Study On The Preparation And Synthesis Mechanism Of Water-soluble CdSe/ZnS Quantum Dots

In recent years, quantum dots (also known as semiconductor nanocrystals) which component by the II-IV group or II-VI group elements are of about 1～10 nm of the material. Its size in three dimensions tens of nanometers, resulted the electronics' movement in every direction within materials are all limited, and thus lead to quantum confinement effect, macroscopic quantum tunneling effect and a series of special effects, which is different from the macroscopic derived materials and electrical optical properties. In comparison with the traditional organic fluorescent dyes, quantum dot has unique fluorescence characteristics, such as wide and continuous excitation spectrum, the emission spectrum controllable, narrow and symmetrical emission peak, larger Stokes displacement, high productivity, strong photobleaching resistance with spatial compatibility, which make quantum dot replace traditional organic dyes, as a kind of new fluorescent probes. Because of quantum size effect and unique optical properties, quantum dots can be widely applied in biomedical fields and photoelectric devices.Compared with the traditional organic phase synthesis, the hydro-phase method for synthesizing quantum dot are affordable, green, simple, and the resulting quantum dots are water-soluble and biocompatible, thus becoming the focal point of more and more people. However, low yield, poor stability shortcomings limit the widely used. By introduce a outer layer covered on nuclear can effectively reduce the quantum dot surface defects, improve its crystal structure, thus get the core/shell quantum dots with high fluorescence performance, high stability. In the study of quantum dots. CdSe with high-energy bandwidth is more mature, covered its surface with ZnS shell which also have a high-energy bandwidth can effectively improve the quantum dot light-emitting efficiency and stability, while its low toxicity, make core-shell quantum dots has significant development prospects. The main work of this thesis in the aqueous phase, the use of ultrasonic method for the synthesis of high performance fluorescent quantum dots, and study the optimum conditions of preparation.In this preparation conditions synthetic ZnS luminescent quantum dots, study it's crystal structure by XRD and indicating that the particle size of about 3 4nm, and the product purely ; emission spectrum width, half-peak width, peak symmetry; fluorescence effects are obvious, good stability.Using a simple, quick synthesized precursor synthesis single-core type CdSe quantum dot, the study found when the reaction solution pH= 9, the material ratio of RSH: Cd2 +: Se^2- is 2:1:0.5,the resulting CdSe quantum dots fluorescent effect best. In the synthesis of single karyotype the basis of CdSe quantum dots, take step epitaxial growth method obtained core/shell CdSe/ZnS quantum dots. The fluorescence quantum yield of core/shell quantum dots increased, fluorescence effect enhanced, stability greatly improved; UV-visible spectra blue shift significantly, showing a good quantum effects; Ultrasonic has an important role in the instant nucleation and nucleation of particle size control.