Kurian Pushpa Ann, Vijayan C, Suchand Sandeep C S, Philip Reji, Sathiyamoorthy K
Indian Institute of Technology, Madras, Chennai 600036, India.
Nanotechnology. 2007 Feb 21;18(7):075708. doi: 10.1088/0957-4484/18/7/075708. Epub 2007 Jan 12.
Strong nonlinear absorption is observed in nanocomposite films containing PbS nanocrystals of mean size of 3.3 nm stabilized in a commercial poly(vinyl acetate) glue by a novel and simple chemical route of synthesis. A significant blueshift of the optical absorption edge indicates strong quantum confinement. The mean nanocrystal size was characterized by x-ray diffraction and transmission electron microscopy. The surface structure of nanocrystals is analysed using infrared spectroscopy. The excitonic transitions are probed by photoacoustic spectroscopy and the results are analysed on the basis of theoretical calculations using envelope function formalism. Results of open aperture z-scan experiments suggest a model involving saturable absorption followed by two-photon absorption at a lower concentration while the data for a higher concentration fitted saturable absorption followed by three-photon absorption. Free carrier absorption due to two-photon-assisted excited state absorption appears to be the predominant mechanism of optical nonlinearity.
通过一种新颖且简单的化学合成路线，在商业聚醋酸乙烯酯胶中稳定存在的平均尺寸为3.3纳米的硫化铅纳米晶体的纳米复合薄膜中观察到了强非线性吸收。光吸收边缘的显著蓝移表明存在强量子限制。通过X射线衍射和透射电子显微镜对平均纳米晶体尺寸进行了表征。利用红外光谱分析了纳米晶体的表面结构。通过光声光谱探测激子跃迁，并基于使用包络函数形式的理论计算对结果进行分析。开孔Z扫描实验结果表明，在较低浓度下，模型涉及饱和吸收后接着双光子吸收，而较高浓度的数据拟合为饱和吸收后接着三光子吸收。双光子辅助激发态吸收引起的自由载流子吸收似乎是光学非线性的主要机制。
