Effect of Cu2+ doping on the structural, electronic and optical properties of ZnAl2O4: A combined experimental and DFT plus U study

Using the sol-gel technique, undoped and Cu2+ doped ZnAl2O4 samples were prepared at 0 <= x <= 1.24 Cu2+ percentages. X-ray diffraction (XRD) analysis confirmed that the prepared samples were cubic and that there was no phase segregation. Energy dispersive X-rays (EDS) was then used to investigate and confirm the purity of Zn, Al, O and Cu samples with no other characteristic peaks. From the XRD spectra of Cu2+ at different concentrations, Cu2+ doping was found not to lead to significant lattice distortion an observation that was corroborated with density functional theory (DFT) calculations. As the Cu2+ concentration was increased a slight shift to higher angles was recorded in XRD analysis, suggesting a larger ionic radius atom substituted by a smaller ionic radius atom. At 283 nm excitation, the doped samples were found to emit in the blue region (at 425 nm and 480 nm) of the color spectrum. Theoretically using DFT with the Hubbard correction term U, the doped system was found to emit at 435 nm which is within the emission range observed experimentally. From the calculated substitutional energies, O-vac was found to have negative formation energies indicating ease of formation form in ZnAl2O4. The binding energy for Cu-zn+O-vac was negative indicating that these two point defects don't exist as pair inside ZnAl2O4. (C) 2017 Elsevier B.V. All rights reserved.