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.

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 (E_G). 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.

MgO–Bi_2−xCr_xO₃ 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 $$\alpha\text{-}{\text{Bi}}_{2}{\text{O}}_{3}$$α -Bi 2 O 3 phase. No peaks attributed to MgO were observed. Cr-doped $$\text{MgO}{-}{\text{Bi}}_{2}{\text{O}}_{3}$$MgO - Bi 2 O 3 in which Bi was substituted showed that $${\text{the tetragonal BiCrO}}_{3}$$the tetragonal BiCrO 3 phase was also present in the $$\text{MgO}{-}{\text{Bi}}_{2}{\text{O}}_{3}$$MgO - Bi 2 O 3 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–Bi_1.93Cr_0.07O₃ composites consisted of micrometer sized grains and were uniformly distributed. Direct transition energy gap, $${E}_{\text{g}}$$E g decreased from 3.14 to 2.77 eV with Cr-doping as determined from UV–Vis spectroscopy. The Cr-doped $$\text{MgO}{-}{\text{Bi}}_{2}{\text{O}}_{3}$$MgO - Bi 2 O 3 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–Bi_2−xCr_xO₃ nanocomposite against the various types of bacteria.

YBa₂Cu₃O_7−δ (Y-123) bulk superconductors with the addition of (0.0, 0.2, 0.4, 0.6, 0.8, and 1.0 wt.%) SnO₂ nanoparticles were synthesised via a thermal treatment method. The influence of SnO₂ addition on the superconducting properties by means of critical temperature, T_c, AC susceptibility, phase formation and microstructures, including its elemental composition analysis, were studied. Sharp superconducting transition, ∆T_c, and diamagnetic transition were obtained for all SnO₂-added samples. It was observed that sample x = 0.4 with a Y-123 phase percentage of 95.8% gives the highest T_c, smallest ∆T_c, and the sharpest diamagnetic transition in the normalised susceptibility curves. The microstructure also showed an excess of Sn precipitates on the sample’s surface at x = 0.8 and above. As such, the best superconducting properties were observed at x = 0.4 SnO₂ addition inside the Y-123 host sample.