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Letteratura scientifica selezionata sul tema "Exciton diffusion coefficient"

Autore: Grafiati

Pubblicato: 2 novembre 2024

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Articoli di riviste sul tema "Exciton diffusion coefficient"

Sotome, Hikaru. "(Invited) Comprehensive Analysis of Exciton Diffusion with Time-Resolved Fluorescence Spectroscopy, Anisotropy and Imaging". ECS Meeting Abstracts MA2024-01, n. 13 (9 agosto 2024): 1065. http://dx.doi.org/10.1149/ma2024-01131065mtgabs.

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Excitons produced in materials play a crucial role in photo-energy conversion such as photovoltaics and electroluminescence devices. The temporal and spatial diffusion of excitons is a key factor for dominating the fundamental performance of optoelectronic materials. In this context, analysis of the exciton diffusion dynamics is an important issue for obtaining the rational design of the materials. Excitons diffusing in materials can be characterized by several parameters such as the energy level, orientation of the transition dipole moment and spatial distribution, and the detection of these properties is required for the comprehensive analysis. In the present study, we show time-resolved fluorescence methods for detecting the above relevant properties of excitons. First, time-resolved fluorescence spectroscopy is a basic technique for analyzing the exciton diffusion dynamics. Fluorescence intensity is detected as functions of observation wavelength and time, and the spectral intensity and shift of fluorescence bands provide information on the population of excitons and their energy level. For example, dynamic Stokes shift indicates downhill energy migration and excitons are trapped by the defective site in molecular aggregates. Second, fluorescence anisotropy can be a good indicator for tracking the exciton diffusion in amorphous materials. Fluorescence anisotropy is sensitive to orientation change in transition dipole moments (TDMs) between absorption and fluorescence. In systems where the relative orientation of adjacent molecules is different from each other, such as amorphous solids, the exciton diffusion is accompanied with the change in TDM. Thus, appropriate modeling of molecular alignment enables quantitative estimation of the exciton diffusion coefficient and diffusion length from the anisotropy signal. Finally, time-resolved imaging is a combination of time-resolved spectroscopy and super-resolution microscopy, and an emergent technique for visualizing real-space propagation of excitons in materials. The diffraction-limited excitation beam produces excitons in several hundreds of nanometers and the subsequent exciton diffusion is evaluated by the spatial width of the fluorescence spot. The temporal broadening of the fluorescence spot directly reflects the exciton distribution and we can intuitively obtain the diffusion coefficient and length. Unlike the conventional methods for bulk materials, the advantage of the time-resolved imaging is the applicability to materials with nano- and meso-scale heterogeneous structure and it enables site-selective evaluation of the exciton transport capability. In the conference site, we will also show the application of the above methods to supramolecular polymers and thermally activated delayed fluorescence materials. Figure 1

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Glazov, M. M., Z. A. Iakovlev e S. Refaely-Abramson. "Phonon-induced exciton weak localization in two-dimensional semiconductors". Applied Physics Letters 121, n. 19 (7 novembre 2022): 192106. http://dx.doi.org/10.1063/5.0122633.

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We theoretically study the contribution of quantum effects to the exciton diffusion coefficient in atomically thin crystals. It is related to the weak localization caused by the interference of excitonic wavefunctions on the trajectories with closed loops. Due to the weak inelasticity of the exciton–phonon interaction, the effect is present even if the excitons are scattered by long-wavelength acoustic phonons. We consider exciton interaction with longitudinal acoustic phonons with linear dispersion and flexural phonons with quadratic dispersion. We identify the regimes where the weak localization effect can be particularly pronounced. We also briefly address the role of free charge carriers in the exciton quantum transport and, within the self-consistent theory of localization, the weak localization effects beyond the lowest order.

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Shibu, Abhishek, Camilla Middleton, Carly O. Kwiatkowski, Meesha Kaushal, Jonathan H. Gillen e Michael G. Walter. "Self-Assembly-Directed Exciton Diffusion in Solution-Processable Metalloporphyrin Thin Films". Molecules 27, n. 1 (22 dicembre 2021): 35. http://dx.doi.org/10.3390/molecules27010035.

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The study of excited-state energy diffusion has had an important impact in the development and optimization of organic electronics. For instance, optimizing excited-state energy migration in the photoactive layer in an organic solar cell device has been shown to yield efficient solar energy conversion. Despite the crucial role that energy migration plays in molecular electronic device physics, there is still a great deal to be explored to establish how molecular orientation impacts energy diffusion mechanisms. In this work, we have synthesized a new library of solution-processable, Zn (alkoxycarbonyl)phenylporphyrins containing butyl (ZnTCB4PP), hexyl (ZnTCH4PP), 2-ethylhexyl (ZnTCEH4PP), and octyl (ZnTCO4PP) alkoxycarbonyl groups. We establish that, by varying the length of the peripheral alkyl chains on the metalloporphyrin macrocycle, preferential orientation and molecular self-assembly is observed in solution-processed thin films. The resultant arrangement of molecules consequently affects the electronic and photophysical characteristics of the metalloporphyrin thin films. The various molecular arrangements in the porphyrin thin films and their resultant impact were determined using UV-Vis absorption spectroscopy, steady-state and time-resolved fluorescence emission lifetimes, and X-ray diffraction in thin films. The films were doped with C60 quencher molecules and the change in fluorescence was measured to derive a relative quenching efficiency. Using emission decay, relative quenching efficiency, and dopant volume fraction as input, insights on exciton diffusion coefficient and exciton diffusion lengths were obtained from a Monte Carlo simulation. The octyl derivative (ZnTCO4PP) showed the strongest relative fluorescence quenching and, therefore, the highest exciton diffusion coefficient (5.29 × 10−3 cm2 s−1) and longest exciton diffusion length (~81 nm). The octyl derivative also showed the strongest out-of-plane stacking among the metalloporphyrins studied. This work demonstrates how molecular self-assembly can be used to modulate and direct exciton diffusion in solution-processable metalloporphyrin thin films engineered for optoelectronic and photonic applications.

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Ortiz, Angy L., Graham S. Collier, Dawn M. Marin, Jennifer A. Kassel, Reynolds J. Ivins, Nicholas G. Grubich e Michael G. Walter. "The effects of heavy atoms on the exciton diffusion properties in photoactive thin films of tetrakis(4-carbomethoxyphenyl)porphyrins". Journal of Materials Chemistry C 3, n. 6 (2015): 1243–49. http://dx.doi.org/10.1039/c4tc02232g.

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The exciton diffusion coefficient (D) and exciton diffusion length (L_D) for three tetrakis(4-carbomethoxyphenyl)porphyrins were obtained by fitting the quenching efficiency and PL lifetime to a 3D exciton Monte Carlo ediffusion model.

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Achtstein, Alexander W., Sabrine Ayari, Sophia Helmrich, Michael T. Quick, Nina Owschimikow, Sihem Jaziri e Ulrike Woggon. "Tuning exciton diffusion, mobility and emission line width in CdSe nanoplatelets via lateral size". Nanoscale 12, n. 46 (2020): 23521–31. http://dx.doi.org/10.1039/d0nr04745g.

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Donatini, Fabrice, e Julien Pernot. "Exciton diffusion coefficient measurement in ZnO nanowires under electron beam irradiation". Nanotechnology 29, n. 10 (9 marzo 2018): 105703. http://dx.doi.org/10.1088/1361-6528/aaa638.

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MORI, K., M. YOKOYA, H. NISHIMURA, M. NAKAYAMA e H. ISHIBASHI. "SCINTILLATION MECHANISM OF Ce3+ DOPED Gd2SiO5". International Journal of Modern Physics B 15, n. 28n30 (10 dicembre 2001): 3877–80. http://dx.doi.org/10.1142/s0217979201008895.

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Measuring the spectra of absorption, luminescence and excitation, and the decay times of the luminescence, at various temperatures, we investigate the scintillation mechanism of Ce 3+ doped Gd 2 SiO 5 (GSO:Ce). We conclude that the excitation energy created by gamma-ray irradiation relaxes to the core exciton states formed by the 4f-4f transitions of Gd 3+, and the core exciton migrates to collide with Ce 3+, and transfers the energy to Ce 3+ to emit the luminescence. We also conclude that the decay time of the Ce 3+ luminescence in GSO:Ce (70 ns for the case of 0.5 mol% of Ce concentration) is decided by the diffusion time of the core exciton. A very small value for the diffusion coefficient of the core exciton is estimated to be 7× 10-7 cm2/s.

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Londi, Giacomo, Rishat Dilmurat, Gabriele D’Avino, Vincent Lemaur, Yoann Olivier e David Beljonne. "Comprehensive modelling study of singlet exciton diffusion in donor–acceptor dyads: when small changes in chemical structure matter". Physical Chemistry Chemical Physics 21, n. 45 (2019): 25023–34. http://dx.doi.org/10.1039/c9cp05201a.

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We compare two small π-conjugated donor–bridge–acceptor organic molecules with the aim of rationalizing the origin for the enhancement in singlet exciton diffusion coefficient and length in 1 with respect to 2.

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Navozenko, O. M., V. M. Yashchuk, Yu P. Piryatinski, D. Gudeiko, A. P. Naumenko e Yu L. Slominskii. "The Peculiarities of Singlet Electronic Excitation Energy Transfer Processes in Alq3 Films". Ukrainian Journal of Physics 65, n. 3 (26 marzo 2020): 196. http://dx.doi.org/10.15407/ujpe65.3.196.

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The absorption and luminescence of new boron-containing dyes in two-component films of Alq3 (matrix)-dye(impurity) (obtained by the method of thermal vacuum deposition) are studied. The comparison of the spectra of absorption, fluorescence, and fluorescence excitation of a dyes in one-component solutions and double-component films shows the existence of the effective electronic excitation energy transfer (EEET) from the matrix to dye molecules. Time-resolved spectra of two-component films also manifest strong EEET in these systems. For the estimation of the average exciton spreading length in Alq3 films, the diffusion model of the motion of singlet excitons is used. The diffusion coefficient is evaluated using time-resolved spectroscopy. The optimum concentrations of dyes in a light-emitting layer of OLED are evaluated based on experimental data and the used model of EEET.

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Ščajev, Patrik. "Excitation and temperature dependent exciton-carrier transport in CVD diamond: Diffusion coefficient, recombination lifetime and diffusion length". Physica B: Condensed Matter 510 (aprile 2017): 92–98. http://dx.doi.org/10.1016/j.physb.2017.01.021.

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Più fonti

Tesi sul tema "Exciton diffusion coefficient"

Diarra, Cheick Oumar. "Modélisation par dynamique moléculaire ab initio du transport des excitons et du transport thermique dans les semiconducteurs organiques pour la collecte d'énergie". Electronic Thesis or Diss., Strasbourg, 2024. http://www.theses.fr/2024STRAD013.

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L'exciton joue un rôle clé dans le fonctionnement des cellules solaires organiques (OSCs). Comprendre sa dynamique dans les semiconducteurs organiques est essentiel, notamment pour améliorer la longueur de diffusion, une propriété déterminante pour la performance des hétérojonctions planaires, envisagées comme une alternative plus stable aux hétérojonctions en volume (BHJ). Dans la première partie de cette thèse, nous avons développé une approche méthodologique robuste et polyvalente pour évaluer la longueur de diffusion de l'exciton dans les semiconducteurs organiques. Cette approche, basée sur AIMD-ROKS, a été validée avec succès dans le cas du polymère P3HT. Elle a également été appliquée à l'accepteur NFA O-IDTBR, révélant des longueurs de diffusion prometteuses, mais encore insuffisantes pour les hétérojonctions planaires. Dans la deuxième partie de la thèse, le transfert de chaleur dans les semiconducteurs organiques a été exploré, élément crucial pour la performance des dispositifs thermoélectriques. Ces études se sont concentrées sur le P3HT, un matériau utilisé en thermoélectricité. Dans un premier temps, la conductivité thermique au sein des chaînes de P3HT a été étudiée, révélant l'influence de la longueur des chaînes de polymère. Ensuite, les transferts de chaleur entre ces chaînes ont également été examinés
The exciton plays a central role in the functioning of organic solar cells (OSCs). Understanding its dynamics in organic semiconductors is essential, particularly to optimize the diffusion length, a key property for the performance of planar heterojunctions, which are considered as a potentially more stable alternative to bulk heterojunctions (BHJ) in certain contexts. In the first part of this thesis, we developed a robust and versatile methodological approach to evaluate the exciton diffusion length in organic semiconductors. This method, based on AIMD-ROKS, was successfully validated for the P3HT polymer. It was also applied to the NFA O-IDTBR acceptor, revealing promising diffusion lengths, though still insufficient for planar heterojunctions. The second part of the thesis explores heat transfer in organic semiconductors, a crucial element for the performance of thermoelectric devices. These studies focused on P3HT, a material used in thermoelectricity. First, the thermal conductivity within P3HT chains was studied, revealing the influence of polymer chain length. Then, heat transfers between these chains were also examined

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Jardin, Eric. "Détermination des coefficients de masquage et d'anéchoisme des matériaux acoustiques à partir de la mesure des coefficients de transmission et de réflexion de panneaux excités en incidence oblique ou de caractéristiques intrinsèques du matériau". Le Mans, 1997. http://www.theses.fr/1997LEMA1022.

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La mesure en cuve des coefficients complexes de reflexion r et de transmission t d'un panneau excite en incidence oblique permet de determiner les coefficients de masquage c#m et d'anechoisme c#a des materiaux utilises en acoustique sous-marine. Ces parametres definissent l'utilisation la plus adaptee en acoustique sous-marine de ces materiaux en tant que reflecteurs dur, reflecteurs mous, materiaux de masquage ou anechoiques. La premiere partie de ce travail repose sur la determination theorique en incidence oblique des coefficients c#a et c#m suivant r et t ou suivant les modules mecaniques qui caracterisent le materiau teste. Nous etudions la precision experimentale attendue sur c#a et c#m en utilisant soit des mesures en cuve de r et t, soit des mesures rheologiques a l'aide d'un viscoelasticimetre et d'un k-metre. La seconde partie de l'etude est consacree a l'optimisation des mesures experimentales de r et t en utilisant des traitements holographiques. En pratique, si l'excitation est une unique onde plane d'incidence normale, la reponse de l'antenne, principalement concentree dans le domaine propagatif du spectre, peut perturber la mesure. Cependant, l'utilisation d'une excitation a bande large dans l'espace des nombres d'onde permet de reduire les effets de la diffraction. A cet effet, nous etudions l'utilisation d'une antenne cylindrique calibree en champ proche et qui genere plusieurs ondes planes d'incidences specifiees. L'antenne cylindrique est synthetisee a partir d'une colonne generant une onde cylindrique. Les coefficients de ponderations optimaux sont calcules pour chaque position de la colonne autour du panneau. La methode est ensuite testee avec un panneau dont les coefficients sont prealablement determines a partir de mesures rheologiques. Les resultats sont satisfaisants pour un angle d'incidence n'excedant pas 53. Lieu de 40 avec les methodes holographiques usuelles.

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Capitoli di libri sul tema "Exciton diffusion coefficient"

Jagdishbhai Patel, Mayur, Himangshu Baishya, Ritesh Kant Gupta, Rabindranath Garai e Parameswar Krishnan Iyer. "Thin Film Solution Processable Perovskite Solar Cell". In Recent Advances in Multifunctional Perovskite Materials. IntechOpen, 2022. http://dx.doi.org/10.5772/intechopen.106056.

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Perovskite has emerged as a promising light-harvesting material for solar cells due to its higher absorption coefficient, bandgap tunability, low-exciton binding energy, and long carrier diffusion length. These lead to high power conversion efficiency >25% for thin film-based perovskite solar cells (PSCs). Additionally, PSCs can be fabricated through simple and cost-effective solution processable techniques, which make this technology more advantageous over the current photovoltaic technologies. Several solution-processable methods have been developed for fabrication of PSCs. In this chapter, the advantages and disadvantages of various solution processable techniques and their scope for large-scale commercialization will be discussed.

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Pederiva, F., C. J. Umrigar e E. Lipparini. "Diffusion Monte Carlo study of circular quantum dots". In Quantum Monte Carlo, 128. Oxford University PressNew York, NY, 2007. http://dx.doi.org/10.1093/oso/9780195310108.003.00131.

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Abstract Several QMC calculations had earlier treated quantum dots of various shapes and sizes by either variational or diffusion methods. This study extended much farther, with ground and low-lying excited states for circular two-dimensional dots with 2 to 13 electrons. The method was fixed-node diffusion QMC with importance sampling. Comparisons were made with Hartree-Fock and density functional calculations at the LSDA level. The system treated was a standard circular quantum dot with N electrons confined in two dimensions by a parabolic potential V = ½kr2 centered at the origin. The masses, dielectric constants, and the potential energy constants were specified as those for a GaAs crystal. Atomic units were replaced by effective atomic units. Anti-symmetry rules were the same as for atomic systems. Trial functions were expressed for each case as sums of one to five Slater determinants from density functional calculations, along with elaborate generalized Jastrow functions. The coefficients required for satisfying cusp conditions were different from those usually found for three-dimensional problems. A total of 23 cases with different numbers of electrons and L, S eigenstates were treated. The first version of the paper contained a few errors. Corrected results (also with lower uncertainties) were reported in a second version.0 In all cases the diffusion QMC energies were lower than the variational QMC energies, which were in turn lower than the HF energies. Fixed-node error was expected to be small. The differences from LSDA density functional energies were small but not negligible.

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Severson, M. W., e V. Buch. "Quantum Monte Carlo simulation of intermolecular excited vibrational states in the cage water hexamer". In Quantum Monte Carlo, 118. Oxford University PressNew York, NY, 2007. http://dx.doi.org/10.1093/oso/9780195310108.003.00121.

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Abstract The general problem discussed in this paper is that of predicting vibrational excitation in large hydrogen-bonded clusters, and, as the authors point out, “It should be realized that the problem is very difficult.” In this case, the cluster is the cage form of the water hexamer, simplified somewhat by use of rigid-body water molecules. The key to the solution is a new procedure for locating the nodes in the wavefunctions for the excited vibrational states. The method begins with an approximately correct candidate nodal surface, obtained as a zero for a normal coordinate in the harmonic approximation, followed by adjustments to meet the essential criteria for a truly correct nodal surface. These criteria are: (1) energies calculated for either side of a node must be the same, (2) the first derivative of the wavefunction must be continuous across the node, and (3) the wavefunction must be orthogonal to the groundstate wave function. It would seem hopeless to make adjustments to satisfy these criteria, but it was discovered they could be met successfully with nodes constructed from normal coordinates, singly in some cases and in linear combinations of up to three coordinates, subject to trial-and-error adjustments of the coefficients. In testing nodal surfaces, the required diffusion QMC calculations were carried out without importance sampling, so that fluxes into the nodal surface from opposite sides could be determined and mismatches eliminated. Despite the complexity of the systems, the energies for ten different low-lying vibrational states were determined. One of these was assigned to the vibration-rotation tunneling band observed in infrared absorption experimentsa.

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Atti di convegni sul tema "Exciton diffusion coefficient"

Riblet, P., AR Cameron e A. Miller. "Spin-Gratings and In-Well Carrier Transport Measurements in GaAs/AlGaAs Multiple Quantum Wells". In Quantum Optoelectronics. Washington, D.C.: Optica Publishing Group, 1997. http://dx.doi.org/10.1364/qo.1997.qthe.3.

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We have recently demonstrated [1] that transient electron spin gratings created by cross-polarised excitation pulses at a wavelength resonant with the heavy hole exciton, can provide a new and unique way of measuring in-well electron drift mobilities in semiconductor multiple quantum well structures. This compares with the usual transient grating method in which only the ambipolar diffusion coefficient can be determined [2]. A comparison of concentration and spin grating decay rates allows the direct measurement of both the electron and hole drift mobilities in the same sample. In this work we extend these measurements to GaAs/AlGaAs multiple quantum wells with different well widths and compare results obtained under conditions of exciton saturation and broadening.

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Quarles, Gregory J., Andrzej Suchocki, Richard C. Powell e Shui Lie. "Energy transfer in emerald laser crystals". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1987. http://dx.doi.org/10.1364/oam.1987.md8.

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Be3Al2(SiO3)6:Cr3+ (emerald) has important potential applications as a tunable vibronic laser material. The spectra of emerald exhibit structure which can be attributed to Cr3+ ions occupying three nonequivalent crystal field sites. We present here the results of characterizing the optical properties of the Cr3+ ions in emerald using time-resolved site-selection (TRSS) spectroscopy and four-wave mixing (FWM) spectroscopy techniques. The temperature and crossing angle dependence of the FWM signal decay rate are consistent with scattering of the probe beam from a laser-induced population grating of Cr3+ ions. The time evolution of the FWM signal at low temperatures is consistent with the theory of partially coherent exciton migration. The diffusion coefficient D for spatial migration of energy was determined from theoretical fits to the FWM data. D was found to increase exponentially with temperature, consistent with phonon-assisted energy transfer processes. TRSS results demonstrate the presence of short-range energy transfer between ions in nonequivalent types of site, which is significantly different from the long-range migration process probed by FWM measurements.

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Smirl, Arthur L., D. S. McCallum, A. N. Cartwright, X. R. Huang, Thomas F. Boggess e T. C. Hasenberg. "Ultrafast Recovery of Hetero n-i-p-i's by Enhanced In-plane Diffusive Transport". In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1992. http://dx.doi.org/10.1364/up.1992.thc19.

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Hetero n-i-p-i's are one of several semiconductor quantum-well devices that use second-order electro-optic effects and that continue to attract interest for possible applications to low-power two-dimensional switching arrays and all-optical spatial light modulators. The turn-on time for a hetero n-i-p-i device is usually determined by transport perpendicular to the quantum wells. More specifically, it is determined by the time required for carriers generated in the quantum wells to escape the wells and to move to screen the built-in electric field, thus shifting the exciton. Consequently, typical turn-on times are of the order of a few ps. By contrast, when used in the conventional single-beam geometry, the recovery (or turn-off) time of hetero n-i-p-i's is determined by the slow recombination of the spatially-separated charges in the doped regions and is typically in the range of µs-ms. If instead, however, we use a two-beam mixing geometry for the device (where gratings are written in the material by the interference of the two beams), then the decay or turn off of the signal is determined by the decay of the gratings by in-plane transport over micron dimensions. Here, we use transient grating techniques to measure the recovery of such photorefractive and photoabsorptive gratings written in all-binary hetero n-i-p-i's. In this geometry, we show that the separation of photo-generated charge actually speeds the recovery by enhancing the effective in-plane ambipolar diffusion coefficient by roughly an order of magnitude (in contrast to the single beam geometry where charge separation elongates the recombination and recovery time).

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Hodgkiss, Justin. "High exciton diffusion coefficients in fused ring electron acceptor films (Conference Presentation)". In Organic, Hybrid, and Perovskite Photovoltaics XX, a cura di Kwanghee Lee, Zakya H. Kafafi, Paul A. Lane e Ana Flávia Nogueira. SPIE, 2019. http://dx.doi.org/10.1117/12.2538441.

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Li, Jinwei, e Yong Shi. "Electron Transport and Recombination in TiO2 Nanofiber Dye Sensitized Solar Cell". In ASME 2011 International Mechanical Engineering Congress and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/imece2011-64979.

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Dye sensitized solar cells (DSSCs), a new type of photo-electrochemical solar cells, are a promising alternative to the silicon based photovoltaic because they hold advantages of low cost, simple manufacturing processes and higher conversion efficiency compared with other types of excitonic solar cell. DSSCs with conversion efficiencies of up to 11% have been achieved with a highly stable electrolyte under AM1.5G conditions. Recently, one dimensional (1D) electrospun TiO2 nanofibers have been used as the DSSC photoanode to improve the electron transport efficiency and enhance the light harvest efficiency by scattering more light in the red part of the solar spectrum. In this paper, stepped light induced transient measurement of photocurrent and voltage (SLIM-PCV) has been employed to study electron transport and recombination in DSSCs. Electron diffusion coefficients and electron lifetimes were measured with differing light intensities. The electron diffusion coefficients and electron lifetimes strong correlate with intensity, which indicates the trap limited diffusion process for electrons in the TiO2 nanofiber DSSC.

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Ito, Sho, Tomoyuki Tsunoda, Hiroshi Itakura, Weiguang Bao, Daisuke Kitazawa e Takeshi Kinoshita. "Experimental Investigation and Numerical Modeling of Hydrodynamic Characteristics of a Heaving Sea Cage". In ASME 2009 28th International Conference on Ocean, Offshore and Arctic Engineering. ASMEDC, 2009. http://dx.doi.org/10.1115/omae2009-79085.

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With the increasing world demand for seafood and environmental problems in coastal aquaculture, offshore area has been increasingly expected to be utilized for aquaculture. The offshore aquaculture system has fewer effects on the surrounding marine environment through the rapid diffusion of organic wastes from the cultured fish than the coastal one. The offshore area then provides clean waters for cultured fish. On the other hand, the offshore aquaculture system is subject to the severe natural condition such as typhoon attack. Actually, in the current aquaculture system, the offshore fish cages are always submerged around 10m below the sea surface to avoid the effects of high waves and strong currents. However, the safety of the sea cage against the incident wave has seldom been examined, while that against the water current has been analyzed by model tests in tank and numerical simulation. In the present study, therefore, we investigated hydrodynamic property of a heaving sea cage as the first step. Forced oscillation tests and wave exciting force tests have been carried out, and numerical modeling have also been made to estimate hydrodynamic characteristics theoretically and to estimate the drag and mass coefficients. Results of the forced oscillation tests show that the added mass and damping coefficient of sea cage models depend on forced oscillation amplitude. This dependence may be mainly attributed to the deformation of net, and we successfully reduce the dependence on the forced oscillation amplitude in the result of reanalysis which takes into account the deformation of net. Results of measured wave exciting force show that wave exciting forces are not linear in wave amplitude. This may be due to the viscous drag effects as well as the deformation of net. On the other hand, we calculated the flow around a sea cage. This is based on velocity potential and supplemented the effect of viscosity by equivalent linearization. In the boundary condition on the sea cage surface, the vertical velocity to the surface is not equal to zero, but determined by the permeate coefficient of the surface. This permeate coefficient is a function of wave amplitude, wave period and porosity of the net. In the future works, deformation of net should be also taken into account in this calculation.

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Powell, Richard C., Faqir M. Hashmi, Andrzej Suchocki, F. Durville e G. Boulon. "Laser-induced grating spectroscopy of Cr3+-doρed garnets". In OSA Annual Meeting. Washington, D.C.: Optica Publishing Group, 1988. http://dx.doi.org/10.1364/oam.1988.wk3.

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Laser-induced grating measurements were made as a function of laser power and write beam crossing angle for various temperatures between 10 and 300 K on Cr3+ ions in Gd3Ga5O12 (GGG), Gd3Sc2Ga3O12 (GSGG), and GGG mixed with Ca, Mg, and Zr ions. Population gratings were produced in the Cr3+ ions, and the diffusion coefficient describing energy migration among the Cr3+ ions was determined from the grating decay rate. The energy migration was found to increase as the temperature was raised for GGG and to decrease with decreasing temperature for GSGG. This difference is attributed to the differences in the crystal field splittings of the excited states in the two hosts. Enhanced energy diffusion was observed in the multiply doped GGG sample. Contributions to the laser-induced gratings from absorption and dispersion changes were determined, and this was used to provide information on radiationless relaxation and excited state absorption processes. For long writing times, long-lived changes in the refractive index were observed and attributed to optically induced color centers.

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Chen, Chao, e Johann Wurzenberger. "Parameterization of an Electrochemical Battery Model Using Impedance Spectroscopy in a Wide Range of Frequency". In WCX SAE World Congress Experience. 400 Commonwealth Drive, Warrendale, PA, United States: SAE International, 2024. http://dx.doi.org/10.4271/2024-01-2194.

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<div class="section abstract"><div class="htmlview paragraph">The parameterization of the electrochemical pseudo-two-dimensional (P2D) model plays an important role as it determines the acceptance and application range of subsequent simulation studies. Electrochemical impedance spectroscopy (EIS) is commonly applied to characterize batteries and to obtain the exchange current density and the solid diffusion coefficient of a given electrode material. EIS measurements performed with frequencies ranging from 1 MHz down to 10 mHz typically do not cover clearly isolated solid state diffusion processes of lithium ions in positive or negative electrode materials. To extend the frequency range down to 10 μHz, the distribution function of relaxation times (DRT) is a promising analysis method. It can be applied to time-domain measurements where the battery is excited by a current pulse and relaxed for a certain period. By means of curve-fitting techniques, the pulse-relaxation measurement can be transferred in a function suitable for the DRT analysis, which is the basis for constructing additional low-frequency impedance points.</div><div class="htmlview paragraph">In this work, the EIS measured in the frequency domain and the simulated EIS derived from the time-domain measurement by the DRT method are combined to cover all electrochemical processes of the battery, especially the lithium-ion diffusion in the electrodes. The electrical equivalent circuit model (ECM) consisting of resistors, ZARC elements and Warburg elements in the frequency domain is applied to fit the EIS curve and identify the P2D model parameters. By investigating the intercalation processes using the distribution function of the differential capacity (DDC) technique, particles with different particle sizes are considered and their corresponding solid diffusion coefficients are identified by the established ECM. The consistency between time- and frequency-domain data is elaborated based on a model of a commercial automotive cell.</div></div>

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Linkersdörfer, S., J. Benzler, K. Luther e J. Troe. "Relaxation of Highly Vibrationally Excited Cycloheptatriene in Liquids Studied by Picosecond UV Absorption Spectroscopy". In International Conference on Ultrafast Phenomena. Washington, D.C.: Optica Publishing Group, 1994. http://dx.doi.org/10.1364/up.1994.wc.2.

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To understand in detail the relaxation of highly vibrationally excited polyatomics in dense fluid media experimental answers on fundamental mechanistic aspects are still urgently needed. It has been demonstrated on the relaxation of azulene that too simple applications of isolated binary collision models do not account for the observed relaxation dynamics in liquid solutions [1] and that e.g. cluster type effects may play a role in media like rare gas liquids [2]. However, much more systematic experimental evidence is necessary to establish how far a gas phase type description of energy transfer rates <ΔE>·Z (with effective collision numbers Z and average amounts of transferred energy <ΔE>) is valid and scales e.g. with D-1 (the inverse self diffusion coefficient of the fluid [3]) as opposed to the onset of basically different energy transfer mechanisms in higher density fluids.

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Cudney, R. S., G. D. Bacher, R. M. Pierce e Jack Feinberg. "Origins of the Photorefractive Phase Shift". In Photorefractive Materials, Effects, and Devices II. Washington, D.C.: Optica Publishing Group, 1991. http://dx.doi.org/10.1364/pmed.1991.tua2.

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There is a spatial phase shift between a sinusoidal light intensity pattern and the resulting refractive index grating formed in a photorefractive crystal. For crystals where diffusion is the dominant mechanism for charge migration, this spatial shift is 1/4 of the grating spacing. Any deviation from this value implies some other transport mechanism, such as an applied or internally developed electric field, or the photogalvanic effect, in which optically excited charges preferentially move in one direction in the crystal. Due to its relevance to beam coupling, this spatial shift has been studied extensively using a variety of methods, most of them interferometric in nature1-5. However, interferometric methods only reveal the phase of the complex beam coupling coefficient, which is not necessarily the spatial phase shift of the electro-optically induced grating. Other effects, such as trap grating coupling, can affect the phase of the total coupling coefficient, and thereby prevent a measurement of the spatial phase shift.

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