Influence of cobalt doping on the structural and third order nonlinear optical properties of MgO nanostructures

This study investigates the third-order nonlinear optical properties of pure and cobalt-doped magnesium oxide (MgO) nanoparticles using the Z-scan method under continuous wave excitation. MgO nanoparticles were synthesized via a modified auto-combustion method with varying cobalt concentrations (0 %, 1 %, 3 %, and 5 %). Structural and morphological analyses were conducted using X-ray diffraction and field emission scanning electron microscopy. UV–visible spectroscopy revealed a bandgap reduction from 2.75 eV to 1.8 eV with increased cobalt doping, suggesting defect formation. Z-scan results indicate significant two-photon absorption, with higher doping levels enhancing third-order nonlinear optical susceptibility $\left({\chi }^{\left(3\right)}\right)$ from 3.78 × 10⁻⁶ to 5.14 × 10⁻⁶ esu. This enhancement correlates with increases in the nonlinear absorption coefficient $\left(\beta \right)$ and nonlinear refractive index $\left(n_2\right)$. These findings highlight the potential of cobalt-doped MgO nanoparticles for advanced nonlinear optical applications.