Annealing temperature effects on the size and band gap of ZnS quantum dots fabricated by co-precipitation technique without capping agent.

ZnS quantum dots (QDs) were fabricated using the co-precipitation technique with no capping agent. The effects of different annealing temperatures (non-annealed, 240 °C and 340 °C for 2 h) on the structural and optical characteristics of ZnS QDs are reported. The samples were examined by XRD, TEM, PL, FTIR, and UV-Vis. An increase in annealing temperature led to an increase in the dot size and a lowering of the energy band gap (EG). The average crystallite size, D of ZnS was between 4.4 and 5.6 nm. The ZnS QDs showed a band gap of 3.75, 3.74 and 3.72 eV for non-annealed, 240 °C, and 340 °C annealed samples. The reflection spectra increased in the visible light and decreased in UV region with an increase in annealing temperature. This work showed that the band gap and size of ZnS QDs could be tuned by varying the annealing temperature.

Structure, optical properties and antimicrobial activities of MgO-Bi2-xCrxO3 nanocomposites prepared via solvent-deficient method.

MgO-Bi2-xCrxO3 nanocomposites for x = 0 and 0.07 were fabricated using the solvent-deficient route. X-ray diffraction method, scanning electron microscopy (SEM), energy dispersive X-ray analysis (EDXA) and UV-Vis spectroscopy were employed to study the properties. The samples were also evaluated for the antibacterial activity. The x = 0 sample showed a dominant monoclinic crystalline structure of [Formula: see text] phase. No peaks attributed to MgO were observed. Cr-doped [Formula: see text] in which Bi was substituted showed that [Formula: see text] phase was also present in the [Formula: see text] composite. The Scherrer formula was employed to determine the crystallite size of the samples. The Cr-doped sample showed a decrease in the crystallite size. The microstructures of the non-doped MgO-Bi2O3 and MgO-Bi1.93Cr0.07O3 composites consisted of micrometer sized grains and were uniformly distributed. Direct transition energy gap, [Formula: see text] decreased from 3.14 to 2.77 eV with Cr-doping as determined from UV-Vis spectroscopy. The Cr-doped [Formula: see text] nanocomposites exhibited two energy gaps at 2.36 and 2.76 eV. The antibacterial activity was determined against gram-negative bacteria (Salmonella typhimurium and Pseudomonas aeruginosa) and gram-positive bacteria (Staphylococcus aureus) by disc diffusion method. Cr-doping led to a decrease in inhibitory activity of MgO-Bi2-xCrxO3 nanocomposite against the various types of bacteria.

Synthesis and comparative study on the structural and optical properties of ZnO doped with Ni and Ag nanopowders fabricated by sol gel technique.

In this work we have tried to prepare Ni and Ag doped ZnO nanopowders using the sol gel technique. The influence of Ni and Ag (1, 3 and 5 mol.%) on the crystalline structure and optical properties of ZnO was investigated. The samples were characterized by XRD, FTIR and UV-visible spectrophotometer. XRD patterns confirmed the wurtzite formation of doped and undoped ZnO nanopowders. The average crystallite sizes of the prepared samples found from XRD were 19 nm for undoped ZnO, from 17 to 22 nm for Ni-ZnO and from 19 to 26 nm for Ag-ZnO. The average crystallite size of Ag-ZnO increased with increasing Ag contents. Different optical properties of Ni-ZnO and Ag-ZnO nanopowders were observed for different Ni and Ag content. The band gaps of Ni-ZnO and Ag-ZnO nanopowders were lower than that of the undoped ZnO (3.1 eV). The band gaps of Ag-ZnO were lower than that of Ni-ZnO. The optical properties of ZnO were enhanced by Ni (mol.%) in the UV region and by Ag (3 and 5 mol.%) in the visible region.