Papers by Keyword: ZnO Nanocrystal

Abstract: The synthesis of ZnO nanocrystals is carried out in alkaline alcoholic solution of zinc acetate dihydrate by sol-gel method. Effects of thermal annealing in nitrogen on photoluminescence (PL) properties of the sol-gel derived ZnO nanocrystals were investigated by PL spectroscopy. With increasing annealing temperature in nitrogen, UV emissions of the ZnO nanocrystals red-shifted from 378 nm to 388 nm while deep-level luminescent bands ranging from 450 to 700 nm with three emission centers at about 502 nm, 538 nm and 602 nm are enhanced, and the green luminescent band gains its intensity at the expense of the yellow and orange luminescent bands. Our results have demonstrated that the origin yellow-green color PL was tuned towards the cyan color PL with increasing the thermal annealing temperature in nitrogen from 344 oC to 813 oC.

Abstract: ZnO nanorods and nanoparticles were successfully modified by NDZ-311w titanate coupling agent. The result of lipophilic degree showed that both ZnO nanocrystals with different morphologies were well lipophilic. Although both values of lipophilic degree firstly became larger and then smaller with the increase of modifier dosage, the different maximal lipophilic degree of ZnO nanorods and nanoparticles could be 68.8% and 77.9%, respectively. By comparing the two curves of lipophilic degree of surface modified ZnO nanocrystals with different morphologies, it could be demonstrated that the optimal dosage of NDZ-311w titanate coupling agent is inversely proportional to the grain size. TEM and XRD results showed that the grain size of ZnO nanoparticles were much smaller than that of ZnO nanorods, which can be the evidence for the equation. Otherwise, the surface modified ZnO nanoparticles displayed better dispersion than unmodified ones.

Abstract: The morphological and optical properties of ZnO nanocrystals prepared by thermal evaporation of Zn powders were studied at both upstream and downstream under different O₂ flow rates. The morphological evolution was observed by scanning electron microscopy. With O₂ flow rates changing from 0.25 sccm to 1 sccm, the caps of the ZnO nanonails become bigger and the stems gradually disappear at upstream, and the diameters at the top of ZnO nanorods become thicker and the length become longer at downstream. Room temperature PL study shows that UV emission is relatively enhanced with increasing O₂ flow rates. Computational fluid dynamics simulation was performed, which indicates that the morphological evolution of the ZnO structures results from the competition between the axial growth and the radial growth based on different O₂ and Zn vapor partial pressure.

Abstract: The “islands” of ZnO nanocrystals on amorphous monodisperse 200 nm SiO2 spheres (core-shell particles) were obtained by simple one-step technique based on low-temperature crystallization from liquid phase. The influence of starting reagents types and concentration of zinc ions in the reaction mixture on the morphology of ZnO shells obtained was studied. Crystalline structure of ZnO nanocrystals obtained was proofed by the X-ray diffraction data. The average diameter of ZnO nanocrystals on SiO2 spheres is 10 nm according to X-ray diffraction (XRD) and transmission electron microscopy (TEM) data. It was shown that SiO2/ZnO particles obtained have high luminescence characteristics. Photoluminescence spectra of core-shell SiO2/ZnO particles show two emission peaks centred at 386 nm and 570 nm. Core-shell SiO2/ZnO particles obtained are perspective for active photonic crystals creation for UV-spectral region.