Topic
Exciton
About: Exciton is a research topic. Over the lifetime, 31603 publications have been published within this topic receiving 810642 citations.
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01 Oct 1996
TL;DR: In this article, a comprehensive model for the low energy excitonic states in 3,4,9,10-perylenetetetracarboxylic dianhydride (PTCDA) was proposed.
Abstract: Excitonic transitions responsible for low energy absorption and fluorescence in dilute solutions and thin films of the organic molecule 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA) have been investigated. Combining the results of concentration-dependent solution and thin film absorption and fluorescence with results on thin film exciton diffusion lengths (presented in the following paper, Paper II), we proposed a comprehensive model for the low energy excitonic states in this archetype molecular crystal. We unambiguously identify an extended free charge transfer state at E F CT = 2.23±0.03 eV which has previously been observed to exhibit effects of quantum confinement in ultrathin layers grown under ultrahigh vacuum. This state self-traps at an energy of E ST CT = 2.11±0.04 eV due to the strong exciton-phonon coupling characteristic of this closely packed organic crystal.
179 citations
TL;DR: In this article, a selfconsistent theory for Frenkel excitons coupled to optical phonons is presented and tested by comparison with numerical calculations, and it is found that the mean-field approach fails to predict accurately vibronic excitations at the upper band edges of the exciton zero-and one-phonon bands.
178 citations
TL;DR: Time-resolved photoluminescence from single InP nanowires containing both wurtzite and zincblende crystalline phases is used to measure the carrier dynamics of quantum confined excitons in a type-II homostructure and demonstrates that the dynamics are consistent with the calculated distribution of confined states for the electrons and holes.
Abstract: We use time-resolved photoluminescence from single InP nanowires containing both wurtzite (WZ) and zincblende (ZB) crystalline phases to measure the carrier dynamics of quantum confined excitons in a type-II homostructure. The observed recombination lifetime increases by nearly 2 orders of magnitude from 170 ps for excitons above the conduction and valence band barriers to more than 8400 ps for electrons and holes that are strongly confined in quantum wells defined by monolayer-scale ZB sections in a predominantly WZ nanowire. A simple computational model, guided by detailed high-resolution transmission electron microscopy measurements from a single nanowire, demonstrates that the dynamics are consistent with the calculated distribution of confined states for the electrons and holes.
178 citations
TL;DR: In this article, the effect of the spin exchange interaction between electron and hole is investigated for the case of excitons originating from one of the valence bands and an $s$-like conduction band, as is the case for IIb-VIb compounds.
Abstract: The effect of the spin-exchange interaction between electron and hole is investigated for the case of excitons originating from one of the $p$-like valence bands and an $s$-like conduction band, as is the case for IIb-VIb compounds. A general exciton matrix is constructed, starting from the work of Pikus. It includes spin-orbit, crystal-field, spin-exchange, and deformation-potential interactions. Use of this matrix then allows a theoretical fit to our experimental data which describes the shift of exciton levels under uniaxial pressure in ZnO, CdS, and CdSe. This fit results in the determination of six deformation potentials, two spin-orbit parameters, the crystal-field parameter, and the exchange parameter. The general theory, when adapted to the zinc-blende structure, allows us to fit our data on cubic ZnS and ZnSe, resulting in a determination of two deformation potentials and the spin-exchange parameter for each compound.
178 citations
TL;DR: A homologous series of six novel oligothiophene-naphthalene diimide-based oligomer semiconductors with a donor-acceptor architecture was synthesized and used to explore a set of criteria for the design of non-fullerene electron acceptor materials for organic solar cells as mentioned in this paper.
Abstract: A homologous series of six novel oligothiophene–naphthalene diimide-based oligomer semiconductors with a donor–acceptor architecture, NDI-nTH (n = 1, 2, 3, 4) and NDI-nT (n = 2, 3), was synthesized and used to explore a set of criteria for the design of non-fullerene electron acceptor materials for organic solar cells. Thin films of the oligomer semiconductors had optical band gaps that varied from 2.1 eV in NDI-1TH and 1.6 eV in NDI-3TH to 1.4 eV in NDI-4TH, demonstrating good potential for light harvesting and exciton generation. The LUMO energy levels of the oligomer semiconductors were similar (ca. −4.0 eV), but the HOMO levels varied from −5.5 eV in NDI-3TH and NDI-4TH to −6.1 eV in NDI-1TH, showing that suitable energy band offsets necessary for efficient photoinduced charge transfer could be achieved with current donor polymers. Single-crystal X-ray structures of NDI-3TH and NDI-4TH showed a slipped face-to-face π-stacking with short intermolecular distances (0.321–0.326 nm), which enabled facile s...
178 citations