Enhancement of visible luminescence and photocatalytic activity of ZnO thin films via Cu doping

Highly transparent Cu doped ZnO thin films were deposited on glass substrates by spray pyrolysis technique. Crystallinity of the films improved at lower doping concentrations due to the easy fitting of Cu dopants in the Zn Lattice sites and preferred highly textured growth along the (002) plane. Higher doping concentration deteriorated the crystallinity and the optical transmission followed the similar trend. EDX spectra analysis confirmed the incorporation of Cu in the doped films. Optical energy gap red-shifted with the addition of Cu contents due to the exchange interactions and difference in iconicity of Zn and Cu. Cu doped films exhibited strong visible emission due to the modulation of the band structure and subsequently new levels acting as emission centres will be formed in the forbidden gap of ZnO. Moreover, the addition of Cu dopants increases the concentration of zinc interstitials as well as zinc and oxygen vacancies which cause more intense emission in the visible region. Cu doped films exhibited excellent photocatalytic activity due to the efficient trapping of photo-generated electrons thereby suppressing the electron-hole recombination and higher doping level slightly decreased the degradation efficiency because excess dopants may act as recombination centres. (C) 2018 Elsevier GmbH. All rights reserved.