Linear, third order nonlinear and optical limiting studies on MZO/FTO thin film system fabricated by spin coating technique for electro-optic applications

Herein, we report the detailed optoelectronic characteristics of low cost fabricated pristine and 1, 5, 10, and 15 wt% Mg-doped ZnO films on the FTO substrate (MZO/FTO) through the spin coating technique. High crystallinity and single phase of the film were confirmed by X-ray diffraction investigation. The average crystallite size was in the range of 46-78 nm. Homogeneous distribution of Mg doping in ZnO was approved by elemental mapping analysis. The fiber-like surface morphology was confirmed by the scanning electron microscopy analysis. Optical transparency was observed in the range of 40-80% for the fabricated films. The optical band gaps for direct and indirect transitions obtained from Tauc's relation are in the range of 3.103-3.283 eV and 2.423-2.968 eV, respectively. It is also observed that the energy gap of MZO films decreases with an increase in Mg doping from 1 to 15%. The respective stable values of absorption and refractive indices are obtained in the range of ∼0.036-0.088 and ∼1.71-2.1. The linear and nonlinear optical susceptibilities as well as the nonlinear refractive index values were calculated. Additionally, Z-scan measurement was carried out at 532 nm wavelength. The nonlinear absorption coefficient and the imaginary part of third-order nonlinear susceptibility were estimated and corresponding values are obtained in the range of 0.35-123 (×10^-5) cm/W and 0.084-29.7 (×10^-8) e.s.u., respectively. Moreover, the optical limiting threshold values were obtained in the range of 2.57-6.34 kJ/cm². The MZO/FTO films are showing strong optical limiting behavior compared to pristine. The output results suggest that MZO films are better contenders for optoelectronic applications.