Browsing by Author "Yerli, O."

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    Attractive versus repulsive excitonic interactions of colloidal quantum dots control blue-to red-shifting (and non-shifting) amplified spontaneous emission
    (American Chemical Society, 2013-11-21) Cihan, A. F.; Kelestemur, Y.; Guzelturk, B.; Yerli, O.; Kurum, U.; Yaglioglu, H. G.; Elmali, A.; Demir, Hilmi Volkan
    Tunable, high-performance, two-photon absorption (TPA)-based amplified spontaneous emission (ASE) from near-unity quantum efficiency colloidal quantum dots (CQDs) is reported. Besides the absolute spectral tuning of ASE, the relative spectral tuning of ASE peak with respect to spontaneous emission was shown through engineering excitonic interactions in quasi-type-II CdSe/CdS core/shell CQDs. With core shell size adjustments, it was revealed that Coulombic exciton-exciton interactions can be tuned to be attractive (type-I-like) or repulsive (type-II-like) leading to red- or blue-shifted ASE peak, respectively, and that nonshifting ASE can be achieved with the right core shell combinations. The possibility of obtaining ASE at a specific wavelength from both type-I-like and type-II-like CQDs was also demonstrated. The experimental observations were supported by parametric quantum-mechanical modeling, shedding light on the type-tunability. These excitonically engineered CQD-solids exhibited TPA-based ASE threshold as low as 6.5 mJ/cm(2) under 800 nm excitation, displaying one of the highest values of TPA cross-section of 44 660 GM.
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    ItemOpen Access
    Reordering orbitals of semiconductor multi-shell quantum dot-quantum well heteronanocrystals
    (American Institute of Physics, 2012-01-27) Sahin, M.; Nizamoglu, S.; Yerli, O.; Demir, Hilmi Volkan
    Based on self-consistent computational modeling of quantum dot-quantum well (QDQW) heteronanocrystals, we propose and demonstrate that conduction-electron and valence-hole orbitals can be reordered by controlling shell thicknesses, unlike widely known core/shell quantum dots (QDs). Multi-shell nanocrystals of CdSe/ZnS/CdSe, which exhibit an electronic structure of 1s-1p-2s-2p-1d-1f for electrons and 1s-1p-2s-2p-1d-2d for holes using thin ZnS and CdSe shells (each with two monolayers), lead to 1s-2s-1p-1d-1f-2p electron-orbitals and 1s-2s-1p-1d-2p-1f hole orbitals upon increasing the shell thicknesses while keeping the same core. This is characteristically different from the only CdSe core and CdSe/ZnS core/shell QDs, both exhibiting only 1s-1p-1d-2s-1f-2p ordering for electrons and holes.