Emission of Cu-related complexes in ZnO:Cu nanocrystals

Abstract

Photoluminescence (PL), its temperature dependence, scanning electronic microscopy (SEM) and X ray diffraction (XRD) have been applied for the comparative study of varying the emission, morphology and crystal structure of ZnO and ZnO:Cu nanocrystals (NCs) versus technological routines, as well as the dependence of ZnO:Cu NC parameters on the Cu concentration. A set of ZnO and ZnO Cu NCs was prepared by the electrochemical (anodization) method at a permanent voltage and different etching durations with follows thermal annealing at 400°C for 2h in ambient air. The size of ZnO NCs decreases from 300nm×540nm down to 200nm×320nm with etching duration increasing. XRD study has confirmed that thermal annealing stimulates the ZnO oxidation and crystallization with the formation of wurtzite ZnO crystal lattice. XRD method has been used for monitoring the lattice parameters and for confirming the Cu doping of ZnO Cu NCs. In ZnO Cu NCs four defect related PL bands are detected with the PL peaks at 1.95–2.00eV (A), 2.15-2.23 eV (B), 2.43–2.50eV (C) and 2.61–2.69eV (D). Highest PL intensities of orange, yellow and green emissions have been obtained in ZnO Cu NCs with the Cu concentration of 2.28at%. At Cu concentration increasing (≥2.28at%) the PL intensities of the bands A, B, C decrease and the new PL band peaked at 2.61–2.69eV at 10K appears in the PL spectrum. The variation of PL intensities for all PL bands versus temperature has been studied and the corresponding activation energies of PL thermal decay have been estimated. The type of Cu-related complexes is discussed using the correlation between the PL spectrum transformation and the variation of XRD parameters in ZnO Cu NCs.