Nonlinear Optical Properties Of Semiconductor Nanoparticles And Metalloporphyrin

Semiconductor nanoparticles, which own large nonlinear refractive index and fast response speed, have been extensively studied in the last decades. The search for new optical materials with strong nonlinear behavior has motivated experiments with surface chemical modification ,because optical properties are closely associated with the large ratio of surface atoms /bulk atoms. In addition, metalloporphyrin, which is a class of metal organic ligand, attracted more and more attention in the past few years due to its special molecular structure and photoelectrical properties .These scientific research arise my interests in preparing metalloporphyrin (such as Co-porphyrin, Fe-porphyrin) and semiconductor nanoparticles by means of surface chemical modification ,and investigating some of their nonlinear optical properties using various optical measurement tools. The following is my work completed in the past three years .Firstly, the meaning of our work, the main character of semiconductor nanoparticles, metalloporphyrin and elementary knowledge related to nonlinear optics are introduced in chapter I and chapter n..Surface modified with Polyvinyl pyrrolidone (PVP) nanoparticles PbS, CdS and PbS/CdS systems are fabricated using sol-gel method under different preparation conditions, which has advantages of easy control of stoichiometric, simple equipments and low cost. Their optical properties are characterized by Z-can technique , UV-visible absorption spectrum and so on .The experimental results indicate that although large nonlinear refractive index is observed in two PbS/CdS systems with different band gap, the sample of bigger band gap exhibit obvious nonlinear absorption in the range ofnonresonance.Moreover, for Co(II)-porphyrin and Fe(III)-porphyrin, nonlinear optical absorption and optical limiting properties are studied respectively. Results suggest that Fe-porphyrin probably become a potential candidate as optical limiting material excited by wavelength 514.5nm Ar + laser. Co(II)-porphyrin all exhibit optical limiting effect excited by three different wavelength Ar + laser:457.9,514.5 and 488 nm and saturable absorption especially for 457.9 nm. However, after Co-porphyrin is kept in 1,4-Dioxane for two weeks, excited by 488nm, it shows apparent reverse saturable absorption and enhanced optical limiting effect, which can be attributed to the absorption cross-section change of exicited state in Co-porphyrin derived probably from the production of Co(III)-porphyrin due to oxidation of 62 on Co(II)-porphyrin. Moreover, the sample after two weeks also shows enhanced optical limiting effect for 457.9nm.Finally, all the above mentioned work is summarized and the further work is proposed .