Browsing by Subject "Quantum Dot"

Filter results by typing the first few letters
Now showing 1 - 3 of 3
  • Thumbnail Image
    ItemOpen Access
    Hartree-Fock approximation of bipolaron state in quantum dots and wires
    (Springer, 2010) Senger, R. T.; Kozal, B.; Chatterjee, A.; Erçelebi, A.
    The bipolaronic ground state of two electrons in a spherical quantum dot or a quantum wire with parabolic boundaries is studied in the strong electron-phonon coupling regime. We introduce a variational wave function that can conveniently conform to represent alternative ground state configurations of the two electrons, namely, the bipolaronic bound state, the state of two individual polarons, and two nearby interacting polarons confined by the external potential. In the bipolaron state the electrons are found to be separated by a finite distance about a polaron size. We present the formation and stability criteria of bipolaronic phase in confined media. It is shown that the quantum dot confinement extends the domain of stability of the bipolaronic bound state of two electrons as compared to the bulk geometry, whereas the quantum wire geometry aggravates the formation of stable bipolarons.
  • Thumbnail Image
    ItemOpen Access
    A photometric investigation of ultra-efficient LEDs with high color rendering index and high luminous efficacy employing nanocrystal quantum dot luminophores
    (Optical Society of America, 2009-12-24) Erdem, T.; Nizamoglu, S.; Sun, X. W.; Demir, Hilmi Volkan
    We report a photometric study of ultra-efficient light emitting diodes (LEDs) that exhibit superior color rendering index (CRI) and luminous efficacy of optical radiation (LER) using semiconductor quantum dot nanocrystal (NC) luminophores. Over 200 million systematically varied NC-LED designs have been simulated to understand feasible performance in terms of CRI vs. LER. We evaluated the effects of design parameters including peak emission wavelength, full-width-at-half-maximum, and relative amplitudes of each NC color component on LED performance. Warm-white LEDs with CRI >90 and LER >380 lm/W at a correlated color temperature of 3000 K are shown to be achieved using nanocrystal luminophores. (C) 2009 Optical Society of America
  • Thumbnail Image
    ItemOpen Access
    Warm-white light-emitting diodes integrated with colloidal quantum dots for high luminous efficacy and color rendering
    (2010) Nizamoglu, S.; Erdem, T.; Sun X.W.; Demir, Hilmi Volkan
    Warm-white LEDs (WLEDs) with high spectral quality and efficiency are required for lighting applications, but current experimental performances are limited. We report on nanocrystal quantum dot (NQD) hybridized WLEDs with high performance that exhibit a high luminous efficacy of optical radiation exceeding 350 lm/Wopt and a high color rendering index close to 90 at a low correlated color temperature <3000 K. These spectrally engineered WLEDs are obtained using a combination of CdSe/ZnS core/shell NQD nanophosphors integrated on blue InGaN/GaN LEDs. © 2010 Optical Society of America.