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

Photoluminescence (PL) properties of tin oxide (SnO 2 ) nanowires are studied in detail using high spectral resolution spectroscopy in a temperature range of 10-300 K. The nanowires have an average diameter of 86 nm. The high quality of the nanowires enables the observation of rich fine structures in the ultraviolet PL spectra at low temperatures. By carefully analyzing the temperature and excitation power dependent spectra, the following emissions are identified: recombination of donor-acceptor pairs, excitons bound to neutral and ionized donor impurities and optical transitions from free electrons to neutral acceptor impurities. Moreover, it is believed that the emission from recombination of free excitons is observed, which is unusual for SnO 2 , a dipole forbidden direct band gap semiconductor.

Cu-doped ZnS nanocrystals were prepared in an inverse microemulsion at room temperature as well as under a hydrothermal condition. X-ray diffraction analysis showed that the diameter of the Cu-doped ZnS nanocrystals particles was about 9 nm. These particles showed a strong photoluminescence intensity and a broad emission band from 490 to 530 nm. The half-width of emission was about 60 nm. Cu-doped ZnS nanocrystals/polymethylmethacrylate composite as a light-emitting layer was used to fabricate a single layer structure electroluminescent device which had low turn on voltage (less than 5 V). The green light of electroluminescence was observed at room temperature. The electroluminescence and photoluminescence spectra were nearly identical at room temperature.

FePt–C films with high coercivity, (001) texture, and small grain size were deposited on MgO∕CrRu/glass substrate by cosputtering FePt and carbon at 350°C. The out-of-plane coercivity measured at room temperature increased from 9.6to15.1kOe when C concentrations increased from 0% to 15%. Further increasing the C contents to 20% and 25% caused the decrease of coercivity to 13.6 and 11.8kOe, respectively. With C doping, a two-layer structure of FePt–C films was formed and fcc-phase FePt particles were found. By optimizing the sputtering process, FePt–C (001) film with coercivity higher than 14.4kOe and columnar FePt grains of 7.5nm in diameter was obtained, which are suitable for ultrahigh density perpendicular recording.