Photophysical Properties Of CdTe Core-shell Semiconductor Quantum Dots

Quantum dot is the central theme of nanotechnology research.Because of its very small size,it has produced many unique characteristics which are different from that of large particles or bulk materials.Core-shell structure quantum dot can reduce the single quantum dot on the outer surface of the dangling bond,repair surface defect of the core,improve the optical properties of quantum dot,so it has wide applications in biological labeling,photovoltaic cell,display,photocatalysis and other fields.In this paper,the fabrication and characterization of CdTe/CdS and CdTe/ZnS core shell semiconductor quantum dot was firstly studied.In the preparation of quantum dot,the preparation method of NaHTe was improved,and the quality of NaHTe was improved in the case of saving a lot of time.The effect of pH value on the reaction rate and the effect of reaction time on the shell thickness of CdTe/CdS and CdTe/ZnS core-shell semiconductor quantum dots were analyzed.Ten kinds of CdTe/CdS,CdTe/ZnS semiconductor quantum dots with different core sizes,different shell thicknesses and different shell materials were synthesized.The samples were characterized by absorption spectra and fluorescence spectra.The effects of shell thickness and core size on absorption spectra and fluorescence spectra were investigated.Secondly,the photophysical properties of the samples were studied.Nonlinear optics and ultrafast dynamics are the research focuses of physical properties in this paper.In the experiment,the samples were measured for nonlinear absorption and nonlinear refraction coefficient by using femtosecond Z-scan technique.The ground state bleaching process and recovery process of samples were studied by femtosecond time-resolved transient absorption spectroscopy.Nonlinear optical effects and ultrafast dynamics of different core sizes and different shell thickness and shell materials of different samples were compared.The nonlinear absorption coefficient,the nonlinear refractive index and the three order nonlinear susceptibility of the material were measured by femtosecond laser pulses in the open and closed Z-scan experiments.The transient absorption spectra and ultrafast dynamics curves of the samples were obtained by transient absorption experiments.This study reveals the influence of two kinds of CdTe core-shell structure quantum dot cladding material,core size and shell thickness on nonlinear optics and ultrafast dynamics,provides a theoretical basis for research about photophysical properties of core-shell structure quantum dot preparation.