Multiband theory of quantum-dot quantum wells: Dark excitons, bright excitons, and charge separation in heteronanostructures

Electron, hole, and exciton states of multishell CdS/HgS/CdS quantum-dot quantum well nanocrystals are determined by use of a multiband theory that includes valence-band mixing, modeled with a 6-band Luttinger-Kohn Hamiltonian, and nonparabolicity of the conduction band. The multiband theory correctly describes the recently observed dark-exciton ground state and the lowest, optically active, bright-exciton states. Charge separation in pair states is identified. Previous single-band theories could not describe these states or account for charge separation.Comment: 10 pages of ReVTex, 6 ps figures, submitted to Phys. Rev.

Chemistry and photophysics of mixed CdS HgS colloids

Aqueous co colloidal systems consisting of two nanocrystalline, size quantized groups II VI semiconductor particles were investigated. Coating the HgS colloids with a layer of CdS leads to core shell like structures with electronic properties differing considerably to the sum of the separate particles. Implantation of HgS in the surface of CdS gives a new system with very colorful fluorescence properties. Evidence for a charge carrier transfer in this system is obtained from optical spectroscopy. Spectroscopic experiments, as well as electron microscopy studies, give insight into the geometrical and energetic structure and the charge carrier dynamics in such system