Emission, Defects, and Structure of ZnO Nanocrystal Films Obtained by Electrochemical Method

Abstract

ZnO nanocrystal (NC) films, prepared by electrochemical etching with varying the technological routines, have been studied by means of photoluminescence (PL), scanning electronic microscopy (SEM), energy dispersion spectroscopy (EDS), Raman scattering, and X ray diffraction (XRD) techniques. Raman and XRD studies have confirmed that annealing stimulates the ZnO oxidation and crystallization with the formation of wurtzite ZnO NCs. The ZnO NC size decreases from 250-300 nm down to 40-60 nm with increasing the etching time. Two PL bands connected with the near-band edge (NBE) and defect-related emissions have been detected. Their intensity stimulation with NC size decreasing has been detected. The NBE emission enhancement is attributed to the week quantum confinement and exciton-light coupling with polariton formation in small ZnO NCs. The luminescence, morphology, and crystal structure of ZnO:Cu NCs versus Cu concentration have been investigated as well. The types of Cu-related complexes are discussed using the correlation between the PL spectrum transformations and XRD parameters. It is shown that the plasmon generation in Cu nanoparticles leads to the surface enhanced Raman scattering (SERS) effect and to PL intensity increasing the defect-related PL bands. The comparison of ZnO and ZnO:Cu NC emissions has been done and discussed.