TiO2浓度对核-壳结构Ag/TiO2纳米复合粒子结构以及三阶非线性光学性质的影响

采用光还原方法制备了核-壳结构的Ag/TiO2纳米复合粒子, 通过TEM、UV-Vis光谱和XRD表征了不同TiO2浓度下Ag/TiO2纳米复合粒子的结构和光学性质. UV-Vis光谱证明了银颗粒的存在, 且复合粒子中的银粒径随着TiO2含量的增加而增加, 同时随着TiO2浓度的增加, 银的吸收峰出现明显的增强和展宽；从TEM照片 发现, Ag/TiO2纳米复合粒子是一种以Ag为核, 外面包覆一层TiO2的核-壳结构, TiO2浓度和Ag+浓度的增加, 使得复合粒子的银颗粒粒径增大. 用Z-扫描技术, 以锁模Ti:sapphire飞秒激光器发出的脉宽为130 fs激光做光源, 在790 nm波长的光作用下, 研究了0.5%(w)Ag+含量, 不同TiO2浓度的Ag/TiO2纳米复合粒子的非线性光学特性. 结果发现, 在790 nm激光作用下, 0.25%(w)TiO2样品膜有双光子吸收和自聚焦非线性折射现象; 而当TiO2浓度为0.70%(w)时, 样品膜的非线性吸收由反饱和吸收转变为饱和吸收.

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

Core-shell Ag/TiO2 nanocomposites with different TiO2 concentration were synthesized by the photoreduction method, in the presence of ethanol. The diameter of the nanoparticles, with various TiO2 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 TiO2 or silver concentration was increased. The nonlinear optical properties of thin films of nanocomposites with different TiO2 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 TiO2: an optical limiting effect at a low concentration, and a sign change at a higher concentration.