No abstract

Zinc oxide ͑ZnO͒ nanoparticles ͑NPs͒ in the size range ϳ7-35 nm are synthesized by ball-milling technique, and microstructural and optical properties of the NPs are studied using varieties of techniques. Results from ball-milled NPs are compared with those of the commercially available ZnO nanopowder. X-ray diffraction pattern of the milled NPs indicates lattice strain in the NPs. High-resolution transmission electron microscopy analysis reveal severe lattice distortion and reduction in lattice spacing in some of the NPs. Optical absorption spectra of milled NPs show enhanced absorption peaked at 368 nm, which is blueshifted with reference to starting ZnO powder. Room-temperature photoluminescence spectra show five peaks consisting of ultraviolet and visible bands, and relative intensity of these peaks drastically changes with increasing milling time. Raman spectra of milled powders show redshift and broadening of the Raman modes of ZnO, and a new Raman mode evolve in the milled NPs. A correlation between the microstructure and optical properties of ZnO NPs is made on the basis of these results. Our results clearly demonstrate that commercially available ZnO nanopowders do not exhibit nanosize effects due to relatively large size of the ZnO NPs. Implications of these results are discussed.

No abstract

Results obtained from the optical absorption and photoluminescence (PL) spectroscopy experiments have shown the formation of excitons in the silver-exchanged glass samples.These findings are reported here for the first time. Further, we investigate the dramatic changes in the photoemission properties of the silver-exchanged glass samples as a function of postannealing temperature. Observed changes are thought to be due to the structural rearrangements of silver and oxygen bonding during the heat treatments of the glass matrix.In fact, photoelectron spectroscopy does reveal these chemical transformations of silverexchanged soda glass samples caused by the thermal effects of annealing in a high vacuumatmosphere. An important correlation between temperature-induced changes of the PL intensity and thermal growth of the silver nanoparticles has been established in this Letter through precise spectroscopic studies.

UV Raman scattering studies show longitudinal optical (LO) mode up to fourth order in wurtzite GaN nanowire system. Fröhlich interaction of electron with the long range electrostatic field of ionic bonded GaN gives rise to enhancement in LO phonon modes. Good crystalline quality, as indicated by the crystallographic as well as luminescence studies, is thought to be responsible for this significant observation. Calculated size dependence, incorporating size corrected dielectric constants, of electron-phonon interaction energy agrees well with measured values and also predict stronger interaction energy than that of the bulk for diameter below ∼3nm.