Influence of Ag, Au and Pd noble metals doping on structural, optical and antimicrobial properties of zinc oxide and titanium dioxide nanomaterials.

Oxide materials (ZnO, TiO2) doped with noble metals were synthesized using the combustion technique. The results of the addition of Ag, Au, and Pd up to a concentration of 2 mol% on the structural, optical, morphological and antimicrobial properties was considered. X-ray diffraction experiments revealed that the crystal structure of the host materials remained unaltered despite doping with noble metals. From the scanning electron microscopy results, it was evident that the doped nanoparticles aggregated in clusters of different sizes in the host matrix. The plasmonic effect was also observed in the absorbance spectra of the different doped materials. The obtained materials have shown promising antimicrobial features. All ZnO materials exhibited a high antimicrobial activity, with very low minimum inhibitory concentration values, against the planktonic growth of all tested Gram-positive and Gram-negative bacterial strains. All doped materials exhibited very good anti-biofilm activity, the lowest minimal biofilm eradication concentration values being registered for ZnO doped with Au and Pd toward Escherichia coli and for ZnO doped with Ag against Candida albicans. These results indicate the potential that these materials have for antimicrobial applications in the fields of biomedicine and environmental protection.

Controlled sol-gel synthesis of oxygen sensing CdO : ZnO hexagonal particles for different annealing temperatures.

CdO : ZnO hexagonal particles were synthesized by a sol-gel precipitation method at different annealing temperatures. A mixed crystal phase of cubic and wurtzite structures was observed from X-ray diffraction patterns. The micrographs showed hexagonal shapes of the CdO : ZnO nanocomposites particles. The energy dispersive X-ray spectroscopy mapping images showed a uniform distribution of the Cd and Zn. The CdO : ZnO nanocomposite pallet annealed at 550 °C has an electrical resistance of 0.366 kΩ at room temperature. The nanocomposites showed an excellent sensing response against oxygen gas with a sensing response of 47% at 200 °C for the CdO : ZnO particles annealed at 550 °C. The sensor response and recovery times were found to be 43s and 45s, respectively. The sensor response was due to the sorption of oxygen ions on the surfaces of the CdO : ZnO hexagonal particles.

Highly efficient infrared to visible up-conversion emission tuning from red to white in Eu/Yb co-doped NaYF4 phosphor.

Eu/Yb co-doped NaYF4 phosphors have been synthesized by the combustion method. The Eu doping was fixed and the effect of Yb doping concentration on the structural, morphological and luminescence properties has been investigated. X-ray diffraction analysis revealed that the phosphors consisted of mixed α- and ß-phases, but the ß-phase was dominant. All elements of the host and dopants, as well as adventitious C, were detected using X-ray photoelectron spectroscopy. The surface morphology showed a microrod-like structure with sharp hexagonal edges. Energy dispersive X-ray spectroscopy spectra proved the formation of the desired materials. The photoluminescence spectra illustrated the optical emission properties of Eu3+ in the red region when excited at 394 nm, while, under the same excitation, Yb3+ ions gave emission at 980 nm. The up-conversion (UC) emission of Eu/Yb co-doped NaYF4 produced a white color at the higher concentration of Yb excited by a 980 nm laser, which was made possible by green emission of Er contamination (from Yb source) and blue emission of Eu2+ ions. The lifetime of the Eu3+ UC luminescence at 615 nm was also affected by the Yb doping concentration. The temperature sensitivity associated with the Er3+ peaks at 520 and 542 nm was assessed as a function of temperature and the maximum of 0.0040 K-1 occurred at 463 K.

Influence of Bi doping on the structure and photoluminescence of ZnO phosphor synthesized by the combustion method.

Bismuth doped ZnO (BZO) phosphors have been synthesized by the combustion method. The effect of Bi doping up to 4mol% on the structural, morphological, optical and photoluminescence (PL) properties have been investigated. X-ray diffraction analysis revealed that the BZO phosphors had the hexagonal wurtzite structure. The nanocrystallite size decreased from 75 to 38nm as the Bi concentration increased up to 3mol%, but then increased slightly for 4mol% Bi. The chemical states of the synthesized BZO phosphors were investigated using X-ray photoelectron spectroscopy and revealed the presence of both Bi3+ and Bi2+ charge states. The surface morphology showed spherical grains with some small particle agglomeration. The grain agglomeration and irregular shapes increased with increasing Bi concentration in the BZO phosphor. The absorption spectra were calculated from the reflection spectra using the Kubelka-Munk function and a blue shift in the absorption was obtained. The optical bandgap varied from 3.08 to 3.11eV for increasing Bi doping concentration. The PL spectra showed a blue emission at 410-500nm and a broad red peak at 650nm. These peaks are attributed to oxygen related defects in the ZnO host. The addition of Bi decreased the red emission and enhanced the blue emission.

Transparent conducting ZnO-CdO mixed oxide thin films grown by the sol-gel method.

Mixed oxides of zinc and cadmium with different proportions were deposited on ordinary glass substrates using the sol-gel spin coating method under optimized deposition conditions using zinc acetate dihydrate and cadmium acetate dihydrate as precursors. X-ray diffraction patterns confirmed the polycrystalline nature of the films. A combination of cubic CdO and hexagonal wurtzite ZnO phases was observed. The oxidation states of Zn, Cd and O in the deposited films were determined by X-ray photoelectron spectroscopic studies. Surface morphology was studied by scanning electron microscopy and atomic force microscopy. The compositional analysis of the thin films was studied by secondary ion mass spectroscopy. The transmittance of the thin films was measured in the range 300-800nm and the optical bandgap was calculated using Tauc's plot method. The bandgap decreased from 3.15eV to 2.15eV with increasing CdO content. The light emission properties of the ZnO:CdO thin films were studied by photoluminescence spectra recorded at room temperature. The current-voltage characteristics were also assessed and showed ohmic behaviour. The resistance decreased with increasing CdO content.