Properties Of Carbon Nanodots Research Articles

Preparation and Fluorescent Wavelength Control of Multi-Color Nitrogen-Doped Carbon Nano-Dots.

It is known that, by taking advantage of heteroatom doping, the electronic states and transition channels in carbon nano-dots (CNDs) can be effectively modulated. Thus, the photoluminescence (PL) properties of CNDs can be changed. For potential applications of CNDs as advanced materials for optoelectronic devices, it is important and significant to develop the practical techniques for doping heteroatoms into CNDs. In this work, we synthesize the multi-color fluorescent by using a fast and effective microwave method where the CNDs are nitrogen-doped. We examine the influence of different ratios of the raw materials on the structure and optical properties of N-CNDs. The results show that the prepared N-CNDs can generate blue (445 nm), green (546 nm), and orange (617 nm) fluorescence or PL with the mass ratio of the raw materials at 1:1, 1:2 and 1:3, respectively. We find that the N content in N-CNDs leads to different surface/edge states in domain. Thus, the wavelength of the PL emission from N-CNDs can be tuned via controlling the N concentration doped into the CNDs. Moreover, it is shown that the intensity of the PL from N-CNDs is mainly positively related to the content of C-O groups attached on the surface/edges of the N-CNDs. This study provides an effective experimental method and technical way to improve the fluorescent emission, and to modulate the color of the PL emission from CNDs.

Solvothermal synthesis of hydrophobic carbon dots in reversed micelles

Synthesis of hydrophobic luminescent carbon nanostructures in non-aqueous solution has been performed. The system consisted of hexane as nonpolar “oil” phase, nonionic polyoxyethylene (4) lauryl ether (Brij L4) as a surfactant, and either water or dextran sulfate aqueous solution as a polar phase. Carbon nanodots (CND) with a particle size of 5.0 ± 0.7 nm were formed by solvothermal treatment at 180 °C of two- (hexane–Brij L4) and three-component (hexane–Brij L4–aqua solutions) systems. It was found that CND with blue-green-yellow photoluminescence (PL) with linear dependence of emission peak position on excitation wavelength and stability of PL over at least 3 weeks were formed from Brij L4. We found that using small volume of water as the third component helps to reorganize Brij L4 molecules which results in CND PL intensity increase by a factor of 1.5 and quantum yield increase from 2.0 to 2.6% compared to CND from the two-component micellar system. Replacing water with dextran sulfate solution resulted in a lower quantum yield to 2.2%. Thus, addition of small amount of water clearly shows an effect of molecular level organization on properties of CND and results in enhanced quantum yield.

Characterization and enhanced nonlinear optical limiting response in carbon nanodots dispersed in solid-state hybrid organically modified silica gel glasses

Freely dispersed carbon nanodots (CNDs) were introduced into a 3-glycidoxy-propyltrimethoxysilane modified silicate gel glass (i.e. an organically modified silica or ORMOSIL) by a highly efficient and simple sol-gel process, which could be easily extended to prepare functional molecules/nanoparticles solid state optoelectronic devices. Scanning electron microscope imaging, Fourier transform infrared spectroscopy, pore structure measurements, ultraviolet–visible spectroscopy, and fluorescence spectroscopy were used to investigate the surface characteristics, structure, texture, and linear optical properties of the CND/SiO2 ORMOSIL gel glasses. Images and UV/Vis spectra confirmed the successful dispersion of CNDs in the ORMOSIL gel glass. The surface characteristics and pore structure of the host SiO2 matrix were markedly changed through the introduction of the CNDs. The linear optical properties of the guest CNDs were also affected by the sol-gel procedure. The nonlinear optical (NLO) properties of the CNDs were investigated by a nanosecond open-aperture Z-scan technique at 532 nm both in liquid and solid matrices. We found that the NLO response of the CNDs was considerably improved after their incorporation into the ORMOSIL gel glasses. Possible enhancement mechanisms were also explored. The nonlinear extinction coefficient gradually increased while the optical limiting (OL) threshold decreased as the CND doping level was increased. This result suggests that the NLO and OL properties of the composite gel glasses can be optimized by tuning the concentration of CNDs in the gel glass matrix. Our findings show that CND/SiO2 ORMOSIL gel glasses are promising candidates for optical limiters to protect sensitive instruments and human eyes from damage caused by high power lasers.

Effect of the Elemental Composition of Precursors from Amino Acids and Their Binary Mixtures on the Photoluminescent Intensity of Carbon Nanodots.

We report on the photoluminescent (PL) properties of carbon nanodots (CNDs) doped with nitrogen and sulfur obtained by the pyrolytic carbonization of amino acids as precursors. Prepared CNDs exhibit stable PL emission under a wide variety of aqueous conditions. The results also provided the way to tune a PL intensity of CNDs by varying the amount of heteroatoms in precursors with a binary mixture of amino acids. The PL quantum yields of the obtained CNDs were determined to be from 0.079 to 0.571.

Third-order nonlinear optical properties of carboxyl group dominant carbon nanodots

We quantitatively investigate the nonlinear optical (NLO) property of carbon nanodots (CNDs, less than 10 nm) by the Z-scan technique using a tunable 532 nm nanosecond laser system.

Modulation of electrochemical property of carbon nanodot by post-chemical reductions

Abstract Influences of chemical reductions on the electrochemical properties of carbon nanodots (CNDs) were investigated. Sequential electron transfer reactions involving CNDs and several electrochromic molecules were analyzed by titration method to deduce electron accepting capabilities and upper-limit reduction potentials. CNDs prepared by alkali-assisted electrochemical oxidation of graphite were reduced by either sodium borohydride or hydrazine to obtain chemically reduced CNDs. Titration analysis of the electron transfer reactions involving methylviologen cation radicals and CNDs revealed that electron uptake per unit weight of CND increased nearly 30% after chemical reductions. Furthermore, detailed analyses of electron discharge processes involving the electron-filled CNDs and several leuco dyes provided fine estimation of upper-limit reduction potential and evidence of reduction potential shifts of CNDs to negative level by chemical reductions.

Effect of reaction temperature on properties of carbon nanodots and their visible-light photocatalytic degradation of tetracyline

Carbon nanodots with diverse sizes, crystal structures, optical properties and can be used as photosensitizer were synthesized via hydrothermal process.