Winfred Mueni Mulwa

PhD Overview

Experimentally, the powders of doped and undoped ZnAl2O4 were effectively synthesized by use of the sol-gel technique. The X-ray diffraction (XRD) pattern for ZnAl2O4 displayed crystalline peaks corresponding to cubic structure and phase dissociation was not observed. Computationally, the local density approximation (LDA) with the Hubbard U correlation was used to compute the structural, electronic and optical properties of ZnAl2O4 and Cu2+:ZnAl2O4. Introduction of Cu2+ ions did not lead to significant lattice distortion and the PL emission peak was at 435 nm with a transition from Cu_3d to Cu_4p. The substitutional energies in Cu2+:ZnAl2O4 predicted negative formation energies for oxygen vacancies suggesting that these vacancies are easily formed in ZnAl2O4. The two point defects (oxygen vacancy and Cu2+ dopant) existed singly as the binding energies were found to be negative.