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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TL;DR: The charge carrier diffusion length in MAPbBr3 of 100 nm is obtained and a linear dependence is observed since the excitation concentration per particle is significantly less than one, while even the bulk shows linear emission intensity dependence at lower excitation concentrations.
Abstract: Characteristics of nanoscale materials are often different from the corresponding bulk properties providing new, sometimes unexpected, opportunities for applications. Here we investigate the properties of 8 nm colloidal nanoparticles of MAPbBr3 perovskites and contrast them to the ones of large microcrystallites representing a bulk. X-ray spectroscopies provide an exciton binding energy of 0.32 ± 0.10 eV in the nanoparticles. This is 5 times higher than the value of bulk crystals (0.084 ± 0.010 eV), and readily explains the high fluorescence quantum yield in nanoparticles. In the bulk, at high excitation concentrations, the fluorescence intensity has quadratic behavior following the Saha-Langmuir model due to the nongeminate recombination of charges forming the emissive exciton states. In the nanoparticles, a linear dependence is observed since the excitation concentration per particle is significantly less than one. Even the bulk shows linear emission intensity dependence at lower excitation concentrations. In this case, the average excitation spacing becomes larger than the carrier diffusion length suppressing the nongeminate recombination. From these considerations we obtain the charge carrier diffusion length in MAPbBr3 of 100 nm.
203 citations
TL;DR: In this paper, the optical dynamics in aggregates of pseudoisocyanine-bromide and iodide and the results of resonance light scattering (RLS), time-resolved emission, and photon echo decay measurements are discussed.
Abstract: This article reports on the optical dynamics in aggregates of pseudoisocyanine‐bromide and iodide. For PIC‐Br in an ethylene glycol/water glass, the results of resonance light scattering (RLS), time‐resolved emission, and photon echo decay measurements are discussed. Band structure calculations based on a linear‐chain model for the J aggregate have also been performed. The results show that the J band can be described as a disordered Frenkel exciton band in which superradiant states exist that extend over about 100 molecules. Numerical simulation studies of the J band, based on Anderson’s Hamiltonian with uncorrelated diagonal site energies, show that the ratio κ of the disorder parameter D over the nearest‐neighbor coupling parameter J12 is about 0.11. Using the frequency dependence of the ratio between the yields of vibrational fluorescence and Raman scattering as a probe, the dephasing process and derived parameters for the bath correlation function at three different temperatures have also been examin...
203 citations
TL;DR: The fluorescence excitation anisotropy spectra of the porphyrin arrays show that the photoexcitation of the high-energy Soret bands are characteristic of the summation of the individual monomeric transitions with its overall dipole moment deviated from the array chain direction, while the low-energySoret bands result from the exciton splitting between the monomersic transition dipoles in line with the array Chain direction.
Abstract: The molecular design of directly meso−meso-linked porphyrin arrays as a new model of light-harvesting antenna as well as a molecular photonic wire was envisaged to bring the porphyrin units closer for rapid energy transfer. For this purpose, zinc(II) 5,15-bis(3,5-bis(octyloxy)phenyl)porphyrin (Z1) and its directly meso−meso-linked porphyrin arrays up to Z128 (Zn, n represents the number of porphyrins) were synthesized. The absorption spectra of these porphyrin arrays change in a systematic manner with an increase in the number of porphyrins; the high-energy Soret bands remain at nearly the same wavelength (413−414 nm), while the low-energy exciton split Soret bands are gradually red-shifted, resulting in a progressive increase in the exciton splitting energy. The exciton splitting is nicely correlated with the values of cos[π/(N + 1)] according to Kasha's exciton coupling theory, providing a value of 4250 cm-1 for the exciton coupling energy in the S2 state. The increasing red-shifts for the Q-bands are r...
202 citations
TL;DR: In this paper, an electron-hole gas in a simple model semiconductor, with direct gap and isotropic, non degenerate bands, was considered and the Bose condensed ground state of that system as a function of density, using a mean field variational ansatz.
Abstract: We consider an electron-hole gas in a simple model semiconductor, with direct gap and isotropic, non degenerate bands. We study the Bose condensed ground state of that system as a function of density, using a mean field variational ansatz. In a first stage, we ignore screening as well as the spin structure of the carriers. We thus describe the smooth transition between Bose condensation of atomic excitons at low densities, and the « excitonic insulator » state and ultimately electron-hole plasma at high densities. As compared to previous treatments, our approach includes the effect of electron-hole pairing on the ground state, within a simple realistic ansatz.
202 citations
TL;DR: In this paper, the fine structure of the neutral exciton in a single self-assembled InGaAs quantum dot is investigated under the effect of an applied uniaxial stress, and it is shown that using this stretching technique, the quantum dot potential is elastically deformable such that the exciton fine structure splitting can be substantially reduced.
Abstract: The fine structure of the neutral exciton in a single self-assembled InGaAs quantum dot is investigated under the effect of an applied uniaxial stress. The spectrum of the excitonic Rayleigh scattering was measured in reflectivity using high-resolution laser spectroscopy while the sample was submitted to a tunable uniaxial stress along its [110] crystal axis. We show that using this stretching technique, the quantum dot potential is elastically deformable such that the exciton fine structure splitting can be substantially reduced.
202 citations