Studies On Third-order Nonlinear Optical Properties Of Semiconductor Nanocomposite Materials

Materials with large third-order nonlinear optical susceptibility and ultrafast response time havepotential applications in all-optical switching, optical limiting device and optical calculator, it has attractedmuch attention of science researchers. There are many nonlinear optical materials, these materials includeorganic compounds, noble metal nanoparticles, semiconductor nanocrystals and so on.Semiconductor nanocrystals have attracted great attention because of their unique nonlinear opticalproperties arised from the quantum confinement effect. A certain semiconductor nanocrystals may exhibitdifferent optical nonlinearity because of different synthesis approaches, diameters and surface conditions,some nonlinear principle need further research. Semiconductor nanoparticles can be embedded intopolymers, these semiconductor nanoparticles/polymers composite materials not only have the nonlinearoptical properties of semiconductor, but also have the flexibility of polymers, which enable these materialshave applications in devices. At the same time, semiconductor nanoparticles in polymers can preventaggregation between nanoparticles. Semiconductor nanoparticles can be modified on to the surface ofmaterials which have nonlinear optical properties, such as graphene, carbon nanotubes. The opticalnonlinearity maybe enhanced by modifying semiconductor nanoparticles on to the given materials.There four chapters in this article. The first chapter describes the synthesis approaches, properties andthird-order nonlinearity of semiconductor nanoparticles. The properties and third-order nonlinearity ofcarbon nanotubes are present as well. The second chapter introduces the principle of third-order optical andthe physical mechanism of nonlinear reflection and nonlinear absorption. The third chapter introduces thethird-order optical nonlinearity of two different PbSe nanocrystal/polymer composite materials. The forthchapter introduces the third-order optical nonlinearity of CdS/MWCNT.The main research results are briefly listed as follows:1. High monodisperse PbSe nanoparticles with diameter about10nm are synthesized by hot-injectionmethod. XRD reveals that the synthesized PbSe is in rock-salt phase. The PbSe nanocrystals are washedand dispersed in MMA, after short hot prepolymerization and low temperature polymerization, the composite marerials was prepared. TEM reveals that the distribution of PbSe nanoparticles is well. Thethird-order optical nonlinear refractive index n2is measured to be-1.62×10-8esu, the thermal lens effect isexcluded.(This work has been submitted to 《Chinese physics B》)2. PbSe/PVA composite material is synthesized by wet chemical route. TEM reveals that the diameterof PbSe is about10nm, SEM reveals that the composite has flat surface. The third-order opticalnonlinearity was measured by picosecond Z scan system, the third-order optical nonlinear refractive indexn2is measured to2.3×10-10esu.(Manuscript has been accepted by《Acta photonica sinica》)3. CdS nanoparticles were coated on the side wall of multiwalled carbon nanotubes (MWCNTs) by awet chemical synthesis approach via noncovalent functionalization of MWCNTs with poly(diallyldimethylammonium chloride)(PDDA). The as prepared material was characterized by X-raydiffraction (XRD), UV-vis absorption, fluorescence and transmission electron microscopy (TEM). Theresults indicate that the diameter of CdS nanoparticles are8nm, and the nanoparticles are uniformly coatedon the surface of MWCNTs. Third-order optical nonlinearity of the as prepared material is studied by usingthe Z scan technique with picosecond laser pulses, the third-order nonlinear susceptibility χ(3)is calculatedto be-4.9×10-12esu.(This work has been submitted to《Optik-International journal for light and electronoptics》)At last, the next step of work content and experiment are presented.