Synergistic effects of nonmetallic (F) and rare-earth (Gd) dopants on opto-structural and magnetic properties of CuO nanoparticles: an experimental study

Abstract

In this thesis, the modified sol-gel route for the synthesis of CuO-based nanoparticles (NPs) was optimized and pristine, p-block element fluorine (F) doped and rare earth element gadolinium (Gd) along with F co-doped CuO NPs were successfully prepared. The structural, elemental, and phase characteristics of the nanoparticles were examined using XRD and XPS analysis. XRD analysis revealed high phase purity with sufficient crystallinity for NPs annealed at various temperatures (500⁰C, 600⁰C, 700⁰C, and 800⁰C). However, F doping reduced the phase stability of CuO, and Cu2O phase emerged. Higher annealing temperature and co-doping with Gd can successfully eliminate this problem. SEM analysis revealed fused irregular shaped particles and gradual reduction of particle size with doping. Diffuse reflectance spectra obtained from UV-visible spectroscopy were utilized to measure the indirect and direct band gaps and it revealed the indirect nature of CuO-based NPs. A decrease in optical band gap with doping was evident which attributes to the generated intra-band defect states. Various optical properties were also derived from the reflectance and absorbance spectra obtained from UV-visible spectroscopy. Significant improvements in optical characteristics were visible with F doping and Gd-F co-doping. Using the Physical Property Measure System (PPMS) magnetic properties of synthesized NPs were studied. Room temperature ferromagnetism (RTFM) with slight paramagnetic (PM) contribution was evident in pure and F-doped CuO NPs. Whereas coexistence of dominant PM with soft ferromagnetism (FM) was observed in the co-doped nanoparticles. BMP model fitted perfectly with the experimental magnetization value indicating the emergence of FM from interactions of polarons. The intriguing optical and magnetic properties of doped CuO nanoparticles make them a promising contender for use in solar cells, magnetic storage devices, magnetic sensors, photocatalytic, photonics, spintronics, etc. applications.