Tunable optical properties of OH-functionalised graphene quantum dots

Geethalakshmi, K. R.; Ng, Teng Yong; Crespo‐Otero, Rachel

doi:10.1039/c6tc02785g

Cited by 43 publications

(32 citation statements)

References 53 publications

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“…[1,[8][9][10][11] The character of chemical groups under photoexcitation is of fundamental importance for the tuning of the photophysics of relevant materials. [12][13][14][15] Recent works found that binding chemical groups onto pristine graphene nanostructures can activate the otherwise forbidden transition from the lowest excited singlet state to the ground singlet state (S 1 !S 0 transition) by altering the optical selection rule. [12][13][14][15] Recent works found that binding chemical groups onto pristine graphene nanostructures can activate the otherwise forbidden transition from the lowest excited singlet state to the ground singlet state (S 1 !S 0 transition) by altering the optical selection rule.…”

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confidence: 99%

“…[7] Therefore, extensive studies have been performed in order to in-depth understand the role of chemical groups in enhancing the luminescent efficiencies of the materials. [12][13][14][15] Recent works found that binding chemical groups onto pristine graphene nanostructures can activate the otherwise forbidden transition from the lowest excited singlet state to the ground singlet state (S 1 !S 0 transition) by altering the optical selection rule. [13,14,16,17] As a result, the magnitude of oscillator strength of the S 1 !S 0 transition can be enlarged, indicating a larger probability of radiative decays in these chemically modified nanostructures.…”

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confidence: 99%

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Nonradiative Excited‐State Decay via Conical Intersection in Graphene Nanostructures

et al. 2019

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Chemical groups are known to tune the luminescent efficiencies of graphene-related nanomaterials, but some species, including the epoxide group (À COCÀ ), are suspected to act as emissionquenching sites. Herein, by performing nonadiabatic excitedstate dynamics simulations, we reveal a fast (within 300 fs) nonradiative excited-state decay of a graphene epoxide nanostructure from the lowest excited singlet (S 1 ) state to the ground (S 0 ) state via a conical intersection (CI), at which the energy difference between the S 1 and S 0 states is approximately zero. This CI is induced after breaking one CÀ O bond at the À COCÀ moiety during excited-state structural relaxation. This study ascertains the role of epoxide groups in inducing the nonradiative recombination of the excited electron-hole, providing important insights into the CI-promoted nonradiative deexcitations and the luminescence tuning of relevant materials. In addition, it shows the feasibility of utilizing nonadiabatic excited-state dynamics simulations to investigate the photophysical processes of the excited states of graphene nanomaterials. Computational DetailsThe ground-and excited-state properties were studied by density functional theory (DFT) and time-dependent DFT (TD-DFT), respectively, as implemented by the Gaussian 09[a] S.

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Nonradiative Excited‐State Decay via Conical Intersection in Graphene Nanostructures

et al. 2019

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“…small shoulder visible near 300 nm is attributed C]O bonds relative to n-p* transitions. 50 In contrast, the 3DNG showed an absorption peak at 276 nm relative to the p-p* transitions of C]C bonds as compared to an optical band gap of 2.42 eV ( Fig. 8(b) and inset).…”

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confidence: 90%

A 3D nitrogen-doped graphene aerogel for enhanced visible-light photocatalytic pollutant degradation and hydrogen evolution

et al. 2020

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Three-dimensional (3D) graphene-based aerogels have attracted widespread interest as promising photocatalysts for dye degradation and hydrogen production. Herein, we have developed a 3D nitrogendoped graphene aerogel (3DNG) from graphitic carbon nitride combined with graphene oxide (GO). The nitrogen dopant in the 3D aerogel was achieved via a thermal treatment at 1000 C, and the 3D aerogel catalyst could retain its 3D porous structure after the thermal treatment. The 3DNG was characterized via FTIR, Raman, TEM, UV-vis, XPS spectroscopies and BET analysis, and the results indicated that this 3DNG with a large surface area of 536 m 2 g À1 and a band gap of 2.42 eV demonstrated a high adsorption capacity and enhanced methylene blue degradation and hydrogen production under visible light irradiation. Characterization also identified that the porous 3D structure with hydrogen bonding and p-p interactions and better charge transfer resulting from the nitrogen doping are the major reasons for the enhanced photocatalytic performance over this 3DNG catalyst.

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“…However, these materials still have many shortcomings in luminous efficiency, color, and stability. [26,31,32] Aggregation of GQDs can result in redshift and broadening of their emission spectra. [26][27][28][29][30] Interestingly, the luminescence properties of GQDs can be regulated not only by their size and modifications but also by their assembly state.…”

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confidence: 99%

“…[23,32,42,43] During the preparation of GQD-MF microspheres, the GQD emission could be affected by various factors including heating, solution pH change, aggregation, and chemical coupling. Fluorescence of GQDs is affected by various factors such as size, doping, edge groups, and aggregation.…”

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White‐Light‐Emitting Melamine‐Formaldehyde Microspheres through Polymer‐Mediated Aggregation and Encapsulation of Graphene Quantum Dots

Zhang

Pan

et al. 2018

Advanced Science

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Graphene quantum dot (GQD) encapsulated melamine‐formaldehyde (MF) polymer microspheres with uniform particle size and tunable high‐quality white‐light emissions are prepared via a polymer‐mediated GQD assembly and encapsulation strategy. In solution, GQDs are first aggregated with MF prepolymer through electrostatic interaction and further encapsulated inside the microspheres formed by polymerization of MF prepolymer under acid catalysis and heating. During this process, the aggregated GQDs are fixed in the MF polymer matrix with their emission extended from blue to full visible range, presenting bright white luminescence under ultraviolet excitation. The prepared white‐light‐emitting GQD‐MF microspheres exhibit uniform morphology with an average particle size of 2.0 ± 0.08 µm and their luminescence properties are effectively regulated by the doping concentration of GQDs in the MF polymer matrix. A series of white‐light‐emitting GQD‐MF microspheres with quantum yields from 0.83 to 0.43, Commission Internationale de L'Eclairage coordinates from (0.28, 0.28) to (0.33, 0.32), and color rendering index from 0.75 to 0.88 are obtained with excellent photostability and thermal stability. By dispersing the GQD‐MF microspheres in cross‐linked polydimethylsiloxane matrix, flexible film with dual functions of high‐quality white‐light‐emitting and light diffusion is obtained and successfully applied for white light‐emitting diode fabrication.

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Tunable optical properties of OH-functionalised graphene quantum dots

Abstract: Functionalisation with OH groups can tune the optical properties of Graphene oxide quantum dots (GO-QDs). Selective functionalisation of positions with large electron–hole separation offers a strategy to control the optical gap and photoluminescence properties.

Cited by 43 publications

References 53 publications

Nonradiative Excited‐State Decay via Conical Intersection in Graphene Nanostructures

Nonradiative Excited‐State Decay via Conical Intersection in Graphene Nanostructures

A 3D nitrogen-doped graphene aerogel for enhanced visible-light photocatalytic pollutant degradation and hydrogen evolution

White‐Light‐Emitting Melamine‐Formaldehyde Microspheres through Polymer‐Mediated Aggregation and Encapsulation of Graphene Quantum Dots

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