Optical, photoluminescence and ferromagnetic properties of Ni-doped ZnO for optoelectronic applications

The current work presents the optical, photoluminescence and ferromagnetic properties of Zn_1−xNi_xO samples with (0.00 ≤ x ≤ 0.20). The samples are well crystallizing in hexagonal wurtzite structure without a significant change in their lattice constants, while the crystallite size, grain size and number of unit cells in ZnO particle are increased. The residual stress is negative (compressive) and almost increases as Ni increases up to 0.10, but it is changed from negative to positive (tensile) at Ni = 0.20. The absorption and reflectance of UV spectra are increased as Ni increases up to 0.20. An absorption band centered at a wavelength of 552 nm is also observed and is gradually shifted by Ni towards longer wavelengths. Interestingly, two direct electronic transitions are found for all samples and two induced bandgaps which are decreased by Ni. While the other optical constants such as linear χ¹ and non-linear third-order susceptibilities χ³, dispersion parameters (E_d, E_o), refractive indexes (n_o, n₂), lattice dielectric constant ε_L, N/m*, optical and electrical conductivities (σ_opt, σ_ele) are increased by Ni, the dissipation factor (tanδ) is decreased. Although some of the continuous peaks of lower PL intensities are recorded at UV band edges and slightly shifted to longer wave lengths (red shift) as Ni increases, strong UV emission peaks at about 390, 420 and 440 nm are recorded. Finally, the signature of a clear weak ferromagnetism ordering at room temperature, with evaluated magnetic parameters such as magnetization M_s, magnetic moments μ and magneto-crystalline anisotropy factor γ, is recorded for Ni ≥ 0.05 doped samples.