Influences of Titania Concentration on the Structure and the Three-order Nonlinear Optical Properties of Core-shell Ag/TiO2 Nanocomposites

Abstract Core-shell Ag/TiO 2 nanocomposites with different TiO 2 concentrations were synthesized by the photoreduction method, in the presence of ethanol. The diameter of the nanoparticles, with various TiO 2 and Ag + content, was determined to be 20–60 nm using a transmission electron microscope (TEM), and the crystal lattice fringes of silver particles were observed. The prepared nanocomposites were characterized by ultraviolet-visible (UV-Vis) spectroscopy and X-ray Diffraction (XRD). The intensity and width of the characteristic peak near 420 nm of the Ag nanoparticles increased as the TiO 2 or silver concentration was increased. The nonlinear optical properties of thin films of nanocomposites with different TiO 2 concentrations were analyzed using Z-scan technique at the wavelength of 790 nm with a pulse width of 130 fs. Two different nonlinear regimes in nonlinear absorption were found by changing the content of TiO 2 : an optical limiting effect at a low concentration, and a sign change at a higher concentration.