Interphase Synthesis And Charaterization Of Quantum Dots At Room Temperature

Recently, luminescent semiconductor nanoparticles (NPs), also known as luminescent semiconductor quantum dots (QDs), have attracted considerable attention as novel biological luminescent labels because of their unique optical properties and the latent value of application.The synthesis ofⅡ-Ⅵsemiconductor quantum dots have been improved very well in microemulsion preparation and aqueous preparation. In comparison to aqueous preparation, there are many advantages in microemulsion preparation, such as mild reaction conditions and better fluorescence performance. Because of the low yield of QDs synthesized in microemulsion, it is important to find or create a novel method to synthesize QDs with eximious-properties and high-yield. It is reported that the CdS quantum dots (QDs) dispersed in organic phase were obtained by the W/O interphase reaction. However, no further studies were reported. Therefore it is necessary to study the synthesis of QDs in the interface of water and oil to get QDs with higher yield and better optical properties.So the aim of this study is to synthesize and characterize CdS, CdSe and CdTe QDs by the W/O interphase reaction.The CdS quantum dots (QDs) were obtained by the interphase reaction method using cadmium oleate and thioacetamide as precursor. Meanwhile, the product was characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), ultraviolet-visible spectroscopy (UV-Vis), and photoluminescence spectroscopy (PL). CdS QDs exhibited a narrow size distribution ranged in 1.8-2.2 nm and a cubic crystal structure. Effects of the reaction time, pH value, the initial concentration ratio of [Cd²⁺]/ [S^2-] and stirring speed on the properties of the product was also investigated. The 4 factors above have no effect on the grain diameter. In addition, this method displays advantages in producing the better dispersed quantum dots with large quantities in comparison to microemulsion preparation and aqueous preparation. Meantime, the possible mechanism of the reaction was simply discussed.The CdSe quantum dots (QDs) were originally obtained by the bilayer-stirring interphase reaction of cadmium oleate dissolved in the organic solvent and Na₂SeSO₃ dispersed in water, respectively. The resultant was characterized by TEM, XRD, UV-Vis, PL. CdSe QDs exhibited a narrow size-distribution ranged in 3.6-4.0 nm and a cubic crystal structure. The particle size increased with the increace of reaction time. Meanwhile, stable CdSe QDs dispersions in hexane can be obtained with optimal starting molar ratio of [Cd²⁺]/ [Se^2-] at 2:1 and stirring speed at 240 rpm. The quantum efficiency can reach 50.4%. The steric clash of oleic acid has special effects on the reactant. Additionally, this method displays advantages in producing the better dispersed particles with large quantities in comparison to conventional methods.Na₂TeO₃ were prepared as Te source, CdCl₂ as Cd source to synthesize different CdTe QDs. With trisodium citrate and SNTA as stabilizing agents, the stable CdTe QDs can be obtained when optimal temperature was 95℃, reaction time was 3 h, and starting molar ratio of [Cd²⁺]/ [Te^2-] was 6:1.All the QDs (CdS, CdSe and CdTe) can be synthesized by the interphase reaction method. Surface active agent and organic solvent played decisive parts during the reaction. This new method in our study may be also useful for preparing other monodispersed and high-yield nanoparticles.