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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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Journal ArticleDOI
TL;DR: In this article, the photoluminescence (PL) spectrum at 12 K peaks at 1.60 eV and has a full width at half maximum of 0.28 eV.
Abstract: Silicon nanocrystals with diameters ranging from [approximate]2 to 5.5 nm were formed by Si ion implantation into SiO2 followed by annealing. After passivation with deuterium, the photoluminescence (PL) spectrum at 12 K peaks at 1.60 eV and has a full width at half maximum of 0.28 eV. The emission is attributed to the recombination of quantum-confined excitons in the nanocrystals. The temperature dependence of the PL intensity and decay rate at several energies between 1.4 and 1.9 eV was determined between 12 and 300 K. The temperature dependence of the radiative decay rate was determined, and is in good agreement with a model that takes into account the energy splitting between the excitonic singlet and triplet levels due to the electron-hole exchange interaction. The exchange energy splitting increases from 8.4 meV for large nanocrystals ([approximate]5.5 nm) to 16.5 meV for small nanocrystals ([approximate]2 nm). For all nanocrystal sizes, the radiative rate from the singlet state is 300–800 times larger than the radiative rate from the triplet state.

196 citations

Journal ArticleDOI
TL;DR: In this article, a unified microscopic theoretical framework for the calculation of optical excitations in molecular and semiconductor materials is presented, where the hierarchy of many-body density matrices for a pair-conserving many-electron model and the Frenkel exciton model is rigorously truncated to a given order in the radiation field.
Abstract: A unified microscopic theoretical framework for the calculation of optical excitations in molecular and semiconductor materials is presented. The hierarchy of many-body density matrices for a pair-conserving many-electron model and the Frenkel exciton model is rigorously truncated to a given order in the radiation field. Closed equations of motion are derived for five generating functions representing the dynamics up to third order in the laser field including phonon degrees of freedom as well as all direct and exchange-type contributions to the Coulomb interaction. By eliminating the phonons perturbatively the authors obtain equations that, in the case of the many-electron system, generalize the semiconductor Bloch equations, are particularly suited for the analysis of the interplay between coherent and incoherent dynamics including many-body correlations, and lead to thermalized exciton (rather than single-particle) distributions at long times. A complete structural equivalence with the Frenkel exciton model of molecular materials is established. [S0034-6861(98)00201-3]

196 citations

Journal ArticleDOI
TL;DR: In this paper, the photoconductivity of CdSe quantum dot films treated with a variety of reagents was measured and the changes in photocurrent with treatment were largely a consequence of increased quantum dot surface passivation and decreased quantum dot spacing, regardless of whether the molecules used for treatment are conjugated or able to cross-link the quantum dots.
Abstract: We present measurements of photoconductivity in CdSe quantum dot films treated with a variety of reagents. While the photocurrent of untreated samples is highly voltage dependent at all voltages, after treatment the photocurrent is much larger, depends strongly on voltage at low voltage, displays a linear region above a voltage threshold, and finally saturates at high voltage. All regions of the current-voltage curves after treatment can be reproduced with a model that requires noninjecting contacts and a field dependent exciton ionization efficiency that saturates to unity. This model is shown to be consistent with the trends observed with different treatments. The changes in photocurrent with treatment are shown to be largely a consequence of increased quantum dot surface passivation and decreased quantum dot spacing, regardless of whether the molecules used for treatment are conjugated or able to cross-link the quantum dots.

196 citations

Journal ArticleDOI
TL;DR: In this paper, a one-dimensional numerical model for the quantitative simulation of multilayer organic light emitting diodes (OLEDs) is presented, which encompasses bipolar charge carrier drift with field-dependent mobilities and space charge effects, charge carrier diffusion, trapping, bulk and interface recombination, singlet exciton diffusion and quenching effects.
Abstract: A one-dimensional numerical model for the quantitative simulation of multilayer organic light emitting diodes (OLEDs) is presented. It encompasses bipolar charge carrier drift with field-dependent mobilities and space charge effects, charge carrier diffusion, trapping, bulk and interface recombination, singlet exciton diffusion and quenching effects. Using field-dependent mobility data measured on unipolar single layer devices, reported energetic levels of highest occupied and lowest unoccupied molecular orbitals, and realistic assumptions for experimentally not direct accessible parameters, current density and luminance of state-of-the-art undoped vapor-deposited two- and three-layer OLEDs with maximum luminance exceeding 10000 cd/m2 were successfully simulated over 4 orders of magnitude. For an adequate description of these multilayer OLEDs with energetic barriers at interfaces between two adjacent organic layers, the model also includes a simple theory of charge carrier barrier crossing and recombinati...

196 citations

Journal ArticleDOI
TL;DR: In this article, the steady-state and time-resolved luminescence characteristics of CdTe nanocrystals with cubic zinc blende structure were studied at room and liquid nitrogen temperatures.
Abstract: Thiol-capped CdTe nanocrystals with cubic zinc blende structure are synthesized in aqueous solution. Their steady-state and time-resolved luminescence characteristics are studied at room and liquid nitrogen temperatures. A strong exciton luminescence peak at 2.3 eV dominates the emission spectrum of CdTe nanocrystals at room temperature, whereas the trap band centered at 2.0 eV undergoes substantial temperature quenching. Luminescence excitation spectra reveal different channels leading to radiative recombination via either excitons or traps. The mean luminescence decay time of CdTe nanocrystals at room temperature decreases from 120 ns at 1.94 eV to 20 ns at 2.43 eV. Luminescence decay kinetics of CdTe nanocrystals are strongly nonexponential and are described by extremely broad lifetime distributions lying within the range from a few hundred picoseconds to a few hundred nanoseconds.

196 citations


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Performance
Metrics
No. of papers in the topic in previous years
YearPapers
20231,269
20222,623
20211,045
20201,157
20191,096
20181,057