Tuning the energy bandgap and nonlinear absorption coefficients of WOx/ZrO2 nanocomposite thin films with the role of weight and doping concentration

The structural, linear and nonlinear optical properties of PMMA/ZrO2 and PMMA/WZrO2 nanocomposites thin films were investigated. Tungstated zirconia nanoparticles were synthesized with different tungsten concentrations (3, 20 and 37% w/w) via solvothermal reflux method. To investigate the effect of weight and doping concentration, thin films with different tungsten ratio (undoped, %3, %20 and %37 W doped) were prepared and also weight percentage of the investigated samples in polymer (10 and 20 wt%) were changed for each doping ratio. The samples were examined using XRD, TEM, XPS and EDX analysis. The linear and nonlinear optical properties were studied by UV-Visible spectrophotometry and Z scan technique. The linear spectra were used to calculate the energy band gap. The fluorescence peak at 375 nm for undoped and doped ZrO2 nanocomposites are assigned to the presence of oxygen vacancies in the nanostructures. A theoretical model including one photon, two photon and free carrier absorptions and their saturations were used to analyze the experimental data. The linear absorption of all samples increased with increasing weight percentage of the films. The films which have a low tungsten ratio (%3 W) showed minimal absorption. The band gap decreased with addition of tungsten and the increasing nanoparticle weight concentration. OA Z-scan experiment results indicated that the addition of the tungsten to PMMA/ZrO2 reduced the nonlinear absorption performance.