Direct Observation of Quantum‐Confined Graphene‐Like States and Novel Hybrid States in Graphene Oxide by Transient Spectroscopy

Wang, Lei; Wang, Hai‐Yu; Wang, Yan; Zhu, Shoujun; Zhang, Yong‐Lai; Zhang, Junhu; Chen, Qi‐Dai; Han, Wei; Xu, Huailiang; Yang, Bai; Sun, Hong–Bo

doi:10.1002/adma.201302927

Cited by 75 publications

(65 citation statements)

References 56 publications

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“…In addition, Yang et al reported that the green emission from oxygen-related function groups is strongly affected by reduction reaction. The charge separation could be observed in the green emission sample 20,21 . We also carry out the reduction experiment for all kinds of N-GQDs.…”

Section: Resultsmentioning

confidence: 94%

“…Although the exact PL mechanism is still under debate, it has been demonstrated the PL of GQDs origining from electron-hole recombination, quantum size effect, zigzag sites, and defect effect 20,21,22 . Eda et al demonstrated that the blue emission was derived from isolated sp 2 cluster within carbon-oxygen sp 3 matrix, leading to radiative recombination of electron and hole 23 .…”

Section: Introductionmentioning

confidence: 99%

“…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%

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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: Resultsmentioning

confidence: 94%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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

et al. 2015

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“…Recently, carbon dots (CDs) have been spotlighted to be a promising substitute to traditional metal-based semiconductor QDs because of their excellent properties, such as broadband optical absorption, good chemical stability, low toxicity, and attractive photoluminescence (PL) properties, [9][10][11] rendering them promising fluorophores for optoelectronic devices. [12][13][14][15][16] Chen's group has suggested CDs as a phosphor for WLEDs; however, these luminophores can hardly generate warm white light with high CRI for indoor lighting because of their low emission efficiency in the yellow and red regions.…”

mentioning

confidence: 99%

High color rendering index white light emitting diodes fabricated from a combination of carbon dots and zinc copper indium sulfide quantum dots

Sun

Zhang

Wang

et al. 2014

Applied Physics Letters

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In a line with most recent trends in developing non-toxic fluorescent nanomaterials, we combined blue emissive carbon dots with green and red emissive zinc copper indium sulfide (ZCIS) core/shell quantum dots (QDs) to achieve white light-emitting diodes (WLEDs) with a high color rendering index of 93. This indicates that ZCIS QDs, with their broad emission bands, can be employed to effectively make up the emission of carbon dots in the yellow and red regions to produce WLEDs in the wide region of color temperature by tuning the volume ratio of these constituting luminophores. Their electroluminescence characteristics including color rendering index, Commission Internationale de l'Eclairage (CIE) color coordinates, and color temperatures were evaluated as a function of forward current. The CIE-1931 chromaticity coordinates of the as-prepared WLEDs, exhibiting good stability, were slightly shifted from (0.321, 0.312) at 10 mA to (0.351, 0.322) at 30 mA, which was mainly caused by the different thermal quenching coefficients of carbon dots and ZCIS QDs.

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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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Direct Observation of Quantum‐Confined Graphene‐Like States and Novel Hybrid States in Graphene Oxide by Transient Spectroscopy

Cited by 75 publications

References 56 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

High color rendering index white light emitting diodes fabricated from a combination of carbon dots and zinc copper indium sulfide quantum dots

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

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