Study On The Synthesis And Photoluminescence Of Carbon Nanoparticles By Pulsed-Laser

Laser irradiation for preparing nanomaterials has become one of the effective approaches and more and more impotrant with laser technique developing. The common technique hardly meets the high temperature and pressure required in phase transition from tranditional carbon materials (graphite and carbon black) to new carbon materials (nanodiamond and nanoonion et al.). However, pulsed laser can provide such conditions by imputing high energy enough in very short time. Thereby, laser irradiation will become a kind of method to synthesize new carbon materials.Although the larger nanodiamonds (30-300 nm in diameter) were formed in higher temperature and pressure produced by short-pulse-width (ns) laser with high laser power indensity, the yield was very low due to too short working time. Ultrafine nanodiamonds with sizes of smaller 10 nm were prepared by irradiating graphite suspension using long-pulse width (ms) laser at room temperature and normal pressure, and the yield was improved in our research group. The low power density and long pulse laser generated a lower temperature and a lower pressure, which determine the stable size of nanodiamonds. On the other hand, the low degree of supercooling allows a rather low growth velocity, and a disordered structure formed at the diamond surface retards the epitaxy growth. The above two factors dynamically limited the final size of nanodiamonds. Moreover, our study showed that the diamond-transition probabilties were high at the small size, which trended to improve the diamond yields.The multiply twinning structure (MTS) of nanodiamonds synthesized by pulsed-laser irradiation was firstly investigated theoretically and experimentally. The thermodynamic calculation shows MTS is more stable than single crystal in a certain size range and statistical results experimentally accords with the theory. A mechanism on the formation of MTS in nanodiamonds was proposed based on Transmission Electron Microscopy (TEM) observation, in which a single crystal successively grows into MTS through intermediate states, such as simple twin and triple twin.Hydrophilic carbon nanoonions were firstly synthesized by irradiating carbon black particles in water using pulsed laser, which exploited their application. All of analyzed techniques showed that the hydrophilic properties of carbon nanoonions orginated from hydrophilic ligands. Based on the theoretical calcaulation, the influences of laser power intensity on the structure of carbon nanoonions were studied in this paper: The higher laser power intensity could make the mass lose by carbon sublimation and resulted in the hole formation in the centre of carbon nanoonions; however, the lower laser power intensity could not produce carbon nanoonions due to lack of enough energy.Fluorescent carbon nanoparticles (CNPs) show high potential on the application of biology labelling and life science, because they own many advantages over the conventional quantum dots based on sulphides, selenides, or tellurides of zinc and cadmium, such as biocompatible, chemically inert, and can be surface-modified. Therefore, it is very important to study the luminescent mechanism. An effective method to synthesize fluorescent CNPs by laser irradiation of the suspension of carbon materials in organic solvent, the synthesis and surface modification of luminescent CNPs were believed to realize simultaneously. Compared with previous works, such a one-step process is simple and easy to be industrialized. Especially, by selecting organic solvents, the surface states could be modified conveniently to realize tuneable light emission. Based on the results of control experiments, the origin of the luminescence is proposed to be the surface states related to the ligands on the surface of CNPs. Especially, CNPs can emit visible light via two-photon excitation by using near-infrared light. The two-photon excitation makes photodynamic therapy harmless to health tissue adjacent to the diseased target tissue.