Effect of Cr/Sb doping and annealing on nonlinear absorption coefficients of SnO2/PMMA nanocomposite films

Cr and Sb doped SnO2 nanoparticles were synthesized by hydrothermal method. The structural measurements of as-grown nanoparticles exhibited that the incorporation of the 3% wt. Cr and Sb dopant into the SnO2 crystal structure led to increasing crystallite size but further doping (7% wt. and 10% wt.) caused to decreasing crystallite size. On the other hand, the annealing processes caused to increasing of the crystallite size. SnO2/PMMA, SnO2:Cr/PMMA and SnO2 :Sb/PMMA nanocomposite films were deposited on fused silica substrate by using spin coating method. The as-deposited nanocomposite films have wide band gap energy and the band gap energies decreased after annealing process due to the increase of the particle sizes. Annealed nanocomposite films have strong transmittance in the ultraviolet and visible region. In order to investigate the effect of doping and annealing on nonlinear absorption properties of the films, open aperture Z-scan experiments were performed. To derive the transmission in open aperture Z-scan data, a theoretical model incorporating one photon, two photon, and free carrier absorptions and their saturations were considered. Nonlinear absorption coefficients and saturation intensity thresholds were extracted from the fitting of the experimental results. Nonlinear absorption coefficients and saturation intensity thresholds increased with increasing of the doping concentration because of the increasing of the defect states in the band gaps and decreased due to the decreasing of the defect state density with annealing. Strong optical limiting behavior observed for %10 Cr and %10 Sb doped SnO2 nanocomposite films.