Common Origin of Green Luminescence in Carbon Nanodots and Graphene Quantum Dots

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

doi:10.1021/nn500368m

Cited by 723 publications

(524 citation statements)

References 37 publications

(69 reference statements)

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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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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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“…During this process, spontaneous emission of radiation can be observed as a way to discard the excess of the energy to stabilize the quantum system. Besides this basic chemistry, the instructor may briefly cite other photoluminescence mechanisms related to the band gap transitions between π-domains or defects on the surface of CQDs [45][46][47]. The fact of the photoluminescence mechanism remains unclear can further lead the students to understand chemistry as a building science.…”

Section: Discussionmentioning

confidence: 99%

Carbon Quantum Dots: A Safe Tool to Learn about Quantum Phenomenon in Nanomaterials

Cruz¹,

Freire²,

Carneiro³

et al. 2017

jlce

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In this paper, a lab experiment to demonstrate quantum phenomena was developed using carbon quantum dots (CQDs), a new carbon-based fluorescent nanomaterial, discovered in 2004. Therefore, a practical class was developed to demonstrate quantum phenomena using cheap and safe chemical products. Over 140 students from biotechnology, pharmacy, engineers and geology courses have successfully performed the proposed lab experiment. By following a short, easy and totally safe procedure, the students were able to synthesize CQDs, as well as to visualize the quantum phenomena related to the light scattering, absorption and emission. It was also possible to obtain the absorption spectrum of the CQD sample, with an absorption band at 325 nm. Additionally, a wavelength-dependent behavior was observed for the synthesized CQDs. This may be used to deeply study quantum confinement effects. Therefore, CQDs can be a powerful and versatile tool to learn about quantum phenomena in nanomaterials.

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“…More importantly, although significant progress has been achieved in the field of CQDs in the past decade, their PL mechanism remains a mystery and a universal explanation is still absent. Besides the mechanism based on the emission of π-conjugated moieties in the cores, it is generally accepted that the PL properties of CQDs are governed by their surface states or defects caused by surface oxidation [52,53], which serve as centers for capturing excitons and make CQDs photoluminescent. As our CQDs have a higher oxygen content compared to their counterparts prepared by other carbon nanomaterials, the number of capture centers on their surfaces is also larger, accounting for their yellow-emitting characteristics.…”

Section: Spectroscopic Properties Most Of the Previous Studies On Cqdmentioning

confidence: 99%

Production of yellow-emitting carbon quantum dots from fullerene carbon soot

et al. 2017

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Carbon quantum dots (CQDs) have emerged as a new generation of photoluminescent nanomaterials with wide applications. Among the various synthetic routes for CQDs, the acid-refluxing method, which belongs to the group of "top-down" methods, offers the advantage of large-scale production of CQDs and uses cheap and abundantly available starting materials. In this study, we evaluated the potential of fullerene carbon soot (FCS), a by-product obtained during the synthesis of fullerene, as the starting material for CQD production. It was found that FCS can be successfully converted to CQDs in high production yield in mixed acids, i.e., concentrated HNO3 and H2SO4, under mild conditions. The fluorescence quantum yield (Φ) of the as-produced CQDs is in the range of 3%-5%, which is the highest value for CQDs obtained from "top-down" methods. Importantly, the CQDs prepared by this method show emission in the yellow range of the visible light, which is advantageous for their various potential applications. Further investigations reveal that the CQDs are highly photostable over a wide pH range and show good resistance against ionic strength and long-term UV irradiation. This further expands their potential use under harsh conditions.

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Common Origin of Green Luminescence in Carbon Nanodots and Graphene Quantum Dots

Cited by 723 publications

References 37 publications

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

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

Carbon Quantum Dots: A Safe Tool to Learn about Quantum Phenomenon in Nanomaterials

Production of yellow-emitting carbon quantum dots from fullerene carbon soot

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