In Situ Synthesis of CdTe/CdSe Core-Shell Quantum Dots

摘要

Quantum dots (QDs) are materials which show quantum confinement effects and have drawn much attention due to the variety of different applications in which they can be used, including biomedical imaging, display devices, pho-tovoltaics, and lasers. Usually, core-shell type QDs are used, because they have reduced surface defects and nonradiative decay. Core-shell QDs are also divided into type-1 and type-2 like bulk semiconductors, depending on their band gap structure. Type-2 core-shell QDs have staggered band offsets, namely, a higher valence band or lower conduction band in the shell than in the core. As a result, the wavefunctions of the electron and hole exist separately, which leads to many novel properties, for example, the red-shift of the emission and a long decay lifetime. Type-2 QDs have attracted considerable attention as a result of the emission tuning with the core size and shell thickness in the near-infrared regions, which is important for biomedical imaging, because of their deep penetration and the absorption windows of biomaterials. There are many type-2 systems, including CdTe/CdSe, CdSe/ZnTe, InP/ GaAs, GaSb/GaAs, and GaAs/AlAs; however, there have been few reports of type-2 QDs prepared using the colloidal method. Among these reports, the CdTe/CdSe type-2 dots reported by Kim et al. are particularly impressive; however, they used highly toxic (CH_3)_2Cd to make the CdSe shell, which is not suitable for large scale synthesis.