The Microwave-Assisted Preparation And Optical Properities Of Cu²⁺ Doped CdTe@ZnS Core-Shell QDs

Quantum dots (QDs) are a kind of nanoparticles composed of Ⅱ-Ⅵ,Ⅲ-Ⅴ,Ⅳ-Ⅳ, or Ⅳ-Ⅵ elements, thus are called colloidal semiconductor nanocrystals. QDs have been widely applied in the chemical and biological fields such as optoelectronic devices, sensors, biological fluorescence labeling, white light-emitting diodes, and solar cells, etc due to their many special optical, mechanical, electric properties caused by the quantum confinement effect. Therefore, it is meaningful to synthesize high-quality QDs with controllable shape and size. Various methods for preparation of QDs were reported and summarized as two kinds, namely organic and aqueous synthesis. QDs obtained by organic synthesis have good monodispersity, crystallinity and high photoluminescence quantum yields. However, the precursors used in this rout are toxic, the reaction is hard to be controlled and the products cannot dissolve in water easily. In contrast, aqueous synthesis is more reproducible, cheaper, less toxic and more environmentally friendly. Ⅱ-Ⅵ colloidal semiconductor nanocrystals synthesized in aqueous phase consist of a very broad fluorescence spectrum, good water-solubility, and high photoluminescence quantum yield. Therefore, they are very suitable for biological label, image and probe applications. In this paper, we have developed a microwave irradiation heating to synthesize water-soluble CdTe QDs, CdTe/ZnS core/shell QDs, and CdTe:Cu2+/ZnS doped core/shell QDs. The influence of reaction experimental conditions on the luminescence properties of the obtained QDs was investigated.(1) Different size of CdTe nanocrystals were synthesized by microwave irradiation route. The influences of reaction conditions including reaction temperature, time, pH value, the concentration of precursor, and the molar ratio of reactants on the photoluminescence properties were systematically investigated. The optimized experimental conditions are as follows:reaction temperature was 130℃, reaction time was 6 mins, pH value of Cd2+ precursor solution was 6.0, the concentration of Cd2+　was 1.13 mM, and the molar ratio of Cd2+:GSH:Te2-　was 1:0.7:0.25.(2) Acqueous CdTe/ZnS nanocrystals with the core/shell structure were obtained. The optical properties of CdTe/ZnS QDs prepared at different conditions were investigated and the core/shell QDs with the highest photoluminescence were obtained at the following conditions:reaction temperature of shell growth was 60 ℃, reaction time was 13 mins, pH value of Zn2+　precursor solution was 8.5, the molar ratio of Cd2+:Zn2+:S2’:MPA was 1:1.25:1:6 and the number of ZnS layer was three.(3) Cu2+　doped CdTe nanocrystals were synthesized by aqueous route. The optimized experimental conditions are as follows:The reaction temperature was 70 ℃, reaction time was 10 mins, the optimized concentration of Cu2+　was 3%. The photoluminescent intensity can be further enhanced by ZnS layer growing. In order to comparison, CdTe/ZnS:Cu2+ QDs were also produced by firstly coating ZnS layer and then doping Cu2+. Under this condition, the optimized Cu2+　concentration was 1%.