Production and characterization of CdSe based binary/binary and ternary/binary heterostructure multi shell quantum dots

Colloidal semiconductor NCs (also known as quantum dots (QDs)) with their diameters range between 2-10 nm have gained a huge interest for both optical and electronical applications such as solar cells, light emitting diodes, lasers, fluorescence imaging and for fundamental studies over the last few decades due to their sizedependent optical, physical and chemical properties. QDs can be synthesized in core (bare) and core/shell forms in accordance to their application interest and are made from III-V and II-VI group semiconductors family in the periodic Table. Their optical, physical and chemical properties can be altered with deposition of shell on core. The introduced shell material's composition or spacer layer in multishell cause changes in charactristics of semiconductors. CdSe semiconductor is a subject of many studies due to their bright luminescence in the visible range of optical spectrum with different particle size. In this thesis, like most of investigations, the optical, physical and structural properties of CdSe based QDs is evaluated. The synthesis of CdSe bare core, CdSe/Cd(Zn)S core/shell, CdSe/Cd1-xZnxS core/ternary shell and CdSe/Cd(Zn)S/Zn(Cd)S core-multishell NCs are done at relatively low temperature. Then, the produced hetero structures are optically and structural characterized using UV-Vis, PL, HRTEM, XRD analysis. On the other hand, interfacial strain amount was obtained theoretically in order to calculate the capped core diameter changes after shell deposition. Interfacial strain effect cause the Bragg's 2Ɵ diffraction degree to slide in XRD analysis. In this phenomenon, this shift noticed toward higher degrees after capping the core with compressive shell while introducing lower compressive shell led in less shift in Bragg's 2Ɵ degrees. Another effect of capping CdSe core with shell of different composition observed in absorption and photoluminescence spectra. The red shift of absorption and photoluminescence peak is recorded in UV-vis and PL spectrum after shell deposition. Depending on the diameter of CdSe NCs, the red shift amount differs in absorption spectra. Using the exciton energy from absorption spectrum, the capped core size of the core was calculated. The conventional Brus equation used to calculate capped core diameter with the obtained exciton energy. For the first time, we substituted interfacial strain amount in Brus equation to observe capped core size changes after deposition of compressive shell. Interfacial strain amount is calculated from continuum elastic theory and core squeeze or stretch was observed after capping process. Result of the obtained theoretically capped core size were compared with the bare CdSe core size from TEM image to evaluate the accuracy of our proposed theoretic method. Logic and good overlap of the theoretical and experimental results showed the accuracy of the proposed theoric method.