|M.Sc Student||Inbal Hesseg|
|Subject||Development of Synthetic Procedures for the Formation of|
Mn Doped Semiconductor Quantum Dots
|Department||Department of Chemistry||Supervisor||Full Professor Lifshitz Efrat|
|Full Thesis text|
Colloidal semiconductor quantum dots (QDs) are crystals of nanoscale dimensions capped with organic molecules, which makes them soluble in various solvents. Many physical (e.g., electronic and optical) properties of nanosize crystals are different from those of the bulk materials. This “quantum size effect” is accounted for by the three-dimensional quantum confinement of the electrons, which results in size-dependent quantization (discretization) of their energy levels. Since colloidal QDs can be easily prepared by wet chemistry methods, they are attractive materials for low-cost and scalable solution-processed optoelectronic devices. In particular, QD-based solar cells are considered to be most promising due to the expected great increase in the device efficiency.
Special attention has been given to CQDs embedded with magnetic impurities, such as a Mn2 ion with half-filled d orbitals at the ground state. The confinement of the impurity within a CQD induces coupling between the host carriers and the impurity atomistic states.
This work describes the synthesis and optical investigation of CQDs embedded with a low dilution of Mn2 ions. CdS/ZnS CQDs were selected for the current study due to the quasi-type-II characteristic of CdSe/CdS core-shell, providing major localization of the hole at the core regime and delocalization of the electron over the entire structure, offering selective interaction of carriers with spin states of the embedded impurities. In addition. the ZnS provides a good passivation to the QDs surface.
This work studies the control, concentration, and precise positioning of the impurity ions at different radial distances from the core center, ending either at the core, at the shell, or at the interface, with the optical investigations revealing strong dependence of the CQDs’ excitonic properties on the Mn2-ion’s position. Finally, we were able to synthesis CdSe QDs embedded with 2% Mn, and CdSe/Mn:CdS/ZnS core-shell-shell QDs with 0.4% of Mn ions. embedded inside the CdS shell.