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Exciton Dynamics (exciton + dynamics)

Distribution by Scientific Domains

Physics and Astronomy	80%

Selected Abstracts

Exciton dynamics probed in carbon nanotube suspensions with narrow diameter distribution

PHYSICA STATUS SOLIDI (B) BASIC SOLID STATE PHYSICS, Issue 13 2006
Tobias Hertel
Abstract We report on a pump,probe study of CoMoCAT nanotube suspensions with narrow chirality distribution. Visible pump pulses and a white light continuum are used for resonant excitation of the strongest dipole allowed E22 subband exciton in the semiconducting (6, 5) tube and for broadband probe of the resulting spectral transients between 1300 nm and 480 nm, respectively. Transient spectra show signatures of both photobleaching (PB) and photoabsorption (PA) with practically identical decay- but slightly different rise-times. The experiments reveal that apparent variations of decay rates at different wavelengths do not reflect dynamics of different relaxation processes but are a consequence of the superposition of PB and blue-shifted PA response. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Exciton dynamics in quantum nano-structures of II,VI diluted magnetic semiconductors fabricated by electron-beam lithography

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 4 2004
A. Uetake
Abstract Exciton dynamics in quantum dots (QDs) of II,VI diluted magnetic semiconductors (DMSs) has been studied by using an electron-beam lithography technique. The peak energy of excitonic photoluminescence in the QDs shows blue shifts up to 3.5 meV toward the dot diameter of 20 nm, indicating a lateral confinement effect for the exciton. The time-dependent energy shift of the exciton due to the localization is small as 2.9 meV, which originates from the suppression of the exciton diffusion due to the finite dot structure. The coupled QDs composed of a DMS magnetic well (MW) and a non-magnetic well (NW) were sucessfully fabricated, where the exciton energy in the NW was designed to be lower than that in the MW. The spin-polarized excitons migrate from the MW to the NW in magnetic fields and the exciton spin injection is demonstrated in the coupled QDs. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Excitonic spectra of orientationally disordered molecular aggregates

PHYSICA STATUS SOLIDI (C) - CURRENT TOPICS IN SOLID STATE PHYSICS, Issue 3 2004
D. B. Balagurov
Abstract We study the Frenkel exciton dynamics in a one-dimensional molecular aggregate with disorder in both the on-site energies and transition dipole moments. Using a tensorial generalization of the coherent-potential approximation, we calculate the linear absorption spectra, the exciton density of states, and the coherence length responsible for the linear optics. In particular, we consider the purely orientational disorder in the transition dipoles, and show that our theory agrees well with the numerical simulations. In addition to features shared by other disordered aggregate models, we show that the strength of orientational disorder affects the anisotropy degree of the optical response with the main components of the optical susceptibility tensor being characterized by nonequal coherence lengths. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Optimization of opto-electronic property and device efficiency of polyfluorenes by tuning structure and morphology

POLYMER INTERNATIONAL, Issue 5 2006
Peng Chen
Abstract Polyfluorene-based oligomers and polymers (PFs) have been studied intensively as active materials for organic optoelectronic devices. In this review, the optimization of the opto-electronic property and device efficiency of polyfluorenes in the field of light-emitting diodes (LEDs) and photovoltaic cells (PVs) by tuning structure and morphology are summarized in terms of two typical modification techniques: copolymerization and blending. The relationships between molecular structures, thin film morphologies, opto-electronic properties and device efficiencies are discussed, and some recent progress in LEDs and PVs is simultaneously reviewed. After the introduction, the basic knowledge of molecular structures and properties of polyfluorene homopolymers is presented as a background for a better understanding of their great potential for opto-electronic applications. Immediately after this, three different opinions on the origin of low-energy emission band at 520,540 nm in polyfluorene-based LEDs are addressed. Rod,coil block copolymers and alternative copolymers are focused on in the next section, which are a vivid embodiment of controlling supramolecular structures and tailoring molecular structures, respectively. In particular, various supramolecular architectures induced by altering coil blocks are carefully discussed. Recent work that shows great improvement in opto-electronic properties or device performance by blending or doping is also addressed. Additionally, the progress of understanding concerning the mechanisms of exciton dynamics is briefly referred to. Copyright © 2006 Society of Chemical Industry [source]