Photophysical Properties Of Cadmium-based Semiconductor Quantum Dots

The Cd-based semiconductor quantum dots are semiconductor nanocrystal that the size of the three-dimensional is 1-10 nm. For the great luminescence properties,the Cd-based semiconductor quantum dots are widely applied. The properties of the semiconductor quantum dots have quantum size effect, quantum confinement effect,surface effect and so on. Because of special quantum confinement effect of the Cd-based semiconductor quantum dots, which play a key role in solar cells, sensors devices, and laser protection and so on, they have been studied widely. Now the mian study of the semiconductor quantum dots are material preparation, nonlinear optics and biological field. Comparing with the single core semiconductor quantum dots, the nonlinear optical properties of the core-shell structure semiconductor quantum dots have a big difference. Therefore, studying the nonlinearity of the single core and core-shell structure semiconductor quantum dots is important to obtain and apply nonlinear optical materials.In this paper, based on top-hat Z-scan technique, we study the nonlinear absorption properties of the three size Cd Te quantum dots under the nanosecond(ns)laser pulses and the picosecond(ps) laser pulses respectively, and study the nonlinear absorption and refraction properties of the three size Cd Te quantum dots and the three size Cd S quantum dots under the femtosecond(fs) laser pulses. Next I study the nonlinear absorption properties of the Cd Te/Cd S core-shell and Cd Te/Zn S core-shell quantum dots under the ns laser pulses and the ps laser pulses respectively, and study the nonlinear absorption and refraction properties of the two kind of core-shell quantum duts under the fs laser pulses. At the same time, make the comparing research and experimental results. The following is the results:1. The nonlinear absorption characteristics of the three size Cd Te quantum dots are saturable absorption under the ns and the ps laser pulses. The nonlinear absorption characteristics of the three size Cd Te quantum dots are saturable absorption, and the three size Cd S quantum dots are reverse saturable absorption under the fs laser pulses.The nonlinear refraction characteristics of the two kind of quantum dots are self-focusing, and the nonlinear refractive index is positive. Cd Te1 quantum dots and Cd S quantum dots are two-photon absorption. The experimental results show that the nonlinear characteristics change strongly with decreasing quantum dot size, duing to quantum confinement effect and surface effect. The experimental results show that Cd-based semiconductor quantum dots materials can influence the optical nonlinear characteristics.2. The nonlinear absorption characteristics of the Cd Te/Cd S quantum dots and Cd Te/Zn S quantum dots are saturable absorption under the ns, ps and the fs laser pulses. The nonlinear refraction characteristics of the two kind of core-shell quantum dots are self-focusing, and the nonlinear refractive index is positive. The nonlinear refraction characteristics of the Cd Te/Cd S quantum dots and Cd Te/Zn S quantum dots are basically stronger than Cd Te quantum dots. The reason is that the surface defect of the core-shell quantum dots are lower than single core quantum dots, and exciton states luminescence is dominant.The experimental results show that Cd-based semiconductor quantum dots size and structure can influence the optical nonlinear characteristics.