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

Publication date: April 2017
Source:Journal of Luminescence, Volume 184
Author(s): W.M. Mulwa, B.F. Dejene, M.O. Onani, C.N.M. Ouma
Using the sol-gel technique, pristine and Cu²⁺ doped gahnite (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 300nm excitation, the doped samples were found to emit in the blue region (at 440nm and 470nm of the color spectrum. Theoretically using DFT with the Hubbard correction term U, the doped system was found to emit at 435nm which is within the emission range observed experimentally. From the calculated substitutional energies, Ovac was found to have negative formation energies indicating ease of formation form in gahnite. The binding energy for CuZn-Ovac was negative indicating that these two point defects don't exist as pair inside gahnite.



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