Journal articles: 'Exciton diffusion coefficient'

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Sotome, Hikaru. "(Invited) Comprehensive Analysis of Exciton Diffusion with Time-Resolved Fluorescence Spectroscopy, Anisotropy and Imaging." ECS Meeting Abstracts MA2024-01, no. 13 (August 9, 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, and S. Refaely-Abramson. "Phonon-induced exciton weak localization in two-dimensional semiconductors." Applied Physics Letters 121, no. 19 (November 7, 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, and Michael G. Walter. "Self-Assembly-Directed Exciton Diffusion in Solution-Processable Metalloporphyrin Thin Films." Molecules 27, no. 1 (December 22, 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, and 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, no. 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, and Ulrike Woggon. "Tuning exciton diffusion, mobility and emission line width in CdSe nanoplatelets via lateral size." Nanoscale 12, no. 46 (2020): 23521–31. http://dx.doi.org/10.1039/d0nr04745g.

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Donatini, Fabrice, and Julien Pernot. "Exciton diffusion coefficient measurement in ZnO nanowires under electron beam irradiation." Nanotechnology 29, no. 10 (March 9, 2018): 105703. http://dx.doi.org/10.1088/1361-6528/aaa638.

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MORI, K., M. YOKOYA, H. NISHIMURA, M. NAKAYAMA, and H. ISHIBASHI. "SCINTILLATION MECHANISM OF Ce3+ DOPED Gd2SiO5." International Journal of Modern Physics B 15, no. 28n30 (December 10, 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, and 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, no. 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, and Yu L. Slominskii. "The Peculiarities of Singlet Electronic Excitation Energy Transfer Processes in Alq3 Films." Ukrainian Journal of Physics 65, no. 3 (March 26, 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 (April 2017): 92–98. http://dx.doi.org/10.1016/j.physb.2017.01.021.

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Yeboah, Douglas, and Jai Singh. "Dependence of Exciton Diffusion Length and Diffusion Coefficient on Photophysical Parameters in Bulk Heterojunction Organic Solar Cells." Journal of Electronic Materials 46, no. 11 (July 19, 2017): 6451–60. http://dx.doi.org/10.1007/s11664-017-5679-2.

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Michaelis de Vasconcellos, Steffen, Robert Schmidt, Roberto Rosati, Samuel Brem, Raul Perea-Causín, Iris Niehues, Johannes Kern, et al. "(Invited) Exciton Transport in Strained 2D Semiconductors." ECS Meeting Abstracts MA2023-02, no. 34 (December 22, 2023): 1626. http://dx.doi.org/10.1149/ma2023-02341626mtgabs.

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Being atomically thin, flexible, and exhibiting considerable light emission and ultrafast non-equilibrium dynamics, semiconducting transition metal dichalcogenides (TMDs) have been considered as promising candidates for next-generation optoelectronic devices. The optical and electronic properties of TMDs are governed by a rich landscape of tightly bound excitons, including regular bright excitons, as well as optically inaccessible dark exciton states. Recently, strain engineering of monolayer TMDs has been introduced to tune their optical properties, such as the exciton transition energy, exciton-phonon coupling, or the Stokes shift [1-3]. Transport of charge carriers is crucial for nanoelectronics. In conventional materials, electronic transport can be conveniently controlled by external electric fields. However, the tightly bound excitons, being neutral particles, are only weakly affected by electrical fields. We demonstrate that mechanical strain can also be used to manipulate the transport of excitons in TMDs. To this end, we apply homogeneous tensile strain to a WS2 monolayer by bending the substrate [1], which causes a redshift of the X0 exciton photoluminescence. By measuring the spatiotemporal photoluminescence after near-resonant excitation with femtosecond laser pulses, we map the spread of excitons and extract the strain-dependent diffusion coefficient [4]. Furthermore, we demonstrate the propagation of excitons in an inhomogeneous strain landscape. We create inhomogeneous tensile strain in TMD monolayers by transferring them onto patterned substrates with nanopillars or by a nanoimprint technique [5]. Due to the redshift of the exciton resonances with applied strain, excitons are expected to move towards high-strain regions in an inhomogeneous strain field - the so-called "funneling" effect. We verify this behavior for the "bright" TMD material monolayer MoSe2. In the case of the "dark" monolayer WS2, we observe exactly the opposite effect. Here, the excitons are expelled from the high-strain regions ("anti-funneling") [6]. By comparing our experimental results with a microscopic theory, we explain this observation by the drift of momentum-dark KΛ excitons, which, in contrast to bright excitons, shift to higher energies with strain. Our joint experiment-theory study highlights the dominant role of momentum-dark excitons for the dynamics in monolayer TMDs and provides crucial design guidelines for TMD devices based on exciton transport. References [1] J. Roldan et al., Journal of Physics: Condensed Matter 27, 313201 (2015) [2] I. Niehues et al., Nano Letters 18, 1751 (2018) [3] I. Niehues et al., Nanoscale 12, 20786 (2020) [4] R. Rosati et al., 2D Materials 8, 015030 (2021) [5] J. Bensmann et al., arXiv:2212.11873 (2022) [6] R. Rosati et al., Nature Communications 12, 7221 (2021)

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Montilla, Francisco, Andrés F. Quintero-Jaime, Francisco Huerta, and César Quijada. "Determination of exciton diffusion coefficient in conjugated polymer films: Novel method based on spectroelectrochemical techniques." Electrochimica Acta 387 (August 2021): 138419. http://dx.doi.org/10.1016/j.electacta.2021.138419.

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Ligthart, Arnout, Xander de Vries, Peter A. Bobbert, and Reinder Coehoorn. "Single-layer method for quantifying the triplet exciton diffusion coefficient in disordered organic semiconductor materials." Organic Electronics 77 (February 2020): 105510. http://dx.doi.org/10.1016/j.orgel.2019.105510.

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Yao, Wendian, Dong Yang, and Dehui Li. "(Poster Award - 2nd Place) Layer-Number Engineered Momentum-Indirect Interlayer Excitons with Large Spectral Tunability." ECS Meeting Abstracts MA2023-02, no. 34 (December 22, 2023): 1642. http://dx.doi.org/10.1149/ma2023-02341642mtgabs.

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The diversity of two-dimensional (2D) materials provides van der Waals heterostructures with abundant degrees of freedom and makes the family a promising candidate to realize novel optoelectronic devices and an attractive platform for exploring physical phenomena. Interlayer excitons in type-II van der Waals heterostructures are equipped with an oriented permanent dipole moment and long lifetime and thus would allow promising applications in excitonic and optoelectronic devices. However, in the widely studied van der Waals heterostructures constructed by transition metal dichalcogenides, the formation of interlayer excitons is limited by the lattice mismatch, rotational and translational alignment between the constituent layers, increasing the complexity of the device fabrication. Here, I will report on the robust momentum-indirect interlayer exciton emission with widely tunable emission energy via layer engineering in transition metal dichalcogenide/2D perovskite heterostructures. The transition metal dichalcogenides with different thicknesses and 2D perovskites with different layer numbers of the inorganic octahedral slabs are stacked to form type-II van der Waals heterostructures without considering special orientation arrangement and momentum mismatch. The presence of interlayer excitons is supported by the excitation-power- and temperature-dependent photoluminescence studies, photoluminescence excitation spectroscopy, time-resolved photoluminescence decay studies and electric field-dependent photoluminescence studies. Taking advantage of the thickness- or layer-number-dependence of the electronic band structure of the constituent materials, the emission energy of the interlayer excitons in our heterostructures can be tuned from 1.3 eV to 1.6 eV, providing strong evidence for the applications of van der Waals interface engineering to broad-spectrum optoelectronics. In addition, the diffusion coefficient of interlayer excitons in our heterostructures can be estimated to be ~10 cm2 s−1, which is at least one order of magnitude larger than that in the van der Waals heterostructures with Moiré superlattice, suggesting a non-localized nature that would be beneficial to the excitonic devices. Our study would offer new insights into the nature of interlayer excitons and provoke further research into their dynamics.

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Paulson, Bjorn, Yeonhee Shin, Akimitsu Okamoto, Yeon-Mok Oh, Jun Ki Kim, and Chan-Gi Pack. "Poly(A)+ Sensing of Hybridization-Sensitive Fluorescent Oligonucleotide Probe Characterized by Fluorescence Correlation Methods." International Journal of Molecular Sciences 22, no. 12 (June 16, 2021): 6433. http://dx.doi.org/10.3390/ijms22126433.

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Ribonucleic acid (RNA) plays an important role in many cellular processes. Thus, visualizing and quantifying the molecular dynamics of RNA directly in living cells is essential to uncovering their role in RNA metabolism. Among the wide variety of fluorescent probes available for RNA visualization, exciton-controlled hybridization-sensitive fluorescent oligonucleotide (ECHO) probes are useful because of their low fluorescence background. In this study, we apply fluorescence correlation methods to ECHO probes targeting the poly(A) tail of mRNA. In this way, we demonstrate not only the visualization but also the quantification of the interaction between the probe and the target, as well as of the change in the fluorescence brightness and the diffusion coefficient caused by the binding. In particular, the uptake of ECHO probes to detect mRNA is demonstrated in HeLa cells. These results are expected to provide new insights that help us better understand the metabolism of intracellular mRNA.

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Ikyo, B. A., A. F. Ochai, and A. Itodo. "Determination of Efficiency Parameters in tin Halide Perovskite Solar Cells." NIGERIAN ANNALS OF PURE AND APPLIED SCIENCES 1 (March 8, 2019): 294–300. http://dx.doi.org/10.46912/napas.52.

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Perovskite solar cells have gained significant attention in photovoltaic research. Just within a few years, the efficiencies of perovskite-based solar cells have been improved significantly to over 20% which makes them comparably efficient to silicon-based solar cells. The reason for such high recorded efficiencies are due to perovskites ease of processing, a high carrier diffusion length, low exciton binding energy and high absorption coefficient. Theoretical calculations were carried out based on the detailed balanced model on some Tin Halide Perovskite absorbers. For CH3 NH3 SnI3 , results obtained for V oc, Joc , FF and n are 1.14V, 34.4 mA/cm 2, 0.725and 5.56% respectively. For CH3 NH3 SnIBr2 values obtained for Voc , J oc, FF are 1.37V, 24.03mA/cm2, 0.784 and 5.22% respectively. For CH3 NH3 SnI2 Br values obtained for Voc , Joc , FF are 1.38V, 20.04 mA/cm2, 0.810 and 4.69% Also for CH3 NH3 SnBr3 , results obtained for Voc , Joc , FF are 1.44V, 14.52mA/cm2, 0.881 and 3.21% respectively.

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Zelenin, Yu A., and T. A. Bilyi. "New hyperbolic statistics for the equilibrium distribution function of interacting electrons." Geofizicheskiy Zhurnal 44, no. 6 (February 22, 2023): 112–19. http://dx.doi.org/10.24028/gj.v44i6.273643.

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New statistics of a low-parameter distribution of the sech (ε, µ) type are presented, which reproduce the results of plasma simulation by the method of dynamics of many particles (DMP) with high accuracy. The distribution is based on a conceptual model of a two-component plasma — virtual quasiparticles of negative energy (exciton phase ε<0); the scattering region of positive energy (gas phase ε>0). Optimization and elementary estimates of the applicability of the sech (ε, µ) distribution statistics were made after the results of DMP experiments. The sech (ε,µ) distribution reduces the number of parameters of the three-piece DMP distribution from 4 energy diffusion coefficients (D1, D2, D3, D4) to two — the chemical potential µ and the asymmetry coefficient α. The functional relationship D1, D2, D3, D4 with the chemical potential of the system µ in the sech (ε, µ) distribution is introduced in a similar way to the Einstein relation between mobility and energy diffusion constants. The functional variety of the differential equation belongs to the family of elliptic functions. It is much wider than the hyperbolic solution given, which has significant physical application for complex values of the energy ε. The proposed simplified scheme grounded in the physical interpretation of negative energies can be written for the electrometric electrons of the atmosphere, which previously presented significant methodological difficulties. The chemical potentials of the fluid (metastable states) and gas phases are presented as functions of the plasma imperfection parameter. The problem is posed as an application to the problem of electrometric electrons in the atmosphere. The proposed distribution is not represented in mathematical statistics and statistical physics; it is new and extremely relevant.

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Sneyd, Alexander J., Tomoya Fukui, David Paleček, Suryoday Prodhan, Isabella Wagner, Yifan Zhang, Jooyoung Sung, et al. "Efficient energy transport in an organic semiconductor mediated by transient exciton delocalization." Science Advances 7, no. 32 (August 2021): eabh4232. http://dx.doi.org/10.1126/sciadv.abh4232.

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Efficient energy transport is desirable in organic semiconductor (OSC) devices. However, photogenerated excitons in OSC films mostly occupy highly localized states, limiting exciton diffusion coefficients to below ~10−2 cm2/s and diffusion lengths below ~50 nm. We use ultrafast optical microscopy and nonadiabatic molecular dynamics simulations to study well-ordered poly(3-hexylthiophene) nanofiber films prepared using living crystallization-driven self-assembly, and reveal a highly efficient energy transport regime: transient exciton delocalization, where energy exchange with vibrational modes allows excitons to temporarily re-access spatially extended states under equilibrium conditions. We show that this enables exciton diffusion constants up to 1.1 ± 0.1 cm2/s and diffusion lengths of 300 ± 50 nm. Our results reveal the dynamic interplay between localized and delocalized exciton configurations at equilibrium conditions, calling for a re-evaluation of exciton dynamics and suggesting design rules to engineer efficient energy transport in OSC device architectures not based on restrictive bulk heterojunctions.

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Wang, Kaijie, Ye Tian, Heng Jiang, Meng Chen, and Shuangyan Xu. "Surface Treatment on Nickel Oxide to Enhance the Efficiency of Inverted Perovskite Solar Cells." International Journal of Photoenergy 2019 (November 4, 2019): 1–7. http://dx.doi.org/10.1155/2019/4360816.

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The organic-inorganic hybrid perovskites such as CH3NH3PbI3 have been considered as one of the most promising candidates for the next-generation photovoltaic materials due to its high absorption coefficient, low exciton binding energy, and long diffusion length. Herein, we have chosen NiOx as the hole transport material because metal oxides exhibit robust properties in air. We synthesized the NiOx film by a common sol-gel method. It is found that high-temperature annealing (500°C) is required to ensure the perovskite solar cell (PSC) with an efficiency over 15%. Low-temperature annealing (100°C) cannot convert the precursor materials to fully covered NiOx film, while the PSC based on mediate-temperature annealing (300°C) NiOx has larger resistance and thus lower efficiency. Fortunately, we have found that UV-ozone treatment on the NiOx film can reduce the resistance of the device based on 300°C annealed NiOx. The champion device can reach 16% efficiency with UV-ozone-treated 300°C annealed NiOx. This work has made it possible to reduce the annealing temperature of the sol-gel NiOx for high-efficiency PSCs, and it is believed that this simple surface treatment can be further employed in other metal oxide-based optoelectronic devices.

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Sabelfeld, Karl, and Ivan Aksyuk. "Stochastic simulation of exciton transport in semiconductor heterostructures." Russian Journal of Numerical Analysis and Mathematical Modelling 39, no. 3 (June 1, 2024): 143–56. http://dx.doi.org/10.1515/rnam-2024-0014.

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Abstract Stochastic simulation algorithm for solving exciton transport in a 3D layered semiconductor heterostructure is developed. The problem is governed by a transient drift-diffusion-recombination equation with Dirichlet and Neumann mixed boundary conditions. The semiconductor is represented as an infinite multilayer of finite thickness along the transverse coordinate z. The multilayer is composed by a set of sublayers of different materials so that the excitons have different diffusion and recombination coefficients in each layer. Continuity of solutions and fluxes at the plane interfaces between layers are imposed. The stochastic simulation algorithm solves the transport problem by tracking exciton trajectories in accordance with the probability distributions represented through the Green function of the problem in each sublayer. The method is meshless, the excitons jump only over the plane boundaries of the layers. This explains the high efficiency of the method. Simulation results for transport problems with different mixed boundary conditions are presented.

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Moorthy, Vijai Meyyappan, and Viranjay M. Srivastava. "Device Modelling and Optimization of Nanomaterial-Based Planar Heterojunction Solar Cell (by Varying the Device Dimensions and Material Parameters)." Nanomaterials 12, no. 17 (August 31, 2022): 3031. http://dx.doi.org/10.3390/nano12173031.

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The objective of this work is to model a multi-disciplinary (multi-physics) organic photovoltaic (OPV) using mathematical modeling and analyzing the behavior of a standard planar heterojunction (PHJ) or bi-layer thin-film photovoltaic device, supporting the optimization of an efficient device for future production and assisting in evaluating and choosing the materials required for the efficient device. In order to increase photodiode performance, the device structure and geometrical properties have also been optimized and evaluated. In this work, the effects of varying the device size and transport parameters on the performance parameters of a PHJ OPV structure comprised of Indium Tin Oxide as the anode (ITO), semiconducting single-wall carbon nanotube (s-SWCNT) as the donor, fullerene C70 as the acceptor, and Aluminium (Al) as the cathode have been analyzed. The conclusion suggests that a highly effective ITO/s-SWCNT/C70/Al PHJ solar cell may be fabricated if the suggested device is appropriately built with a thin layer and a high exciton diffusion length, bi-molecular recombination coefficient, and improved mobility charge carriers, in particular hole mobility in the cell’s donor layer. In addition, the displayed current–voltage (I–V) characteristics of the proposed PHJ device are clearly indicated, with the ITO/s-SWCNT/C70/Al combination having the greatest short-circuit current density (Jsc) value of 5.61 mA/cm2, open-circuit voltage (Voc) of 0.7 V, fill factor (FF) of 79% and efficiency (ɳ) of 3.1%. Results show that the electrical performance of organic solar cells is sensitive to the thickness of the photoactive substance. These results open the path for developing inexpensive and highly efficient solar cells.

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Mangrulkar, Mayuribala, and Keith J. Stevenson. "The Progress of Additive Engineering for CH3NH3PbI3 Photo-Active Layer in the Context of Perovskite Solar Cells." Crystals 11, no. 7 (July 13, 2021): 814. http://dx.doi.org/10.3390/cryst11070814.

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Methylammonium lead triiodide (CH3NH3PbI3/MAPbI3) is the most intensively explored perovskite light-absorbing material for hybrid organic–inorganic perovskite photovoltaics due to its unique optoelectronic properties and advantages. This includes tunable bandgap, a higher absorption coefficient than conventional materials used in photovoltaics, ease of manufacturing due to solution processability, and low fabrication costs. In addition, the MAPbI3 absorber layer provides one of the highest open-circuit voltages (Voc), low Voc loss/deficit, and low exciton binding energy, resulting in better charge transport with decent charge carrier mobilities and long diffusion lengths of charge carriers, making it a suitable candidate for photovoltaic applications. Unfortunately, MAPbI3 suffers from poor photochemical stability, which is the main problem to commercialize MAPbI3-based perovskite solar cells (PSCs). However, researchers frequently adopt additive engineering to overcome the issue of poor stability. Therefore, in this review, we have classified additives as organic and inorganic additives. Organic additives are subclassified based on functional groups associated with N/O/S donor atoms; whereas, inorganic additives are subcategorized as metals and non-metal halide salts. Further, we discussed their role and mechanism in terms of improving the performance and stability of MAPbI3-based PSCs. In addition, we scrutinized the additive influence on the morphology and optoelectronic properties to gain a deeper understanding of the crosslinking mechanism into the MAPbI3 framework. Our review aims to help the research community, by providing a glance of the advancement in additive engineering for the MAPbI3 light-absorbing layer, so that new additives can be designed and experimented with to overcome stability challenges. This, in turn, might pave the way for wide scale commercial use.

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Shukla, Naman, K. Anil Kumar, Madhu Allalla, and Sanjay Tiwari. "Analysis of High Efficient Perovskite Solar Cells Using Machine Learning." Journal of Ravishankar University (PART-B) 35, no. 1 (March 8, 2022): 09–15. http://dx.doi.org/10.52228/jrub.2022-35-1-2.

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Affordable manufacturing along with high efficiency perovskite solar cell in photovoltaic technology has everyone's attention. Perovskite, which is in the lead role in solar cells, is full of characteristics such as high absorption coefficient, low exciton binding energy, charge carrier capable of having better mobility as well as more diffusion length and availability in suitable energy band. The application of machine learning technology is proving to be a boon to ensure optimum implementation with different properties in photovoltaic device, design, simple construction process and low-cost price. Machine learning is a branch of artificial intelligence which includes large data aggregation, precise structure property installation, demonstration and final model after model validation. The most of the source of database is the simulation and experimental results, calculations and related literature surveys which have a comprehensive compilation of the performance of hybrid perovskite device, collection of structures and properties of elements. Structure-property relationship installation comes under feature engineering which establishes a clear relationship between structure and the properties. In other demonstration process, proper algorithms are selected, data is generated and tested as well as pure estimated values are taken. This article contains a detailed discussion on the involvement of machine learning technology to build high-performance Perovskite solar cells. Proper selection as well as designing of active perovskite absorbent layer by machine learning successfully establishes results by including other parts such as non-toxic (lead free) and stability. Mature machine learning technology becomes a very essential method in determining the solvent combination of hybrid perovskite and in estimating design of the entire solar cell to ensure optimum implementation in the sector of perovskite solar technology. Finally, a phased concept has been briefly discussed to meet the challenges of machine learning and potential future compatibilities related to the prevalence.

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Sharipov, Alexander, Boris Loukhovitski, and Alexey Pelevkin. "Diffusion Coefficients of Electronically Excited Molecules." Physical-Chemical Kinetics in Gas Dynamics 22, no. 1 (2021): 1–12. http://dx.doi.org/10.33257/phchgd.22.1.913.

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Sharipov, A. S., B. I. Loukhovitski, and A. V. Pelevkin. "Diffusion Coefficients of Electronically Excited Molecules." Fluid Dynamics 58, no. 4 (August 2023): 787–95. http://dx.doi.org/10.1134/s0015462823600943.

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Chandrabose, Sreelakshmi, Kai Chen, Alex J. Barker, Joshua J. Sutton, Shyamal K. K. Prasad, Jingshuai Zhu, Jiadong Zhou, et al. "High Exciton Diffusion Coefficients in Fused Ring Electron Acceptor Films." Journal of the American Chemical Society 141, no. 17 (April 9, 2019): 6922–29. http://dx.doi.org/10.1021/jacs.8b12982.

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Lian, Tianquan. "(Keynote) Rational Design of Quantum Dot/Mediator Interfaces for Triplet Energy Transfer and Photon Upconversion." ECS Meeting Abstracts MA2022-02, no. 20 (October 9, 2022): 911. http://dx.doi.org/10.1149/ma2022-0220911mtgabs.

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Photon upconversion, where two or more low energy photons are converted into one high energy photon, shows great potential in bioimaging, catalysis and solar energy conversion. Photon upconversion has traditionally been realized with lanthanide-doped nanoparticles, or organic dye sensitized triplet-triplet annihilation (TTA) based upconversion platforms. In recent years, QD sensitized triplet-triplet annihilation based upconversion systems have achieved impressive upconversion quantum efficiency and demonstrated many unique advantages, including high photostability, large extinction coefficient, high spectral coverage and tunability, and low singlet-triplet energy gap. In this talk, we discuss our recent work in developing and understanding QD/mediator interface for efficient QD-sensitized photon upconversion. We summarize the main results of time-resolved spectroscopic studies of various factors affecting the rate of triplet energy transfer (TET) from the QD to the surface attached mediator (TET1) and from the mediator to the emitter in solution (TET2). To identify the key design rules, we compare three PbS sensitized upconversion systems using three mediator molecules with the same tetracene triplet acceptor at different distances from the QD. Our results show that the mediator triplet state is mostly formed by direct TET from quantum dot. With increasing distance between the mediator and PbS QD, the efficiency of the TET1 from the QD to the mediator decreases due to a decrease in the rate of this triplet energy transfer step, while the efficiency of the TET2 from the mediator to emitter increases due to a reduction in the QD induced mediator triplet state decay (via the external heavy atom effect). The rate constant of TET2 is three orders of magnitude slower than the diffusion limited value. We show that the effect of QD/mediator on the total unconversion efficiency measured under CW illumination conditions can be well accounted for by the independently determined efficiencies of TET1 and TET2 steps, providing important insight on the design and rational improvement of efficient photon upconversion systems. Ongoing detailed mechanistic studies of the TET1 process shows that both QD bright and dark exciton states contribute to the TET process and higher lying bridge states play significant role in enhancing TET from core/shell QDs.

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Lian, Tianquan. "(Invited) Rational Design of Quantum Dot/Mediator Interfaces for Triplet Energy Transfer and Photon Upconversion." ECS Meeting Abstracts MA2023-01, no. 14 (August 28, 2023): 1362. http://dx.doi.org/10.1149/ma2023-01141362mtgabs.

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Photon upconversion, where two or more low energy photons are converted into one high energy photon, shows great potential in bioimaging, catalysis and solar energy conversion. Photon upconversion has traditionally been realized with lanthanide-doped nanoparticles, or organic dye sensitized triplet-triplet annihilation (TTA) based upconversion platforms. In recent years, QD sensitized triplet-triplet annihilation based upconversion systems have achieved impressive upconversion quantum efficiency and demonstrated many unique advantages, including high photostability, large extinction coefficient, high spectral coverage and tunability, and low singlet-triplet energy gap. In this talk, we discuss our recent work in developing and understanding QD/mediator interface for efficient QD-sensitized photon upconversion. We summarize the main results of time-resolved spectroscopic studies of various factors affecting the rate of triplet energy transfer (TET) from the QD to the surface attached mediator (TET1) and from the mediator to the emitter in solution (TET2). To identify the key design rules, we compare three PbS sensitized upconversion systems using three mediator molecules with the same tetracene triplet acceptor at different distances from the QD. Our results show that the mediator triplet state is mostly formed by direct TET from quantum dot. With increasing distance between the mediator and PbS QD, the efficiency of the TET1 from the QD to the mediator decreases due to a decrease in the rate of this triplet energy transfer step, while the efficiency of the TET2 from the mediator to emitter increases due to a reduction in the QD induced mediator triplet state decay (via the external heavy atom effect). The rate constant of TET2 is three orders of magnitude slower than the diffusion limited value. We show that the effect of QD/mediator on the total unconversion efficiency measured under CW illumination conditions can be well accounted for by the independently determined efficiencies of TET1 and TET2 steps, providing important insight on the design and rational improvement of efficient photon upconversion systems. Ongoing detailed mechanistic studies of the TET1 process shows that both QD bright and dark exciton states contribute to the TET process and higher lying bridge states play significant role in enhancing TET from core/shell QDs.

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30

Nagaya Wong, Narumi, Seung Kyun Ha, Kristopher Williams, Wenbi Shcherbakov-Wu, James W. Swan, and William A. Tisdale. "Robust estimation of charge carrier diffusivity using transient photoluminescence microscopy." Journal of Chemical Physics 157, no. 10 (September 14, 2022): 104201. http://dx.doi.org/10.1063/5.0100075.

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Transient microscopy has emerged as a powerful tool for imaging the diffusion of excitons and free charge carriers in optoelectronic materials. In many excitonic materials, extraction of diffusion coefficients can be simplified because of the linear relationship between signal intensity and local excited state population. However, in materials where transport is dominated by free charge carriers, extracting diffusivities accurately from multidimensional data is complicated by the nonlinear dependence of the measured signal on the local charge carrier density. To obtain accurate estimates of charge carrier diffusivity from transient microscopy data, statistically robust fitting algorithms coupled to efficient 3D numerical solvers that faithfully relate local carrier dynamics to raw experimental measurables are sometimes needed. Here, we provide a detailed numerical framework for modeling the spatiotemporal dynamics of free charge carriers in bulk semiconductors with significant solving speed reduction and for simulating the corresponding transient photoluminescence microscopy data. To demonstrate the utility of this approach, we apply a fitting algorithm using a Markov chain Monte Carlo sampler to experimental data on bulk CdS and methylammonium lead bromide (MAPbBr3) crystals. Parameter analyses reveal that transient photoluminescence microscopy can be used to obtain robust estimates of charge carrier diffusivities in optoelectronic materials of interest, but that other experimental approaches should be used for obtaining carrier recombination constants. Additionally, simplifications can be made to the fitting model depending on the experimental conditions and material systems studied. Our open-source simulation code and fitting algorithm are made freely available to the scientific community.

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Fusco, Roberta, Vincenza Granata, Mario Sansone, Robert Grimm, Paolo Delrio, Daniela Rega, Fabiana Tatangelo, et al. "Intravoxel Incoherent Motion Model of Diffusion Weighted Imaging and Diffusion Kurtosis Imaging in Differentiating of Local Colorectal Cancer Recurrence from Scar/Fibrosis Tissue by Multivariate Logistic Regression Analysis." Applied Sciences 10, no. 23 (December 1, 2020): 8609. http://dx.doi.org/10.3390/app10238609.

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Purpose: The aim of the study is to evaluate the potential of Intravoxel incoherent motion model of diffusion weighted imaging (DWI) and diffusion kurtosis imaging (DKI) in the differentiation of local colorectal cancer recurrence (LCR) from scar/fibrosis tissue in patients that underwent chemo-radiation therapy followed by the total mesorectal excision (TME) for locally advanced rectal cancer (LARC). Methods: Fifty-six patients were retrospectively included for the image analysis. Diffusion and perfusion parameters were extracted by DWI data (apparent diffusion coefficient (ADC), pseudo-diffusion coefficient (Dp), perfusion fraction (fp), and tissue diffusivity (Dt)) and DKI data (mean of diffusion coefficient (MD) and mean of diffusional Kurtosis). Wilcoxon-Mann-Whitney U test, receiver operating characteristic (ROC) analyses, and area under ROC curve (AUC) were used in a univariate statistical analysis. Backward stepwise multivariate logistic regression analysis was also performed. Results: LCR was found in 34 patients and treatment related changes such as scar/fibrosis tissue in 22 patients. At univariate analysis, low performance was reached by the mean value of Kurtosis with and AUC of 0.72 and an accuracy of 75%, respectively. Considering a regression model obtained as weighted sum of the ADC, Kurtosis, fp and Dp mean values, reached an AUC of 0.82 with a sensitivity of 72%, a specificity of 93%, and an accuracy of 81%. Conclusions: DWI derived parameters combined with DKI derived metrics in a multivariate model could allow differentiating of local colorectal recurrence from scar/fibrosis tissue after TME of LARC.

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Chen, Chuan, Guanzhao Wen, Zijie Xiao, Jun Peng, Rong Hu, Zhifeng Chen, Chengyun Zhang, and Wei Zhang. "Charge Photogeneration and Recombination Dynamics in PTQ10:Y6 Solar Cells." Photonics 9, no. 12 (November 23, 2022): 892. http://dx.doi.org/10.3390/photonics9120892.

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In this work, charge photogeneration dynamics in PTQ10:Y6 solar cells were studied by steady-state and time-resolved spectroscopies. For neat donor and acceptor films, we determined the exciton diffusion coefficients of PTQ10 and Y6 as 1.3 × 10−3 cm2·s−1 and 6.8 × 10−3 cm2·s−1, respectively. Furthermore, we find the LUMO and HOMO level offsets of 0.14 eV and 0.11 eV are sufficient for the dissociation of donor and acceptor excitons, respectively. For PTQ10:Y6 blend films, we find DIO additive could increase the scales of acceptor and donor phases. The acceptor phase increased slightly from 17.2 nm to 20.0 nm, while the donor phase increased from 2.3 nm to 5.8 nm. In addition, we find bimolecular recombination is a critical form for carrier recombination and DIO additive can significantly suppress the carrier recombination rate of PTQ10:Y6 active layer in an ultrafast time scale. This work is helpful for understanding the charge photogeneration processes in non-fullerene polymer solar cells.

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33

Bates, Matthew, Sophia Y. Lunt, and Richard R. Lunt. "Impact of charge character on anionic cyanine-based organic salt photovoltaics." Journal of Applied Physics 132, no. 8 (August 28, 2022): 085501. http://dx.doi.org/10.1063/5.0104901.

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Small bandgap organic compounds with absorption in the near-infrared are exciting materials for a variety of applications ranging from light harvesters in photovoltaics to active agents in photodynamic therapy. Organic salts, a class of small molecule organic compounds comprised of an ionic chromophore and a counterion, have been used in opaque and transparent photovoltaics, primarily as donor materials in bilayer architectures. They possess excellent molecular extinction coefficients with near-infrared selective absorption, adjustable bandgaps, and tunable energy levels. To approach organic salt photovoltaics from a new perspective, we fabricated devices with an unexplored group of anionic salts comprised of a near-infrared absorbing chromophore paired with a varying number of cationic counterions. We observed different donor and acceptor decay trends in external quantum efficiencies that allowed us to separate and independently quantify exciton diffusion and charge transfer for each salt. Increased charge character on the chromophore greatly improves hole transport, as anions with a net −3 charge have charge collection lengths greater than four times those of corresponding singly charged chromophores. This presents an interesting platform for independent quantification of exciton diffusion and charge transport of an active material in a single photovoltaic device and demonstration of the important role of charge on the chromophore. The dependence of charge transport capabilities on charge character of the chromophore will be a useful tool in the design of future organic salts to engineer materials for higher efficiency transparent photovoltaics.

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BRAUN, OLEG M., IRINA I. ZELENSKAYA, and YURI S. KIVSHAR. "DIFFUSION IN THE FRENKEL–KONTOROVA MODEL WITH ANHARMONIC INTERATOMIC INTERACTIONS." International Journal of Modern Physics B 08, no. 17 (July 30, 1994): 2353–89. http://dx.doi.org/10.1142/s0217979294000968.

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Low-temperature diffusion and transport properties of the generalized Frenkel–Kontorova model are investigated analytically in the framework of a phenomenological approach which treats a system of strongly interacting atoms as a system of weaklyinteracting quasiparticles (kinks). The model takes into account realistic (anharmonic) interaction of particles subjected into a periodic substrate potential, and such a generalization leads to a series of novel effects which we expect are related to the experimentally-observed phenomena in several quasi-one-dimensional systems. Analysing the concentration dependences in the framework of the kink phenomenology, we use the renormalization procedure when the atomic structure with a complex unit cell is treated as (more simple) periodic structure of kinks. Using phenomenology of the ideal kink gas, the low-temperature states of the chain are described as those consisting of "residual" kinks supplemented by thermally-excited kinks. This approach allows us to describe the ground states of the chain as a hierarchy of "melted" kink lattices. Dynamical and diffusion properties of the system are then described in terms of the kink dynamics and kink diffusion. The motion equation for a single kink is reduced to a Langevin-type equation which is investigated with the help of the Kramers theory. Susceptibility, conductivity, self-diffusion and chemical diffusion coefficients of the chain are calculated as functions of the kink diffusion coefficient. In this way, we qualitatively analyze, for the first time to our knowledge, dependence of the different diffusion coefficients on the concentration of atoms in the chain. The results are applied to describe peculiarities in conductivity and diffusion coefficients of quasi-one-dimensional systems, in particular, superionic conductors and anisotropic layers of atoms adsorbed on crystal surfaces which were earlier investigated experimentally.

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35

Pataraya, A. D., and T. A. Pataraya. "Non-linear dynamo waves in an incompressible medium when the turbulence dissipative coefficients depend on temperature." Annales Geophysicae 15, no. 1 (January 31, 1997): 97–100. http://dx.doi.org/10.1007/s00585-997-0097-z.

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Abstract. Non-linear α-ω; dynamo waves existing in an incompressible medium with the turbulence dissipative coefficients depending on temperature are studied in this paper. We investigate of α-ω solar non-linear dynamo waves when only the first harmonics of magnetic induction components are included. If we ignore the second harmonics in the non-linear equation, the turbulent magnetic diffusion coefficient increases together with the temperature, the coefficient of turbulent viscosity decreases, and for an interval of time the value of dynamo number is greater than 1. In these conditions a stationary solution of the non-linear equation for the dynamo wave's amplitude exists; meaning that the magnetic field is sufficiently excited. The amplitude of the dynamo waves oscillates and becomes stationary. Using these results we can explain the existence of Maunder's minimum.

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Takeda, Jun, Takenari Goto, and Masahiro Matsuoka. "Lifetime and Diffusion Coefficient of Free and Momentarily Localized Excitons in Red-HgI2." Journal of the Physical Society of Japan 57, no. 9 (September 15, 1988): 3248–55. http://dx.doi.org/10.1143/jpsj.57.3248.

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37

Flanders, Nathan C., Matthew S. Kirschner, Pyosang Kim, Thomas J. Fauvell, Austin M. Evans, Waleed Helweh, Austin P. Spencer, Richard D. Schaller, William R. Dichtel, and Lin X. Chen. "Large Exciton Diffusion Coefficients in Two-Dimensional Covalent Organic Frameworks with Different Domain Sizes Revealed by Ultrafast Exciton Dynamics." Journal of the American Chemical Society 142, no. 35 (July 11, 2020): 14957–65. http://dx.doi.org/10.1021/jacs.0c05404.

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Lavenda, B. H. "On the Law of Equipartition for Translational Motion of Excited Molecules in Equilibrium with Thermal Radiation." Zeitschrift für Naturforschung A 44, no. 4 (April 1, 1989): 273–77. http://dx.doi.org/10.1515/zna-1989-0404.

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Abstract Einstein’s radiation theory consists of two parts: the derivation of Planck's radiation law from a physical mechanism of absorption and emission of radiation by excited molecules that are in thermal equilibrium with the radiation field and a demonstration of the validity of the law of equipartition of energy for the translational motion of the molecules. Several incongruities are observed: Einstein could not have legitimately substituted back into his dynamical equilibrium condition, valid at any finite temperature, a limiting condition between the coefficients of absorption and stimulated emission that he obtained in the high temperature limit. His justification of the law of equipartition involves, on the one hand, treating the motion of the excited molecule as brownian motion while, on the other hand, employing special relativity to obtain an expression for the diffusion coefficient. In the former the velocity of the molecule is a stochastic variable while in the latter it is a uniform velocity. Hence equipartition does not hold for the translational motion.

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39

Borowicz, Paweł, and Bernhard Nickel. "The Kinetics of Joined Action of Triplet-Triplet Annihilation and First-Order Decay of Molecules in T1State in the Case of Nondominant First-Order Process: The Kinetic Model in the Case of Spatially Periodic Excitation." Journal of Spectroscopy 2013 (2013): 1–16. http://dx.doi.org/10.1155/2013/346826.

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In this paper the model developed for estimation of the diffusion coefficient of the molecules in the triplet state is presented. The model is based on the intuitive modification of the Smoluchowski equation for the time-dependent rate parameter. Since the sample is irradiated with the spatially periodic pattern nonexponential effects can be expected in the areas of the constructive interference of the exciting laser beams. This nonexponential effects introduce changes in the observed kinetics of the diffusion-controlled triplet-triplet annihilation. Due to irradiation with so-called long excitation pulse these non-exponential effects are very weak, so they can be described with introducing very simple correction to the kinetic model described in the first paper of this series. The values of diffusion coefficient of anthracene are used to calculate the annihilation radius from the data for spatially homogeneous excitation.

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40

Kucharek, H., M. Scholder, and A. P. Matthews. "Three-dimensional simulation of the electromagnetic ion/ion beam instability: cross field diffusion." Nonlinear Processes in Geophysics 7, no. 3/4 (December 31, 2000): 167–72. http://dx.doi.org/10.5194/npg-7-167-2000.

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Abstract. In a system with at least one ignorable spatial dimension charged particles moving in fluctuating fields are tied to the magnetic field lines. Thus, in one-and two-dimensional simulations cross-field diffusion is inhibited and important physics may be lost. We have investigated cross-field diffusion in self-consistent 3-D magnetic turbulence by fully 3-dimensional hybrid simulation (macro-particle ions, massless electron fluid). The turbulence is generated by the electromagnetic ion/ion beam instability. A cold, low density, ion beam with a high velocity stream relative to the background plasma excites the right-hand resonant instability. Such ion beams may be important in the region of the Earth's foreshock. The field turbulence scatters the beam ions parallel as well as perpendicular to the magnetic field. We have determined the parallel and perpendicular diffusion coefficient for the beam ions in the turbulent wave field. The result compares favourably well (within a factor 2) with hard-sphere scattering theory for the cross-field diffusion coefficient. The cross-field diffusion coefficient is larger than that obtained in a static field with a Kolmogorov type spectrum and similar total fluctuation power. This is attributed to the resonant behaviour of the particles in the fluctuating field.

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Suzuki, S., and H. Itoh. "Determination of diffusion, reflection and deexcitation coefficients of metastable excited Ne(3P2) atom." Journal of Physics D: Applied Physics 49, no. 18 (April 5, 2016): 185202. http://dx.doi.org/10.1088/0022-3727/49/18/185202.

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Song, Xiaolei, Ji Yi, and Jing Bai. "A Parallel Reconstruction Scheme in Fluorescence Tomography Based on Contrast of Independent Inversed Absorption Properties." International Journal of Biomedical Imaging 2006 (2006): 1–7. http://dx.doi.org/10.1155/ijbi/2006/70839.

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Based on an independent forward model in fluorescent tomography, a parallel reconstructed scheme for inhomogeneous mediums with unknown absorption property is proposed in this paper. The method considers the two diffusion equations as separately describing the propagation of excited light in tissues with and without fluorescent probes inside. Then the concentration of fluorophores is obtained directly through the difference between two estimations of absorption coefficient which can be parallel inversed. In this way, the multiparameter estimation problem in fluorescent tomography is transformed into two independent single-coefficient determined schemes of diffusion optical tomography (DOT). Any algorithms proved to be efficient and effective in DOT can be directly applied here. In this study the absorption property is estimated from the independent diffusion equations by a gradient-based optimization method with finite element method (FEM) solving the forward model. Simulation results of three representative occasions show that the reconstructed method can well estimate fluorescent property and tissue absorption distribution.

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Cheon, Na Young, Hyun-Suk Kim, Jung-Eun Yeo, Orlando D. Schärer, and Ja Yil Lee. "Single-molecule visualization reveals the damage search mechanism for the human NER protein XPC-RAD23B." Nucleic Acids Research 47, no. 16 (August 2, 2019): 8337–47. http://dx.doi.org/10.1093/nar/gkz629.

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Abstract DNA repair is critical for maintaining genomic integrity. Finding DNA lesions initiates the entire repair process. In human nucleotide excision repair (NER), XPC-RAD23B recognizes DNA lesions and recruits downstream factors. Although previous studies revealed the molecular features of damage identification by the yeast orthologs Rad4-Rad23, the dynamic mechanisms by which human XPC-RAD23B recognizes DNA defects have remained elusive. Here, we directly visualized the motion of XPC-RAD23B on undamaged and lesion-containing DNA using high-throughput single-molecule imaging. We observed three types of one-dimensional motion of XPC-RAD23B along DNA: diffusive, immobile and constrained. We found that consecutive AT-tracks led to increase in proteins with constrained motion. The diffusion coefficient dramatically increased according to ionic strength, suggesting that XPC-RAD23B diffuses along DNA via hopping, allowing XPC-RAD23B to bypass protein obstacles during the search for DNA damage. We also examined how XPC-RAD23B identifies cyclobutane pyrimidine dimers (CPDs) during diffusion. XPC-RAD23B makes futile attempts to bind to CPDs, consistent with low CPD recognition efficiency. Moreover, XPC-RAD23B binds CPDs in biphasic states, stable for lesion recognition and transient for lesion interrogation. Taken together, our results provide new insight into how XPC-RAD23B searches for DNA lesions in billions of base pairs in human genome.

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Cheshire, Thomas P., Jéa Boodry, Erin A. Kober, M. Kyle Brennaman, Paul G. Giokas, David F. Zigler, Andrew M. Moran, et al. "A quantitative model of charge injection by ruthenium chromophores connecting femtosecond to continuous irradiance conditions." Journal of Chemical Physics 157, no. 24 (December 28, 2022): 244703. http://dx.doi.org/10.1063/5.0127852.

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A kinetic framework for the ultrafast photophysics of tris(2,2-bipyridine)ruthenium(II) phosphonated and methyl-phosphonated derivatives is used as a basis for modeling charge injection by ruthenium dyes into a semiconductor substrate. By including the effects of light scattering, dye diffusion, and adsorption kinetics during sample preparation and the optical response of oxidized dyes, quantitative agreement with multiple transient absorption datasets is achieved on timescales spanning femtoseconds to nanoseconds. In particular, quantitative agreement with important spectroscopic handles—the decay of an excited state absorption signal component associated with charge injection in the UV region of the spectrum and the dynamical redshift of a ∼500 nm isosbestic point—validates our kinetic model. Pseudo-first-order rate coefficients for charge injection are estimated in this work, with an order of magnitude ranging from 1011 to 1012 s−1. The model makes the minimalist assumption that all excited states of a particular dye have the same charge injection coefficient, an assumption that would benefit from additional theoretical and experimental exploration. We have adapted this kinetic model to predict charge injection under continuous solar irradiation and find that as many as 68 electron transfer events per dye per second take place, significantly more than prior estimates in the literature.

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Neimontas, K., R. Aleksiejūnas, M. Sūdžius, Kęstutis Jarašiūnas, and Peder Bergman. "Optical Studies of Nonequilibrium Carrier Dynamics in Highly Excited 4H-SiC Epitaxial Layers." Materials Science Forum 483-485 (May 2005): 413–16. http://dx.doi.org/10.4028/www.scientific.net/msf.483-485.413.

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We applied picosecond four-wave mixing technique to investigate carrier diffusion and recombination in n-type 4H-SiC epilayers. The dependence of bipolar diffusion coefficient D on photocarrier density was measured in range from ~ 1017 to ~ 1020 cm-3. We determined a decrease of D value from 3.4 to 2.2 cm2/s with increase of the photoexcitation level in range from ~ 1017 to ~ 1019 cm-3, and found its increase up to 3.8 cm2/s at carrier density above 1020 cm-3. Auger recombination governed decrease of carrier lifetime from 11 ns at ~ 1017 cm-3 to 1.8 ns at ~ 1020 cm- 3 has also been observed.

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46

Li, Shenghong, and Junting Lv. "Stochastic stability and the moment Lyapunov exponent for a gyro-pendulum system driven by a bounded noise." Mechanical Sciences 14, no. 2 (December 13, 2023): 545–55. http://dx.doi.org/10.5194/ms-14-545-2023.

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Abstract. The stochastic stability of a gyro-pendulum system parametrically excited by a real noise is investigated by the moment Lyapunov exponent in the paper. Using the spherical polar and non-singular linear stochastic transformations and combining these with Khasminskii's method, the diffusion process and the eigenvalue problem of the moment Lyapunov exponent are obtained. Then, applying the perturbation method and Fourier cosine series expansion, we derive an infinite-order matrix whose leading eigenvalue is the second-order expansion g2(p) of the moment Lyapunov exponent. Thus, an infinite sequence for g2(p) is constructed, and its convergence is numerically verified. Finally, the influences of the system and noise parameters on stochastic stability are given such that the stochastic stability is strengthened with the increased drift coefficient and the diffusion coefficient has the opposite effect; among the system parameters, only the increase in k and A0 strengthens moment stability.

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Iglev, Hristo, Martin K. Fischer, and Alfred Laubereau. "Electron detachment from anions in aqueous solutions studied by two- and three-pulse femtosecond spectroscopy." Pure and Applied Chemistry 82, no. 10 (June 30, 2010): 1919–26. http://dx.doi.org/10.1351/pac-con-09-12-04.

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The electron photodetachment of the aqueous halides and hydroxide is studied after resonant excitation in the lowest charge-transfer-to-solvent (CTTS) state. The initially excited state is followed by an intermediate assigned to a donor-electron pair that displays a competition of recombination and separation. Using pump–repump–probe (PREP) spectroscopy, the pair species is verified via a secondary excitation with separation of the pairs so that the yield of released electrons is increased. The observed recombination process on the one hand and the similar absorptions of the intermediate and the hydrated electron on the other hand suggest that the donor-electron pairs incorporate only few if not just one water molecule. The geminate dynamics measured in the various CTTS systems reveal a strong influence of the parent radical. The electron survival probability decreases significantly from 0.77 to 0.29 going from F– to OH–. The extracted dissociation rates of the halogen-electron pairs seem to be proportional to the mutual diffusion coefficients of the geminate particles, while such a relation between the recombination rate and the diffusion coefficient is not found. Results for I– show that excitation of a higher-lying CTTS state opens a new relaxation channel, which directly leads to a fully hydrated electron, while the relaxation channel discussed above is not significantly affected.

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48

Li, G., A. Bruno, M. A. Lee, N. Lugaz, G. A. de Nolfo, and J. M. Ryan. "Interpreting the Observed Positive Correlation between the Event-integrated Fluence and the Rollover Energy of Solar Energetic Particle Events by the PAMELA Mission with Coupled Hydromagnetic Wave Excitation and Proton Acceleration at Shocks in the Low Corona." Astrophysical Journal 936, no. 1 (September 1, 2022): 91. http://dx.doi.org/10.3847/1538-4357/ac81c2.

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Abstract An analytical model for diffusive shock acceleration (DSA) at one-dimensional stationary planar shocks in the lower corona is presented. The model introduces an upstream escape boundary through which a constant flux of protons streaming upstream out of the system is allowed. The nonvanishing flux of streaming protons out of the system limits the maximum attainable energy of DSA and produces a rollover in the high-energy spectra of the shock-accelerated protons. The condition for the rollover energy derived from the model can account for the approximately linear relation between the natural logarithm of event-integrated fluences and the natural logarithm of rollover energies as demonstrated in Bruno et al. Solar energetic particle (SEP) events with higher integrated fluences in principle exhibit higher rollover energies since proton-excited hydromagnetic waves in the turbulent sheath reduce the proton diffusion coefficient and throttle the upstream streaming of protons. The consistency between the observation and the theory of DSA at shocks in the lower corona serves as evidence for the shock origin of protons of the highest energies in large SEP events.

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Harrison, P. "Differentiating between constant and concentration-dependent diffusion coefficients via the optical spectroscopy of excitons in quantum wells." Semiconductor Science and Technology 11, no. 7 (July 1, 1996): 1022–25. http://dx.doi.org/10.1088/0268-1242/11/7/008.

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50

Kaulachs, I., A. Ivanova, A. Tokmakov, M. Roze, I. Mihailovs, and M. Rutkis. "Perovskite CH3NH3PbI3–XClx Solar Cells and their Degradation (Part 1: A Short Review)." Latvian Journal of Physics and Technical Sciences 58, no. 1 (January 29, 2021): 44–52. http://dx.doi.org/10.2478/lpts-2021-0005.

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Abstract:

Abstract Development of hybrid organic-inorganic perovskite solar cells (PSC) has been one of the hottest research topics since 2013. Within brief literature review, we would like to achieve two objectives. Firstly, we would like to indicate that a whole set of physical properties, such as high change carrier mobility, very low recombination rates, large carrier life time and diffusion length, large absorption coefficients and very weak exciton binding energies, are defining high power conversion efficiency (PCE) of methyl ammonium lead trihalide SC. The second objective is to draw attention to some, in our opinion, important aspects that previously have not been satisfactory addressed in literature. Although degradation of PSC is widely discussed, processes at very first exposure to ambient conditions after deposition of top electrode are uncovered.

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Journal articles on the topic 'Exciton diffusion coefficient'

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