Cu-, Eu-, or Mn-doped ZnS nanocrystalline phosphors were prepared at room temperature using a chemical synthesis method. Transmission electron microscopy observation shows that the size of the ZnS clusters is in the 3–18 nm range. New luminescence characteristics such as strong and stable visible-light emissions with different colors were observed from the doped ZnS nanocrystals at room temperature. These results strongly suggest that impurities, especially transition metals and rare-earth metals-activated ZnS nanoclusters form a new class of luminescent materials.

No abstract

ZnS:Mn luminescent nanomaterials were first prepared in an inverse microemulsion at room temperature as well as under a hydrothermal condition. Mn-doped ZnS nanoparticles obtained are distributed from 3 to 18 nm in diameter as determined by transmission electron microscopy. The crystalline nature of the materials is clearly demonstrated by the X-ray diffraction results. Compared with Mn-doped ZnS materials synthesized through the conventional aqueous reaction, the nanoparticles prepared in a microemulsion show a significant enhancement in photoluminescence. In particular, the photoluminescence of particles prepared in microemulsion under hydrothermal treatment was found to be enhanced by a factor of 60 as compared to that of the material obtained through the direct aqueous reaction at room temperature. This dramatic increase in photoluminescence yield is attributed to the surface passivation of nanoparticles by the adsorption of surfactants in microemulsion, the formation of sphalerite with cubic zinc blende structure, and Mn migration into the interior lattice of ZnS host.

Long carbon nanotubes (CNTs) have many important applications. However, long CNTs may self-fold and therefore compromise their applications. The authors have determined the critical length for self-folding as 4πEI∕γ, where EI and γ are the CNT bending stiffness and binding energy, respectively. This simple expression has been verified by atomistic simulations. For single-wall CNTs, the critical self-folding length ranges from a few hundred nanometers to about 2μm. For multiwall CNTs, the critical length increases rapidly with the number of walls and exceeds 10μm for a 14-wall CNT.

No abstract