Revealing the tunable photoluminescence properties of graphene quantum dots

Sk, Mahasin Alam; Ananthanarayanan, Arundithi; Huang, Lin; Lim, Kok Hwa; Chen, Peng

doi:10.1039/c4tc01191k

Cited by 596 publications

(533 citation statements)

References 45 publications

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“…The excitation-dependent photoluminescence (PL) is probably due to the presence of different sizes of oligomers with polyheptazine imide 53 or gh-C 3 N 4 units, which forms multiple states in the gap of PCNs. 54 These states are absent in CNNS (Fig. 5, Fig.…”

Section: Discussionmentioning

confidence: 99%

Shining Light on Carbon Nitrides: Leveraging Temperature To Understand Optical Gap Variations

Melissen

Bahers

et al. 2018

Chem. Mater.

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Polymeric carbon nitride (PCN)-based materials have opened new research avenues in the photocatalytic field. The understanding of parameters underlying the optical properties of PCNs is critical to improve their performance. Herein, the optical properties of PCNs are investigated with a combination of Time-Dependent Density Functional Theory (TD-DFT) calculations and laboratory characterizations, including Variable Temperature (VT)-XRD, VT-UV-Vis and VT-IR techniques, on samples prepared using a broad range of synthesis temperatures. Upon increasing the synthesis temperature from 390 to 600°C, the optical gap E opt g (eV) narrows from 2.92 to 2.67, and on further increasing the synthesis temperature to 700°C, widens to 3.03 and another absorption at ∼2.2 eV is observed. The TD-DFT calculations show that E opt g of PCNs converges rapidly with heptazine oligomer size, indicating localized photophysics behavior and justifying a molecular approach. Calculations exploring geometrical variations upon increasing the temperature at which the optical properties were determined revealed that the net effect of these variations were limited, suggesting a vibrational origin of the observed decrease in the gap. The absorption at ∼2.2 eV is tentatively attributed to fully polymerized graphitic PCN oligomers as suggested by the excitation wavelength-dependent photoluminescence emission behavior. The results provide novel insights into the optical properties of PCNs, providing directions for the development of the next generation of PCN-based photocatalysts with optimal light harvesting abilities.

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Section: Discussionmentioning

confidence: 99%

Shining Light on Carbon Nitrides: Leveraging Temperature To Understand Optical Gap Variations

Melissen

Bahers

et al. 2018

Chem. Mater.

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“…37 A coronene is a polycyclic aromatic hydrocarbon comprising six peri-fused benzene rings with the chemical formula C 24 H 12. Moreover, the coronene model is composed of small sp 2 clusters and is isolated by sp 3 carbon, which is close to individual GQDs without oxygen functional groups, and it has been previously employed as a reduced model of graphene for quantum calculations in lithium-sulfur battery studies. 37,38 The relative energies calculated by DFT for the reactants and products indicate that replacing the terminal hydroxyl group by a sulfur dianion results in a lower energy state. The relative energies are shown in Figure 5, where it is clear that the energies of the product decrease when sulfur dianions are replaced with the terminal hydroxyl group.…”

Section: Electrochemical Tests For Li-s Batteriesmentioning

confidence: 99%

Graphene quantum dots: structural integrity and oxygen functional groups for high sulfur/sulfide utilization in lithium sulfur batteries

et al. 2016

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Lithium-sulfur (Li-S) batteries are expected to overcome the limit of current energy storage devices by delivering high specific energy with low material cost. However, the potential of Li-S batteries has not yet been realized because of several technical barriers. Poor electrochemical performance is mainly attributed to the low electrical conductivity of the fully charged and discharged species, the irreversible loss of polysulfide anions and the decrease in the number of electrochemically active reaction sites during battery operation. Here, we report that the introduction of graphene quantum dots (GQDs) into the sulfur cathode dramatically enhanced sulfur/sulfide utilization, yielding high performance. In addition, the GQDs induced structural integrity of the sulfur-carbon electrode composite by oxygen-rich functional groups. This hierarchical architecture enabled fast charge transfer while minimizing the loss of lithium polysulfides, which is attributed to the physicochemical properties of GQDs. The mechanisms through which excellent cycling and rate performance are achieved were thoroughly studied by analyzing capacity versus voltage profiles. Furthermore, experimental observations and theoretical calculations further clarified the role played by GQDs by proving that C-S bonding occurs. Thus, the introduction of GQDs into Li-S batteries will provide an important breakthrough allowing their use as high-performance and low-cost batteries for next-generation energy storage systems. INTRODUCTIONRechargeable lithium-ion batteries are widely used in various applications, such as portable devices, bio-medical implants and electric vehicles, because of their high energy and power density. 1,2 However, current lithium-ion batteries based on the graphite and transition metal oxide couple have nearly reached their ceiling with respect to storage capability because of the limitations associated with their electrical properties and crystal structure. Therefore, breakthroughs in new energy storage systems that can surpass the current performance barrier of lithium-ion batteries should be brought about in a timely manner. Recently, Li-S batteries that can operate by the reversible electrochemical transformation between sulfur (S 8 ) and dilithium sulfide (Li 2 S) have attracted great attention because they can deliver high energy with a moderate voltage owing to the direct use of

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“…In particular, innovative carbon-based nanomaterials such as graphene quantum dots (GQDs) and graphene oxide quantum dots (GOQDs) have attracted much interest as stable, nontoxic, photoluminescent nanomaterials with possible applications in chemical and biological sensors, drug delivery, bio-imaging and energy conversion [7][8][9][10][11][12][13]. The physical origin of the photoluminescence (PL) from these carbonbased nanoparticles is still quite controversial and different mechanisms have been suggested, possibly acting together, mainly based on quantum confinement in sp 2 domains with a strong influence from edge and oxygen-containing functional groups [14][15][16][17][18]. Nonetheless, several groups have reported a characteristic fluorescence with uniform and stable features in aqueous solution of GOQDs prepared by a variety of methods, either based on bottom-up or on top-down synthesis from graphite [19][20][21][22][23][24][25][26][27].…”

Section: Introductionmentioning

confidence: 99%

Sensitivity to Heavy-Metal Ions of Unfolded Fullerene Quantum Dots

Ciotta¹,

Paoloni²,

Prosposito³

et al. 2017

Preprint

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A novel type of graphene-like quantum dots, synthesized by oxidation and cage-opening of C60 buckminsterfullerene, has been studied as a fluorescent and absorptive probe for heavy-metal ions.The lattice structure of such unfolded fullerene quantum dots (UFQDs) is distinct from that of graphene since it includes both carbon hexagons and pentagons. The basic optical properties, however, are similar to those of regular graphene oxide quantum dots. On the other hand, UFQDs behave quite differently in the presence of heavy-metal ions, in that multiple sensitivity to Cu 2+ , Pb 2+ and As(III) was observed through comparable quenching of the fluorescent emission and different variations of the transmittance spectrum. By dynamic light scattering measurements we confirmed, for the first time in metal sensing, that this response is due to multiple complexation and subsequent aggregation of UFQDs. Nonetheless, the explanation of the distinct behaviour of transmittance in the presence of As(III) and the formation of precipitate with Pb 2+ require further studies. These differences, however, also make it possible to discriminate between the three metal ions in view of the implementation of a selective multiple sensor.

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Revealing the tunable photoluminescence properties of graphene quantum dots

Abstract: Photoluminescence of graphene quantum-dot can be sensitively tuned by size, edge configurations, shape, chemical functionalities, defects, heteroatom-doping and hybridization states.

Cited by 596 publications

References 45 publications

Shining Light on Carbon Nitrides: Leveraging Temperature To Understand Optical Gap Variations

Shining Light on Carbon Nitrides: Leveraging Temperature To Understand Optical Gap Variations

Graphene quantum dots: structural integrity and oxygen functional groups for high sulfur/sulfide utilization in lithium sulfur batteries

Sensitivity to Heavy-Metal Ions of Unfolded Fullerene Quantum Dots

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