Emission States Variation of Single Graphene Quantum Dots

Ghosh, Subhabrata; Oleksiievets, Nazar; Enderlein, Joerg; Chizhik, Alexey I.

doi:10.1021/acs.jpclett.0c02008

Cited by 11 publications

(10 citation statements)

References 32 publications

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“…4b, c . The width of the main emission peak distribution was ~43 meV (~15 nm), which was narrower than that of the reported single CD at ~180–480 meV (~40–120 nm) 38 , 39 . Statistical analysis of peak positions and spectral band separation in single-particle spectra revealed that the single CD PL was nearly identical to that of the CDs at the ensemble level, with well-resolved vibrionic structures, and it was consistent with nearly monodisperse optical properties 40 .…”

Section: Resultscontrasting

confidence: 62%

Electron–phonon coupling-assisted universal red luminescence of o-phenylenediamine-based carbon dots

et al. 2022

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Due to the complex core–shell structure and variety of surface functional groups, the photoluminescence (PL) mechanism of carbon dots (CDs) remain unclear. o-Phenylenediamine (oPD), as one of the most common precursors for preparing red emissive CDs, has been extensively studied. Interestingly, most of the red emission CDs based on oPD have similar PL emission characteristics. Herein, we prepared six different oPD-based CDs and found that they had almost the same PL emission and absorption spectra after purification. Structural and spectral characterization indicated that they had similar carbon core structures but different surface polymer shells. Furthermore, single-molecule PL spectroscopy confirmed that the multi-modal emission of those CDs originated from the transitions of different vibrational energy levels of the same PL center in the carbon core. In addition, the phenomenon of “spectral splitting” of single-particle CDs was observed at low temperature, which confirmed these oPD-based CDs were unique materials with properties of both organic molecules and quantum dots. Finally, theoretical calculations revealed their potential polymerization mode and carbon core structure. Moreover, we proposed the PL mechanism of red-emitting CDs based on oPD precursors; that is, the carbon core regulates the PL emission, and the polymer shell regulates the PL intensity. Our work resolves the controversy on the PL mechanism of oPD-based red CDs. These findings provide a general guide for the mechanism exploration and structural analysis of other types of CDs.

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Section: Resultscontrasting

confidence: 62%

Electron–phonon coupling-assisted universal red luminescence of o-phenylenediamine-based carbon dots

et al. 2022

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“…Nevertheless, a universally accepted explanation is still missing. Using a single-particle based multimodal study, Chizhik and colleagues showed that the PL of individual GQDs primarily depends on the structure of the dot itself rather than the surrounding chemical environments . Interestingly, the adopted synthesis methodology determines the structure of the dot.…”

Section: A Few Examples Showing Well-characterized Cds Are Promising ...mentioning

confidence: 99%

Roles of Impurity and Sample Heterogeneity in Intriguing Photoluminescence Properties of Zero-Dimensional (0D) Carbonaceous Materials

2022

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Zero-dimensional (0D) carbonaceous materials, such as graphene quantum dots (GQDs) and fluorescent carbon dots (FCDs), are in the limelight for their intriguing optical and material properties. Excellent results of initial photophysical studies with these emergent nanodots garnered intense interest among the researchers that suggested an immediate opportunity of replacing cytotoxic fluorescent dyes with carbonaceous dots (CDs) in bioimaging and related applications. Several exciting properties of CDs, including the excitation-dependent multicolor emission, slow carrier cooling, subpicosecond (subps) interfacial charge transfer, and quantum emission, are of paramount importance for various real applications. Despite the initial success, their large-scale implementations in daily life remained challenging, mainly because of several serious issues, including elusive structures (especially for FCDs), the controversial origin of their emissions, and a lack of proper knowledge while correlating an unusual photophysical property to an intrinsic phenomenon. Such limitations not only present hurdles to their practical utilizations but also call into question their real potential. Recent reports have suggested that many of these exciting properties stemmed from external factors like the presence of a molecular impurity, sample heterogeneity (i.e., a mixture of CD subsets with different spectral identities), and the adopted synthesis methodology (i.e., top-down vs bottom-up). Hence, only a rigorous sample purification cannot help in realizing the actual merit of these emergent materials unless a sample-specific synthesis procedure is followed. A combination of both renders the maximum integrity to the CD samples. This review highlights several exciting properties of these coveted materials and how they are disturbed by the parameters discussed above. We further emphasize the actual promises of these materials, as shown by the recent fluorescence-based temporal and spectral studies. The results of these studies are even more fascinating compared to that of inadequately purified samples. Finally, we propose a standard sample purification methodology applicable to all types of carbonaceous materials.

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“…Graphene nanoribbons (GNRs) [1,2], graphene quantum dots (GQDs) or graphene nanosheet [3], twisted bilayer graphene (TwBLG) and its heterostructures can not only adjust the energy band structure of zero band gap [4][5][6][7][8], but also present novel physical properties superior to 2D graphene materials [9][10][11][12] (superconductivity, topology, frac-tional quantum Hall effect and so on). These physical properties make the above-mentioned micro-nano materials extremely widely used in the field of optoelectronics [13][14][15][16][17][18].…”

Section: Introductionmentioning

confidence: 99%

Encapsulated layer induces boundary effect and twist angle adjust absorption in h-BN/graphene/h-BN heterostructure

Miao

Gai

Jing

et al. 2022

Mater. Res. Express

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This work studied the optical absorption properties and electronic properties of graphene nanosheets encapsulated in h-BN at different twisted angles based on first principles. UV-Vis spectrum shows that compared with the monolayer graphene nanosheets, the absorption’s peak of the encapsulated graphene nanosheets show a red shift and its molar absorption coefficient decreased significantly. The molar absorption coefficients of h-BN/graphene/h-BN heterostructures show an increasing trend when the graphene nanosheets are twisted relative to the packaging layer (twisted angles are 0°, 15°, 21.8°, 27.8° and 30°, respectively). More curiously, charge density difference (CDD) indicates that the region of electron aggregation in excited state mainly occurs at the centre of graphene nanosheets due to the introduction of h-BN packaging layer. The smoothed isosurface diagram of electron hole pairs shows that the distribution breadth of electron hole pair density decreases compared with that before encapsulation, and the distribution breadth of electron increase is larger than that of hole. With the increase of twisted angles, the distribution breadth of electron hole pair density increases gradually. Both CDD and smoothed isosurface diagram show that the system has strong boundary effect. This provides a method to adjust the photoelectric properties of graphene nanosheets by using different twisted angles, and provides a theoretical basis for its application in the field of micro-nano optoelectronics.

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Emission States Variation of Single Graphene Quantum Dots

Cited by 11 publications

References 32 publications

Electron–phonon coupling-assisted universal red luminescence of o-phenylenediamine-based carbon dots

Electron–phonon coupling-assisted universal red luminescence of o-phenylenediamine-based carbon dots

Roles of Impurity and Sample Heterogeneity in Intriguing Photoluminescence Properties of Zero-Dimensional (0D) Carbonaceous Materials

Encapsulated layer induces boundary effect and twist angle adjust absorption in h-BN/graphene/h-BN heterostructure

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