Radiative defects, emission and structure of ZnO nanocrystals (NCs) have been studied by means of the scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), X-ray diffraction (XRD) and photoluminescence (PL) techniques. ZnO NCs were prepared by etching Zn sheets and annealing at 200-400 degrees C in ambient air. The NC size and volume of ZnO crystalline phase increase with annealing temperature rising from 200 degrees C up to 400 degrees C. Simultaneously, XRD parameters and inter-planar distances in ZnO NCs vary no monotonically: decreasing upon annealing at 200-360 degrees C and increasing at 400 degrees C annealing. The PL intensity variation of orange, yellow, green and blue PL bands correlates with the change of XRD parameters. The study of PL band thermal decays, within the range 10-300 K, permits to estimate decay activation energies and to analyze the nature of donors and acceptors responsible for the orange, yellow and green PL bands in ZnO NCs. The electrochemical method allows varying the PL intensity of different PL bands by a controllable way that is interesting for ZnO NC film application in "white" light emitting device structures. (C) 2016 Elsevier Ltd. All rights reserved.