Effect of ZnO doping co-carried out by Co–Cu on nonlinear optical properties prepared by the spin coating method

In the present work, thin films of ZnO co-doped with Co and Cu cations were obtained on glass substrate, combining the sol gel process and spin-coating technique. For the compound, the general chemical formula used was: Zn_1-x-zCo_xCu_zO, [(x; z) = (0.00; 0.00), (0.02; 0.02), (0.04; 0.04) and (0.06; 0.06)]. For pure ZnO film, the surface morphology is composed by small spherical grains that present interstitial spaces, while the films obtained from the simultaneous Co and Cu insertion in the ZnO structure are more dense and interstitial spaces disappear. For all films, the X-ray diffraction patterns testify the monophasic phase formation, typical of the hexagonal structure of ZnO. In addition, the films presented preferential orientation in the (002) direction. It was demonstrated that the Zn²⁺ cations by Co²⁺ and Cu²⁺ cations replacement, causes relevant modifications in the lattice parameter (c), crystallite size (D), dislocation density (δ), strain (ε_c) and stress (σ_c) of the hexagonal structure wurtzite from ZnO. The Co and Cu cations inclusion in the ZnO host lattice, alto caused a decrease in the optical band gap energy (3.37 for 3.16 eV), which is related to the charge transfer between the 4f level electrons and the conduction band or valence band of ZnO. Finally, for all films thin the linear and non-linear optical constants were computed and analyzed, showing variations that depend on the concentration of the dopant cations.