional groups or their arrangements 38–40 . In order to alter the optical band gap, we subject aqueous suspensions of graphene oxide to oxidizing ozone treatment inside the ultrasonic bath for the periods of 0 to 35 minutes which was previously utilized to convert RGO (Reduced Graphene Oxide) into GO 17 .…”

Section: Resultsmentioning

confidence: 99%

Optical Band Gap Alteration of Graphene Oxide via Ozone Treatment

Hasan

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Ryan

et al. 2017

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Graphene oxide (GO) is a graphene derivative that emits fluorescence, which makes GO an attractive material for optoelectronics and biotechnology. In this work, we utilize ozone treatment to controllably tune the band gap of GO, which can significantly enhance its applications. Ozone treatment in aqueous GO suspensions yields the addition/rearrangement of oxygen-containing functional groups suggested by the increase in vibrational transitions of C-O and C=O moieties. Concomitantly it leads to an initial increase in GO fluorescence intensity and significant (100 nm) blue shifts in emission maxima. Based on the model of GO fluorescence originating from sp2 graphitic islands confined by oxygenated addends, we propose that ozone-induced functionalization decreases the size of graphitic islands affecting the GO band gap and emission energies. TEM analyses of GO flakes confirm the size decrease of ordered sp2 domains with ozone treatment, whereas semi-empirical PM3 calculations on model addend-confined graphitic clusters predict the inverse dependence of the band gap energies on sp2 cluster size. This model explains ozone-induced increase in emission energies yielding fluorescence blue shifts and helps develop an understanding of the origins of GO fluorescence emission. Furthermore, ozone treatment provides a versatile approach to controllably alter GO band gap for optoelectronics and bio-sensing applications.

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“…This indicates that oxygen doping leads to longer life time of carriers generated after exciton dissociation at the interface. Recently, graphene oxide and its derivatives [40][41][42] have been extensively studied for not only their promising functionality [43][44][45] but also low-cost synthesis and applications. 46,47 Selective O-doping in OPV as modeled in this paper may be made during the synthesis process of the HBC before its self-organization to the supramolecular solar-cell structure.…”

Section: Discussionmentioning

confidence: 99%

Doping effect on photoabsorption and charge-separation dynamics in light-harvesting organic molecule

et al. 2016

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Using ab-initio theoretical methods, we demonstrate possible enhancement of photo-conversion efficiency of an organic solar cell via intentional doping in molecular graphene-fullerene heterojunction [the hexabenzocoronene (HBC)-triethylene glycol (TEG)–C60 molecule]. Photoabsorption analysis indicates oxygen substitution into HBC leads to an extension of the spectra up to an infrared regime. A quantum-mechanical molecular dynamics simulation incorporating nonadiabatic electronic transitions reveals that a dissociated charge state (D+ and A-) in the O-doped system is more stable than the pristine case due to the presence of an effective barrier by the TEG HOMO/LUMO level. We also find that oxygen doping in HBC enhances the intermolecular carrier mobility after charge separation. On the other hand, the pristine molecule undergoes rapid recombination between donor and acceptor charges at the interface. These analyses suggest that the graphene oxidation opens a new window in the application of organic super-molecules to solar cells.

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Excitonic Photoluminescence from Nanodisc States in Graphene Oxides

Cited by 55 publications

References 43 publications

Correlated Optical and Magnetic Properties in Photoreduced Graphene Oxide

Correlated Optical and Magnetic Properties in Photoreduced Graphene Oxide

Optical Band Gap Alteration of Graphene Oxide via Ozone Treatment

Doping effect on photoabsorption and charge-separation dynamics in light-harvesting organic molecule

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