Hydrothermal Synthesis And Luminescent Properties Of ZnSe And ZnSe:Cu Quantum Dots

Quantum dots (QDs) exhibit unique optical properties because of their quantum confinement effects, and gradually begin to play an important role in the fields such as photoelectric device, solar cell and environmental monitoring. More importantly, water-soluble QDs are widely applied in the biomedical research field. Nowadays, the cadmium chalcogenide (CdS, CdTe and CdSe) have been studied extensively, however, their application in biomedicine has been limited for the biotoxicity of cadmium. ZnSe QDs, a wide band gap semiconductor, can overcome this disadvantage because of its less toxicity. Unfortunately, ZnSe QDs obtained by traditional synthesis methods are unstability and have low luminescent efficiency. Therefore, the synthesis of water-soluble and color-tunable ZnSe QDs with high luminous performance and stability has become a research hotspot.In this article, the blue-emitting ZnSe QDs and green-emitting ZnSe:Cu QDs were synthesized via the hydrothermal method in aqueous solution, and their luminescence properties were also studied. The synthesized QDs were characterized by FETEM, XRD, DTA-TG, EDS, UV-Vis absorption spectroscopy and fluorescence emission spectroscopy. The influences of factors such as types of stabilizers, the usage amount of stabilizer, precursor ratios, precursor solution pH, reaction time and hydrothermal temperature on the luminescence properties of ZnSe QDs were thoroughly investigated. The main contents and conclusions are as follows:1. Water-soluble ZnSe QDs were synthesized by using 3-mercaptopropionic acid (MPA) as stabilizer through on hydrothermal method. The influences of factors such as MPA/Zn mole ratio, Se/Zn mole ratio, precursor solution pH, reaction time and hydrothermal temperature on the luminescence properties of ZnSe QDs were studied. When the synthesis process was carried out under optimized hydrothermal conditions obtained through single factor experiment (MPA-to-Zn mole ratio,3.3; Se-to-Zn mole ratio,0.2; pH value of precursor solution,6.0; reaction temperature,140℃; and reaction time,10 h), the as-synthesized ZnSe QDs has the best fluorescence property, the particles are spherical approximately with 2 nm in diameter with the cubic zinc blende structure.2. The fluorescence intensity of ZnSe QDs synthesized using glutathione (GSH) as stabilizer was obvious higher than that synthesized using thioglycolic acid (TGA),3-mercaptopropionic acid (MPA) and L-cysteine (L-Cys). Besides, the fluorescence spectra of as-synthesized ZnSe QDs showed a strong band edge emission and a trap emission which was weak to almost none, showing that the QDs stabled by GSH has a better fluorescence properties.3. When ZnSe QDs were synthesized by hydrothermal method using GSH as stabilizer, the influences of factors such as GSH/Zn mole ratio, Se/Zn mole ratio, precursor solution pH, reaction time and hydrothermal temperature on the luminescence properties of ZnSe QDs were investigated. When the synthesis was carried out under optimized hydrothermal conditions obtained through single factor experiment (GSH-to-Zn mole ratio,1.2; Se-to-Zn mole ratio,0.2; pH value of precursor solution,10.0; reaction temperature,140℃; and reaction time,45 min), the as-synthesized ZnSe QDs showed the best fluorescence property, which were spherical approximately with 2-3 nm in diameter with the cubic zinc blende structure. The formation and growth mechanism of the core-shell structure under hydrothermal conditions were discussed in detail. Under hydrothermal condition, the thiol ligands (-SH) are easy to decompose to form a layer of ZnS shell on the surface of ZnSe nuclei.4. The green emitting ZnSe:Cu QDs were synthesized by hydrothermal method based on ZnSe QDs, and the influence of factors such as hydrothermal temperature, GSH/Zn mole ratio, precursor solution pH and doping amount of Cu2+ ions on the luminescence properties of ZnSe QDs were thoroughly investigated. The optimal parameters obtained through single factor experiment were as follows:the mole ratio of GSH/Zn/Se was 6:5:1, pH value was 10.5, the doping amount of Cu2+ ions was 5% and the reaction time was 60 min. The as-synthesized ZnSe:Cu QDs are still nearly spherical in morphology with cubic zinc blende in structure, the average diameter are approximately 4 nm. The diffraction peaks of ZnSe:Cu QDs had no obvious shifts compared with that of ZnSe QDs.