Tesis sobre el tema "Exciton dynamic"
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Heiber, Michael C. "Dynamic Monte Carlo Modeling of Exciton Dissociation and Geminate Recombination in Organic Solar Cells". University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1353092083.
Texto completoTamai, Yasunari. "Excited State Dynamics in Nanostructured Polymer Systems". 京都大学 (Kyoto University), 2013. http://hdl.handle.net/2433/174961.
Texto completoVisnevski, Dmitri. "Collective dynamics of excitons and exciton-polaritons in nanoscale heterostructures". Phd thesis, Université Blaise Pascal - Clermont-Ferrand II, 2013. http://tel.archives-ouvertes.fr/tel-00914332.
Texto completoAbbas, Chahine. "Optical spectroscopy of indirect excitons and electron spins in semiconductor nanostructures". Thesis, Montpellier, 2019. http://www.theses.fr/2019MONTS049.
Texto completoThis work provides an optical study of spin dynamics in two different systems: electrons gas in n-doped CdTe thin layers, and indirect excitons in asymmetric GaAs coupled quantum wells. Time and polar resolved photoluminescence and pump-probe spectroscopy allowed the determination of both the lifetime and the relaxation time of indirect excitons.The global behaviour of the dedicated biased sample has been described, major technical constraints have been pointed out and optimal working conditions have been identified. In photoluminescence, we obtained a lifetime of 15 ns and a spin relaxation time of 5 ns. Pump-probe spectroscopy with an exceptional delay range shown that longer characteristic times could be obtained increasing the delay between two laser pulses.An other optical method has been used to study electrons in CdTe thin layers. Spin noise spectroscopy has recently emerged as an ideal tool to study dynamics of spin systems through their spontaneous fluctuations which are encoded in the polarisation state of a laser beam by means of Faraday rotation. Common spin noise setups provide only temporal fluctuations, spatial information being lost averaging the signal on the laser spot. Here, we demonstrate the first implementation of a spin noise setup providing both spatial and temporal spin correlations thanks to a wave vector selectivity of the scattered light. This gave us the opportunity to measure both the spin relaxation time and the spin diffusion coefficient. This complete vision of the spin dynamics in CdTe has been compared to our understanding of spin physics in GaAs. Against all odds, this knowledge seems not to be directly transposable from GaAs to CdTe
Sajjad, Muhammad Tariq. "Exciton dynamics in carbon nanotubes". Thesis, University of Surrey, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.576127.
Texto completoBouet, Louis. "Valley dynamics and excitonic properties in monolayer transition metal dichalcogenides". Thesis, Toulouse, INSA, 2015. http://www.theses.fr/2015ISAT0033/document.
Texto completoThe possibility of isolating transition metal dichalcogenide monolayers by simple experimental means has been demonstrated in 2005, by the same technique used for graphene. This has sparked extremely diverse and active research by material scientists, physicists and chemists on these perfectly two-dimensional (2D) materials. Their physical properties inmonolayer formare appealing both fromthe point of view of fundamental science and for potential applications. Transition metal dichalcogenidemonolayers such asMoS2 have a direct optical bandgap in the visible and show strong absorption of the order of 10% per monolayer. For transistors based on single atomic layers, the presence of a gap allows to obtain high on/off ratios.In addition to potential applications in electronics and opto-electronics these 2D materials allow manipulating a new degree of freedom of electrons, in addition to the spin and the charge : Inversion symmetry breaking in addition to the strong spin-orbit coupling result in very original optical selection rules. The direct bandgap is situated at two non-equivalent valleys in k-space, K+ and K−. Using a specific laser polarization, carriers can be initialized either in the K+ or K− valley, allowing manipulating the valley index of the electronic states. This opens up an emerging research field termed "valleytronics". The present manuscript contains a set of experiments allowing understanding and characterizing the optoelectronic properties of these new materials. The first chapter is dedicated to the presentation of the scientific context. The original optical and electronic properties of monolayer transition metal dichalcogenides are demonstrated using a simple theoreticalmodel. The second chapter presents details of the samples and the experimental setup. Chapters 3 to 6 present details of the experiments carried out and the results obtained. We verify experimentally the optical selection rules. We identify the different emission peaks in the monolayer materials MoS2, WSe2 and MoSe2. In time resolved photoluminescence measurements we study the dynamics of photo-generated carriersand their polarization. An important part of this study is dedicated to experimental investigations of the properties of excitons, Coulomb bound electron-hole pairs. In the final experimental chapter, magneto-Photoluminescence allows us to probe the electronic band structure and to lift the valley degeneracy
Brüggemann, Ben. "Theory of ultrafast exciton dynamics in photosynthetic antenna systems". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät I, 2004. http://dx.doi.org/10.18452/15037.
Texto completoThe multi-exciton description of excitation energy transfer in chromophore complexes and biological light harvesting antenna systems is extended to include the exciton-exciton annihilation processes. To achieve a complete microscopic description the approach is based on intra--chromophore internal conversion processes which leads to non-radiative transitions from higher to lower lying exciton manifolds. Besides an inclusion of exciton-exciton annihilation the used multi-exciton density matrix theory also accounts for a coupling to low-frequency vibrational modes and the radiation field. Concentrating on transitions from the two- to the single-exciton manifold exact and approximate expressions for the annihilation rate are derived. A first application of the introduced extended multi-exciton density matrix theory is given by the computation of ultrafast transient absorption spectra. To elucidate the process of exciton-exciton annihilation in intensity dependent transient absorption data the approach is applied to the B850 ring of the LH2 found in rhodobacter sphaeroides. The signatures of exciton-exciton annihilation as well as the influence of static disorder are discussed in detail. The simulations of transient absorption including static disorder and orientational averaging are in good agreement with experimental data. The recently published structure of the Photosystem I (PS1) of Synechococcus elongatus made it for the first time possible to introduce an excitonic model for the 96 chlorophylls embedded in the protein matrix of that core-antenna system, as presented in this work. The challenge has been to reproduce linear frequency domain spectra in a wide temperature range as well as the time resolved fluorescence. The couplings and the dipole-moments of the chlorophylls are extracted from the x-ray crystal structure. Since the position of the energetic levels of the chlorophylls depend on the respective surrounding their determination is achieved by fitting low temperature absorption, linear dichroism and circular dichroism at the same time. After assigning some chromophores to the red-most states, an evolutionary algorithm is used to get the best fit. The quality of the resulting PS1 model (additionally accounting for inhomogeneous line broadening) is confirmed in calculating time dependent fluorescence spectra which show a good agreement with recent experimental results. The outlined method is also applicable to other photosynthetic antenna systems. The above described exciton models successfully explain the respective measurements. In a second step, they will be used to propose a new type of experiment, the exciton control experiment. Based on an exciton model for the FMO complex of Prosthecochloris aestuarii and the proposed PS1 model of Synechococcus elongatus one studies the laser pulse formation of excitonic wavepackets, i.e. a coherent superposition of excitonic states similar to vibrational wavepackets. Optimal Control theory is used to calculate the shape of femtosecond laser pulses that leads to a spatial localization of excitation energy. The possibility to populate such a localized target state is demonstrated, even in the presence of disorder or exciton-exciton annihilation, and it is shown that the efficiency of localization as well as the length the most suited pulses strongly depend on temperature.
Nelson, Delene J. "Exciton operators, communication relations and dynamics". Thesis, National Library of Canada = Bibliothèque nationale du Canada, 1997. http://www.collectionscanada.ca/obj/s4/f2/dsk2/ftp01/MQ33420.pdf.
Texto completoLagoudakis, Pavlos G. "Exciton polariton dynamics in semiconductor microcavities". Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274583.
Texto completoGrevatt, Treena. "Exciton spin dynamics in quantum wells". Thesis, University of Southampton, 1996. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.242274.
Texto completoWen, Patrick Ph D. Massachusetts Institute of Technology. "Correlated exciton dynamics in semiconductor nanostructures". Thesis, Massachusetts Institute of Technology, 2013. http://hdl.handle.net/1721.1/82325.
Texto completoCataloged from PDF version of thesis.
Includes bibliographical references (p. 211-223).
The absorption and dissipation of energy in semiconductor nanostructures are often determined by excited electron dynamics. In semiconductors, one fundamentally important electronic state is an exciton, an excited electron bound to a positively charged vacancy. Excitons can become correlated with other excitons, mutually influencing one another and exhibiting collective properties. The focus of this dissertation concerns the origins, effects, and control of correlated excitons in semiconductor nanostructures. Correlated Coulomb interactions can occur between excitons, resulting in energy shifts and dephasing in each exciton. Two-dimensional Fourier-transform optical spectroscopy is a powerful tool to understand Coulomb correlations; the technique relates exciton dynamics during distinct time periods. However, the technique is still limited by weak spectral features. Using two-dimensional pulse shaping methods, waveforms of excitation fields were tailored to selectively amplify spectral features of correlated exciton states in gallium arsenide quantum wells. With the aid of theoretical models, 2D spectra of quantum wells revealed clear contributions of Coulomb correlations to the exciton dynamics. Time and power dependent properties of the 2D spectra indicate several mechanisms for exciton interactions that are neglected in commonly used theoretical models. If a semiconductor material is fabricated within a microcavity, optical fields can be trapped around the semiconductor, strongly distorting properties of the semiconductor excitons and forming new quasi-particles called exciton-polaritons. Theoretical work has suggested exciton-polariton Coulomb correlation strengths can be reduced compared to that of excitons. Using two-dimensional Fourier-transform optical spectroscopy, control of Coulomb correlations was demonstrated by varying the cavity structure. The cavity fields were also shown to induce high-order correlated interactions among exciton-polaritons. A macroscopic quantum degenerate system of exciton-polaritons can also become correlated, exhibiting long-range order typical of a Bose-Einstein condensate. However, unlike a Bose-Einstein condensate, exciton-polartions are not typically in thermal equilibrium. Using a sample with exciton-polariton lifetimes longer than previous samples, the macroscopic behavior of exciton-polaritons was investigated by imaging the exciton-polariton photoluminescence. Condensation depended significantly on spatially-varying potential energy surfaces. Using optically-induced harmonic potential barriers, thermal equilibrium among exciton-polaritons was achieved, with exciton-polaritons forming a Bose-Einstein distribution at densities above and below the condensation phase transition.
by Patrick Wen.
Ph.D.
Tozer, Oliver. "Exciton dynamics in disordered conjugated polymers". Thesis, University of Oxford, 2016. https://ora.ox.ac.uk/objects/uuid:1d899235-07fe-4a06-8146-d1b2bb113850.
Texto completoLee, Chee Kong Ph D. Massachusetts Institute of Technology. "Simulating exciton dynamics in organic semiconductors". Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/121782.
Texto completoCataloged from PDF version of thesis.
Includes bibliographical references (pages 105-116).
Organic semiconductors are carbon-based semiconductors with number of unique benefits over traditional semiconductors such as low production costs, versatile synthesis processes, and high portability. Unlike traditional crystalline semiconductors that exhibit high level of homogeneity, organic semiconductors are spatially and temporally heterogeneous due to the weak van der Waals intermolecular forces. In this thesis we utilize computational and theoretical methods to investigate how this heterogeneity affects the electronic properties in organic semiconductors. In particular, we focus on two microscopic processes fundamental to the performance of organic semiconductors: the transport of Frenkel exciton and dissociation of charge-transfer (CT) exciton. Frenkel excitons are tightly bound electron-hole pairs created upon photo-excitation of molecules and they carry the excess energy imparted by photons.
We employ theoretical approach that combines molecular dynamics and semi-empirical electronic structure calculations to reveal the effects of molecular disorder on Frenkel exciton transport in oligothiophene-based molecular semiconductors. Using this approach, we find that the magnitude and details of molecular disorder (i.e. spatial and temporal correlations) could have huge impact on exciton transport in this class of materials. CT excitons are electron-hole pairs partially separated across the donor-acceptor interface. To generate free charges, the oppositely charged electron and hole must overcome an electrostatic binding energy before they undergo ground state recombination. We explore the CT exciton dissociate mechanism and magnetic field effects through a model of quantum spin dynamics combined with a stochastic coarse-grained model of charge transport.
We demonstrate that simulations carried out on our model are capable of reproducing experimental results as well as generating theoretical predictions related to the efficiency of organic electronic materials. Next, we consider the effect of disorder in electronic energy levels on dissociation yield and demonstrate that it is maximized with a finite amount of disorder as a result of non-equilibrium effect.
by Chee Kong Lee.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Chemistry
Nalitov, Anton. "Spin dynamics ande topological effects in physics of indirect excitons and microcavity polaritons". Thesis, Clermont-Ferrand 2, 2015. http://www.theses.fr/2015CLF22569/document.
Texto completoThe present thesis manuscript is devoted to new phenomena in physics of light-matter quasiparticles in heterostructures, related to spin and topology. It is divided into four parts. Chapter 1 gives a necessary background, introducing basic properties of microcavity polaritons and indirect excitons in coupled quantum wells. Chapter 2 is focused on spin dynamics and topological defects formation in indirect exciton many-body systems. The last 2 chapters are related to microcavity-based structures. Chapter 3 is devoted to polariton spin dynamics in optical parametric oscillators. Finally, Chapter 4 studies pillar microcavity lattices and introduces the polariton topological insulator
Daniel, C. "Exciton transfer dynamics in supramolecular semiconductor nanostructures". Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.598264.
Texto completoSiddique, Sofia. "Exciton dynamics in polymer wrapped carbon nanotubes". Thesis, University of Surrey, 2015. http://epubs.surrey.ac.uk/807206/.
Texto completoChatterjee, Sangam. "Exciton formation dynamics in semiconductor quantum wells". Diss., The University of Arizona, 2003. http://hdl.handle.net/10150/280403.
Texto completoCadirci, Musa. "Ultrafast charge dynamics in novel colloidal quantum dots". Thesis, University of Manchester, 2014. https://www.research.manchester.ac.uk/portal/en/theses/ultrafast-charge-dynamics-in-novel-colloidal-quantum-dots(865aba90-9d60-478d-8f49-ad4785516688).html.
Texto completoRoe, Mitchell Gregg. "Dynamics of photogenerated excitons and polarons in emeraldine base /". The Ohio State University, 1987. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487585645577477.
Texto completoBrand, Matthew Anthony. "Optical time resolved spin dynamics in III V semiconductor quantum wells". Thesis, University of Southampton, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.289510.
Texto completoChow, Colin M., Hongyi Yu, Aaron M. Jones, John R. Schaibley, Michael Koehler, David G. Mandrus, R. Merlin, Wang Yao y Xiaodong Xu. "Phonon-assisted oscillatory exciton dynamics in monolayer MoSe2". NATURE PUBLISHING GROUP, 2017. http://hdl.handle.net/10150/627085.
Texto completoMa, Xuekai [Verfasser]. "Nonlinear dynamics of exciton-polariton condensates / Xuekai Ma". Paderborn : Universitätsbibliothek, 2017. http://d-nb.info/1137944048/34.
Texto completoSteiner, Colby Peyton. "Single and multi-exciton dynamics in nanoscale semiconductors". Thesis, Massachusetts Institute of Technology, 2016. http://hdl.handle.net/1721.1/104977.
Texto completoThis electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.
Cataloged from student-submitted PDF version of thesis.
Includes bibliographical references (pages 205-225).
Recent advancements in the synthesis and fabrication of nanoscale semiconductors and optoelectronic devices are revolutionizing an array of industries. Nonlinear spectroscopy is a powerful tool for studying the unique optical and electronic properties of these semiconductors. This thesis describes experiments using a unique multi-dimensional spectrometer to study three semiconductors: double-walled J-aggregate nanotubes, cuprous oxide, and monolayer transition metal dichalcogenides. First, we use two-dimensional correlation spectroscopy and cryogenic tunneling electron microscopy to correlate the excitonic and structural properties of J-aggregate nanotubes in solution. We observe weak coupling between inner and outer wall excitons in both isolated and bundled nanotubes. We also use two-dimensional rephasing spectroscopy to measure the homogeneous and inhomogeneous linewidths in solution at 295 K and in a glass at 10 K and determine dynamic and static disorder dominate, respectively. In addition, we observe photo-induced damage and recovery of nanotubes in the solid state. Quantum process tomography is used to unambiguously elucidate the single-exciton dynamics of J-aggregate nanotubes in solution. Inversion of spectroscopic signals from eight transient grating experiments completely characterizes the time evolution of the single-exciton density matrix by determining the process matrix. We confirm the weak coupling of inner and outer wall excitons and observe no contributions from non-secular processes. Second, we use two-quantum spectroscopy to make the first experimental observation of two-exciton correlations (i.e. biexcitons) in cuprous oxide. The direct measurement of two-exciton correlations supports the proposed mechanism of biexciton-Auger recombination for the efficient suppression of the Bose-Einstein condensation of excitons. Third, we use two-dimensional rephasing spectroscopy to observe substantial inhomogeneous broadening due to large static disorder in monolayer transition metal dichalcogenides. We also use two-dimensional correlation spectroscopy to reveal interactions of excitons with in-plane optical and acoustic phonons. Lastly, we use one- and two-quantum spectroscopy to measure unprecedentedly large inorganic, biexciton binding energies due to reduced dielectric screening in the atomically thin limit. The exciton and phonon dynamics revealed in these experiments contribute to our understanding of the elementary excitations in organic and inorganic nanostructured semiconductors. It is our hope these insights will help guide the design of next generation devices utilizing nanoscale semiconductors.
by Colby Peyton Steiner.
Ph. D. in Physical Chemistry
Brüggemann, Ben. "Theory of ultrafast exciton dynamics in photosynthetic antenna systems". [S.l. : s.n.], 2004. http://deposit.ddb.de/cgi-bin/dokserv?idn=972544046.
Texto completoSchwab, Matthias [Verfasser]. "Exciton Dynamics in Semiconductor Quantum Dot Structures / Matthias Schwab". Aachen : Shaker, 2005. http://d-nb.info/118657657X/34.
Texto completoAl, Otaify Ali Abdullah. "Ultrafast charge dynamics in novel nanoparticles". Thesis, University of Manchester, 2015. https://www.research.manchester.ac.uk/portal/en/theses/ultrafast-charge-dynamics-in-novel-nanoparticles(ec75ab4e-71cd-4051-8683-be3c724746c5).html.
Texto completoVillamil, Franco Carolina. "Ultrafast dynamics of excitons and charge carriers in colloidal perovskite nanostructures studied by time-resolved optical spectroscopies". Thesis, université Paris-Saclay, 2020. http://www.theses.fr/2020UPASF012.
Texto completoHalide perovskites have emerged as very promising photoactive materials due to their outstanding optoelectronic properties combined with low-cost processability. In spite of their successful implementation in photovoltaic or light-emitting devices, a deep understanding of the dynamics of relaxation and recombination is still missing in order to enhance the device performances. This thesis focuses on the study of two major fundamental processes occurring in colloidal halide perovskite nanostructures: the hot charge carrier/exciton relaxation (“cooling”), after excitation above the optical bandgap, and the non-radiative Auger recombination, taking place after high-fluence or high-photon energy excitation. In particular, time-resolved photoluminescence and femtosecond transient absorption spectroscopy were used to investigate the confinement and composition effects in strongly confined two-dimensional (2D) lead iodide perovskite nanoplatelets (NPLs), that were synthesized following the development and optimizations of colloidal methods. For the investigation of the cooling dynamics, a global analysis method based on single value decomposition was used, where the temporal evolution of the spectral lineshapes was modeled with a sequential kinetic scheme. This method was succesfully applied to effectively describe the continuous energy relaxation in weakly-confined thick FAPbI₃ nanoplates (FA=formamidinium) and allowed disantangleting the hot phonon bottleneck from the Auger reheating effects at high excitation fluence. Furthermore, the global analysis was essential to investigate the cooling dynamics in strongly confined 2D NPLs presenting large Stark effects and discrete excitonic band-edge transition far away from the continuum of states (exciton binding energy in several hundreds of meV). As in the weakly confined samples, the cooling rate of the NPLs decreases with the excitation fluence. However, it is faster in more-strongly confined samples, evidencing the absence of an intrinsic phonon bottleneck. Furthermore, the cooling rate and its evolution with the exciton density were found independent of the nature of the internal cations (FA, MA=methylammonium and Cs=cesium). However, when comparing with the rate measured in 2D layered perovskite thin film with equivalent quantum well thickness, the results strongly suggest a role of the surface ligands in the possibility to release the excess energy to the surrounding environment. This ligand-mediated relaxation mechanism becomes dominent in the thinner NPL samples with enhanced exciton/ligand vibrational mode coupling. Then, the multiple exciton recombination dominated by non-radiative Auger recombination (AR) was studied in the strongly-confined 2D perovskite NPLs. Due to the large asymmetric geometry and the limited exciton wavefunction delocalization, the AR rate strongly depends on the exciton density via the initial average inter-exciton distance. At low fluence, this distance is in several tens of nanometers such as the AR is limited by the exciton diffusion in the 2D plane. It thus occurs on a timescale of several hundreds of picoseconds and depends on the sample dimensionality (thickness and lateral sizes). In contrast, high excitation fluences produce “overlapping” excitons with inter-exciton distances of only a few times the exciton Bohr radius, resulting in AR times of less than 10 ps and independent of the NPL composition nor geometry. Finally, the exciton population dynamics of 2D NPLs after excitation in the ultraviolet was measured. The strong dependence of the AR with the inter-exciton distance allows the identification of multiple exciton generation (MEG), which involves the reaction of “geminate biexcitons” produced by the absorption of a single high-energy photon
Wijesundara, Kushal Chinthaka. "Ultrafast Exciton Dynamics and Optical Control in Semiconductor Quantum Dots". Ohio University / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=ohiou1336648375.
Texto completoPeckus, Domantas. "Ultrafast exciton and charge carrier dynamics in nanostructured molecular layers". Doctoral thesis, Lithuanian Academic Libraries Network (LABT), 2013. http://vddb.library.lt/obj/LT-eLABa-0001:E.02~2013~D_20131220_150447-81409.
Texto completoDėl savo unikalių savybių organiniai puslaidininkiai gali būti plačiai pritaikyti įvairiuose optoelektroniniuose prietaisuose: organiniuose šviestukuose, organiniuose lazeriuose, organiniuose tranzistoriuose ir organiniuose šviesos elementuose. Visi šie pritaikymai yra galimi dėl organinių molekulių laidumo. Nepaisant didelių organinių puslaidininkių perspektyvų, jie vis dar yra nukonkuruojami neorganinių puslaidininkių. Pagrindinis šių tezių tikslas yra detaliai ištirti eksitonų ir krūvininkų dinamikos procesus grynuose organiniuose puslaidininkiuose ir jų mišiniuose su fulereno dariniais. Buvo matuoti organiniai ir silicio organiniai puslaidininkiai: poli-di-n-heksilsilanas (PDHS), polifluoreno dariniai F8BT ir PSF-BT, merocianinas MD376. Mišiniuose naudoti fulerenai buvo C60 ir jo darinys PCBM. Tyrimams buvo naudoti ultraspartūs skirtuminės sugerties, fluorescencijos ir integralinės fotosrovės matavimai. PDHS tyrimai atskleidė, kad neorganinės matricos sumažina nespindulinį relaksacijos kanalą. PDHS nanokompozitai gali būti naudojami polimero fluorescencijos savybių: stabilumo, kvantinio našumo pagerinimui. Polifluorenų F8BT ir PSF-BT grynų plėvelių tyrimų metu nustatyti eksitonų-eksitonų anihiliacijos ir eksitonų migracijos skirtumai. Vidumolekulinės krūvio pernašos būsenos formavimasis buvo pasiūlytas PSF-BT grynoms plėvelėms. Pristatyta ilgi gyvuojančių krūvininkų porų formavimosi schema PSF-BT/PCBM mišiniuose. Krūvio pernašos būsenų formavimasis buvo ištirtas... [toliau žr. visą tekstą]
Watkins, Pete. "Modelling of charge and exciton dynamics in organic solar cells". Thesis, University of Bath, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.421254.
Texto completoChang, Wendi. "Modification of exciton energies and dynamics for thin film optoelectronics". Thesis, Massachusetts Institute of Technology, 2017. http://hdl.handle.net/1721.1/109011.
Texto completoCataloged from PDF version of thesis.
Includes bibliographical references (pages 157-171).
Organic and nano-crystal thin film semiconductors have proven to be effective materials for a range of optoelectronic applications including light emitting diodes, visible wavelength lasers, photovoltaics, and sensors. Mediating photons and charges, excitons are responsible for electrical and optical properties in these energetically disordered media. To improve current technology and develop novel applications, a thorough understanding of exciton dynamics is crucial. This thesis focuses on modifying exciton dynamics in organic and nanocrystal thin films with spectroscopic monitoring for optoelectronic applications. First, we study local dielectric effects in doped organic thin films, which depends on material deposition and molecular density. An external pressure technique is used to modify molecular density, tuning exciton energies and dynamics as explained by solvation theory and exciton energy transfer. We extend this molecular density tuning method, coupled with other measurements, including optical imaging, magnetic field effect, and electric field effect to modify and monitor charge transfer (CT) exciton energy and dynamics. As intermediaries between excitons and free charges in organic photovoltaic donor-acceptor material systems, CT exciton state dynamics is still a subject of much debate. The effect of CT spin states on photocurrent generation is explored, revealing guidelines for material selection and molecule engineering with potential benefits in optimizing molecular density. Further investigation of low-energy CT exciton transport leads to evidence of spatial motion between interfacial states, driven by local energy disorder. These techniques and results directly apply to optimizing OPV devices, but may also be extended to other applications. This thesis also includes an investigate of ultrafast electric field effect on organic and colloidal quantum dot thin films, largely unexplored in previous works. We observe exciton luminescence and non-perturbative energy tuning of exciton states under terahertz electromagnetic radiation, developing a potential platform for detectors and cameras for coherent terahertz sensing. Lastly, we discuss a new fabrication technique to integrate organic thin films into micro-electro-mechanical system microcavity device designs. The demonstrated electrically tunable microcavity structures not only applicable as wavelength-tunable lasers and pressure sensors, but also presents a good example of fabrication flexibility and challenges of employing organic and nano-crystal thin films.
by Wendi Chang.
Ph. D.
Kell, Adam. "Energy transfer and exciton dynamics in photosynthetic pigment–protein complexes". Diss., Kansas State University, 2016. http://hdl.handle.net/2097/32539.
Texto completoChemistry
Ryszard J. Jankowiak
The structure-function relationships of natural pigment–protein complexes are of great interest, as the electronic properties of the pigments are tuned by the protein environment to achieve high quantum yields and photon utilization. Determination of electronic structure and exciton dynamics in protein complexes is complicated by static disorder and uncertainties in the properties of system-bath coupling. The latter is described by the phonon profile (or spectral density), whose shape can only be reliably measured experimentally for the lowest energy state. Low-temperature, laser-based spectroscopies are applied towards model pigment–protein complexes, i.e., the Fenna-Matthews-Olson (FMO) and water-soluble chlorophyll-binding (WSCP) complexes, in order to study system-bath coupling and energy transfer pathways. Site-selective techniques, e.g., hole burning (HB) and fluorescence line narrowing, are utilized to overcome static disorder and reveal details on homogeneous broadening. In addition, excitonic calculations with non-Markovian lineshapes provide information on electronic structure and exciton dynamics. A new lognormal functional form of the spectral density is recommended which appropriately defines electron-phonon parameters, i.e., Huang-Rhys factor and reorganization energy. Absorbance and fluorescence spectral shifts and HB spectra reveal that samples of FMO may contain a subpopulation of destabilized proteins with modified HB efficiencies. Simulations of spectra corresponding to intact proteins indicate that the entire trimer has to be taken into account in order to properly describe fluorescence and HB spectra. The redshifted fluorescence spectrum of WSCP is described by uncorrelated energy transfer as opposed to previous models of excited state protein relaxation. Also, based on nonconservative HB spectra measured for WSCP, a mechanism of electron transfer between chlorophylls and aromatic amino acids is proposed.
Reynolds, Luke X. "Transient optical studies of exciton dynamics in organic solar cells". Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/10102.
Texto completoZhu, Han Ph D. Massachusetts Institute of Technology. "Charge and exciton dynamics in quantum dot light-emitting diodes". Thesis, Massachusetts Institute of Technology, 2019. https://hdl.handle.net/1721.1/123240.
Texto completoCataloged from PDF version of thesis.
Includes bibliographical references (pages [159]-174).
Colloidal quantum dot based light-emitting diodes (QD-LEDs) offer the possibility of bright, saturated, and tunable emission for the next generation of display and solid state lighting technologies. In this thesis, we study how the interplay of charges and excitons in a QD-LED affect its operational behavior. In order to construct a physical model of a QD-LED, we start by developing quantitative characterization methods that directly measure charge accumulation and electric field in an operating device. Comparison of measured internal device variables with observed electroluminescence and current density allows us to disentangle the deleterious effects of charge imbalance, electric field, and Joule heating on the external quantum efficiency. We also find that the magnitude of electron accumulation on the QD film is sensitive to its interface with the neighboring hole transport layer (HTL) and can reach nearly one electron per QD even in the best performing device. We next investigate how exciton formation is affected by the high charge density. Since the degree of electron charging of a nanocrystal shifts the energy barrier for hole injection, the kinetics of exciton formation are dependent on electron occupation statistics on the QD film. Using kinetic Monte Carlo simulations that explicitly incorporate both long and short range Coulomb interactions, we find that energetic disorder of the QD film strongly enhances the formation of negatively charged excitons by increasing the population of two-electron occupied QDs. Finally, we demonstrate that the photoluminescence yield of a QD film can be intentionally quenched by up to 99.5% in a QD-LED under reverse bias. This paves the way for a voltage-tuned optical down-conversion device using colloidal QDs.
by Han Zhu.
Ph. D.
Ph.D. Massachusetts Institute of Technology, Department of Physics
Tanese, Dimitrii. "Non-linear dynamics of one-dimensional polaritons gases in semiconductor microcavities". Paris 6, 2013. http://www.theses.fr/2013PA066795.
Texto completoThis PhD thesis is dedicated to the study of one-dimensional polariton gases in semiconductor microcavities. Thanks to the control on the etching of the microstructures, a full engineering of the 1D potential has been obtained and several geometries have been investigated. We have studied the propagation of polaritons inside photonic wires and we evidenced strong reduction of the backscattering against disorder driven by interparticle interactions. Polariton condensation has been investigated in a one-dimensional periodic potential. We have shown how repulsive interactions create localized states inside the energy gap. The nature of these states depends on the relative strength between interparticle interactions and the interactions with the excitonic reservoir. In a time resolved-experiment we have shown the dynamical transition from a regime dominated by interactions with the reservoir to a regime where self-interactions give rise to the formation of gap solitons. Additionally, the potential induced by the interactions with the reservoir allowed us to combine an energy gradient with the periodic lattice. In this configuration, we have observed polaritons Bloch oscillations. Thanks to the potential engineering, we have also implemented a Fibonacci quasi-periodic potential. In this configuration, we have observed the fractal character of the polariton spectrum. Finally, we present a polariton interferometer. The optical control of the phase of the polariton flow allows controlling the intensity and the polarization of the beam transmitted through the device
Rao, Akshay. "On the dynamics of excitons and charges in organic photovoltaics". Thesis, University of Cambridge, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.609909.
Texto completoSwatton, Stewart Nathan Ridgley. "Dynamic excited state properties of organic dyes". Thesis, University of Exeter, 1998. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.244422.
Texto completoKolata, Kolja [Verfasser] y Sangam [Akademischer Betreuer] Chatterjee. "Exciton Dynamics in Perfluoropentacene Single Crystals / Kolja Kolata. Betreuer: Sangam Chatterjee". Marburg : Philipps-Universität Marburg, 2015. http://d-nb.info/1068315571/34.
Texto completoHofmann, Simone. "Exciton Dynamics in White Organic Light-Emitting Diodes comprising Triplet Harvesting". Doctoral thesis, Saechsische Landesbibliothek- Staats- und Universitaetsbibliothek Dresden, 2013. http://nbn-resolving.de/urn:nbn:de:bsz:14-qucosa-117447.
Texto completoIn dieser Arbeit werden verschiedene Ansätze zur Effizienzsteigerung in weißen organischen lichtemittierenden Dioden (OLEDs) erforscht. Hierfür werden im Besonderen Diffusions- und Transferprozesse von angeregten Singulett- und Triplettzuständen untersucht. Zur Erzeugung von weißem Licht wird die sogenannte “triplet harvesting” Methode verwendet, bei der die sonst nicht zur Emission beitragenden Triplettzustände eines fluoreszenten blauen Emitters auf einen hocheffizienten phosphoreszenten Emitter übertragen werden. Dieser liefert dann zusätzliche Emission im niederenergetischen Spektralbereich. Durch triplet harvesting kann die interne Quantenausbeute in OLEDs beträchtlich gesteigert werden. Zunächst wird der bekannte blaue Emitter 4P-NPD als Modellbeispiel untersucht. Mittels zeitlich aufgelöster Spektroskopie kann triplet harvesting auf einen gelben bzw. roten Emitter direkt nachgewiesen werden. Allerdings ist auf Grund der niedrigen Triplettenergie triplet harvesting auf einen grünen Emitter nicht möglich. In Anbetracht dieser Tatsache werden unter Zuhilfenahme quantenchemischer Betrachtungen zwei neue Emittermoleküle, 8M-4P-NPD und 8M-4P-FPD, synthetisiert und auf ihre Eigenschaften und ihre Eignung für triplet harvesting untersucht. Dabei wird zum ersten Mal eine weiße OLED realisiert, in der triplet harvesting von einem blauen Emitter direkt auf einen grünen und einen roten Emitter erfolgt. Des Weiteren wird bei den untersuchten triplet harvesting OLEDs ein zusätzlicher Singulettübertrag auf den phosphoreszenten Emitter beobachtet. Dieser Effekt wird zur Bestimmung der Singulettdiffusionslänge in 4P-NPD genutzt. Der phosphoreszente Emitter dient dabei als Singulettsensor. Über eine Variation des Abstands zwischen Singulettgenerationszone und Sensor wird eine Singulettdiffusionslänge von 4,6 nm bestimmt. Ein weiterer Ansatz zur Effizienzsteigerung besteht in der Optimierung einer aus zwei OLEDs zusammengesetzten Tandem OLED. Bei einer Leuchtdichte von 1000 cd/m² erzielt diese weiße Tandem OLED eine externe Quanteneffizienz von 25% und eine Leistungseffizienz von 33 lm/W mit einem Farbwiedergabeindex (CRI) von 62 und Commission Internationale de l’Eclairage (CIE) Farbkoordinaten von (0,53/0,43). Diese Effizienzen sind vergleichbar mit dem aktuellen Forschungsstand weißer OLEDs. Schließlich wird diese hocheffiziente weiße Tandemstruktur auf eine alternative Elektrode bestehend aus flachgedrückten Silbernanodrähten aufgebracht. Im Vergleich zur konventionellen OLED mit Indiumzinnoxid (ITO) Elektrode erreicht diese ähnlich hohe Effizienzen sowie eine verbesserte Farbstabilität bezüglich des Betrachtungswinkels, was auf die Streueigenschaften der Nanodrähte zurückgeführt werden kann. Bei einer Leuchtdichte von 1000 cd/m² zeigt die OLED mit Silbernanodrahtelektrode Effizienzen von 24% und 30 lm/W bei einem CRI von 69 und CIE Koordinaten von (0,49/0,47)
Ehrenreich, Philipp [Verfasser]. "Exciton Dynamics and Charge Separation in Polymer Thin Films / Philipp Ehrenreich". Konstanz : Bibliothek der Universität Konstanz, 2018. http://d-nb.info/1163537993/34.
Texto completoBirech, Zephania. "Exciton dynamics in tetracene single crystals studied using femtosecond laser spectroscopy". Thesis, Stellenbosch : Stellenbosch University, 2012. http://hdl.handle.net/10019.1/71699.
Texto completoCameron, Alasdair R. "Exciton saturation dynamics and spin gratings in multiple quantum well semiconductors". Thesis, University of St Andrews, 1997. http://hdl.handle.net/10023/14661.
Texto completoBuller, Jakov. "Structure and Dynamics of Microcavity Exciton-Polaritons in Acoustic Square Lattices". Doctoral thesis, Humboldt-Universität zu Berlin, 2018. http://dx.doi.org/10.18452/19328.
Texto completoMicrocavity (MC) exciton-polaritons can form condensates, i.e. macroscopic quantum states (MQSs), as well under a periodic potential modulation. The modulation by a surface acoustic wave (SAW) provides a powerful tool for the formation of tunable lattices of MQSs in semiconductor MC. In this work, fundamental aspects of the structure and dynamics of exciton-polariton condensate in acoustic square lattices were investigated by probing its wavefunction in real- and momentum space using spectral- and time-resolved studies. The MQSs were resonantly excited in an optical parametric oscillator configuration. The tomographic study revealed that the exciton-polariton condensate structure self-organises in a concentric structure, which consists of a single, two-dimensional gap soliton (2D GS) surrounded by one-dimensional MQSs and an incoherent background. 2D GS size tends to saturate with increasing particle density. The experimental results are supported by a theoretical model based on the variational solution of the Gross-Pitaevskii equation. Time-resolved studies showed the evolution of the 2D GS wavefunction at the acoustic velocity. Interestingly, the photoluminescence (PL) intensity emitted by the 2D GS as well as its coherence length oscillate with time. The PL oscillation amplitude depends on the intensity and the size of the exciting laser spot, and increases considerably for excitation intensities close to the optical threshold power for the formation of the MQS. In the outlook, the formation of Tamm-Plasmon/Exciton-Polariton (TPEP) hybrid states and their modulation by SAWs was theoretically discussed. Here, the upper DBR is partly replaced by a thin metal layer placed on top of the MC. In this case, TPEP form by the superposition of Tamm plasmons at the metal-semiconductor interface and the exciton-polaritons in the MC.
Debnath, Arunangshu. "Dynamics and control of open quantum systems : applications to exciton dynamics in quantum dots and vibrational dynamics in carboxyhemoglobin". Toulouse 3, 2013. http://thesesups.ups-tlse.fr/2107/.
Texto completoThis thesis work analyses aspects of dissipative quantum dynamics, with a view to look for further possibilities of controlling the dynamics with shaped laser pulses. The first part concerns the problem of efficient population transfer in mesoscopic zero-dimensional solid state systems - InAs quantum dots embedded in GaAs matrix. In these systems the consequences of laser driving induced dissipation of exciton dynamics are analyzed, in relation to adiabatic population transfer. Specifically, the problem of robust creation of exciton and biexciton states are addressed through numerical simulations and analytical approaches using a non-Markovian density matrix based analysis, suitable for dealing with dissipative quantum dynamics under strong laser fields. A physical picture describing phonon induced dissipation among dressed state has emerged as a consistent interpretation of the underlying dynamics. Furthermore, suitable parameter regimes where efficient population transfer can be achieved are proposed. The second part deals with the population transfer to high lying vibrational states of the CO stretching mode of carboxy-hemoglobin molecule in the native protein environment. On the basis of a fluctuating potential for the CO stretching mode, ultrafast pump-probe spectra are simulated using quantum wave packet propagation. To this end, Local Control Theory was employed to find design a set of laser pulses which accomplish the 'vibrational ladder climbing' and selective state preparation despite the detrimental fluctuations induced by the protein environment. These results will be providing benchmarks for the future experimental efforts
Martelli, F. "WAVEPACKET APPROACHES TO DISSIPATIVE QUANTUM DYNAMICS". Doctoral thesis, Università degli Studi di Milano, 2010. http://hdl.handle.net/2434/150221.
Texto completoNoller, Bastian M. "Excited-State Dynamics of Organic Intermediates". kostenfrei, 2009. http://www.opus-bayern.de/uni-wuerzburg/volltexte/2009/3607/.
Texto completoBrinne, Roos Johanna. "Reaction dynamics on highly excited states". Doctoral thesis, Stockholms universitet, Fysikum, 2009. http://urn.kb.se/resolve?urn=urn:nbn:se:su:diva-27122.
Texto completoVolkov, Victor Vitorovich. "Bacteriorhodopsin excited state dynamics and photochemistry". Diss., Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/26308.
Texto completoSiller, Lidija. "Electronically excited states in surface dynamics". Thesis, University of Cambridge, 1995. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.363321.
Texto completoSills, Andrew Michael. "Excited state dynamics in semiconductor nanostructures". Thesis, University of Leeds, 2017. http://etheses.whiterose.ac.uk/18891/.
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