Exciton

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

Direct pseudopotential calculation of exciton coulomb and exchange energies in semiconductor quantum dots

Abstract: The effects of electron-hole interaction on the exciton energy of semiconductor quantum dots are calculated using pseudopotential wave functions. A comparison with the widely used, but never tested, effective-mass approximation (EMA) shows that the electron-hole Coulomb energy is significantly ( $\ensuremath{\sim}40%$) overestimated by the EMA, and that the scaling with the dot size $R$ is sublinear in $1/R$. The exchange splitting is much smaller than the Coulomb energy, and in the case of CdSe quantum dots shows significant deviations from the ${1/R}^{3}$ scaling predicted by the EMA.

Defect-related photoluminescence of hexagonal boron nitride

Abstract: Photoluminescence of polycrystalline hexagonal boron nitride (hBN) was measured by means of time- and energy-resolved spectroscopy methods. The observed bands are related to donor-acceptor pair transitions, impurities, and structural defects. The excitation of samples by high-energy photons above 5.4 eV enables a phenomenon of photostimulated luminescence (PSL), which is due to distantly trapped conduction band electrons and valence band holes. These trapped charges are metastable and their re-excitation with low-energy photons results in anti-Stokes photoluminescence. The comparison of photoluminescence excitation spectra and PSL excitation spectra allows band analysis that supports the hypothesis of Frenkel-type exciton in hBN with a large binding energy.

Interchain effects in the ultrafast photophysics of a semiconducting polymer: THz time-domain spectroscopy of thin films and isolated chains in solution

Abstract: We compare the generation and decay dynamics of charges and excitons in a model polymer semiconductor (MEH-PPV) in solution and drop-cast thin films, by recording the sub-ps transient complex conductivity using THz time-domain spectroscopy. The results show that the quantum efficiency of charge generation is two orders of magnitude smaller in solution (~10–5) than in the solid film (~10–3). The proximity of neighboring chains in the films apparently facilitates (hot) exciton dissociation, presumably by allowing the electron and hole to separate on different polymer strands. For both samples, photoexcitation leads to the predominant formation of bound charge pairs (excitons) that can be detected through their polarizability. Surprisingly, the polarizability per absorbed photon is a factor of 3 larger in solution than in the film, suggesting that interchain interactions in the film do not result in a substantial delocalization of the exciton wave function.

The Structure and Dynamics of Molecular Excitons

Abstract: The photophysical behavior of organic semiconductors is governed by their excitonic states. In this review, I classify the three different exciton types (Frenkel singlet, Frenkel triplet, and charge transfer) typically encountered in organic semiconductors. Experimental challenges that arise in the study of solid-state organic systems are discussed. The steady-state spectroscopy of intermolecular delocalized Frenkel excitons is described, using crystalline tetracene as an example. I consider the problem of a localized exciton diffusing in a disordered matrix in detail, and experimental results on conjugated polymers and model systems suggest that energetic disorder leads to subdiffusive motion. Multiexciton processes such as singlet fission and triplet fusion are described, emphasizing the role of spin state coherence and magnetic fields in studying singlet ↔ triplet pair interconversion. Singlet fission provides an example of how all three types of excitons (triplet, singlet, and charge transfer) may interact to produce useful phenomena for applications such as solar energy conversion.