Influence of Ru dopants on the structural, optical, and magnetic properties of nickel oxide nanoparticles

The co-precipitation method was adopted to synthesize Ni1-xRuxO nanoparticles, with x = 0.000, 0.005, and 0.010. The X-Ray Diffraction patterns showed the formation of the NiO phase without any secondary phases or impurities due to the doping. The Ru-dopants are well incorporated into the lattice without changing its structural properties, owing to the comparable ionic radii of Ru3+ and Ni2+ ions. The doped samples have cubic morphology with reduced sizes, as seen in Transmission Electron Microscope images. The Fourier Transform Infra-Red and X-Ray Photo-induced spectra (XPS) assured the purity and the successful doping of trivalent Ru ions into NiO nanoparticles. Moreover, the XPS spectra revealed the generation of more oxygen vacancies with Ru-doping. The optical properties were investigated by Ultra-Violet and Photoluminescence (PL) spectroscopies. The Ru-doped samples have higher transmittance that is beneficial for transparent electrodes and optoelectronic devices. The TAUC and derivative plots were used to estimate the bandgap energies. The Ru-doped samples demonstrated suppressed bandgap energies, mainly due to the formation of additional energy levels near the valence band. The visible region of the PL spectra was investigated to track the deep-level defects. All the samples have traces of nickel vacancies, oxygen vacancies, and oxygen interstitials. The magnetic studies were tested by Vibrating Sample Magnetometer at room temperature. The M - H loops were then fitted by the different models of the law of approach to saturation. The best-fitted model was the one accounting for the exchange and anisotropy fields. The pure and Ru-doped samples showed a weak ferromagnetic behavior with a slight increase in the linear magnetization with Ru dopants, due to the antiferromagnetic Ru-Ru interactions.