We report that nanoscale carbon particles (carbon dots) upon simple surface passivation are strongly photoluminescent in both solution and the solid state. The luminescence emission of the carbon dots is stable against photobleaching, and there is no blinking effect. These strongly emissive carbon dots may find applications similar to or beyond those of their widely pursued silicon counterparts.

The photoluminescence in carbon dots (surface-passivated small carbon nanoparticles) could be quenched efficiently by electron acceptor or donor molecules in solution, namely that photo-excited carbon dots are both excellent electron donors and excellent electron acceptors, thus offering new opportunities for their potential uses in light energy conversion and related applications.Quantum-sized semiconductor nanoparticles (quantum dots) have emerged as an important class of photoactive nano-materials for a variety of purposes and applications. [1][2][3][4] For the utilization of semiconductor quantum dots in light energy conversion and related areas, there have been extensive investigations on their photoresponse and photoinduced charge separation and electron transfer processes. [5][6][7][8] Alternative to the traditional semiconductors, other quantum-sized nanoparticles have been explored and developed for similar photophysical and photochemical properties. Of particular interest and significance is the recent finding that small carbon nanoparticles could be surface-passivated by organic molecules or polymers to become highly photoactive, exhibiting strong photoluminescence in the visible and near-infrared spectral regions. 9-15 These photoluminescent carbon nano-particles, dubbed "carbon dots" (Scheme 1), were found to be physico-chemically and photochemically stable and nonblinking in their luminescent emissions. 9 Here we report that the photoluminescence from carbon dots could be quenched highly efficiently by either electron acceptor or electron donor molecules in solution, namely that the photo-excited carbon dots are excellent as both electron donors and electron acceptors. These interesting photoinduced electron transfer properties may offer new opportunities in potentially using carbon dots for light energy conversion and related applications, in addition to their being valuable to the effort on mechanistic elucidation.The carbon dots in this study were prepared by using the same procedures as those reported previously. 9 In the preparation, the small carbon nanoparticles (separated from the laser ablation-produced powdery sample) were refluxed in aqueous nitric acid solution for the purpose of oxidizing surface carbons into carboxylic acids, followed by thionyl chloride treatment and then amidation with the oligomeric ethylene glycol diamine H 2 NCH 2 (C 2 H 4 O) 35 C 2 H 4 CH 2 NH 2 (PEG 1500N ) to form the carbon dots with surface-attached PEGs (Scheme 1). The transmission electron microscopy (TEM) results ( Fig. 1) suggested that these dots were well-dispersed, with sizes averaging about 4.2 nm (based on statistical analyses of more than 300 dots), as also supported by the atomic force microscopy (AFM) results (Fig. 1).Photoluminescence spectra of the carbon dots in aqueous or organic solutions were generally broad ( NIH Public Access Author ManuscriptChem Commun (Camb) 3). Obviously 2,4-dinitrotoluene was a much more effective quencher than 4-nitrotoluene, consistent with its being a s...

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Single-walled and multiple-walled carbon nanotubes were functionalized with poly(vinyl alcohol) (PVA) in esterification reactions. Similar to the parent PVA, the functionalized carbon nanotube samples are soluble in highly polar solvents such as DMSO and water. The common solubilities have allowed the intimate mixing of the functionalized nanotubes with the matrix polymer for the wet-casting of nanocomposite thin films. The PVA-carbon nanotube composite films are of high optical quality, without any observable phase separation, and the carbon nanotubes in the films are as well-dispersed as in solution.The functionalization of carbon nanotubes by the matrix polymer is apparently an effective way in the homogeneous nanotube dispersion for high-quality polymeric carbon nanocomposite materials. Results from characterizations of the solubilized carbon nanotubes and the nanocomposite thin films are presented and discussed.