Synthesis And Luminescent Properties Of Znse Quantum Dots

Semiconductor quantum dots (QDs) have attracted much interest as novel bright phosphors for biological and medicine applications. Compared to organic dyes, QDs exhibit quantum confinement effects and have unique optical properties, such as broad excitation by all wavelengths smaller than the emission wavelength, narrow and symmetric emission with tunable colors, large Stokes shift and excellent photostability. The cadmium chalcogenide (CdS, CdTe and CdSe) with high brightness have been extensively studied at present. Unfortunately, the toxicity of cadmium is a concern that will limit the use of these visible emitting QDs. ZnSe, a wide band gap semiconductor, can replace the cadmium chalcogenide because of its less toxic. However, ZnSe QDs have the low quantum efficiency. Therefore, our work is to synthesize the high quality, water-soluble and color-tunable ZnSe QDs.The blue-emitting ZnSe QDs were synthesized via the chemical coprecipitation method in aqueous solution. Thioglycolic acid (TGA) was used as stabilizing agent, Se powder and zinc acetate in water were taken as precursors for the synthesis of the ZnSe QDs. X-ray powder diffraction (XRD) showed that ZnSe QDs have the cubic zinc blende structure; the transmission electron microscopy (TEM) exhibited that ZnSe QDs are spherical approximately with 3 nm in diameter. Some reaction factors (such as oil bathing temperature, reaction time, the amount of NaHse and TGA usage, and pH value), which influence on the luminescence properties of ZnSe QDs, were investigated by the fluorescence spectra. The results indicated that the high quality ZnSe QDs were obtained under these conditions-the mol ratio of zinc acetate /TGA/ Se is 1:1.2:0.125, the pH value is 9.5 and the reaction time is 3 h under 90℃. The fresh ZnSe QDs have high fluorescence intensity after an UV-irradiation treatment, which indicates that the UV-irradiation can reduce the surface defect states of ZnSe QDs. And the growth mechanism of ZnSe coincides with Ostwald mechanism.The green emitting ZnSe:Cu QDs were obtained based on ZnSe QDs. The phase and microstructure of ZnSe:Cu have been characterized by XRD and TEM. The results revealed that ZnSe:Cu QDs have cubic zinc blende structure and are spherical approximately with about 6 nm in diameter. The factors such as reaction time, the value of TGA, pH value, and the value of Cu²⁺ ions play important roles on the luminescence properties of ZnSe:Cu QDs. The optimal parameters for ZnSe:Cu are the following: the mol ratio of zinc acetate /TGA/ Se is 1:2.0:0.125, pH value is 9.5, the doping content of Cu²⁺ ions is 1.5 % and the reaction time is 2 h. These QDs were found to be stable in air under room temperature for at least 30 days, and had increased luminescence properties.Lastly, the synthesis, characterization, luminescence properties, and the doped mechanism of ZnSe:Mn QDs were studied. The formation of ZnSe:Mn QDs was presumed to be the nucleation-doping at a reasonable low temperature, that is, a pure MnSe nanocluster core coated with a pure ZnSe shell. The influences (such as the value of TGA, pH value, the doped value of Mn²⁺ ions, and the reaction time) on the luminescence properties of ZnSe:Mn QDs were discussed according to the fluorescence spectra. The results showed that ZnSe:Mn QDs were synthesized in a short time(<1h). When the mol ratio of zinc acetate /TGA/Se is 1:1.2:0.125, pH value is 9.2 and the doping content of Mn²⁺ ions is 1 %, ZnSe:Mn QDs have a high luminescence intensity.