Hydrothermal synthesis and cathodoluminescence of ZnO crystalline powders and coatings

Nanocrystalline ZnO powders and coatings of ZnO were obtained under soft hydrothermal conditions. The growth systems contained various ZnO-precursors (as-prepared Zn-hydroxide, chemical ZnO, Zn(NO3)2), solvents (LiOH, KOH, NH4OH) and Zn-substrate. ZnO growth morphology was found to depend on the chemical composition of the solvent: Li+ suppresses the growth of (0 0 0 1) faces, NH4+ promotes it. Aspect ratio of crystals is controlled by solvent type and concentration. Luminescent properties have been studied using impulse laser or cathode excitation. The ratio IUV/IVIS in luminescence spectra was found to depend on the excitation mode. Laser excitation allows to obtain UV-band with higher intensity in comparison with cathode excitation. The most intensive UV luminescence was found for polycrystalline coatings on Zn-substrates obtained in the systems with KOH as a solvent. Mathematic treatment of the ICL spectra was carried out; the wide VIS-band was found to consist of the series of overlapping bands. UV luminescence quenching centers were suggested to be connected mainly with the irradiation in VIS-region with c  λ>700nm.