Revealing effect of cobalt dopant on crystallography and optical characteristics of nanostructured cupric oxide

Abstract

Cupric oxide is an interesting semiconducting material that has the potential to be applied in various technological utilizations. To understand the modified structure, the effects of Co doping at different concentrations (0, 1, 3, and 5 mol%) on the crystal structure, morphology, and optical properties of CuO nanoparticles synthesized by the co-precipitation method through heating at 400 °C for 2 h have been investigated. Synthesized samples were characterized by various techniques. X-ray diffractometer (XRD) results showed a monoclinic structure of CuO and impurity phase Co2O3 appearing when doping 5 mol% Cobalt. The crystallite size was found in the range of 25–48 nm. The crystallinity, texture coefficient, crystallite size, lattice constants, strain, and some physical properties (stress, Young's modulus, and strain energy) were calculated from the obtained XRD data. As a result, the lower Young's modulus and strain energy values of (111) crystal plane promoted the preferable growth in the direction. Fourier transform infrared spectrometer (FT-IR) was used to understand the chemical structure and confirm the substitution of Co in the samples. Scanning electron microscopy technique (SEM) was used to study morphology, appearing in the micron irregular flat plates that change to spherical particles when cobalt addition increases. Transmission electron microscope (TEM) micrographs show that structures of CuO are highly crystalline in nature and also provide clear evidence of spherical nanostructures in the Co-doped CuO. The Brunau–Emmet–Teller analysis method (BET) depicts a surface area improvement, showing 6.532 m2/g for the CuO and 19.285 m2/g for the 5 mol% Co-doped CuO sample. As more Co content, the decreasing energy bandgap of 2.75 to 2.58 eV was approximated using the Ultraviolet–Visible spectroscopy (UV–Vis) result. Photoluminescence spectra (PL) were found at about 440 and 470 nm, replied to oxygen vacancy (Vo) and copper vacancy (VCu), which are a sublevel affecting energy bandgap change. The role of Co dopant in improving the morphology and optical properties was discussed, associating with the structural characteristics and emerging intrinsic defects.