No abstract

No abstract

No abstract

Alkali treatment coupled with high pressure defibrillation and acid treatment have been tried on banana fibers obtained from the pseudo stem of the banana plant Musa sapientum. The structure and morphology of the fibers have been found to be affected on the basis of the concentration of the alkali and acid and also on the pressure applied. Steam explosion in alkaline medium followed by acidic medium is found to be effective in the depolymerization and defibrillation of the fiber to produce banana nanowhiskers. The chemical constituents of raw and steam exploded fibers were analyzed according to the ASTM standards. Structural analysis of steam exploded fibers was carried out by FTIR and XRD. The fiber diameter and percentage crystallinity of the modified fibers were investigated using X-ray diffraction studies. Characterization of the fibers by SFM and TEM supports the evidence for the development of nanofibrils of banana fibers.

The exfoliation of graphene from pristine graphite in a liquid phase was achieved successfully via sonication followed by centrifugation method. Ultraviolet–visible (UV–vis) spectra of the obtained graphene dispersions at different exfoliation time indicated that the concentration of graphene dispersion increased markedly with increasing exfoliation time. The sheet-like morphology of the exfoliated graphene was revealed by Scanning Electron Microscopy (SEM) image. Further, the morphological change in different exfoliation time was investigated by Atomic Force Microscopy (AFM). A complete structural and defect characterization was probed using micro-Raman spectroscopic technique. The shape and position of the 2D band of Raman spectra revealed the formation of bilayer to few layer graphene. Also, Raman mapping confirmed the presence of uniformly distributed bilayer graphene sheets on the substrate.

No abstract

ZnO is a unique material that offers about a dozen different application possibilities. In spite of the fact that the ZnO lattice is amenable to metal ion doping (3d and 4f), the physics of doping in ZnO is not completely understood. This paper presents a review of previous research works on ZnO and also highlights results of our research activities on ZnO. The review pertains to the work on Al and Mg doping for conductivity and band gap tuning in ZnO followed by a report on transition metal (TM) ion doped ZnO. This review also highlights the work on the transport and optical studies of TM ion doped ZnO, nanostructured growth (ZnO polycrystalline and thin films) by different methods and the formation of unique nano- and microstructures obtained by pulsed laser deposition and chemical methods. This is followed by results on ZnO encapsulated Fe3O4 nanoparticles that show promising trends suitable for various applications. We have also reviewed the non-linear characteristic studies of ZnO based heterostructures followed by an analysis on the work carried out on ZnO based phosphors, which include mainly the nanocrystalline ZnO encapsulated SiO2, a new class of phosphor that is suitable for white light emission.

M5(PO4)3X apatites are well known for their technological importance as phosphors, laser hosts and biocompatible materials. Divalent-europium-activated alkaline earth chloroapatites are of special importance for their application as the blue component in high-efficiency trichromatic fluorescent lamps. In these apatites, Eu2+ yields narrow-band emission in the blue region corresponding to the 4f65d to 8S7/2 allowed electric dipole transition. It has been found that the dominant emission band observed can be assigned to Eu2+ occupying MII sites of the apatite system having C1h symmetry. In the case of barium chloroapatites one could also observe Eu2+ emission from a second type of site (MI) that is available in the apatite system. The weak emission observed in the latter can be attributed to the intense spectral overlap with the former site(s) and thermal quenching effects. The exchange coupling between the 4f6 and 5d electrons of Eu2+ manifests itself in 'stair-case' features in the excitation spectrum and the strength of the exchange interaction is highly dependent on the host apatite(s). Also, in the Eu2+, Mn2+ co-doped system, energy transfer is found to occur from the former to the latter and the transfer is regulated by an exchange process. Various results based on these facts are discussed in detail.