Scopus İndeksli Yayınlar Koleksiyonu
Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395
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Article Citation - WoS: 3Citation - Scopus: 3The Electronic and Optical Properties of a Triexciton in CdSe/ZnS Core/Shell Quantum Dot Nanocrystals(Taylor & Francis Ltd, 2016-02-21) Akturk, Abdurrahman; Tas, Hatice; Koksal, Koray; Sahin, MehmetIn the study, we aim to investigate the electronic and optical properties of single excitons, biexcions and triexcitons in a CdSe/ZnS core/shell quantum dot nanocrystal. The electronic structure has been determined by solving of the Poisson-Schrodinger equations self-consistently. In calculations, the exchange-correlation effects between identical particles have been taken into account in the frame of the local density approximation. We have demonstrated that the optical properties of triexciton systems are remarkably different from the single and biexciton systems. Absorption peaks or transition energies of the triexciton system are well separated from those of single- and bi-exciton systems. We have observed that the core-radius dependent transition energy variations of triexcitons are higher when compared with single- and bi-excitonic systems. The transition energy shifts of double and triple excitons with respect to the single exciton have been calculated as a function of the core radius and we have shown that the energy shifts are inversely proportional with the radius. We have also investigated the radius-dependent changes in binding energies and lifetimes of the structures and the comparative results have been discussed in a detail manner.Article Citation - WoS: 3Citation - Scopus: 3Superior CdSe/ZnS@Fe2O3 Yolk-Shell Nanoparticles as Optically Active MRI Contrast Agents(Wiley-VCH Verlag GmbH, 2022-07) Ekici, Derya D.; Mutlugun, EvrenWe have developed a robust synthesis methodology for quantum dots (QDs) nanoparticles with magnetic properties designed for biomodal imaging. These nanocrsytlas consists of a semiconductor quantum dot core with engineered fluorescence, which is located in a paramagnetic iron oxide shell that acts as a magnetic resonance imaging (MRI) contrast agent. Yolk-shell CdSe/ZnS@Fe2O3 nanoparticles (NPs) are synthesized via sonochemical decomposition of iron pentacarbonyl (Fe(CO)(5)) using the oleylamine (OAm) as the ligand. The sonochemical synthesis method of magnetic fluorescent NPs that can be used as MRI contrast agents provided advantages such as improved quantum efficiency and homogeneous size distributions. It has been determined that the luminescence efficiency of quantum dots decreases in coatings that can be made at high temperatures by thermal decomposition. In order to eliminate the disadvantage of elevated temperatures, the sonochemical decomposition method, which allows coating at low temperatures, has been used. With this method, yolk-shell (CdSe/ZnS@Fe2O3) nanoparticles were produced with high photoluminescence quantum efficiency and homogeneous size distributions. The synthesis magnetic fluorescent NPs optimized was determined to have the injection temperature of Fe(CO)(5) at 60 degrees C, Fe(CO)(5)/CdSe@ZnS ratio 0.7, OAm/Fe(CO)(5) volume ratio 1.43 with an oxidation time 5 min. Under these conditions, the quantum efficiency was found to be 78 %, nanoparticle sizes between 11-14 nm and r(1) value was 0.199, r(2) value was 0.518 in MRI analysis. These optically active magnetic fluorescent nanoparticles as positive contrast agents (T1 weighted) are predicted to pave the way for the future of advanced bio-imaging systems.