Exciton

About: Exciton is a research topic. Over the lifetime, 31603 publications have been published within this topic receiving 810642 citations.

Exciton localization and the Stokes’ shift in InGaN epilayers

Abstract: We report a comparative study of the emission and absorption spectra of a range of commercial InGaN light-emitting diodes and high-quality epilayers A working definition of the form of the absorption edge for alloys is proposed, which allows a unique definition of the Stokes’ shift A linear dependence of the Stokes’ shift on the emission peak energy is then demonstrated for InGaN using experimental spectra of both diode and epilayer samples, supplemented by data from the literature In addition, the broadening of the absorption edge is shown to increase as the emission peak energy decreases These results are discussed in terms of the localization of excitons at highly indium-rich quantum dots within a phase-segregated alloy

Condensation of indirect excitons in coupled AlAs/GaAs quantum wells.

Abstract: The photoluminescence of excitons confined in an electric field tunable coupled AlAs/GaAs quantum well has been investigated at $T\ensuremath{\ge}350$ mK and magnetic fields $H\ensuremath{\le}14$ T. In the indirect regime where electrons and holes are separated both in real and in $k$ space, the magnetic field was found to result in (i) a strong change of both the photoluminescence intensity and decay time which is attributed to anomalies in the exciton transport and (ii) an appearance of a huge broad band noise in the photoluminescence intensity which is evidence for exciton condensation.

Hypochromism and other spectral properties of helical polynucleotides

Abstract: Exciton interaction in a double-stranded helical polymer, such as a homogeneous polynucleotide, leads to a splitting of each excited electronic energy level of the monomer into two exciton bands of energy levels Consideration of the selection rules derived from zeroth-order functions shows that for double-stranded polynucleotides pi yields pi * transitions are allowed to, at most, one exciton level of each band, both polarized perpendicularly to the helix axis; whereas, n yields pi * transitions are allowed only to one level of the upper band, that being polarized parallel to the helix axis Examination of the spectral properties of the four constituents of deoxribonucleic acid (DNA) reveals that although exciton bands probably exist in regions of spectral overlap, there should be isolated energy levels lying below the main exciton bands These levels may act as localized energy traps during excitation propagation through the helix In order to treat the problem of hypochromism, it is necessary to use first-order functions An equation is developed which takes into account the effect of exciton interaction and dispersion-force interaction on the oscillator strength of the helix Application of this equation to a helical, double-stranded polyadenylic acid having the configuration of DNA indicates that perturbationmore » resulting from dispersion-force interaction among the bases can account for the observed hypochromism (auth)« less

Exciton-LO-phonon couplings in spherical semiconductor microcrystallites

Abstract: Exciton-LO-phonon couplings in CdS x Sc 1-x semiconductor microcrystallites (x=0.12±0.05) are investigated by measuring the temperature dependence of the width and energy of excitons by electroabsorption. The LO phonons are shown semiquantitatively to contribute to the experimentally obtained temperaure dependencies of the width and energy of excitons. The dependence of the coupling constant (the Huang-Rhys parameter) on the radius of microcrystallites is calculated for CdSe and GaAs microcrystallites. The phonon confinement effects are considered with "free-standing" and "rigid"-boundary conditions. As for the exciton state, nonparabolicity of the conduction band and the valence-band mixing are considered in order to obtain a precise exciton wave function, which is crucially important in calculating the Huang-Rhys parameter in a microcrystallite. The exciton-confined-optical-phonon interaction Harniltonian is constructed for a microcrystallite. It is found that the Huang-Rhys parameters have a minimum at a radius of 70 A for CdSe and 270 A for GaAs microcrystallites. The size dependence of the Huang-Rhys parameter is also calculated for a microcrystallite with an extra charge at the spherical-particle center. The lowest (s,S 3/2 ) state in the trapped state is found to have small transition probability and g values of 1 in CdSe (R =30 A) and 0.01 in GaAs? = 100 A). The higher states are found to have larger transition probability and g values of 0.7 in CdSe (R =30 A) and 0.01 in GaAs (R = 100 A). These results suggest that large g values observed experimentally in CdS and CdSe microcrystallites originate from extrinsic effects such as the presence of charged point defects inside the microcrystallite.