Synthesis, Characterization And Application Of CdSe Quantum Dots

Semiconductor quantum dot (QD) is a kind of three-dimensional confined cluster with some special physical effects, such as quantum size confinement, quantum tunneling, and coulomb blockade. In recent years, QDs have been widely used in biology and medicine, especially in multiplexed biological detection, labelling and imaging.CdSe QD is one of the most studied materials among the II-VI semiconductor QDs, as well as the most promising QD used in biological labelling. In this paper, QDs synthesized by various methods and their applications have been summarized. Experimentally, the mono-disperse CdSe QDs have been successfully synthesized by the colloid chemical method, moreover, the effects of post-heat-treatment on the crystal structure and optical property of CdSe QDs have been investigated. Furthermore, the applications of QDs have been attempted. The main results achieved in this paper are listed as below:1. Monodispersive CdSe QDs of cubic zinc blende structure, which has strong quantum confinement effect, have been synthesized by TOPO-assisted coordinating solvent method. The peaks of absorption spectra of CdSe QDs shows a blue-shift dramatically compared with that of the bulk material. As the reaction time increases, QDs grow larger, the absorption and luminescence peaks undergo red-shifts gradually as well. A mechanism of crystal structure transformation of CdSe QDs has been proposed and the formation of zinc blende structure is discussed.2. The effects of heat-treatment on structural, morphological and optical properies of CdSe QDs have been studied. It is found that the CdSe QDs increase in size and they aggregate after heattreatment. As annealing temperature increases, the crystal structure of QDs transforms from zinc blende to wurtzite, and the luminescence peaks are redshifted gradually. There is an exceptional luminescence peak for the small-sized QDs (4nm) annealed at 400 ℃ and the large-sized QDs (7nm) at 350℃, respectively, which may be attributed to the oxidation of QDs when annealed.3. CdSe QDs-SiO₂ glass composite has been prepared by a unique ultrasonic assisted method. Its luminescence property as well as the evolution of crystalline structure after annealing at different temperatures has been investigated. It is found that due to the great power of ultrasonic or the change of chemical environment, the luminescence peak of CdSe QDs is blueshifted compared with that of the as-synthesized one, and it disappears after 3 weeks storage of QDs-glass due to the degradation of QDs. The transformation of crystalstructure of CdSe QDs from zinc blend to wurtzite is also found in the QDs-glass composite as the annealing temperature increases.4. A metal-SiCVCdSe QDs-semiconductor capacitor has been prepared by a simple dip-coating method. Discrete current fluctuations in the current-voltage (I-V) characteristics of this capacitor provide a convincing evidence of the quantized charging of the QDs, demonstrating the potential viability for the fabrication of single electron storage devices.5. CdSe QDs of zinc blende structure have been synthesized by a simple ethylenediamine-assisted method. They exhibit a strong luminescence peak at around 630nm and will transform into wurtzite structure when annealed at 500°C.