Photoluminescence and Raman scattering study in ZnO:Cu nanocrystals

Photoluminescence (PL), scanning electronic microscopy (SEM), Raman scattering, X ray diffraction (XRD) and energy dispersion spectroscopy (EDS) have been applied for the comparative study of ZnO and ZnO:Cu nanocrystals (NCs). NCs were created by the electrochemical (anodization) method with different NC sizes (from 300×550 nm down to 170×320 nm) and were annealed at 400 °C for 2 h in ambient air. Raman and XRD studies have shown that thermal annealing stimulates the ZnO crystallization with the creation of wurtzite crystal lattice. XRD and EDS methods have been used for the confirmation doping of the ZnO NCs by Cu atoms and to show that the metallic Cu nanoparticles have been embedded in the porous ZnO NC films. It is shown that the Raman intensity for all Raman peaks in ZnO Cu NC systems is higher threefold in comparison with those in ZnO NC films owing to, apparently, the surface enhanced Raman scattering (SERS) effect. In crystalline ZnO and ZnO Cu NCs four PL bands appear with the PL peaks at 1.54, 2.08, 2.50 and 3.08 eV. The reasons of emission transformation in different samples and the nature of optical transitions have been discussed. It is shown that the plasmon generation in metallic Cu nanoparticles stimulates the SERS effect at Raman scattering, the PL intensity enhancement of defect related emission bands, but, at the same time, leads to decreasing the PL intensity of near band edge emission in ZnO Cu NC systems.