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Doped carbon-based materials have attracted considerable attentions due to their extraordinary optical, thermal, and electronic properties. Herein, we demonstrate a facile and universal approach, which involves the hydrothermal treatment of citric acid and phosphonitrilic chloride trimer (Cl6N3P3), for the production of nitrogen and phosphorus co-doped graphene quantum dots (N, P-GQDs). The obtained N, P-GQDs with a mean size of about 3.4 nm exhibit bright yellow fluorescence, good-solubility, and attractive optical stability. Although the quantum yield as high as 34.8% has been proved in our synthesized N, P-GQDs, the fluorescence can be also fleetly and selectively quenched by Fe3+ ions. Therefore, high-performance Fe3+ sensors are fabricated with N, P-GQDs, with an ultra-sensitive detection limit of 146 nM. Furthermore, high ionic strength, mild acids, and alkaline are demonstrated to have a small impact on the fluorescence intensity of the N, P-GQDs. Finally, the as-synthesized N, P-GQDs, with bright luminescence and excellent biocompatibility, are applied for bioimaging, e.g., fibroblast cells. [ABSTRACT FROM AUTHOR]

The application of graphene in the field of microelectronics is becoming more and more urgent with the emergence of bottlenecks in silicon-based semiconductor technology, and the ability of controllable doping in graphene is, therefore, strongly demanded to tune their electronic or optoelectronic properties for the fabrication of high-performance devices. Herein, through seeding zero-dimensional (0D) nitrogen doped graphene quantum dots (N-GQDs) on a catalytic substrate, the graphene monolayer with nitrogen doping is obtained via chemical vapor deposition (CVD). X-ray photoelectron spectroscopy (XPS) characterization shows the doping concentration reaches up to 32%. Experimental and theoretical investigations reveal that N-GQDs act as the nucleation sites for the epitaxial growth of doped graphene monolayers. Finally, infrared photodetector built on N doped graphene (NG) film is fabricated, accompanying with high detectivity (~1.52 × 1010 cm Hz1/2 W − 1) and responsivity (79 mA W − 1) at the wavelength of 1550 nm. Our study may provide a controllable and convenient approach to achieve doped graphene, which paves the way for the application of graphene in the field of microelectronics. [Display omitted] • Our study provides a controllable and convenient approach to achieve doped graphene. • The concentration of dopants in graphene is strictly discerned in accordance with preliminary seeding for N-GQDs. • By seeding of N-GQDs, the graphene monolayer with nitrogen doping is obtained via CVD. • The N doped graphene film with high dopant concentration (32%) is achieved. • The infrared photodetector built on NG film is fabricated with high detectivity and responsivity at 1550 nm. [ABSTRACT FROM AUTHOR]

The development of an environmental-friendly and scalable preparation approach for graphene quantum dots (GQDs) with high quantum yield is a focus area for GQDs. Hence, we describe an atom economic green chemistry strategy for nitrogen-doped GQDs (N-GQDs). The yield of N-GQDs is 98.5%. Moreover, due to the simple reaction and processes, N-GQDs can be synthesized on a large scale (the throughput of N-GQDs is 10 g). Besides, the intrinsic bandgap PL of N-GQDs can be adjusted by size modulation. The emission wavelength of N-GQDs is modulated from 405 nm to 698 nm with a high quantum yield (0.89–0.62). Furthermore, with the general nucleophilic addition reaction of indigo, the PL response-ability of the obtained GQDs can be further tuned. Different precursors with heteroatoms (such as S and Se) can be used for the preparation of dual- heteroatoms co-doped GQDs (N, S-GQDs and N, Se-GQDs). We also confirmed the utilization of the red-near-infrared emitted N-GQDs (emission wavelength: 698 nm) with high quantum yield (0.62) in bio-imaging. [Display omitted] • An environment-friendly, scalable preparation approach for GQDs was developed. • The yield of GQDs is 98.5 wt% • The preparation approach is atom economic. • The emission wavelength of N-GQDs is modulated with a high quantum yield. [ABSTRACT FROM AUTHOR]

The as-fabricated N-GQDs possess a homogeneous size of 3.8 nm, good crystallinity, pip photostability, good water soluble, and a high quantum yield of about 25 %. In addition, it is found that the fluorescence of N-GQDs can be obviously quenched by tetracycline (TC) and elevated temperature. The detection limit of TC is 0.21 μmol L−1, and the fluorescence intensity shows a linear reduction between 25 °C and 100 °C. Owing to the superior optoelectronic properties, white light emitting diodes (WLEDs) using the N-GQDs as the phosphor are fabricated, and the CIE coordinates is (0.357, 0.315) with the color temperature of 4427 K. • The N-GQDs with high blue fluorescence are synthesized by the one-pot hydrothermal method from benzimidazoles. • The N-GQDs enable various applications in tetracycline detection, temperature sensing and high-performance WLEDs. • The detection limit of tetracycline is 0.21 μmol L−1, and the fluorescence intensity shows a linear reduction between 25 °C and 100 °C. • White light emitting diodes (WLEDs) using the N-GQDs as the phosphor are fabricated, and the CIE coordinates is (0.357, 0.315) with the color temperature of 4427 K. In this work, nitrogen-doped graphene quantum dots (N-GQDs) with high blue fluorescence are synthesized by the one-pot hydrothermal method from benzimidazoles. The as-fabricated N-GQDs possess a homogeneous size of 3.8 nm, good crystallinity, pip photostability, good water soluble, and a high quantum yield of about 25 %. In addition, it is found that the fluorescence of N-GQDs can be obviously quenched by tetracycline (TC) and elevated temperature. The detection of TC is implemented, with a detection limit of 0.21 μmol L−1. For the temperature sensing, the fluorescence intensity shows a linear reduction between 25 °C and 100 °C. Moreover, reversible and stable abilities of temperature sensing are demonstrated. Owing to the superior optoelectronic properties, white light emitting diodes (WLEDs) using the N-GQDs as the phosphor are fabricated, and the CIE coordinates is (0.357, 0.315) with the color temperature of 4427 K. The results reported here will expand the multiple applications of N-GQDs in environment monitoring, biosensing engineering and optoelectronic devices. [ABSTRACT FROM AUTHOR]

• This work aimed to the synergistic effect of nitrogen-doped graphene quantum dots. • We demonstrated the selectivity and sensitivity PL detection of homocysteine based on the synergistic effect of surface catalysis and photoluminescence sensing for nitrogen doped graphene quantum dots. • The detection limit is 5 × 10−11 M, which is much lower than most reported detection methods. • We also demonstrated that nitrogen-doped graphene quantum dots were able to display a PL response to homocysteine in the living cells. • This work is helpful for the development of other PL sensors based on graphene quantum dots. As a new photoluminescence functional material, graphene quantum dots have aroused widely entertaining. However, the complicated surficial chemistry micro-circumstance of graphene quantum dots hinders the further study of graphene quantum dots. In this paper, we demonstrate that the selectivity and sensitivity photoluminescence (PL) detection of homocysteine based on the synergistic effect of surface catalysis and photoluminescence sensing for nitrogen-doped graphene quantum dots (N-GQDs). Due to the localized superacid microenvironment of N-GQDs, the homocysteine cyclized into homocysteine thiolactone efficiently and selectively. Meanwhile, the aromatic N in N-GQDs adsorbs homocysteine thiolactone selectively. The following static quenching results in the outstanding selectivity and sensitivity PL quenching of N-GQDs with the presence of homocysteine. The detection limit is 5 × 10−11 M, which is much lower than most reported detection methods. We also demonstrate that N-GQDs are able to display a PL response to homocysteine in the living cells. [ABSTRACT FROM AUTHOR]

Rapid and sensitive fluorescence nanomaterials sensor with satisfactory selectivity has gained numerous importance for detecting multiple metal ions. Graphene quantum dot (GQD) has attracted a great deal of attentions. Herein, yellow emissive GQDs with a high quantum yield of 0.34 were achieved by nitrogen-doping. The as-prepared N-GQDs exhibited excitation-independent behavior and high optical stability. Furthermore, based on the complexation between Fe3+ and N-GQDs, the fluorescence intensity of the N-GQDs could be greatly quenched by the addition of a small amount of Fe3+ ions. The linearity range is 0–80 μM with a detection limit of 63 nM. For this reason, the proposed method was demonstrated to be selective and suitable for Fe3+ analysis in natural water samples. And, N-GQDs with the biosafety have the potentials for intracellular Fe3+ detection. Unlabelled Image • We reported a rapid and sensitive fluorescence nanomaterials sensor with satisfactory selectivity. • Yellow emitted N-GQDs with a quantum yield of 0.34 have been prepared by hydrothermal treatment of dopamine. • The as-prepared N-GQDs exhibited excitation-independent behavior and high optical stability. • The fluorescence intensity of the N-GQDs could be greatly quenched by adding a small amount of Fe3+ ions. • The linearity range is 0.2-80 μM with a detection limit of 63 nM. [ABSTRACT FROM AUTHOR]

In this paper, a simple, economical, and green strategy is developed for producing nitrogen doped graphene quantum dots (N-GQDs) with multicolor light emission by hydrothermal treatment of Passiflora edulia Sims. The synthesized N-GQDs exhibit ideal ionic stability, hydrophilicity and anti-photobcleaching properties, and the quantum yield reaches up to about 29%. Because of with the fluorescence quenching effect, the achieved N-GQDs allow to detect Ag+ in a linear range of 10 nM–160 μM, and the limit of detection is calculated to be 1.2 nM according to the S/N of 3. Noteworthy, N-GQDs with blue, green and yellow light emissions are demonstrated via regulating the reaction time and temperature, implying a promising fluorescence adjustability. Furthermore, the N-GQDs-based fluorescent probe exhibits low cytotoxicity and favorable biocompatibility. Depending on the superior properties, our N-GQDs are applied in fluorescent ink and multicolor cell imaging. Eventually, the developed sensor is highly selective and accurate for Ag+ analysis in real water, which demonstrates the promising practical use in environmental determination and/or biomedical engineering. [ABSTRACT FROM AUTHOR]