Rapid Annealing of Black ZnO Thin Films Prepared by Pulsed Laser Deposition
ZnO thin films were deposited by pulsed laser deposition (fluence 2.2 J/cm2) in vacuum on different substrates kept at room temperature. This temperature allowed for fast film growing, however the as-prepared films had low transparency. To improve this optical property, keeping up at the same time the high electric conductivity of the films, post-annealing procedures in vacuum and in air were carried out. The influence of these procedures on the optical absorption, photoluminescence and electrical properties has been investigated. It is shown that the annealing in air improves only the transparency of such a film, however its conductivity decreases markedly. In turn, vacuum annealing for 3 min. at 600° C results in better transparency of the films, with their electric conductivity kept high.
Defect Luminescence of Yag Nanopowders and Crystals
Undoped and rare-earth-ion-doped Y3Al5O12 (YAG) nanopowders are prepared by the sol-gel low-temperature combustion method. The luminescence characteristics of the YAG, YAG: Ce, YAG:Pr, and YAG: Ce/Pr nanopowders are compared with those of the single crystals. The luminescence band peaking around 3.1 eV is complex and excited at about 3.6 eV, 3.9 eV and 4.3 eV. The 3.1 eV emission was peculiar to all the samples studied. The Stokes shift of this band is ~0.5 eV. The decay time of the ~3.1 eV emission at 80 K is ~14 ns and the slower decay (afterglow) components are practically absent. The 3.1 eV luminescence was suggested to arise from different intrinsic lattice defects.
Photocatalytic activity of TiO2 and ZnO nanopowders is studied depending on the morphology, grain sizes and method of synthesizing. Photocatalysis of the prepared powders was evaluated by degradation of the methylene blue aqueous solution. Absorbance spectra (190-100 nm) were measured during exposure of the solution to UV light. The relationships between the photocatalytic activity and the particle size, crystal polymorph phases and grain morphology were analyzed. The photocatalytic activity of prepared TiO2 nanopowders has been found to depend of the anatase-to-rutile phase ratio. Comparison is given for the photocatalytic activity of ZnO nanopowders prepared by sol-gel and solar physical vapour deposition (SPVD) methods
Transparent ZnO ceramics are of interest for use as material for high-efficiency fast scintillators. Doping ZnO ceramics in order to improve complex of their properties is a promising direction. In the present research, the role of indium in the ZnO nanopowders surface interactions and in the change of microstructures and photoluminescence (PL) characteristics of sintered cera-mics is considered. Undoped and 0.13 wt% In doped ZnO ceramics are obtained by hot pressing sintering. It has been found that indium leads to the transition of initially faceted ZnO particles to rounded, contributing to good sintering with formation of diffusion active grain boundaries (GBs). Unlike ZnO ceramics, ZnO:In ceramics microstructure is characterised by the trans-crystalline mode of fracture, faceted GBs with places of zig-zag forms and predominant distribution of In at the GBs. Such indium induced modifications of GBs promote removal of point defects and reduce PL parameter α = Idef/Iexc in comparison with the undoped ceramics. Results characterise ZnO:In cera-mics with improved GBs properties as a prospective material for scintillators.