Thermal annealing and dopant dependence of nonlinear absorption characteristics in ZnO Nanoparticle/PMMA films

Abstract

Cr and Sb doped ZnO/PMMA nanocomposite films were investigated to understand the effect of doping and annealing on linear and nonlinear optical properties. ZnO, ZnO:Cr and ZnO:Sb nanoparticles were synthesized by hydrothermal method. The structural results showed that the incorporation Cr and Sb dopant to the ZnO crystal lattice led to decreasing of the crystallite sizes from 30.3 nm to 24.4 nm due to the increasing of the number of defect states inside the energy band gap. The crystallite size of the synthesis nanoparticles increased with annealing due to the decreasing defects in the band gap. The band gap energies were estimated to be 5.240 eV, 5.260 eV, 5.246, 5.253 eV and 5.280 eV for undoped, Cr and Sb doped ZnO/PMMA nanocomposite films, respectively. After annealing, the band gap energies decreased to 2.505 eV, 2.510 eV, 2.610 eV, 2.755 eV and 2.597 eV values due to the increasing of the crystallite sizes of the nanoparticles, respectively. The transmittances of the films varied with Cr and Sb doping and annealing process. The open aperture Z-scan technique was used to measure the nonlinear absorption properties of investigated films at ns regime. The nonlinear absorption coefficient values were found to be 4.95 × 105 cm/GW, 7.21 × 105 cm/GW, 1.69 × 106 cm/GW, 8.18 × 105 cm/GW and 2.09 × 106 cm/GW for ZnO/PMMA, ZnO:Cr/PMMA and ZnO:Sb/PMMA nanocomposite films, respectively. The saturation intensity thresholds increased with doping from 5.15 GW/cm2 to 10.40 GW/cm2. After annealing, the nonlinear absorption coefficient values were found to be 2.14 × 105 cm/GW, 2.99 × 105 cm/GW, 4.85 × 105 cm/GW, 3.43 × 105 cm/GW and 6.91 × 105 cm/GW for ZnO/PMMA, ZnO:Cr/PMMA and ZnO:Sb/PMMA, respectively.