Thursday, April 8, 2010
Hybrid Exciton in Organic-Semiconductor Quantum Dot Systems
Que Huong Nguyen
The formation of a hybridization state of Wannier Mott exciton and Frenkel exciton in different hetero-structure configurations involving quantum dots has been investigated. The hybrid excitons exist at the interfaces of the semiconductors quantum dots and the organic medium, having unique properties and a large optical non-linearity. The coupling at resonance is very strong and tunable by changing the parameters of the systems (dot radius, dot–dot distance, generation of the organic dendrites and the materials of the system etc). Different semiconductor quantum dot–organic material combination systems have been considered such as a semiconductor quantum dot lattice embedded in an organic host, a semiconductor quantum dot at the center of an organic dendrite, a semiconductor quantum dot coated by an organic shell.
The formation and the properties of the organic-semiconductor hybrid excitons have been modulated by electric and magnetic fields. The hybrid excitons are as sensitive to external perturbation as Wannier-Mott excitons. We investigate the effect of mutual presence of electric and magnetic fields on the hybrid exciton of the isolated semiconductor quantum dot such as CdSe (core) clothed by an organic or glass coating for two configuration of fields when the electric and magnetic fields are parallel and orthogonal. The fields affect the eigenfunctions (by a Stark -effect distortion and by the magnetic field induced distortion) and the Frenkel-Wannier coupling term. Upon the application of the magnetic and electric fields the coupling term between the two kinds of excitons increases. The most important feature of this system is by adjusting the magnetic and electric fields, one can tune the resonance between the two kinds of excitons to get different regions of mixing to obtain the expected high non-linearity.
Refreshments at 11:00 AM. Seminar begins at 11:10 AM.
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