| Since the invention of laser led to the generation of nonlinear optics,nonlinear optical materials have been studied extensively due to their applications in optcial switch,optical limitting,optical communication and optical computation,etc. Remarkable progress have been made in this field.Among various nonlinear optical materials,such as organic materials,metal nanoparticles,nonlinear crystals,etc., semiconductor nanocomposites made by semiconductor nanoparticles dispersed in organic polymer,because of much novel and unique excellence in their optical nonlinearities,have gradually been receiving more and more attention and becoming one of researching hotspots in nonlinear optical materials.Semiconductor nanocomposites possess not only intrinsic photo-electronic performance,but also long range stability and good machinability.In addition,nanoparticles can be dispersed uniformly in composites.However,this kind of materials have been studied only for a short time,many new phenomena and regularities still need deep research.This thesis mainly investigate linear and nonlinear properties of ZnS and CdS semiconductor nanocomposites by employing absorption spectra,photoluminescence spectra,transmission electron microscopy and picosecond laser z-scan system. Experimental results are discussed based on microscopic morphology of nanoparticles and experimental conditions.Origins of optical nonlinearities of these two kinds of nanocomposites are analyzed from quantum size effect,surface effect and thermally induced nonlinearity.The impact of semiconductor nanoparticle density and annealing temperature on linear and nonlinear optical properties of the materals are investigated. Some related regularities between density and nonlienar properties and between annealing temperature and nonlinear properties are discovered by comparison.The effect of the microscopic morphology of nanoparticles on nonlinear optical properties of these materials is disscused so that some valuable references for deep studying these kinds of new materials can be provided.This thesis is composed of four chapters and each chapter's contents are as follows:In the first chapter,research background,current status of development of nonlinear optics and research progress of nonlinear optical materials,especially research background and current status of development of semiconductor nanocomposites,are briefly introduced.The theory and method of Z-scan technique for measuring nonlinear optical coefficients are introduced.In the second chapter,the third order nonlinear optical properties of ZnS- polyvinyl pyrrolidone nanocomposite suspension excited by picosecond laser at 532nm have been investigated detailedly.The nonlinear optical refractive indexes,absorption coefficients and the third-order nonlinear susceptibility of the samples are obtained.It is found through comparing results that nonlinearity of nanoparticles is concentration dependent. It is explained from microscopic morphology and experimental conditions why the nonlinearity of the sample in this study is different from the related samples in previous studies elsewhere.(Our studies in this section were published in JOURNAL OF PHYSICS D,January,2009).In the third chapter,the linear and nonlinear optical properties of CdS nanoparticles dispered in polyethylene glycol(400) annealing at different temperatures are systematically investigated.The results show that the absorption and fluorescence spectra of the films are red-shifted with the annealing temperature,the films excited by picosecond laser at 1064 nm exhibit positive nonlinear absorption and negative nonlinear refraction coefficient and the third-order nonlinear susceptibility of the films is abtained to be 10-9 esu by fitting the experimental data.The nonlinear susceptibility of the films becomes larger with the annealing temperature,which is explained from the quantum size effect,surface effect and the microscopic morphology of the semiconductor nanocomposite.(Manuscript in this section has been submitted to APPLIED PHYSICS LETTERS)In the fourth chapter,discussions and conclusions for the whole thesis are made.
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