Browsing by Subject "Exciton"
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Item Open Access Excitonics of colloidal nanocrystals for next-generation optoelectronics(Bilkent University, 2016-05) Güzeltürk, BurakItem Open Access FRET-LEDs involving colloidal quantum dot nanophosphors(Webcom Communications, 2010) Nizamoğlu, S.; Sari, E.; Baek, J. H.; Lee, I. H.; Sun, X. W.; Demir, Hilmi VolkanSemiconductor nanocrystal quantum dots (NQD) with their narrow and tuneable emission are promising candidates to serve as color convertors integrated on light-emitting diodes (LEDs). The use of nonradiative energy transfer, also known as Förster-type resonance energy transfer (FRET), in such NQD nanophosphors provides additional benefits for color-conversion in solid state lighting. In this paper we discuss these NQD-integrated FRET-LEDs for lighting applications.Item Open Access Measuring the ultrafast spectral diffusion and vibronic coupling dynamics in CdSe colloidal quantum wells using two-dimensional electronic spectroscopy(American Chemical Society, 2023-02-14) Nguyen, H. L.; Do, T. N.; Durmuşoğlu, E. G.; İzmir, M.; Sarkar, R.; Pal, S.; Prezhdo, O. V.; Demir, Hilmi Volkan; Tan, H.-S.We measure the ultrafast spectral diffusion, vibronic dynamics, and energy relaxation of a CdSe colloidal quantum wells (CQWs) system at room temperature using two-dimensional electronic spectroscopy (2DES). The energy relaxation of light-hole (LH) excitons and hot carriers to heavy-hole (HH) excitons is resolved with a time scale of ∼210 fs. We observe the equilibration dynamics between the spectroscopically accessible HH excitonic state and a dark state with a time scale of ∼160 fs. We use the center line slope analysis to quantify the spectral diffusion dynamics in HH excitons, which contains an apparent sub-200 fs decay together with oscillatory features resolved at 4 and 25 meV. These observations can be explained by the coupling to various lattice phonon modes. We further perform quantum calculations that can replicate and explain the observed dynamics. The 4 meV mode is observed to be in the near-critically damped regime and may be mediating the transition between the bright and dark HH excitons. These findings show that 2DES can provide a comprehensive and detailed characterization of the ultrafast spectral properties in CQWs and similar nanomaterials.Item Open Access Quantum dot light-emitting diode with quantum dots inside the hole transporting layers(American Chemical Society, 2013) Leck K.S.; Divayana, Y.; Zhao, D.; Young, X.; Abiyasa, A. P.; Mutlugun, E.; Gao, Y.; Liu, S.; Tan S.T.; Sun, X. W.; Demir, Hilmi VolkanWe report a hybrid, quantum dot (QD)-based, organic light-emitting diode architecture using a noninverted structure with the QDs sandwiched between hole transporting layers (HTLs) outperforming the reference device structure implemented in conventional noninverted architecture by over five folds and suppressing the blue emission that is otherwise observed in the conventional structure because of the excess electrons leaking towards the HTL. It is predicted in the new device structure that 97.44% of the exciton formation takes place in the QD layer, while 2.56% of the excitons form in the HTL. It is found that the enhancement in the external quantum efficiency is mainly due to the stronger confinement of exciton formation to the QDs.