PREPARATION AND STUDIES OF FLUORESCENT CARBON NANOMATERIALS

There have been rapid advances in the development and applications of semiconductor quantum dots (QDs) represented by CdSe/ZnS. However, a serious limitation of these QDs is the necessary use of toxic heavy metals. Fluorescent \u27carbon dots\u27 (surface passivated carbon nanoparticles) are developed as alternative to classical semiconductor QDs. The carbon dots could be made to be highly fluorescence, with emission quantum yields close to 60%. Their optical properties resemble bandgap transitions found in nanoscale semiconductors, suggesting that carbon particles at the nanoscale acquire essentially semiconductor-like characteristics. The fluorescence in carbon dots could be quenched efficiently by electron acceptor or donor molecules in solution, namely that photoexcited 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. Carbon dots were doped by various inorganic salts, and the spectroscopic performances of carbon dots were found to be strongly related to the types of dopants. Experiment results showed that the fluorescence brightness of carbon dots was significantly enhanced by ZnS, ZnO or TiO2 as a dopant. Further fractionating the doped carbon dots resulted in some dots of the quantum yields up to 75%. As known in the literature, well-dispersed and functionalized carbon nanotubes exhibit visible fluorescence emissions due to passivated defects on the nanotube surface. It was found in this study that the defects in nanotubes could be decorated by an inorganic salt, which augmented the passivation effect of organic functionalization to result in dramatically enhanced emission intensities under both one- and two-photon excitation conditions. The structures and properties of the functionalized carbon nanotubes with inorganic coating were thoroughly characterized by using spectroscopy and microscopy techniques. The fluorescence decoration with the coating may serve as a tool in the study of surface defects in carbon nanotubes, and these brightly fluorescent pseudo-one-dimensional nanomaterials may be exploited for optical applications