Scopus İndeksli Yayınlar Koleksiyonu

Permanent URI for this collectionhttps://hdl.handle.net/20.500.12573/395

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Author: search.filters.author.Koc, FatihWoS Q: search.filters.wosQuartile.Q2

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Now showing 1 - 5 of 5
  • Article
    Citation - WoS: 3
    Citation - Scopus: 7
    The Electronic and Optical Properties of an Exciton, Biexciton and Charged Excitons in CdSe/CdTe-Based Multi-Shell Type-II Quantum Dot Nanocrystals
    (Springer Heidelberg, 2019-09-17) Koc, Fatih; Sahin, Mehmet
    It has been recently reported that multi-shell type-II quantum dot nanocrystals (QDNCs) have higher quantum yields. Besides these higher quantum yields of multi-shell type-II QDNCs, additional second layer has been a critical influence on the formation mechanisms of the excitonic structures. Understanding of bound and unbound cases of the excitonic structures in multi-shell type-II QDNCs gives some important information for applications. In this study, we have investigated the electronic and optical properties of a single exciton (X), biexciton (XX), and positively and negatively charged excitons (X+ and X-) in CdSe/CdTe-based multi-shell type-II QDNCs. In the study, three different structure compositions, i.e., CdSe/ CdTe, CdSe/CdTe/CdS, and CdSe/CdTe/ZnTe, have been considered. We have observed that CdS and ZnTe materials have drastically changed the electronic and optical properties of the bare CdSe/CdTe type-II QDNCs.
  • Article
    Citation - WoS: 41
    Citation - Scopus: 45
    Optical Properties in a ZnS/CdS Core/Shell Spherical Quantum Dot: Electric and Magnetic Field and Donor Impurity Effects
    (MDPI, 2023-01-29) Toscano-Negrette, Rafael G.; Leon-Gonzalez, Jose C.; Vinasco, Juan A.; Morales, A. L.; Koc, Fatih; Kavruk, Ahmet Emre; Duque, C. A.
    A theoretical analysis of optical properties in a ZnS/CdS/ZnS core/shell/shell spherical quantum dot was carried out within the effective mass approximation. The corresponding Schrodinger equation was solved using the finite element method via the 2D axis-symmetric module of COMSOL-Multiphysics software. Calculations included variations of internal dot radius, the application of electric and magnetic fields (both oriented along z-direction), as well as the presence of on-center donor impurity. Reported optical properties are the absorption and relative refractive index change coefficients. These quantities are related to transitions between the ground and first excited states, with linearly polarized incident radiation along the z-axis. It is found that transition energy decreases with the growth of internal radius, thus causing the red-shift of resonant peaks. The same happens when the external magnetic field increases. When the strength of applied electric field is increased, the opposite effect is observed, since there is a blue-shift of resonances. However, dipole matrix moments decrease drastically with the increase of the electric field, leading to a reduction in amplitude of optical responses. At the moment impurity effects are activated, a decrease in the value of the energies is noted, significantly affecting the ground state, which is more evident for small internal radius. This is reflected in an increase in transition energies.
  • Article
    Citation - WoS: 13
    Citation - Scopus: 15
    Advanced Tunability of Optical Properties of CdS/ZnSe Multi-Shell Quantum Dot by the Band Edge Engineering
    (Elsevier, 2023-01) Koc, Fatih; Kavruk, Ahmet Emre; Sahin, Mehmet
    In this study, the advanced manipulability of wave functions in a type-II multi-shell hetero-nanostructure (MS-HNS) and the tunability of radiative exciton lifetime over a wide range with and/or without changing in transition energies has been demonstrated by the band edge engineering. For this purpose, the electronic and optical properties of exciton (X) and biexciton (XX) in a spherical CdS/ZnSe/ZnTe/CdSe HNS have been explored in detail. In the calculations, effects of all Coulombic interactions between the charges have been taken into account on the wave functions. Moreover, in the case of XX, the exchange-correlation potential between the same charged particles has also been considered. The results have been presented as a function of CdS core radius and ZnSe shell thickness and the probable physical reasons have been discussed in detail.
  • Article
    Citation - WoS: 24
    Citation - Scopus: 25
    A Model for the Recombination and Radiative Lifetime of Trions and Biexcitons in Spherically Shaped Semiconductor Nanocrystals
    (Amer Inst Physics, 2013-05-06) Sahin, Mehmet; Koc, Fatih
    In this letter, we propose a different model to determine the recombination oscillator strength of trions and biexcitons for bound and unbound cases in the effective mass approximation. The validity of our model has been confirmed by the radiative lifetime of the trion and biexciton in a spherical quantum dot. The results show that the model works with sufficient accuracy in comparison with results of more complex methods such as quantum Monte Carlo techniques and atomistic calculations. (C) 2013 AIP Publishing LLC.
  • Article
    Citation - WoS: 26
    Citation - Scopus: 29
    A Detailed Investigation of Electronic and Optical Properties of the Exciton, the Biexciton and Charged Excitons in a Multi-Shell Quantum Dot Nanocrystal
    (IOP Publishing Ltd, 2014-06-19) Akturk, Abdurrahman; Sahin, Mehmet; Koc, Fatih; Erdinc, Ahmet
    In the present study, the electronic and optical properties of the exciton (X), the biexciton (XX) and charged excitons (X- and X+) in a multi-shell quantum dot nanocrystal have been systematically explored in detail. The electronic properties have been determined in the framework of the single-band effective mass approximation. For this purpose, the Poisson-Schrodinger equations have been solved self-consistently in the Hartree approximation. In the electronic structure calculations for XX, X- and X+, the quantum mechanical exchange-correlation potentials between particles of the same type have been taken into account in the local density approximation. Some optical parameters, such as the overlap integrals, recombination oscillator strengths, radiative lifetimes, etc, have been determined by using the single-particle energy levels and wavefunctions obtained. A different approximation, reported in Sahin and Koc 2013 Appl. Phys. Lett. 102 183103, has been used in the recombination oscillator strength calculations. The results have been presented comparatively as a function of the shell thicknesses, and the well widths and probable physical reasons underlying them have been discussed in detail.