Unraveling Bright Molecule‐Like State and Dark Intrinsic State in Green‐Fluorescence Graphene Quantum Dots via Ultrafast Spectroscopy

Wang, Lei; Zhu, Shoujun; Wang, Hai‐Yu; Wang, Ya-Feng; Hao, Yawei; Zhang, Junhu; Chen, Qi‐Dai; Zhang, Yong‐Lai; Han, Wei; Yang, Bai; Sun, Hong‐Bo

doi:10.1002/adom.201200020

Cited by 153 publications

(76 citation statements)

References 36 publications

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“…Yang et al provided further evidence from transient spectra. A charge separation could exist between sp 2 cluster and defect states, leading to a defect state luminescence in a dominated role for green emission GQDs 20,21,25,26 . However, there is rare report on the synthesis of highly luminescent GQDs with tailoring color emissions like inorganic nanocrystals.…”

Section: Introductionmentioning

confidence: 99%

Tailoring color emissions from N-doped graphene quantum dots for bioimaging applications

et al. 2015

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Unlike inorganic quantum dots, fluorescent graphene quantum dots (GQDs) display excitation-dependent multiple color emission. In this study, we report N-doped GQDs (N-GQDs) with tailored single color emission by tuning p-conjugation degree, which is comparable to the inorganic quantum dot. Starting from citric acid and diethylenetriamine, as prepared N-GQDs display blue, green, and yellow light emission by changing the reaction solvent from water, dimethylformamide (DMF), and solvent free. The X-ray photoelectron spectroscopy, ultraviolet-visible spectra results clearly show the N-GQDs with blue emission (N-GQDs-B) have relatively short effective conjugation length and more carboxyl group because H 2 O is a polar protic solvent, which tends to donate proton to the reagent to depress the H 2 O elimination reaction. On the other hand, the polar aprotic solvent (DMF) cannot donate hydrogen, the elimination of H 2 O is promoted and more nitrogen units enter GQD framework. With the increase of effective p-conjugation length and N content, the emission band of N-GQDS red-shifts to green and yellow. We also demonstrate that N-GQDs could be a potential great biomarker for fluorescent bioimaging.

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Section: Introductionmentioning

confidence: 99%

Tailoring color emissions from N-doped graphene quantum dots for bioimaging applications

et al. 2015

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“…[1,2] Plausible reasons could be quantum confinement, size heterogeneity,a nd the participation of defect/trap states. [3][4][5][6] Recently,L ie and co-workersa ttributed the origin of green luminescence in CDs to special edge effects controlled by edge carbon atoms and C=Of unctional groups. [7] However, Peng et al observed size-dependent PL responses from fluorescent CDs are also reported.…”

Section: Introductionmentioning

confidence: 99%

Understanding the Photoluminescence Mechanism of Nitrogen‐Doped Carbon Dots by Selective Interaction with Copper Ions

Ganiga

Cyriac

2016

ChemPhysChem

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Doped fluorescent carbon dots (CDs) have drawn widespread attention because of their diverse applications and attractive properties. The present report focusses on the origin of photoluminescence in nitrogen-doped CDs (NCDs), which is unraveled by the interaction with Cu(2+) ions. Detailed spectroscopic and microscopic studies reveal that the broad steady-state photoluminescence emission of the NCDs originates from the direct recombination of excitons (high energy) and the involvement of defect states (low energy). In addition, highly selective detection of Cu(2+) is achieved, with a detection limit of 10 μm and a dynamic range of 10 μm-0.4 mm. The feasibility of the present sensor for the detection of Cu(2+) in real water samples is also presented.

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“…Ultrafast spectroscopy is a powerful tool for investigating the electronic structure, excitonic properties and carrier dynamics for various new types of fluorescent nanomaterials, for example, graphene oxide, 35,36 graphene quantum dots (QDs), 37 carbon nanodots, 38,39 polymer nanoparticles, 40 direct bandgap semiconductor QDs 41243 and Si NCs. 44249 In our previous work, we produced novel Si NCs with unprecedented ultrabright fluorescence and single-exponential decay.…”

Section: Introductionmentioning

confidence: 99%

Ultrafast optical spectroscopy of surface-modified silicon quantum dots: unraveling the underlying mechanism of the ultrabright and color-tunable photoluminescence

Wang

et al. 2015

Light Sci Appl

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In this work, the fundamental mechanism of ultrabright fluorescence from surface-modified colloidal silicon quantum dots is investigated in depth using ultrafast spectroscopy. The underlying energy band structure corresponding to such highly efficient direct bandgap-like emissions in our surface-modified silicon quantum dots is unraveled by analyzing the transient optical spectrum, which demonstrates the significant effect of surface molecular engineering. It is observed that special surface modification, which creates novel surface states, is responsible for the different emission wavelengths and the significant improvement in the photoluminescence quantum yields. Following this essential understanding, surface-modified silicon quantum dots with deep blue to orange emission are successfully prepared without changing their sizes. Keywords: quantum confinement; silicon quantum dots; surface molecular engineering; ultrafast spectroscopy; wave function modification INTRODUCTIONCrystalline silicon has been the most important semiconductor material in the modern electronics industry due to its excellent electronic properties. However, as a well-known indirect bandgap semiconductor, the optical properties of crystalline silicon are relatively poor, which limits its applications in silicon photonics. To pursue the desired optical performance in silicon materials, nanostructured silicon objects with enhanced photoluminescence (PL) have attracted increasing interest. 1213 Most notably, due to the three-dimensional quantum confinement effect in silicon nanocrystals (Si NCs), the momentum conservation rule is relaxed, and the spatial distributions of photogenerated exciton wave functions tend to extend to the surface of nanoparticles, which provides an efficient approach to manipulate the energy structure of silicon. 14218 Thus, the excitonic emission from Si NCs are usually thought to follow three models: (i) 'direct' transition from a quantization-related bandgap; (ii) indirect approaches, i.e., with the help of other emission centers; and (iii) surface and/or strain engineering. 19 For the 'direct' approach, the observed size-dependent PL behavior in Si NCs can be well explained by the quantum confinement effect. However, such Si NCs can hold strong PL only in the deep red region with limited stability, and their PL lifetimes from these 'direct'

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Unraveling Bright Molecule‐Like State and Dark Intrinsic State in Green‐Fluorescence Graphene Quantum Dots via Ultrafast Spectroscopy

Cited by 153 publications

References 36 publications

Tailoring color emissions from N-doped graphene quantum dots for bioimaging applications

Tailoring color emissions from N-doped graphene quantum dots for bioimaging applications

Understanding the Photoluminescence Mechanism of Nitrogen‐Doped Carbon Dots by Selective Interaction with Copper Ions

Ultrafast optical spectroscopy of surface-modified silicon quantum dots: unraveling the underlying mechanism of the ultrabright and color-tunable photoluminescence

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