WorldWideScience

Sample records for excitonic energy transfer

  1. Plasmon-Exciton Resonant Energy Transfer: Across Scales Hybrid Systems

    Directory of Open Access Journals (Sweden)

    Mohamed El Kabbash

    2016-01-01

    Full Text Available The presence of an excitonic element in close proximity of a plasmonic nanostructure, under certain conditions, may lead to a nonradiative resonant energy transfer known as Exciton Plasmon Resonant Energy Transfer (EPRET process. The exciton-plasmon coupling and dynamics have been intensely studied in the last decade; still many relevant aspects need more in-depth studies. Understanding such phenomenon is not only important from fundamental viewpoint, but also essential to unlock many promising applications. In this review we investigate the plasmon-exciton resonant energy transfer in different hybrid systems at the nano- and mesoscales, in order to gain further understanding of such processes across scales and pave the way towards active plasmonic devices.

  2. Energy and Information Transfer Via Coherent Exciton Wave Packets

    Science.gov (United States)

    Zang, Xiaoning

    associated excitations were dubbed twisted excitons. Twisted exciton packets can be manipulated as they travel down molecular chains, and this has applications in quantum information science as well. In each setting considered, exciton dynamics were initially studied using a simple tight-binding formalism. This misses the actual many-body interactions and multiple energy levels associated real systems. To remedy this, I adapted an existing time-domain Density Functional Theory code and applied it to study the dynamics of exciton wave packets on quasi-one-dimensional systems. This required the use of high-performance computing and the construction of a number of key auxiliary codes. Establishing the requisite methodology constituted a substantial part of the entire thesis. Surprisingly, this effort uncovered a computational issue associated with Rabi oscillations that had been incorrectly characterized in the literature. My research elucidated the actual problem and a solution was found. This new methodology was an integral part of the overall computational analysis. The thesis then takes up the a detailed consideration of the prospect for creating systems that support a strong measure of transport coherence. While physical implementations include molecular assemblies, solid-state superlattices, and even optical lattices, I decided to focus on assemblies of nanometer-sized silicon quantum dots. First principles computational analysis was used to quantify reorganization within individual dots and excitonic coupling between dots. Quantum dot functionalizations were identified that make it plausible to maintain a measure of excitonic coherence even at room temperatures. Attention was then turned to the use of covalently bonded bridge material to join quantum dots in a way that facilitates efficient exciton transfer. Both carbon and silicon structures were considered by considering the way in which subunits might be best brought together. This resulted in a set of design criteria

  3. Radiative energy transfer from MoS2 excitons to surface plasmons

    Science.gov (United States)

    Kang, Yimin; Li, Bowen; Fang, Zheyu

    2017-12-01

    In this work, we demonstrated the energy transfer process from few-layer MoS2 to gold dimer arrays via ultrafast pump-probe spectroscopy. With the overlap between the MoS2 exciton and the designed plasmon dipolar modes in the frequency domain, the exciton energy can be radiatively transferred to plasmonic structures, excited the localized surface plasmon resonance, and then enhanced the oscillation of coherent acoustic phonons. Power-dependent differential reflection signals and an analytical model based on the rate equation of exciton density were carried out to quantitatively study the energy transfer process. Our finding explores the energy flow between MoS2 excitons and surface plasmons, and can be contributed to the design of exciton-plasmon structures utilizing ultrathin materials.

  4. Triplet energy transfer and triplet exciton recycling in singlet fission sensitized organic heterojunctions

    Science.gov (United States)

    Hamid, Tasnuva; Yambem, Soniya D.; Crawford, Ross; Roberts, Jonathan; Pandey, Ajay K.

    2017-08-01

    Singlet exciton fission is a process where an excited singlet state splits into two triplets, thus leading to generation of multiple excitons per absorbed photon in organic semiconductors. Herein, we report a detailed exciton management approach for multiexciton harvesting over a broadband region of the solar spectrum in singlet fission sensitized organic photodiodes. Through systematic studies on the model cascade of pentacene/rubrene/C60, we found that efficient photocurrent generation from pentacene can still occur despite the presence of a >10nm thick interlayer of rubrene in between the pentacene/C60 heterojunction. Our results show that thin rubrene interlayers of thickness operation a rather interesting result. We discuss the role of rubrene interlayer film discontinuity, triplet exciton reflection from rubrene interlayer and triplet energy transfer from rubrene to pentacene layer followed by diffusion of triplet excitons through rubrene as plausible mechanisms that would enable triplet excitons from pentacene to generate significant photocurrent in a multilayer organic heterojunction.

  5. Efficient Exciton Diffusion and Resonance-Energy Transfer in Multi-Layered Organic Epitaxial Nanofibers

    DEFF Research Database (Denmark)

    Tavares, Luciana; Cadelano, Michele; Quochi, Francesco

    2015-01-01

    Multi-layered epitaxial nanofibers are exemplary model systems for the study of exciton dynamics and lasing in organic materials due to their well-defined morphology, high luminescence efficiencies, and color tunability. We resort to temperature-dependent cw and picosecond photoluminescence (PL......) spectroscopy to quantify exciton diffusion and resonance-energy transfer (RET) processes in multi-layered nanofibers consisting of alternating layers of para-hexaphenyl (p6P) and α-sexithiophene (6T), serving as exciton donor and acceptor material, respectively. The high probability for RET processes...... is confirmed by Quantum Chemical calculations. The activation energy for exciton diffusion in p6P is determined to be as low as 19 meV, proving p6P epitaxial layers also as a very suitable donor material system. The small activation energy for exciton diffusion of the p6P donor material, the inferred high p6P...

  6. Modelling excitonic-energy transfer in light-harvesting complexes

    OpenAIRE

    Kramer, Tobias; Kreisbeck, Christoph

    2013-01-01

    The theoretical and experimental study of energy transfer in photosynthesis has revealed an interesting transport regime, which lies at the borderline between classical transport dynamics and quantum-mechanical interference effects. Dissipation is caused by the coupling of electronic degrees of freedom to vibrational modes and leads to a directional energy transfer from the antenna complex to the target reaction-center. The dissipative driving is robust and does not rely on fine-tuning of spe...

  7. Scaling Relations and Optimization of Excitonic Energy Transfer Rates between One-Dimensional Molecular Aggregates

    NARCIS (Netherlands)

    Chuang, Chern; Knoester, Jasper; Cao, Jianshu

    2014-01-01

    We theoretically study the distance, chain length, and temperature dependence of the electronic couplings as well as the excitonic energy transfer rates between one-dimensional (1D) chromophore aggregates. In addition to the well-known geometry dependent factor that leads to the deviation from

  8. Ionization of Water Clusters is Mediated by Exciton Energy Transfer from Argon Clusters

    Energy Technology Data Exchange (ETDEWEB)

    Golan, Amir; Ahmed, Musahid

    2012-01-25

    The exciton energy deposited in an argon cluster, (Arn ,< n=20>) using VUV radiation is transferred to softly ionize doped water clusters, ((H2O)n, n=1-9) leading to the formation of non-fragmented clusters. Following the initial excitation, electronic energy is channeled to ionize the doped water cluster while evaporating the Ar shell, allowing identification of fragmented and complete water cluster ions. Examination of the photoionization efficiency curve shows that cluster evaporation from excitons located above 12.6 eV are not enough to cool the energized water cluster ion, and leads to their dissociation to (H2O)n-2H+ (protonated) clusters.

  9. Modelling excitonic-energy transfer in light-harvesting complexes

    CERN Document Server

    Kramer, Tobias

    2014-01-01

    The theoretical and experimental study of energy transfer in photosynthesis has revealed an interesting transport regime, which lies at the borderline between classical transport dynamics and quantum-mechanical interference effects. Dissipation is caused by the coupling of electronic degrees of freedom to vibrational modes and leads to a directional energy transfer from the antenna complex to the target reaction-center. The dissipative driving is robust and does not rely on fine-tuning of specific vibrational modes. For the parameter regime encountered in the biological systems new theoretical tools are required to directly compare theoretical results with experimental spectroscopy data. The calculations require to utilize massively parallel graphics processor units (GPUs) for efficient and exact computations.

  10. Non-Markovian quantum jumps in excitonic energy transfer

    Energy Technology Data Exchange (ETDEWEB)

    Rebentrost, Patrick; Chakraborty, Rupak; Aspuru-Guzik, Alan

    2009-01-01

    We utilize the novel non-Markovian quantum jump (NMQJ) approach to stochastically simulate exciton dynamics derived from a time-convolutionless master equation. For relevant parameters and time scales, the time-dependent, oscillatory decoherence rates can have negative regions, a signature of non-Markovian behavior and of the revival of coherences. This can lead to non-Markovian population beatings for a dimer system at room temperature. We show that strong exciton-phonon coupling to low frequency modes can considerably modify transport properties. We observe increased excitontransport, which can be seen as an extension of recent environment-assisted quantum transport concepts to the non-Markovian regime. Within the NMQJ method, the Fenna–Matthew–Olson protein is investigated as a prototype for larger photosynthetic complexes.

  11. A simple model for exploring the role of quantum coherence and the environment in excitonic energy transfer.

    Science.gov (United States)

    Manikandan, Sreenath K; Shaji, Anil

    2015-07-28

    We investigate the role of quantum coherence in modulating the energy transfer rate between two independent energy donors and a single acceptor participating in an excitonic energy transfer process. The energy transfer rate depends explicitly on the nature of the initial coherent superposition state of the two donors and we connect it to the observed absorption profile of the acceptor and the stimulated emission profile of the energy donors. We consider simple models with mesoscopic environments interacting with the donors and the acceptor and compare the expression we obtained for the energy transfer rate with the results of numerical integration.

  12. Study of exciton transfer in dense quantum dot nanocomposites

    Science.gov (United States)

    Guzelturk, Burak; Hernandez-Martinez, Pedro Ludwig; Sharma, Vijay Kumar; Coskun, Yasemin; Ibrahimova, Vusala; Tuncel, Donus; Govorov, Alexander O.; Sun, Xiao Wei; Xiong, Qihua; Demir, Hilmi Volkan

    2014-09-01

    Nanocomposites of colloidal quantum dots (QDs) integrated into conjugated polymers (CPs) are key to hybrid optoelectronics, where engineering the excitonic interactions at the nanoscale is crucial. For such excitonic operation, it was believed that exciton diffusion is essential to realize nonradiative energy transfer from CPs to QDs. In this study, contrary to the previous literature, efficient exciton transfer is demonstrated in the nanocomposites of dense QDs, where exciton transfer can be as efficient as 80% without requiring the assistance of exciton diffusion. This is enabled by uniform dispersion of QDs at high density (up to ~70 wt%) in the nanocomposite while avoiding phase segregation. Theoretical modeling supports the experimental observation of weakly temperature dependent nonradiative energy transfer dynamics. This new finding provides the ability to design hybrid light-emitting diodes that show an order of magnitude enhanced external quantum efficiencies.Nanocomposites of colloidal quantum dots (QDs) integrated into conjugated polymers (CPs) are key to hybrid optoelectronics, where engineering the excitonic interactions at the nanoscale is crucial. For such excitonic operation, it was believed that exciton diffusion is essential to realize nonradiative energy transfer from CPs to QDs. In this study, contrary to the previous literature, efficient exciton transfer is demonstrated in the nanocomposites of dense QDs, where exciton transfer can be as efficient as 80% without requiring the assistance of exciton diffusion. This is enabled by uniform dispersion of QDs at high density (up to ~70 wt%) in the nanocomposite while avoiding phase segregation. Theoretical modeling supports the experimental observation of weakly temperature dependent nonradiative energy transfer dynamics. This new finding provides the ability to design hybrid light-emitting diodes that show an order of magnitude enhanced external quantum efficiencies. Electronic supplementary

  13. Role of delocalized exciton states of light-harvesting pigments in excitation energy transfer in natural photosynthesis

    Science.gov (United States)

    Fetisova, Zoya; Mauring, Koit; Taisova, Alexandra

    1995-02-01

    Photosynthesis is an extremely efficient converter of light into chemical energy, with an observed quantum yield for primary photochemistry approximately 90%. To achieve this the photosynthetic apparatus must be highly optimized, and some of the design principles that may be involved have been suggested. The role of delocalized exciton states of light-harvesting pigments in the energy transfer process has been considered by mathematical simulation of the light-harvesting process in model systems. Namely, it has been shown that aggregation of antenna pigments (allowing to consider each aggregate as a supermolecule) is biologically expedient, as an efficient strategy for light harvesting in photosynthesis. The question of whether this design principle is realized in a natural antenna has been examined for the 3D chlorosomal superantenna of green bacteria with the hole-burning spectroscopy. Spectral hole burning studies of intact cells of green bacteria Chlorobium phaeovibriodes. Chloroflexus aurantiacus and Chlorobium limicola have proven that the Qy- absorption system of antenna bacteriochlorophylls e or c (BChl e or BChl c) should be interpreted in terms of the delocalized exciton level structure of an aggregate. For the first time the 0-0 transition band of the lowest exciton state of BChl e and BChl c aggregates has been directly detected as the lowest energy inhomogeneously broadened band of the 1.8 K near-infrared excitation spectrum. These lowest energy bands have different spectral position of their maximums: approximately 739 nm in C.phaeovibriodes (BChl e band), approximately 752 nm in C.aurantiacus (BChl c band) and approximately 774 nm in C.limicola (BChl c band) cells. However, these bands display a number of fundamentally similar spectral features: (1) The magnitude of inhomogeneous broadening of these bands is 90 - 100 cm-1; (2) The width of each band is 2 - 3 times less than that of the monomeric BChl c (or BChl e) in vitro at 5 K; (3) Each band

  14. Communication: Broad manifold of excitonic states in light-harvesting complex 1 promotes efficient unidirectional energy transfer in vivo

    Science.gov (United States)

    Sohail, Sara H.; Dahlberg, Peter D.; Allodi, Marco A.; Massey, Sara C.; Ting, Po-Chieh; Martin, Elizabeth C.; Hunter, C. Neil; Engel, Gregory S.

    2017-10-01

    In photosynthetic organisms, the pigment-protein complexes that comprise the light-harvesting antenna exhibit complex electronic structures and ultrafast dynamics due to the coupling among the chromophores. Here, we present absorptive two-dimensional (2D) electronic spectra from living cultures of the purple bacterium, Rhodobacter sphaeroides, acquired using gradient assisted photon echo spectroscopy. Diagonal slices through the 2D lineshape of the LH1 stimulated emission/ground state bleach feature reveal a resolvable higher energy population within the B875 manifold. The waiting time evolution of diagonal, horizontal, and vertical slices through the 2D lineshape shows a sub-100 fs intra-complex relaxation as this higher energy population red shifts. The absorption (855 nm) of this higher lying sub-population of B875 before it has red shifted optimizes spectral overlap between the LH1 B875 band and the B850 band of LH2. Access to an energetically broad distribution of excitonic states within B875 offers a mechanism for efficient energy transfer from LH2 to LH1 during photosynthesis while limiting back transfer. Two-dimensional lineshapes reveal a rapid decay in the ground-state bleach/stimulated emission of B875. This signal, identified as a decrease in the dipole strength of a strong transition in LH1 on the red side of the B875 band, is assigned to the rapid localization of an initially delocalized exciton state, a dephasing process that frustrates back transfer from LH1 to LH2.

  15. 8.4% efficient fullerene-free organic solar cells exploiting long-range exciton energy transfer

    National Research Council Canada - National Science Library

    Cnops, Kjell; Rand, Barry P; Cheyns, David; Verreet, Bregt; Empl, Max A; Heremans, Paul

    2014-01-01

    .... Here we present a simple three-layer architecture comprising two non-fullerene acceptors and a donor, in which an energy-relay cascade enables an efficient two-step exciton dissociation process...

  16. Exciton Energy Transfer from Halide Terminated Nanocrystals to Graphene in Solar Photovoltaics

    Science.gov (United States)

    Ajayi, Obafunso; Abramson, Justin; Anderson, Nicholas; Owen, Jonathan; Zhao, Yue; Kim, Phillip; Gesuele, Felice; Wong, Chee Wei

    2011-03-01

    Graphene, a zero-gap semiconductor, has been identified as an ideal electrode for nanocrystal solar cell photovoltaic applications due to its high carrier mobility. Further advances in efficient current extraction are required towards this end. We investigate the resonant energy transfer dynamics between photoexcited nanocrystals and graphene, where the energy transfer rate is characterized by the fluorescent quenching of the quantum dots in the presence of graphene. Energy transfer has been shown to have a d -4 dependence on the nanocrystal distance from the graphene surface, with a correction due to blinking statistics. We investigate this relationship with single and few layer graphene. We study halide-terminated CdSe quantum dots; where the absence of the insulating outershell improves the electronic coupling of the donor-acceptor system leads to improved electron transfer. We observe quenching of the halide terminated nanocrystals on graphene, with the quenching factor ρ defined as IQ /IG (the relative intensities on quartz and graphene).

  17. On the relation between local and charge-transfer exciton bindingenergies in organic photovoltaic materials

    NARCIS (Netherlands)

    de Gier, Hilde Dorothea; Braam, Henderika; Havenith, Remco

    2015-01-01

    In organic photovoltaic devices two types of excitons can be generated for which different binding energies can be defined: the binding energy of the local exciton generated immediately after light absorption on the polymer and the binding energy of the charge-transfer exciton generated through the

  18. Directing energy transport in organic photovoltaic cells using interfacial exciton gates.

    Science.gov (United States)

    Menke, S Matthew; Mullenbach, Tyler K; Holmes, Russell J

    2015-04-28

    Exciton transport in organic semiconductors is a critical, mediating process in many optoelectronic devices. Often, the diffusive and subdiffusive nature of excitons in these systems can limit device performance, motivating the development of strategies to direct exciton transport. In this work, directed exciton transport is achieved with the incorporation of exciton permeable interfaces. These interfaces introduce a symmetry-breaking imbalance in exciton energy transfer, leading to directed motion. Despite their obvious utility for enhanced exciton harvesting in organic photovoltaic cells (OPVs), the emergent properties of these interfaces are as yet uncharacterized. Here, directed exciton transport is conclusively demonstrated in both dilute donor and energy-cascade OPVs where judicious optimization of the interface allows exciton transport to the donor-acceptor heterojunction to occur considerably faster than when relying on simple diffusion. Generalized systems incorporating multiple exciton permeable interfaces are also explored, demonstrating the ability to further harness this phenomenon and expeditiously direct exciton motion, overcoming the diffusive limit.

  19. Surface plasmon-mediated energy transfer of electrically-pumped excitons

    Energy Technology Data Exchange (ETDEWEB)

    An, Kwang Hyup; Shtein, Max; Pipe, Kevin P.

    2015-08-25

    An electrically pumped light emitting device emits a light when powered by a power source. The light emitting device includes a first electrode, a second electrode including an outer surface, and at least one active organic semiconductor disposed between the first and second electrodes. The device also includes a dye adjacent the outer surface of the second electrode such that the second electrode is disposed between the dye and the active organic semiconductor. A voltage applied by the power source across the first and second electrodes causes energy to couple from decaying dipoles into surface plasmon polariton modes, which then evanescently couple to the dye to cause the light to be emitted.

  20. High-pressure and high-magnetic-field study of energy transfer from excitons into local d electrons in a CdTe/(Cd, Mn)Te quantum well structure

    CERN Document Server

    Yokoi, H; Fujiwara, S; Tozer, S W; Kim, Y; Takeyama, S; Wojtowicz, T; Karczewski, G; Kossut, J

    2002-01-01

    Photoluminescence measurements have been conducted for a CdTe/Cd sub 1 sub - sub x Mn sub x Te (x = 0.4) single-quantum-well structure at low temperatures under pressures to 0.49 GPa and magnetic fields to 60 T. At the ambient pressure, a new emission was induced by the application of a magnetic field. The emission has been assigned to exciton emission from the barrier layer, which is suppressed below 9 T due to the energy transfer from the exciton to local d electrons. At 0.49 GPa, the emission recovered at 44 T. In the field region where the energy transfer occurs, an anomalous red-shift of the exciton energy was observed clearly for the case of the ambient pressure. The alloy potential fluctuation effect and the magnetopolaron effect are examined as candidates for the mechanism to cause this phenomenon.

  1. The Symmetrical Quasi-Classical Model for Electronically Non-Adiabatic Processes Applied to Energy Transfer Dynamics in Site-Exciton Models of Light-Harvesting Complexes.

    Science.gov (United States)

    Cotton, Stephen J; Miller, William H

    2016-03-08

    In a recent series of papers, it has been illustrated that a symmetrical quasi-classical (SQC) windowing model applied to the Meyer-Miller (MM) classical vibronic Hamiltonian provides an excellent description of a variety of electronically non-adiabatic benchmark model systems for which exact quantum results are available for comparison. In this paper, the SQC/MM approach is used to treat energy transfer dynamics in site-exciton models of light-harvesting complexes, and in particular, the well-known 7-state Fenna-Mathews-Olson (FMO) complex. Again, numerically "exact" results are available for comparison, here via the hierarchical equation of motion (HEOM) approach of Ishizaki and Fleming, and it is seen that the simple SQC/MM approach provides very reasonable agreement with the previous HEOM results. It is noted, however, that unlike most (if not all) simple approaches for treating these systems, because the SQC/MM approach presents a fully atomistic simulation based on classical trajectory simulation, it places no restrictions on the characteristics of the thermal baths coupled to each two-level site, e.g., bath spectral densities (SD) of any analytic functional form may be employed as well as discrete SD determined experimentally or from MD simulation (nor is there any restriction that the baths be harmonic), opening up the possibility of simulating more realistic variations on the basic site-exciton framework for describing the non-adiabatic dynamics of photosynthetic pigment complexes.

  2. Exciton modeling of energy-transfer dynamics in the LHCII complex of higher plants: A redfield theory approach

    NARCIS (Netherlands)

    Novoderezhkin, V.; Salverda, J.M.; van Amerongen, H.; van Grondelle, R.

    2003-01-01

    We propose an exciton model for the peripheral plant light-harvesting complex LHCII that allows us to explain the absorption (OD) and linear dichroism (LD) spectra, the superradiance (SR), the pump-probe transient absorption (TA), the three-pulse photon echo peak shift (3PEPS), and transient grating

  3. Exciton modeling of energy-transfer dynamics in the LHCII complex of higher plants: a Redfield theory approach

    NARCIS (Netherlands)

    Novoderezhkin, V.; Salverda, J.M.; Amerongen, van H.; Grondelle, van R.

    2003-01-01

    We propose an exciton model for the peripheral plant light-harvesting complex LHCII that allows us to explain the absorption (OD) and linear dichroism (LD) spectra, the superradiance (SR), the pump-probe transient absorption (TA), the three-pulse photon echo peak shift (3PEPS), and transient grating

  4. Influence of exciton-phonons coupling on the exciton binding energy in monolayer transition metal dichalcogenides

    Science.gov (United States)

    Wang, Zi-Wu; Li, Wei-Ping; Xiao, Yao; Li, Run-Ze; Li, Zhi-Qing

    2017-06-01

    We theoretically investigate the correction of exciton binding energy arising from the exciton-optical phonon coupling in monolayer transition metal dichalcogenides (TMDs) using the linear operator and Lee-Low-Pines unitary transformation methods. We take into account not only the exciton coupling with intrinsic longitudinal optical phonon modes but also the surface optical phonon modes induced by polar substrates supporting monolayer TMDs. We find that the exciton binding energies are corrected on a large scale due to these exciton-optical phonon couplings. We discuss the dependences of exciton binding energy on the cut-off wave vector of optical phonon modes, the polarization strength of substrate materials, and the distance between polar substrates and TMDs. These results provide potential explanations for the divergence of the exciton binding energy between the experiment and theory in TMDs.

  5. Excitation energy transfer processes in condensed matter theory and applications

    CERN Document Server

    Singh, Jai

    1994-01-01

    Applying a unified quantum approach, contributors offer fresh insights into the theoretical developments in the excitation energy transfer processes in condensed matter This comprehensive volume examines Frenkel and Wannier excitonic processes; rates of excitonic processes; theory of laser sputter and polymer ablation; and polarons, excitonic polarons and self-trapping

  6. Exciton and Hole-Transfer Dynamics in Polymer: Fullerene Blends

    Directory of Open Access Journals (Sweden)

    van Loosdrecht P. H. M.

    2013-03-01

    Full Text Available Ultrafast hole transfer dynamics from fullerene derivative to polymer in bulk heterojunction blends are studied with visible-pump - IR-probe spectroscopy. The hole transfer process is found to occur in 50/300 fs next to the interface, while a longer 15-ps time is attributed to exciton diffusion towards interface in PC71BM domains. High polaron generation efficiency in P3HT blends indicates excellent intercalation between the polymer and the fullerene even at highest PC71BM concentration thereby yielding a valuable information on the blend morphology.

  7. Energy storage by means of exciton droplets

    Energy Technology Data Exchange (ETDEWEB)

    Zuev, V.A.; Litovchenko, V.G.

    1980-01-01

    Certain characteristics of electron-hole droplets and ball lightning are investigated and compared with a view to evaluating energy storage and transfer processes. Models for plasma processes in the atmosphere and in semiconductors are briefly examined.

  8. Excitonic processes at organic heterojunctions

    Science.gov (United States)

    He, ShouJie; Lu, ZhengHong

    2018-02-01

    Understanding excitonic processes at organic heterojunctions is crucial for development of organic semiconductor devices. This article reviews recent research on excitonic physics that involve intermolecular charge transfer (CT) excitons, and progress on understanding relationships between various interface energy levels and key parameters governing various competing interface excitonic processes. These interface excitonic processes include radiative exciplex emission, nonradiative recombination, Auger electron emission, and CT exciton dissociation. This article also reviews various device applications involving interface CT excitons, such as organic light-emitting diodes (OLEDs), organic photovoltaic cells, organic rectifying diodes, and ultralow-voltage Auger OLEDs.

  9. Energy Gap Law for Exciton Dynamics in Gold Cluster Molecules.

    Science.gov (United States)

    Kwak, Kyuju; Thanthirige, Viraj Dhanushka; Pyo, Kyunglim; Lee, Dongil; Ramakrishna, Guda

    2017-10-05

    The energy gap law relates the nonradiative decay rate to the energy gap separating the ground and excited states. Here we report that the energy gap law can be applied to exciton dynamics in gold cluster molecules. Size-dependent electrochemical and optical properties were investigated for a series of n-hexanethiolate-protected gold clusters ranging from Au25 to Au333. Voltammetric studies reveal that the highest occupied molecular orbital-lowest unoccupied molecular orbital (HOMO-LUMO) gaps of these clusters decrease with increasing cluster size. Combined femtosecond and nanosecond time-resolved transient absorption measurements show that the exciton lifetimes decrease with increasing cluster size. Comparison of the size-dependent exciton lifetimes with the HOMO-LUMO gaps shows that they are linearly correlated, demonstrating the energy gap law for excitons in these gold cluster molecules.

  10. Nonmonotonic energy harvesting efficiency in biased exciton chains

    NARCIS (Netherlands)

    Vlaming, S.M.; Malyshev, V.A.; Knoester, J.

    2007-01-01

    We theoretically study the efficiency of energy harvesting in linear exciton chains with an energy bias, where the initial excitation is taking place at the high-energy end of the chain and the energy is harvested (trapped) at the other end. The efficiency is characterized by means of the average

  11. The convergence of longitudinal excitons onto the Γ5 transverse exciton in GaN and the thermal activation energy of longitudinal excitons.

    Science.gov (United States)

    Elgawadi, Amal; Gainer, Gordon; Krasinski, Jerzy

    2013-08-21

    The crystal orientation dependence of GaN excitons was investigated via the photoluminescence (PL) technique. The PL emissions at a temperature of 10 K were obtained from two experimental configurations where the emission K vector (the propagation vector) was either parallel (K ∥ c) or perpendicular (K ∥ c) to the crystal c-axis. Longitudinal, transverse and donor-bound excitons were observed in the two configurations. However, the longitudinal excitons converged onto the transverse free exciton Γ5 in the K⊥c emission. This behavior was discussed in terms of electron screening due to the scattering of electrons moving perpendicular to charged dislocation lines. Additionally, the thermal activation energy of the longitudinal excitons was calculated from the temperature dependent PL measurements collected from the K ∥ c emission, and was found to be 5 to 6 times as high as the binding energy of the free excitons. This high energy was interpreted tentatively in view of the creation of polaritons in strong exciton-photon coupling regimes. These findings present fundamental concepts for applications such as vertical cavity surface-emitting lasers (VCSELs) and polariton lasers.

  12. Silica-Coated Mn-Doped CsPb(Cl/Br)3 Inorganic Perovskite Quantum Dots: Exciton-to-Mn Energy Transfer and Blue-Excitable Solid-State Lighting.

    Science.gov (United States)

    Chen, Daqin; Fang, Gaoliang; Chen, Xiao

    2017-11-22

    Tunability of emitting colors of perovskite quantum dots (PQDs) was generally realized via composition/size modulation. Due to their bandgap absorption and ionic crystal features, the mixing of multiple PQDs inevitably suffers from reabsorption and anion-exchange effects. Herein, we address these issues with high-content Mn2+-doped CsPbCl3 PQDs that can yield blue-excitable orange Mn2+ emission benefited from exciton-to-Mn energy transfer and Cl-to-Br anion exchange. Silica-coating was applied to improve air stability of PQDs, suppress the loss of Mn2+, and avoid anion-exchange between different PQDs. As a direct benefit of intense multicolor emissions from Mn2+-doped PQD@SiO2 solid phosphors, a prototype white light-emitting diode with excellent optical performance and superior light stability was constructed using green CsPbBr3@SiO2 and orange Mn: CsPb(Cl/Br)3@SiO2 composites as color converters, verifying their potential applications in the field of optoelectronics.

  13. Energy transfer in macromolecular arrays

    Science.gov (United States)

    Andrews, David L.; Jenkins, Robert D.

    2003-11-01

    Macromolecular systems comprised of many light-sensitive centres (the photosynthetic unit, dendrimers, and other highly symmetric multichromophore arrays) are important structures offering challenges to theoreticians and synthetic chemists alike. Here we outline novel photophysical interactions predicted and observed in such arrays. Using the tools of molecular quantum electrodynamics (QED) we present quantum amplitudes for a variety of higher-order resonance energy transfer (RET) schemes associated with well-known nonlinear optical effects such as two- and three-photon absorption. The initial analysis is extended to account for situations where the participant donor species are identical and exist in a highly symmetric environment, leading to the possible formation of excitons. It emerges from the QED theory that such excitons are closely associated with the higher-order RET processes. General results are interpreted by analyzing particular molecular architectures which offer interesting features such as rate enhancement or limitation and exciton pathway quenching. Applications in the areas of photosynthesis, molecular logic gates and low-intensity fluorescence energy transfer are predicted.

  14. Direct measurement of exciton dissociation energy in polymers

    Directory of Open Access Journals (Sweden)

    J. Toušek

    2017-01-01

    Full Text Available Exciton dissociation energy was obtained based on the comparison of thickness of the space charge region estimated from the measurement of capacitance of prepared Schottky diode and from the measurement of photovoltage spectra. While the capacitance measurements provide information about the total width of the space charge region (SCR the surface photovoltaic effect brings information only about the part of the SCR where electric field is sufficiently high to cause dissociation. For determination of the dissociation energy it is sufficient to find the electric potential in the SCR where the process starts.

  15. Exciton size and quantum transport in nanoplatelets

    Energy Technology Data Exchange (ETDEWEB)

    Pelzer, Kenley M., E-mail: kpelzer@anl.gov; Gray, Stephen K. [Center for Nanoscale Materials, Argonne National Laboratory, 9700 Cass Ave., Argonne, Illinois 60439 (United States); Darling, Seth B. [Center for Nanoscale Materials, Argonne National Laboratory, 9700 Cass Ave., Argonne, Illinois 60439 (United States); Institute for Molecular Engineering, University of Chicago, 5747 S. Ellis Ave., Chicago, Illinois 60637 (United States); Schaller, Richard D. [Center for Nanoscale Materials, Argonne National Laboratory, 9700 Cass Ave., Argonne, Illinois 60439 (United States); Department of Chemistry, Northwestern University, 2145 Sheridan Rd., Evanston, Illinois 60208 (United States)

    2015-12-14

    Two-dimensional nanoplatelets (NPLs) are an exciting class of materials with promising optical and energy transport properties. The possibility of efficient energy transport between nanoplatelets raises questions regarding the nature of energy transfer in these thin, laterally extended systems. A challenge in understanding exciton transport is the uncertainty regarding the size of the exciton. Depending on the material and defects in the nanoplatelet, an exciton could plausibly extend over an entire plate or localize to a small region. The variation in possible exciton sizes raises the question how exciton size impacts the efficiency of transport between nanoplatelet structures. Here, we explore this issue using a quantum master equation approach. This method goes beyond the assumptions of Förster theory to allow for quantum mechanical effects that could increase energy transfer efficiency. The model is extremely flexible in describing different systems, allowing us to test the effect of varying the spatial extent of the exciton. We first discuss qualitative aspects of the relationship between exciton size and transport and then conduct simulations of exciton transport between NPLs for a range of exciton sizes and environmental conditions. Our results reveal that exciton size has a strong effect on energy transfer efficiency and suggest that manipulation of exciton size may be useful in designing NPLs for energy transport.

  16. Organic solar cells: understanding the role of Förster resonance energy transfer.

    Science.gov (United States)

    Feron, Krishna; Belcher, Warwick J; Fell, Christopher J; Dastoor, Paul C

    2012-12-12

    Organic solar cells have the potential to become a low-cost sustainable energy source. Understanding the photoconversion mechanism is key to the design of efficient organic solar cells. In this review, we discuss the processes involved in the photo-electron conversion mechanism, which may be subdivided into exciton harvesting, exciton transport, exciton dissociation, charge transport and extraction stages. In particular, we focus on the role of energy transfer as described by F¨orster resonance energy transfer (FRET) theory in the photoconversion mechanism. FRET plays a major role in exciton transport, harvesting and dissociation. The spectral absorption range of organic solar cells may be extended using sensitizers that efficiently transfer absorbed energy to the photoactive materials. The limitations of F¨orster theory to accurately calculate energy transfer rates are discussed. Energy transfer is the first step of an efficient two-step exciton dissociation process and may also be used to preferentially transport excitons to the heterointerface, where efficient exciton dissociation may occur. However, FRET also competes with charge transfer at the heterointerface turning it in a potential loss mechanism. An energy cascade comprising both energy transfer and charge transfer may aid in separating charges and is briefly discussed. Considering the extent to which the photo-electron conversion efficiency is governed by energy transfer, optimisation of this process offers the prospect of improved organic photovoltaic performance and thus aids in realising the potential of organic solar cells.

  17. Organic Solar Cells: Understanding the Role of Förster Resonance Energy Transfer

    Science.gov (United States)

    Feron, Krishna; Belcher, Warwick J.; Fell, Christopher J.; Dastoor, Paul C.

    2012-01-01

    Organic solar cells have the potential to become a low-cost sustainable energy source. Understanding the photoconversion mechanism is key to the design of efficient organic solar cells. In this review, we discuss the processes involved in the photo-electron conversion mechanism, which may be subdivided into exciton harvesting, exciton transport, exciton dissociation, charge transport and extraction stages. In particular, we focus on the role of energy transfer as described by Förster resonance energy transfer (FRET) theory in the photoconversion mechanism. FRET plays a major role in exciton transport, harvesting and dissociation. The spectral absorption range of organic solar cells may be extended using sensitizers that efficiently transfer absorbed energy to the photoactive materials. The limitations of Förster theory to accurately calculate energy transfer rates are discussed. Energy transfer is the first step of an efficient two-step exciton dissociation process and may also be used to preferentially transport excitons to the heterointerface, where efficient exciton dissociation may occur. However, FRET also competes with charge transfer at the heterointerface turning it in a potential loss mechanism. An energy cascade comprising both energy transfer and charge transfer may aid in separating charges and is briefly discussed. Considering the extent to which the photo-electron conversion efficiency is governed by energy transfer, optimisation of this process offers the prospect of improved organic photovoltaic performance and thus aids in realising the potential of organic solar cells. PMID:23235328

  18. Organic Solar Cells: Understanding the Role of Förster Resonance Energy Transfer

    Directory of Open Access Journals (Sweden)

    Paul C. Dastoor

    2012-12-01

    Full Text Available Organic solar cells have the potential to become a low-cost sustainable energy source. Understanding the photoconversion mechanism is key to the design of efficient organic solar cells. In this review, we discuss the processes involved in the photo-electron conversion mechanism, which may be subdivided into exciton harvesting, exciton transport, exciton dissociation, charge transport and extraction stages. In particular, we focus on the role of energy transfer as described by F¨orster resonance energy transfer (FRET theory in the photoconversion mechanism. FRET plays a major role in exciton transport, harvesting and dissociation. The spectral absorption range of organic solar cells may be extended using sensitizers that efficiently transfer absorbed energy to the photoactive materials. The limitations of F¨orster theory to accurately calculate energy transfer rates are discussed. Energy transfer is the first step of an efficient two-step exciton dissociation process and may also be used to preferentially transport excitons to the heterointerface, where efficient exciton dissociation may occur. However, FRET also competes with charge transfer at the heterointerface turning it in a potential loss mechanism. An energy cascade comprising both energy transfer and charge transfer may aid in separating charges and is briefly discussed. Considering the extent to which the photo-electron conversion efficiency is governed by energy transfer, optimisation of this process offers the prospect of improved organic photovoltaic performance and thus aids in realising the potential of organic solar cells.

  19. Roles of binding energy and diffusion length of singlet and triplet excitons in organic heterojunction solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Narayan, Monishka Rita [Centre for Renewable Energy and Low Emission Technology, Charles Darwin University, Darwin, NT 0909 (Australia); Singh, Jai [School of Engineering and IT, Charles Darwin University, Darwin, NT 0909 (Australia)

    2012-12-15

    The influence of binding energy and diffusion length on the dissociation of excitons in organic solids is studied. The binding energy and excitonic Bohr radius of singlet and triplet excitons are calculated and compared using the dissociation energy of 0.3 eV, which is provided by the lowest unoccupied molecular orbital offset in heterojunction organic solar cells. A relation between the diffusion coefficient and diffusion length of singlet and triplet excitons is derived using the Foerster and Dexter transfer processes and are plotted as a function of the donor-acceptor separation. The diffusion length reduces nearly to a zero if the distance between donor and acceptor is increased to more than 1.5 nm. It is found that the donor-acceptor separation needs to be {<=} 1.5 nm for easy dissociation on singlet excitons leading to better conversion efficiency in heterojunction organic solar cells. (copyright 2012 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)

  20. Anisotropic plasmons, excitons, and electron energy loss spectroscopy of phosphorene

    Science.gov (United States)

    Ghosh, Barun; Kumar, Piyush; Thakur, Anmol; Chauhan, Yogesh Singh; Bhowmick, Somnath; Agarwal, Amit

    2017-07-01

    In this article, we explore the anisotropic electron energy loss spectrum (EELS) in monolayer phosphorene based on ab initio time-dependent density-functional-theory calculations. Similarly to black phosphorus, the EELS of undoped monolayer phosphorene is characterized by anisotropic excitonic peaks for energies in the vicinity of the band gap and by interband plasmon peaks for higher energies. On doping, an additional intraband plasmon peak also appears for energies within the band gap. Similarly to other two-dimensional systems, the intraband plasmon peak disperses as ωpl∝√{q } in both the zigzag and armchair directions in the long-wavelength limit and deviates for larger wave vectors. The anisotropy of the long-wavelength plasmon intraband dispersion is found to be inversely proportional to the square root of the ratio of the effective masses: ωpl(q y ̂) /ωpl(q x ̂) =√{mx/my } .

  1. Combined Inter- and Intramolecular Charge-Transfer Processes for Highly Efficient Fluorescent Organic Light-Emitting Diodes with Reduced Triplet Exciton Quenching.

    Science.gov (United States)

    Moon, Chang-Ki; Suzuki, Katsuaki; Shizu, Katsuyuki; Adachi, Chihaya; Kaji, Hironori; Kim, Jang-Joo

    2017-05-01

    Inter- and intramolecular charge-transfer processes are combined using an exciplex-forming host and a thermally activated delayed fluorescent dopant, for fabricating efficient fluorescent organic light-emitting diodes along with the reduced efficiency roll-off at high current densities. Extra conversion on the host from triplet exciplexes to singlet exciplexes followed by energy transfer to the dopant reduces population of triplet excitons on dopant molecules, thereby reducing the triplet exciton annihilations at high current densities. © 2017 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Single-Molecule Investigation of Energy Dynamics in a Coupled Plasmon-Exciton System

    Science.gov (United States)

    Imada, Hiroshi; Miwa, Kuniyuki; Imai-Imada, Miyabi; Kawahara, Shota; Kimura, Kensuke; Kim, Yousoo

    2017-07-01

    We investigate the near-field interaction between an isolated free-base phthalocyanine molecule and a plasmon localized in the gap between an NaCl-covered Ag(111) surface and the tip apex of a scanning tunneling microscope. When the tip is located in the close proximity of the molecule, asymmetric dips emerge in the broad luminescence spectrum of the plasmon generated by the tunneling current. The origin of the dips is explained by energy transfer between the plasmon and molecular excitons and a quantum mechanical interference effect, where molecular vibrations provide additional degrees of freedom in the dynamic process.

  3. Improved value for the silicon free exciton binding energy

    Directory of Open Access Journals (Sweden)

    Martin A. Green

    2013-11-01

    Full Text Available The free exciton binding energy is a key parameter in silicon material and device physics. In particular, it provides the necessary link between the energy threshold for valence to conduction band optical absorption and the bandgap determining electronic properties. The long accepted low temperature binding energy value of 14.7 ± 0.4 meV is reassessed taking advantage of developments subsequent to its original determination, leading to the conclusion that this value is definitely an underestimate. Using three largely independent experimental data sets, an improved low temperature value of 15.01 ± 0.06 meV is deduced, in good agreement with the most comprehensive theoretical calculations to date.

  4. Correlation between charge transfer exciton recombination and photocurrent in polymer/fullerene solar cells

    NARCIS (Netherlands)

    Hallermann, Markus; Da Como, Enrico; Feldmann, Jochen; Izquierdo, Marta; Filippone, Salvatore; Martin, Nazario; Juechter, Sabrina; von Hauff, Elizabeth

    2010-01-01

    We correlate carrier recombination via charge transfer excitons (CTEs) with the short circuit current, J sc, in polymer/fullerene solar cells. Near infrared photoluminescence spectroscopy of CTE in three blends differing for the fullerene acceptor, gives unique insights into solar cell

  5. Quantum Confinement of Hybrid Charge Transfer Excitons in GaN/InGaN/Organic Semiconductor Quantum Wells.

    Science.gov (United States)

    Panda, Anurag; Forrest, Stephen R

    2017-12-13

    We investigate hybrid charge transfer exciton (HCTE) confinement in organic-inorganic (OI) quantum wells (QWs) comprising a thin InGaN layer bound on one side by GaN and on the other by the organic semiconductors, tetraphenyldibenzoperiflanthene (DBP) or 4,4'-bis(N-carbazolyl)-1,1'-biphenyl (CBP). A binding energy of 10 meV is calculated for the Coulombically bound free HCTE state between a delocalized electron in GaN and a hole localized in DBP. The binding energy of the HCTE increases to 165 meV when the electron is confined to a 1.5 nm In0.21Ga0.79N QW (HCTEQW). The existence of the HCTEQW is confirmed by measuring the voltage-dependent DBP exciton dissociation yield at the OI heterojunction in the QW devices that decrease with increasing In concentration and decreasing electric field, matching the trends predicted by Poole-Frenkel emission. Combining spectroscopic measurements with optical models, we find that 14 ± 3% of the excitons that reach the GaN/DBP heterojunction form HCTEs and dissociate into free charges, while the remainder recombine. A high nonradiative recombination rate through defect states at the heterointerface account for the lack of observation of HCTEQW photoluminescence from GaN/InGaN/CBP QWs at temperatures as low as 10 K.

  6. External electric field effect on exciton binding energy in InGaAsP/InP cylindrical quantum wires

    Energy Technology Data Exchange (ETDEWEB)

    Wang, Hailong, E-mail: hlwang@mail.qfnu.edu.cn [College of Physics and Engineering, Qufu Normal University, Qufu 273165 (China); Wang, Wenjuan [College of Physics and Engineering, Qufu Normal University, Qufu 273165 (China); Gong, Qian; Wang, Shumin [State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050 (China)

    2016-12-15

    Exciton binding energies in InGaAsP/InP cylindrical quantum wires are calculated through variational method under the framework of effective-mass envelope-function approximation. It is shown that the variation of exciton binding energy is highly dependent on radius of the wire, material composition and external electric field. Exciton binding energy is a non-monotonic function of wire radius. It increases until it reaches a maximum, and then decreases as the wire radius decreases. With the increase of In composition, the wire radius need increase to reach the maximum value of exciton binding energy. It is also found that the external electric field has little effect on exciton binding energy. However, the excitonic effect will be destroyed when external electric field is large enough. In addition, the Stark shift of exciton binding energy is also calculated.

  7. Migration-assisted energy transfer at conjugated polymer/metal interfaces

    NARCIS (Netherlands)

    Markov, DE; Blom, PWM

    2005-01-01

    The dynamics of exciton quenching in a conjugated polymer due to the presence of metal films is analyzed using time-resolved photoluminescence. The quenching is governed by direct radiationless energy transfer to the metal and is further enhanced by diffusion of excitons into the depletion area of

  8. Exciton Seebeck effect in molecular systems.

    Science.gov (United States)

    Yan, Yun-An; Cai, Shaohong

    2014-08-07

    We investigate the exciton dynamics under temperature difference with the hierarchical equations of motion. Through a nonperturbative simulation of the transient absorption of a heterogeneous trimer model, we show that the temperature difference causes exciton population redistribution and affects the exciton transfer time. It is found that one can reproduce not only the exciton population redistribution but also the change of the exciton transfer time induced by the temperature difference with a proper tuning of the site energies of the aggregate. In this sense, there exists a site energy shift equivalence for any temperature difference in a broad range. This phenomenon is similar to the Seebeck effect as well as spin Seebeck effect and can be named as exciton Seebeck effect.

  9. Energy scaling for multi-exciton complexes in semiconductor quantum dots

    Science.gov (United States)

    Ipatov, Andrey; Gerchikov, Leonid; Christiano, Jordan

    2017-08-01

    The ground state properties of an multi-exciton (ME) complex localized in a nanoscale semiconductor quantum dot (QD) have been studied. The calculations have been performed using the envelope function approximation for electron and hole motion in the QD. The many-body quantum mechanical treatment of the electron-hole dynamics was done within the Density Functional Theory approach. The ground state energy dependencies upon QD radius, number of electron-hole pairs, QD dielectric function and effective masses of electron and holes have been analyzed. It is demonstrated that when multi-exciton complex is strongly localized within the QD, the physical properties of the system are determined by a single parameter, the ratio of QD and free exciton radii, and its binding energy is given by the function of this parameter multiplied by the binding energy of an isolated exciton in bulk semiconductor.

  10. Determination of the Exciton Binding Energy in CdSe Quantum Dots

    Energy Technology Data Exchange (ETDEWEB)

    Meulenberg, R; Lee, J; Wolcott, A; Zhang, J; Terminello, L; van Buuren, T

    2009-10-27

    The exciton binding energy (EBE) in CdSe quantum dots (QDs) has been determined using x-ray spectroscopy. Using x-ray absorption and photoemission spectroscopy, the conduction band (CB) and valence band (VB) edge shifts as a function of particle size have been determined and combined to obtain the true band gap of the QDs (i.e. without and exciton). These values can be compared to the excitonic gap obtained using optical spectroscopy to determine the EBE. The experimental EBE results are compared with theoretical calculations on the EBE and show excellent agreement.

  11. Intermolecular Singlet and Triplet Exciton Transfer Integrals from Many-Body Green's Functions Theory.

    Science.gov (United States)

    Wehner, Jens; Baumeier, Björn

    2017-04-11

    A general approach to determine orientation and distance-dependent effective intermolecular exciton transfer integrals from many-body Green's functions theory is presented. On the basis of the GW approximation and the Bethe-Salpeter equation (BSE), a projection technique is employed to obtain the excitonic coupling by forming the expectation value of a supramolecular BSE Hamiltonian with electron-hole wave functions for excitations localized on two separated chromophores. Within this approach, accounting for the effects of coupling mediated by intermolecular charge transfer (CT) excitations is possible via perturbation theory or a reduction technique. Application to model configurations of pyrene dimers shows an accurate description of short-range exchange and long-range Coulomb interactions for the coupling of singlet and triplet excitons. Computational parameters, such as the choice of the exchange-correlation functional in the density-functional theory (DFT) calculations that underly the GW-BSE steps and the convergence with the number of included CT excitations, are scrutinized. Finally, an optimal strategy is derived for simulations of full large-scale morphologies by benchmarking various approximations using pairs of dicyanovinyl end-capped oligothiophenes (DCV5T), which are used as donor material in state-of-the-art organic solar cells.

  12. Intermolecular Singlet and Triplet Exciton Transfer Integrals from Many-Body Green’s Functions Theory

    Science.gov (United States)

    2017-01-01

    A general approach to determine orientation and distance-dependent effective intermolecular exciton transfer integrals from many-body Green’s functions theory is presented. On the basis of the GW approximation and the Bethe–Salpeter equation (BSE), a projection technique is employed to obtain the excitonic coupling by forming the expectation value of a supramolecular BSE Hamiltonian with electron–hole wave functions for excitations localized on two separated chromophores. Within this approach, accounting for the effects of coupling mediated by intermolecular charge transfer (CT) excitations is possible via perturbation theory or a reduction technique. Application to model configurations of pyrene dimers shows an accurate description of short-range exchange and long-range Coulomb interactions for the coupling of singlet and triplet excitons. Computational parameters, such as the choice of the exchange-correlation functional in the density-functional theory (DFT) calculations that underly the GW-BSE steps and the convergence with the number of included CT excitations, are scrutinized. Finally, an optimal strategy is derived for simulations of full large-scale morphologies by benchmarking various approximations using pairs of dicyanovinyl end-capped oligothiophenes (DCV5T), which are used as donor material in state-of-the-art organic solar cells. PMID:28234472

  13. Coherent Dynamics of Mixed Frenkel and Charge-Transfer Excitons in Dinaphtho[2,3-b:2'3'-f]thieno[3,2-b]-thiophene Thin Films: The Importance of Hole Delocalization.

    Science.gov (United States)

    Fujita, Takatoshi; Atahan-Evrenk, Sule; Sawaya, Nicolas P D; Aspuru-Guzik, Alán

    2016-04-07

    Charge-transfer states in organic semiconductors play crucial roles in processes such as singlet fission and exciton dissociation at donor/acceptor interfaces. Recently, a time-resolved spectroscopy study of dinaphtho[2,3-b:2'3'-f]thieno[3,2-b]-thiophene (DNTT) thin films provided evidence for the formation of mixed Frenkel and charge-transfer excitons after the photoexcitation. Here, we investigate optical properties and excitation dynamics of the DNTT thin films by combining ab initio calculations and a stochastic Schrödinger equation. Our theory predicts that the low-energy Frenkel exciton band consists of 8-47% CT character. The quantum dynamics simulations show coherent dynamics of Frenkel and CT states in 50 fs after the optical excitation. We demonstrate the role of charge delocalization and localization in the mixing of CT states with Frenkel excitons as well as the role of their decoherence.

  14. Impact of charge-transfer excitons in regioregular polythiophene on the charge separation at polythiophene-fullerene heterojunctions

    Science.gov (United States)

    Polkehn, M.; Tamura, H.; Burghardt, I.

    2018-01-01

    This study addresses the mechanism of ultrafast charge separation in regioregular oligothiophene-fullerene assemblies representative of poly-3-hexylthiophene (P3HT)-[6,6]-phenyl-C61 butyric acid methyl ester (PCBM) heterojunctions, with special emphasis on the inclusion of charge transfer excitons in the oligothiophene phase. The formation of polaronic inter-chain charge separated species in highly ordered oligothiophene has been demonstrated in recent experiments and could have a significant impact on the net charge transfer to the fullerene acceptor. The present approach combines a first-principles parametrized multi-site Hamiltonian, based on time-dependent density functional theory calculations, with accurate quantum dynamics simulations using the multi-layer multi-configuration time-dependent Hartree method. Quantum dynamical studies are carried out for up to 182 electronic states and 112 phonon modes. The present analysis follows up on our previous study of (Huix-Rotllant et al 2015 J. Phys. Chem. Lett. 6 1702) and significantly expands the scope of this analysis by including the dynamical role of charge transfer excitons. Our investigation highlights the pronounced mixing of photogenerated Frenkel excitons with charge transfer excitons in the oligothiophene domain, and the opening of new transfer channels due the creation of such charge-separated species. As a result, it turns out that the interfacial donor/acceptor charge transfer state can be largely circumvented due to the presence of charge transfer excitons. However, the latter states in turn act as a trap, such that the free carrier yield observed on ultrafast time scales is tangibly reduced. The present analysis underscores the complexity of the transfer pathways at P3HT-PCBM type junctions.

  15. Energy transfer in structured and unstructured environments

    DEFF Research Database (Denmark)

    Iles-Smith, Jake; Dijkstra, Arend G.; Lambert, Neill

    2016-01-01

    We explore excitonic energy transfer dynamics in a molecular dimer system coupled to both structured and unstructured oscillator environments. By extending the reaction coordinate master equation technique developed by Iles-Smith et al. [Phys. Rev. A 90, 032114 (2014)], we go beyond the commonly...... used Born-Markov approximations to incorporate system-environment correlations and the resultant non-Markovian dynamical effects. We obtain energy transfer dynamics for both underdamped and overdamped oscillator environments that are in perfect agreement with the numerical hierarchical equations...... of motion over a wide range of parameters. Furthermore, we show that the Zusman equations, which may be obtained in a semiclassical limit of the reaction coordinate model, are often incapable of describing the correct dynamical behaviour. This demonstrates the necessity of properly accounting for quantum...

  16. Unraveling the Exciton Binding Energy and the Dielectric Constant in Single-Crystal Methylammonium Lead Triiodide Perovskite.

    Science.gov (United States)

    Yang, Zhuo; Surrente, Alessandro; Galkowski, Krzysztof; Bruyant, Nicolas; Maude, Duncan K; Haghighirad, Amir Abbas; Snaith, Henry J; Plochocka, Paulina; Nicholas, Robin J

    2017-04-20

    We have accurately determined the exciton binding energy and reduced mass of single crystals of methylammonium lead triiodide using magneto-reflectivity at very high magnetic fields. The single crystal has excellent optical properties with a narrow line width of ∼3 meV for the excitonic transitions and a 2s transition that is clearly visible even at zero magnetic field. The exciton binding energy of 16 ± 2 meV in the low-temperature orthorhombic phase is almost identical to the value found in polycrystalline samples, crucially ruling out any possibility that the exciton binding energy depends on the grain size. In the room-temperature tetragonal phase, an upper limit for the exciton binding energy of 12 ± 4 meV is estimated from the evolution of 1s-2s splitting at high magnetic field.

  17. FDTD and transfer matrix methods for evaluating the performance of photonic crystal based microcavities for exciton-polaritons

    Science.gov (United States)

    Liu, Yi-Cheng; Byrnes, Tim

    2016-11-01

    We investigate alternative microcavity structures for exciton-polaritons consisting of photonic crystals instead of distributed Bragg reflectors. Finite-difference time-domain simulations and scattering transfer matrix methods are used to evaluate the cavity performance. The results are compared with conventional distributed Bragg reflectors. We find that in terms of the photon lifetime, the photonic crystal based microcavities are competitive, with typical lifetimes in the region of ∼20 ps being achieved. The photonic crystal microcavities have the advantage that they are compact and are frequency adjustable, showing that they are viable to investigate exciton-polariton condensation physics.

  18. Carrier multiplication in semiconductor nanocrystals detected by energy transfer to organic dye molecules.

    Science.gov (United States)

    Xiao, Jun; Wang, Ying; Hua, Zheng; Wang, Xiaoyong; Zhang, Chunfeng; Xiao, Min

    2012-01-01

    Carrier multiplication describes an interesting optical phenomenon in semiconductors whereby more than one electron-hole pair, or exciton, can be simultaneously generated upon absorption of a single high-energy photon. So far, it has been highly debated whether the carrier multiplication efficiency is enhanced in semiconductor nanocrystals as compared with their bulk counterpart. The controversy arises from the fact that the ultrafast optical methods currently used need to correctly account for the false contribution of charged excitons to the carrier multiplication signals. Here we show that this charged exciton issue can be resolved in an energy transfer system, where biexcitons generated in the donor nanocrystals are transferred to the acceptor dyes, leading to an enhanced fluorescence from the latter. With the biexciton Auger and energy transfer lifetime measurements, an average carrier multiplication efficiency of ~17.1% can be roughly estimated in CdSe nanocrystals when the excitation photon energy is ~2.46 times of their energy gap.

  19. Binding energy of excitons formed from spatially separated electrons and holes in insulating quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Pokutnyi, S. I., E-mail: pokutnyi-sergey@inbox.ru [National Academy of Sciences of Ukraine, Chuiko Institute of Surface Chemistry (Ukraine); Kulchin, Yu. N.; Dzyuba, V. P. [Russian Academy of Sciences, Institute of Automation and Control Processes, Far East Branch (Russian Federation)

    2015-10-15

    It is found that the binding energy of the ground state of an exciton formed from an electron and a hole spatially separated from each other (the hole is moving within a quantum dot, and the electron is localized above the spherical (quantum dot)–(insulating matrix) interface) in a nanosystem containing insulating Al{sub 2}O{sub 3} quantum dots is substantially increased (by nearly two orders of magnitude) compared to the exciton binding energy in an Al{sub 2}O{sub 3} single crystal. It is established that, in the band gap of an Al{sub 2}O{sub 3} nanoparticle, a band of exciton states (formed from spatially separated electrons and holes) appears. It is shown that there exists the possibility of experimentally detecting the ground and excited exciton states in the band gap of Al{sub 2}O{sub 3} nanoparticles at room temperature from the absorption spectrum of the nanosystem.

  20. Binding Energy and Lifetime of Excitons in InxGa1-xAs/GaAs Quantum Wells

    DEFF Research Database (Denmark)

    Orani, D.; Polimeni, A.; Patane, A.

    1997-01-01

    We report a systematic study of exciton binding energies and lifetimes in InGaAs/GaAs quantum wells. The experimental binding energies have been deduced from photoluminescence excitation measurements taking into account the contribution of the 2s state of the exciton and the line broadening....... The experimental results have been compared with accurate calculations in a four-band model, where exciton energies take into account the polaron correction. The theory accounts for all the experimental observations and provides a good quantitative agreement with the experimental values....

  1. Exciton Resonances in Novel Silicon Carbide Polymers

    Science.gov (United States)

    Burggraf, Larry; Duan, Xiaofeng

    2015-05-01

    A revolutionary technology transformation from electronics to excitionics for faster signal processing and computing will be advantaged by coherent exciton transfer at room temperature. The key feature required of exciton components for this technology is efficient and coherent transfer of long-lived excitons. We report theoretical investigations of optical properties of SiC materials having potential for high-temperature excitonics. Using Car-Parinello simulated annealing and DFT we identified low-energy SiC molecular structures. The closo-Si12C12 isomer, the most stable 12-12 isomer below 1100 C, has potential to make self-assembled chains and 2-D nanostructures to construct exciton components. Using TDDFT, we calculated the optical properties of the isomer as well as oligomers and 2-D crystal formed from the isomer as the monomer unit. This molecule has large optical oscillator strength in the visible. Its high-energy and low-energy transitions (1.15 eV and 2.56 eV) are nearly pure one-electron silicon-to-carbon transitions, while an intermediate energy transition (1.28 eV) is a nearly pure carbon-to-silicon one-electron charge transfer. These results are useful to describe resonant, coherent transfer of dark excitons in the nanostructures. Research supported by the Air Force Office of Scientific Research.

  2. Controlling the exciton energy of a nanowire quantum dot by strain fields

    Energy Technology Data Exchange (ETDEWEB)

    Chen, Yan; Zhang, Jiaxiang; Ding, Fei, E-mail: f.ding@ifw-dresden.de [Institute for Integrative Nanosciences, IFW Dresden, Helmholtz Strasse 20, 01069 Dresden (Germany); Zadeh, Iman Esmaeil; Jöns, Klaus D.; Fognini, Andreas; Zwiller, Val [Kavli Institute of Nanoscience, Delft University of Technology, 2600 GA Delft (Netherlands); Reimer, Michael E. [Institute for Quantum Computing and Department of Electrical and Computer Engineering, University of Waterloo, Waterloo, N2L 3G1 (Canada); Dalacu, Dan; Poole, Philip J. [National Research Council, Ottawa, Ontario K1A 0R6 (Canada); Schmidt, Oliver G. [Institute for Integrative Nanosciences, IFW Dresden, Helmholtz Strasse 20, 01069 Dresden (Germany); Material Systems for Nanoelectronics, Chemnitz University of Technology, Reichenhainer Strasse 70, 09107 Chemnitz (Germany)

    2016-05-02

    We present an experimental route to engineer the exciton energies of single quantum dots in nanowires. By integrating the nanowires onto a piezoelectric crystal, we controllably apply strain fields to the nanowire quantum dots. Consequently, the exciton energy of a single quantum dot in the nanowire is shifted by several meVs without degrading its optical intensity and single-photon purity. Second-order autocorrelation measurements are performed at different strain fields on the same nanowire quantum dot. The suppressed multi-photon events at zero time delay clearly verify that the quantum nature of single-photon emission is well preserved under external strain fields. The work presented here could facilitate on-chip optical quantum information processing with the nanowire based single photon emitters.

  3. Cascaded plasmon-plasmon coupling mediated energy transfer across stratified metal-dielectric nanostructures.

    Science.gov (United States)

    Golmakaniyoon, Sepideh; Hernandez-Martinez, Pedro Ludwig; Demir, Hilmi Volkan; Sun, Xiao Wei

    2016-10-04

    Surface plasmon (SP) coupling has been successfully applied to nonradiative energy transfer via exciton-plasmon-exciton coupling in conventionally sandwiched donor-metal film-acceptor configurations. However, these structures lack the desired efficiency and suffer poor photoemission due to the high energy loss. Here, we show that the cascaded exciton-plasmon-plasmon-exciton coupling in stratified architecture enables an efficient energy transfer mechanism. The overlaps of the surface plasmon modes at the metal-dielectric and dielectric-metal interfaces allow for strong cross-coupling in comparison with the single metal film configuration. The proposed architecture has been demonstrated through the analytical modeling and numerical simulation of an oscillating dipole near the stratified nanostructure of metal-dielectric-metal-acceptor. Consistent with theoretical and numerical results, experimental measurements confirm at least 50% plasmon resonance energy transfer enhancement in the donor-metal-dielectric-metal-acceptor compared to the donor-metal-acceptor structure. Cascaded plasmon-plasmon coupling enables record high efficiency for exciton transfer through metallic structures.

  4. Ultrafast energy transfer within the photosystem II core complex.

    Science.gov (United States)

    Pan, Jie; Gelzinis, Andrius; Chorošajev, Vladimir; Vengris, Mikas; Senlik, S Seckin; Shen, Jian-Ren; Valkunas, Leonas; Abramavicius, Darius; Ogilvie, Jennifer P

    2017-06-14

    We report 2D electronic spectroscopy on the photosystem II core complex (PSII CC) at 77 K under different polarization conditions. A global analysis of the high time-resolution 2D data shows rapid, sub-100 fs energy transfer within the PSII CC. It also reveals the 2D spectral signatures of slower energy equilibration processes occurring on several to hundreds of picosecond time scales that are consistent with previous work. Using a recent structure-based model of the PSII CC [Y. Shibata, S. Nishi, K. Kawakami, J. R. Shen and T. Renger, J. Am. Chem. Soc., 2013, 135, 6903], we simulate the energy transfer in the PSII CC by calculating auxiliary time-resolved fluorescence spectra. We obtain the observed sub-100 fs evolution, even though the calculated electronic energy shows almost no dynamics at early times. On the other hand, the electronic-vibrational interaction energy increases considerably over the same time period. We conclude that interactions with vibrational degrees of freedom not only induce population transfer between the excitonic states in the PSII CC, but also reshape the energy landscape of the system. We suggest that the experimentally observed ultrafast energy transfer is a signature of excitonic-polaron formation.

  5. Quasiperiodic energy dependence of exciton relaxation kinetics in the sexithiophene crystal.

    Science.gov (United States)

    Petelenz, Piotr; Zak, Emil

    2014-10-16

    Femtosecond kinetics of fluorescence rise in the sexithiophene crystal is studied on a microscopic model of intraband relaxation, where exciton energy is assumed to be dissipated by phonon-accompanied scattering, with the rates calculated earlier. The temporal evolution of the exciton population is described by a set of kinetic equations, solved numerically to yield the population buildup at the band bottom. Not only the time scale but also the shape of the rise curves is found to be unusually sensitive to excitation energy, exhibiting unique quasiperiodic dependence thereon, which is rationalized in terms of the underlying model. Further simulations demonstrate that the main conclusions are robust with respect to experimental factors such as finite temperature and inherent spectral broadening of the exciting pulse, while the calculated fluorescence rise times are found to be in excellent agreement with experimental data available to date. As the rise profiles are composed of a number of exponential contributions, which varies with excitation energy, the common practice of characterizing the population buildup in the emitting state by a single value of relaxation time turns out to be an oversimplification. New experiments giving further insight into the kinetics and mechanism of intraband exciton relaxation are suggested.

  6. Red-shifted carrier multiplication energy threshold and exciton recycling mechanisms in strongly interacting silicon nanocrystals.

    Science.gov (United States)

    Marri, Ivan; Govoni, Marco; Ossicini, Stefano

    2014-09-24

    We present density functional theory calculations of carrier multiplication properties in a system of strongly coupled silicon nanocrystals. Our results suggest that nanocrystal-nanocrystal interaction can lead to a reduction of the carrier multiplication energy threshold without altering the carrier multiplication efficiency at high energies, in agreement with experiments. The time evolution of the number of electron-hole pairs generated in a system of strongly interacting nanocrystals upon absorption of high-energy photons is analyzed by solving a system of coupled rate equations, where exciton recycling mechanisms are implemented. We reconsider the role played by Auger recombination which is here accounted also as an active, nondetrimental process.

  7. Surprisingly High Conductivity and Efficient Exciton Blocking in Fullerene/Wide-Energy-Gap Small Molecule Mixtures.

    Science.gov (United States)

    Bergemann, Kevin J; Amonoo, Jojo A; Song, Byeongseop; Green, Peter F; Forrest, Stephen R

    2015-06-10

    We find that mixtures of C60 with the wide energy gap, small molecular weight semiconductor bathophenanthroline (BPhen) exhibit a combination of surprisingly high electron conductivity and efficient exciton blocking when employed as buffer layers in organic photovoltaic cells. Photoluminescence quenching measurements show that a 1:1 BPhen/C60 mixed layer has an exciton blocking efficiency of 84 ± 5% compared to that of 100% for a neat BPhen layer. This high blocking efficiency is accompanied by a 100-fold increase in electron conductivity compared with neat BPhen. Transient photocurrent measurements show that charge transport through a neat BPhen buffer is dispersive, in contrast to nondispersive transport in the compound buffer. Interestingly, although the conductivity is high, there is no clearly defined insulating-to-conducting phase transition with increased insulating BPhen fraction. Thus, we infer that C60 undergoes nanoscale (80%) BPhen fractions.

  8. Exciton binding energies and absorption in intermixed GaAs-AlGaAs quantum wells

    Science.gov (United States)

    Meney, Alistair T.

    1992-12-01

    The optical properties of excitons in layer-intermixed GaAs-AlGaAs quantum wells are studied theoretically. The electronic dispersion is obtained using the 6×6 Luttinger-Kohn Hamiltonian for the valence bands, and an accurate expression for the conduction band dispersion which includes the effects of nonparabolicity and warping to fourth order in k. The HH1-CB1 (1s) and LH1-CB1(1s) exciton binding energies are calculated as a function of diffusion time. The absorption for both TE and TM polarization is obtained at several wavelengths, and is seen to decrease significantly with increased intermixing. The decrease in absorption is larger for narrow wells, where the effects of intermixing are more pronounced for a given diffusion time.

  9. Strongly Asymmetric Spectroscopy in Plasmon-Exciton Hybrid Systems due to Interference-Induced Energy Repartitioning

    Science.gov (United States)

    Ding, Si-Jing; Li, Xiaoguang; Nan, Fan; Zhong, Yu-Ting; Zhou, Li; Xiao, Xudong; Wang, Qu-Quan; Zhang, Zhenyu

    2017-10-01

    Recent intense effort has been devoted to exploring different manifestations of resonant excitations of strongly coupled plasmons and excitons, but so far such studies have been limited to situations where the Fano- or Rabi-type spectra are largely symmetric at zero detuning. Using a newly developed full quantum mechanical model, here we reveal the existence of a highly asymmetric spectroscopic regime for both the Rabi splitting and transparency dip. The asymmetric nature is inherently tied to the non-negligible exciton absorbance and is caused by substantial interference-induced energy repartitioning of the resonance peaks. This theoretical framework can be exploited to reveal the quantum behaviors of the two excitation entities with varying mutual coupling strengths in both linear and nonlinear regimes. We also use prototypical systems of rhodamine molecules strongly coupled with AuAg alloyed nanoparticles and well-devised control experiments to demonstrate the validity and tunability of the energy repartitioning and correlated electronic state occupations, as captured by the variations in the asymmetric spectroscopy and corresponding nonlinear absorption coefficient as a function of the Au:Ag ratio. The present study helps to substantially enrich our microscopic understanding of strongly coupled plasmon-exciton systems.

  10. Direct Imaging of Frenkel Exciton Transport by Ultrafast Microscopy.

    Science.gov (United States)

    Zhu, Tong; Wan, Yan; Huang, Libai

    2017-07-18

    Long-range transport of Frenkel excitons is crucial for achieving efficient molecular-based solar energy harvesting. Understanding of exciton transport mechanisms is important for designing materials for solar energy applications. One major bottleneck in unraveling of exciton transport mechanisms is the lack of direct measurements to provide information in both spatial and temporal domains, imposed by the combination of fast energy transfer (typically ≤1 ps) and short exciton diffusion lengths (typically ≤100 nm). This challenge requires developing experimental tools to directly characterize excitation energy transport, and thus facilitate the elucidation of mechanisms. To address this challenge, we have employed ultrafast transient absorption microscopy (TAM) as a means to directly image exciton transport with ∼200 fs time resolution and ∼50 nm spatial precision. By mapping population in spatial and temporal domains, such approach has unraveled otherwise obscured information and provided important parameters for testing exciton transport models. In this Account, we discuss the recent progress in imaging Frenkel exciton migration in molecular crystals and aggregates by ultrafast microscopy. First, we establish the validity of the TAM methods by imaging singlet and triplet exciton transport in a series of polyacene single crystals that undergo singlet fission. A new singlet-mediated triplet transport pathway has been revealed by TAM, resulting from the equilibrium between triplet and singlet exciton populations. Such enhancement of triplet exciton transport enables triplet excitons to migrate as singlet excitons and leads to orders of magnitude faster apparent triplet exciton diffusion rate in the picosecond and nanosecond time scales, favorable for solar cell applications. Next we discuss how information obtained by ultrafast microscopy can evaluate coherent effects in exciton transport. We use tubular molecular aggregates that could support large exciton

  11. Quantum Coherence as a Witness of Vibronically Hot Energy Transfer in Bacterial Reaction Centre

    CERN Document Server

    Paleček, David; Westenhoff, Sebastian; Zigmantas, Donatas

    2016-01-01

    Photosynthetic proteins have evolved over billions of years so as to undergo optimal energy transfer to the sites of charge separation. Based on spectroscopically detected quantum coherences, it has been suggested that this energy transfer is partially wavelike. This conclusion critically depends on assignment of the coherences to the evolution of excitonic superpositions. Here we demonstrate for a bacterial reaction centre protein that long-lived coherent spectroscopic oscillations, which bear canonical signatures of excitonic superpositions, are essentially vibrational excited state coherences shifted to the ground state of the chromophores . We show that appearance of these coherences is brought about by release of electronic energy during the energy transfer. Our results establish how energy migrates on vibrationally hot chromophores in the reaction centre and they call for a re-examination of claims of quantum energy transfer in photosynthesis.

  12. Assistance of molecular vibrations on coherent energy transfer in photosynthesis from the view of a quantum heat engine.

    Science.gov (United States)

    Zhang, Zhedong; Wang, Jin

    2015-04-02

    Recently, the quantum nature in the energy transport in solar cells and light-harvesting complexes has attracted much attention as being triggered by the experimental observations. We model the light-harvesting complex (i.e., PEB50 dimer) as a quantum heat engine (QHE) and study the effect of the undamped intramolecule vibrational modes on the coherent energy-transfer process and quantum transport. We find that the exciton-vibration interaction has nontrivial contribution to the promotion of quantum yield as well as transport properties of the QHE at steady state by enhancing the quantum coherence quantified by entanglement entropy. The perfect quantum yield over 90% has been obtained, with the exciton-vibration coupling. We attribute these improvements to the renormalization of the electronic couplings effectively induced by exciton-vibration interaction and the subsequent delocalization of excitons. Finally, we demonstrate that the thermal relaxation and dephasing can help the excitation energy transfer in the PEB50 dimer.

  13. Tracing of backward energy transfer from LH1 to LH2 in photosynthetic membranes grown under high and low irradiation.

    Directory of Open Access Journals (Sweden)

    Lanzani G.

    2013-03-01

    Full Text Available By introducing derivative transient absorption spectroscopy, we obtain rate constants for backward and forward energy transfer between LH1 and LH2 complexes in purple bacterial membranes. We find that backward energy transfer is strongly reduced in membranes grown under low irradiation conditions, compared to high light grown ones. We conclude that backward energy transfer is managed actively by the bacteria to avoid LH1 exciton deactivation under high irradiation conditions. The analytical method is generally applicable to excitonically coupled systems.

  14. Intramolecular Energy Transfer, Charge Transfer & Hydrogen Bond

    Indian Academy of Sciences (India)

    Ultrafast Dynamics of Chemical Reactions in Condensed Phase: Intramolecular Energy Transfer, Charge Transfer & Hydrogen Bond · PowerPoint Presentation · Slide 3 · Slide 4 · Slide 5 · Slide 6 · Slide 7 · Slide 8 · Slide 9 · Slide 10 · Slide 11 · Slide 12 · Slide 13 · Slide 14 · Slide 15 · Slide 16 · Slide 17 · Slide 18 · Slide 19.

  15. Ultrafast exciton dynamics at molecular surfaces

    Science.gov (United States)

    Monahan, Nicholas R.

    Further improvements to device performance are necessary to make solar energy conversion a compelling alternative to fossil fuels. Singlet exciton fission and charge separation are two processes that can heavily influence the power conversion efficiency of a solar cell. During exciton fission one singlet excitation converts into two triplet excitons, potentially doubling the photocurrent generated by higher energy photons. There is significant discord over the singlet fission mechanism and of particular interest is whether the process involves a multiexciton intermediate state. I used time-resolved two-photon photoemission to investigate singlet fission in hexacene thin films, a model system with strong electronic coupling. My results indicate that a multiexciton state forms within 40 fs of photoexcitation and loses singlet character on a 280 fs timescale, creating two triplet excitons. This is concordant with the transient absorption spectra of hexacene single crystals and definitively proves that exciton fission in hexacene proceeds through a multiexciton state. This state is likely common to all strongly-coupled systems and my results suggest that a reassessment of the generally-accepted singlet fission mechanism is required. Charge separation is the process of splitting neutral excitons into carriers that occurs at donor-acceptor heterojunctions in organic solar cells. Although this process is essential for device functionality, there are few compelling explanations for why it is highly efficient in certain organic photovoltaic systems. To investigate the charge separation process, I used the model system of charge transfer excitons at hexacene surfaces and time-resolved two-photon photoemission. Charge transfer excitons with sufficient energy spontaneously delocalize, growing from about 14 nm to over 50 nm within 200 fs. Entropy drives this delocalization, as the density of states within the Coulomb potential increases significantly with energy. This charge

  16. Photoluminescence and energy transfer in PVK/DCM blends

    Science.gov (United States)

    Bruno, Annalisa; Del Mauro, Anna De Girolamo; Nenna, Giuseppe; Maglione, Maria Grazia; Minarini, Carla

    2012-07-01

    In this work, the photophysical proprieties of 4-(dicyanomethylene)-2-methyl-6-(p-dimethylaminostyryl)-4H-pyran (DCM) dye in the poly-vinylcarbazole (PVK) matrix are analyzed with a particular attention to the energy transfer processes between the matrix and the dye. PVP films with varying weight percent (from 1 to 8 wt%) of DCM have been fabricated. The presence of DCM induces a red shift in the emission spectra of the blend and a quenching effect in the excitons lifetime increasing the concentration of the dopants. These two phenomena have been studied in terms of energy processes inside the blends.

  17. Role of excitons in the energy resolution of scintillators used for medical imaging

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Jai [School of Engineering and IT, B-purple-12, Faculty of EHS, Charles Darwin University, Darwin NT 0909 (Australia)

    2010-11-01

    Theoretical investigations suggest that the nonproportionality in a scintillator is caused by the high excitation density created within the track of an X-ray or {gamma} ray photon entering in a scintillating crystal. In this paper an analytical expression for the scintillator yield is derived. For the case of BaF{sub 2} scintillator the role of excitons created within the {gamma}-ray track in the scintillator yield is studied. By comparing the results of two theories an analytical expression is also derived for an energy parameter which could otherwise only be determined by fitting the theoretical yield to the experimental data.

  18. Highly accurate analytical energy of a two-dimensional exciton in a constant magnetic field

    Energy Technology Data Exchange (ETDEWEB)

    Hoang, Ngoc-Tram D. [Department of Physics, Ho Chi Minh City University of Pedagogy 280, An Duong Vuong Street, District 5, Ho Chi Minh City (Viet Nam); Nguyen, Duy-Anh P. [Department of Natural Science, Thu Dau Mot University, 6, Tran Van On Street, Thu Dau Mot City, Binh Duong Province (Viet Nam); Hoang, Van-Hung [Department of Physics, Ho Chi Minh City University of Pedagogy 280, An Duong Vuong Street, District 5, Ho Chi Minh City (Viet Nam); Le, Van-Hoang, E-mail: levanhoang@tdt.edu.vn [Atomic Molecular and Optical Physics Research Group, Ton Duc Thang University, 19 Nguyen Huu Tho Street, Tan Phong Ward, District 7, Ho Chi Minh City (Viet Nam); Faculty of Applied Sciences, Ton Duc Thang University, 19 Nguyen Huu Tho Street, Tan Phong Ward, District 7, Ho Chi Minh City (Viet Nam)

    2016-08-15

    Explicit expressions are given for analytically describing the dependence of the energy of a two-dimensional exciton on magnetic field intensity. These expressions are highly accurate with the precision of up to three decimal places for the whole range of the magnetic field intensity. The results are shown for the ground state and some excited states; moreover, we have all formulae to obtain similar expressions of any excited state. Analysis of numerical results shows that the precision of three decimal places is maintained for the excited states with the principal quantum number of up to n=100.

  19. Generation of multiple excitons in Ag2S quantum dots: Single high-energy versus multiple-photon excitation

    KAUST Repository

    Sun, Jingya

    2014-02-20

    We explored biexciton generation via carrier multiplication (or multiple-exciton generation) by high-energy photons and by multiple-photon absorption in Ag2S quantum dots (QDs) using femtosecond broad-band transient absorption spectroscopy. Irrespective of the size of the QDs and how the multiple excitons are generated in the Ag2S QDs, two distinct characteristic time constants of 9.6-10.2 and 135-175 ps are obtained for the nonradiative Auger recombination of the multiple excitons, indicating the existence of two binding excitons, namely, tightly bound and weakly bound excitons. More importantly, the lifetimes of multiple excitons in Ag 2S QDs were about 1 and 2 orders of magnitude longer than those of comparable size PbS QDs and single-walled carbon nanotubes, respectively. This result is significant because it suggests that by utilizing an appropriate electron acceptor, there is a higher possibility to extract multiple electron-hole pairs in Ag2S QDs, which should improve the performance of QD-based solar cell devices. © 2014 American Chemical Society.

  20. Excitation energy transfer in a classical analogue of photosynthetic antennae.

    Science.gov (United States)

    Mančal, Tomáš

    2013-09-26

    We formulate a classical pure dephasing system-bath interaction model in a full correspondence to the well-studied quantum model of natural light-harvesting antennae. The equations of motion of our classical model not only represent the correct classical analogy to the quantum description of excitonic systems, but they also have exactly the same functional form. We demonstrate derivation of classical dissipation and relaxation tensor in second order perturbation theory. We find that the only difference between the classical and quantum descriptions is in the interpretation of the state and in certain limitations imposed on the parameters of the model by classical physics. The effects of delocalization, transfer pathway interference, and the transition from coherent to diffusive transfer can be found already in the classical realm. The only qualitatively new effect occurring in quantum systems is the preference for a downhill energy transfer and the resulting possibility of trapping the energy in the lowest energy state.

  1. Excitonic, vibrational, and van der Waals interactions in electron energy loss spectroscopy.

    Science.gov (United States)

    Mizoguchi, T; Miyata, T; Olovsson, W

    2017-09-01

    The pioneer, Ondrej L. Krivanek, and his collaborators have opened up many frontiers for the electron energy loss spectroscopy (EELS), and they have demonstrated new potentials of the EELS method for investigating materials. Here, inspired by those achievements, we show further potentials of EELS based on the results of theoretical calculations, that is excitonic and van der Waals (vdW) interactions, as well as vibrational information of materials. Concerning the excitonic interactions, we highlight the importance of the two-particle calculation to reproduce the low energy-loss near-edge structure (ELNES), the Na-L 2,3 edge of NaI and the Li-K edge of LiCl and LiFePO 4 . Furthermore, an unusually strong excitonic interaction at the O-K edge of perovskite oxides, SrTiO 3 and LaAlO 3 , is shown. The effect of the vdW interaction in the ELNES is also investigated, and we observe that the magnitude of the vdW effect is approximately 0.1eV in the case of the ELNES from a solid and liquid, whereas its effect is almost negligible in the case of the ELNES from the gaseous phase owing to the long inter-molecular distance. In addition to the "static" information, the influence of the "dynamic" behavior of atoms in materials to EELS is also investigated. We show that measurements of the infrared spectrum are possible by using a modern monochromator system. Furthermore, an estimation of the atomic vibration in core-loss ELNES is also presented. We show the acquisition of vibrational information using the ELNES of liquid methanol and acetic acid, solid Al 2 O 3 , and oxygen gas. Copyright © 2017 Elsevier B.V. All rights reserved.

  2. Electron energy loss spectroscopy of excitons in two-dimensional-semiconductors as a function of temperature

    KAUST Repository

    Tizei, Luiz H. G.

    2016-04-21

    We have explored the benefits of performing monochromated Electron Energy Loss Spectroscopy(EELS) in samples at cryogenic temperatures. As an example, we have observed the excitonic absorption peaks in single layer Transition Metal Dichalcogenides. These peaks appear separated by small energies due to spin orbit coupling. We have been able to distinguish the split for MoS2 below 300 K and for MoSe2 below 220 K. However, the distinction between peaks is only clear at 150 K. We have measured the change in absorption threshold between 150 K and 770 K for MoS2 and MoSe2. We discuss the effect of carbon and ice contamination in EELSspectra. The increased spectral resolution available made possible with modern monochromators in electron microscopes will require the development of stable sample holders which reaches temperatures far below that of liquid nitrogen.

  3. Self-energy effect and Coulomb potential modulation of the exciton in monolayer MoS2 on polar substrate

    Science.gov (United States)

    Wang, Zi-Wu; Xiao, Yao; Li, Run-Ze; Li, Wei-Ping; Li, Zhi-Qing

    2017-11-01

    We theoretically investigate the correction of exciton binding energy in monolayer MoS2 resulting from the exciton couples with surface optical (SO) phonons induced by polar substrate. The total correction of binding energy can be divided into the self-energy effect and modification of Coulomb potential using the unitary transformation method. We find that both the self-energy and Coulomb potential vary from tens of meV to several hundreds of meV depending on the cut-off wave vector of SO phonon modes, polarizability of substrate materials and internal distance between the monolayer MoS2 and polar substrate. An effective Coulomb potential is obtained by combining the modified term into the Coulomb potential. This potentially could be widely used in various two-dimensional materials. Our theoretical results not only propose the ways to externally control the exciton binding energy in experiment, but also enrich the understanding of the exciton properties in the dielectric environment.

  4. Elementary Energy Transfer Pathways in Allochromatium vinosum Photosynthetic Membranes

    Energy Technology Data Exchange (ETDEWEB)

    Lüer, Larry; Carey, Anne-Marie; Henry, Sarah; Maiuri, Margherita; Hacking, Kirsty; Polli, Dario; Cerullo, Giulio; Cogdell, Richard J.

    2015-11-01

    Allochromatium vinosum (formerly Chromatium vinosum) purple bacteria are known to adapt their light-harvesting strategy during growth according to environmental factors such as temperature and average light intensity. Under low light illumination or low ambient temperature conditions, most of the LH2 complexes in the photosynthetic membranes form a B820 exciton with reduced spectral overlap with LH1. To elucidate the reason for this light and temperature adaptation of the LH2 electronic structure, we performed broadband femtosecond transient absorption spectroscopy as a function of excitation wavelength in A. vinosum membranes. A target analysis of the acquired data yielded individual rate constants for all relevant elementary energy transfer (ET) processes. We found that the ET dynamics in high-light-grown membranes was well described by a homogeneous model, with forward and backward rate constants independent of the pump wavelength. Thus, the overall B800→B850→B890→ Reaction Center ET cascade is well described by simple triexponential kinetics. In the low-light-grown membranes, we found that the elementary backward transfer rate constant from B890 to B820 was strongly reduced compared with the corresponding constant from B890 to B850 in high-light-grown samples. The ET dynamics of low-light-grown membranes was strongly dependent on the pump wavelength, clearly showing that the excitation memory is not lost throughout the exciton lifetime. The observed pump energy dependence of the forward and backward ET rate constants suggests exciton diffusion via B850→ B850 transfer steps, making the overall ET dynamics nonexponential. Our results show that disorder plays a crucial role in our understanding of low-light adaptation in A. vinosum.

  5. Elementary Energy Transfer Pathways in Allochromatium vinosum Photosynthetic Membranes

    Science.gov (United States)

    Lüer, Larry; Carey, Anne-Marie; Henry, Sarah; Maiuri, Margherita; Hacking, Kirsty; Polli, Dario; Cerullo, Giulio; Cogdell, Richard J.

    2015-01-01

    Allochromatium vinosum (formerly Chromatium vinosum) purple bacteria are known to adapt their light-harvesting strategy during growth according to environmental factors such as temperature and average light intensity. Under low light illumination or low ambient temperature conditions, most of the LH2 complexes in the photosynthetic membranes form a B820 exciton with reduced spectral overlap with LH1. To elucidate the reason for this light and temperature adaptation of the LH2 electronic structure, we performed broadband femtosecond transient absorption spectroscopy as a function of excitation wavelength in A. vinosum membranes. A target analysis of the acquired data yielded individual rate constants for all relevant elementary energy transfer (ET) processes. We found that the ET dynamics in high-light-grown membranes was well described by a homogeneous model, with forward and backward rate constants independent of the pump wavelength. Thus, the overall B800→B850→B890→ Reaction Center ET cascade is well described by simple triexponential kinetics. In the low-light-grown membranes, we found that the elementary backward transfer rate constant from B890 to B820 was strongly reduced compared with the corresponding constant from B890 to B850 in high-light-grown samples. The ET dynamics of low-light-grown membranes was strongly dependent on the pump wavelength, clearly showing that the excitation memory is not lost throughout the exciton lifetime. The observed pump energy dependence of the forward and backward ET rate constants suggests exciton diffusion via B850→ B850 transfer steps, making the overall ET dynamics nonexponential. Our results show that disorder plays a crucial role in our understanding of low-light adaptation in A. vinosum. PMID:26536265

  6. Nature does not rely on long-lived electronic quantum coherence for photosynthetic energy transfer

    Science.gov (United States)

    Duan, Hong-Guang; Prokhorenko, Valentyn I.; Cogdell, Richard J.; Ashraf, Khuram; Stevens, Amy L.; Thorwart, Michael; Miller, R. J. Dwayne

    2017-08-01

    During the first steps of photosynthesis, the energy of impinging solar photons is transformed into electronic excitation energy of the light-harvesting biomolecular complexes. The subsequent energy transfer to the reaction center is commonly rationalized in terms of excitons moving on a grid of biomolecular chromophores on typical timescales light-harvesting complexes, we anticipate that this finding is general and directly applies to even larger photoactive biomolecular complexes.

  7. Energy transfer with semiconductor nanocrystals

    NARCIS (Netherlands)

    Rogach, A.L.; Klar, T.A.; Lupton, J.M.; Meijerink, A.; Feldmann, J.

    2009-01-01

    Fo¨ rster (or fluorescence) resonant energy transfer (FRET) is a powerful spectroscopic technique to study interactions, conformational and distance changes, in hybrid nanosystems. Semiconductor nanocrystals, also known as colloidal quantum dots, are highly efficient fluorophores with a strong

  8. Effects of Herzberg-Teller vibronic coupling on coherent excitation energy transfer

    Science.gov (United States)

    Zhang, Hou-Dao; Qiao, Qin; Xu, Rui-Xue; Yan, YiJing

    2016-11-01

    In this work, we study the effects of non-Condon vibronic coupling on the quantum coherence of excitation energy transfer, via the exact dissipaton-equation-of-motion evaluations on excitonic model systems. Field-triggered excitation energy transfer dynamics and two dimensional coherent spectroscopy are simulated for both Condon and non-Condon vibronic couplings. Our results clearly demonstrate that the non-Condon vibronic coupling intensifies the dynamical electronic-vibrational energy transfer and enhances the total system-and-bath quantum coherence. Moreover, the hybrid bath dynamics for non-Condon effects enriches the theoretical calculation, and further sheds light on the interpretation of the experimental nonlinear spectroscopy.

  9. Excitation energy transfer in a non-markovian dynamical disordered environment: localization, narrowing, and transfer efficiency.

    Science.gov (United States)

    Chen, Xin; Silbey, Robert J

    2011-05-12

    The non-markovian effect of a fluctuating environment plays an important role in electronic excitation transfer in organic disordered media, such as light-harvesting systems and conjugated polymers. Stochastic Liouville equations (SLE) are used to study the interaction between excitons and the environment. We model the non-markovian environment phenomenologically with a dichotomic process. An exact approach to solve the SLE based on Shapiro and Loginov's differentiation formulas allows us to rigorously study the effect of the non-markovian environment on excitation energy transfer, such as coherence conservation and its implication for transfer efficiency. This simple SLE model goes beyond the perturbative second-order master equation valid for both the weak coupling and short time correlation conditions. In addition, we discuss why our non-markovian model is a good approximation to the SLE model driven by the stationary Gauss-Markov process (Ornstein-Uhlenbeck process) over a broad range of fluctuation strengths and correlation times. Numerical results based on our SLE model for dimeric aggregates and the Fenna-Matthews-Olson (FMO) complex reveal the important interplay of intermolecular coupling, correlation time, and fluctuation strength, and their effects on the exciton relaxation process due to the environmental phonon. The results also uncover the connection between localization and motional narrowing, and the efficiency of electronic excitation transfer, demonstrating that the non-markovian environment is critical for chromophore aggregates to achieve an optimal transfer rate in a noisy environment and to contribute to the robustness of the FMO excitation energy transfer network.

  10. Disorder-induced exciton localization and violation of optical selection rules in supramolecular nanotubes

    NARCIS (Netherlands)

    Vlaming, S. M.; Bloemsma, E. A.; Nietiadi, M. Linggarsari; Knoester, J.

    2011-01-01

    Using numerical simulations, we study the effect of disorder on the optical properties of cylindrical aggregates of molecules with strong excitation transfer interactions. The exciton states and the energy transport properties of such molecular nanotubes attract considerable interest for application

  11. Energy transfer processes in solar energy conversion

    Energy Technology Data Exchange (ETDEWEB)

    Fayer, M.D.

    1986-11-01

    By combining picosecond optical experiments and detailed statistical mechanics theory we continue to increase our understanding of the complex interplay of structure and dynamics in important energy transfer situations. A number of different types of problems will be focused on experimentally and theoretically. They are excitation transport among chromophores attached to finite size polymer coils; excitation transport among chromophores in monolayers, bilayers, and finite and infinite stacks of layers; excitation transport in large vesicle systems; and photoinduced electron transfer in glasses and liquids, focusing particularly on the back transfer of the electron from the photogenerated radical anion to the radical cation. 33 refs., 13 figs.

  12. Stray energy transfer during endoscopy.

    Science.gov (United States)

    Jones, Edward L; Madani, Amin; Overbey, Douglas M; Kiourti, Asimina; Bojja-Venkatakrishnan, Satheesh; Mikami, Dean J; Hazey, Jeffrey W; Arcomano, Todd R; Robinson, Thomas N

    2017-10-01

    Endoscopy is the standard tool for the evaluation and treatment of gastrointestinal disorders. While the risk of complication is low, the use of energy devices can increase complications by 100-fold. The mechanism of increased injury and presence of stray energy is unknown. The purpose of the study was to determine if stray energy transfer occurs during endoscopy and if so, to define strategies to minimize the risk of energy complications. A gastroscope was introduced into the stomach of an anesthetized pig. A monopolar generator delivered energy for 5 s to a snare without contacting tissue or the endoscope itself. The endoscope tip orientation, energy device type, power level, energy mode, and generator type were varied to mimic in vivo use. The primary outcome (stray current) was quantified as the change in tissue temperature (°C) from baseline at the tissue closest to the tip of the endoscope. Data were reported as mean ± standard deviation. Using the 60 W coag mode while changing the orientation of the endoscope tip, tissue temperature increased by 12.1 ± 3.5 °C nearest the camera lens (p energy transfer (p = 0.04 and p = 0.002, respectively) as did utilizing the low-voltage cut mode (6.6 ± 0.5 °C, p energy transfer compared to a standard generator (1.5 ± 3.5 °C vs. 9.5 ± 0.8 °C, p energy is transferred within the endoscope during the activation of common energy devices. This could result in post-polypectomy syndrome, bleeding, or perforation outside of the endoscopist's view. Decreasing the power, utilizing low-voltage modes and/or an impedance-monitoring generator can decrease the risk of complication.

  13. Mapping the exciton diffusion in semiconductor nanocrystal solids.

    Science.gov (United States)

    Kholmicheva, Natalia; Moroz, Pavel; Bastola, Ebin; Razgoniaeva, Natalia; Bocanegra, Jesus; Shaughnessy, Martin; Porach, Zack; Khon, Dmitriy; Zamkov, Mikhail

    2015-03-24

    Colloidal nanocrystal solids represent an emerging class of functional materials that hold strong promise for device applications. The macroscopic properties of these disordered assemblies are determined by complex trajectories of exciton diffusion processes, which are still poorly understood. Owing to the lack of theoretical insight, experimental strategies for probing the exciton dynamics in quantum dot solids are in great demand. Here, we develop an experimental technique for mapping the motion of excitons in semiconductor nanocrystal films with a subdiffraction spatial sensitivity and a picosecond temporal resolution. This was accomplished by doping PbS nanocrystal solids with metal nanoparticles that force the exciton dissociation at known distances from their birth. The optical signature of the exciton motion was then inferred from the changes in the emission lifetime, which was mapped to the location of exciton quenching sites. By correlating the metal-metal interparticle distance in the film with corresponding changes in the emission lifetime, we could obtain important transport characteristics, including the exciton diffusion length, the number of predissociation hops, the rate of interparticle energy transfer, and the exciton diffusivity. The benefits of this approach to device applications were demonstrated through the use of two representative film morphologies featuring weak and strong interparticle coupling.

  14. Exciton broadening in WS2/graphene heterostructures

    Science.gov (United States)

    Hill, Heather M.; Rigosi, Albert F.; Raja, Archana; Chernikov, Alexey; Roquelet, Cyrielle; Heinz, Tony F.

    2017-11-01

    We have used optical spectroscopy to observe spectral broadening of WS2 exciton reflectance peaks in heterostructures of monolayer WS2 capped with mono- to few-layer graphene. The broadening is found to be similar for the A and B excitons and on the order of 5-10 meV. No strong dependence on the number of graphene layers was observed within experimental uncertainty. The broadening can be attributed to charge- and energy-transfer processes between the two materials, providing an observed lower bound for the corresponding time scales of 65 fs.

  15. Effects of inter-molecular charge-transfer excitons on the external quantum efficiency of zinc-porphyrin/C{sub 60} heterojunction photovoltaic cells

    Energy Technology Data Exchange (ETDEWEB)

    Ryuzaki, Sou; Kai, Toshihiro; Onoe, Jun [Department of Nuclear Engineering, Tokyo Institute of Technology, Tokyo 152-8550 (Japan); Toda, Yasunori; Adachi, Satoru, E-mail: jonoe@nr.titech.ac.jp [Department of Applied Physics, Hokkaido University, Sapporo, Hokkaido 060-8628 (Japan)

    2011-04-13

    We have examined the structural effects of zinc-octaethylporphyrin [Zn(OEP)] films used as a donor on the external quantum efficiency (EQE) of organic heterojunction photovoltaic (OPV) cells [ITO/Zn(OEP)/C{sub 60}/Al], and investigated what exactly causes the improvement of EQE. When the structure of the Zn(OEP) films changed from amorphous to crystalline, the maximum EQE increased from 36% to 42%, which is greater than that of around 35% for previously reported OPV cells using buffer materials (Peumans and Forrest 2001 Appl. Phys. Lett. 79 126). The crystallization of Zn(OEP) films is found to increase the number of inter-molecular charge-transfer (IMCT) excitons and to enlarge the mobility of carriers and IMCT excitons, thus significantly improving the EQE of the photoabsorption band under illumination due to the IMCT excitons.

  16. Förster Resonance Energy Transfer and Harvesting in II-VI Fractional Monolayer Structures

    Science.gov (United States)

    Shubina, T. V.; Semina, M. A.; Belyaev, K. G.; Rodina, A. V.; Toropov, A. A.; Ivanov, S. V.

    2017-07-01

    We report on Förster resonance energy transfer in the dense arrays of epitaxial quantum dots (QDs), formed by fractional monolayer CdSe insertions within a ZnSe matrix. In such arrays comprising the QDs of different sizes, the energy transfer can take place between the ground levels of small QDs and the excited levels of large radiating QDs, when these states are in resonance. This mechanism provides directional excitation of a limited number of the large QDs possessing the excited levels. It reveals itself by the shrinkage of photoluminescence (PL) bands and the appearance of the narrow single excitonic lines in micro-PL spectra. The strong shortening of characteristic PL decay times in the energy-donating QDs is observed when the distance between them and the energy-accepting QDs decreases. Photoluminescence excitation spectroscopy demonstrates the switching of the dominant energy transfer mechanism at the energy predicted by theoretical modeling of the excitonic levels in the QD arrays. Our results pave the way for engineering of the architecture of excitonic levels in the QD arrays to realize efficient nano-emitters.

  17. Exciton multiplication from first principles.

    Science.gov (United States)

    Jaeger, Heather M; Hyeon-Deuk, Kim; Prezhdo, Oleg V

    2013-06-18

    Third-generation photovolatics require demanding cost and power conversion efficiency standards, which may be achieved through efficient exciton multiplication. Therefore, generating more than one electron-hole pair from the absorption of a single photon has vast ramifications on solar power conversion technology. Unlike their bulk counterparts, irradiated semiconductor quantum dots exhibit efficient exciton multiplication, due to confinement-enhanced Coulomb interactions and slower nonradiative losses. The exact characterization of the complicated photoexcited processes within quantum-dot photovoltaics is a work in progress. In this Account, we focus on the photophysics of nanocrystals and investigate three constituent processes of exciton multiplication, including photoexcitation, phonon-induced dephasing, and impact ionization. We quantify the role of each process in exciton multiplication through ab initio computation and analysis of many-electron wave functions. The probability of observing a multiple exciton in a photoexcited state is proportional to the magnitude of electron correlation, where correlated electrons can be simultaneously promoted across the band gap. Energies of multiple excitons are determined directly from the excited state wave functions, defining the threshold for multiple exciton generation. This threshold is strongly perturbed in the presence of surface defects, dopants, and ionization. Within a few femtoseconds following photoexcitation, the quantum state loses coherence through interactions with the vibrating atomic lattice. The phase relationship between single excitons and multiple excitons dissipates first, followed by multiple exciton fission. Single excitons are coupled to multiple excitons through Coulomb and electron-phonon interactions, and as a consequence, single excitons convert to multiple excitons and vice versa. Here, exciton multiplication depends on the initial energy and coupling magnitude and competes with electron

  18. Mutations to R. sphaeroides Reaction Center Perturb Energy Levels and Vibronic Coupling but Not Observed Energy Transfer Rates.

    Science.gov (United States)

    Flanagan, Moira L; Long, Phillip D; Dahlberg, Peter D; Rolczynski, Brian S; Massey, Sara C; Engel, Gregory S

    2016-03-10

    The bacterial reaction center is capable of both efficiently collecting and quickly transferring energy within the complex; therefore, the reaction center serves as a convenient model for both energy transfer and charge separation. To spectroscopically probe the interactions between the electronic excited states on the chromophores and their intricate relationship with vibrational motions in their environment, we examine coherences between the excited states. Here, we investigate this question by introducing a series of point mutations within 12 Å of the special pair of bacteriochlorophylls in the Rhodobacter sphaeroides reaction center. Using two-dimensional spectroscopy, we find that the time scales of energy transfer dynamics remain unperturbed by these mutations. However, within these spectra, we detect changes in the mixed vibrational-electronic coherences in these reaction centers. Our results indicate that resonance between bacteriochlorophyll vibrational modes and excitonic energy gaps promote electronic coherences and support current vibronic models of photosynthetic energy transfer.

  19. Direct determination of monolayer MoS2 and WSe2 exciton binding energies on insulating and metallic substrates

    KAUST Repository

    Park, Soohyung

    2018-01-03

    Understanding the excitonic nature of excited states in two-dimensional (2D) transition-metal dichalcogenides (TMDCs) is of key importance to make use of their optical and charge transport properties in optoelectronic applications. We contribute to this by the direct experimental determination of the exciton binding energy (E b,exc) of monolayer MoS2 and WSe2 on two fundamentally different substrates, i.e. the insulator sapphire and the metal gold. By combining angle-resolved direct and inverse photoelectron spectroscopy we measure the electronic band gap (E g), and by reflectance measurements the optical excitonic band gap (E exc). The difference of these two energies is E b,exc. The values of E g and E b,exc are 2.11 eV and 240 meV for MoS2 on sapphire, and 1.89 eV and 240 meV for WSe2 on sapphire. On Au E b,exc is decreased to 90 meV and 140 meV for MoS2 and WSe2, respectively. The significant E b,exc reduction is primarily due to a reduction of E g resulting from enhanced screening by the metal, while E exc is barely decreased for the metal support. Energy level diagrams determined at the K-point of the 2D TMDCs Brillouin zone show that MoS2 has more p-type character on Au as compared to sapphire, while WSe2 appears close to intrinsic on both. These results demonstrate that the impact of the dielectric environment of 2D TMDCs is more pronounced for individual charge carriers than for a correlated electron–hole pair, i.e. the exciton. A proper dielectric surrounding design for such 2D semiconductors can therefore be used to facilitate superior optoelectronic device function.

  20. Energy transfer pathways in semiconducting carbon nanotubes revealed using two-dimensional white-light spectroscopy.

    Science.gov (United States)

    Mehlenbacher, Randy D; McDonough, Thomas J; Grechko, Maksim; Wu, Meng-Yin; Arnold, Michael S; Zanni, Martin T

    2015-04-13

    Thin film networks of highly purified semiconducting carbon nanotubes (CNTs) are being explored for energy harvesting and optoelectronic devices because of their exceptional transport and optical properties. The nanotubes in these films are in close contact, which permits energy to flow through the films, although the pathways and mechanisms for energy transfer are largely unknown. Here we use a broadband continuum to collect femtosecond two-dimensional white-light spectra. The continuum spans 500 to 1,300 nm, resolving energy transfer between all combinations of bandgap (S1) and higher (S2) transitions. We observe ultrafast energy redistribution on the S2 states, non-Förster energy transfer on the S1 states and anti-correlated energy levels. The two-dimensional spectra reveal competing pathways for energy transfer, with S2 excitons taking routes depending on the bandgap separation, whereas S1 excitons relax independent of the bandgap. These observations provide a basis for understanding and ultimately controlling the photophysics of energy flow in CNT-based devices.

  1. Spiro-linked hyperbranched architecture in electrophosphorescent conjugated polymers for tailoring triplet energy back transfer.

    Science.gov (United States)

    Shao, Shiyang; Ma, Zhihua; Ding, Junqiao; Wang, Lixiang; Jing, Xiabin; Wang, Fosong

    2012-04-17

    A spiro-linked hyperbranched architecture has been incorporated into electrophosphorescent conjugated polymers for the first time, aiming at simultaneously tailoring the intra- and intermolecular triplet energy back transfer from the phosphorescent guest to the conjugated polymer host. Based on a prototype with this unique structure, slower decay of triplet excitons, and 5-8 fold enhancement of device efficiencies are obtained compared with the conventional blending counterpart. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  2. Localized diabatization applied to excitons in molecular crystals

    Science.gov (United States)

    Jin, Zuxin; Subotnik, Joseph E.

    2017-06-01

    Traditional ab initio electronic structure calculations of periodic systems yield delocalized eigenstates that should be understood as adiabatic states. For example, excitons are bands of extended states which superimpose localized excitations on every lattice site. However, in general, in order to study the effects of nuclear motion on exciton transport, it is standard to work with a localized description of excitons, especially in a hopping regime; even in a band regime, a localized description can be helpful. To extract localized excitons from a band requires essentially a diabatization procedure. In this paper, three distinct methods are proposed for such localized diabatization: (i) a simple projection method, (ii) a more general Pipek-Mezey localization scheme, and (iii) a variant of Boys diabatization. Approaches (i) and (ii) require localized, single-particle Wannier orbitals, while approach (iii) has no such dependence. These methods should be very useful for studying energy transfer through solids with ab initio calculations.

  3. Ab initio-based exciton model of amide I vibrations in peptides: definition, conformational dependence, and transferability.

    Science.gov (United States)

    Gorbunov, Roman D; Kosov, Daniil S; Stock, Gerhard

    2005-06-08

    Various aspects of the ab initio-based parametrization of an exciton model of amide I vibrations in peptides are discussed. Adopting "glycine dipeptide" (Ac-Gly-NHCH3) as a simple building-block model that describes the vibrational interaction between two peptide units, we perform comprehensive quantum-chemical calculations to investigate the effect and importance of the level of theory, the choice of local coordinates, and the localization method. A solvent continuum model description turns out important to obtain planar CONH peptide units when a full geometry optimization (which is necessary to obtain the correct frequencies) is performed. To study the conformational dependence of the amide I vibrations, we calculate (phi,psi) maps of the local-mode frequencies and couplings. Performing conformational averages of the (phi,psi) maps with respect to the most important peptide conformational states in solution (alpha, beta, P(II), and C5), we discuss the relation between these measurable quantities and the corresponding conformation of the peptide. Finally, the transferability of these maps to dipeptides with hydrophilic and hydrophobic side chains as well as to tripeptides with charged end groups is investigated.

  4. The Assistance of Molecular Vibrations on Coherent Energy Transfer in Photosynthesis from the View of Quantum Heat Engine

    CERN Document Server

    Zhang, Zhedong

    2015-01-01

    Recently the quantum nature in the energy transport in solar cell and light-harvesting complexes have attracted much attention, as being triggered by the experimental observations. We model the light-harvesting complex (i.e., PEB50 dimer) as a quantum heat engine (QHE) and study the effect of the undamped intra-molecule vibrational modes on the coherent energy transfer process and quantum transport. We find that the exciton-vibration interaction has non-trivial contribution to the promotion of quantum yield as well as transport properties of the quantum heat engine at steady state, by enhancing the quantum coherence quantified by entanglement entropy. The perfect quantum yield over 90% has been obtained, with theexciton-vibration coupling. We attribute these improvements to the renormalization of the electronic couplings effectively induced by exciton-vibration interaction and the subsequent delocalization of excitons. Finally we demonstrate that the thermal relaxation and dephasing can help the excitation en...

  5. Effect of periodic potential on exciton states in semiconductor carbon nanotubes

    Energy Technology Data Exchange (ETDEWEB)

    Roslyak, Oleksiy, E-mail: oroslyak@fordham.edu [Department of Physics and Engineering Physics, Fordham University, Bronx, NY 10458 (United States); Piryatinski, Andrei, E-mail: apiryat@lanl.gov [Theoretical Division, Los Alamos National Laboratory, Los Alamos, NM 87545 (United States)

    2016-12-20

    We develop a theoretical background to treat exciton states in semiconductor single-walled carbon nanotubes (SWCNTs) in the presence of a periodic potential induced by a surface acoustic wave (SAW) propagating along SWCNT. The formalism accounts for the electronic band splitting into the Floquet sub-bands induced by the Bragg scattering on the SAW potential. Optical transitions between the Floquet states and correlated electron–hole pairs (excitons) are numerically examined. Formation of new van Hove singularities within the edges of Floquet sub-bands and associated transfer of the exciton oscillator strengths resulting in the photoluminescence quenching are predicted. The simulations demonstrate the exciton energy red Stark shift and reduction in the exciton binding energy. Comparison of our results with reported theoretical and experimental studies is provided.

  6. Probing long-lived dark excitons in self-assembled quantum dots

    DEFF Research Database (Denmark)

    Johansen, Jeppe; Julsgaard, Brian; Stobbe, Søren

    2010-01-01

    size. The energy dependence is compared to a recent model from the literature, in which the spin flip is due to the combined action of short-range exchange interaction and acoustic phonons. We furthermore observe a pronounced enhancement of the spin-flip rate close to semiconductor-air interfaces......Long-lived dark exciton states are formed in self-assembled quantum dots due to the combination of the angular momentum of electrons and holes. The lifetime of dark excitons are determined by spin-flip processes that transfer dark excitons into radiative bright excitons. We employ time......-resolved spontaneous emission measurements in a modified local density of optical states to unambiguously record the spin-flip rate. Pronounced variations in the spin-flip rate with the quantum dot emission energy are observed demonstrating that the exciton storage time can be extended by controlling the quantum dot...

  7. Excitons in solid C60

    Energy Technology Data Exchange (ETDEWEB)

    Shirley, Eric L.; Benedict, Lorin X.; Louie, Steven G.

    1995-10-01

    Exciton levels in undoped, solid C60 are calculated using a model Hamiltonian. We find excitation energies of 1.58 and 1.30 eV for the lowest singlet and triplet exciton, respectively, in comparison with the measured energies of 1.83 and 1.55 eV. Singlet and triplet states have similar energy diagrams, wherein exciton states having T{sub 2g}, T{sub 1g},G{sub g}, and H{sub g} symmetries are separated by up to several tenths of an electron volt. As a function of crystal momentum, exciton energies exhibit dispersion from 20 to 40 meV. Theoretical pressure derivatives of exciton energies are presented.

  8. Soft x-ray excitonics

    Science.gov (United States)

    Moulet, A.; Bertrand, J. B.; Klostermann, T.; Guggenmos, A.; Karpowicz, N.; Goulielmakis, E.

    2017-09-01

    The dynamic response of excitons in solids is central to modern condensed-phase physics, material sciences, and photonic technologies. However, study and control have hitherto been limited to photon energies lower than the fundamental band gap. Here we report application of attosecond soft x-ray and attosecond optical pulses to study the dynamics of core-excitons at the L2,3 edge of Si in silicon dioxide (SiO2). This attosecond x-ray absorption near-edge spectroscopy (AXANES) technique enables direct probing of the excitons’ quasiparticle character, tracking of their subfemtosecond relaxation, the measurement of excitonic polarizability, and observation of dark core-excitonic states. Direct measurement and control of core-excitons in solids lay the foundation of x-ray excitonics.

  9. Fragment transition density method to calculate electronic coupling for excitation energy transfer

    Energy Technology Data Exchange (ETDEWEB)

    Voityuk, Alexander A., E-mail: alexander.voityuk@icrea.cat [Institució Catalana de Recerca i Estudis Avançats, 08010 Barcelona, Spain and Institut de Química Computacional i Catàlisi (IQCC), Universitat de Girona 17071 Girona (Spain)

    2014-06-28

    A general approach, the Fragment Transition Density (FTD) scheme, is introduced to estimate electronic coupling for excitation energy transfer in a molecular system. Within this method, the excitation energies and transition densities of the system are used to derive the coupling matrix element. The scheme allows one to treat systems where exciton donor and acceptor are close together and their exchange interaction and orbital overlap are significant. The FTD method can be applied in combination with any quantum mechanical approach to treat excited states of general nature including single-, double-, and higher excitations. Using FTD approach, we derive excitonic couplings for several systems computed with the CIS, TD DFT and MS-CASPT2 methods. In particular, it is shown that the estimated coupling values in DNA π-stacks are strongly affected by the short-range electronic interaction of adjacent nucleobases.

  10. Temperature-dependent resonance energy transfer from semiconductor quantum wells to graphene.

    Science.gov (United States)

    Yu, Young-Jun; Kim, Keun Soo; Nam, Jungtae; Kwon, Se Ra; Byun, Hyeryoung; Lee, Kwanjae; Ryou, Jae-Hyun; Dupuis, Russell D; Kim, Jeomoh; Ahn, Gwanghyun; Ryu, Sunmin; Ryu, Mee-Yi; Kim, Jin Soo

    2015-02-11

    Resonance energy transfer (RET) has been employed for interpreting the energy interaction of graphene combined with semiconductor materials such as nanoparticles and quantum-well (QW) heterostructures. Especially, for the application of graphene as a transparent electrode for semiconductor light emitting diodes, the mechanism of exciton recombination processes such as RET in graphene-semiconductor QW heterojunctions should be understood clearly. Here, we characterized the temperature-dependent RET behaviors in graphene/semiconductor QW heterostructures. We then observed the tuning of the RET efficiency from 5% to 30% in graphene/QW heterostructures with ∼60 nm dipole-dipole coupled distance at temperatures of 300 to 10 K. This survey allows us to identify the roles of localized and free excitons in the RET process from the QWs to graphene as a function of temperature.

  11. Temperature dependence of exciton peak energies in ZnS, ZnSe, and ZnTe epitaxial films

    Science.gov (United States)

    Pässler, R.; Griebl, E.; Riepl, H.; Lautner, G.; Bauer, S.; Preis, H.; Gebhardt, W.; Buda, B.; As, D. J.; Schikora, D.; Lischka, K.; Papagelis, K.; Ves, S.

    1999-10-01

    High-quality ZnS, ZnSe, and ZnTe epitaxial films were grown on (001)-GaAs-substrates by molecular beam epitaxy. The 1s-exciton peak energy positions have been determined by absorption measurements from 2 K up to about room temperature. For ZnS and ZnSe additional high-temperature 1s-exciton energy data were obtained by reflectance measurements performed from 300 up to about 550 K. These complete E1s(T) data sets are fitted using a recently developed analytical model. The high-temperature slopes of the individual E1s(T) curves and the effective phonon temperatures of ZnS, ZnSe, and ZnTe are found to scale almost linearly with the corresponding zero-temperature energy gaps and the Debye temperatures, respectively. Various ad hoc formulas of Varshni type, which have been invoked in recent articles for numerical simulations of restricted E1s(T) data sets for cubic ZnS, are discussed.

  12. Excitons and Davydov splitting in sexithiophene from first-principles many-body Green's function theory.

    Science.gov (United States)

    Leng, Xia; Yin, Huabing; Liang, Dongmei; Ma, Yuchen

    2015-09-21

    Organic semiconductors have promising and broad applications in optoelectronics. Understanding their electronic excited states is important to help us control their spectroscopic properties and performance of devices. There have been a large amount of experimental investigations on spectroscopies of organic semiconductors, but theoretical calculation from first principles on this respect is still limited. Here, we use density functional theory (DFT) and many-body Green's function theory, which includes the GW method and Bethe-Salpeter equation, to study the electronic excited-state properties and spectroscopies of one prototypical organic semiconductor, sexithiophene. The exciton energies of sexithiophene in both the gas and bulk crystalline phases are very sensitive to the exchange-correlation functionals used in DFT for ground-state structure relaxation. We investigated the influence of dynamical screening in the electron-hole interaction on exciton energies, which is found to be very pronounced for triplet excitons and has to be taken into account in first principles calculations. In the sexithiophene single crystal, the energy of the lowest triplet exciton is close to half the energy of the lowest singlet one. While lower-energy singlet and triplet excitons are intramolecular Frenkel excitons, higher-energy excitons are of intermolecular charge-transfer type. The calculated optical absorption spectra and Davydov splitting are in good agreement with experiments.

  13. High Performing Ternary Solar Cells through Förster Resonance Energy Transfer between Nonfullerene Acceptors.

    Science.gov (United States)

    Yang, Lei; Gu, Wenxing; Hong, Ling; Mi, Yang; Liu, Feng; Liu, Ming; Yang, Yufei; Sharma, Bigyan; Liu, Xinfeng; Huang, Hui

    2017-08-16

    Nonradiative Förster resonance energy transfer (FRET) is an important mechanism of organic solar cells, which can improve the exciton migration over a long distance, resulting in improvement of efficiency of solar cells. However, the current observations of FRET are very limited, and the efficiencies are less than 9%. In this study, FRET effect was first observed between two nonfullerene acceptors in ternary solar cells, which improved both the absorption range and exciton harvesting, leading to the dramatic enhancement in the short circuit current and power conversion efficiency. Moreover, this strategy is proved to be a versatile platform for conjugated polymers with different bandgaps, resulting in a remarkable efficiency of 10.4%. These results demonstrated a novel method to enhance the efficiency of organic soar cells.

  14. Coherence in Energy Transfer and Photosynthesis

    Science.gov (United States)

    Chenu, Aurélia; Scholes, Gregory D.

    2015-04-01

    Ultrafast energy transfer is used to transmit electronic excitation among the many molecules in photosynthetic antenna complexes. Recent experiments and theories have highlighted the role of coherent transfer in femtosecond studies of these proteins, suggesting the need for accurate dynamical models to capture the subtle characteristics of energy transfer mechanisms. Here we discuss how to think about coherence in light harvesting and electronic energy transfer. We review the various fundamental concepts of coherence, spanning from classical phenomena to the quantum superposition, and define coherence in electronic energy transfer. We describe the current status of experimental studies on light-harvesting complexes. Insights into the microscopic process are presented to highlight how and why this is a challenging problem to elucidate. We present an overview of the applicable dynamical theories to model energy transfer in the intermediate coupling regime.

  15. Direct observation of multistep energy transfer in LHCII with fifth-order 3D electronic spectroscopy

    Science.gov (United States)

    Zhang, Zhengyang; Lambrev, Petar H.; Wells, Kym L.; Garab, Győző; Tan, Howe-Siang

    2015-07-01

    During photosynthesis, sunlight is efficiently captured by light-harvesting complexes, and the excitation energy is then funneled towards the reaction centre. These photosynthetic excitation energy transfer (EET) pathways are complex and proceed in a multistep fashion. Ultrafast two-dimensional electronic spectroscopy (2DES) is an important tool to study EET processes in photosynthetic complexes. However, the multistep EET processes can only be indirectly inferred by correlating different cross peaks from a series of 2DES spectra. Here we directly observe multistep EET processes in LHCII using ultrafast fifth-order three-dimensional electronic spectroscopy (3DES). We measure cross peaks in 3DES spectra of LHCII that directly indicate energy transfer from excitons in the chlorophyll b (Chl b) manifold to the low-energy level chlorophyll a (Chl a) via mid-level Chl a energy states. This new spectroscopic technique allows scientists to move a step towards mapping the complete complex EET processes in photosynthetic systems.

  16. Plasmon-enhanced energy transfer for improved upconversion of infrared radiation in doped-lanthanide nanocrystals.

    Science.gov (United States)

    Sun, Qi-C; Mundoor, Haridas; Ribot, Josep C; Singh, Vivek; Smalyukh, Ivan I; Nagpal, Prashant

    2014-01-08

    Upconversion of infrared radiation into visible light has been investigated for applications in photovoltaics and biological imaging. However, low conversion efficiency due to small absorption cross-section for infrared light (Yb(3+)), and slow rate of energy transfer (to Er(3+) states) has prevented application of upconversion photoluminescence (UPL) for diffuse sunlight or imaging tissue samples. Here, we utilize resonant surface plasmon polaritons (SPP) waves to enhance UPL in doped-lanthanide nanocrystals. Our analysis indicates that SPP waves not only enhance the electromagnetic field, and hence weak Purcell effect, but also increase the rate of resonant energy transfer from Yb(3+) to Er(3+) ions by 6 fold. While we do observe strong metal mediated quenching (14-fold) of green fluorescence on flat metal surfaces, the nanostructured metal is resonant in the infrared and hence enhances the nanocrystal UPL. This strong Coulombic effect on energy transfer can have important implications for other fluorescent and excitonic systems too.

  17. Bound Exciton Complexes

    Science.gov (United States)

    Meyer, B. K.

    In the preceding chapter, we concentrated on the properties of free excitons. These free excitons may move through the sample and hit a trap, a nonradiative or a radiative recombination center. At low temperatures, the latter case gives rise to either deep center luminescence, mentioned in Sect. 7.1 and discussed in detail in Chap. 9, or to the luminescence of bound exciton complexes (BE or BEC). The chapter continues with the most prominent of these BECs, namely A-excitons bound to neutral donors. The next aspects are the more weakly BEs at ionized donors. The Sect. 7.4 treats the binding or localization energies of BEC from a theoretical point of view, while Sect. 7.5 is dedicated to excited states of BECs, which contain either holes from deeper valence bands or an envelope function with higher quantum numbers. The last section is devoted to donor-acceptor pair transitions. There is no section devoted specifically to excitons bound to neutral acceptors, because this topic is still partly controversially discussed. Instead, information on these A0X complexes is scattered over the whole chapter, however, with some special emphasis seen in Sects. 7.1, 7.4, and 7.5.

  18. Excitation energy transfer in individual light-harvesting chlorosome from green photosynthetic bacterium Chloroflexus aurantiacus at cryogenic temperature

    Science.gov (United States)

    Saga, Yoshitaka; Tamiaki, Hitoshi; Shibata, Yutaka; Itoh, Shigeru

    2005-06-01

    The excitation energy transfer from bacteriochlorophyll(BChl)- c self-aggregates to energy-accepting BChl- a in proteins (baseplates) in an individual photosynthetic light-harvesting complex (chlorosome) of a green filamentous photosynthetic bacterium Chloroflexus aurantiacus was successfully observed at cryogenic temperature. The ratio of intensity of the fluorescence peak of BChl- a to that of BChl- c self-aggregates in individual chlorosomes, which demonstrated relative efficiency of the excitation energy transfer, was heterogeneous between 0.09 and 0.72. This suggests that excitonic interaction between BChl- c self-aggregates and BChl- a in baseplates was heterogeneous among individual chlorosomes.

  19. Design and geometry of hybrid white light-emitted diodes for efficient energy transfer from the quantum well to the nanocrystals

    DEFF Research Database (Denmark)

    Kopylov, Oleksii; Huck, Alexander; Shirazi, Roza

    2013-01-01

    We demonstrate light color conversion in patterned InGaN light-emitting diodes (LEDs), which is enhanced via nonradiative exciton resonant energy transfer (RET) from the electrically driven diode to colloidal semiconductor nanocrystals (NCs). Patterning of the diode is essential for the coupling...

  20. Machine learning exciton dynamics

    Energy Technology Data Exchange (ETDEWEB)

    Häse, Florian [Harvard Univ., Cambridge, MA (United States); Technische Univ. Munchen, Garching (Germany). Dept. Physik; Valleau, Stéphanie [Harvard Univ., Cambridge, MA (United States); Pyzer-Knapp, Edward [Harvard Univ., Cambridge, MA (United States); Aspuru-Guzik, Alán [Harvard Univ., Cambridge, MA (United States)

    2016-04-01

    Obtaining the exciton dynamics of large photosynthetic complexes by using mixed quantum mechanics/molecular mechanics (QM/MM) is computationally demanding. We propose a machine learning technique, multi-layer perceptrons, as a tool to reduce the time required to compute excited state energies. With this approach we predict time-dependent density functional theory (TDDFT) excited state energies of bacteriochlorophylls in the Fenna–Matthews–Olson (FMO) complex. Additionally we compute spectral densities and exciton populations from the predictions. Different methods to determine multi-layer perceptron training sets are introduced, leading to several initial data selections. In addition, we compute spectral densities and exciton populations. Once multi-layer perceptrons are trained, predicting excited state energies was found to be significantly faster than the corresponding QM/MM calculations. We showed that multi-layer perceptrons can successfully reproduce the energies of QM/MM calculations to a high degree of accuracy with prediction errors contained within 0.01 eV (0.5%). Spectral densities and exciton dynamics are also in agreement with the TDDFT results. The acceleration and accurate prediction of dynamics strongly encourage the combination of machine learning techniques with ab initio methods.

  1. Nature does not rely on long-lived electronic quantum coherence for photosynthetic energy transfer

    CERN Document Server

    Duan, Hong-Guang; Cogdell, Richard; Ashraf, Khuram; Stevens, Amy L; Thorwart, Michael; Miller, R J Dwayne

    2016-01-01

    During the first steps of photosynthesis, the energy of impinging solar photons is transformed into electronic excitation energy of the light-harvesting biomolecular complexes. The subsequent energy transfer to the reaction center is understood in terms of exciton quasiparticles which move on a grid of biomolecular sites on typical time scales less than 100 femtoseconds (fs). Since the early days of quantum mechanics, this energy transfer is described as an incoherent Forster hopping with classical site occupation probabilities, but with quantum mechanically determined rate constants. This orthodox picture has been challenged by ultrafast optical spectroscopy experiments with the Fenna-Matthews-Olson protein in which interference oscillatory signals up to 1.5 picoseconds were reported and interpreted as direct evidence of exceptionally long-lived electronic quantum coherence. Here, we show that the optical 2D photon echo spectra of this complex at ambient temperature in aqueous solution do not provide evidenc...

  2. Noise-assisted energy transfer in quantum networks and light-harvesting complexes

    Energy Technology Data Exchange (ETDEWEB)

    Chin, A W; Caruso, F; Huelga, S F; Plenio, M B [Institut fuer Theoretische Physik, Universitaet Ulm, D-89069, Ulm (Germany); Datta, A, E-mail: alex.chin@uni-ulm.d [Institute for Mathematical Sciences, Imperial College London, 53 Exhibition Road, London SW7 2PG (United Kingdom)

    2010-06-15

    We provide physically intuitive mechanisms for the effect of noise on excitation energy transfer (EET) in networks. Using these mechanisms of dephasing-assisted transport (DAT) in a hybrid basis of both excitons and sites, we develop a detailed picture of how noise enables energy transfer with efficiencies well above 90% across the Fenna-Matthew-Olson (FMO) complex, a type of light-harvesting molecule. We demonstrate explicitly how noise alters the pathways of energy transfer across the complex, suppressing ineffective pathways and facilitating direct ones to the reaction centre. We explain that the fundamental mechanisms underpinning DAT are expected to be robust with respect to the considered noise model but show that the specific details of the exciton-phonon coupling, which remain largely unknown in these type of complexes, and in particular the impact of non-Markovian effects, result in variations of dynamical features that should be amenable to experimental verification with current or planned technology. A detailed understanding of DAT in natural compounds could open up a new paradigm of 'noise-engineering' by which EET can be optimized in artificial light-harvesting structures.

  3. Comparing multiple exciton generation in quantum dots to impact ionization in bulk semiconductors: implications for enhancement of solar energy conversion.

    Science.gov (United States)

    Beard, Matthew C; Midgett, Aaron G; Hanna, Mark C; Luther, Joseph M; Hughes, Barbara K; Nozik, Arthur J

    2010-08-11

    Multiple exciton generation (MEG) in quantum dots (QDs) and impact ionization (II) in bulk semiconductors are processes that describe producing more than one electron-hole pair per absorbed photon. We derive expressions for the proper way to compare MEG in QDs with II in bulk semiconductors and argue that there are important differences in the photophysics between bulk semiconductors and QDs. Our analysis demonstrates that the fundamental unit of energy required to produce each electron-hole pair in a given QD is the band gap energy. We find that the efficiency of the multiplication process increases by at least 2 in PbSe QDs compared to bulk PbSe, while the competition between cooling and multiplication favors multiplication by a factor of 3 in QDs. We also demonstrate that power conversion efficiencies in QD solar cells exhibiting MEG can greatly exceed conversion efficiencies of their bulk counterparts, especially if the MEG threshold energy can be reduced toward twice the QD band gap energy, which requires a further increase in the MEG efficiency. Finally, we discuss the research challenges associated with achieving the maximum benefit of MEG in solar energy conversion since we show the threshold and efficiency are mathematically related.

  4. Resonance energy transfer: Dye to metal nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Wari, M. N.; Pujar, G. H.; Inamdar, S. R., E-mail: him-lax3@yahoo.com [Laser Spectroscopy Programme, Department of Physics, Karnatak University, Dharwad-580003 (India)

    2015-06-24

    In the present study, surface energy transfer (SET) from Coumarin 540A (C540 A) to Gold nanoparticle (Au) is demonstrated. The observed results show pronounced effect on the photoluminescence intensity and shortening of the lifetime of Coumarin 540A upon interaction with the spherical gold nanoparticle, also there are measured effects on radiative rate of the dye. Experimental results are analyzed with fluorescence resonance energy transfer (FRET) and SET theories. The results obtained from distance-dependent quenching provide experimental evidence that the efficiency curve slope and distance of quenching is best modeled by surface energy transfer process.

  5. Exciton-related energies of the 1s-like states of excitons in GaAs-Ga{sub 1-x}Al{sub x}As double quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Miranda, Guillermo L. [Fisica Teorica y Aplicada, Escuela de Ingenieria de Antioquia, A.A. 7516, Medellin (Colombia); Mora-Ramos, M.E. [Facultad de Ciencias, Universidad Autonoma del Estado de Morelos, Av. Universidad 1001, C.P. 62209, Cuernavaca, Morelos (Mexico); Duque, C.A., E-mail: cduque_echeverri@yahoo.es [Instituto de Fisica, Universidad de Antioquia, AA 1226, Medellin (Colombia)

    2012-10-15

    The dependencies of the binding energies of the lowest four 1s-like exciton states in GaAs-(Ga,Al)As coupled double quantum wells (CDQW) on the geometric parameters of the system are theoretically studied. A variational approach, together with the parabolic band and effective mass approximations, were considered in order to perform the numerical calculations. It is shown that in the case of a symmetric system there is a degeneracy between the heavy-hole even and odd states and this degeneracy can be removed by the presence of a sufficiently narrow middle barrier. In contrast to this fact, the electron even and odd states are never degenerated. It is detected that, if the system is asymmetric, there will appear binding energies anticrossings between the heavy-hole states at the point of the asymmetric {yields} symmetric QW transition. - Highlights: Black-Right-Pointing-Pointer Study of 1s-like exciton states in double quantum wells. Black-Right-Pointing-Pointer Binding energy decreases with the presence of second well. Black-Right-Pointing-Pointer Binding energy of (2,2) state can be larger than (1,1) state. Black-Right-Pointing-Pointer Central barrier can remove degeneracy of states. Black-Right-Pointing-Pointer Anticrossing between states can be induced via symmetries.

  6. Doping location-dependent energy transfer dynamics in Mn-doped CdS/ZnS nanocrystals.

    Science.gov (United States)

    Chen, Hsiang-Yun; Maiti, Sourav; Son, Dong Hee

    2012-01-24

    Dynamics of energy transfer and charge carrier localization in Mn-doped CdS/ZnS core/shell nanocrystals correlated with doping location and concentration are studied via transient absorption measurement of exciton relaxation dynamics. The strong dependence of exciton-Mn energy transfer rate on doping location was directly resolved in the transient bleach recovery and electron intraband absorption data by using layer-by-layer synthesized Mn-doped nanocrystals. With 1.2 nm decrease in doping radius in the ZnS shell, energy transfer rate increases by 6 fold. We identified that hole trapping is the major competing process that inhibits the energy transfer in Mn-doped CdS/ZnS nanocrystals. From the branching ratio of the energy transfer and hole trapping, combined with luminescence quantum yield measurement, we also obtained doping location-dependent radiative relaxation quantum yield of Mn(2+) ions that is as high as 0.95. © 2011 American Chemical Society

  7. Optical Energy Transfer and Conversion System

    Science.gov (United States)

    Stone, William C. (Inventor); Hogan, Bartholomew P. (Inventor)

    2015-01-01

    An optical power transfer system comprising a fiber spooler, a fiber optic rotary joint mechanically connected to the fiber spooler, and an electrical power extraction subsystem connected to the fiber optic rotary joint with an optical waveguide. Optical energy is generated at and transferred from a base station through fiber wrapped around the spooler, through the rotary joint, and ultimately to the power extraction system at a remote mobility platform for conversion to another form of energy.

  8. Targeting Low-Energy Ballistic Lunar Transfers

    Science.gov (United States)

    Parker, Jeffrey S.

    2010-01-01

    Numerous low-energy ballistic transfers exist between the Earth and Moon that require less fuel than conventional transfers, but require three or more months of transfer time. An entirely ballistic lunar transfer departs the Earth from a particular declination at some time in order to arrive at the Moon at a given time along a desirable approach. Maneuvers may be added to the trajectory in order to adjust the Earth departure to meet mission requirements. In this paper, we characterize the (Delta)V cost required to adjust a low-energy ballistic lunar transfer such that a spacecraft may depart the Earth at a desirable declination, e.g., 28.5(white bullet), on a designated date. This study identifies the optimal locations to place one or two maneuvers along a transfer to minimize the (Delta)V cost of the transfer. One practical application of this study is to characterize the launch period for a mission that aims to launch from a particular launch site, such as Cape Canaveral, Florida, and arrive at a particular orbit at the Moon on a given date using a three-month low-energy transfer.

  9. Wireless energy transfer between anisotropic metamaterials shells

    Energy Technology Data Exchange (ETDEWEB)

    Díaz-Rubio, Ana; Carbonell, Jorge; Sánchez-Dehesa, José, E-mail: jsdehesa@upv.es

    2014-06-15

    The behavior of strongly coupled Radial Photonic Crystals shells is investigated as a potential alternative to transfer electromagnetic energy wirelessly. These sub-wavelength resonant microstructures, which are based on anisotropic metamaterials, can produce efficient coupling phenomena due to their high quality factor. A configuration of selected constitutive parameters (permittivity and permeability) is analyzed in terms of its resonant characteristics. The coupling to loss ratio between two coupled resonators is calculated as a function of distance, the maximum (in excess of 300) is obtained when the shells are separated by three times their radius. Under practical conditions an 83% of maximum power transfer has been also estimated. -- Highlights: •Anisotropic metamaterial shells exhibit high quality factors and sub-wavelength size. •Exchange of electromagnetic energy between shells with high efficiency is analyzed. •Strong coupling is supported with high wireless transfer efficiency. •End-to-end energy transfer efficiencies higher than 83% can be predicted.

  10. Excitons in tunnel coupled CdTe and (Cd,Mn)Te quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Terletskii, Oleg; Ryabchenko, Sergiy; Tereshchenko, Oleksandr [Institute of Physics NASU, pr. Nauki 46, 03680 Kyiv (Ukraine); Sugakov, Volodymyr; Vertsimakha, Ganna [Institute for Nuclear Research NASU, pr. Nauki 47, 03680 Kyiv (Ukraine); Karczewski, Grzegorz [Institute of Physics PAS, Al. Lotnikow 32/46, PL-02-668 Warsaw (Poland)

    2017-05-15

    The photoluminescence (PL) from structures containing Cd{sub 0.95}Mn{sub 0.05}Te and CdTe quantum wells (QWs) separated by a narrow (1.94 nm) barrier was studied. The PL lines of comparable intensities from several possible exciton states were observed simultaneously at energy distances substantially exceeding kT. This means that the energy transfer in the studied systems is slower than the radiative recombination of the confined excitons. For the CdTe QW width of about 8.7-9 nm, indirect excitons with the electron and heavy hole chiefly localized in the CdTe and Cd{sub 1-x}Mn{sub x}Te QWs, respectively, were detected in the magnetic field. These indirect excitons have PL energy of about 10-20 meV above the PL line of the direct excitons in the CdTe QW. The observation of the PL from the indirect excitons which are not the lowest excitations in the structure is a distinctive feature of the system. Photoluminescence intensity dependence on the energy and the magnetic field. (copyright 2017 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim)

  11. Dynamic properties of excitons in ZnO/AlGaN/GaN hybrid nanostructures.

    Science.gov (United States)

    Forsberg, Mathias; Hemmingsson, Carl; Amano, Hiroshi; Pozina, Galia

    2015-01-20

    Hybrid samples based on ZnO colloidal nanocrystals (NCs) deposited on AlGaN/GaN quantum well (QW) structures with different top barrier thickness d = 3, 6 and 9 nm are studied by time-resolved photoluminescence. Thermal behavior of the QW exciton lifetime in the hybrids and in the bare QW structures has been compared and it has been found that the QW exciton recombination rate increases in the hybrid having d = 3 nm and decreases in the hybrid with d = 6 nm, while no change has been observed for the structure with d = 9 nm. It is suggested that non-radiative resonance energy transfer from the QW excitons to the ZnO NCs and a variation of the surface potential can both influence the QW exciton lifetime in the hybrids.

  12. Excitation energy transfer in the photosystem I

    Energy Technology Data Exchange (ETDEWEB)

    Webber, Andrew N

    2012-09-25

    Photosystem I is a multimeric pigment protein complex in plants, green alage and cyanobacteria that functions in series with Photosystem II to use light energy to oxidize water and reduce carbon dioxide. The Photosystem I core complex contains 96 chlorophyll a molecules and 22 carotenoids that are involved in light harvesting and electron transfer. In eucaryotes, PSI also has a peripheral light harvesting complex I (LHCI). The role of specific chlorophylls in excitation and electron transfer are still unresolved. In particular, the role of so-called bridging chlorophylls, located between the bulk antenna and the core electron transfer chain, in the transfer of excitation energy to the reaction center are unknown. During the past funding period, site directed mutagenesis has been used to create mutants that effect the physical properties of these key chlorophylls, and to explore how this alters the function of the photosystem. Studying these mutants using ultrafast absorption spectroscopy has led to a better understanding of the process by which excitation energy is transferred from the antenna chlorophylls to the electron transfer chain chlorophylls, and what the role of connecting chlorophylls and A_0 chlorophylls is in this process. We have also used these mutants to investigate whch of the central group of six chlorophylls are involved in the primary steps of charge separation and electron transfer.

  13. Energy Transfer Kinetics in Photosynthesis as an Inspiration for Improving Organic Solar Cells.

    Science.gov (United States)

    Nganou, Collins; Lackner, Gerhard; Teschome, Bezu; Deen, M Jamal; Adir, Noam; Pouhe, David; Lupascu, Doru C; Mkandawire, Martin

    2017-06-07

    Clues to designing highly efficient organic solar cells may lie in understanding the architecture of light-harvesting systems and exciton energy transfer (EET) processes in very efficient photosynthetic organisms. Here, we compare the kinetics of excitation energy tunnelling from the intact phycobilisome (PBS) light-harvesting antenna system to the reaction center in photosystem II in intact cells of the cyanobacterium Acaryochloris marina with the charge transfer after conversion of photons into photocurrent in vertically aligned carbon nanotube (va-CNT) organic solar cells with poly(3-hexyl)thiophene (P3HT) as the pigment. We find that the kinetics in electron hole creation following excitation at 600 nm in both PBS and va-CNT solar cells to be 450 and 500 fs, respectively. The EET process has a 3 and 14 ps pathway in the PBS, while in va-CNT solar cell devices, the charge trapping in the CNT takes 11 and 258 ps. We show that the main hindrance to efficiency of va-CNT organic solar cells is the slow migration of the charges after exciton formation.

  14. Spatially indirect excitons in coupled quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Lai, Chih-Wei Eddy [Univ. of California, Berkeley, CA (United States)

    2004-03-01

    Microscopic quantum phenomena such as interference or phase coherence between different quantum states are rarely manifest in macroscopic systems due to a lack of significant correlation between different states. An exciton system is one candidate for observation of possible quantum collective effects. In the dilute limit, excitons in semiconductors behave as bosons and are expected to undergo Bose-Einstein condensation (BEC) at a temperature several orders of magnitude higher than for atomic BEC because of their light mass. Furthermore, well-developed modern semiconductor technologies offer flexible manipulations of an exciton system. Realization of BEC in solid-state systems can thus provide new opportunities for macroscopic quantum coherence research. In semiconductor coupled quantum wells (CQW) under across-well static electric field, excitons exist as separately confined electron-hole pairs. These spatially indirect excitons exhibit a radiative recombination time much longer than their thermal relaxation time a unique feature in direct band gap semiconductor based structures. Their mutual repulsive dipole interaction further stabilizes the exciton system at low temperature and screens in-plane disorder more effectively. All these features make indirect excitons in CQW a promising system to search for quantum collective effects. Properties of indirect excitons in CQW have been analyzed and investigated extensively. The experimental results based on time-integrated or time-resolved spatially-resolved photoluminescence (PL) spectroscopy and imaging are reported in two categories. (i) Generic indirect exciton systems: general properties of indirect excitons such as the dependence of exciton energy and lifetime on electric fields and densities were examined. (ii) Quasi-two-dimensional confined exciton systems: highly statistically degenerate exciton systems containing more than tens of thousands of excitons within areas as small as (10 micrometer)2 were

  15. Manifestations of Vibronic Coupling Effects in Molecular Spectroscopy: from the Quenching of Excitonic Energy Splittings to the Clements Bands of SO2

    Science.gov (United States)

    Koppel, Horst

    2013-06-01

    We investigate the excitation of vibrational modes and its impact on the excitonic energy splittings in doubly hydrogen-bonded molecular dimers. The experimental analysis, performed in collaboration by S. Leutwyler and coworkers (Univ. Bern), is based on high-resolution resonant two-photon ionization spectroscopy. The potential energy surfaces underlying the theoretical investigation are obtained at the RICC2/aug-cc-pVTZ level and are used for the dynamical analysis in the framework of a well-established vibronic coupling approach. The vertical electronic Davydov splitting of the S_1 and S_2 excited states exceeds the observed excitonic splitting by a factor of 10--40. This discrepancy can be understood by considering the quenching of the excitonic splitting by the excitation of vibrational modes in the electronic transition. Two different approaches have been employed and found to reconcile theory and experiment. The analysis of the vibronic structure of the S_2 ← S_0 excitation spectrum focusses on the ortho-cyanophenol dimer as a representative example. Most of the observed spectral features can be reproduced by the calculations, although some deviations remain. In the second part, new results on the UV absorption spectrum of SO_2 will be presented. This is complementary to the excitonic systems in that higher vibrational energies are involved and a conical intersection is accessible to the nuclear motion. Using the concept of regularized diabatic states in combination with high-accuracy MRCI potential energy surfaces, semi-quantitative agreement with the complex experimental (low-resolution) spectrum has been achieved for the first time. P. Ottiger, S. Leutwyler and H. Köppel, J. Chem. Phys. 136, 174308 (2012). S. Kopec, P. Ottiger, S. Leutwyler and H. Köppel, J. Chem. Phys. 137, 184312 (2012). H. Köppel and B. Schubert, Mol. Phys. 104, 1069 (2006). C. Leveque, A. Komainda, R. Taieb and H. Köppel, J. Chem. Phys. 138, 044320 (2013).

  16. Measurement of the separation dependence of resonant energy transfer between cadmium selenide/zinc sulfide

    Science.gov (United States)

    Shafiei, Farbod

    An apparatus has been built to study the separation dependence of the interaction between small and large resonant groups of CdSe/ZnS nanocrystallite quantum dots (NQDs). A near-field scanning optical microscope (NSOM) is used to bring a group of mono-disperse 6 nm diameter dots close (near-field range) to a 8 nm diameter group of dots which are deposited on a solid immersion lens. 3rd excited excitonic energy level of large NQD does match the ground excitonic energy level of small NQDs. Combination of spectral and positional filtering allows us to measure the interaction between small numbers of NQDs, with the ultimate goal of identifying the interaction between individual dots. Quenching of the small NQDs photoluminescence signal has been observed as the small NQDs get to close proximity of large NQDs. Separation between two groups of the NQDs was changing in the range of 15-40nm during the experiment. The transition probability between these two groups of NQDs is theoretically obtained to be (2.72x10--47m 6)=R6. Forster radius, as a signature of energy transfer efficiency is extracted from experimental data to be 17 nm.

  17. Interactive Joint Transfer of Energy and Information

    DEFF Research Database (Denmark)

    Popovski, Petar; Fouladgar, A. M.; Simeone, Osvaldo

    2013-01-01

    resources, such as radio waves, particles and qubits, can conceivably reuse, at least part, of the received resources. This paper aims at illustrating some of the new challenges that arise in the design of communication networks in which the signals exchanged by the nodes carry both information and energy......In some communication networks, such as passive RFID systems, the energy used to transfer information between a sender and a recipient can be reused for successive communication tasks. In fact, from known results in physics, any system that exchanges information via the transfer of given physical....... To this end, a baseline two-way communication system is considered in which two nodes communicate in an interactive fashion. In the system, a node can either send an “on” symbol (or “1”), which costs one unit of energy, or an “off” signal (or “0”), which does not require any energy expenditure. Upon reception...

  18. Recent advances in energy transfer in bulk and nanoscale luminescent materials: from spectroscopy to applications.

    Science.gov (United States)

    Liu, Xiaofeng; Qiu, Jianrong

    2015-12-07

    Transfer of energy occurs endlessly in our universe by means of radiation. Compared to energy transfer (ET) in free space, in solid state materials the transfer of energy occurs in a rather confined manner, which is usually mediated by real or virtual particles, including not only photons, but also electrons, phonons, and excitons. In the present review, we discuss the recent advances in optical ET by resonance mediated with photons in solid materials as well as their nanoscale counterparts, with focus on the photoluminescence behavior pertaining to ET between optically active centers, such as rare earth (RE) ions. This review begins with a brief discussion on the classification of optical ET together with an overview of the theoretical formulations and experimental method for the examination of ET. We will then present a comprehensive discussion on the ET in practical systems in which normal photoluminescence, upconversion and quantum cutting resulted from ET involving metal ions, QDs, organic species, 2D materials and plasmonic nanostructures. Diverse ET systems are therefore simply categorized into cases of ion-ion interactions and non-ion interactions. Special attention has been paid to the progress in the manipulation of spatially confined ET in nanostructured systems including core-shell structures, as well as the ET in multiple exciton generation found in QDs and organic molecules, which behave quite similarly to resonance ET between metal ion centers. Afterwards, we will discuss the broad spectrum of applications of ET in the aforementioned systems, including solid state lighting, solar energy utilization, bio-imaging and diagnosis, and sensing. In the closing part, along with a short summary, we discuss further research focus regarding the problems and possible future directions of optical ET in solids.

  19. Atomistic model for excitons: Capturing Strongly Bound Excitons in Monolayer Transition-Metal Dichalcogenides

    Science.gov (United States)

    Tseng, Frank; Simsek, Ergun; Gunlycke, Daniel

    2015-03-01

    Monolayer transition-metal dichalcogenides form a direct bandgap predicted in the visible regime making them attractive host materials for various electronic and optoelectronic applications. Due to a weak dielectric screening in these materials, strongly bound electron-hole pairs or excitons have binding energies up to at least several hundred meV's. While the conventional wisdom is to think of excitons as hydrogen-like quasi-particles, we show that the hydrogen model breaks down for these experimentally observed strongly bound, room-temperature excitons. To capture these non-hydrogen-like photo-excitations, we introduce an atomistic model for excitons that predicts both bright excitons and dark excitons, and their broken degeneracy in these two-dimensional materials. For strongly bound exciton states, the lattice potential significantly distorts the envelope wave functions, which affects predicted exciton peak energies. The combination of large binding energies and non-degeneracy of exciton states in monolayer transition metal dichalogendies may furthermore be exploited in room temperature applications where prolonged exciton lifetimes are necessary. This work has been funded by the Office of Naval Research (ONR), directly and through the Naval Research Laboratory (NRL). F.T and E.S acknowledge support from NRL through the NRC Research Associateship Program and ONR Summer Faculty Program, respectively.

  20. Nonclassical energy transfer in photosynthetic FMO complex

    Directory of Open Access Journals (Sweden)

    Abramavicius Vytautas

    2013-03-01

    Full Text Available Excitation energy transfer in a photosynthetic FMO complex has been simulated using the stochastic Schrödinger equation. Fluctuating chromophore transition energies are simulated from the quantum correlation function which allows to properly include the finite temperature. The resulting excitation dynamics shows fast thermalization of chromophore occupations into proper thermal equilibrium. The relaxation process is characterized by entropy dynamics, which shows nonclassical behavior.

  1. Energy transfer during the hydroentanglement of fibres

    CSIR Research Space (South Africa)

    Moyo, D

    2012-10-01

    Full Text Available , and the resultant degree of fibre entanglement, determines the tensile strength of the nonwoven fabric as a consequence of the inter-fibre friction. Here, the relationship between hydroentangling energy from the waterjets and the changes it brings about... in the nonwoven fabric strength were studied. In the study, the energies of the waterjets transferred to every fabric sample as a function of the waterjet pressure, machine speed, machine efficiency and the web area weight were quantified, and the resultant...

  2. Quantum efficiency enhancement in nanocrystals using nonradiative energy transfer with optimized donor-acceptor ratio for hybrid LEDs

    Science.gov (United States)

    Nizamoglu, Sedat; Akin, Onur; Demir, Hilmi Volkan

    2009-06-01

    The quantum efficiency enhancement in nanocrystal solids is critically important for their efficient use as luminophors on color-conversion light emitting diodes (LEDs). For this purpose, we investigate energy gradient mixture of nanocrystal solids for recycling their trapped excitons by varying their donor-acceptor nanocrystal ratios and study the resulting quantum efficiency enhancement as a function of the donor-acceptor ratio in the solid film for hybrid LEDs. We achieve a maximum quantum efficiency enhancement of 17% in these nanocrystal solids when the donor-acceptor ratio is 1:1, demonstrating their highly modified time-resolved photoluminescence decays to reveal the kinetics of strong energy transfer between them.

  3. Energy Efficient Storage and Transfer of Cryogens

    Science.gov (United States)

    Fesmire, James E.

    2013-01-01

    Cryogenics is globally linked to energy generation, storage, and usage. Thermal insulation systems research and development is an enabling part of NASA's technology goals for Space Launch and Exploration. New thermal testing methodologies and materials are being transferred to industry for a wide range of commercial applications.

  4. Risk transfer via energy savings insurance

    Energy Technology Data Exchange (ETDEWEB)

    Mills, Evan

    2001-10-01

    Among the key barriers to investment in energy efficiency improvements are uncertainties about attaining projected energy savings and apprehension about potential disputes over these savings. The fields of energy management and risk management are thus intertwined. While many technical methods have emerged to manage performance risks (e.g. building commissioning), financial risk transfer techniques are less developed in the energy management arena than in other more mature segments of the economy. Energy Savings Insurance (ESI) - formal insurance of predicted energy savings - is one method of transferring financial risks away from the facility owner or energy services contractor. ESI offers a number of significant advantages over other forms of financial risk transfer, e.g. savings guarantees or performance bonds. ESI providers manage risk via pre-construction design review as well as post-construction commissioning and measurement and verification of savings. We found that the two mos t common criticisms of ESI - excessive pricing and onerous exclusions - are not born out in practice. In fact, if properly applied, ESI can potentially reduce the net cost of energy savings projects by reducing the interest rates charged by lenders, and by increasing the level of savings through quality control. Debt service can also be ensured by matching loan payments to projected energy savings while designing the insurance mechanism so that payments are made by the insurer in the event of a savings shortfall. We estimate the U.S. ESI market potential of $875 million/year in premium income. From an energy-policy perspective, ESI offers a number of potential benefits: ESI transfers performance risk from the balance sheet of the entity implementing the energy savings project, thereby freeing up capital otherwise needed to ''self-insure'' the savings. ESI reduces barriers to market entry of smaller energy services firms who do not have sufficiently strong balance

  5. Optical spectroscopy of excited exciton states in MoS2 monolayers in van der Waals heterostructures

    Science.gov (United States)

    Robert, C.; Semina, M. A.; Cadiz, F.; Manca, M.; Courtade, E.; Taniguchi, T.; Watanabe, K.; Cai, H.; Tongay, S.; Lassagne, B.; Renucci, P.; Amand, T.; Marie, X.; Glazov, M. M.; Urbaszek, B.

    2018-01-01

    The optical properties of MoS2 monolayers are dominated by excitons, but for spectrally broad optical transitions in monolayers exfoliated directly onto SiO2 substrates detailed information on excited exciton states is inaccessible. Encapsulation in hexagonal boron nitride (hBN) allows approaching the homogenous exciton linewidth, but interferences in the van der Waals heterostructures make direct comparison between transitions in optical spectra with different oscillator strength more challenging. Here we reveal in reflectivity and in photoluminescence excitation spectroscopy the presence of excited states of the A exciton in MoS2 monolayers encapsulated in hBN layers of calibrated thickness, allowing us to extrapolate an exciton binding energy of ≈220 meV. We theoretically reproduce the energy separations and oscillator strengths measured in reflectivity by combining the exciton resonances calculated for a screened two-dimensional Coulomb potential with transfer matrix calculations of the reflectivity for the van der Waals structure. Our analysis shows a very different evolution of the exciton oscillator strength with principal quantum number for the screened Coulomb potential as compared to the ideal two-dimensional hydrogen model.

  6. Scaling laws of Rydberg excitons

    Science.gov (United States)

    Heckötter, J.; Freitag, M.; Fröhlich, D.; Aßmann, M.; Bayer, M.; Semina, M. A.; Glazov, M. M.

    2017-09-01

    Rydberg atoms have attracted considerable interest due to their huge interaction among each other and with external fields. They demonstrate characteristic scaling laws in dependence on the principal quantum number n for features such as the magnetic field for level crossing or the electric field of dissociation. Recently, the observation of excitons in highly excited states has allowed studying Rydberg physics in cuprous oxide crystals. Fundamentally different insights may be expected for Rydberg excitons, as the crystal environment and associated symmetry reduction compared to vacuum give not only optical access to many more states within an exciton multiplet but also extend the Hamiltonian for describing the exciton beyond the hydrogen model. Here we study experimentally and theoretically the scaling of several parameters of Rydberg excitons with n , for some of which we indeed find laws different from those of atoms. For others we find identical scaling laws with n , even though their origin may be distinctly different from the atomic case. At zero field the energy splitting of a particular multiplet n scales as n-3 due to crystal-specific terms in the Hamiltonian, e.g., from the valence band structure. From absorption spectra in magnetic field we find for the first crossing of levels with adjacent principal quantum numbers a Br∝n-4 dependence of the resonance field strength, Br, due to the dominant paramagnetic term unlike for atoms for which the diamagnetic contribution is decisive, resulting in a Br∝n-6 dependence. By contrast, the resonance electric field strength shows a scaling as Er∝n-5 as for Rydberg atoms. Also similar to atoms with the exception of hydrogen we observe anticrossings between states belonging to multiplets with different principal quantum numbers at these resonances. The energy splittings at the avoided crossings scale roughly as n-4, again due to crystal specific features in the exciton Hamiltonian. The data also allow us to

  7. Excitation energy transfer in natural photosynthetic complexes and chlorophyll trefoils: hole-burning and single complex/trefoil spectroscopic studies

    Energy Technology Data Exchange (ETDEWEB)

    Ryszard Jankowiak, Kansas State University, Department of Chemistry, CBC Bldg., Manhattan KS, 66505; Phone: (785) 532-6785

    2012-09-12

    In this project we studied both natural photosynthetic antenna complexes and various artificial systems (e.g. chlorophyll (Chl) trefoils) using high resolution hole-burning (HB) spectroscopy and excitonic calculations. Results obtained provided more insight into the electronic (excitonic) structure, inhomogeneity, electron-phonon coupling strength, vibrational frequencies, and excitation energy (or electron) transfer (EET) processes in several antennas and reaction centers. For example, our recent work provided important constraints and parameters for more advanced excitonic calculations of CP43, CP47, and PSII core complexes. Improved theoretical description of HB spectra for various model systems offers new insight into the excitonic structure and composition of low-energy absorption traps in very several antenna protein complexes and reaction centers. We anticipate that better understanding of HB spectra obtained for various photosynthetic complexes and their simultaneous fits with other optical spectra (i.e. absorption, emission, and circular dichroism spectra) provides more insight into the underlying electronic structures of these important biological systems. Our recent progress provides a necessary framework for probing the electronic structure of these systems via Hole Burning Spectroscopy. For example, we have shown that the theoretical description of non-resonant holes is more restrictive (in terms of possible site energies) than those of absorption and emission spectra. We have demonstrated that simultaneous description of linear optical spectra along with HB spectra provides more realistic site energies. We have also developed new algorithms to describe both nonresonant and resonant hole-burn spectra using more advanced Redfield theory. Simultaneous description of various optical spectra for complex biological system, e.g. artificial antenna systems, FMO protein complexes, water soluble protein complexes, and various mutants of reaction centers

  8. Multilayer-MCTDH approach to the energy transfer dynamics in the LH2 antenna complex

    Science.gov (United States)

    Shibl, Mohamed F.; Schulze, Jan; Al-Marri, Mohammed J.; Kühn, Oliver

    2017-09-01

    The multilayer multiconfiguration time-dependent Hartree method is used to study the coupled exciton-vibrational dynamics in a high-dimensional nonameric model of the LH2 antenna complex of purple bacteria. The exciton-vibrational coupling is parametrized within the Huang-Rhys model according to phonon and intramolecular vibrational modes derived from an experimental bacteriochlorophyll spectral density. In contrast to reduced density matrix approaches, the Schrödinger equation is solved explicitly, giving access to the full wave function. This facilitates an unbiased analysis in terms of the coupled dynamics of excitonic and vibrational degrees of freedom. For the present system, we identify spectator modes for the B800 to B800 transfer and we find a non-additive effect of phonon and intramolecular vibrational modes on the B800 to B850 exciton transfer.

  9. PbSe Nanocrystal Excitonic Solar Cells

    KAUST Repository

    Choi, Joshua J.

    2009-11-11

    We report the design, fabrication, and characterization of colloidal PbSe nanocrystal (NC)-based photovoltaic test structures that exhibit an excitonic solar cell mechanism. Charge extraction from the NC active layer is driven by a photoinduced chemical potential energy gradient at the nanostructured heterojunction. By minimizing perturbation to PbSe NC energy levels and thereby gaining insight into the "intrinsic" photovoltaic properties and charge transfer mechanism of PbSe NC, we show a direct correlation between interfacial energy level offsets and photovoltaic device performance. Size dependent PbSe NC energy levels were determined by cyclic voltammetry and optical spectroscopy and correlated to photovoltaic measurements. Photovoltaic test structures were fabricated from PbSe NC films sandwiched between layers of ZnO nanoparticles and PEDOT:PSS as electron and hole transporting elements, respectively. The device current-voltage characteristics suggest a charge separation mechanism that Is distinct from previously reported Schottky devices and consistent with signatures of excitonic solar cells. Remarkably, despite the limitation of planar junction structure, and without film thickness optimization, the best performing device shows a 1-sun power conversion efficiency of 3.4%, ranking among the highest performing NC-based solar cells reported to date. © 2009 American Chemical Society.

  10. Enhanced exciton diffusion length via cooperative quantum transport

    Science.gov (United States)

    Mohseni, Masoud; Abasto, Damian; Lloyd, Seth; Zanardi, Paolo

    2011-03-01

    The energy transfer rate in biomolecular systems is typically calculated from the transition probability of an excitation hopping from one molecule to another using Förster energy transfer based on dipole-dipole interaction of individual molecules in the perturbative regime. However, due to strong interactions of among a group of molecules the excitation can become highly delocalized leading to an effective large dipole moment with an enhanced oscillator strength. Under certain symmetries, this could lead to an enhancement in exicton transfer rate via cooperative donation or acceptance of an excitation. Here, we explore this phenomenon in various multichromophoric geometries, under different symmetries, initial conditions, and dynamics. We study the behavior of the exciton diffusion length under the effects of disorders and environmental fluctuations and quantify the crossover from ballistic to diffusive regimes. Specifically, for a quasi-1 D array of rings containing N chromophores interacting with a bosonic bath, an interplay of time scales dictates the exciton dynamics. In the ``far-field'' regime, environmental interactions are dominating and the system properties are approaching those of the incoherent equilibrium Gibbs state. However, in the ``near-field'' the coherent interactions among dipole aggregates dominate other time scales and exciton diffusion length is enhanced by a factor of √{ N } .

  11. Synthesis and Exciton Dynamics of Donor-Orthogonal Acceptor Conjugated Polymers: Reducing the Singlet–Triplet Energy Gap

    KAUST Repository

    Freeman, David M. E.

    2017-06-09

    The presence of energetically low-lying triplet states is a hallmark of organic semiconductors. Even though they present a wealth of interesting photophysical properties, these optically dark states significantly limit optoelectronic device performance. Recent advances in emissive charge-transfer molecules have pioneered routes to reduce the energy gap between triplets and

  12. Lateral redistribution of excitons in CdSe/ZnSe quantum dots

    Science.gov (United States)

    Strassburg, M.; Dworzak, M.; Born, H.; Heitz, R.; Hoffmann, A.; Bartels, M.; Lischka, K.; Schikora, D.; Christen, J.

    2002-01-01

    Lateral redistribution processes of excitons localized in CdSe/ZnSe quantum dot structures are investigated by time-integrated and time-resolved spectroscopy. The photoluminescence properties are governed by lateral energy transfer within a dense ensemble of quantum dots. The quantum dots differ in size and Cd concentration and provide a complex potential landscape with localization sites for excitons. At low temperatures, lateral transfer by tunneling leads to a redshift with increasing delay after pulsed excitation. The mobility edge was determined to 2.561 eV. Above 100 K, thermally activated escape and recapture of excitons cause a strong redshift of the PL maximum in the first 500 ps.

  13. Memory-assisted exciton diffusion in the chlorosome light-harvesting antenna of green sulfur bacteria

    CERN Document Server

    Fujita, Takatoshi; Saikin, Semion K; Aspuru-Guzik, Alan

    2012-01-01

    Chlorosomes are likely the largest and most efficient natural light-harvesting photosynthetic antenna systems. They are composed of large numbers of bacteriochlorophylls organized into supramolecular aggregates. We explore the microscopic origin of the fast excitation energy transfer in the chlorosome using the recently-resolved structure and atomistic-detail simulations. Despite the dynamical disorder effects on the electronic transitions of the bacteriochlorophylls, our simulations show that the exciton delocalizes over the entire aggregate in about 200 fs. The memory effects associated to the dynamical disorder assist the exciton diffusion through the aggregates and enhance the diffusion coefficients as a factor of two as compared to the model without memory. Furthermore, exciton diffusion in the chlorosome is found to be highly anisotropic with the preferential transfer towards the baseplate, which is the next functional element in the photosynthetic system.

  14. Assessment of quantum chemical methods and basis sets for excitation energy transfer

    Energy Technology Data Exchange (ETDEWEB)

    Fink, Reinhold F. [Institute of Physical Chemistry, University of Wuerzburg, Am Hubland, D-97074 Wuerzburg (Germany); Pfister, Johannes; Zhao Hongmei [Institute of Organic Chemistry, University of Wuerzburg, Am Hubland, D-97074 Wuerzburg (Germany); Engels, Bernd [Institute of Organic Chemistry, University of Wuerzburg, Am Hubland, D-97074 Wuerzburg (Germany)], E-mail: bernd@chemie.uni-wuerzburg.de

    2008-05-04

    The validity of several standard quantum chemical approaches and other models for the prediction of exciton energy transfer is investigated using the HOMO-LUMO excited states of benzene dimer as an example. The configuration interaction singles (CIS), time-dependent Hartree-Fock (TD-HF), time dependent density functional theroy (TD-DFT), and complete-active-space self-consistent-field (CASSCF) methods are applied with a supermolecule approach and compared to the previously established monomer transition density method and the ideal dipole approximation. Strong and physically incorrect admixture of charge-transfer states makes TD-DFT inappropriate for investigations of potential energy surfaces in such dimer systems. CIS, TD-HF and CASSCF perform qualitatively correct. TD-HF seems to be a particularly appropriate method due to its general applicability and overall good performance for the excited state and for transition properties. Double-zeta basis sets with polarisation functions are found to be sufficient to predict transfer rates of dipole allowed excitations. Efficient excitation energy transfer is predicted between degenerate excited states while avoided curve crossings of nearly spaced {pi}-aggregates are identified as a possible trapping mechanism.

  15. Dependence of Exciton Diffusion Length and Diffusion Coefficient on Photophysical Parameters in Bulk Heterojunction Organic Solar Cells

    Science.gov (United States)

    Yeboah, Douglas; Singh, Jai

    2017-11-01

    Recently, the dependence of exciton diffusion length (LD ) on some photophysical parameters of organic solids has been experimentally demonstrated, however no systematic theoretical analysis of this phenomenon has been carried out. We have conducted a theoretical study by using the Förster resonance energy transfer and Dexter carrier transfer mechanisms together with the Einstein-Smoluchowski diffusion equation to derive analytical models for the diffusion lengths (LD ) and diffusion coefficients (D) of singlet (S) and triplet (T) excitons in organic solids as functions of spectral overlap integral (J) , photoluminescence (PL) quantum yield (φD ) , dipole moment (μT ) and refractive index (n) of the photoactive material. The exciton diffusion lengths and diffusion coefficients in some selected organic solids were calculated, and we found that the singlet exciton diffusion length (LDS ) increases with φD and J, and decreases with n. Also, the triplet exciton diffusion length (LDT ) increases with φD and decreases with μT . These may be achieved through doping the organic solids into broad optical energy gap host materials as observed in previous experiments. The calculated exciton diffusion lengths are compared with experimental values and a reasonably good agreement is found between them. The results presented are expected to provide insight relevant to the synthesis of new organic solids for fabrication of bulk heterojunction organic solar cells characterized by better power conversion efficiency.

  16. Creation of Excitons Excited by Light with a Spatial Mode

    Science.gov (United States)

    Syouji, Atsushi; Saito, Shingo; Otomo, Akira

    2017-12-01

    When light is absorbed into matter, its degrees of freedom (i.e., energy, polarization, and phase) are transferred to the matter and conserved. In this study, we demonstrate that elementary excitations in matter, which are one-photon-forbidden transition states, become allowed states because of the phase conservation across the entire cross section of excitation light. In particular, when 1S orthoexcitons of the yellow series in the semiconductor cuprous oxide (Cu2O) were resonantly excited by light with a spatial mode, an increase in the Γ 3 - -phonon-emission peak intensity of the excitons was detected depending on the spatial mode. Using group-theory-based analysis, we show that the irreducible representation of a one-photon-forbidden exciton, which is one of the orthoexcitons, can be transmuted to an allowed state by taking the direct product with the polar vector produced from the spatial mode of the light. Although the transition process of the exciton is locally characterized by the usual quadrupole interaction, the phase conservation at each position at which the sample is irradiated causes the exciton to be in the same spatial-mode state. That causes a change in the transition selection rule. The selection rule relaxation due to the spatial mode of the light was also applied for paraexciton creation.

  17. Energy transfer problems of ball lightning

    Energy Technology Data Exchange (ETDEWEB)

    Egely, G.

    1986-04-01

    The paper analyzes the energy transport phenomenon of ball lightnings, but momentum and charge transport phenomena are considered as well. The physical properties as energy density and transfer are investigated using several observers' accounts of interactions with different objects. It is shown that contrary to previous assumptions the ball lightning has negative electric charge, and very high internal energy density. Both internal and external energy source models are analyzed, and it is shown that regardless to the details of a given model neither of them can explain actual observations. This has been validated by a well documented case study, and by several additional observations. An entirely new, testable model is suggested, which is able to stand for all observed properties of ball lightnings, and it explains the cause of rarity of ball lightnings, and the reasons of the unsuccessful experimental efforts. It is shown that the plasma sphere is just a visible side effect of a more important phenomenon.

  18. Resonance Energy Transfer Molecular Imaging Application in Biomedicine

    Directory of Open Access Journals (Sweden)

    NIE Da-hong1,2;TANG Gang-hua1,3

    2016-11-01

    Full Text Available Resonance energy transfer molecular imaging (RETI can markedly improve signal intensity and tissue penetrating capacity of optical imaging, and have huge potential application in the deep-tissue optical imaging in vivo. Resonance energy transfer (RET is an energy transition from the donor to an acceptor that is in close proximity, including non-radiative resonance energy transfer and radiative resonance energy transfer. RETI is an optical imaging technology that is based on RET. RETI mainly contains fluorescence resonance energy transfer imaging (FRETI, bioluminescence resonance energy transfer imaging (BRETI, chemiluminescence resonance energy transfer imaging (CRETI, and radiative resonance energy transfer imaging (RRETI. RETI is the hot field of molecular imaging research and has been widely used in the fields of biology and medicine. This review mainly focuses on RETI principle and application in biomedicine.

  19. Beyond Förster resonance energy transfer in biological and nanoscale systems.

    Science.gov (United States)

    Beljonne, David; Curutchet, Carles; Scholes, Gregory D; Silbey, Robert J

    2009-05-14

    After photoexcitation, energy absorbed by a molecule can be transferred efficiently over a distance of up to several tens of angstroms to another molecule by the process of resonance energy transfer, RET (also commonly known as electronic energy transfer, EET). Examples of where RET is observed include natural and artificial antennae for the capture and energy conversion of light, amplification of fluorescence-based sensors, optimization of organic light-emitting diodes, and the measurement of structure in biological systems (FRET). Forster theory has proven to be very successful at estimating the rate of RET in many donor-acceptor systems, but it has also been of interest to discover when this theory does not work. By identifying these cases, researchers have been able to obtain, sometimes surprising, insights into excited-state dynamics in complex systems. In this article, we consider various ways that electronic energy transfer is promoted by mechanisms beyond those explicitly considered in Forster RET theory. First, we recount the important situations when the electronic coupling is not accurately calculated by the dipole-dipole approximation. Second, we examine the related problem of how to describe solvent screening when the dipole approximation fails. Third, there are situations where we need to be careful about the separability of electronic coupling and spectral overlap factors. For example, when the donors and/or acceptors are molecular aggregates rather than individual molecules, then RET occurs between molecular exciton states and we must invoke generalized Forster theory (GFT). In even more complicated cases, involving the intermediate regime of electronic energy transfer, we should consider carefully nonequilibrium processes and coherences and how bath modes can be shared. Lastly, we discuss how information is obscured by various forms of energetic disorder in ensemble measurements and we outline how single molecule experiments continue to be

  20. Efficient energy transfer in light-harvesting systems, I: optimal temperature, reorganization energy and spatial-temporal correlations

    Energy Technology Data Exchange (ETDEWEB)

    Wu Jianlan; Liu Fan; Shen Young; Cao Jianshu; Silbey, Robert J, E-mail: jianshu@mit.ed, E-mail: silbey@mit.ed [Department of Chemistry, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139 (United States)

    2010-10-15

    Understanding the mechanisms of efficient and robust energy transfer in light-harvesting systems provides new insights for the optimal design of artificial systems. In this paper, we use the Fenna-Matthews-Olson (FMO) protein complex and phycocyanin 645 (PC 645) to explore the general dependence on physical parameters that help maximize the efficiency and maintain its stability. With the Haken-Strobl model, the maximal energy transfer efficiency (ETE) is achieved under an intermediate optimal value of dephasing rate. To avoid the infinite temperature assumption in the Haken-Strobl model and the failure of the Redfield equation in predicting the Forster rate behavior, we use the generalized Bloch-Redfield (GBR) equation approach to correctly describe dissipative exciton dynamics, and we find that maximal ETE can be achieved under various physical conditions, including temperature, reorganization energy and spatial-temporal correlations in noise. We also identify regimes of reorganization energy where the ETE changes monotonically with temperature or spatial correlation and therefore cannot be optimized with respect to these two variables.

  1. Energy transfer and kinetics in mechanochemistry.

    Science.gov (United States)

    Chen, Zhiliang; Lu, Shengyong; Mao, Qiongjing; Buekens, Alfons; Wang, Yuting; Yan, Jianhua

    2017-11-01

    Mechanochemistry (MC) exerts extraordinary degradation and decomposition effects on many chlorinated, brominated, and even fluorinated persistent organic pollutants (POPs). However, its application is still limited by inadequate study of its reaction kinetic aspects. In the present work, the ball motion and energy transfer in planetary ball mill are investigated in some detail. Almost all milling parameters are summarised in a single factor-total effective impact energy. Furthermore, the MC kinetic between calcium oxide/Al and hexachlorobenzene is well established and modelled. The results indicate that total effective impact energy and reagent ratio are the two factors sufficient for describing the MC degradation degree of POPs. The reaction rate constant only depends on the chemical properties of reactants, so it could be used as an important index to appraise the quality of MC additives. This model successfully predicts the reaction rate for different operating conditions, indicating that it could be suitably applied for conducting MC reactions in other reactors.

  2. Electronic energy transfer in tetracene-doped p-terphenyl nanoparticles: Extraordinarily high fluorescence enhancement and quenching efficiency

    Energy Technology Data Exchange (ETDEWEB)

    Mitsui, Masaaki, E-mail: smmitsu@ipc.shizuoka.ac.jp; Kawano, Yuya

    2013-06-20

    Highlights: ► Tc/pTP-NPs at various doping ratios are produced by reprecipitation in water. ► The energy transfer in Tc/pTP-NPs is investigated. ► More than 10{sup 4}pTP donors were quenched by a single Tc acceptor. ► Efficient energy transfer is attributed to the rapid exciton diffusion in the NPs. - Abstract: A series of tetracene (Tc)-doped p-terphenyl (pTP) nanoparticles (Tc/pTP-NPs) were produced at various doping ratios by reprecipitation in water. The Tc/pTP-NPs are disk-like with a mean diameter of 75 nm and height of 7 nm, which were determined by scanning electron microscopy and atomic force microscopy, and exhibited electronic delocalization through H-type aggregation of the pTP molecules. Electronic energy transfer in the Tc/pTP-NPs was examined using steady-state and time-resolved fluorescence spectroscopy and fluorescence anisotropy experiments: pTP-NPs serve as an excellent light-harvesting nano-matrix with a large absorption coefficient that exceeds 10{sup 9} M{sup −1} cm{sup −1}. Furthermore, Stern–Volmer analysis of the donor emission was performed by changing the dopant concentration; this showed that a single Tc acceptor quenched more than 10{sup 4}pTP donors. Comparison of the experimental and theoretical energy transfer efficiencies indicated that the efficient energy transfer can be attributed to two-dimensional exciton diffusion in the host nanoparticles.

  3. Effect of Spectral Density Shapes on the Excitonic Structure and Dynamics of the Fenna-Matthews-Olson Trimer from Chlorobaculum tepidum.

    Science.gov (United States)

    Kell, Adam; Blankenship, Robert E; Jankowiak, Ryszard

    2016-08-11

    The Fenna-Matthews-Olson (FMO) trimer (composed of identical subunits) from the green sulfur bacterium Chlorobaculum tepidum is an important protein model system to study exciton dynamics and excitation energy transfer (EET) in photosynthetic complexes. In addition, FMO is a popular model for excitonic calculations, with many theoretical parameter sets reported describing different linear and nonlinear optical spectra. Due to fast exciton relaxation within each subunit, intermonomer EET results predominantly from the lowest energy exciton states (contributed to by BChl a 3 and 4). Using experimentally determined shapes for the spectral densities, simulated optical spectra are obtained for the entire FMO trimer. Simultaneous fits of low-temperature absorption, fluorescence, and hole-burned spectra place constraints on the determined pigment site energies, providing a new Hamiltonian that should be further tested to improve modeling of 2D electronic spectroscopy data and our understanding of coherent and dissipation effects in this important protein complex.

  4. Excitonic magnetism in d6 perovskites

    Science.gov (United States)

    Afonso, J. Fernández; Kuneš, J.

    2017-03-01

    We use the LDA+U method to study the possibility of exciton condensation in perovskites of transition metals with the d6 electronic configuration such as LaCoO3. For realistic interaction parameters we find several distinct solutions exhibiting a spin-triplet exciton condensate, which gives rise to a local spin density distribution while the ordered moments are vanishingly small. Rhombohedral distortion from the ideal cubic structure suppresses the ordered state, contrary to the spin-orbit coupling which enhances the excitonic condensation energy. We explain the trends observed in the numerical simulations with the help of a simplified strong-coupling model. Our results indicate that LaCoO3 is close to the excitonic instability and suggest ways how to achieve the exciton condensation.

  5. Distributed Wireless Power Transfer With Energy Feedback

    Science.gov (United States)

    Lee, Seunghyun; Zhang, Rui

    2017-04-01

    Energy beamforming (EB) is a key technique for achieving efficient radio-frequency (RF) transmission enabled wireless energy transfer (WET). By optimally designing the waveforms from multiple energy transmitters (ETs) over the wireless channels, they can be constructively combined at the energy receiver (ER) to achieve an EB gain that scales with the number of ETs. However, the optimal design of EB waveforms requires accurate channel state information (CSI) at the ETs, which is challenging to obtain practically, especially in a distributed system with ETs at separate locations. In this paper, we study practical and efficient channel training methods to achieve optimal EB in a distributed WET system. We propose two protocols with and without centralized coordination, respectively, where distributed ETs either sequentially or in parallel adapt their transmit phases based on a low-complexity energy feedback from the ER. The energy feedback only depends on the received power level at the ER, where each feedback indicates one particular transmit phase that results in the maximum harvested power over a set of previously used phases. Simulation results show that the two proposed training protocols converge very fast in practical WET systems even with a large number of distributed ETs, while the protocol with sequential ET phase adaptation is also analytically shown to converge to the optimal EB design with perfect CSI by increasing the training time. Numerical results are also provided to evaluate the performance of the proposed distributed EB and training designs as compared to other benchmark schemes.

  6. Ultrafast exciton migration in an HJ-aggregate: Potential surfaces and quantum dynamics

    Science.gov (United States)

    Binder, Robert; Polkehn, Matthias; Ma, Tianji; Burghardt, Irene

    2017-01-01

    Quantum dynamical and electronic structure calculations are combined to investigate the mechanism of exciton migration in an oligothiophene HJ aggregate, i.e., a combination of oligomer chains (J-type aggregates) and stacked aggregates of such chains (H-type aggregates). To this end, a Frenkel exciton model is parametrized by a recently introduced procedure [Binder et al., J. Chem. Phys. 141, 014101 (2014)] which uses oligomer excited-state calculations to perform an exact, point-wise mapping of coupled potential energy surfaces to an effective Frenkel model. Based upon this parametrization, the Multi-Layer Multi-Configuration Time-Dependent Hartree (ML-MCTDH) method is employed to investigate ultrafast dynamics of exciton transfer in a small, asymmetric HJ aggregate model composed of 30 sites and 30 active modes. For a partially delocalized initial condition, it is shown that a torsional defect confines the trapped initial exciton, and planarization induces an ultrafast resonant transition between an HJ-aggregated segment and a covalently bound "dangling chain" end. This model is a minimal realization of experimentally investigated mixed systems exhibiting ultrafast exciton transfer between aggregated, highly planarized chains and neighboring disordered segments.

  7. Excitonic quasimolecules in nanosystems of quantum dots

    Science.gov (United States)

    Pokutnyi, Sergey I.

    2017-09-01

    The theory of excitonic quasimolecules (biexcitons) (formed of spatially separated electrons and holes) in a nanosystem that consists of semiconductor quantum dots synthesized in a borosilicate glass matrix is presented. It is shown that exciton quasimolecule formation is of a threshold character and is possible in nanosystem, if the spacing between the quantum dots surfaces is larger than a certain critical spacing. It was found that the binding energy of the singlet ground state of an exciton quasimolecule, consisting of two semiconductor quantum dots is a significant large values, larger than the binding energy of the biexciton in a semiconductor single crystal by almost two orders of magnitude.

  8. Wireless energy transfer through non-resonant magnetic coupling

    DEFF Research Database (Denmark)

    Peng, Liang; Breinbjerg, Olav; Mortensen, Asger

    2010-01-01

    We demonstrate by theoretical analysis and experimental verification that mid-range wireless energy transfer systems may take advantage of de-tuned coupling devices, without jeopardizing the energy transfer efficiency. Allowing for a modest de-tuning of the source coil, energy transfer systems co...

  9. Nonextensive kinetics of fluorescence resonance energy transfer.

    Science.gov (United States)

    Rolinski, Olaf J; Birch, David J S

    2008-10-14

    Some fluorescence dyes in complex media, such as those found in biology, demonstrate nonextensive kinetics, which implies representing their fluorescence decays in terms of lifetime distributions rather than simple exponentials. Complex kinetics usually discourage application to lifetime sensors, as it is believed, that additional molecular mechanisms employed for detection of an analyte will make the resulting kinetics ambiguous and the sensor response inconclusive. In this paper we investigate theoretically the applicability of complex dye kinetics as a fluorescence resonance energy transfer based lifetime sensor and demonstrate that the nonextensive nature of its kinetics does not decrease the sensing performance, and indeed even provides richer structural information than a simple exponential behavior.

  10. Low-Energy Ballistic Transfers to Lunar Halo Orbits

    Science.gov (United States)

    Parker, Jeffrey S.

    2009-01-01

    Recent lunar missions have begun to take advantage of the benefits of low-energy ballistic transfers between the Earth and the Moon rather than implementing conventional Hohmann-like lunar transfers. Both Artemis and GRAIL plan to implement low-energy lunar transfers in the next few years. This paper explores the characteristics and potential applications of many different families of low-energy ballistic lunar transfers. The transfers presented here begin from a wide variety of different orbits at the Earth and follow several different distinct pathways to the Moon. This paper characterizes these pathways to identify desirable low-energy lunar transfers for future lunar missions.

  11. Nonphotochemical Hole-Burning Studies of Energy Transfer Dynamics in Antenna Complexes of Photosynthetic Bacteria

    Energy Technology Data Exchange (ETDEWEB)

    Matsuzaki, Satoshi [Iowa State Univ., Ames, IA (United States)

    2001-01-01

    This thesis contains the candidate's original work on excitonic structure and energy transfer dynamics of two bacterial antenna complexes as studied using spectral hole-burning spectroscopy. The general introduction is divided into two chapters (1 and 2). Chapter 1 provides background material on photosynthesis and bacterial antenna complexes with emphasis on the two bacterial antenna systems related to the thesis research. Chapter 2 reviews the underlying principles and mechanism of persistent nonphotochemical hole-burning (NPHB) spectroscopy. Relevant energy transfer theories are also discussed. Chapters 3 and 4 are papers by the candidate that have been published. Chapter 3 describes the application of NPHB spectroscopy to the Fenna-Matthews-Olson (FMO) complex from the green sulfur bacterium Prosthecochloris aestuarii; emphasis is on determination of the low energy vibrational structure that is important for understanding the energy transfer process associated within three lowest energy Qy-states of the complex. The results are compared with those obtained earlier on the FMO complex from Chlorobium tepidum. In Chapter 4, the energy transfer dynamics of the B800 molecules of intact LH2 and B800-deficient LH2 complexes of the purple bacterium Rhodopseudomonas acidophila are compared. New insights on the additional decay channel of the B800 ring of bacteriochlorophylla (BChla) molecules are provided. General conclusions are given in Chapter 5. A version of the hole spectrum simulation program written by the candidate for the FMO complex study (Chapter 3) is included as an appendix. The references for each chapter are given at the end of each chapter.

  12. Energy transfer dynamics in an RC-LH1-PufX tubular photosynthetic membrane

    Science.gov (United States)

    Hsin, J.; Strümpfer, J.; Şener, M.; Qian, P.; Hunter, C. N.; Schulten, K.

    2010-08-01

    Light absorption and the subsequent transfer of excitation energy are the first two steps in the photosynthetic process, carried out by protein-bound pigments, mainly bacteriochlorophylls (BChls), in photosynthetic bacteria. BChls are anchored in light-harvesting (LH) complexes, such as light-harvesting complex I (LH1), which directly associates with the reaction center (RC), forming the RC-LH1 core complex. In Rhodobacter sphaeroides, RC-LH1 core complexes contain an additional protein, PufX, and assemble into dimeric RC-LH1-PufX core complexes. In the absence of LH complex II (LH2), the former complexes can aggregate into a helically ordered tubular photosynthetic membrane. We have examined the excitation transfer dynamics in a single RC-LH1-PufX core complex dimer using the hierarchical equations of motion for dissipative quantum dynamics that accurately, yet in a computationally costly manner, treat the coupling between BChls and their protein environment. A widely employed description, the generalized Förster (GF) theory, was also used to calculate the transfer rates of the same excitonic system in order to verify the accuracy of this computationally cheap method. Additionally, in light of the structural uncertainties in the Rba. sphaeroides RC-LH1-PufX core complex, geometrical alterations were introduced into the BChl organization. It is shown that the energy transfer dynamics are not affected by the considered changes in the BChl organization and that the GF theory provides accurate transfer rates. An all-atom model for a tubular photosynthetic membrane is then constructed on the basis of electron microscopy data, and the overall energy transfer properties of this membrane are computed.

  13. Dark excitons in transition metal dichalcogenides

    Science.gov (United States)

    Malic, Ermin; Selig, Malte; Feierabend, Maja; Brem, Samuel; Christiansen, Dominik; Wendler, Florian; Knorr, Andreas; Berghäuser, Gunnar

    2018-01-01

    Monolayer transition metal dichalcogenides (TMDs) exhibit a remarkably strong Coulomb interaction that manifests in tightly bound excitons. Due to the complex electronic band structure exhibiting several spin-split valleys in the conduction and valence band, dark excitonic states can be formed. They are inaccessibly by light due to the required spin-flip and/or momentum transfer. The relative position of these dark states with respect to the optically accessible bright excitons has a crucial impact on the emission efficiency of these materials and thus on their technological potential. Based on the solution of the Wannier equation, we present the excitonic landscape of the most studied TMD materials including the spectral position of momentum- and spin-forbidden excitonic states. We show that the knowledge of the electronic dispersion does not allow to conclude about the nature of the material's band gap since excitonic effects can give rise to significant changes. Furthermore, we reveal that an exponentially reduced photoluminescence yield does not necessarily reflect a transition from a direct to a nondirect gap material, but can be ascribed in most cases to a change of the relative spectral distance between bright and dark excitonic states.

  14. Effect of heterojunction on exciton binding energy and electron-hole recombination probability in CdSe/ZnS quantum dots.

    Science.gov (United States)

    Elward, Jennifer M; Chakraborty, Arindam

    2015-02-10

    Presence of heterojunctions is important for generation of free charge carriers and the dissociation of bound electron-hole pairs in semiconductor nanoparticles. This work presents a theoretical investigation of the effect of core/shell heterojunction on electron-hole interaction in CdSe/ZnS quantum dots. The excitonic wave function in the CdSe/ZnS dots was calculated using the electron-hole explicitly correlated Hartree-Fock (eh-XCHF) method and the effect of successive addition of the ZnS shell on exciton binding energy, electron-hole recombination probability, and the electron-hole separation distance was investigated. It was found that the scaling of all the three quantities as a function of dot diameter did not follow conventional volume scaling laws of core-only dots, and the scaling laws were significantly altered due to the presence of the heterojunction. The spatial localization of the quasiparticles in the core/shell quantum dot was analyzed by calculating the 1-particle reduced density from the eh-XCHF wave function and partitioning the density spatially into core and shell regions. It was found that in the 15 nm CdSe/ZnS dot, the relative probability of the electron localization in the shell region was higher than the hole by a factor of 3. The degree of spatial localization of the quasiparticles was found to depend strongly on the initial size of the CdSe core in the core/shell quantum dot. It was found that a reduction in the CdSe core diameter by a factor of 1.7 resulted in an enhancement of the preferential localization of the electron in the shell region by a factor of 11.3. The results demonstrate that large CdSe/ZnS quantum dots with a small CdSe core have the necessary characteristics for efficient exciton dissociation and generation of free charge carriers.

  15. Suppressing Energy Loss due to Triplet Exciton Formation in Organic Solar Cells: The Role of Chemical Structures and Molecular Packing

    KAUST Repository

    Chen, Xiankai

    2017-04-21

    In the most efficient solar cells based on blends of a conjugated polymer (electron donor) and a fullerene derivative (electron acceptor),ultrafast formation of charge-transfer (CT) electronic states at the donor-acceptor interfaces and efficient separation of these CT states into free charges, lead to internal quantum efficiencies near 100%. However, there occur substantial energy losses due to the non-radiative recombinations of the charges, mediated by the loweset-energy (singlet and triplet) CT states; for example, such recombinations can lead to the formation of triplet excited electronic states on the polymer chains, which do not generate free charges. This issue remains a major factor limiting the power conversion efficiencies (PCE) of these devices. The recombination rates are, however, difficult to quantify experimentally. To shed light on these issues, here, an integrated multi-scale theoretical approach that combines molecular dynamics simulations with quantum chemistry calculations is employed in order to establish the relationships among chemical structures, molecular packing, and non-radiative recombination losses mediated by the lowest-energy charge-transfer states.

  16. Solvent-Controlled Branching of Localized versus Delocalized Singlet Exciton States and Equilibration with Charge Transfer in a Structurally Well-Defined Tetracene Dimer

    Energy Technology Data Exchange (ETDEWEB)

    Cook, Jasper D. [Department; Carey, Thomas J. [Department; Arias, Dylan H. [National Renewable Energy Laboratory, Golden, Colorado 80401, United States; Johnson, Justin C. [National Renewable Energy Laboratory, Golden, Colorado 80401, United States; Damrauer, Niels H. [Department

    2017-11-21

    A detailed photophysical picture is elaborated for a structurally well-defined and symmetrical bis-tetracene dimer in solution. The molecule was designed for interrogation of the initial photophysical steps (S1 - 1TT) in intramolecular singlet fission (SF). (Triisopropylsilyl)acetylene substituents on the dimer TIPS-BT1 as well as a monomer model TIPS-Tc enable a comparison of photophysical properties, including transient absorption dynamics, as solvent polarity is varied. In nonpolar toluene solutions, TIPS-BT1 decays via radiative and nonradiative pathways to the ground state with no evidence for dynamics related to the initial stages of SF. This contrasts with the behavior of the previously reported unsubstituted dimer BT1 and is likely a consequence of energetic perturbations to the singlet excited-state manifold of TIPS-BT1 by the (trialkylsilyl)acetylene substituents. In polar benzonitrile, two key findings emerge. First, photoexcited TIPS-BT1 shows a bifurcation into both arm-localized (S1-loc) and dimer-delocalized (S1-dim) singlet exciton states. The S1-loc decays to the ground state, and weak temperature dependence of its emissive signatures suggests that once it is formed, it is isolated from S1-dim. Emissive signatures of the S1-dim state, on the other hand, are strongly temperature-dependent, and transient absorption dynamics show that S1-dim equilibrates with an intramolecular charge-transfer state in 50 ps at room temperature. This equilibrium decays to the ground state with little evidence for formation of long-lived triplets nor 1TT. These detailed studies spectrally characterize many of the key states in intramolecular SF in this class of dimers but highlight the need to tune electronic coupling and energetics for the S1 - 1TT photoreaction.

  17. Synthesis and Characterization of Metal-Organic Frameworks (MOFs) for Photon Collection and Energy Transfer

    Science.gov (United States)

    So, Monica C.

    . To address problem (a), we incorporated antenna molecules (i.e. perylene diimides) to expand light collection and then transfer energy to the primary chromophores. To address problem (b), we observed that excitons can achieve up to 2,025 hops in a porphyrin-based metal-organic framework (MOF) single crystal within its 3 ns lifetime. By precisely aligning the chromophores in the MOF, we showed that long-distance exciton transport (i.e. ultra-fast, sequential hopping) was consistent with the well-established Forster theory. To address problems (c) and (d), we introduced MOF components one step at a time to optimize optical path length and crystal-thickness. This allowed us to incorporate MOFs (normally bulk crystals) into a MOF film. The approach exploited both MOF chemistry and layer-by-layer (LbL) assembly of crystalline MOFs in a highly controlled fashion on functional surfaces. We also incorporated good light-harvesting molecules as struts in MOFs to increase the visible absorption. Designing MOF-based OPVs can provide insight into solar energy conversion. This can potentially lead to much higher efficiencies, based on the simultaneous resolution of the four challenges hindering OPV performance.

  18. Energy transfer dynamics in trimers and aggregates of light-harvesting complex II probed by 2D electronic spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Enriquez, Miriam M.; Zhang, Cheng; Tan, Howe-Siang, E-mail: howesiang@ntu.edu.sg [Division of Chemistry and Biological Chemistry, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore 637371 (Singapore); Akhtar, Parveen; Garab, Győző; Lambrev, Petar H., E-mail: lambrev@brc.hu [Institute of Plant Biology, Biological Research Centre, Hungarian Academy of Sciences, P.O. Box 521, H-6701 Szeged (Hungary)

    2015-06-07

    The pathways and dynamics of excitation energy transfer between the chlorophyll (Chl) domains in solubilized trimeric and aggregated light-harvesting complex II (LHCII) are examined using two-dimensional electronic spectroscopy (2DES). The LHCII trimers and aggregates exhibit the unquenched and quenched excitonic states of Chl a, respectively. 2DES allows direct correlation of excitation and emission energies of coupled states over population time delays, hence enabling mapping of the energy flow between Chls. By the excitation of the entire Chl b Q{sub y} band, energy transfer from Chl b to Chl a states is monitored in the LHCII trimers and aggregates. Global analysis of the two-dimensional (2D) spectra reveals that energy transfer from Chl b to Chl a occurs on fast and slow time scales of 240–270 fs and 2.8 ps for both forms of LHCII. 2D decay-associated spectra resulting from the global analysis identify the correlation between Chl states involved in the energy transfer and decay at a given lifetime. The contribution of singlet–singlet annihilation on the kinetics of Chl energy transfer and decay is also modelled and discussed. The results show a marked change in the energy transfer kinetics in the time range of a few picoseconds. Owing to slow energy equilibration processes, long-lived intermediate Chl a states are present in solubilized trimers, while in aggregates, the population decay of these excited states is significantly accelerated, suggesting that, overall, the energy transfer within the LHCII complexes is faster in the aggregated state.

  19. Enhancing radiative energy transfer through thermal extraction

    Science.gov (United States)

    Tan, Yixuan; Liu, Baoan; Shen, Sheng; Yu, Zongfu

    2016-06-01

    Thermal radiation plays an increasingly important role in many emerging energy technologies, such as thermophotovoltaics, passive radiative cooling and wearable cooling clothes [1]. One of the fundamental constraints in thermal radiation is the Stefan-Boltzmann law, which limits the maximum power of far-field radiation to P0 = σT4S, where σ is the Boltzmann constant, S and T are the area and the temperature of the emitter, respectively (Fig. 1a). In order to overcome this limit, it has been shown that near-field radiations could have an energy density that is orders of magnitude greater than the Stefan-Boltzmann law [2-7]. Unfortunately, such near-field radiation transfer is spatially confined and cannot carry radiative heat to the far field. Recently, a new concept of thermal extraction was proposed [8] to enhance far-field thermal emission, which, conceptually, operates on a principle similar to oil immersion lenses and light extraction in light-emitting diodes using solid immersion lens to increase light output [62].Thermal extraction allows a blackbody to radiate more energy to the far field than the apparent limit of the Stefan-Boltzmann law without breaking the second law of thermodynamics. Thermal extraction works by using a specially designed thermal extractor to convert and guide the near-field energy to the far field, as shown in Fig. 1b. The same blackbody as shown in Fig. 1a is placed closely below the thermal extractor with a spacing smaller than the thermal wavelength. The near-field coupling transfers radiative energy with a density greater than σT4. The thermal extractor, made from transparent and high-index or structured materials, does not emit or absorb any radiation. It transforms the near-field energy and sends it toward the far field. As a result, the total amount of far-field radiative heat dissipated by the same blackbody is greatly enhanced above SσT4, where S is the area of the emitter. This paper will review the progress in thermal

  20. Exciton absorption spectrum of thin Ag sub 2 ZnI sub 4

    CERN Document Server

    Yunakova, O N; Kovalenko, E N

    2002-01-01

    In Ag sub 2 ZnI sub 4 compound thin films one investigated into the electron spectrum of absorption within 3-6 eV photon energy range. The boundary of interband absorption is determined to correspond to the direct permitted transitions with E sub g = 3.7 eV forbidden gap width. A strong exciton band at E = 3.625 eV (80 K) GAMMA half width temperature run of which within 80-390 K range is governed by exciton-phonon interaction typical for quasi-single-dimensional excitons, is adjacent to the absorption boundary. At T <= 390 K one observes a bend in E(T) and GAMMA(T) dependences associated with generation of the Frenkel defects and followed by transfer of Ag ions to the interstices and vacancies of the compound crystalline lattice

  1. Properties of Excitons Bound to Ionized Donors

    DEFF Research Database (Denmark)

    Skettrup, Torben; Suffczynski, M.; Gorzkowski, W.

    1971-01-01

    Binding energies, interparticle distances, oscillator strengths, and exchange corrections are calculated for the three-particle complex corresponding to an exciton bound to an ionized donor. The results are given as functions of the mass ratio of the electron and hole. Binding of the complex...... is obtained for mass ratios up to 0.426. The interparticle distances are up to 50 times larger than the corresponding exciton radius. The oscillator strengths are about 104 times greater than those of free excitons, while the exchange corrections for the complex are comparable to those of free excitions...

  2. Enhancing radiative energy transfer through thermal extraction

    Directory of Open Access Journals (Sweden)

    Tan Yixuan

    2016-06-01

    Full Text Available Thermal radiation plays an increasingly important role in many emerging energy technologies, such as thermophotovoltaics, passive radiative cooling and wearable cooling clothes [1]. One of the fundamental constraints in thermal radiation is the Stefan-Boltzmann law, which limits the maximum power of far-field radiation to P0 = σT4S, where σ is the Boltzmann constant, S and T are the area and the temperature of the emitter, respectively (Fig. 1a. In order to overcome this limit, it has been shown that near-field radiations could have an energy density that is orders of magnitude greater than the Stefan-Boltzmann law [2-7]. Unfortunately, such near-field radiation transfer is spatially confined and cannot carry radiative heat to the far field. Recently, a new concept of thermal extraction was proposed [8] to enhance far-field thermal emission, which, conceptually, operates on a principle similar to oil immersion lenses and light extraction in light-emitting diodes using solid immersion lens to increase light output [62].Thermal extraction allows a blackbody to radiate more energy to the far field than the apparent limit of the Stefan-Boltzmann law without breaking the second law of thermodynamics.

  3. Localized surface plasmon mediated energy transfer in the vicinity of core-shell nanoparticle

    Energy Technology Data Exchange (ETDEWEB)

    Shishodia, Manmohan Singh, E-mail: manmohan@gbu.ac.in; Juneja, Soniya [Department of Applied Physics, School of Vocational Studies and Applied Sciences, Gautam Buddha University, Greater Noida 201308 (India)

    2016-05-28

    Multipole spectral expansion based theory of energy transfer interactions between a donor and an acceptor molecule in the vicinity of a core-shell (nanoshell or core@shell) based plasmonic nanostructure is developed. In view of the diverse applications and rich plasmonic features such as tuning capability of surface plasmon (SP) frequencies, greater sensitivity to the change of dielectric environment, controllable redirection of electromagnetic radiation, closed form expressions for Energy Transfer Rate Enhancement Factor (ETREF) near core-shell particle are reported. The dependence of ETREF on different parameters is established through fitting equations, perceived to be of key importance for developing appropriate designs. The theoretical approach developed in the present work is capable of treating higher order multipoles, which, in turn, are also shown to play a crucial role in the present context. Moreover, closed form expressions derived in the present work can directly be used as formula, e.g., for designing SP based biosensors and estimating energy exchange between proteins and excitonic interactions in quantum dots.

  4. Exciton dynamics at the heteromolecular interface between N,N′-dioctyl-3,4,9,10-perylenedicarboximide and quaterrylene, studied using time-resolved photoluminescence

    Directory of Open Access Journals (Sweden)

    Nobuya Hiroshiba

    2014-06-01

    Full Text Available To elucidate the exciton dynamics at the heteromolecular interface, the temperature dependence of time-resolved photoluminescence (TRPL spectra of neat-N,N′-dioctyl-3,4,9,10-perylenedicarboximide (PTCDI-C8 and PTCDI-C8/Quaterrylene (QT heteromolecular thin films was investigated. The lifetimes of excitons were evaluated to identify the Frenkel (FE, high energy charge-transfer (CTEhigh, low energy charge-transfer (CTElow, and excimer exciton states. The thermal activation energy (Δact of CTElow in PTCDI-C8 thin film was evaluated as 25 meV, which is 1/5 of that of FE, indicating that CTElow is more thermally sensitive than FE in PTCDI-C8 thin film. We investigated the exciton transport length (l along the vertical direction against the substrate surface in PTCDI-C8/QT thin film at 30 K, and demonstrated that lFE = 9.9 nm, lCTElow = 4.2 nm, lCTEhigh = 4.3 nm, and lexcimer = 11.9 nm. To elucidate the difference in l among these excitons, the activation energies (Ea for quenching at the heteromolecular interface were investigated. Ea values were estimated to be 13.1 meV for CTElow and 18.6 meV for CTEhigh. These values agree with the thermal sensitivity of CTEs as reported in a previous static PL study. This latter situation is different from the case of FE and excimer excitons, which are transported via a resonant process and have no temperature dependence. The small Ea values of CTEs suggest that exciton transport takes place via a thermal hopping process in CTEs. The present experimental study provides information on nano-scaled exciton dynamics in a well-defined PTCDI-C8 (2 ML/QT (2 ML system.

  5. Nanophotonics: Energy Transfer towards Enhanced Luminescent Chemosensing

    Directory of Open Access Journals (Sweden)

    Roy Aad

    2015-04-01

    Full Text Available We discuss a recently proposed novel photonic approach for enhancing the fluorescence of extremely thin chemosensing polymer layers. We present theoretical and experimental results demonstrating the concept of gain-assisted waveguided energy transfer (G-WET on a very thin polymer nanolayer spincoated on an active ZnO thin film. The G-WET approach is shown to result in an 8-fold increase in polymer fluorescence. We then extend the G-WET concept to nanostructured media. The benefits of using active nanostructured substrates on the sensitivity and fluorescence of chemosensing polymers are discussed. Preliminary theoretical results on enlarged sensing surface and photonic band-gap are presented.

  6. Coherent quantum dynamics of excitons in monolayer transition metal dichalcogenides

    KAUST Repository

    Moody, Galan

    2016-03-14

    Transition metal dichalcogenides (TMDs) have garnered considerable interest in recent years owing to their layer thickness-dependent optoelectronic properties. In monolayer TMDs, the large carrier effective masses, strong quantum confinement, and reduced dielectric screening lead to pronounced exciton resonances with remarkably large binding energies and coupled spin and valley degrees of freedom (valley excitons). Coherent control of valley excitons for atomically thin optoelectronics and valleytronics requires understanding and quantifying sources of exciton decoherence. In this work, we reveal how exciton-exciton and exciton-phonon scattering influence the coherent quantum dynamics of valley excitons in monolayer TMDs, specifically tungsten diselenide (WSe2), using two-dimensional coherent spectroscopy. Excitation-density and temperature dependent measurements of the homogeneous linewidth (inversely proportional to the optical coherence time) reveal that exciton-exciton and exciton-phonon interactions are significantly stronger compared to quasi-2D quantum wells and 3D bulk materials. The residual homogeneous linewidth extrapolated to zero excitation density and temperature is ~1:6 meV (equivalent to a coherence time of 0.4 ps), which is limited only by the population recombination lifetime in this sample. © (2016) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.

  7. The nature of singlet excitons in oligoacene molecular crystals

    KAUST Repository

    Yamagata, H.

    2011-01-01

    A theory for polarized absorption in crystalline oligoacenes is presented, which includes Frenkel exciton coupling, the coupling between Frenkel and charge-transfer (CT) excitons, and the coupling of all neutral and ionic excited states to the dominant ring-breathing vibrational mode. For tetracene, spectra calculated using all Frenkel couplings among the five lowest energy molecular singlet states predict a Davydov splitting (DS) of the lowest energy (0-0) vibronic band of only -32cm-1, far smaller than the measured value of 631cm-1 and of the wrong sign-a negative sign indicating that the polarizations of the lower and upper Davydov components are reversed from experiment. Inclusion of Frenkel-CT coupling dramatically improves the agreement with experiment, yielding a 0-0 DS of 601cm-1 and a nearly quantitative reproduction of the relative spectral intensities of the 0-n vibronic components. Our analysis also shows that CT mixing increases with the size of the oligoacenes. We discuss the implications of these results on exciton dissociation and transport. © 2011 American Institute of Physics.

  8. Fine structure of the exciton electroabsorption in semiconductor superlattices

    Energy Technology Data Exchange (ETDEWEB)

    Monozon, B.S., E-mail: borismonozon@mail.ru [Physics Department, Marine Technical University, 3 Lotsmanskaya Str., 190008 St.Petersburg (Russian Federation); Schmelcher, P. [Zentrum für Optische Quantentechnologien, The Hamburg Centre for Ultrafast Imaging, Universität Hamburg, Luruper Chaussee 149, 22761 Hamburg (Germany)

    2017-02-15

    Wannier-Mott excitons in a semiconductor layered superlattice (SL) are investigated analytically for the case that the period of the superlattice is much smaller than the 2D exciton Bohr radius. Additionally we assume the presence of a longitudinal external static electric field directed parallel to the SL axis. The exciton states and the optical absorption coefficient are derived in the tight-binding and adiabatic approximations. Strong and weak electric fields providing spatially localized and extended electron and hole states, respectively, are studied. The dependencies of the exciton states and the exciton absorption spectrum on the SL parameters and the electric field strength are presented in an explicit form. We focus on the fine structure of the ground quasi-2D exciton level formed by the series of closely spaced energy levels adjacent from the high frequencies. These levels are related to the adiabatically slow relative exciton longitudinal motion governed by the potential formed by the in-plane exciton state. It is shown that the external electric fields compress the fine structure energy levels, decrease the intensities of the corresponding optical peaks and increase the exciton binding energy. A possible experimental study of the fine structure of the exciton electroabsorption is discussed.

  9. Kinetic energy transfer during the tennis serve

    Directory of Open Access Journals (Sweden)

    C.L. de Subijana

    2010-12-01

    Full Text Available Several studies have established the pattern used in the over arm hitting and throwing movements, however to date there has not been one which statistically expresses the Kinetic Link Principle of the tennis serve. The main goals of this study were: first to investigate the kinetic energy transmission pattern using a complete mechanical body model and second, to create a tool which could help evaluating the individual technique of a tennis player. This tool was a statistical procedure which expressed the individual technique of a player as a mathematical function. Fourteen and twelve flat tennis serves of two top tennis players landing in an aiming area were recorded with two synchronized video cameras at 125 Hz. The experimental technique was 3D photogrammetry. A 28 points body model with five solid-rigid (the pelvis, the thorax, the upper arms and the racquet was built. The kinetic energies from the body segments were considered the biomechanical parameters. The mean speeds of the balls were 41.9 m/s (150.9 km/hr and 38.1 m/s (137.2 km/hr. A Kinetic Sequential Action Muscle principle based on the kinetic energy transfer was probed statistically by mean a correlation analysis [3]. This pattern showed the existence of a proximal to distal sequence of kinetic energy maximums. A significant (p<0.05 discriminant function for each player could predict the category of the serve (“good” or “bad” in the 78.6% and 100% of the cases. This function facilitated the understanding of the individual technique of a tennis player showing that this could be a tool for the tennis training complementary to the qualitative (observational analysis.

  10. Energy Transfer Efficiency from ZnO-Nanocrystals to Eu3+ Ions Embedded in SiO2 Film for Emission at 614 nm

    Science.gov (United States)

    Pita, Kantisara

    2017-01-01

    In this work, we study the energy transfer mechanism from ZnO nanocrystals (ZnO-nc) to Eu3+ ions by fabricating thin-film samples of ZnO-nc and Eu3+ ions embedded in a SiO2 matrix using the low-cost sol-gel technique. The time-resolved photoluminescence (TRPL) measurements from the samples were analyzed to understand the contribution of energy transfer from the various ZnO-nc emission centers to Eu3+ ions. The decay time obtained from the TRPL measurements was used to calculate the energy transfer efficiencies from the ZnO-nc emission centers, and these results were compared with the energy transfer efficiencies calculated from steady-state photoluminescence emission results. The results in this work show that high transfer efficiencies from the excitonic and Zn defect emission centers is mostly due to the energy transfer from ZnO-nc to Eu3+ ions which results in the radiative emission from the Eu3+ ions at 614 nm, while the energy transfer from the oxygen defect emissions is most probably due to the energy transfer from ZnO-nc to the new defects created due to the incorporation of the Eu3+ ions. PMID:28796195

  11. Energy Transfer Efficiency from ZnO-Nanocrystals to Eu3+Ions Embedded in SiO₂ Film for Emission at 614 nm.

    Science.gov (United States)

    Mangalam, Vivek; Pita, Kantisara

    2017-08-10

    In this work, we study the energy transfer mechanism from ZnO nanocrystals (ZnO-nc) to Eu 3+ ions by fabricating thin-film samples of ZnO-nc and Eu 3+ ions embedded in a SiO₂ matrix using the low-cost sol-gel technique. The time-resolved photoluminescence (TRPL) measurements from the samples were analyzed to understand the contribution of energy transfer from the various ZnO-nc emission centers to Eu 3+ ions. The decay time obtained from the TRPL measurements was used to calculate the energy transfer efficiencies from the ZnO-nc emission centers, and these results were compared with the energy transfer efficiencies calculated from steady-state photoluminescence emission results. The results in this work show that high transfer efficiencies from the excitonic and Zn defect emission centers is mostly due to the energy transfer from ZnO-nc to Eu 3+ ions which results in the radiative emission from the Eu 3+ ions at 614 nm, while the energy transfer from the oxygen defect emissions is most probably due to the energy transfer from ZnO-nc to the new defects created due to the incorporation of the Eu 3+ ions.

  12. Energy Transfer Efficiency from ZnO-Nanocrystals to Eu3+ Ions Embedded in SiO2 Film for Emission at 614 nm

    Directory of Open Access Journals (Sweden)

    Vivek Mangalam

    2017-08-01

    Full Text Available In this work, we study the energy transfer mechanism from ZnO nanocrystals (ZnO-nc to Eu3+ ions by fabricating thin-film samples of ZnO-nc and Eu3+ ions embedded in a SiO2 matrix using the low-cost sol-gel technique. The time-resolved photoluminescence (TRPL measurements from the samples were analyzed to understand the contribution of energy transfer from the various ZnO-nc emission centers to Eu3+ ions. The decay time obtained from the TRPL measurements was used to calculate the energy transfer efficiencies from the ZnO-nc emission centers, and these results were compared with the energy transfer efficiencies calculated from steady-state photoluminescence emission results. The results in this work show that high transfer efficiencies from the excitonic and Zn defect emission centers is mostly due to the energy transfer from ZnO-nc to Eu3+ ions which results in the radiative emission from the Eu3+ ions at 614 nm, while the energy transfer from the oxygen defect emissions is most probably due to the energy transfer from ZnO-nc to the new defects created due to the incorporation of the Eu3+ ions.

  13. Mixing of exciton and charge-transfer states in Photosystem II reaction centers: Modeling of stark spectra with modified redfield theory

    NARCIS (Netherlands)

    Novoderezhkin, V.I.; Dekker, J.P.; van Grondelle, R.

    2007-01-01

    We propose an exciton model for the Photosystem II reaction center (RC) based on a quantitative simultaneous fit of the absorption, linear dichroism, circular dichroism, steady-state fluorescence, triplet-minus-singlet, and Stark spectra together with the spectra of pheophytin-modified RCs, and

  14. The relationship between the electric field induced dissociation of charge transfer (CT) excitons and the photocurrent in novel hybrid small molecular/polymeric solar cells

    Energy Technology Data Exchange (ETDEWEB)

    Inal, Sahika; Neher, Dieter [Universitaet Potsdam (Germany). Institut fuer Physik und Astronomie; Sellinger, Alan [Institute of Materials Research and Engineering, Singapore (China)

    2010-07-01

    Complete dissociation of coulombically bound interfacial states is an ultimate step accounting for photovoltaic performance. Recent work has proposed that the emission of CT-exciton, i.e. an exciplex, is a competing process to the generation of free charges. Here, we investigated the photophysical processes in a bulk heterojunction system using a soluble poly(p-phenylenevinylene) donor and a novel small molecular electron acceptor based on Vinazene (2-vinyl-4,5-dicyanoimidazole). Recent work has shown that this blend exhibits a featureless emission, prominent at long wavelengths of the spectrum, which was attributed to a CT-exciton. We monitored the field induced dissociation of these CT-excitons by means of steady state and time resolved PL spectroscopy. Shortened decay times and reduced PL emission in blend film evidence the dissociation of the emissive intermolecular pair by the external electric field. Analyzing the dependence of the photocurrent and external quantum efficiency on the external field, the fate of the separated exciplex pairs is tackled. It is suggested that the formation of free carriers involves channels other than CT-excitons in such blends.

  15. The security energy encryption in wireless power transfer

    Science.gov (United States)

    Sadzali, M. N.; Ali, A.; Azizan, M. M.; Albreem, M. A. M.

    2017-09-01

    This paper presents a concept of security in wireless power transfer (WPT) by applying chaos theory. Chaos theory is applied as a security system in order to safeguard the transfer of energy from a transmitter to the intended receiver. The energy encryption of the wireless power transfer utilizes chaos theory to generate the possibility of a logistic map for the chaotic security key. The simulation for energy encryption wireless power transfer system was conducted by using MATLAB and Simulink. By employing chaos theory, the chaotic key ensures the transmission of energy from transmitter to its intended receiver.

  16. Integrated analysis of energy transfers in elastic-wave turbulence.

    Science.gov (United States)

    Yokoyama, Naoto; Takaoka, Masanori

    2017-08-01

    In elastic-wave turbulence, strong turbulence appears in small wave numbers while weak turbulence does in large wave numbers. Energy transfers in the coexistence of these turbulent states are numerically investigated in both the Fourier space and the real space. An analytical expression of a detailed energy balance reveals from which mode to which mode energy is transferred in the triad interaction. Stretching energy excited by external force is transferred nonlocally and intermittently to large wave numbers as the kinetic energy in the strong turbulence. In the weak turbulence, the resonant interactions according to the weak turbulence theory produce cascading net energy transfer to large wave numbers. Because the system's nonlinearity shows strong temporal intermittency, the energy transfers are investigated at active and moderate phases separately. The nonlocal interactions in the Fourier space are characterized by the intermittent bundles of fibrous structures in the real space.

  17. Charge Versus Energy Transfer in Atomically Thin Graphene-Transition Metal Dichalcogenide van der Waals Heterostructures

    Science.gov (United States)

    Froehlicher, Guillaume; Lorchat, Etienne; Berciaud, Stéphane

    2018-01-01

    Made from stacks of two-dimensional materials, van der Waals heterostructures exhibit unique light-matter interactions and are promising for novel optoelectronic devices. The performance of such devices is governed by near-field coupling through, e.g., interlayer charge and/or energy transfer. New concepts and experimental methodologies are needed to properly describe two-dimensional heterointerfaces. Here, we report an original study of interlayer charge and energy transfer in atomically thin metal-semiconductor [i.e., graphene-transition metal dichalcogenide (TMD, here molybdenum diselenide, MoSe2 )] heterostructures using a combination of microphotoluminescence and Raman scattering spectroscopies. The photoluminescence intensity in graphene /MoSe2 is quenched by more than 2 orders of magnitude and rises linearly with the incident photon flux, demonstrating a drastically shortened (about 1 ps) room-temperature MoSe2 exciton lifetime. Key complementary insights are provided from a comprehensive analysis of the graphene and MoSe2 Raman modes, which reveals net photoinduced electron transfer from MoSe2 to graphene and hole accumulation in MoSe2 . Remarkably, the steady-state Fermi energy of graphene saturates at 290 ±15 meV above the Dirac point. This reproducible behavior is observed both in ambient air and in vacuum and is discussed in terms of intrinsic factors (i.e., band offsets) and environmental effects. In this saturation regime, balanced photoinduced flows of electrons and holes may transfer to graphene, a mechanism that effectively leads to energy transfer. Using a broad range of incident photon fluxes and diverse environmental conditions, we find that the presence of net photoinduced charge transfer has no measurable impact on the near-unity photoluminescence quenching efficiency in graphene /MoSe2 . This absence of correlation strongly suggests that energy transfer to graphene (either in the form of electron exchange or dipole-dipole interaction) is the

  18. Charge Versus Energy Transfer in Atomically Thin Graphene-Transition Metal Dichalcogenide van der Waals Heterostructures

    Directory of Open Access Journals (Sweden)

    Guillaume Froehlicher

    2018-01-01

    Full Text Available Made from stacks of two-dimensional materials, van der Waals heterostructures exhibit unique light-matter interactions and are promising for novel optoelectronic devices. The performance of such devices is governed by near-field coupling through, e.g., interlayer charge and/or energy transfer. New concepts and experimental methodologies are needed to properly describe two-dimensional heterointerfaces. Here, we report an original study of interlayer charge and energy transfer in atomically thin metal-semiconductor [i.e., graphene-transition metal dichalcogenide (TMD, here molybdenum diselenide, MoSe_{2}] heterostructures using a combination of microphotoluminescence and Raman scattering spectroscopies. The photoluminescence intensity in graphene/MoSe_{2} is quenched by more than 2 orders of magnitude and rises linearly with the incident photon flux, demonstrating a drastically shortened (about 1 ps room-temperature MoSe_{2} exciton lifetime. Key complementary insights are provided from a comprehensive analysis of the graphene and MoSe_{2} Raman modes, which reveals net photoinduced electron transfer from MoSe_{2} to graphene and hole accumulation in MoSe_{2}. Remarkably, the steady-state Fermi energy of graphene saturates at 290±15  meV above the Dirac point. This reproducible behavior is observed both in ambient air and in vacuum and is discussed in terms of intrinsic factors (i.e., band offsets and environmental effects. In this saturation regime, balanced photoinduced flows of electrons and holes may transfer to graphene, a mechanism that effectively leads to energy transfer. Using a broad range of incident photon fluxes and diverse environmental conditions, we find that the presence of net photoinduced charge transfer has no measurable impact on the near-unity photoluminescence quenching efficiency in graphene/MoSe_{2}. This absence of correlation strongly suggests that energy transfer to graphene (either in the form of electron

  19. Visualization of Excitonic Structure in the Fenna-Matthews-OlsonPhotosynthetic Complex by Polarization-Dependent Two-DimensionalElectronic Spectroscopy

    Energy Technology Data Exchange (ETDEWEB)

    Department of Chemistry, The University of Chicago; Department of Biology, Department of Chemistry, Washington University; Fleming, Graham; Read, Elizabeth L.; Schlau-Cohen, Gabriela S.; Engel, Gregory S.; Wen, Jianzhong; Blankenship, Robert E.; Fleming, Graham R.

    2008-05-26

    Photosynthetic light-harvesting proceeds by the collection and highly efficient transfer of energy through a network of pigment-protein complexes. Inter-chromophore electronic couplings and interactions between pigments and the surrounding protein determine energy levels of excitonic states and dictate the mechanism of energy flow. The excitonic structure (orientation of excitonic transition dipoles) of pigment-protein complexes is generally deduced indirectly from x-ray crystallography in combination with predictions of transition energies and couplings in the chromophore site basis. Here, we demonstrate that coarse-grained excitonic structural information in the form of projection angles between transition dipole moments can be obtained from polarization-dependent two-dimensional electronic spectroscopy of an isotropic sample, particularly when the nonrephasing or free polarization decay signal rather than the photon echo signal is considered. The method provides an experimental link between atomic and electronic structure and accesses dynamical information with femtosecond time resolution. In an investigation of the Fenna-Matthews-Olson complex from green sulfur bacteria, energy transfer connecting two particular exciton states in the protein is isolated as being the primary contributor to a cross peak in the nonrephasing 2D spectrum at 400 fs under a specific sequence of polarized excitation pulses. The results suggest the possibility of designing experiments using combinations of tailored polarization sequencesto separate and monitor individual relaxation pathways.

  20. Exciton in closed and opened quantum dot

    Directory of Open Access Journals (Sweden)

    M.V.Tkach

    2007-01-01

    Full Text Available The theory of exciton spectrum in spherically symmetric states for the three- shell closed spherical quantum dot is proposed. The evolution of the exciton spectrum while varying the outer well thickness from zero (stationary spectrum of single closed spherical quantum dot to infinity (quasistationary spectrum of a single open spherical quantum dot is investigated. The mechanism of damping (semiwidth of quasistationary states due to the redistribution over the energy levels of probability of exciton location in the space of two inner shells of nanosystem is studied. It is shown that the three shell closed spherical quantum dot of a rather big thickness of the outer well quite sufficiently and exactly reflects the basic properties of the quasistationary exciton spectrum in a single open spherical quantum dot.

  1. Excitonic physics in a Dirac quantum dot

    Science.gov (United States)

    Raca, V.; Milovanović, M. V.

    2017-11-01

    We present a description of vacuum polarization in a circular Dirac quantum dot in two spatial dimensions assuming α —the relative strength of the Coulomb interaction small enough to render an approximation with a single electron (hole) lowest energy level relevant. Applying this approximation, we find that for αc≈1.05 the lowest level is half filled irrespective of the number of flavors that are present. The ground state can be represented as a superposition of particular (even number) excitonic states which constitute an excitonic cloud that evolves in a crossover manner. The ground state is degenerate with an intervalley excitonic state at αc≈1.05 , a critical strength, that in our approximation marks a point with single electron and exciton resonances.

  2. Formation of plasmon pulses in the cooperative decay of excitons of quantum dots near a metal surface

    Energy Technology Data Exchange (ETDEWEB)

    Shesterikov, A. B.; Gubin, M. Yu. [Vladimir State University (Russian Federation); Gladush, M. G. [Russian Academy of Sciences, Institute of Spectroscopy (Russian Federation); Prokhorov, A. V., E-mail: avprokhorov33@mail.ru [Vladimir State University (Russian Federation)

    2017-01-15

    The formation of pulses of surface electromagnetic waves at a metal–dielectric boundary is considered in the process of cooperative decay of excitons of quantum dots distributed near a metal surface in a dielectric layer. It is shown that the efficiency of exciton energy transfer to excited plasmons can, in principle, be increased by selecting the dielectric material with specified values of the complex permittivity. It is found that in the mean field approximation, the semiclassical model of formation of plasmon pulses in the system under study is reduced to the pendulum equation with the additional term of nonlinear losses.

  3. Energy transfer in anisotropic systems: A. Excitation migration in substitutionally disordered one-dimensional solids. B. The spectroscopy of molecules adsorbed on metal surfaces

    Energy Technology Data Exchange (ETDEWEB)

    Zwemer, D.A.

    1978-11-01

    The energy and dynamics of excited states in a variety of anisotropic environments, including isotopically and chemically mixed crystals and molecular overlayers adsorbed on a nickel (111) surface, are investigated. The relationship between local and long-range structure and spectroscopic properties is explored. A theory for energy transfer in substitutionally disordered solids is presented. Explicit expressions for the ''diffusion'' coefficients and the energy partitioning ratios in binary systems are derived. Energy transfer between localized states is found to be facilitated by concurrent tunnelling and thermal promotion. Experimental results for triplet energy partitioning between mobile and stationary trap states as a function of mobile trap concentration in the ternary d/sub 2/-1,2,4,5-tetrachlorobenzene--h/sub 2/-1,2,4,5-tetrachlorobenzene--pyrazine system are analyzed. It is shown that both tunnelling and thermal detrapping contribute to triplet exciton mobility below 4.2 K. Singlet exciton migration makes an important contribution to trap equilibration before intersystem crossing to the triplet manifold. Spin coherence experiments are used to determine the energy level structure, physical geometry, and exciton dynamics of a series of impurity-induced traps in 1,2,4,5-tetrachlorobenzene. The uv spectra of pyrazine, pyridine, and naphthalene adsorbed on a nickel single crystal (111) surface are measured by spectroscopic ellipsometry at low temperatures. The excited electronic and vibronic energy levels measured are similar to bulk molecular crystal values, but pyrazine and pyridine show small, but significant deviations. The ordering of molecular overlays is observed spectroscopically and information about overlayer crystal structure is deduced. 148 references, 48 figures, 5 tables.

  4. Exciton laser rate equations

    Directory of Open Access Journals (Sweden)

    Garkavenko A. S.

    2011-08-01

    Full Text Available The rate equations of the exciton laser in the system of interacting excitons have been obtained and the inverted population conditions and generation have been derived. The possibility of creating radically new gamma-ray laser has been shown.

  5. Scalable high-performance algorithm for the simulation of exciton-dynamics. Application to the light harvesting complex II in the presence of resonant vibrational modes

    DEFF Research Database (Denmark)

    Kreisbeck, Christoph; Kramer, Tobias; Aspuru-Guzik, Alán

    2014-01-01

    the exciton dynamics within a density-matrix formalism are known, but are restricted to small systems with less than ten sites due to their computational complexity. To study the excitonic energy transfer in larger systems, we adapt and extend the exact hierarchical equation of motion (HEOM) method to various...... high-performance many-core platforms using the Open Compute Language (OpenCL). For the light-harvesting complex II (LHC II) found in spinach, the HEOM results deviate from predictions of approximate theories and clarify the time-scale of the transfer-process. We investigate the impact of resonantly...

  6. Energy transfer in erbium doped optical waveguides based on silicon

    NARCIS (Netherlands)

    Kik, Pieter Geert

    2000-01-01

    Energy transfer in erbium doped optical waveguides based on silicon This thesis describes the energy transfer processes occurring in materials that can be used for the fabrication of silicon compatible optical integrated circuits, operating at 1.54 mm.The thesis consists of three parts: Part I

  7. Ultrafast Energy Transfer in an Artificial Photosynthetic Antenna

    Directory of Open Access Journals (Sweden)

    van Grondelle R.

    2013-03-01

    Full Text Available We temporally resolved energy transfer kinetics in an artificial light-harvesting dyad composed of a phthalocyanine covalently linked to a carotenoid. Upon carotenoid photo-excitation, energy transfers within ≈100fs (≈52% efficiency to the phthalocyanine.

  8. Mode-to-mode energy transfers in convective patterns

    Indian Academy of Sciences (India)

    Abstract. We investigate the energy transfer between various Fourier modes in a low- dimensional model for thermal convection. We have used the formalism of mode-to-mode energy transfer rate in our calculation. The evolution equations derived using this scheme is the same as those derived using the hydrodynamical ...

  9. Significance of a Recurring Function in Energy Transfer

    Science.gov (United States)

    Mishra, Subodha

    2017-01-01

    The appearance of a unique function in the energy transfer from one system to the other in different physical situations such as electrical, mechanical, optical, and quantum mechanical processes is established in this work. Though the laws governing the energy transformation and its transfer from system to system are well known, here we notice a…

  10. Theoretical study on electronic structure of bathocuproine: Renormalization of the band gap in the crystalline state and the large exciton binding energy

    Science.gov (United States)

    Yanagisawa, Susumu; Hatada, Shin-No-Suke; Morikawa, Yoshitada

    Bathocuproine (BCP) is a promising organic material of a hole blocking layer in organic light-emitting diodes or an electron buffer layer in organic photovoltaic cells. The nature of the unoccupied electronic states is a key characteristic of the material, which play vital roles in the electron transport. To elucidate the electronic properties of the molecular or crystalline BCP, we use the GW approximation for calculation of the fundamental gap, and the long-range corrected density functional theory for the molecular optical absorption. It is found that the band gap of the BCP single crystal is 4.39 eV, and it is in agreement with the recent low-energy inverse photoemission spectroscopy measurement. The polarization energy is estimated to be larger than 1 eV, demonstrating the large polarization effects induced by the electronic clouds surrounding the injected charge. The theoretical optical absorption energy is 3.68 eV, and the exciton binding energy is estimated to be 0.71 eV, implying the large binding in the eletron-hole pair distributed around the small part of the molecular region. This work was supported by the Grants-in-Aid for Young Scientists (B) (No. 26810009), and for Scientific Research on Innovative Areas ``3D Active-Site Science'' (No. 26105011) from Japan Society for the Promotion of Science.

  11. Dissociating excitons photogenerated in semiconducting carbon nanotubes at polymeric photovoltaic heterojunction interfaces.

    Science.gov (United States)

    Bindl, Dominick J; Safron, Nathaniel S; Arnold, Michael S

    2010-10-26

    Semiconducting single-walled carbon nanotubes (s-SWCNTs) have strong near-infrared and visible absorptivity and exceptional charge transport characteristics, rendering them highly attractive semiconductor absorbers for photovoltaic and photodetector technologies. However, these applications are limited by a poor understanding of how photogenerated charges, which are bound as excitons in s-SWCNTs, can be dissociated in large-area solid-state devices. Here, we measure the dissociation of excitons in s-SWCNT thin films that form planar heterojunction interfaces with polymeric photovoltaic materials using an exciton dissociation-sensitive photocapacitor measurement technique that is advantageously insensitive to optically induced thermal photoconductive effects. We find that fullerene and polythiophene derivatives induce exciton dissociation, resulting in electron and hole transfer, respectively, away from optically excited s-SWCNTs. Significantly weaker or no charge transfer is observed using wider gap polymers due to insufficient energy offsets. These results are expected to critically guide the development of thin film s-SWCNT-based photosensitive devices.

  12. Förster resonance energy transfer enhanced color-conversion using colloidal semiconductor quantum dots for solid state lighting

    Science.gov (United States)

    Nizamoglu, Sedat; Demir, Hilmi Volkan

    2009-10-01

    In this paper, we present Förster resonance energy transfer (FRET)-enhanced color-conversion using colloidal semiconductor quantum dot nanocrystals (NCs) to make reddish-orange light-emitting diodes for use in ultraefficient solid state lighting. To achieve FRET enhancement at 614 nm, we use an energy gradient hybrid structure made of cyan- and orange-emitting CdSe/ZnS NCs (λPL=492 and 588 nm in solution, respectively). This enables recycling of trapped excitons using FRET and achieves a relative quantum efficiency enhancement of 15.1% in reddish-orange full color-conversion for the integrated hybrid cyan-orange NC layer with respect to the case of full color-conversion using only orange NCs without FRET.

  13. Exciton Mapping at Subwavelength Scales in Two-Dimensional Materials

    KAUST Repository

    Tizei, Luiz H. G.

    2015-03-01

    Spatially resolved electron-energy-loss spectroscopy (EELS) is performed at diffuse interfaces between MoS2 and MoSe2 single layers. With a monochromated electron source (20 meV) we successfully probe excitons near the interface by obtaining the low loss spectra at the nanometer scale. The exciton maps clearly show variations even with a 10 nm separation between measurements; consequently, the optical band gap can be measured with nanometer-scale resolution, which is 50 times smaller than the wavelength of the emitted photons. By performing core-loss EELS at the same regions, we observe that variations in the excitonic signature follow the chemical composition. The exciton peaks are observed to be broader at interfaces and heterogeneous regions, possibly due to interface roughness and alloying effects. Moreover, we do not observe shifts of the exciton peak across the interface, possibly because the interface width is not much larger than the exciton Bohr radius.

  14. Visual prosthesis wireless energy transfer system optimal modeling.

    Science.gov (United States)

    Li, Xueping; Yang, Yuan; Gao, Yong

    2014-01-16

    Wireless energy transfer system is an effective way to solve the visual prosthesis energy supply problems, theoretical modeling of the system is the prerequisite to do optimal energy transfer system design. On the basis of the ideal model of the wireless energy transfer system, according to visual prosthesis application condition, the system modeling is optimized. During the optimal modeling, taking planar spiral coils as the coupling devices between energy transmitter and receiver, the effect of the parasitic capacitance of the transfer coil is considered, and especially the concept of biological capacitance is proposed to consider the influence of biological tissue on the energy transfer efficiency, resulting in the optimal modeling's more accuracy for the actual application. The simulation data of the optimal model in this paper is compared with that of the previous ideal model, the results show that under high frequency condition, the parasitic capacitance of inductance and biological capacitance considered in the optimal model could have great impact on the wireless energy transfer system. The further comparison with the experimental data verifies the validity and accuracy of the optimal model proposed in this paper. The optimal model proposed in this paper has a higher theoretical guiding significance for the wireless energy transfer system's further research, and provide a more precise model reference for solving the power supply problem in visual prosthesis clinical application.

  15. Carrier diffusion as a measure of carrier/exciton transfer rate in InAs/InGaAsP/InP hybrid quantum dot-quantum well structures emitting at telecom spectral range

    Science.gov (United States)

    Rudno-Rudziński, W.; Biegańska, D.; Misiewicz, J.; Lelarge, F.; Rousseau, B.; Sek, G.

    2018-01-01

    We investigate the diffusion of photo-generated carriers (excitons) in hybrid two dimensional-zero dimensional tunnel injection structures, based on strongly elongated InAs quantum dots (called quantum dashes, QDashes) of various heights, designed for emission at around 1.5 μm, separated by a 3.5 nm wide barrier from an 8 nm wide In0.64Ga0.36As0.78P0.22 quantum well (QW). By measuring the spectrally filtered real space images of the photoluminescence patterns with high resolution, we probe the spatial extent of the emission from QDashes. Deconvolution with the exciting light spot shape allows us to extract the carrier/exciton diffusion lengths. For the non-resonant excitation case, the diffusion length depends strongly on excitation power, pointing at carrier interactions and phonons as its main driving mechanisms. For the case of excitation resonant with absorption in the adjacent QW, the diffusion length does not depend on excitation power for low excitation levels since the generated carriers do not have sufficient excess kinetic energy. It is also found that the diffusion length depends on the quantum-mechanical coupling strength between QW and QDashes, controlled by changing the dash size. It influences the energy difference between the QDash ground state of the system and the quantum well levels, which affects the tunneling rates. When that QW-QDash level separation decreases, the probability of capturing excitons generated in the QW by QDashes increases, which is reflected by the decreased diffusion length from approx. 5 down to 3 μm.

  16. The back and forth of energy transfer between carotenoids and chlorophylls and its role in the regulation of light harvesting.

    Science.gov (United States)

    Holleboom, Christoph-Peter; Walla, Peter J

    2014-02-01

    Many aspects in the regulation of photosynthetic light-harvesting of plants are still quite poorly understood. For example, it is still a matter of debate which physical mechanism(s) results in the regulation and dissipation of excess energy in high light. Many researchers agree that electronic interactions between chlorophylls (Chl) and certain states of carotenoids are involved in these mechanisms. However, in particular, the role of the first excited state of carotenoids (Car S1) is not easily revealed, because of its optical forbidden character. The use of two-photon excitation is an elegant approach to address directly this state and to investigate the energy transfer in the direction Car S1 → Chl. Meanwhile, it has been applied to a large variety of systems starting from simple carotenoid-tetrapyrrole model compounds up to entire plants. Here, we present a systematic summary of the observations obtained by two-photon excitation about Car S1 → Chl energy transfer in systems with increasing complexity and the correlation to fluorescence quenching. We compare these observations directly with the energy transfer in the opposite direction, Chl → Car S1, for the same systems as obtained in pump-probe studies. We discuss what surprising aspects of this comparison led us to the suggestion that quenching excitonic Car-Chl interactions could contribute to the regulation of light harvesting, and how this suggestion can be connected to other models proposed.

  17. The Grover energy transfer algorithm for relativistic speeds

    Energy Technology Data Exchange (ETDEWEB)

    Garcia-Escartin, Juan Carlos; Chamorro-Posada, Pedro, E-mail: juagar@yllera.tel.uva.e [Dpto. de TeorIa de la Senal y Comunicaciones e Ingenieria Telematica, Universidad de Valladolid, ETSI de Telecomunicacion, Campus Miguel Delibes, Paseo Belen 15, 47011 Valladolid (Spain)

    2010-11-12

    Grover's algorithm for quantum search can also be applied to classical energy transfer. The procedure takes a system in which the total energy is equally distributed among N subsystems and transfers most of it to one marked subsystem. We show that in a relativistic setting the efficiency of this procedure can be improved. We will consider the transfer of relativistic kinetic energy in a series of elastic collisions. In this case, the number of steps of the energy transfer procedure approaches 1 as the initial velocities of the objects become closer to the speed of light. This is a consequence of introducing nonlinearities in the procedure. However, the maximum attainable transfer will depend on the particular combination of speed and number of objects. In the procedure, we will use N elements, as in the classical non-relativistic case, instead of the log{sub 2}(N) states of the quantum algorithm.

  18. Pair transfer processes probed at deep sub barrier energies

    Directory of Open Access Journals (Sweden)

    Scarlassara F.

    2011-10-01

    Full Text Available Multinucleon transfer cross sections in the system 40Ca+96Zr have been measured at bombarding energies ranging from the Coulomb barrier to ~ 25% below. Target-like (lighter recoils in inverse kinematics have been completely identif ed in A,Z and Q-value with the large solid angle magnetic spectrometer PRISMA. The experimental slopes of the neutron transfer probabilities at large internuclear separation are consistent with the values derived from the binding energies. A phenomenological interpretation of the transfer probabilities indicates the presence of enhanced values for the even number of neutron transfers.

  19. Plasmon assisted control of photo-induced excitation energy transfer in a molecular chain

    Science.gov (United States)

    Wang, Luxia; May, Volkhard

    2017-08-01

    The strong and ultrafast laser pulse excitation of a molecular chain in close vicinity to a spherical metal nano-particle (MNP) is studied theoretically. Due to local-field enhancement around the MNP, pronounced excited-state formation has to be expected for the part of the chain which is in proximity to the MNP. Here, the description of this phenomenon will be based on a uniform quantum theory of the MNP-molecule system. It accounts for local-field effects due to direct consideration of the strong excitation energy transfer coupling between the MNP and the various molecules. The molecule-MNP distances are chosen in such a way as to achieve a correct description of the MNP via dipole-plasmon excitations. Short plasmon life-times are incorporated in the framework of a density matrix approach. By extending earlier work the present description allows for multi-exciton formation and multiple dipole-plasmon excitation. The region of less intense and not-too-short optical excitation is identified as being best suited for excitation energy localization in the chain.

  20. Geo energy research and development: technology transfer update

    Energy Technology Data Exchange (ETDEWEB)

    Traeger, R.K.; Dugan, V.L.

    1983-01-01

    Sandia Geo Energy Programs in geothermal, coal, oil and gas, and synfuel technologies have been effective in transferring research concepts to applications in private industry. This report updates the previous summary (SAND82-0211, March 1982) to include recent technology transfers and to reflect recent changes in philosophy on technology transfer. Over 40 items transferred to industry have been identified in the areas of Hardware, Risk Removal and Understanding. Successful transfer is due largely to personal interactions between Sandia engineers and the technical staffs of private industry.

  1. Magnetic excitons in singlet-ground-state ferromagnets

    DEFF Research Database (Denmark)

    Birgeneau, R.J.; Als-Nielsen, Jens Aage; Bucher, E.

    1971-01-01

    The authors report measurements of the dispersion of singlet-triplet magnetic excitons as a function of temperature in the singlet-ground-state ferromagnets fcc Pr and Pr3Tl. Well-defined excitons are observed in both the ferromagnetic and paramagnetic regions, but with energies which are nearly...

  2. A planning framework for transferring building energy technologies

    Energy Technology Data Exchange (ETDEWEB)

    Farhar, B C; Brown, M A; Mohler, B L; Wilde, M; Abel, F H

    1990-07-01

    Accelerating the adoption of new and existing cost-effective technologies has significant potential to reduce the energy consumed in US buildings. This report presents key results of an interlaboratory technology transfer planning effort in support of the US Department of Energy's Office of Building Technologies (OBT). A guiding assumption for planning was that OBT's R D program should forge linkages with existing programs whose goals involved enhancing energy efficiency in buildings. An ad hoc Technology Transfer Advisory Group reviewed the existing analysis and technology transfer program, brainstormed technology transfer approaches, interviewed DOE program managers, identified applicable research results, and developed a framework that management could use in deciding on the best investments of technology transfer resources. Representatives of 22 organizations were interviewed on their views of the potential for transferring energy efficiency technologies through active linking with OBT. The report describes these programs and interview results; outlines OBT tools, technologies, and practices to be transferred; defines OBT audiences; identifies technology transfer functions and presents a framework devised using functions and audiences; presents some 60 example technology transfer activities; and documents the Advisory Group's recommendations. 37 refs., 3 figs., 12 tabs.

  3. Anomalous surplus energy transfer observed with multiple FRET acceptors.

    Directory of Open Access Journals (Sweden)

    Srinagesh V Koushik

    2009-11-01

    Full Text Available Förster resonance energy transfer (FRET is a mechanism where energy is transferred from an excited donor fluorophore to adjacent chromophores via non-radiative dipole-dipole interactions. FRET theory primarily considers the interactions of a single donor-acceptor pair. Unfortunately, it is rarely known if only a single acceptor is present in a molecular complex. Thus, the use of FRET as a tool for measuring protein-protein interactions inside living cells requires an understanding of how FRET changes with multiple acceptors. When multiple FRET acceptors are present it is assumed that a quantum of energy is either released from the donor, or transferred in toto to only one of the acceptors present. The rate of energy transfer between the donor and a specific acceptor (k(D-->A can be measured in the absence of other acceptors, and these individual FRET transfer rates can be used to predict the ensemble FRET efficiency using a simple kinetic model where the sum of all FRET transfer rates is divided by the sum of all radiative and non-radiative transfer rates.The generality of this approach was tested by measuring the ensemble FRET efficiency in two constructs, each containing a single fluorescent-protein donor (Cerulean and either two or three FRET acceptors (Venus. FRET transfer rates between individual donor-acceptor pairs within these constructs were calculated from FRET efficiencies measured after systematically introducing point mutations to eliminate all other acceptors. We find that the amount of energy transfer observed in constructs having multiple acceptors is significantly greater than the FRET efficiency predicted from the sum of the individual donor to acceptor transfer rates.We conclude that either an additional energy transfer pathway exists when multiple acceptors are present, or that a theoretical assumption on which the kinetic model prediction is based is incorrect.

  4. Excitation energy transfer in isolated chlorosomes from Chloroflexus aurantiacus

    Science.gov (United States)

    Martiskainen, Jari; Linnanto, Juha; Kananavičius, Robertas; Lehtovuori, Viivi; Korppi-Tommola, Jouko

    2009-07-01

    Chlorosomes from green photosynthetic bacteria Chloroflexus aurantiacus have been studied by time-resolved femtosecond transient absorption spectroscopy. The fastest kinetics of 200-300 fs resolved, was interpreted to stem for intra-chlorosomal excitation energy transfer. Energy transfer from the antenna to the baseplate appeared as a major 9.2 ps rise component detected at the baseplate probe wavelength. Excitation energy transfer rates were evaluated for a model chlorosome. Calculated rod to rod, and rods to baseplate rate constants of 200-400 fs and 10-20 ps, respectively, are in accord with the experimental results.

  5. Theoretical and experimental study of the excitonic binding energy in GaAs/AlGaAs single and coupled double quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Lopes, E.M., E-mail: eldermantovani@yahoo.com.br [Departamento de Física, Química e Biologia, Universidade Estadual Paulista, C. P. 266, Presidente Prudente, São Paulo 17700-000 (Brazil); César, D.F. [Departamento de Física, Universidade Federal de São Carlos, C. P. 676, São Carlos, São Paulo (Brazil); Franchello, F.; Duarte, J.L.; Dias, I.F.L.; Laureto, E. [Departamento de Física, Universidade Estadual de Londrina, C. P. 6001, Londrina, Paraná (Brazil); Elias, D.C.; Pereira, M.V.M.; Guimarães, P.S.S. [Departamento de Física, Instituto de Ciências Exatas, Universidade Federal de Minas Gerais, C. P. 702, Belo Horizonte, Minas Gerais (Brazil); Quivy, A.A. [Laboratório de Novos Materiais Semicondutores, Instituto de Física, Universidade de São Paulo, C. P. 66318, São Paulo (Brazil)

    2013-12-15

    This paper discusses the theoretical and experimental results obtained for the excitonic binding energy (E{sub b}) in a set of single and coupled double quantum wells (SQWs and CDQWs) of GaAs/AlGaAs with different Al concentrations (Al%) and inter-well barrier thicknesses. To obtain the theoretical E{sub b} the method proposed by Mathieu, Lefebvre and Christol (MLC) was used, which is based on the idea of fractional-dimension space, together with the approach proposed by Zhao et al., which extends the MLC method for application in CDQWs. Through magnetophotoluminescence (MPL) measurements performed at 4 K with magnetic fields ranging from 0 T to 12 T, the diamagnetic shift curves were plotted and adjusted using two expressions: one appropriate to fit the curve in the range of low intensity fields and another for the range of high intensity fields, providing the experimental E{sub b} values. The effects of increasing the Al% and the inter-well barrier thickness on E{sub b} are discussed. The E{sub b} reduction when going from the SQW to the CDQW with 5 Å inter-well barrier is clearly observed experimentally for 35% Al concentration and this trend can be noticed even for concentrations as low as 25% and 15%, although the E{sub b} variations in these latter cases are within the error bars. As the Zhao's approach is unable to describe this effect, the wave functions and the probability densities for electrons and holes were calculated, allowing us to explain this effect as being due to a decrease in the spatial superposition of the wave functions caused by the thin inter-well barrier. -- Highlights: • Magnetophotoluminescence results from coupled double quantum wells are reported. • Theoretical and experimental values for excitonic binding energy (E{sub b}) are obtained. • The effects of increasing the inter-well barrier height and thickness on E{sub b} are discussed. • An E{sub b} reduction is observed when going from zero to the 5 Å inter-well barrier

  6. Synthesis and Exciton Dynamics of Triplet Sensitized Conjugated Polymers

    KAUST Repository

    Andernach, Rolf

    2015-07-22

    We report the synthesis of a novel polythiophene-based host-guest copolymer incorporating a Pt-porphyrin complex (TTP-Pt) into the backbone for efficient singlet to triplet polymer exciton sensitization. We elucidated the exciton dynamics in thin films of the material by means of Transient Absorption Spectrosopcy (TAS) on multiple timescales and investigated the mechanism of triplet exciton formation. During sensitization, single exciton diffusion is followed by exciton transfer from the polymer backbone to the complex where it undergoes intersystem crossing to the triplet state of the complex. We directly monitored the triplet exciton back transfer from the Pt-porphyrin to the polymer and find that 60% of the complex triplet excitons are transferred with a time constant of 1087 ps. We propose an equilibrium between polymer and porphyrin triplet states as a result of the low triplet diffusion length in the polymer backbone and hence an increased local triplet population resulting in increased triplet-triplet annihilation. This novel system has significant implications for the design of novel materials for triplet sensitized solar cells and up-conversion layers.

  7. Energy efficient building design. A transfer guide for local governments

    Energy Technology Data Exchange (ETDEWEB)

    1992-03-01

    The fundamental concepts of the building design process, energy codes and standards, and energy budgets are introduced. These tools were combined into Energy Design Guidelines and design contract requirements. The Guidelines were repackaged for a national audience and a videotape for selling the concept to government executives. An effort to test transfer of the Guidelines to outside agencies is described.

  8. Low absorption state of phycocyanin from Acaryochloris marina antenna system: On the interplay between ionic strength and excitonic coupling

    Science.gov (United States)

    Nganou, Collins

    2013-07-01

    This paper studies the excitonic factor in the excited state energy transfer of phycobilisome (PBS) by using a polarized time-resolved pump-probe and by changing the ionic strength of the cofactors' medium in the PBS of Acaryochloris marina (A. marina). As a result, the interplay between the surrounding medium and the closely excited adjacent cofactors is shown to be a negligible factor of the excitonic decay kinetics at 618 nm of the phycocyanin (PC), while it appears as a driving factor of an increase in excitonic delocalization at 630 nm. The obtained anisotropy values are consistent with the contribution of ionic strength in the excitonic mechanism in PBS. These values were 0.38 in high ionic strength and 0.4 in low ionic strength at 618 nm, and 0.52 in high ionic strength and 0.4 in low ionic strength at 630-635 nm. The anisotropy value of 0.52 in high phosphate is similar at 630 nm and 635 nm, which is consistent with an excitonic delocalization band at 635 nm. The 635 nm band is suggested to show the true low energy level of PC in A. marina PBS. The anisotropy decay kinetic at 630 nm suggests that the excited state population of PC is not all equilibrated in 3 ps because of the existence of the 10 ps decay kinetic component. The presence of the slow kinetic decay component in high, and low ionic strength, is consistent with a 10 and 14 ps energy transfer pathway, while the 450 fs kinetic decay component is consistent with the presence of an additional excitation energy transfer pathway between adjacent α84 and β84. Furthermore, the 450 fs decay kinetic is suggested to be trapped in the trimer, while the 400 fs decay kinetic rules out an excitonic flow from low energy level PC to allophycoyanin. This excitonic flow may occur between β84 in adjacent trimers, towards the low energy state of the PBS rod.

  9. Triplet-triplet energy transfer and protection mechanisms against singlet oxygen in photosynthesis

    Science.gov (United States)

    Kihara, Shigeharu

    individual BChl pigments within that photosynthetic antenna complex are accessed via their triplet state dynamics. It is found that the currently used exciton model of FMO needs to be revised. It is also shown that triplet excited states can be readily transferred between the molecules. It is proposed that the triplet energy transfer between the BChl molecules can also serve as a protection mechanism. Finally, it is inferred that at least one of the BChl molecules within the FMO has a triplet state energy that is lower than that of singlet oxygen. This effectively prevents the formation of singlet oxygen and protects the complex from oxidative damage. The energy of BChl is apparently lowered by the specific protein environment, as in solution its energy is measured to be somewhat higher than the energy of singlet oxygen. Finally, the results of the triplet energy transfer within the cytochrome b6f complex are presented. This part of the work is not conclusive, and some of the problems encountered in experiments are described, as well as a new method of sample degassing developed for this type of study is presented.

  10. The Roles of Structural Order and Intermolecular Interactions in Determining Ionization Energies and Charge-Transfer State Energies in Organic Semiconductors

    KAUST Repository

    Graham, Kenneth

    2016-08-17

    The energy landscape in organic semiconducting materials greatly influences charge and exciton behavior, which are both critical to the operation of organic electronic devices. These energy landscapes can change dramatically depending on the phases of material present, including pure phases of one molecule or polymer and mixed phases exhibiting different degrees of order and composition. In this work, ultraviolet photoelectron spectroscopy measurements of ionization energies (IEs) and external quantum efficiency measurements of charge-transfer (CT) state energies (ECT) are applied to molecular photovoltaic material systems to characterize energy landscapes. The results show that IEs and ECT values are highly dependent on structural order and phase composition. In the sexithiophene:C60 system both the IEs of sexithiophene and C60 shift by over 0.4 eV while ECT shifts by 0.5 eV depending on molecular composition. By contrast, in the rubrene:C60 system the IE of rubrene and C60 vary by ≤0.11 eV and ECT varies by ≤0.04 eV as the material composition varies. These results suggest that energy landscapes can exist whereby the binding energies of the CT states are overcome by energy offsets between charges in CT states in mixed regions and free charges in pure phases. © 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.

  11. INTRAMOLECULAR CHARGE AND ENERGY TRANSFER IN MULTICHROMOPHORIC AROMATIC SYSTEMS

    Energy Technology Data Exchange (ETDEWEB)

    Edward C. Lim

    2008-09-09

    A concerted experimental and computational study of energy transfer in nucleic acid bases and charge transfer in dialkylaminobenzonitriles, and related electron donor-acceptor molecules, indicate that the ultrafast photoprocesses occur through three-state conical interactions involving an intermediate state of biradical character.

  12. Fluorescence and Intramolecular Energy Transfer in Polyphenylene Dendrimers

    NARCIS (Netherlands)

    Liu, Daojun; Feyter, Steven De; Cotlet, Mircea; Stefan, Alina; Wiesler, Uwe-Martin; Herrmann, Andreas; Grebel-Koehler, Dörthe; Qu, Jianqiang; Müllen, Klaus; Schryver, Frans C. De

    2003-01-01

    The fluorescence of polyphenylene dendrimers and the intramolecular energy transfer in polyphenylene dendrimers containing a perylenediimide core have been investigated in this paper. Polyphenylene dendrimers composed of tens or hundreds of out-of-plane twisted phenyl units exhibit strong

  13. Energy transfers and magnetic energy growth in small-scale dynamo

    KAUST Repository

    Kumar, Rohit Raj

    2013-12-01

    In this letter we investigate the dynamics of magnetic energy growth in small-scale dynamo by studying energy transfers, mainly energy fluxes and shell-to-shell energy transfers. We perform dynamo simulations for the magnetic Prandtl number Pm = 20 on 10243 grid using the pseudospectral method. We demonstrate that the magnetic energy growth is caused by nonlocal energy transfers from the large-scale or forcing-scale velocity field to small-scale magnetic field. The peak of these energy transfers moves towards lower wave numbers as dynamo evolves, which is the reason why the integral scale of the magnetic field increases with time. The energy transfers U2U (velocity to velocity) and B2B (magnetic to magnetic) are forward and local. Copyright © EPLA, 2013.

  14. Interwell excitons in GaAs superlattices

    DEFF Research Database (Denmark)

    Birkedal, Dan; Sayed, Karim El; Sanders, G.

    1996-01-01

    The formation of spatially indirect excitons in superlattices with narrow minibands is theoretically and experimentally investigated. We identify the experimental conditions for the observation of interwell excitons and find a distinct excitonic state energetically located between the Is exciton ...

  15. Dirac cones and Dirac saddle points of bright excitons in monolayer transition metal dichalcogenides.

    Science.gov (United States)

    Yu, Hongyi; Liu, Gui-Bin; Gong, Pu; Xu, Xiaodong; Yao, Wang

    2014-05-12

    In monolayer transition metal dichalcogenides, tightly bound excitons have been discovered with a valley pseudospin optically addressable through polarization selection rules. Here, we show that this valley pseudospin is strongly coupled to the exciton centre-of-mass motion through electron-hole exchange. This coupling realizes a massless Dirac cone with chirality index I = 2 for excitons inside the light cone, that is, bright excitons. Under moderate strain, the I = 2 Dirac cone splits into two degenerate I = 1 Dirac cones, and saddle points with a linear Dirac spectrum emerge. After binding an extra electron, the charged exciton becomes a massive Dirac particle associated with a large valley Hall effect protected from intervalley scattering. Our results point to unique opportunities to study Dirac physics, with exciton's optical addressability at specifiable momentum, energy and pseudospin. The strain-tunable valley-orbit coupling also implies new structures of exciton condensates, new functionalities of excitonic circuits and mechanical control of valley pseudospin.

  16. Plexcitonic nanoparticles: plasmon-exciton coupling in nanoshell-J-aggregate complexes.

    Science.gov (United States)

    Fofang, Nche T; Park, Tae-Ho; Neumann, Oara; Mirin, Nikolay A; Nordlander, Peter; Halas, Naomi J

    2008-10-01

    Stable Au nanoshell-J-aggregate complexes are formed that exhibit coherent coupling between the localized plasmons of a nanoshell and the excitons of molecular J-aggregates adsorbed on its surface. By tuning the nanoshell plasmon energies across the exciton line of the J-aggregate, plasmon-exciton coupling energies for these complexes are obtained. The strength of this interaction is dependent on the specific plasmon mode of the nanoparticle coupled to the J-aggregate exciton. From a model based on Gans theory, we obtain an expression for the plasmon-exciton hybridized states of the complex.

  17. On Kinetics Modeling of Vibrational Energy Transfer

    Science.gov (United States)

    Gilmore, John O.; Sharma, Surendra P.; Cavolowsky, John A. (Technical Monitor)

    1996-01-01

    Two models of vibrational energy exchange are compared at equilibrium to the elementary vibrational exchange reaction for a binary mixture. The first model, non-linear in the species vibrational energies, was derived by Schwartz, Slawsky, and Herzfeld (SSH) by considering the detailed kinetics of vibrational energy levels. This model recovers the result demanded at equilibrium by the elementary reaction. The second model is more recent, and is gaining use in certain areas of computational fluid dynamics. This model, linear in the species vibrational energies, is shown not to recover the required equilibrium result. Further, this more recent model is inconsistent with its suggested rate constants in that those rate constants were inferred from measurements by using the SSH model to reduce the data. The non-linear versus linear nature of these two models can lead to significant differences in vibrational energy coupling. Use of the contemporary model may lead to significant misconceptions, especially when integrated in computer codes considering multiple energy coupling mechanisms.

  18. Electronic coherence and the kinetics of inter-complex energy transfer in light-harvesting systems.

    Science.gov (United States)

    Huo, Pengfei; Miller, Thomas F

    2015-12-14

    We apply real-time path-integral dynamics simulations to characterize the role of electronic coherence in inter-complex excitation energy transfer (EET) processes. The analysis is performed using a system-bath model that exhibits the essential features of light-harvesting networks, including strong intra-complex electronic coupling and weak inter-complex coupling. Strong intra-complex coupling is known to generate both static and dynamic electron coherences, which delocalize the exciton over multiple chromophores and potentially influence the inter-complex EET dynamics. With numerical results from partial linearized density matrix (PLDM) real-time path-integral calculations, it is found that both static and dynamic coherence are correlated with the rate of inter-complex EET. To distinguish the impact of these two types of intra-complex coherence on the rate of inter-complex EET, we use Multi-Chromophore Förster Resonance Energy Transfer (MC-FRET) theory to map the original parameterization of the system-bath model to an alternative parameterization for which the effects of static coherence are preserved while the effects of dynamic coherence are largely eliminated. It is then shown that both parameterizations of the model (i.e., the original that supports dynamic coherence and the alternative that eliminates it), exhibit nearly identical EET kinetics and population dynamics over a wide range of parameters. These observations are found to hold for cases in which either the EET donor or acceptor is a dimeric complex and for cases in which the dimeric complex is either symmetric or asymmetric. The results from this study suggest that dynamic coherence plays only a minor role in the actual kinetics of inter-complex EET, whereas static coherence largely governs the kinetics of incoherent inter-complex EET in light-harvesting networks.

  19. Dependence of the energy transfer to graphene on the excitation energy

    Energy Technology Data Exchange (ETDEWEB)

    Mackowski, Sebastian, E-mail: mackowski@fizyka.umk.pl; Kamińska, Izabela [Institute of Physics, Faculty of Physics, Astronomy and Informatics, Nicolaus Copernicus University, Grudziadzka 5, 87-100 Torun (Poland)

    2015-07-13

    Fluorescence studies of natural photosynthetic complexes on a graphene layer demonstrate pronounced influence of the excitation wavelength on the energy transfer efficiency to graphene. Ultraviolet light yields much faster decay of fluorescence, with average efficiencies of the energy transfer equal to 87% and 65% for excitation at 405 nm and 640 nm, respectively. This implies that focused light changes locally the properties of graphene affecting the energy transfer dynamics, in an analogous way as in the case of metallic nanostructures. Demonstrating optical control of the energy transfer is important for exploiting unique properties of graphene in photonic and sensing architectures.

  20. Energy transfers in dynamos with small magnetic Prandtl numbers

    KAUST Repository

    Kumar, Rohit

    2015-06-25

    We perform numerical simulation of dynamo with magnetic Prandtl number Pm = 0.2 on 10243 grid, and compute the energy fluxes and the shell-to-shell energy transfers. These computations indicate that the magnetic energy growth takes place mainly due to the energy transfers from large-scale velocity field to large-scale magnetic field and that the magnetic energy flux is forward. The steady-state magnetic energy is much smaller than the kinetic energy, rather than equipartition; this is because the magnetic Reynolds number is near the dynamo transition regime. We also contrast our results with those for dynamo with Pm = 20 and decaying dynamo. © 2015 Taylor & Francis.

  1. Excitonic dynamical Franz-Keldysh effect

    DEFF Research Database (Denmark)

    Nordstrøm, K.B.; Johnsen, Kristinn; Allen, S.J.

    1998-01-01

    The dynamical Franz-Keldysh effect is exposed by exploring near-band-gap absorption in the presence of intense THz electric fields. It bridges the gap between the de Franz-Keldysh effect and multiphoton absorption and competes with the THz ac Stark effect in shifting the energy of the excitonic...... resonance. A theoretical model which includes the strong THz field nonperturbatively via a nonequilibrium Green functions technique is able to describe the dynamical Franz-Keldysh effect in the presence of excitonic absorption....

  2. Exciton dynamics in perturbed vibronic molecular aggregates

    Directory of Open Access Journals (Sweden)

    C. Brüning

    2016-07-01

    Full Text Available A site specific perturbation of a photo-excited molecular aggregate can lead to a localization of excitonic energy. We investigate this localization dynamics for laser-prepared excited states. Changing the parameters of the electric field significantly influences the exciton localization which offers the possibility for a selective control of this process. This is demonstrated for aggregates possessing a single vibrational degree of freedom per monomer unit. It is shown that the effects identified for the molecular dimer can be generalized to larger aggregates with a high density of vibronic states.

  3. Energy transfer in scattering by rotating potentials

    Indian Academy of Sciences (India)

    Quantum mechanical scattering theory is studied for time-dependent Schrödinger operators, in particular for particles in a rotating potential. Under various assumptions about the decay rate at infinity we show uniform boundedness in time for the kinetic energy of scattering states, existence and completeness of wave ...

  4. The feasibility of coherent energy transfer in microtubules.

    Science.gov (United States)

    Craddock, Travis John Adrian; Friesen, Douglas; Mane, Jonathan; Hameroff, Stuart; Tuszynski, Jack A

    2014-11-06

    It was once purported that biological systems were far too 'warm and wet' to support quantum phenomena mainly owing to thermal effects disrupting quantum coherence. However, recent experimental results and theoretical analyses have shown that thermal energy may assist, rather than disrupt, quantum coherent transport, especially in the 'dry' hydrophobic interiors of biomolecules. Specifically, evidence has been accumulating for the necessary involvement of quantum coherent energy transfer between uniquely arranged chromophores in light harvesting photosynthetic complexes. The 'tubulin' subunit proteins, which comprise microtubules, also possess a distinct architecture of chromophores, namely aromatic amino acids, including tryptophan. The geometry and dipolar properties of these aromatics are similar to those found in photosynthetic units indicating that tubulin may support coherent energy transfer. Tubulin aggregated into microtubule geometric lattices may support such energy transfer, which could be important for biological signalling and communication essential to living processes. Here, we perform a computational investigation of energy transfer between chromophoric amino acids in tubulin via dipole excitations coupled to the surrounding thermal environment. We present the spatial structure and energetic properties of the tryptophan residues in the microtubule constituent protein tubulin. Plausibility arguments for the conditions favouring a quantum mechanism of signal propagation along a microtubule are provided. Overall, we find that coherent energy transfer in tubulin and microtubules is biologically feasible. © 2014 The Author(s) Published by the Royal Society. All rights reserved.

  5. Excitons in van der Waals heterostructures

    DEFF Research Database (Denmark)

    Latini, Simone; Olsen, Thomas; Thygesen, Kristian Sommer

    2015-01-01

    The existence of strongly bound excitons is one of the hallmarks of the newly discovered atomically thin semiconductors. While it is understood that the large binding energy is mainly due to the weak dielectric screening in two dimensions, a systematic investigation of the role of screening on two...

  6. Energy transfer process of anisothermal wall-bounded flows

    Energy Technology Data Exchange (ETDEWEB)

    Aulery, Frédéric, E-mail: frederic.aulery@gmail.com [PROMES CNRS – UPR 8521, Rambla de la Thermodynamique, Tecnosud, Perpignan (France); Toutant, Adrien [PROMES CNRS – UPR 8521, Rambla de la Thermodynamique, Tecnosud, Perpignan (France); Université de Perpignan Via Domitia, 52 avenue Paul Alduy, 66860 Perpignan Cedex 9 (France); Bataille, Françoise [PROMES CNRS – UPR 8521, Rambla de la Thermodynamique, Tecnosud, Perpignan (France); Florida State University, Department of Mathematics, Tallahassee, FL (United States); Zhou, Ye, E-mail: zhou3@llnl.gov [Lawrence Livermore National Laboratory, Livermore, CA (United States)

    2015-07-31

    Strong temperature gradients introduce a major external agency into the wall-bounded turbulent flows. In these flows, the temperature field and the turbulent velocity field are highly correlated. In fact, standard RANS turbulent models are not able to accurately reproduce these flows. In order to improve the performance of the models, we need to understand how the energy is produced, transferred, and dissipated in a strong anisothermal wall-bounded flow. This letter presents a first detailed investigation on the roles played by each contributor in the energy transfer equation. - Highlights: • Turbulent flows subject to high temperature gradients are considered. • The influence of the “temperature gradients” on the energy transfer process is determined. • Inverse energy cascade in an anisotropic flow is observed.

  7. Boosting the performance of red PHOLEDs by exciton harvesting

    Science.gov (United States)

    Chang, Y.-L.; Wang, Z. B.; Helander, M. G.; Qiu, J.; Lu, Z. H.

    2012-09-01

    Significant development has been made on phosphorescent organic light emitting diodes (PHOLEDs) over the past decade, which eventually resulted in the commercialization of widely distributed active-matrix organic light emitting diode displays for mobile phones. However, higher efficiency PHOLEDs are still needed to further reduce the cost and lower the power consumption for general lighting and LED backlight applications. In particular, red PHOLEDs currently have in general the lowest efficiencies among the three primary colors, due most likely to the energy-gap law. Therefore, a number of groups have of made use of various device configurations, including insertion of a carrier blocking or exciton confining layer, doping the transport layers, as well as employing multiple emissive zone structures to improve the device efficiency. However, these approaches are rather inconvenient for commercial applications. In this work, we have developed a simpler way to boost the performance of red PHOLEDs by incorporating an exciton harvesting green emitter, which transfers a large portion of the energy to the co-deposited red emitter. A high external quantum efficiency (EQE) of 20.6% was achieved, which is among the best performances for red PHOLEDs.

  8. Enhanced photoluminescence of Co{sup 2+} ions in ZnCoO/ZnMgO multiple quantum wells and the fluorescence energy transfer mechanism

    Energy Technology Data Exchange (ETDEWEB)

    Ashfaq, J.M.; Hu, B.C.; Zhou, N.; Li, X.L.; Ma, C.Y.; Zhang, Q.Y., E-mail: qyzhang@dlut.edu.cn

    2015-02-15

    Using a pulsed laser deposition system, ZnCoO/ZnMgO multiple quantum well (MQW) samples were grown on c-plane sapphire substrate with a ∼20 nm thick ZnO buffer layer. Compared with monolayer ZnCoO film, the MQW samples exhibited obviously enhanced Co{sup 2+} photoluminescence (PL) at ∼1.80 eV and multiple-phonon resonant Raman scattering (RRS). The enhancement in multiple-phonon RRS was due to the introduction of ZnMgO barrier layer. The enhanced Co{sup 2+} PL was assigned to the quantum confinement effect (QCE) of MQW samples. However, QCE was found not helpful to prevent the band-gap PL quenching. Co{sup 2+} 3d electronic states were proved to be highly localized and a mechanism of fluorescence resonance energy transfer (FRET) between ZnO excitons and the localized Co{sup 2+} 3d states was proposed. - Highlights: • Enhanced Co{sup 2+} PL and multiple-phonon RRS have been observed in ZnCoO/ZnMgO MQW samples. • Quantum confinement effect and ZnMgO barrier layers are responsible for the enhancement of Co{sup 2+} PL and multiple-phonon RRS, respectively. • Band-gap PL quenching is suggested to be due to the fluorescence resonance energy transfer from the excitons to the localized Co{sup 2+} 3d states.

  9. Storing excitons in transition-metal dichalcogenides using dark states

    Science.gov (United States)

    Gunlycke, Daniel; Tseng, Frank; Simsek, Ergun

    Monolayer transition-metal dichalcogenides exhibit strongly bound excitons confined to two dimensions. One challenge in exploiting these excitons is that they have a finite life time and collapse through electron-hole recombination. We propose that the exciton life time could be extended by transitioning the exciton population into dark states. The symmetry of these dark states require the electron and hole to be spatially separated, which not only causes these states to be optically inactive but also inhibits electron-hole recombination. Based on an atomistic model we call the Triangular Lattice Exciton (3ALE) model, we derive transition matrix elements and approximate selection rules showing that excitons could be transitioned into and out of dark states using a pulsed infrared laser. For illustration, we also present exciton population scenarios based on different recombination decay constants. Longer exciton lifetimes could make these materials candidates for applications in energy management and quantum information processing. This work was supported by the Office of Naval Research, directly and through the Naval Research Laboratory.

  10. Photogenerated Exciton Dissociation in Highly Coupled Lead Salt Nanocrystal Assemblies

    KAUST Repository

    Choi, Joshua J.

    2010-05-12

    Internanocrystal coupling induced excitons dissociation in lead salt nanocrystal assemblies is investigated. By combining transient photoluminescence spectroscopy, grazing incidence small-angle X-ray scattering, and time-resolved electric force microscopy, we show that excitons can dissociate, without the aid of an external bias or chemical potential gradient, via tunneling through a potential barrier when the coupling energy is comparable to the exciton binding energy. Our results have important implications for the design of nanocrystal-based optoelectronic devices. © 2010 American Chemical Society.

  11. Production and transfer of energy and information in Hamiltonian systems.

    Science.gov (United States)

    Antonopoulos, Chris G; Bianco-Martinez, Ezequiel; Baptista, Murilo S

    2014-01-01

    We present novel results that relate energy and information transfer with sensitivity to initial conditions in chaotic multi-dimensional Hamiltonian systems. We show the relation among Kolmogorov-Sinai entropy, Lyapunov exponents, and upper bounds for the Mutual Information Rate calculated in the Hamiltonian phase space and on bi-dimensional subspaces. Our main result is that the net amount of transfer from kinetic to potential energy per unit of time is a power-law of the upper bound for the Mutual Information Rate between kinetic and potential energies, and also a power-law of the Kolmogorov-Sinai entropy. Therefore, transfer of energy is related with both transfer and production of information. However, the power-law nature of this relation means that a small increment of energy transferred leads to a relatively much larger increase of the information exchanged. Then, we propose an "experimental" implementation of a 1-dimensional communication channel based on a Hamiltonian system, and calculate the actual rate with which information is exchanged between the first and last particle of the channel. Finally, a relation between our results and important quantities of thermodynamics is presented.

  12. Production and transfer of energy and information in Hamiltonian systems.

    Directory of Open Access Journals (Sweden)

    Chris G Antonopoulos

    Full Text Available We present novel results that relate energy and information transfer with sensitivity to initial conditions in chaotic multi-dimensional Hamiltonian systems. We show the relation among Kolmogorov-Sinai entropy, Lyapunov exponents, and upper bounds for the Mutual Information Rate calculated in the Hamiltonian phase space and on bi-dimensional subspaces. Our main result is that the net amount of transfer from kinetic to potential energy per unit of time is a power-law of the upper bound for the Mutual Information Rate between kinetic and potential energies, and also a power-law of the Kolmogorov-Sinai entropy. Therefore, transfer of energy is related with both transfer and production of information. However, the power-law nature of this relation means that a small increment of energy transferred leads to a relatively much larger increase of the information exchanged. Then, we propose an "experimental" implementation of a 1-dimensional communication channel based on a Hamiltonian system, and calculate the actual rate with which information is exchanged between the first and last particle of the channel. Finally, a relation between our results and important quantities of thermodynamics is presented.

  13. Nanophotonic control of Forster Resonance Energy Transfer

    CERN Document Server

    Zijlstra, Niels; Vos, Willem L; Subramaniam, Vinod; Blum, Christian

    2011-01-01

    Here we report on the experimental details of a study on the influence of the photonic environment on the emission of a FRET system. We modified the local density of optical states (LDOS) by placing the FRET system at precisely defined distances to a metallic mirror. We measured the energy donor lifetime in the presence of the FRET acceptor and the lifetime of an identical sample lacking an acceptor fluorophore for different LDOS. From the lifetimes we determined the FRET rate as well as the FRET efficiency for each sampled LDOS.

  14. TRANSFER

    African Journals Online (AJOL)

    Abstract. Quenching of curcumine fluorescence by thionine, both immobilised in cellulose acetate occurs in accordance with the Forster mechanism of energy transfer. The rate constant of energy transfer for this donor - acceptor pair is found to be 9.4 x 109 L ' mol S1 with R0 = 37±1 Б. When this donor - acceptor pair is ...

  15. Phonon-Driven Oscillatory Plasmonic Excitonic Nanomaterials

    Energy Technology Data Exchange (ETDEWEB)

    Kirschner, Matthew S. [Department; Ding, Wendu [Department; Li, Yuxiu [Center; College; Chapman, Craig T. [Department; Lei, Aiwen [College; Lin, Xiao-Min [Center; Chen, Lin X. [Department; Chemical; Schatz, George C. [Department; Schaller, Richard D. [Department; Center

    2017-12-08

    We demonstrate that coherent acoustic phonons derived from plasmonic nanoparticles can modulate electronic interactions with proximal excitonic molecular species. A series of gold bipyramids with systematically varied aspect ratios and corresponding localized surface plasmon resonance energies, functionalized with a J-aggregated thiacarbocyanine dye molecule, produce two hybridized states that exhibit clear anti-crossing behavior with a Rabi splitting energy of 120 meV. In metal nanoparticles, photoexcitation generates coherent acoustic phonons that cause oscillations in the plasmon resonance energy. In the coupled system, these photo-generated oscillations alter the metal nanoparticle’s energetic contribution to the hybridized system and, as a result, change the coupling between the plasmon and exciton. We demonstrate that such modulations in the hybridization is consistent across a wide range of bipyramid ensembles. We also use Finite-Difference Time Domain calculations to develop a simple model describing this behavior. Such oscillatory plasmonic-excitonic nanomaterials (OPENs) offer a route to manipulate and dynamically-tune the interactions of plasmonic/excitonic systems and unlock a range of potential applications.

  16. Crystalline Nanoporous Frameworks: a Nanolaboratory for Probing Excitonic Device Concepts.

    Energy Technology Data Exchange (ETDEWEB)

    Allendorf, Mark D.; Azoulay, Jason; Ford, Alexandra Caroline; Foster, Michael E.; El Gabaly Marquez, Farid; Leonard, Francois Leonard; Leong-Hau, Kirsty; Stavila, Vitalie; Talin, Albert Alec; Wong, Brian M.; Brumbach, Michael T.; Van Gough, D.; Lambert, Timothy N.; Rodriguez, Mark A.; Spoerke, Erik David; Wheeler, David Roger; Deaton, Joseph C.; Centrone, Andrea; Haney, Paul; Kinney, R.; Szalai, Veronika; Yoon, Heayoung P.

    2014-09-01

    in disordered systems. Implementing this concept also creates entirely new dimensions for device fabrication that could both improve performance, increase durability, and reduce costs with unprecedented control of over properties. This report summarizes the key results of this project and is divided into sections based on publications that resulted from the work. We begin in Section 2 with an investigation of light harvesting and energy transfer in a MOF infiltrated with donor and acceptor molecules of the type typically used in OPV devices (thiophenes and fullerenes, respectively). The results show that MOFs can provide multiple functions: as a light harvester, as a stabilizer and organizer or the infiltrated molecules, and as a facilitator of energy transfer. Section 3 describes computational design of MOF linker groups to accomplish light harvesting in the visible and facilitate charge separation and transport. The predictions were validated by UV-visible absorption spectroscopy, demonstrating that rational design of MOFs for light-harvesting purposes is feasible. Section 4 extends the infiltration concept discussed in Section to, which we now designate as "Molecule@MOF" to create an electrically conducting framework. The tailorability and high conductivity of this material are unprecedented, meriting publication in the journal Science and spawning several Technical Advances. Section 5 discusses processes we developed for depositing MOFs as thin films on substrates, a critical enabling technology for fabricating MOF-based electronic devices. Finally, in Section 6 we summarize results showing that a MOF thin film can be used as a sensitizer in a DSSC, demonstrating that MOFs can serve as active layers in excitonic devices. Overall, this project provides several crucial proofs-of- concept that the potential of MOFs for use in optoelectronic devices that we predicted several years ago [ 3 ] can be realized in practice.

  17. Significance of a Recurring Function in Energy Transfer

    Science.gov (United States)

    Mishra, Subodha

    2017-05-01

    The appearance of a unique function in the energy transfer from one system to the other in different physical situations such as electrical, mechanical, optical, and quantum mechanical processes is established in this work. Though the laws governing the energy transformation and its transfer from system to system are well known, here we notice a unity in diversity; a unique function appears in various cases of energy transfer whether it is a classical or a quantum mechanical process. We consider four examples, well known in elementary physics, from the fields of electricity, mechanics, optics, and quantum mechanics. We find that this unique function is in fact the transfer function corresponding to all these physical situations, and the interesting and intriguing finding is that the inverse Laplace transform of this transfer function, which is the impulse-response function of the systems when multiplied by a factor of -½, is the solution of a linear differential equation for an "instantly forced critically damped harmonic oscillator." It is important to note that though the physical phenomena considered are quite distinct, the underlying process in the language of impulse-response of the system in the time domain is a unique one. To the best of our knowledge we have not seen anywhere the above analysis of determining the unique function or its description as a transfer function in literature.

  18. A new energy transfer model for turbulent free shear flow

    Science.gov (United States)

    Liou, William W.-W.

    1992-01-01

    A new model for the energy transfer mechanism in the large-scale turbulent kinetic energy equation is proposed. An estimate of the characteristic length scale of the energy containing large structures is obtained from the wavelength associated with the structures predicted by a weakly nonlinear analysis for turbulent free shear flows. With the inclusion of the proposed energy transfer model, the weakly nonlinear wave models for the turbulent large-scale structures are self-contained and are likely to be independent flow geometries. The model is tested against a plane mixing layer. Reasonably good agreement is achieved. Finally, it is shown by using the Liapunov function method, the balance between the production and the drainage of the kinetic energy of the turbulent large-scale structures is asymptotically stable as their amplitude saturates. The saturation of the wave amplitude provides an alternative indicator for flow self-similarity.

  19. An estimate of spherical impactor energy transfer for mechanical frequency up-conversion energy harvester

    Directory of Open Access Journals (Sweden)

    L. R. Corr

    2016-08-01

    Full Text Available Vibration energy harvesters, which use the impact mechanical frequency up-conversion technique, utilize an impactor, which gains kinetic energy from low frequency ambient environmental vibrations, to excite high frequency systems that efficiently convert mechanical energy to electrical energy. To take full advantage of the impact mechanical frequency up-conversion technique, it is prudent to understand the energy transfer from the low frequency excitations, to the impactor, and finally to the high frequency systems. In this work, the energy transfer from a spherical impactor to a multi degree of freedom spring / mass system, due to Hertzian impact, is investigated to gain insight on how best to design impact mechanical frequency up-conversion energy harvesters. Through this academic work, it is shown that the properties of the contact (or impact area, i.e., radius of curvature and material properties, only play a minor role in energy transfer and that the equivalent mass of the target system (i.e., the spring / mass system dictates the total amount of energy transferred during the impact. The novel approach of utilizing the well-known Hertzian impact methodology to gain an understanding of impact mechanical frequency up-conversion energy harvesters has made it clear that the impactor and the high frequency energy generating systems must be designed together as one system to ensure maximum energy transfer, leading to efficient ambient vibration energy harvesters.

  20. Oxygen Passivation Mediated Tunability of Trion and Excitons in MoS2

    KAUST Repository

    Gogoi, Pranjal Kumar

    2017-08-17

    Using wide spectral range in situ spectroscopic ellipsometry with systematic ultrahigh vacuum annealing and in situ exposure to oxygen, we report the complex dielectric function of MoS2 isolating the environmental effects and revealing the crucial role of unpassivated and passivated sulphur vacancies. The spectral weights of the A (1.92 eV) and B (2.02 eV) exciton peaks in the dielectric function reduce significantly upon annealing, accompanied by spectral weight transfer in a broad energy range. Interestingly, the original spectral weights are recovered upon controlled oxygen exposure. This tunability of the excitonic effects is likely due to passivation and reemergence of the gap states in the band structure during oxygen adsorption and desorption, respectively, as indicated by ab initio density functional theory calculation results. This Letter unravels and emphasizes the important role of adsorbed oxygen in the optical spectra and many-body interactions of MoS2.

  1. The role of internal dynamics in the coherent evolution of indirect excitons

    Science.gov (United States)

    Grasselli, Federico; Bertoni, Andrea; Goldoni, Guido

    2017-08-01

    We study the time-dependent quantum scattering of a spatially indirect exciton by an external potential, taking fully into account the relative quantum dynamics of the electron-hole (e-h) pair. Exact calculations for an e-h wave packet show that transfer of energy between centre-of-mass (c.m.) and relative degrees of freedom may result in a genuine correction to the evolution during the scattering and eventually at asymptotic times. We show in experimentally relevant regimes and device configurations, that transmission resonances, tunnelling probabilities, diffraction patterns and wave packet fragmentation of indirect excitons are largely determined by the internal dynamics, and could not be reproduced by point-like dipole models or mean-field calculations. We show that a properly-designed local self-energy potential to be added to the c.m. Hamiltonian embeds the effects of the c.m.-internal motion correlation at a small fraction of the computation load needed for full-propagation calculations. The explicit form of this self-energy emphasises the dominant role of internal virtual transitions in determining scattering coefficients of indirect excitons.

  2. Final Technical Report for the Energy Frontier Research Center Understanding Charge Separation and Transfer at Interfaces in Energy Materials (EFRC:CST)

    Energy Technology Data Exchange (ETDEWEB)

    Vanden Bout, David A. [Univ. of Texas, Austin, TX (United States)

    2015-09-14

    Our EFRC was founded with the vision of creating a broadly collaborative and synergistic program that would lead to major breakthroughs in the molecular-level understanding of the critical interfacial charge separation and charge transfer (CST) processes that underpin the function of candidate materials for organic photovoltaic (OPV) and electrical-energy-storage (EES) applications. Research in these energy contexts shares an imposing challenge: How can we understand charge separation and transfer mechanisms in the presence of immense materials complexity that spans multiple length scales? To address this challenge, our 50-member Center undertook a total of 28 coordinated research projects aimed at unraveling the CST mechanisms that occur at interfaces in these nanostructured materials. This rigorous multi-year study of CST interfaces has greatly illuminated our understanding of early-timescale processes (e.g., exciton generation and dissociation dynamics at OPV heterojunctions; control of Li+-ion charging kinetics by surface chemistry) occurring in the immediate vicinity of interfaces. Program outcomes included: training of 72 graduate student and postdoctoral energy researchers at 5 institutions and spanning 7 academic disciplines in science and engineering; publication of 94 peer-reviewed journal articles; and dissemination of research outcomes via 340 conference, poster and other presentations. Major scientific outcomes included: implementation of a hierarchical strategy for understanding the electronic communication mechanisms and ultimate fate of charge carriers in bulk heterojunction OPV materials; systematic investigation of ion-coupled electron transfer processes in model Li-ion battery electrode/electrolyte systems; and the development and implementation of 14 unique technologies and instrumentation capabilities to aid in probing sub-ensemble charge separation and transfer mechanisms.

  3. Realistic Quantum Control of Energy Transfer in Photosynthetic Processes

    Directory of Open Access Journals (Sweden)

    Reda M. El-Shishtawy

    2016-12-01

    Full Text Available The occurrence of coherence phenomenon as a result of the interference of the probability amplitude terms is among the principle features of quantum mechanics concepts. Current experiments display the presence of quantum techniques whose coherence is supplied over large interval times. Specifically, photosynthetic mechanisms in light-harvesting complexes furnish oscillatory behaviors owing to quantum coherence. In this manuscript, we study the coherent quantum energy transfer for a single-excitation and nonlocal correlation in a dimer system (donor+acceptor displayed by two-level systems (TLSs, interacting with a cavity field with a time-dependent coupling effect considering the realistic situation of coupling between each TLS and the cavity field. We analyze and explore the specific conditions which are viable with real experimental realization for the ultimate transfer of quantum energy and nonlocal quantum correlation. We show that the enhancement of the probability for a single-excitation energy transfer greatly benefits from the energy detuning, photon-number transition, classicality of the field, and the time-dependent coupling effect. We also find that the entanglement between the donor and acceptor is very sensitive to the physical parameters and it can be generated during the coherent energy transfer.

  4. Optimal Energy Transfer in Light-Harvesting Systems

    Directory of Open Access Journals (Sweden)

    Lipeng Chen

    2015-08-01

    Full Text Available Photosynthesis is one of the most essential biological processes in which specialized pigment-protein complexes absorb solar photons, and with a remarkably high efficiency, guide the photo-induced excitation energy toward the reaction center to subsequently trigger its conversion to chemical energy. In this work, we review the principles of optimal energy transfer in various natural and artificial light harvesting systems. We begin by presenting the guiding principles for optimizing the energy transfer efficiency in systems connected to dissipative environments, with particular attention paid to the potential role of quantum coherence in light harvesting systems. We will comment briefly on photo-protective mechanisms in natural systems that ensure optimal functionality under varying ambient conditions. For completeness, we will also present an overview of the charge separation and electron transfer pathways in reaction centers. Finally, recent theoretical and experimental progress on excitation energy transfer, charge separation, and charge transport in artificial light harvesting systems is delineated, with organic solar cells taken as prime examples.

  5. Rotational Energy Transfer of N2 Gas Determined Using a New Ab Initio Potential Energy Surface

    Science.gov (United States)

    Huo, Winifred M.; Stallcop, James R.; Partridge, Harry; Langhoff, Stephen R. (Technical Monitor)

    1997-01-01

    Rotational energy transfer between two N2 molecules is a fundamental process of some importance. Exchange is expected to play a role, but its importance is somewhat uncertain. Rotational energy transfer cross sections of N2 also have applications in many other fields including modeling of aerodynamic flows, laser operations, and linewidth analysis in nonintrusive laser diagnostics. A number of N2-N2 rigid rotor potential energy surface (PES) has been reported in the literature.

  6. A Design Study Of A Wireless Power Transfer System For Use To Transfer Energy From A Vibration Energy Harvester

    Science.gov (United States)

    Grabham, N. J.; Harden, C.; Vincent, D.; Beeby, S. P.

    2016-11-01

    A wirelessly powered remote sensor node is presented along with its design process. The purpose of the node is the further expansion of the sensing capabilities of the commercial Perpetuum system used for condition monitoring on trains and rolling stock which operates using vibration energy harvesting. Surplus harvested vibration energy is transferred wirelessly to a remote satellite sensor to allow measurements over a wider area to be made. This additional data is to be used for long term condition monitoring. Performance measurements made on the prototype remote sensor node are reported and advantages and disadvantages of using the same RF frequency for power and data transfer are identified.

  7. Phonon-mediated path-interference in electronic energy transfer.

    Science.gov (United States)

    Hossein-Nejad, Hoda; Olaya-Castro, Alexandra; Scholes, Gregory D

    2012-01-14

    We present a formalism to quantify the contribution of path-interference in phonon-mediated electronic energy transfer. The transfer rate between two molecules is computed by considering the quantum mechanical amplitudes associated with pathways connecting the initial and final sites. This includes contributions from classical pathways, but also terms arising from interference of different pathways. We treat the vibrational modes coupled to the molecules as a non-Markovian harmonic oscillator bath, and investigate the correction to transfer rates due to the lowest-order interference contribution. We show that depending on the structure of the harmonic bath, the correction due to path-interference may have a dominant vibrational or electronic character, and can make a notable contribution to the transfer rate in the steady state.

  8. Fluorescence resonance energy transfer from tryptophan in human ...

    Indian Academy of Sciences (India)

    TECS

    After excitation, competition prevails between the various decay processes, namely, fluorescence and non-radiative deactivations, inclu- ding energy transfer to the surrounding molecules. Efficiency of FRET is known to depend on the in- verse sixth power of the intermolecular distance bet- ween the donor and the acceptor ...

  9. Energy transfer and thermal studies of Pr doped cerium oxalate ...

    Indian Academy of Sciences (India)

    Administrator

    School of Pure and Applied Physics, Mahatma Gandhi University, Kottayam, India. MS received 7 December 2009; revised 12 August 2010. Abstract. Energy transfer process at room temperature for cerium (sensitizer) oxalate single crystals doped with different concentrations (10, 13, 15, 17 and 20%) of praseodymium ions ...

  10. Metaphors Describing Energy Transfer through Ecosystems: Helpful or Misleading?

    Science.gov (United States)

    Wernecke, Ulrike; Schwanewedel, Julia; Harms, Ute

    2018-01-01

    Energy transfer in ecosystems is an abstract and challenging topic for learners. Metaphors are widely used in scientific and educational discourse to communicate ideas about abstract phenomena. However, although considered valuable teaching tools, metaphors are ambiguous and can be misleading when used in educational contexts. Educational…

  11. Fluorescence resonance energy transfer (FRET) measurement by gradual acceptor photobleaching.

    NARCIS (Netherlands)

    van Munster, E.B.; Kremers, G.J.; Adjobo Hermans, M.J.W.; Gadella, Th.W.J.

    2005-01-01

    Fluorescence resonance energy transfer (FRET) is an extremely effective tool to detect molecular interaction at suboptical resolutions. One of the techniques for measuring FRET is acceptor photobleaching: the increase in donor fluorescence after complete acceptor photobleaching is a measure of the

  12. Energy transfer in photosynthesis: experimental insights and quantitative models

    NARCIS (Netherlands)

    van Grondelle, R.; Novoderezhkin, V.

    2006-01-01

    We overview experimental and theoretical studies of energy transfer in the photosynthetic light-harvesting complexes LH1, LH2, and LHCII performed during the past decade since the discovery of high-resolution structure of these complexes. Experimental findings obtained with various spectroscopic

  13. Distance dependence of fluorescence resonance energy transfer

    Indian Academy of Sciences (India)

    Administrator

    excitations namely, graphene, a two-dimensional semiconducting sheet and the case of such a ..... graphene. We now consider the process of energy transfer from a fluorescent dye to graphene (see figure 1). 6,7. We use the tight-binding model for graphene. 8. The ...... to a monolayer of semiconductor nanocrystals.

  14. Fluorescence resonance energy transfer from tryptophan in human ...

    Indian Academy of Sciences (India)

    Home; Journals; Journal of Chemical Sciences; Volume 119; Issue 2. Fluorescence resonance energy transfer from tryptophan in human serum albumin to a bioactive indoloquinolizine system. Paramita Das Arabinda Mallick Basudeb Haldar Alok Chakrabarty Nitin Chattopadhyay. Volume 119 Issue 2 March 2007 pp 77-82 ...

  15. Excitation energy transfer from dye molecules to doped graphene

    Indian Academy of Sciences (India)

    Excitation energy transfer from dye molecules to doped graphene. #. R S SWATHIa and K L SEBASTIANb,∗. aSchool of Chemistry, Indian Institute of Science Education and Research, Thiruvananthapuram 695 016, India. bDepartment of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, ...

  16. Excitation energy transfer from dye molecules to doped graphene

    Indian Academy of Sciences (India)

    Recently, we have reported theoretical studies on the rate of energy transfer from an electronically excited molecule to graphene. It was found that graphene is a very efficient quencher of the electronically excited states and that the rate -4. The process was found to be effective up to 30 which is well beyond the ...

  17. Ultrafast fluorescence resonance energy transfer in a bile salt ...

    Indian Academy of Sciences (India)

    Fluorescence resonance energy transfer (FRET) from Coumarin 153 (C153) to Rhodamine 6G (R6G) in a secondary aggregate of a bile salt (sodium deoxycholate, NaDC) is studied by femtosecond up-conversion. The emission spectrum of C153 in NaDC is analysed in terms of two spectra-one with emission maximum at ...

  18. Wireless energy transfer: Dielectric lens antennas for beam shaping in wireless power-transfer applications

    Science.gov (United States)

    Gonçalves, Ricardo; Carvalho, Nuno B.; Pinho, Pedro

    2017-02-01

    In the current contest of wireless systems, the last frontier remains the cut of the power cord. In that sense, the interest over wireless energy transfer technologies in the past years has grown exponentially. However, there are still many challenges to be overcome in order to enable wireless energy transfer full potential. One of the focus in the development of such systems is the design of very-high-gain, highly efficient, antennas that can compensate for the propagation loss of radio signals over the air. In this paper, we explore the design and manufacturing process of dielectric lenses, fabricated using a professional-grade desktop 3D printer. Lens antennas are used in order to increase beam efficiency and therefore maximize the efficiency of a wireless power-transfer system operating at microwave frequencies in the Ku band. Measurements of two fabricated prototypes showcase a large directivity, as predicted with simulations. xml:lang="fr"

  19. Tightly bound indirect exciton in single-layer hybrid organic-inorganic perovskite semiconductor

    Science.gov (United States)

    Li, Jing; Liu, Tao; Liew, Timothy C. H.

    2017-10-01

    We theoretically study the direct and indirect excitons (IXs) in a single-layer hybrid organic-inorganic perovskite (HOIP) semiconductor. Due to the 2D nature, the single-layer HOIP supports the large binding energy of IXs and direct excitons over a wide range of applied electric fields, which exceed the thermal energy of room temperature. Moreover, the ground-state IX has a lower energy than that of direct exciton, which will extend the coherence and relaxation time of IXs. This is beneficial to optoelectronic applications and excitonic information processing devices of IXs.

  20. The temperature behavior and mechanism of exciton luminescence in quantum dots.

    Science.gov (United States)

    Zatsepin, A F; Biryukov, D Yu

    2017-07-19

    The processes of direct and indirect optical excitation of spatially confined excitons in quantum dots (QDs) embedded in a silica thin-film matrix have been reported and discussed. A generalized scheme for the electronic transitions is employed for a detailed description of luminescence temperature behavior using various excitation methods. This scheme considers three different models of exciton relaxation and substantiates the occupation of the triplet radiative states as a result of singlet-triplet intersystem crossing or excitation energy transfer from free excitons of the matrix. Analytical expressions describing five types of different temperature curves were derived. It is established that their shapes are exactly defined by the excitation mechanism and the parameters involved in the numerical model. The conditions allowing the estimation of the energy and kinetic characteristics of QD photoluminescence are formulated. We have shown that the confinement effect causes a decrease in the thermal activation barriers and frequency characteristics for non-radiative transitions. An application of the developed concepts allows predicting and estimating the temperature dependences for direct and indirect optically excited QD luminescence employing silicon nanoclusters in a silica thin-film matrix as an example.

  1. Imaging exciton-polariton transport in MoSe2 waveguides

    Science.gov (United States)

    Hu, F.; Luan, Y.; Scott, M. E.; Yan, J.; Mandrus, D. G.; Xu, X.; Fei, Z.

    2017-06-01

    The exciton-polariton (EP), a half-light and half-matter quasiparticle, is potentially an important element for future photonic and quantum technologies. It provides both strong light-matter interactions and long-distance propagation that is necessary for applications associated with energy or information transfer. Recently, strongly coupled cavity EPs at room temperature have been demonstrated in van der Waals (vdW) materials due to their strongly bound excitons. Here, we report a nano-optical imaging study of waveguide EPs in MoSe2, a prototypical vdW semiconductor. The measured propagation length of the EPs is sensitive to the excitation photon energy and reaches over 12 µm. The polariton wavelength can be conveniently altered from 600 nm down to 300 nm by controlling the waveguide thickness. Furthermore, we found an intriguing back-bending polariton dispersion close to the exciton resonance. The observed EPs in vdW semiconductors could be useful in future nanophotonic circuits operating in the near-infrared to visible spectral regions.

  2. Modeling crossed-beam energy transfer for inertial confinement fusion

    Energy Technology Data Exchange (ETDEWEB)

    Marion, D. J. Y. [CEA, DAM, DIF, F-91297 Arpajon Cedex (France); Univ. Bordeaux, CEA, CNRS, CELIA, UMR5107, F-33400 Talence (France); Debayle, A., E-mail: arnaud.debayle@cea.fr; Masson-Laborde, P.-E.; Loiseau, P.; Casanova, M. [CEA, DAM, DIF, F-91297 Arpajon Cedex (France)

    2016-05-15

    We developed a numerical code that describes both the energy transfer occurring when two or more laser beams overlap in a weakly non-homogeneous plasma, and the beam energy losses associated with the electron-ion collisions. The numerical solutions are validated with both the exact analytical solutions in homogeneous plasmas, and with new approximate analytical solutions in non-homogeneous plasmas that include the aforementioned inverse bremsstrahlung effect. Comparisons with kinetic particle-in-cell simulations are satisfactory, provided the acoustic wave-breaking limit and the self-focusing regime are not reached. An application of the Cross-Beam Energy Transfer model is shown for a typical case of indirect-drive implosion in a gold hohlraum.

  3. Excitons confined in quantum dots spheroidal prolate; Excitones confinados en puntos cuanticos esferoidales prolatos

    Energy Technology Data Exchange (ETDEWEB)

    Corella M, A.; Rosas, R.A.; Marin, J.L.; Riera, R. [Depto. de Fisica, Universidad de Sonora, A.P. 1626, Hermosillo, Sonora (Mexico)

    2004-07-01

    The variational method is used to solve in approximately way the Schroedinger wave equation associated to a Wannier-Mott exciton confined within a spheroidal quantum dot. The confinement effect on the ground-state energy of the electron-hole pair trapped inside a crystallite with this geometry, and with soft or hard walls, is analyzed. The walls can be modeled as finite or infinite potential barriers with suitable border conditions, which will depend on the considered case. The results of this work are compared with those obtained by other authors through more sophisticated methods. A comparison with experimental data of CdS crystallites embedded in materials of different composition is made, too. For a finite potential barrier, a critical size of the crystallite from which the exciton escapes of the quantum dot, is predicted. This is in opposition with the infinite potential barrier model where the exciton never can leave the region where it is confined. (Author)

  4. Excitonic transitions in MBE grown h-GaN with cubic inclusions

    Science.gov (United States)

    Strauf, Stefan; Michler, Peter; Gutowski, Jürgen; Selke, Hartmut; Birkle, Udo; Einfeldt, Sven; Hommel, Detlef

    1998-06-01

    Undoped and magnesium doped MBE grown GaN epilayers on sapphire substrates show a particular variety of near-bandgap luminescent transitions. Despite the large lattice mismatch to the substrate, pronounced free- and bound-exciton transitions allow for an estimation of the excitonic binding energies. For the given thickness range (about 1 μm), we find an almost strain-relaxed situation with the main exciton transition energies well corresponding to the bulk values. On their low-energy side, we identify lines having been tentatively assigned to stacking fault excitons, and interface-related exciton transitions correlated to extended defects and/or dislocations in this spatial region. Evidence of cubic inclusions of a size up to 500 nm is doubtless given by observing sharp c-GaN related donor-bound exciton emission and respective structures in transmission electron microscope investigations.

  5. State-of-the-Art Developments of Acoustic Energy Transfer

    Directory of Open Access Journals (Sweden)

    Md Rabiul Awal

    2016-01-01

    Full Text Available Acoustic energy transfer (AET technology has drawn significant industrial attention recently. This paper presents the reviews of the existing AETs sequentially, preferably, from the early stage. From the review, it is evident that, among all the classes of wireless energy transfer, AET is the safest technology to adopt. Thus, it is highly recommended for sensitive area and devices, especially implantable devices. Though, the efficiency for relatively long distances (i.e., >30 mm is less than that of inductive or capacitive power transfer; however, the trade-off between safety considerations and performances is highly suitable and better than others. From the presented statistics, it is evident that AET is capable of transmitting 1.068 kW and 5.4 W of energy through wall and in-body medium (implants, respectively. Progressively, the AET efficiency can reach up to 88% in extension to 8.6 m separation distance which is even superior to that of inductive and capacitive power transfer.

  6. Tunable excitons in bilayer graphene

    Science.gov (United States)

    Ju, Long; Wang, Lei; Cao, Ting; Taniguchi, Takashi; Watanabe, Kenji; Louie, Steven G.; Rana, Farhan; Park, Jiwoong; Hone, James; Wang, Feng; McEuen, Paul L.

    2017-11-01

    Excitons, the bound states of an electron and a hole in a solid material, play a key role in the optical properties of insulators and semiconductors. Here, we report the observation of excitons in bilayer graphene (BLG) using photocurrent spectroscopy of high-quality BLG encapsulated in hexagonal boron nitride. We observed two prominent excitonic resonances with narrow line widths that are tunable from the mid-infrared to the terahertz range. These excitons obey optical selection rules distinct from those in conventional semiconductors and feature an electron pseudospin winding number of 2. An external magnetic field induces a large splitting of the valley excitons, corresponding to a g-factor of about 20. These findings open up opportunities to explore exciton physics with pseudospin texture in electrically tunable graphene systems​.

  7. Rates of mass, momentum, and energy transfer at the magnetopause

    Science.gov (United States)

    Hill, T. W.

    1979-01-01

    Empirical estimates of the global rates of transfer of solar wind mass, tangential momentum, and energy at the Earth's magnetopause are presented for comparison against model estimates based on the four principal mechanisms that have been proposed to explain such transfer. The comparisons, although not quite conclusive, strongly favor a model that incorporates some combination of direct magnetic connection and anomalous cross field diffusion. An additional global constraint, the rate at which magnetic flux is cycled through the magnetospheric convection system, strongly suggests that direct magnetic connection plays a significant if not dominant role in the solar wind/magnetosphere interaction.

  8. Ultrafast Spectroscopic Investigation of Energy Transfer in Site-Directed Mutants of the Fenna-Matthews-Olson (FMO) Antenna Complex from Chlorobaculum tepidum.

    Science.gov (United States)

    Magdaong, Nikki Cecil M; Saer, Rafael G; Niedzwiedzki, Dariusz M; Blankenship, Robert E

    2017-05-11

    Ultrafast transient absorption (TA) and time-resolved fluorescence (TRF) spectroscopic studies were performed on several mutants of the bacteriochlorophyll (BChl) a-containing Fenna-Matthews-Olson (FMO) complex from the green sulfur bacterium Chlorobaculum tepidum. These mutants were generated to perturb a particular BChl a site and determine its effects on the optical spectroscopic properties of the pigment-protein complex. Measurements conducted at 77 K under both oxidizing and reducing conditions revealed changes in the dynamics of the various spectral components as compared to the data set from wild-type FMO. TRF results show that under reducing conditions all FMO samples decay with a similar lifetime in the ∼2 ns range. The oxidized samples revealed varying fluorescence lifetimes of the terminal BChl a emitter, considerably shorter than those recorded for the reduced samples, indicating that the quenching mechanism in wild-type FMO is still present in the mutants. Global fitting of TA data yielded similar overall results, and in addition, the lifetimes of early decaying components were determined. Target analyses of TA data for select FMO samples generated kinetic models that better simulate the TA data. A comparison of the lifetime of excitonic components for all samples reveals that the mutations affect mainly the early kinetic components, but not that of the lowest energy exciton, which reflects the flexibility of energy transfer in FMO.

  9. Exciton spectrum in multi-shell hexagonal semiconductor nanotube

    Directory of Open Access Journals (Sweden)

    O.M. Makhanets

    2012-10-01

    Full Text Available The theory of exciton spectrum in multi-shell hexagonal semiconductor nanotube is developed within the effective masses and rectangular potentials approximations using the method of effective potential. It is shown that the exciton binding energy for all states non-monotonously depends on the inner wire diameter, approaching several minimal and maximal magnitudes. The obtained theoretical results explain well the experimental positions of luminescence peaks for GaAs/Al0.4Ga0.6As nanotubes.

  10. Plasmonic Structure Enhanced Exciton Generation at the Interface between the Perovskite Absorber and Copper Nanoparticles

    Directory of Open Access Journals (Sweden)

    Sheng Hsiung Chang

    2014-01-01

    Full Text Available The refractive index and extinction coefficient of a triiodide perovskite absorber (TPA were obtained by fitting the transmittance spectra of TPA/PEDOT:PSS/ITO/glass using the transfer matrix method. Cu nanoplasmonic structures were designed to enhance the exciton generation in the TPA and to simultaneously reduce the film thickness of the TPA. Excitons were effectively generated at the interface between TPA and Cu nanoparticles, as observed through the 3D finite-difference time-domain method. The exciton distribution is advantageous for the exciton dissociation and carrier transport.

  11. Plasmonic Structure Enhanced Exciton Generation at the Interface between the Perovskite Absorber and Copper Nanoparticles

    Science.gov (United States)

    Lin, Kuen-Feng; Chiang, Chien-Hung; Wu, Chun-Guey

    2014-01-01

    The refractive index and extinction coefficient of a triiodide perovskite absorber (TPA) were obtained by fitting the transmittance spectra of TPA/PEDOT:PSS/ITO/glass using the transfer matrix method. Cu nanoplasmonic structures were designed to enhance the exciton generation in the TPA and to simultaneously reduce the film thickness of the TPA. Excitons were effectively generated at the interface between TPA and Cu nanoparticles, as observed through the 3D finite-difference time-domain method. The exciton distribution is advantageous for the exciton dissociation and carrier transport. PMID:25295290

  12. 2013 MOLECULAR ENERGY TRANSFER GORDON RESEARCH CONFERENCE (JANUARY 13-18, 2013 - VENTURA BEACH MARRIOTT, VENTURA CA

    Energy Technology Data Exchange (ETDEWEB)

    Reid, Scott A. [Marquette University

    2012-10-18

    Sessions covered all areas of molecular energy transfer, with 10 sessions of talks and poster sessions covering the areas of :  Energy Transfer in Inelastic and Reactive Scattering  Energy Transfer in Photoinitiated and Unimolecular Reactions  Non-adiabatic Effects in Energy TransferEnergy Transfer at Surfaces and Interfaces  Energy Transfer in Clusters, Droplets, and Aerosols  Energy Transfer in Solution and Solid  Energy Transfer in Complex Systems  Energy Transfer: New vistas and horizons  Molecular Energy Transfer: Where Have We Been and Where are We Going?

  13. Effect of optical excitation energy on the red luminescence of Eu3+ in GaN

    Science.gov (United States)

    Peng, H. Y.; Lee, C. W.; Everitt, H. O.; Lee, D. S.; Steckl, A. J.; Zavada, J. M.

    2005-01-01

    Photoluminescence (PL) excitation spectroscopy mapped the photoexcitation wavelength dependence of the red luminescence (D05→F27) from GaN:Eu. Time-resolved PL measurements revealed that for excitation at the GaN bound exciton energy, the decay transients are almost temperature insensitive between 86 K and 300 K, indicating an efficient energy transfer process. However, for excitation energies above or below the GaN bound exciton energy, the decaying luminescence indicates excitation wavelength- and temperature-dependent energy transfer influenced by intrinsic and Eu3+-related defects.

  14. Reduced density matrix hybrid approach: Application to electronic energy transfer

    Energy Technology Data Exchange (ETDEWEB)

    Berkelbach, Timothy C.; Reichman, David R. [Department of Chemistry, Columbia University, 3000 Broadway, New York, New York 10027 (United States); Markland, Thomas E. [Department of Chemistry, Stanford University, 333 Campus Drive, Stanford, California 94305 (United States)

    2012-02-28

    Electronic energy transfer in the condensed phase, such as that occurring in photosynthetic complexes, frequently occurs in regimes where the energy scales of the system and environment are similar. This situation provides a challenge to theoretical investigation since most approaches are accurate only when a certain energetic parameter is small compared to others in the problem. Here we show that in these difficult regimes, the Ehrenfest approach provides a good starting point for a dynamical description of the energy transfer process due to its ability to accurately treat coupling to slow environmental modes. To further improve on the accuracy of the Ehrenfest approach, we use our reduced density matrix hybrid framework to treat the faster environmental modes quantum mechanically, at the level of a perturbative master equation. This combined approach is shown to provide an efficient and quantitative description of electronic energy transfer in a model dimer and the Fenna-Matthews-Olson complex and is used to investigate the effect of environmental preparation on the resulting dynamics.

  15. Quantum simulator of an open quantum system using superconducting qubits: exciton transport in photosynthetic complexes

    Science.gov (United States)

    Mostame, Sarah; Rebentrost, Patrick; Eisfeld, Alexander; Kerman, Andrew J.; Tsomokos, Dimitris I.; Aspuru-Guzik, Alán

    2012-10-01

    Open quantum system approaches are widely used in the description of physical, chemical and biological systems. A famous example is electronic excitation transfer in the initial stage of photosynthesis, where harvested energy is transferred with remarkably high efficiency to a reaction center. This transport is affected by the motion of a structured vibrational environment, which makes simulations on a classical computer very demanding. Here we propose an analog quantum simulator of complex open system dynamics with a precisely engineered quantum environment. Our setup is based on superconducting circuits, a well established technology. As an example, we demonstrate that it is feasible to simulate exciton transport in the Fenna-Matthews-Olson photosynthetic complex. Our approach allows for a controllable single-molecule simulation and the investigation of energy transfer pathways as well as non-Markovian noise-correlation effects.

  16. Model Property Based Material Balance and Energy Conservation Analysis for Process Industry Energy Transfer Systems

    OpenAIRE

    Fumin Ma; Gregory M. P. O’Hare; Tengfei Zhang; Michael J. O’Grady

    2015-01-01

    Conventional historical data based material and energy balance analyses are static and isolated computations. Such methods cannot embody the cross-coupling effect of energy flow, material flow and information flow in the process industry; furthermore, they cannot easily realize the effective evaluation and comparison of different energy transfer processes by alternating the model module. In this paper, a novel method for material balance and energy conservation analysis of process industry en...

  17. Electroabsorption Spectroscopy Measurements of the Exciton Binding Energy, ElectronHole Reduced Effective Mass, and Band Gap in the Perovskite CHsub3NHsub3PbIsub3

    Science.gov (United States)

    2016-07-28

    spectra at the fundamental absorption edge in thin - film CH3NH3PbI3 and have shown that at 300 K the χ(3) EA response can be interpreted in terms of the...measurements on polycrystalline thin films . In addition, recent time-resolved terahertz spectroscopy measurements have been interpreted as evidence that bound...microwave photoconductance studies on thin - film samples have been attributed to exciton dissociation.31,42 A classic method to unambiguously determine

  18. A wireless energy transfer platform, integrated at the bedside.

    Science.gov (United States)

    De Clercq, Hans; Puers, Robert

    2013-01-01

    This paper presents the design of a wireless energy transfer platform, integrated at the bedside. The system contains a matrix of identical inductive power transmitters, which are optimised to provide power to a wearable sensor network, with the purpose of wirelessly recording vital signals over an extended period of time. The magnetic link, operates at a transfer frequency of 6.78MHz and is able to transfer a power of 3.3mW to the remote side at an inter-coil distance of 100mm. The total efficiency of the power link is 26%. Moreover, the platform is able to dynamically determine the position of freely moving sensor nodes and selectively induce a magnetic field in the area where the sensor nodes are positioned. As a result, the patient will not be subjected to unnecessary radiation and the specific absorption rate standards are met more easily.

  19. Regulation control and energy management scheme for wireless power transfer

    Science.gov (United States)

    Miller, John M.

    2015-12-29

    Power transfer rate at a charging facility can be maximized by employing a feedback scheme. The state of charge (SOC) and temperature of the regenerative energy storage system (RESS) pack of a vehicle is monitored to determine the load due to the RESS pack. An optimal frequency that cancels the imaginary component of the input impedance for the output signal from a grid converter is calculated from the load of the RESS pack, and a frequency offset f* is made to the nominal frequency f.sub.0 of the grid converter output based on the resonance frequency of a magnetically coupled circuit. The optimal frequency can maximize the efficiency of the power transfer. Further, an optimal grid converter duty ratio d* can be derived from the charge rate of the RESS pack. The grid converter duty ratio d* regulates wireless power transfer (WPT) power level.

  20. Excitonic photoluminescence and photoresponse of ZnS nanowires

    Energy Technology Data Exchange (ETDEWEB)

    Dai, Jun, E-mail: daijun@just.edu.cn [Department of Physics, Jiangsu University of Science and Technology, Zhenjiang 212003 (China); Song, Xing [School of Material Science and Engineering, Jiangsu University, Zhenjiang 212003 (China); Zheng, Hongge [Department of Physics, Jiangsu University of Science and Technology, Zhenjiang 212003 (China); Wu, Chunxia, E-mail: chxwu7771@yahoo.com.cn [School of Material Science and Engineering, Jiangsu University, Zhenjiang 212003 (China)

    2016-05-01

    Single crystal ZnS nanowires are fabricated by vapor phase transport method on sapphire substrate in the presence of Au catalyst. The morphology, composition, and crystal structure are characterized by field emission scanning electron microscopy (FESEM), X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM). XRD and HRTEM reveal that the ZnS nanowires have perfect single crystal wurtzite structure. The temperature-dependent photoluminescence spectra show that the ZnS nanowires present pure near-bandgap ultraviolet exciton recombination emission at 347 nm. The exciton-related optical properties, including exciton activation energy, temperature-dependent exciton energy and Varshni coefficients describing exciton energy variation, are systematically discussed. In addition, an individual ZnS nanowire-based ultraviolet photodetector is fabricated, which shows good photoresponse ability and fast response rate. The result shows that the ZnS nanowires are particularly suitable for UV photodetectors. - Highlights: • Single crystal ultrathin ZnS nanowires with diameter of 20–100 nm were fabricated by vapor phase transport method. • Exciton-related optical properties were fitted by temperature-dependent photoluminescence spectra. • Single ZnS nanowire ultraviolet photodetector with good photoswitch ability and high photocurrent was demonstrated.

  1. Exciton Band Structure in Two-Dimensional Materials.

    Science.gov (United States)

    Cudazzo, Pierluigi; Sponza, Lorenzo; Giorgetti, Christine; Reining, Lucia; Sottile, Francesco; Gatti, Matteo

    2016-02-12

    Low-dimensional materials differ from their bulk counterparts in many respects. In particular, the screening of the Coulomb interaction is strongly reduced, which can have important consequences such as the significant increase of exciton binding energies. In bulk materials the binding energy is used as an indicator in optical spectra to distinguish different kinds of excitons, but this is not possible in low-dimensional materials, where the binding energy is large and comparable in size for excitons of very different localization. Here we demonstrate that the exciton band structure, which can be accessed experimentally, instead provides a powerful way to identify the exciton character. By comparing the ab initio solution of the many-body Bethe-Salpeter equation for graphane and single-layer hexagonal boron nitride, we draw a general picture of the exciton dispersion in two-dimensional materials, highlighting the different role played by the exchange electron-hole interaction and by the electronic band structure. Our interpretation is substantiated by a prediction for phosphorene.

  2. Interglobular Diffusion of an Energy Donor in Triplet-Triplet Energy Transfer in Proteins

    Directory of Open Access Journals (Sweden)

    Andrey G. Melnikov

    2013-01-01

    Full Text Available The triplet-triplet energy transfer between polar molecules of luminescent probe (eosin as an energy donor and nonpolar molecules of energy acceptor (anthracene is studied. Both the donor and the acceptor are bound to human serum albumin by noncovalent bonds. A dependence of rate constant of triplet-triplet energy transfer on human serum albumin concentration is revealed. A rate constant of eosin output from protein globules is determined. It is shown that the energy transfer occurs as a result of interglobular diffusion of eosin. The obtained results indicate that a protein-luminescent probe based sensor can be used for testing a concentration of polycyclic aromatic hydrocarbons in proteins.

  3. Quantum dot-dye hybrid systems for energy transfer applications

    Energy Technology Data Exchange (ETDEWEB)

    Ren, Ting

    2010-07-01

    In this thesis, we focus on the preparation of energy transfer-based quantum dot (QD)-dye hybrid systems. Two kinds of QD-dye hybrid systems have been successfully synthesized: QD-silica-dye and QD-dye hybrid systems. In the QD-silica-dye hybrid system, multishell CdSe/CdS/ZnS QDs were adsorbed onto monodisperse Stoeber silica particles with an outer silica shell of thickness 2-24 nm containing organic dye molecules (Texas Red). The thickness of this dye layer has a strong effect on the total sensitized acceptor emission, which is explained by the increase in the number of dye molecules homogeneously distributed within the silica shell, in combination with an enhanced surface adsorption of QDs with increasing dye amount. Our conclusions were underlined by comparison of the experimental results with Monte-Carlo simulations, and by control experiments confirming attractive interactions between QDs and Texas Red freely dissolved in solution. New QD-dye hybrid system consisting of multishell QDs and organic perylene dyes have been synthesized. We developed a versatile approach to assemble extraordinarily stable QD-dye hybrids, which uses dicarboxylate anchors to bind rylene dyes to QD. This system yields a good basis to study the energy transfer between QD and dye because of its simple and compact design: there is no third kind of molecule linking QD and dye; no spacer; and the affinity of the functional group to the QD surface is strong. The FRET signal was measured for these complexes as a function of both dye to QD ratio and center-to-center distance between QD and dye by controlling number of covered ZnS layers. Data showed that fluorescence resonance energy transfer (FRET) was the dominant mechanism of the energy transfer in our QD-dye hybrid system. FRET efficiency can be controlled by not only adjusting the number of dyes on the QD surface or the QD to dye distance, but also properly choosing different dye and QD components. Due to the strong stability, our QD

  4. Multiple Exciton Generation in Colloidal Nanocrystals

    Directory of Open Access Journals (Sweden)

    Charles Smith

    2013-12-01

    Full Text Available In a conventional solar cell, the energy of an absorbed photon in excess of the band gap is rapidly lost as heat, and this is one of the main reasons that the theoretical efficiency is limited to ~33%. However, an alternative process, multiple exciton generation (MEG, can occur in colloidal quantum dots. Here, some or all of the excess energy is instead used to promote one or more additional electrons to the conduction band, potentially increasing the photocurrent of a solar cell and thereby its output efficiency. This review will describe the development of this field over the decade since the first experimental demonstration of multiple exciton generation, including the controversies over experimental artefacts, comparison with similar effects in bulk materials, and the underlying mechanisms. We will also describe the current state-of-the-art and outline promising directions for further development.

  5. Electromagnetic Energy Absorption due to Wireless Energy Transfer: A Brief Review

    Directory of Open Access Journals (Sweden)

    Syafiq A.

    2016-01-01

    Full Text Available This paper reviews an implementation of evaluating compliance of wireless power transfer systems with respect to human electromagnetic exposure limits. Methods for both numerical analysis and measurements are discussed. The objective is to evaluate the rate of which energy is absorbed by the human body when exposed to a wireless energy transfer, although it can be referred to the absorption of other forms of energy by tissue. An exposure assessment of a representative wireless power transfer system, under a limited set of operating conditions, is provided in order to estimate the maximum SAR levels. The aim of this review is to conclude the possible side effect to the human body when utilizing wireless charging in daily life so that an early severe action can be taken when using wireless transfer.

  6. Interaction and Dephasing of Excitons in ZnSe Quantum Wires

    DEFF Research Database (Denmark)

    Wagner, Hans Peter; Langbein, Wolfgang; Hvam, Jørn Märcher

    1999-01-01

    We study the coherent formation of biexcitons in wet-etched ZnSe quantum wires of lateral sizes down to 23 nm by transient degenerate four-wave mixing. We observe an increase of the biexciton binding energy with decreasing wire width reaching 30% energy enhancement in the smallest wire structure...... compared to the mesa structure which is attributed to a quenching of the exciton-exciton scattering efficiency by density dependent measurements. The exciton dephasing is found to increase with decreasing wire width which is assigned to an enhanced repulsive exchange interaction between excitons of equal...

  7. Exciton dephasing and biexciton binding in CdSe/ZnSe islands

    DEFF Research Database (Denmark)

    Wagner, Hans Peter; Tranitz, H.-P.; Preis, H

    1999-01-01

    The dephasing of excitons and the formation of biexcitons in self-organized CdSe/ZnSe islands grown by molecular-beam epitaxy is investigated using spectrally resolved four-wave mixing. A distribution of exciton-exciton scattering efficiencies and dephasing times in the range of 0.5-10 ps are obs...... energy slightly increases from 21.5 to 23 meV, while its broadening decreases from 5.5 to 3 meV. This is attributed to a strong three-dimensional confinement with improving shape uniformity for decreasing exciton energy. [S0163-1829(99)04739-6]....

  8. Ultrafast dynamics of excitons in delafossite CuScO2 thin films

    Science.gov (United States)

    Liu, Fucai; Makino, T.; Hiraga, H.; Fukumura, T.; Kong, Yongfa; Kawasaki, M.

    2010-05-01

    Ultrafast carrier dynamics were investigated in a delafossite CuScO2, a material with a remarkably large binding energy of exciton (˜0.4 eV), using femtosecond transient transmission spectroscopy. Differential transmission spectra showed dispersive structures in the excitonic resonance energies. We have observed a delayed rise-up on a time scale of 10 ps, suggesting slow carrier cooling. It is followed by a slower decay, time constant of which corresponds to the lifetime of exciton (approximately 0.75 ns). These results were analyzed in terms of the generalized many-body Elliott model, accounting for a screening effect of excitons.

  9. Exciton Effects in Optical Absorption of Boron-Nitride Nanotubes

    CERN Document Server

    Harigaya, Kikuo

    2007-01-01

    Exciton effects are studied in single-wall boron-nitride (BN) nanotubes. Linear absorption spectra are calculated with changing the chiral index of the zigzag nanotubes. We consider the extended Hubbard model with atomic energies at the boron and nitrogen sites. Exciton effects are calculated using the configuration interaction technique. The Coulomb interaction dependence of the band gap, the lowest exciton energy, and the binding energy of the exciton are discussed. The optical gap of the (5,0) nanotube is about 6 eV at the onsite interaction U=2t with the hopping integral t=1.2 eV. The binding energy of the exciton is 0.50 eV for these parameters. This energy agrees well with that of other theoretical investigations. We find that the energy gap and the binding energy are almost independent of the geometries of the nanotubes. This novel property is in contrast with that of the carbon nanotubes which show metallic and semiconducting properties depending on the chiral index.

  10. Resolving ultrafast exciton migration in organic solids at the nanoscale

    Science.gov (United States)

    Penwell, Samuel B.; Ginsberg, Lucas D. S.; Noriega, Rodrigo; Ginsberg, Naomi S.

    2017-11-01

    Effectiveness of molecular-based light harvesting relies on transport of excitons to charge-transfer sites. Measuring exciton migration, however, has been challenging because of the mismatch between nanoscale migration lengths and the diffraction limit. Instead of using bulk substrate quenching methods, here we define quenching boundaries all-optically with sub-diffraction resolution, thus characterizing spatiotemporal exciton migration on its native nanometre and picosecond scales. By transforming stimulated emission depletion microscopy into a time-resolved ultrafast approach, we measure a 16-nm migration length in poly(2,5-di(hexyloxy)cyanoterephthalylidene) conjugated polymer films. Combined with Monte Carlo exciton hopping simulations, we show that migration in these films is essentially diffusive because intrinsic chromophore energetic disorder is comparable to chromophore inhomogeneous broadening. Our approach will enable previously unattainable correlation of local material structure to exciton migration character, applicable not only to photovoltaic or display-destined organic semiconductors but also to explaining the quintessential exciton migration exhibited in photosynthesis.

  11. Excitonic connectivity between photosystem II units: what is it, and how to measure it?

    Science.gov (United States)

    Stirbet, Alexandrina

    2013-10-01

    In photosynthetic organisms, light energy is absorbed by a complex network of chromophores embedded in light-harvesting antenna complexes. In photosystem II (PSII), the excitation energy from the antenna is transferred very efficiently to an active reaction center (RC) (i.e., with oxidized primary quinone acceptor Q(A)), where the photochemistry begins, leading to O2 evolution, and reduction of plastoquinones. A very small part of the excitation energy is dissipated as fluorescence and heat. Measurements on chlorophyll (Chl) fluorescence and oxygen have shown that a nonlinear (hyperbolic) relationship exists between the fluorescence yield (Φ(F)) (or the oxygen emission yield, (Φ(O2)) and the fraction of closed PSII RCs (i.e., with reduced Q(A)). This nonlinearity is assumed to be related to the transfer of the excitation energy from a closed PSII RC to an open (active) PSII RC, a process called PSII excitonic connectivity by Joliot and Joliot (CR Acad Sci Paris 258: 4622-4625, 1964). Different theoretical approaches of the PSII excitonic connectivity, and experimental methods used to measure it, are discussed in this review. In addition, we present alternative explanations of the observed sigmoidicity of the fluorescence induction and oxygen evolution curves.

  12. Superfluidity of dipolar excitons in a transition metal dichalcogenide double layer

    Science.gov (United States)

    Berman, Oleg L.; Kezerashvili, Roman Ya.

    2017-09-01

    We study formation and superfluidity of dipolar excitons in double layer heterostructures formed by two transition metal dichalcogenide (TMDC) atomically thin layers. Considering screening effects for an electron-hole interaction via the harmonic oscillator approximation for the Keldysh potential, the analytical expressions for the exciton energy spectrum and the mean field critical temperature Tc for the superfluidity are obtained. It is shown that binding energies of A excitons are larger than for B excitons. The mean field critical temperature for a two-component dilute exciton system in a TMDC double layer is analyzed and shown that the latter is an increasing function of the factor Q , determined by the effective masses of A and B excitons and their reduced mass. Comparison of the calculations for Tc performed by employing the Coulomb and Keldysh interactions demonstrates the importance of screening effects in TMDC.

  13. Model Property Based Material Balance and Energy Conservation Analysis for Process Industry Energy Transfer Systems

    Directory of Open Access Journals (Sweden)

    Fumin Ma

    2015-10-01

    Full Text Available Conventional historical data based material and energy balance analyses are static and isolated computations. Such methods cannot embody the cross-coupling effect of energy flow, material flow and information flow in the process industry; furthermore, they cannot easily realize the effective evaluation and comparison of different energy transfer processes by alternating the model module. In this paper, a novel method for material balance and energy conservation analysis of process industry energy transfer system is developed based on model property. Firstly, a reconfigurable energy transfer process model, which is independent of energy types and energy-consuming equipment, is presented from the viewpoint of the cross-coupling effect of energy flow, material flow and information flow. Thereafter the material balance determination is proposed based on both a dynamic incidence matrix and dynamic balance quantity. Moreover, the model-weighted conservation determination theorem is proved, and the energy efficiency analysis method is also discussed. Results confirmed the efficacy of the proposed methods, confirming its potential for use by process industry in energy efficiency analyses.

  14. State-to-state dynamics of molecular energy transfer

    Energy Technology Data Exchange (ETDEWEB)

    Gentry, W.R.; Giese, C.F. [Univ. of Minnesota, Minneapolis (United States)

    1993-12-01

    The goal of this research program is to elucidate the elementary dynamical mechanisms of vibrational and rotational energy transfer between molecules, at a quantum-state resolved level of detail. Molecular beam techniques are used to isolate individual molecular collisions, and to control the kinetic energy of collision. Lasers are used both to prepare specific quantum states prior to collision by stimulated-emission pumping (SEP), and to measure the distribution of quantum states in the collision products by laser-induced fluorescence (LIF). The results are interpreted in terms of dynamical models, which may be cast in a classical, semiclassical or quantum mechanical framework, as appropriate.

  15. Constrained geometric dynamics of the Fenna-Matthews-Olson complex: the role of correlated motion in reducing uncertainty in excitation energy transfer.

    Science.gov (United States)

    Fokas, Alexander S; Cole, Daniel J; Chin, Alex W

    2014-12-01

    The trimeric Fenna-Mathews-Olson (FMO) complex of green sulphur bacteria is a well-studied example of a photosynthetic pigment-protein complex, in which the electronic properties of the pigments are modified by the protein environment to promote efficient excitonic energy transfer from antenna complexes to the reaction centres. By a range of simulation methods, many of the electronic properties of the FMO complex can be extracted from knowledge of the static crystal structure. However, the recent observation and analysis of long-lasting quantum dynamics in the FMO complex point to protein dynamics as a key factor in protecting and generating quantum coherence under laboratory conditions. While fast inter- and intra-molecular vibrations have been investigated extensively, the slow, conformational dynamics which effectively determine the optical inhomogeneous broadening of experimental ensembles has received less attention. The following study employs constrained geometric dynamics to study the flexibility in the protein network by efficiently generating the accessible conformational states from the published crystal structure. Statistical and principle component analyses reveal highly correlated low frequency motions between functionally relevant elements, including strong correlations between pigments that are excitonically coupled. Our analysis reveals a hierarchy of structural interactions which enforce these correlated motions, from the level of monomer-monomer interfaces right down to the α-helices, β-sheets and pigments. In addition to inducing strong spatial correlations across the conformational ensemble, we find that the overall rigidity of the FMO complex is exceptionally high. We suggest that these observations support the idea of highly correlated inhomogeneous disorder of the electronic excited states, which is further supported by the remarkably low variance (typically <5%) of the excitonic couplings of the conformational ensemble.

  16. Analysis of the Coupling Coefficient in Inductive Energy Transfer Systems

    Directory of Open Access Journals (Sweden)

    Rafael Mendes Duarte

    2014-01-01

    Full Text Available In wireless energy transfer systems, the energy is transferred from a power source to an electrical load without the need of physical connections. In this scope, inductive links have been widely studied as a way of implementing these systems. Although high efficiency can be achieved when the system is operating in a static state, it can drastically decrease if changes in the relative position and in the coupling coefficient between the coils occur. In this paper, we analyze the coupling coefficient as a function of the distance between two planar and coaxial coils in wireless energy transfer systems. A simple equation is derived from Neumann’s equation for mutual inductance, which is then used to calculate the coupling coefficient. The coupling coefficient is computed using CST Microwave Studio and compared to calculation and experimental results for two coils with an excitation signal of up to 10 MHz. The results showed that the equation presents good accuracy for geometric parameters that do not lead the solution of the elliptic integral of the first kind to infinity.

  17. Resonant energy transfer based biosensor for detection of multivalent proteins.

    Energy Technology Data Exchange (ETDEWEB)

    Song, X. (Xuedong); Swanson, Basil I.

    2001-01-01

    We have developed a new fluorescence-based biosensor for sensitive detection of species involved in a multivslent interaction. The biosensor system utilizes specific interactions between proteins and cell surface receptors, which trigger a receptor aggregation process. Distance-dependent fluorescence self-quenching and resonant energy transfer mechanisms were coupled with a multivalent interaction to probe the receptor aggregation process, providing a sensitive and specific signal transduction method for such a binding event. The fluorescence change induced by the aggregation process can be monitored by different instrument platforms, e.g. fluorimetry and flow cytometry. In this article, a sensitive detection of pentavalent cholera toxin which recognizes ganglioside GM1 has been demonstrated through the resonant energy transfer scheme, which can achieve a double color change simultaneously. A detection sensitivity as high as 10 pM has been achieved within a few minutes (c.a. 5 minutes). The simultaneous double color change (an increase of acceptor fluorescence and a decrease of donor fluorescence intensity) of two similar fluorescent probes provides particularly high detection reliability owing to the fact that they act as each other's internal reference. Any external perturbation such as environmental temperature change causes no significant change in signal generation. Besides the application for biological sensing, the method also provides a useful tool for investigation of kinetics and thermodynamics of a multivalent interaction. Keywords: Biosensor, Fluorescence resonant energy transfer, Multivalent interaction, Cholera Toxin, Ganglioside GM1, Signal Transduction

  18. metal-induced energy transfer (MIET) (Conference Presentation)

    Science.gov (United States)

    Karedla, Narain V. S.; Isbaner, Sebastian; Chizhik, Alexey I.; Gregor, Ingo; Enderlein, Joerg; Chizhik, Anna M.

    2017-02-01

    We present a new concept for measuring distance values of single molecules from a surface with nanometer accuracy using the energy transfer from the excited molecule to surface plasmons of a metal film [1]. We measure the fluorescence lifetime of individual dye molecules deposited on a dielectric spacer as a function of a spacer thickness. By using our theoretical model [2], we convert the lifetime values into the axial distance of individual molecules. Similar to Förster resonance energy transfer (FRET), this allows emitters to be localized with nanometer accuracy, but in contrast to FRET the distance range at which efficient energy transfer takes place is an order of magnitude larger. Together with orientation measurements [3], one can potentially use smMIET to localize single emitters with a nanometer precision isotropically, which will facilitate intra- and intermolecular distance measurements in biomolecules and complexes, circumventing the requirement of the knowledge of mutual orientations between two dipole emitters which severely limits the quantification of such distances from a conventional single-pair FRET (spFRET) experiment. [1] Karedla, N., Chizhik, A.I., Gregor, I., Chizhik, A.M., Schulz, O., Enderlein, J., ChemPhysChem, 15, 705-711 (2014). [2] Enderlein J., Biophyical Journal, 78, 2151-8 (2000). [3] Karedla, N., Stein, S. C., Hähnel, D., Gregor, I., Chizhik, A., and Enderlein, J., Physical Review Letters, 115, 173002 (2015).

  19. Excitons in ultrathin organic-inorganic perovskite crystals

    Science.gov (United States)

    Yaffe, Omer; Chernikov, Alexey; Norman, Zachariah M.; Zhong, Yu; Velauthapillai, Ajanthkrishna; van der Zande, Arend; Owen, Jonathan S.; Heinz, Tony F.

    2015-07-01

    We demonstrate the formation of large sheets of layered organic-inorganic perovskite (OIPC) crystals, as thin as a single unit cell, prepared by mechanical exfoliation. The resulting two-dimensional OIPC nanosheets of 2.4 nm thickness are direct semiconductors with an optical band gap of 2.4 eV. They exhibit unusually strong light-matter interaction with an optical absorption as high as 25% at the main excitonic resonance, as well as bright photoluminescence. We extract an exciton binding energy of 490 meV from measurement of the series of excited exciton states. The properties of the excitons are shown to be strongly influenced by the changes in the dielectric surroundings. The environmental sensitivity of these ultrathin OIPC sheets is further reflected in the strong suppression of a thermally driven phase transition present in the bulk crystals.

  20. Excitonic giant-dipole potentials in cuprous oxide

    Science.gov (United States)

    Kurz, Markus; Grünwald, Peter; Scheel, Stefan

    2017-06-01

    In this paper we predict the existence of a novel species of Wannier excitons when exposed to crossed electric and magnetic fields. In particular, we present a theory of giant-dipole excitons in Cu2O in crossed fields. Within our theoretical approach we perform a pseudoseparation of the center-of-mass motion for the field-dressed excitonic species, thereby obtaining an effective single-particle Hamiltonian for the relative motion. For arbitrary gauge fields we exactly separate the gauge-dependent kinetic-energy terms from the effective single-particle interaction potential. Depending on the applied field strengths and the specific field orientation, the potential for the relative motion of electron and hole exhibits an outer well at spatial separations up to several micrometers and depths up to 380 μ eV , leading to possible permanent excitonic electric dipole moments of around 3 ×106 D.

  1. Exciton Migration and Amplified Quenching on Two-Dimensional Metal–Organic Layers

    Energy Technology Data Exchange (ETDEWEB)

    Cao, Lingyun; Lin, Zekai; Shi, Wenjie; Wang, Zi; Zhang, Cankun; Hu, Xuefu; Wang, Cheng; Lin, Wenbin (UC); (Xiamen)

    2017-05-10

    The dimensionality dependency of resonance energy transfer is of great interest due to its importance in understanding energy transfer on cell membranes and in low-dimension nanostructures. Light harvesting two-dimensional metal–organic layers (2D-MOLs) and three-dimensional metal–organic frameworks (3D-MOFs) provide comparative models to study such dimensionality dependence with molecular accuracy. Here we report the construction of 2D-MOLs and 3D-MOFs from a donor ligand 4,4',4''-(benzene-1,3,5-triyl-tris(ethyne-2,1-diyl))tribenzoate (BTE) and a doped acceptor ligand 3,3',3''-nitro-4,4',4''-(benzene-1,3,5-triyl-tris(ethyne-2,1-diyl))tribenzoate (BTE-NO2). These 2D-MOLs and 3D-MOFs are connected by similar hafnium clusters, with key differences in the topology and dimensionality of the metal–ligand connection. Energy transfer from donors to acceptors through the 2D-MOL or 3D-MOF skeletons is revealed by measuring and modeling the fluorescence quenching of the donors. We found that energy transfer in 3D-MOFs is more efficient than that in 2D-MOLs, but excitons on 2D-MOLs are more accessible to external quenchers as compared with those in 3D-MOFs. These results not only provide support to theoretical analysis of energy transfer in low dimensions, but also present opportunities to use efficient exciton migration in 2D materials for light-harvesting and fluorescence sensing.

  2. Energy-donor phosphorescence quenching study of triplet–triplet energy transfer between UV absorbers

    Energy Technology Data Exchange (ETDEWEB)

    Kikuchi, Azusa; Nakabai, Yuya [Department of Chemistry, Graduate School of Engineering, Yokohama National University, Tokiwadai, Hodogaya-ku, Yokohama 240-8501 (Japan); Oguchi-Fujiyama, Nozomi; Miyazawa, Kazuyuki [Shiseido Research Center, Hayabuchi, Tsuzuki-ku, Yokohama 224-8558 (Japan); Yagi, Mikio, E-mail: yagimiki@ynu.ac.jp [Department of Chemistry, Graduate School of Engineering, Yokohama National University, Tokiwadai, Hodogaya-ku, Yokohama 240-8501 (Japan)

    2015-10-15

    The intermolecular triplet–triplet energy transfer from a photounstable UV-A absorber, 4-tert-butyl-4′-methoxydibenzoylmethane (BMDBM), to UV-B absorbers, 2-ethylhexyl 4-methoxycinnamate (octyl methoxycinnamate, OMC), octocrylene (OCR) and dioctyl 4-methoxybenzylidenemalonate (DOMBM) has been observed using a 355 nm laser excitation in rigid solutions at 77 K. The decay curves of the energy-donor phosphorescence in the presence of the UV-B absorbers deviate from the exponential decay at the initial stage of the decay. The Stern–Volmer formulation is not valid in rigid solutions because molecular diffusion is impossible. The experimental results indicate that the rate constant of triplet–triplet energy transfer from BMDBM to the UV-B absorbers, k{sub T–T}, decreases in the following order: k{sub T–T} (BMDBM–DOMBM)>k{sub T–T} (BMDBM–OMC)≥k{sub T–T} (BMDBM–OCR). The presence of DOMBM enhances the photostability of the widely used combination of UV-A and UV-B absorbers, BMDBM and OCR. The effects of the triplet–triplet energy transfer on the photostability of BMDBM are discussed. - Highlights: • The intermolecular triplet–triplet energy transfer between UV absorbers was observed. • The phosphorescence decay deviates from exponential at the initial stage of decay. • The effects of triplet–triplet energy transfer on the photostability are discussed.

  3. Heat transfer and flow in solar energy and bioenergy systems

    Science.gov (United States)

    Xu, Ben

    The demand for clean and environmentally benign energy resources has been a great concern in the last two decades. To alleviate the associated environmental problems, reduction of the use of fossil fuels by developing more cost-effective renewable energy technologies becomes more and more significant. Among various types of renewable energy sources, solar energy and bioenergy take a great proportion. This dissertation focuses on the heat transfer and flow in solar energy and bioenergy systems, specifically for Thermal Energy Storage (TES) systems in Concentrated Solar Power (CSP) plants and open-channel algal culture raceways for biofuel production. The first part of this dissertation is the discussion about mathematical modeling, numerical simulation and experimental investigation of solar TES system. First of all, in order to accurately and efficiently simulate the conjugate heat transfer between Heat Transfer Fluid (HTF) and filler material in four different solid-fluid TES configurations, formulas of an e?ective heat transfer coe?cient were theoretically developed and presented by extending the validity of Lumped Capacitance Method (LCM) to large Biot number, as well as verifications/validations to this simplified model. Secondly, to provide design guidelines for TES system in CSP plant using Phase Change Materials (PCM), a general storage tank volume sizing strategy and an energy storage startup strategy were proposed using the enthalpy-based 1D transient model. Then experimental investigations were conducted to explore a novel thermal storage material. The thermal storage performances were also compared between this novel storage material and concrete at a temperature range from 400 °C to 500 °C. It is recommended to apply this novel thermal storage material to replace concrete at high operating temperatures in sensible heat TES systems. The second part of this dissertation mainly focuses on the numerical and experimental study of an open-channel algae

  4. Engineering and manipulating exciton wave packets

    Science.gov (United States)

    Zang, Xiaoning; Montangero, Simone; Carr, Lincoln D.; Lusk, Mark T.

    2017-05-01

    When a semiconductor absorbs light, the resulting electron-hole superposition amounts to a uncontrolled quantum ripple that eventually degenerates into diffusion. If the conformation of these excitonic superpositions could be engineered, though, they would constitute a new means of transporting information and energy. We show that properly designed laser pulses can be used to create such excitonic wave packets. They can be formed with a prescribed speed, direction, and spectral make-up that allows them to be selectively passed, rejected, or even dissociated using superlattices. Their coherence also provides a handle for manipulation using active, external controls. Energy and information can be conveniently processed and subsequently removed at a distant site by reversing the original procedure to produce a stimulated emission. The ability to create, manage, and remove structured excitons comprises the foundation for optoexcitonic circuits with application to a wide range of quantum information, energy, and light-flow technologies. The paradigm is demonstrated using both tight-binding and time-domain density functional theory simulations.

  5. Exciton band structure in bacterial peripheral light-harvesting complexes.

    Science.gov (United States)

    Trinkunas, Gediminas; Zerlauskiene, Oksana; Urbonienė, Vidita; Chmeliov, Jevgenij; Gall, Andrew; Robert, Bruno; Valkunas, Leonas

    2012-05-03

    The variability of the exciton spectra of bacteriochlorophyll molecules in light-harvesting (LH) complexes of photosynthetic bacteria ensures the excitation energy funneling trend toward the reaction center. The decisive shift of the energies is achieved due to exciton spectra formation caused by the resonance interaction between the pigments. The possibility to resolve the upper Davydov sub-band corresponding to the B850 ring and, thus, to estimate the exciton bandwidth by analyzing the temperature dependence of the steady-state absorption spectra of the LH2 complexes is demonstrated. For this purpose a self-modeling curve resolution approach was applied for analysis of the temperature dependence of the absorption spectra of LH2 complexes from the photosynthetic bacteria Rhodobacter (Rba.) sphaeroides and Rhodoblastus (Rbl.) acidophilus. Estimations of the intradimer resonance interaction values as follows directly from obtained estimations of the exciton bandwidths at room temperature give 385 and 397 cm(-1) for the LH2 complexes from the photosynthetic bacteria Rba. sphaeroides and Rhl. acidophilus, respectively. At 4 K the corresponding couplings are slightly higher (391 and 435 cm(-1), respectively). The retained exciton bandwidth at physiological conditions supports the decisive role of the exciton coherence determining light absorption in bacterial light-harvesting antenna complexes.

  6. Enhanced photovoltaic performance of ultrathin Si solar cells via semiconductor nanocrystal sensitization: energy transfer vs. optical coupling effects.

    Science.gov (United States)

    Hoang, Son; Ashraf, Ahsan; Eisaman, Matthew D; Nykypanchuk, Dmytro; Nam, Chang-Yong

    2016-03-21

    Excitonic energy transfer (ET) offers exciting opportunities for advances in optoelectronic devices such as solar cells. While recent experimental attempts have demonstrated its potential in both organic and inorganic photovoltaics (PVs), what remains to be addressed is quantitative understanding of how different ET modes contribute to PV performance and how ET contribution is differentiated from the classical optical coupling (OC) effects. In this study, we implement an ET scheme using a PV device platform, comprising CdSe/ZnS nanocrystal energy donor and 500 nm-thick ultrathin Si acceptor layers, and present the quantitative mechanistic description of how different ET modes, distinguished from the OC effects, increase the light absorption and PV efficiency. We find that nanocrystal sensitization enhances the short circuit current of ultrathin Si solar cells by up to 35%, of which the efficient ET, primarily driven by a long-range radiative mode, contributes to 38% of the total current enhancement. These results not only confirm the positive impact of ET but also provide a guideline for rationally combining the ET and OC effects for improved light harvesting in PV and other optoelectronic devices.

  7. Exciton dynamics in cuprous oxide

    NARCIS (Netherlands)

    Fishman, D. A.; Revcolevschi, A.; van Loosdrecht, P. H. M.; Stutzmann, M

    2006-01-01

    This work addresses the mid-infrared properties of cuprous oxide and in particular induced absorption due to the presence of excitons. We probe the population of the non-radiative ground state of para-excitons via laser-induced changes of the transmission in the "hydrogenic" 1s-2p/1s-3p transition

  8. Exciton Formation in Disordered Semiconductors

    DEFF Research Database (Denmark)

    Klochikhin, A.; Reznitsky, A.; Permogorov, S.

    1999-01-01

    Stationary luminescence spectra of disordered solid solutions can be accounted by the model of localized excitons. Detailed analysis of the long time decay kinetics of luminescence shows that exciton formation in these systems is in great extent due to the bimolecular reaction of separated carrie...

  9. Coherent control of optical absorption and the energy transfer pathway of an infrared quantum dot hybridized with a VO2 nanoparticle

    Science.gov (United States)

    Hatef, Ali; Zamani, Naser; Johnston, William

    2017-04-01

    We systematically investigate the optical response of a semiconductor quantum dot (QD) hybridized with a vanadium dioxide nanoparticle (VO2NP) in the infrared (IR) region. The VO2NP features a semiconductor to metal phase change characteristic below and above a critical temperature that leads to an abrupt change in the particle’s optical properties. This feature means that the QD-VO2NP hybrid system can support the coherent coupling of exciton-polaritons and exciton-plasmon polaritons in the semiconductor and metal phases of the VO2NP, respectively. In our calculations, the VO2NP phase transition is modelled with a filling fraction (f), representing the fraction of the VO2NP in the metallic phase. The phase transition is driven by the hybrid system’s interaction with a continuous wave (CW) IR laser field. In this paper, we show how control over the filling fraction results in the enhancement or suppression of the QD’s linear absorption. These variations in the QD absorption is due to dramatic changes in the effective local field experienced by the QD and the non-radiative energy transfer from the QD to the VO2NP. The presented results have the potential to be applied to the design of thermal sensors at the nanoscale.

  10. Interlayer Exciton Optoelectronics in a 2D Heterostructure p-n Junction.

    Science.gov (United States)

    Ross, Jason S; Rivera, Pasqual; Schaibley, John; Lee-Wong, Eric; Yu, Hongyi; Taniguchi, Takashi; Watanabe, Kenji; Yan, Jiaqiang; Mandrus, David; Cobden, David; Yao, Wang; Xu, Xiaodong

    2017-02-08

    Semiconductor heterostructures are backbones for solid-state-based optoelectronic devices. Recent advances in assembly techniques for van der Waals heterostructures have enabled the band engineering of semiconductor heterojunctions for atomically thin optoelectronic devices. In two-dimensional heterostructures with type II band alignment, interlayer excitons, where Coulomb bound electrons and holes are confined to opposite layers, have shown promising properties for novel excitonic devices, including a large binding energy, micron-scale in-plane drift-diffusion, and a long population and valley polarization lifetime. Here, we demonstrate interlayer exciton optoelectronics based on electrostatically defined lateral p-n junctions in a MoSe 2 -WSe 2 heterobilayer. Applying a forward bias enables the first observation of electroluminescence from interlayer excitons. At zero bias, the p-n junction functions as a highly sensitive photodetector, where the wavelength-dependent photocurrent measurement allows the direct observation of resonant optical excitation of the interlayer exciton. The resulting photocurrent amplitude from the interlayer exciton is about 200 times smaller than the resonant excitation of intralayer exciton. This implies that the interlayer exciton oscillator strength is 2 orders of magnitude smaller than that of the intralayer exciton due to the spatial separation of electron and hole to the opposite layers. These results lay the foundation for exploiting the interlayer exciton in future 2D heterostructure optoelectronic devices.

  11. Optimal aeroassisted coplanar orbital transfer using an energy model

    Science.gov (United States)

    Halyo, Nesim; Taylor, Deborah B.

    1989-01-01

    The atmospheric portion of the trajectories for the aeroassisted coplanar orbit transfer was investigated. The equations of motion for the problem are expressed using reduced order model and total vehicle energy, kinetic plus potential, as the independent variable rather than time. The order reduction is achieved analytically without an approximation of the vehicle dynamics. In this model, the problem of coplanar orbit transfer is seen as one in which a given amount of energy must be transferred from the vehicle to the atmosphere during the trajectory without overheating the vehicle. An optimal control problem is posed where a linear combination of the integrated square of the heating rate and the vehicle drag is the cost function to be minimized. The necessary conditions for optimality are obtained. These result in a 4th order two-point-boundary-value problem. A parametric study of the optimal guidance trajectory in which the proportion of the heating rate term versus the drag varies is made. Simulations of the guidance trajectories are presented.

  12. Exciton energy recycling from ZnO defect levels: towards electrically driven hybrid quantum-dot white light-emitting-diodes

    Science.gov (United States)

    Zhao, Xin; Liu, Weizhen; Chen, Rui; Gao, Yuan; Zhu, Binbin; Demir, Hilmi Volkan; Wang, Shijie; Sun, Handong

    2016-03-01

    An electrically driven quantum-dot hybrid white light-emitting diode is fabricated via spin coating CdSe quantum dots onto a GaN/ZnO nanorod matrix. For the first time, quantum dots are excited by fluorescence resonance energy transfer from the carriers trapped at surface defect levels. The prototype device exhibits achromatic emission, with a chromaticity coordinate of (0.327, 0.330), and correlated color temperature similar to sunlight.An electrically driven quantum-dot hybrid white light-emitting diode is fabricated via spin coating CdSe quantum dots onto a GaN/ZnO nanorod matrix. For the first time, quantum dots are excited by fluorescence resonance energy transfer from the carriers trapped at surface defect levels. The prototype device exhibits achromatic emission, with a chromaticity coordinate of (0.327, 0.330), and correlated color temperature similar to sunlight. Electronic supplementary information (ESI) available. See DOI: 10.1039/c5nr09261b

  13. Quasi-white light emission involving Förster resonance energy transfer in a new organic inorganic tin chloride based material (AMPS)[SnCl6]H2O

    Science.gov (United States)

    Dammak, Thameur; Abid, Younes

    2017-04-01

    This work deals with optical properties of a new organic inorganic material: 3, 3‧-Diaminodiphenyl-sulfone tin chloride with the formula (C12H14N2O2S)[SnCl6]H2O abbreviated as (AMPS)[SnCl6]H2O. Single crystals of (AMPS)[SnCl6]H2O were elaborated by the solvent evaporation method and investigated by X-ray diffraction, optical absorption (OA), photoluminescence (PL) and photoluminescence excitation (PLE). The crystal structure is composed of discrete [SnCl6] anions surrounded by organic (AMPS) cations and H2O molecules. For optical investigations, thin films have been prepared by spin-coating method from the ethanol solution of the material. Photoluminescence measurements show a quasi-white light and intense emission which can be observed even with naked eye at room temperature. This emission is believed to be due to excitonic recombination involving a Förster resonance energy transfer mechanism in which (AMPS) molecule acts as a donor and [SnCl6] molecule acts as an acceptor. Moreover, the temperature dependence study of the photoluminescence in term of Varshni and Arrhenius models reveals the free character of the inorganic exciton and shows that the organic exciton is rather localized.

  14. The excitonic insulator route through a dynamical phase transition induced by an optical pulse

    Energy Technology Data Exchange (ETDEWEB)

    Brazovskii, S., E-mail: brazov@lptms.u-psud.fr [Université Paris-Saclay, LPTMS, CNRS, Univ. Paris-sud (France); Kirova, N. [Université Paris-Saclay, LPS, CNRS, Univ. Paris-sud (France)

    2016-03-15

    We consider a dynamical phase transition induced by a short optical pulse in a system prone to thermodynamical instability. We address the case of pumping to excitons whose density contributes directly to the order parameter. To describe both thermodynamic and dynamic effects on equal footing, we adopt a view of the excitonic insulator for the phase transition and suggest a formation of the Bose condensate for the pumped excitons. The work is motivated by experiments in donor–acceptor organic compounds with a neutral- ionic phase transition coupled to the spontaneous lattice dimerization and to charge transfer excitons. The double nature of the ensemble of excitons leads to an intricate time evolution, in particular, to macroscopic quantum oscillations from the interference between the Bose condensate of excitons and the ground state of the excitonic insulator. The coupling of excitons and the order parameter also leads to self-trapping of their wave function, akin to self-focusing in optics. The locally enhanced density of excitons can surpass a critical value to trigger the phase transformation, even if the mean density is below the required threshold. The system is stratified in domains that evolve through dynamical phase transitions and sequences of merging. The new circumstances in experiments and theory bring to life, once again, some remarkable inventions made by L.V. Keldysh.

  15. Multiple exciton generation in chiral carbon nanotubes: Density functional theory based computation

    Science.gov (United States)

    Kryjevski, Andrei; Mihaylov, Deyan; Kilina, Svetlana; Kilin, Dmitri

    2017-10-01

    We use a Boltzmann transport equation (BE) to study time evolution of a photo-excited state in a nanoparticle including phonon-mediated exciton relaxation and the multiple exciton generation (MEG) processes, such as exciton-to-biexciton multiplication and biexciton-to-exciton recombination. BE collision integrals are computed using Kadanoff-Baym-Keldysh many-body perturbation theory based on density functional theory simulations, including exciton effects. We compute internal quantum efficiency (QE), which is the number of excitons generated from an absorbed photon in the course of the relaxation. We apply this approach to chiral single-wall carbon nanotubes (SWCNTs), such as (6,2) and (6,5). We predict efficient MEG in the (6,2) and (6,5) SWCNTs within the solar spectrum range starting at the 2Eg energy threshold and with QE reaching ˜1.6 at about 3Eg, where Eg is the electronic gap.

  16. Harmonic Quantum Coherence of Multiple Excitons in PbS/CdS Core-Shell Nanocrystals

    Science.gov (United States)

    Tahara, Hirokazu; Sakamoto, Masanori; Teranishi, Toshiharu; Kanemitsu, Yoshihiko

    2017-12-01

    The generation and recombination dynamics of multiple excitons in nanocrystals (NCs) have attracted much attention from the viewpoints of fundamental physics and device applications. However, the quantum coherence of multiple exciton states in NCs still remains unclear due to a lack of experimental support. Here, we report the first observation of harmonic dipole oscillations in PbS/CdS core-shell NCs using a phase-locked interference detection method for transient absorption. From the ultrafast coherent dynamics and excitation-photon-fluence dependence of the oscillations, we found that multiple excitons cause the harmonic dipole oscillations with ω , 2 ω , and 3 ω oscillations, even though the excitation pulse energy is set to the exciton resonance frequency, ω . This observation is closely related to the quantum coherence of multiple exciton states in NCs, providing important insights into multiple exciton generation mechanisms.

  17. Control of excitons in a bent bunch of molecular aggregates by dipole-dipole interaction with quantum dots

    Science.gov (United States)

    Zabolotskii, A. A.

    2017-10-01

    The nonlocal dipole-dipole interaction is studied between excitations in chromophores forming a bunch or a tube of J-aggregates and closely spaced quantum dots (QDs). Equations describing the evolution of exciton pulses in a quasi-one-dimensional medium are derived taking into account the interaction with the transition resonant to nanoparticles. It is shown that the efficient controllable resonance energy transfer can occur in the system between QDs and an exciton pulse. The efficiency of this process significantly increases if the bunch of aggregates is deformed to bend nanoparticles round. It is shown that the interaction of permanent dipole moments of QDs and chromophores leads to the formation of a potential barrier or a well. It is found that the combined influence of these factors can be used to efficiently control the dynamics of pulses in aggregates.

  18. Exciton condensation in strongly correlated electron bilayers

    NARCIS (Netherlands)

    Rademaker, Louk; van den Brink, J.; Zaanen, Jan; Hilgenkamp, H.

    2013-01-01

    We studied the possibility of exciton condensation in Mott insulating bilayers. In these strongly correlated systems, an exciton is the bound state of a double occupied and empty site. In the strong coupling limit, the exciton acts as a hard-core boson. Its physics is captured by the exciton t -J

  19. Exciton-plasmon coupling interactions: from principle to applications

    Directory of Open Access Journals (Sweden)

    Cao En

    2018-01-01

    Full Text Available The interaction of exciton-plasmon coupling and the conversion of exciton-plasmon-photon have been widely investigated experimentally and theoretically. In this review, we introduce the exciton-plasmon interaction from basic principle to applications. There are two kinds of exciton-plasmon coupling, which demonstrate different optical properties. The strong exciton-plasmon coupling results in two new mixed states of light and matter separated energetically by a Rabi splitting that exhibits a characteristic anticrossing behavior of the exciton-LSP energy tuning. Compared to strong coupling, such as surface-enhanced Raman scattering, surface plasmon (SP-enhanced absorption, enhanced fluorescence, or fluorescence quenching, there is no perturbation between wave functions; the interaction here is called the weak coupling. SP resonance (SPR arises from the collective oscillation induced by the electromagnetic field of light and can be used for investigating the interaction between light and matter beyond the diffraction limit. The study on the interaction between SPR and exaction has drawn wide attention since its discovery not only due to its contribution in deepening and broadening the understanding of SPR but also its contribution to its application in light-emitting diodes, solar cells, low threshold laser, biomedical detection, quantum information processing, and so on.

  20. Exciton-plasmon coupling interactions: from principle to applications

    Science.gov (United States)

    Cao, En; Lin, Weihua; Sun, Mengtao; Liang, Wenjie; Song, Yuzhi

    2018-01-01

    The interaction of exciton-plasmon coupling and the conversion of exciton-plasmon-photon have been widely investigated experimentally and theoretically. In this review, we introduce the exciton-plasmon interaction from basic principle to applications. There are two kinds of exciton-plasmon coupling, which demonstrate different optical properties. The strong exciton-plasmon coupling results in two new mixed states of light and matter separated energetically by a Rabi splitting that exhibits a characteristic anticrossing behavior of the exciton-LSP energy tuning. Compared to strong coupling, such as surface-enhanced Raman scattering, surface plasmon (SP)-enhanced absorption, enhanced fluorescence, or fluorescence quenching, there is no perturbation between wave functions; the interaction here is called the weak coupling. SP resonance (SPR) arises from the collective oscillation induced by the electromagnetic field of light and can be used for investigating the interaction between light and matter beyond the diffraction limit. The study on the interaction between SPR and exaction has drawn wide attention since its discovery not only due to its contribution in deepening and broadening the understanding of SPR but also its contribution to its application in light-emitting diodes, solar cells, low threshold laser, biomedical detection, quantum information processing, and so on.

  1. Exciton-plasmon coupling in monolayer molybdenum disulfide

    Science.gov (United States)

    Ziegler, Jed; Newaz, A. K. M.; Bolotin, Kirill; Haglund, Richard

    2013-03-01

    Two-dimensional materials such as monolayer molybdenum disulfide (MoS2) represent a unique platform for investigating the dynamics of exciton-plasmon coupling. We report on the generation and modulation of coherent and incoherent coupled states between excitons in monolayer MoS2 and plasmons in an array of gold nanoparticle deposited onto the surface of MoS2. We study the behavior of these coherent states, termed plexcitons using a combination of photoluminescence, extinction and ultrafast spectroscopies. The close proximity of the two characteristic exciton bands of MoS2 presents multiple coherent coupling configurations, including A-or-B exciton-plasmon, and A-and-B exciton-plasmon interactions. These configurations of plexciton formation that are shown to modulate both the extinction and photoluminescence spectra of the hybrid system. This includes broadband photoluminescence and Fano-type resonances. This behavior is distinct from the spectral response of the MoS2 and plasmonic components of the system. Incoherent exciton-plasmon coupling, achieved by detuning from the plasmon extinction peaks, enhances the interaction of MoS2 with light by focusing the plasmon energy. Depending on which coupling configuration is chosen, our results show that the MoS2/plasmon hybrid systems can act as high efficiency light harvesters, broadband emitters and as tunable visible and NIR photodetectors. Support by Defense Threat Reduction Agency (HDTRA1-1-10-1-0047) and NSF DMR-1056859

  2. Spatial mapping of exciton lifetimes in single ZnO nanowires

    Directory of Open Access Journals (Sweden)

    J. S. Reparaz

    2013-07-01

    Full Text Available We investigate the spatial dependence of the exciton lifetimes in single ZnO nanowires. We have found that the free exciton and bound exciton lifetimes exhibit a maximum at the center of nanowires, while they decrease by 30% towards the tips. This dependence is explained by considering the cavity-like properties of the nanowires in combination with the Purcell effect. We show that the lifetime of the bound-excitons scales with the localization energy to the power of 3/2, which validates the model of Rashba and Gurgenishvili at the nanoscale.

  3. Coherent Exciton and Biexciton Nonlinearities in Semiconductor Nanostructures: Effects of Disorder

    DEFF Research Database (Denmark)

    Langbein, Wolfgang; Borri, Paola; Hvam, Jørn Märcher

    1999-01-01

    The coherent response of excitons in semiconductor nanostructures measured in four-wave mixing (FWM) depends strongly on the inhomogenous broadening of the exciton transition. We investigate InAs/Al0.3Ga0.7As single quantum wells (SQW) and AlxGa1-xAs mixed crystals. Additional to the usual phase...... rate difference between two subsystems within the inhomogeneous distribution is strongly dependent on their energy difference. BIF is strongly affecting the cross-linear polarized FWM response. The signal for positive delay is dominated by the transitions from the one-exciton state X to the two-exciton-states...

  4. Charged excitons in doped extended Hubbard model systems

    NARCIS (Netherlands)

    van den Brink, J.; Eder, R; Sawatzky, G.A

    1997-01-01

    We show that the charge transfer excitons in a Hubbard model system including nearest-neighbor Coulomb interactions effectively attain some charge in doped systems and become visible in photoelectron and inverse photoelectron spectroscopies. This shows that the description of a doped system by an

  5. Boosting infrared energy transfer in 3D nanoporous gold antennas.

    Science.gov (United States)

    Garoli, D; Calandrini, E; Bozzola, A; Ortolani, M; Cattarin, S; Barison, S; Toma, A; De Angelis, F

    2017-01-05

    The applications of plasmonics to energy transfer from free-space radiation to molecules are currently limited to the visible region of the electromagnetic spectrum due to the intrinsic optical properties of bulk noble metals that support strong electromagnetic field confinement only close to their plasma frequency in the visible/ultraviolet range. In this work, we show that nanoporous gold can be exploited as a plasmonic material for the mid-infrared region to obtain strong electromagnetic field confinement, co-localized with target molecules into the nanopores and resonant with their vibrational frequency. The effective optical response of the nanoporous metal enables the penetration of optical fields deep into the nanopores, where molecules can be loaded thus achieving a more efficient light-matter coupling if compared to bulk gold. In order to realize plasmonic resonators made of nanoporous gold, we develop a nanofabrication method based on polymeric templates for metal deposition and we obtain antenna arrays resonating at mid-infrared wavelengths selected by design. We then coat the antennas with a thin (3 nm) silica layer acting as the target dielectric layer for optical energy transfer. We study the strength of the light-matter coupling at the vibrational absorption frequency of silica at 1240 cm-1 through the analysis of the experimental Fano lineshape that is benchmarked against identical structures made of bulk gold. The boost in the optical energy transfer from free-space mid-infrared radiation to molecular vibrations in nanoporous 3D nanoantenna arrays can open new application routes for plasmon-enhanced physical-chemical reactions.

  6. Single particle tracking and single molecule energy transfer

    CERN Document Server

    Bräuchle, Christoph; Michaelis, Jens

    2009-01-01

    Closing a gap in the literature, this handbook gathers all the information on single particle tracking and single molecule energy transfer. It covers all aspects of this hot and modern topic, from detecting virus entry to membrane diffusion, and from protein folding using spFRET to coupled dye systems, as well recent achievements in the field. Throughout, the first-class editors and top international authors present content of the highest quality, making this a must-have for physical chemists, spectroscopists, molecular physicists and biochemists.

  7. Cell Microtubules as Cavities Quantum Coherence and Energy Transfer?

    CERN Document Server

    Mavromatos, Nikolaos E

    2000-01-01

    A model is presented for dissipationless energy transfer in cell microtubules due to quantum coherent states. The model is based on conjectured (hydrated) ferroelectric properties of microtubular arrangements. Ferroelectricity is essential in providing the necessary isolation against thermal losses in thin interior regions, full of ordered water, near the tubulin dimer walls of the microtubule. These play the role of cavity regions, which are similar to electromagnetic cavities of quantum optics. As a result, the formation of (macroscopic) quantum coherent states of electric dipoles on the tubulin dimers may occur. Some experiments, inspired by quantum optics, are suggested for the falsification of this scenario.

  8. Nanoparticles for heat transfer and thermal energy storage

    Science.gov (United States)

    Singh, Dileep; Cingarapu, Sreeram; Timofeeva, Elena V.; Moravek, Michael

    2015-07-14

    An article of manufacture and method of preparation thereof. The article of manufacture and method of making the article includes an eutectic salt solution suspensions and a plurality of nanocrystalline phase change material particles having a coating disposed thereon and the particles capable of undergoing the phase change which provides increase in thermal energy storage. In addition, other articles of manufacture can include a nanofluid additive comprised of nanometer-sized particles consisting of copper decorated graphene particles that provide advanced thermal conductivity to heat transfer fluids.

  9. Nonlinear resonances and energy transfer in finite granular chains.

    Science.gov (United States)

    Lydon, Joseph; Theocharis, Georgios; Daraio, Chiara

    2015-02-01

    In the present work we test experimentally and compute numerically the stability and dynamics of harmonically driven monoatomic granular chains composed of an increasing number of particles N(N=1-50). In particular, we investigate the inherent effects of dissipation and finite size on the evolution of bifurcation instabilities in the statically compressed case. The findings of the study suggest that the nonlinear bifurcation phenomena, which arise due to finite size, can be useful for efficient energy transfer away from the drive frequency in transmitted waves.

  10. Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells

    Directory of Open Access Journals (Sweden)

    Stoichko D. Dimitrov

    2016-01-01

    Full Text Available The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.

  11. Singlet Exciton Lifetimes in Conjugated Polymer Films for Organic Solar Cells

    KAUST Repository

    Dimitrov, Stoichko

    2016-01-13

    The lifetime of singlet excitons in conjugated polymer films is a key factor taken into account during organic solar cell device optimization. It determines the singlet exciton diffusion lengths in polymer films and has a direct impact on the photocurrent generation by organic solar cell devices. However, very little is known about the material properties controlling the lifetimes of singlet excitons, with most of our knowledge originating from studies of small organic molecules. Herein, we provide a brief summary of the nature of the excited states in conjugated polymer films and then present an analysis of the singlet exciton lifetimes of 16 semiconducting polymers. The exciton lifetimes of seven of the studied polymers were measured using ultrafast transient absorption spectroscopy and compared to the lifetimes of seven of the most common photoactive polymers found in the literature. A plot of the logarithm of the rate of exciton decay vs. the polymer optical bandgap reveals a medium correlation between lifetime and bandgap, thus suggesting that the Energy Gap Law may be valid for these systems. This therefore suggests that small bandgap polymers can suffer from short exciton lifetimes, which may limit their performance in organic solar cell devices. In addition, the impact of film crystallinity on the exciton lifetime was assessed for a small bandgap diketopyrrolopyrrole co-polymer. It is observed that the increase of polymer film crystallinity leads to reduction in exciton lifetime and optical bandgap again in agreement with the Energy Gap Law.

  12. Power Loss Analysis and Comparison of Segmented and Unsegmented Energy Coupling Coils for Wireless Energy Transfer.

    Science.gov (United States)

    Tang, Sai Chun; McDannold, Nathan J

    2015-03-01

    This paper investigated the power losses of unsegmented and segmented energy coupling coils for wireless energy transfer. Four 30-cm energy coupling coils with different winding separations, conductor cross-sectional areas, and number of turns were developed. The four coils were tested in both unsegmented and segmented configurations. The winding conduction and intrawinding dielectric losses of the coils were evaluated individually based on a well-established lumped circuit model. We found that the intrawinding dielectric loss can be as much as seven times higher than the winding conduction loss at 6.78 MHz when the unsegmented coil is tightly wound. The dielectric loss of an unsegmented coil can be reduced by increasing the winding separation or reducing the number of turns, but the power transfer capability is reduced because of the reduced magnetomotive force. Coil segmentation using resonant capacitors has recently been proposed to significantly reduce the operating voltage of a coil to a safe level in wireless energy transfer for medical implants. Here, we found that it can naturally eliminate the dielectric loss. The coil segmentation method and the power loss analysis used in this paper could be applied to the transmitting, receiving, and resonant coils in two- and four-coil energy transfer systems.

  13. Editorial on indirect excitons: Physics and applications

    Science.gov (United States)

    2017-08-01

    This special issue contains 9 original review papers, research papers and discussion papers on indirect excitons. An exciton is a Coulomb-correlated electron-hole pair. Frenkel excitons dominate optical properties of organic semiconductors, while Wannier-Mott excitons are responsible for the hydrogen-like absorption spectra of inorganic semiconductors at low temperatures. The interest to the physics of excitons has strongly increased in the new century. This interest is motivated by unique bosonic properties of excitons that lead to the phenomena of exciton-polariton lasing and stimulated scattering, build-up of the spontaneous coherence and polarisation in cold exciton gases. In addition to the rich fundamental physics, excitons offer the perspective of applications in opto-electronic devices such as exciton transistors, switches, optical integrated circuits, etc.

  14. Quantum simulator of an open quantum system using superconducting qubits: exciton transport in photosynthetic complexes

    Science.gov (United States)

    Mostame, Sarah; Rebentrost, Patrick; Eisfeld, Alexander; Kerman, Andrew J.; Tsomokos, Dimitris I.; Aspuru-Guzik, Alan

    2012-02-01

    In the initial stage of photosynthesis, light-harvested energy is transferred with remarkably high efficiency to a reaction center, with the vibrational environment assisting the transport mechanism. It is of great interest to mimic this process with present-day technologies. Here we propose an analog quantum simulator of open system dynamics, where noise engineering of the environment has a central role. In particular, we propose the use of superconducting qubits for the simulation of exciton transport in the Fenna-Matthew-Olson protein, a prototypical photosynthetic complex. Our method allows for a single-molecule implementation and the investigation of energy transfer pathways as well as non-Markovian and spatiotemporal noise-correlation effects.

  15. Crossed-beam energy transfer in direct-drive implosions

    Energy Technology Data Exchange (ETDEWEB)

    Seka, W; Edgell, D H; Michel, D T; Froula, D H; Goncharov, V N; Craxton, R S; Divol, L; Epstein, R; Follett, R; Kelly, J H; Kosc, T Z; Maximov, A V; McCrory, R L; Meyerhofer, D D; Michel, P; Myatt, J F; Sangster, T C; Shvydky, A; Skupsky, S

    2012-05-22

    Direct-drive-implosion experiments on the OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] have showed discrepancies between simulations of the scattered (non-absorbed) light levels and measured ones that indicate the presence of a mechanism that reduces laser coupling efficiency by 10%-20%. This appears to be due to crossed-beam energy transfer (CBET) that involves electromagnetic-seeded, low-gain stimulated Brillouin scattering. CBET scatters energy from the central portion of the incoming light beam to outgoing light, reducing the laser absorption and hydrodynamic efficiency of implosions. One-dimensional hydrodynamic simulations including CBET show good agreement with all observables in implosion experiments on OMEGA. Three strategies to mitigate CBET and improve laser coupling are considered: the use of narrow beams, multicolor lasers, and higher-Z ablators. Experiments on OMEGA using narrow beams have demonstrated improvements in implosion performance.

  16. Crossed-beam energy transfer in direct-drive implosions

    Energy Technology Data Exchange (ETDEWEB)

    Igumenshchev, I. V.; Seka, W.; Edgell, D. H.; Michel, D. T.; Froula, D. H.; Craxton, R. S.; Epstein, R.; Follett, R.; Kelly, J. H.; Kosc, T. Z.; Myatt, J. F.; Sangster, T. C.; Shvydky, A.; Skupsky, S.; Stoeckl, C. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623-1299 (United States); Goncharov, V. N.; Maximov, A. V. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623-1299 (United States); Department of Mechanical Engineering, University of Rochester, Rochester, New York 14623 (United States); Divol, L.; Michel, P. [Lawrence Livermore National Laboratory, Livermore, California 94551 (United States); McCrory, R. L. [Laboratory for Laser Energetics, University of Rochester, 250 East River Road, Rochester, New York 14623-1299 (United States); Department of Mechanical Engineering, University of Rochester, Rochester, New York 14623 (United States); Department of Physics and Astronomy, University of Rochester, Rochester, New York 14623 (United States); and others

    2012-05-15

    Direct-drive-implosion experiments on the OMEGA laser [T. R. Boehly et al., Opt. Commun. 133, 495 (1997)] have showed discrepancies between simulations of the scattered (non-absorbed) light levels and measured ones that indicate the presence of a mechanism that reduces laser coupling efficiency by 10%-20%. This appears to be due to crossed-beam energy transfer (CBET) that involves electromagnetic-seeded, low-gain stimulated Brillouin scattering. CBET scatters energy from the central portion of the incoming light beam to outgoing light, reducing the laser absorption and hydrodynamic efficiency of implosions. One-dimensional hydrodynamic simulations including CBET show good agreement with all observables in implosion experiments on OMEGA. Three strategies to mitigate CBET and improve laser coupling are considered: the use of narrow beams, multicolor lasers, and higher-Z ablators. Experiments on OMEGA using narrow beams have demonstrated improvements in implosion performance.

  17. Exciton localization-delocalization transition in an extended dendrimer

    Energy Technology Data Exchange (ETDEWEB)

    Pouthier, Vincent, E-mail: vincent.pouthier@univ-fcomte.fr [Institut UTINAM, Université de Franche-Comté, CNRS UMR 6213, 25030 Besançon Cedex (France)

    2013-12-21

    Exciton-mediated quantum state transfer between the periphery and the core of an extended dendrimer is investigated numerically. By mapping the dynamics onto that of a linear chain, it is shown that a localization-delocalization transition arises for a critical value of the generation number G{sub c} ≈ 5. This transition originates in the quantum interferences experienced by the excitonic wave due to the multiple scatterings that arise each time the wave tunnels from one generation to another. These results suggest that only small-size dendrimers could be used for designing an efficient quantum communication protocol.

  18. Effect of high linear energy transfer radiation on biological membranes

    Energy Technology Data Exchange (ETDEWEB)

    Choudhary, D.; Srivastava, M.; Kale, R.K. [Radiation Biology Lab., Jawaharlal Nehru Univ., New Delhi (India); Sarma, A. [Nuclear Science Centre, New Delhi (India)

    1998-10-01

    Cellular membranes are vital elements, and their integrity is extremely essential for the viability of the cells. We studied the effects of high linear energy transfer (LET) radiation on the membranes. Rabbit erythrocytes (1 x 10{sup 7} cells/ml) and microsomes (0.6 mg protein/ml) prepared from liver of rats were irradiated with {sup 7}Li ions of energy 6.42 MeV/u and {sup 16}O ions of energy 4.25 MeV/u having maximum LET values of 354 keV/{mu}m and 1130 keV/{mu}m, respectively. {sup 7}Li- and {sup 16}O-induced microsomal lipid peroxidation was found to increase with fluence. The {sup 16}O ions were more effective than {sup 7}Li ions, which could be due to the denser energy distribution in the track and the yield of free radicals. These findings suggested that the biological membranes could be peroxidized on exposure to high-LET radiation. Inhibition of the lipid peroxidation was observed in the presence of a membrane-active drug, chlorpromazine (CPZ), which could be due to scavenging of free radicals (mainly HO. and ROO.), electron donation, and hydrogen transfer reactions. The {sup 7}Li and {sup 16}O ions also induced hemolysis in erythrocytes. The extent of hemolysis was found to be a function of time and fluence, and showed a characteristic sigmoidal pattern. The {sup 16}O ions were more effective in the lower fluence range than {sup 7}Li ions. These results were compared with lipid peroxidation and hemolysis induced by gamma-radiation. (orig.) With 7 figs., 3 tabs., 30 refs.

  19. Light harvesting via energy transfer in the dye solar cell

    Energy Technology Data Exchange (ETDEWEB)

    Siegers, Conrad

    2007-11-09

    The PhD-thesis ''Light Harvesting via Energy Transfer in the Dye Solar Cell'' (University of Freiburg, July 2007) describes the conceptual design, synthesis and testing of energy donor acceptor sensitizers for the dye solar cell (DSC). Under monochromatic illumination solar cells sensitized with the novel donor acceptor systems revealed a higher power conversion efficiency than cells containing exclusively the acceptor component. The following approach led to this conclusion: (i) the choice of suitable chromophores as energy donor and acceptor moieties according to the Foerster-theory, (ii) the synthesis of different donor acceptor systems, (iii) the development of a methodology allowing the quantification of energy transfer within dye solar cells, and (iv) the evaluation of characteristics of DSCs that were sensitized with the different donor acceptor systems. The acceptor chromophores used in this work were derived from [Ru(dcbpy)2acac]Cl (dcbpy = 4,4'-dicarboxy-2,2'-bipyridin, acac = acetylacetonato). This complex offered the opportunity to introduce substituents at the acac-ligand's terminal CH3 groups without significantly affecting its excellent photoelectrochemical properties. Alkylated 4-amino-1,8-naphthalimides (termed Fluorols in the following) were used as energy donor chromophores. This class of compounds fulfils the requirements for efficient energy transfer to [Ru(dcbpy)2acac]Cl. Covalently linking donor and acceptor chromophores to one another was achieved by two different concepts. A dyad comprising one donor and one acceptor chromophore was synthesized by subsequent hydrosilylation steps of an olefin-bearing donor and an acceptor precursor to the dihydrosilane HSiMe2-CH2CH2-SiMe2H. A series of polymers comprising multiple donor and acceptor units was made by the addition of alkyne-bearing chromophores to hyperbranched polyglycerol azide (''Click-chemistry''). In this series the donor acceptor

  20. Heat transfer and energy efficiency in infrared paper dryers

    Energy Technology Data Exchange (ETDEWEB)

    Pettersson, Magnus

    1999-11-01

    Infrared (IR) dryers are widely used in the paper industry, mainly in the production of coated paper grades. The thesis deals with various aspects of heat transfer and energy use in infrared heaters and dryers as employed in the paper industry. Both gas-fired and electric IR dryers are considered and compared. The thesis also provides an introduction to infrared heaters and infrared drying, including a review of recent literature in the field. The transport of thermal radiation inside a paper sheet was investigated and different IR dryers were compared in terms of their ability to transfer energy to the internal parts of a paper sheet. Although there were evident differences in the absorption of radiation between gas-fired and electric IR dryers, the distinction was found not to be as important as has generally been believed. The main differences appeared to be due to the choice of a one- or a two-sided dryer solution, rather than the spectral distributions emitted by the dryers. A method for evaluating the radiation efficiency of IR heaters was proposed. An electric IR heater was evaluated in the laboratory. The radiation efficiency of the heater was shown to be strongly dependent on the power level. The maximum efficiency, found at high power level, was close to 60 %. A procedure for evaluation of the total energy transfer efficiency of an infrared paper dryer was proposed and used in the evaluation of an electric IR dryer operating in an industrial coating machine. The efficiency of the dryer was roughly 40 %. A model for an electric IR heater was developed. The model includes non-grey radiative heat transfer between the different parts of the heater, as well as conduction in reflector material and convective cooling of the surfaces. Using IR module voltage as the only input, model predictions of temperatures and heat flux were found to agree well with experimental data both at steady state and under transient conditions. The model was also extended to include

  1. Energy transfer from lower energy to higher-energy electrons mediated by whistler waves in the radiation belts

    Science.gov (United States)

    Shklyar, D. R.

    2017-01-01

    We study the problem of energy exchange between waves and particles, which leads to energization of the latter, in an unstable plasma typical of the radiation belts. The ongoing Van Allen Probes space mission brought this problem among the most discussed in space physics. A free energy which is present in an unstable plasma provides the indispensable condition for energy transfer from lower energy particles to higher-energy particles via resonant wave-particle interaction. This process is studied in detail by the example of electron interactions with whistler mode wave packets originated from lightning-induced emission. We emphasize that in an unstable plasma, the energy source for electron energization is the energy of other particles, rather than the wave energy as is often assumed. The way by which the energy is transferred from lower energy to higher-energy particles includes two processes that operate concurrently, in the same space-time domain, or sequentially, in different space-time domains, in which a given wave packet is located. In the first process, one group of resonant particles gives the energy to the wave. The second process consists in wave absorption by another group of resonant particles, whose energy therefore increases. We argue that this mechanism represents an efficient means of electron energization in the radiation belts.

  2. Excitons in InP/InAs inhomogeneous quantum dots

    CERN Document Server

    Assaid, E; Khamkhami, J E; Dujardin, F

    2003-01-01

    Wannier excitons confined in an InP/InAs inhomogeneous quantum dot (IQD) have been studied theoretically in the framework of the effective mass approximation. A finite-depth potential well has been used to describe the effect of the quantum confinement in the InAs layer. The exciton binding energy has been determined using the Ritz variational method. The spatial correlation between the electron and the hole has been taken into account in the expression for the wavefunction. It has been shown that for a fixed size b of the IQD, the exciton binding energy depends strongly on the core radius a. Moreover, it became apparent that there are two critical values of the core radius, a sub c sub r sub i sub t and a sub 2 sub D , for which important changes of the exciton binding occur. The former critical value, a sub c sub r sub i sub t , corresponds to a minimum of the exciton binding energy and may be used to distinguish between tridimensional confinement and bidimensional confinement. The latter critical value, a ...

  3. Enhanced efficiency in single-host white organic light-emitting diode by triplet exciton conversion

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Qingyang, E-mail: wqy1527@163.com [State Key laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012 (China); Zhang, Shiming [State Key laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012 (China); Département of Chemical Engineering, École Polytechnique de Montréal, Montréal, Québec, Canada H3C3J7 (Canada); Yue, Shouzhen; Zhang, Zhensong [State Key laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012 (China); Xie, Guohua [Institut für Angewandte Photophysik, Technische Universtität Dresden, Dresden 01062 (Germany); Zhao, Yi; Liu, Shiyong [State Key laboratory on Integrated Optoelectronics, College of Electronic Science and Engineering, Jilin University, Changchun 130012 (China)

    2013-11-15

    The authors observe that the external quantum efficiency (EQE) of the Iridium (III) bis(4-phenylthieno [3,2-c]pyridinato-N,C{sup 2′})acetylacetonate (PO-01) based yellow organic light-emitting diode (OLED) is significantly increased by uniformly co-doping Iridium (III)bis[(4,6-difluorophenyl)-pyridinato-N,C{sup 2−}] (FIrpic) and PO-01 into the same wide band-gap host of N,N{sup ′}-dicarbazolyl-3, 5-benzene (mCP). Detailed investigation indicates that the efficiency enhancement is ascribed to effective triplet exciton gathering by FIrpic, followed by energy transfer to PO-01. Compared to the control device, which has maximum EQE of 10.5%, an improved maximum EQE of 13.2% is obtained in the optimization white device based on FIrpic and PO-01 emission according to this principle. This work makes it easier for a single host white OLED to simultaneously harvest high efficiency in both blue and yellow units. Comprehensive experimental results show that this phenomenon can also be found and utilized in other popular hosts to realize more efficient white devices. -- Highlights: • This work makes easier for a single host white OLED to harvest high efficiency in both blue and yellow units. • Efficiency enhancement is ascribed to effective triplet exciton gathering by FIrpic, followed by energy transfer to PO-01. • This phenomenon can also be found and utilized in other popular hosts to realize more efficient white devices.

  4. Dephasing and interaction of excitons CdSe/ZnSe islands

    DEFF Research Database (Denmark)

    Wagner, H. P.; Tranitz, H.-P.; Preis, H.

    2000-01-01

    The dephasing of excitons in self-organized CdSe/ZnSe islands grown by molecular-beam epitaxy is investigated using spectrally resolved four-wave mixing. A distribution of dephasing times is observed, indicating the existence of localized excitons with different relaxation times at comparable tra...... transition energies. Polarization-dependent measurements identify the formation of biexcitons. The observed large biexciton binding energy of 22meV increases with decreasing exciton energy, which is attributed to an increasing three-dimensional confinement.......The dephasing of excitons in self-organized CdSe/ZnSe islands grown by molecular-beam epitaxy is investigated using spectrally resolved four-wave mixing. A distribution of dephasing times is observed, indicating the existence of localized excitons with different relaxation times at comparable...

  5. Excitons in semiconducting quantum filaments of CdS and CdSe with dielectric barriers

    CERN Document Server

    Dneprovskij, V S; Shalygina, O A; Lyaskovskij, V L; Mulyarov, E A; Gavrilov, S A; Masumoto, I

    2002-01-01

    The peculiarities of the luminescence spectra obtained by different polarization and intensity of the pumping excitation and luminescence kinetics of the CdS and CdSe nanocrystals are explained by the exciton transitions in the semiconducting quantum threads with dielectric barriers. The exciton transition energies correspond to the calculated ones with an account of both their dimensional quantization and the effect of the excitons dielectric intensification. It is shown that the excitons transition energies do not change by the change in the quantum threads diameter within the wide range, while the increase in the one-dimensional forbidden zone width of quantum thread by the decrease in its diameter is compensated through the decrease in the excitons binding energy

  6. Thermal effects in exciton harvesting in biased one-dimensional systems

    NARCIS (Netherlands)

    Vlaming, S. M.; Malyshev, V.A.; Knoester, J.

    2008-01-01

    The study of energy harvesting in chain-like structures is important due to its relevance to a variety of interesting physical systems. Harvesting is understood as the combination of exciton transport through intra-band exciton relaxation (via scattering on phonon modes) and subsequent quenching by

  7. Supersonic exciton gratings: coherent inter-polariton scattering in semiconductor microcavities

    DEFF Research Database (Denmark)

    Birkedal, Dan; Vadim, Lyssenko; Hvam, Jørn Märcher

    2002-01-01

    We report on a coherent nonlinear phenomenon in a semiconductor microcavity (SMC), which has no parallel for QW excitons. When two different polariton modes of the SMC are impulsively excited they undergo normal mode oscillations (NMOs) with coherent energy exchange between the exciton and the ca...

  8. Subdiffusive exciton motion in systems with heavy-tailed disorder

    NARCIS (Netherlands)

    Vlaming, S. M.; Malyshev, V.A.; Eisfeld, A.; Knoester, J.

    2013-01-01

    We study the transport of collective excitations (Frenkel excitons) in systems with static disorder in the transition energies, not limiting ourselves to Gaussian transition energy distributions. Instead, we generalize this model to the wider class of Levy stable distributions, characterized by

  9. Carbon nanotubes as excitonic insulators.

    Science.gov (United States)

    Varsano, Daniele; Sorella, Sandro; Sangalli, Davide; Barborini, Matteo; Corni, Stefano; Molinari, Elisa; Rontani, Massimo

    2017-11-13

    Fifty years ago Walter Kohn speculated that a zero-gap semiconductor might be unstable against the spontaneous generation of excitons-electron-hole pairs bound together by Coulomb attraction. The reconstructed ground state would then open a gap breaking the symmetry of the underlying lattice, a genuine consequence of electronic correlations. Here we show that this excitonic insulator is realized in zero-gap carbon nanotubes by performing first-principles calculations through many-body perturbation theory as well as quantum Monte Carlo. The excitonic order modulates the charge between the two carbon sublattices opening an experimentally observable gap, which scales as the inverse of the tube radius and weakly depends on the axial magnetic field. Our findings call into question the Luttinger liquid paradigm for nanotubes and provide tests to experimentally discriminate between excitonic and Mott insulators.

  10. Angular momentum transport with twisted exciton wave packets

    Science.gov (United States)

    Zang, Xiaoning; Lusk, Mark T.

    2017-10-01

    A chain of cofacial molecules with CN or CN h symmetry supports excitonic states with a screwlike structure. These can be quantified with the combination of an axial wave number and an azimuthal winding number. Combinations of these states can be used to construct excitonic wave packets that spiral down the chain with well-determined linear and angular momenta. These twisted exciton wave packets can be created and annihilated using laser pulses, and their angular momentum can be optically modified during transit. This allows for the creation of optoexcitonic circuits in which information, encoded in the angular momentum of light, is converted into excitonic wave packets that can be manipulated, transported, and then reemitted. A tight-binding paradigm is used to demonstrate the key ideas. The approach is then extended to quantify the evolution of twisted exciton wave packets in a many-body, multilevel time-domain density functional theory setting. In both settings, numerical methods are developed that allow the site-to-site transfer of angular momentum to be quantified.

  11. Realization of an all optical exciton-polariton router

    Energy Technology Data Exchange (ETDEWEB)

    Marsault, Félix; Nguyen, Hai Son; Tanese, Dimitrii; Lemaître, Aristide; Galopin, Elisabeth; Sagnes, Isabelle; Amo, Alberto [Laboratoire de Photonique et de Nanostructures, LPN/CNRS, Route de Nozay, 91460 Marcoussis (France); Bloch, Jacqueline, E-mail: jacqueline.bloch@lpn.cnrs.fr [Laboratoire de Photonique et de Nanostructures, LPN/CNRS, Route de Nozay, 91460 Marcoussis (France); Physics Department, Ecole Polytechnique, F-91128 Palaiseau Cedex (France)

    2015-11-16

    We report on the experimental realization of an all optical router for exciton-polaritons. This device is based on the design proposed by Flayac and Savenko [Appl. Phys. Lett. 103, 201105 (2013)], in which a zero-dimensional island is connected through tunnel barriers to two periodically modulated wires of different periods. Selective transmission of polaritons injected in the island, into either of the two wires, is achieved by tuning the energy of the island state across the band structure of the modulated wires. We demonstrate routing of ps polariton pulses using an optical control beam which controls the energy of the island quantum states, thanks to polariton-exciton interactions.

  12. Photophysical properties and energy transfer mechanism of PFO/Fluorol 7GA hybrid thin films

    Energy Technology Data Exchange (ETDEWEB)

    Al-Asbahi, Bandar Ali, E-mail: alasbahibandar@gmail.com [School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor (Malaysia); Department of Physics, Faculty of Science, Sana' a University (Yemen); Jumali, Mohammad Hafizuddin Haji, E-mail: hafizhj@ukm.my [School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor (Malaysia); Yap, Chi Chin; Flaifel, Moayad Husein [School of Applied Physics, Faculty of Science and Technology, Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor (Malaysia); Salleh, Muhamad Mat [Institute of Microengineering and Nanoelectronics (IMEN), Universiti Kebangsaan Malaysia (UKM), 43600 Bangi, Selangor (Malaysia)

    2013-10-15

    Photophysical properties of poly (9,9′-di-n-octylfluorenyl-2.7-diyl) (PFO)/2-butyl-6- (butylamino)benzo [de] isoquinoline-1,3-dione (Fluorol 7GA) and energy transfer between them have been investigated. In this work, both PFO and Fluorol 7GA act as donor and acceptor, respectively. Based on the absorption and luminescence measurements, the photophysical and energy transfer properties such as fluorescence quantum yield (Φ{sub f}), fluorescence lifetime (τ), radiative rate constant (k{sub r}), non-radiative rate constant (k{sub nr}), quenching rate constant (k{sub SV}), energy transfer rate constant (k{sub ET}), energy transfer probability (P{sub DA}), energy transfer efficiency (η), critical concentration of acceptor (C{sub o}), energy transfer time (τ{sub ET}) and critical distance of energy transfer (R{sub o}) were calculated. Large values of k{sub SV}, k{sub ET} and R{sub o} suggested that Förster-type energy transfer was the dominant mechanism for the energy transfer between the excited donor and ground state acceptor molecules. It was observed that the Förster energy transfer together with the trapping process are crucial for performance improvement in ITO/(PFO/Fluorol7GA)/Al device. -- Highlights: • The efficient of energy transfer from PFO to Fluorol 7GA was evidenced. • The resonance energy transfer (Förster type) is the dominant mechanism. • Hsu et al. model was used to calculate Φ{sub f}, τ, k{sub r} and k{sub nr} of PFO thin film. • Several of the photophysical and energy transfer properties were calculated. • Trapping process and Förster energy transfer led to improve the device performance.

  13. Excitonic optical response of carbon chains confined in single-walled carbon nanotubes

    Science.gov (United States)

    Bonabi, Farzad; Brun, Søren J.; Pedersen, Thomas G.

    2017-10-01

    It has been recently shown that long linear carbon chains (carbyne) can be formed inside multiwalled carbon nanotubes (CNTs). Encapsulation of carbyne inside the CNT affects the electronic structure of the chain by the long-range Coulomb interaction. This introduces an indirect band gap in the combined CNT-chain system and results in a change in the optical band gap. We study the excitonic optical response of the combined system using the Bethe-Salpeter and Wannier equations based on density functional theory and tight-binding band structures. The optical properties of isolated CNTs and chains are strongly affected by excitonic effects and the CNT-chain system follows a similar trend. The interaction between the CNT and chain results in new bright excitons as well as charge transfer excitons, where electrons are localized on the CNT and holes on the chain, yielding new dark excitons in the combined system.

  14. Phonon-assisted absorption of excitons in Cu2O

    Science.gov (United States)

    Schöne, Florian; Stolz, Heinrich; Naka, Nobuko

    2017-09-01

    The basic theoretical foundation for the modeling of phonon-assisted absorption spectra in direct band-gap semiconductors, introduced by Elliott 60 years ago [R. J. Elliott, Phys. Rev. 108, 1384 (1957), 10.1103/PhysRev.108.1384] using second order perturbation theory, results in a square root shaped dependency close to the absorption edge. A careful analysis of the experiments [N. Naka et al., Jpn. J. Appl. Phys. 44, 5096 (2005), 10.1143/JJAP.44.5096] reveals that for the yellow S excitons in Cu2O the lineshape does not follow that square root dependence. The reexamination of the theory shows that the basic assumptions of constant matrix elements and constant energy denominators is invalid for semiconductors with dominant exciton effects like Cu2O , where the phonon-assisted absorption proceeds via intermediate exciton states. The overlap between these and the final exciton states strongly determines the dependence of the absorption on the photon energy. To describe the experimental observed line shape of the indirect absorption of the yellow S exciton states we find it necessary to assume a momentum dependent deformation potential for the optical phonons.

  15. Hot exciton cooling and multiple exciton generation in PbSe quantum dots.

    Science.gov (United States)

    Kumar, Manoj; Vezzoli, Stefano; Wang, Zilong; Chaudhary, Varun; Ramanujan, Raju V; Gurzadyan, Gagik G; Bruno, Annalisa; Soci, Cesare

    2016-11-16

    Multiple exciton generation (MEG) is a promising process to improve the power conversion efficiency of solar cells. PbSe quantum dots (QDs) have shown reasonably high MEG quantum yield (QY), although the photon energy threshold for this process is still under debate. One of the reasons for this inconsistency is the complicated competition of MEG and hot exciton cooling, especially at higher excited states. Here, we investigate MEG QY and the origin of the photon energy threshold for MEG in PbSe QDs of three different sizes by studying the transient absorption (TA) spectra, both at the band gap (near infrared, NIR) and far from the band gap energy (visible range). The comparison of visible TA spectra and dynamics for different pump wavelengths, below, around and above the MEG threshold, provides evidence of the role of the Σ transition in slowing down the exciton cooling process that can help MEG to take over the phonon relaxation process. The universality of this behavior is confirmed by studying QDs of three different sizes. Moreover, our results suggest that MEG QY can be determined by pump-probe experiments probed above the band gap.

  16. Optimal dephasing for ballistic energy transfer in disordered linear chains

    Science.gov (United States)

    Zhang, Yang; Celardo, G. Luca; Borgonovi, Fausto; Kaplan, Lev

    2017-11-01

    We study the interplay between dephasing, disorder, and coupling to a sink on transport efficiency in a one-dimensional chain of finite length N , and in particular the beneficial or detrimental effect of dephasing on transport. The excitation moves along the chain by coherent nearest-neighbor hopping Ω , under the action of static disorder W and dephasing γ . The last site is coupled to an external acceptor system (sink), where the excitation can be trapped with a rate Γtrap. While it is known that dephasing can help transport in the localized regime, here we show that dephasing can enhance energy transfer even in the ballistic regime. Specifically, in the localized regime we recover previous results, where the optimal dephasing is independent of the chain length and proportional to W or W2/Ω . In the ballistic regime, the optimal dephasing decreases as 1 /N or 1 /√{N } , respectively, for weak and moderate static disorder. When focusing on the excitation starting at the beginning of the chain, dephasing can help excitation transfer only above a critical value of disorder Wcr, which strongly depends on the sink coupling strength Γtrap. Analytic solutions are obtained for short chains.

  17. Unravelling radiative energy transfer in solid-state lighting

    Science.gov (United States)

    Melikov, Rustamzhon; Press, Daniel Aaron; Ganesh Kumar, Baskaran; Sadeghi, Sadra; Nizamoglu, Sedat

    2018-01-01

    Today, a wide variety of organic and inorganic luminescent materials (e.g., phosphors, quantum dots, etc.) are being used for lighting and new materials (e.g., graphene, perovskite, etc.) are currently under investigation. However, the understanding of radiative energy transfer is limited, even though it is critical to understand and improve the performance levels of solid-state lighting devices. In this study, we derived a matrix approach that includes absorption, reabsorption, inter-absorption and their iterative and combinatorial interactions for one and multiple types of fluorophores, which is simplified to an analytical matrix. This mathematical approach gives results that agree well with the measured spectral and efficiency characteristics of color-conversion light-emitting diodes. Moreover, it also provides a deep physical insight by uncovering the entire radiative interactions and their contribution to the output optical spectrum. The model is universal and applicable for all kinds of fluorophores.

  18. Variety in excitation energy transfer processes from phycobilisomes to photosystems I and II.

    Science.gov (United States)

    Ueno, Yoshifumi; Aikawa, Shimpei; Niwa, Kyosuke; Abe, Tomoko; Murakami, Akio; Kondo, Akihiko; Akimoto, Seiji

    2017-09-01

    The light-harvesting antennas of oxygenic photosynthetic organisms capture light energy and transfer it to the reaction centers of their photosystems. The light-harvesting antennas of cyanobacteria and red algae, called phycobilisomes (PBSs), supply light energy to both photosystem I (PSI) and photosystem II (PSII). However, the excitation energy transfer processes from PBS to PSI and PSII are not understood in detail. In the present study, the energy transfer processes from PBS to PSs in various cyanobacteria and red algae were examined in vivo by selectively exciting their PSs or PBSs, and measuring the resulting picosecond to nanosecond time-resolved fluorescences. By observing the delayed fluorescence spectrum of PBS-selective excitation in Arthrospira platensis, we demonstrated that energy transfer from PBS to PSI via PSII (PBS→PSII→PSI transfer) occurs even for PSI trimers. The contribution of PBS→PSII→PSI transfer was species dependent, being largest in the wild-type of red alga Pyropia yezoensis (formerly Porphyra yezoensis) and smallest in Synechococcus sp. PCC 7002. Comparing the time-resolved fluorescence after PSs- and PBS-selective excitation, we revealed that light energy flows from CP43 to CP47 by energy transfer between the neighboring PSII monomers in PBS-PSII supercomplexes. We also suggest two pathways of energy transfer: direct energy transfer from PBS to PSI (PBS→PSI transfer) and indirect transfer through PSII (PBS→PSII→PSI transfer). We also infer that PBS→PSI transfer conveys light energy to a lower-energy red chlorophyll than PBS→PSII→PSI transfer.

  19. Plasmonic, excitonic and exciton-plasmonic photoinduced nanocomposites

    Science.gov (United States)

    Bityurin, N.; Ermolaev, N.; Smirnov, A. A.; Afanasiev, A.; Agareva, N.; Koryukina, T.; Bredikhin, V.; Kamensky, V.; Pikulin, A.; Sapogova, N.

    2016-03-01

    UV irradiation of materials consisting of a polymer matrix that possesses precursors of different kinds can result in creation of nanoparticles within the irradiated domains. Such photoinduced nanocomposites are promising for photonic applications due to the strong alteration of their optical properties compared to initial non-irradiated materials. We report our results on the synthesis and investigation of plasmonic, excitonic and exciton-plasmonic photoinduced nanocomposites. Plasmonic nanocomposites contain metal nanoparticles of noble metals with a pronounced plasmon resonance. Excitonic nanocomposites possess semiconductor nanoclusters (quantum dots). We consider the CdS-Au pair because the luminescent band of CdS nanoparticles enters the plasmon resonance band of gold nanoparticles. The obtaining of such particles within the same composite materials is promising for the creation of media with exciton-plasmon resonance. We demonstrate that it is possible to choose appropriate precursor species to obtain the initially transparent poly(methyl methacrylate) (PMMA) films containing both types of these molecules either separately or together. Proper irradiation of these materials by a light-emitting diode operating at the wavelength of 365 nm provides material alteration demonstrating light-induced optical absorption and photoluminescent properties typical for the corresponding nanoparticles. Thus, an exciton-plasmonic photoinduced nanocomposite is obtained. It is important that here we use the precursors that are different from those usually employed.

  20. Incident energy transfer equation and its solution by collocation spectral method for one-dimensional radiative heat transfer

    Science.gov (United States)

    Hu, Zhang-Mao; Tian, Hong; Li, Ben-Wen; Zhang, Wei; Yin, Yan-Shan; Ruan, Min; Chen, Dong-Lin

    2017-10-01

    The ray-effect is a major discretization error in the approximate solution method for the radiative transfer equation (RTE). To overcome this problem, the incident energy transfer equation (IETE) is proposed. The incident energy, instead of radiation intensity, is obtained by directly solving this new equation. Good numerical properties are found for the incident energy transfer equation. To show the properties of numerical solution, the collocation spectral method (CSM) is employed to solve the incident energy transfer equation. Three test cases are taken into account to verify the performance of the incident energy transfer equation. The result shows that the radiative heat flux obtained based on IETE is much more accurate than that based on RTE, which means that the IETE is very effective in eliminating the impacts of ray-effect on the heat flux. However, on the contrary, the radiative intensity obtained based on IETE is less accurate than that based on RTE due to the ray-effect. So, this equation is more suitable for those radiative heat transfer problems, in which the radiation heat flux and incident energy are needed rather than the radiation intensity.

  1. Bose-Einstein condensation and superfluidity of dipolar excitons in a phosphorene double layer

    Science.gov (United States)

    Berman, Oleg L.; Gumbs, Godfrey; Kezerashvili, Roman Ya.

    2017-07-01

    We study the formation of dipolar excitons and their superfluidity in a phosphorene double layer. The analytical expressions for the single dipolar exciton energy spectrum and wave function are obtained. It is predicted that a weakly interacting gas of dipolar excitons in a double layer of black phosphorus exhibits superfluidity due to the dipole-dipole repulsion between the dipolar excitons. In calculations are employed the Keldysh and Coulomb potentials for the interaction between the charge carriers to analyze the influence of the screening effects on the studied phenomena. It is shown that the critical velocity of superfluidity, the spectrum of collective excitations, concentrations of the superfluid and normal component, and mean-field critical temperature for superfluidity are anisotropic and demonstrate the dependence on the direction of motion of dipolar excitons. The critical temperature for superfluidity increases if the exciton concentration and the interlayer separation increase. It is shown that the dipolar exciton binding energy and mean-field critical temperature for superfluidity are sensitive to the electron and hole effective masses. The proposed experiment to observe a directional superfluidity of excitons is addressed.

  2. Bistable Topological Insulator with Exciton-Polaritons

    Science.gov (United States)

    Kartashov, Yaroslav V.; Skryabin, Dmitry V.

    2017-12-01

    The functionality of many nonlinear and quantum optical devices relies on the effect of optical bistability. Using microcavity exciton-polaritons in a honeycomb arrangement of microcavity pillars, we report the resonance response and bistability of topological edge states. A balance between the pump, loss, and nonlinearity ensures a broad range of dynamical stability and controls the distribution of power between counterpropagating states on the opposite edges of the honeycomb lattice stripe. Tuning energy and polarization of the pump photons, while keeping their momentum constant, we demonstrate control of the propagation direction of the dominant edge state. Our results facilitate the development of practical applications of topological photonics.

  3. Proton Linear Energy Transfer measurement using Emulsion Cloud Chamber

    Energy Technology Data Exchange (ETDEWEB)

    Shin, Jae-ik [Proton Therapy Center, National Cancer Center (Korea, Republic of); Division of Heavy Ion Clinical Research, Korea Institute of Radiological & Medical Sciences (KIRAMS), Seoul (Korea, Republic of); Park, Seyjoon [Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University, School of Medicine, Seoul (Korea, Republic of); Kim, Haksoo; Kim, Meyoung [Proton Therapy Center, National Cancer Center (Korea, Republic of); Jeong, Chiyoung [Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul (Korea, Republic of); Cho, Sungkoo [Department of Radiation Oncology, Samsung Medical Center, Sungkyunkwan University, School of Medicine, Seoul (Korea, Republic of); Lim, Young Kyung; Shin, Dongho [Proton Therapy Center, National Cancer Center (Korea, Republic of); Lee, Se Byeong, E-mail: sblee@ncc.re.kr [Proton Therapy Center, National Cancer Center (Korea, Republic of); Morishima, Kunihiro; Naganawa, Naotaka; Sato, Osamu [Department of Physics, Nagoya University, Nagoya (Japan); Kwak, Jungwon [Department of Radiation Oncology, Asan Medical Center, University of Ulsan College of Medicine, Seoul (Korea, Republic of); Kim, Sung Hyun [Center for Underground Physics, Institute for Basic Science (IBS), Daejeon (Korea, Republic of); Cho, Jung Sook [Department of refinement education, Dongseo University, Busan (Korea, Republic of); Ahn, Jung Keun [Department of Physics, Korea University, Seoul (Korea, Republic of); Kim, Ji Hyun; Yoon, Chun Sil [Gyeongsang National University, Jinju (Korea, Republic of); Incerti, Sebastien [CNRS, IN2P3, CENBG, UMR 5797, F-33170 Gradignan (France); Université Bordeaux 1, CENBG, UMR 5797, F-33170 Gradignan (France)

    2015-04-15

    This study proposes to determine the correlation between the Volume Pulse Height (VPH) measured by nuclear emulsion and Linear Energy Transfer (LET) calculated by Monte Carlo simulation based on Geant4. The nuclear emulsion was irradiated at the National Cancer Center (NCC) with a therapeutic proton beam and was installed at 5.2 m distance from the beam nozzle structure with various thicknesses of water-equivalent material (PMMA) blocks to position with specific positions along the Bragg curve. After the beam exposure and development of the emulsion films, the films were scanned by S-UTS developed in Nagoya University. The proton tracks in the scanned films were reconstructed using the ‘NETSCAN’ method. Through this procedure, the VPH can be derived from each reconstructed proton track at each position along the Bragg curve. The VPH value indicates the magnitude of energy loss in proton track. By comparison with the simulation results obtained using Geant4, we found the correlation between the LET calculated by Monte Carlo simulation and the VPH measured by the nuclear emulsion.

  4. Proton Linear Energy Transfer measurement using Emulsion Cloud Chamber

    Science.gov (United States)

    Shin, Jae-ik; Park, Seyjoon; Kim, Haksoo; Kim, Meyoung; Jeong, Chiyoung; Cho, Sungkoo; Lim, Young Kyung; Shin, Dongho; Lee, Se Byeong; Morishima, Kunihiro; Naganawa, Naotaka; Sato, Osamu; Kwak, Jungwon; Kim, Sung Hyun; Cho, Jung Sook; Ahn, Jung Keun; Kim, Ji Hyun; Yoon, Chun Sil; Incerti, Sebastien

    2015-04-01

    This study proposes to determine the correlation between the Volume Pulse Height (VPH) measured by nuclear emulsion and Linear Energy Transfer (LET) calculated by Monte Carlo simulation based on Geant4. The nuclear emulsion was irradiated at the National Cancer Center (NCC) with a therapeutic proton beam and was installed at 5.2 m distance from the beam nozzle structure with various thicknesses of water-equivalent material (PMMA) blocks to position with specific positions along the Bragg curve. After the beam exposure and development of the emulsion films, the films were scanned by S-UTS developed in Nagoya University. The proton tracks in the scanned films were reconstructed using the 'NETSCAN' method. Through this procedure, the VPH can be derived from each reconstructed proton track at each position along the Bragg curve. The VPH value indicates the magnitude of energy loss in proton track. By comparison with the simulation results obtained using Geant4, we found the correlation between the LET calculated by Monte Carlo simulation and the VPH measured by the nuclear emulsion.

  5. Hole burning with pressure and electric field: A window on the electronic structure and energy transfer dynamics of bacterial antenna complexes

    Energy Technology Data Exchange (ETDEWEB)

    Wu, H.M.

    1999-02-12

    Light-harvesting (LH) complexes of cyclic (C{sub n}) symmetry from photosynthetic bacteria are studied using absorption and high pressure- and Stark-hole burning spectroscopies. The B800 absorption band of LH2 is inhomogeneously broadened while the B850 band of LH2 and the B875 band of the LH1 complex exhibit significant homogeneous broadening due to ultra-fast inter-exciton level relaxation. The B800{r_arrow}B850 energy transfer rate of ({approximately}2 ps){sup {minus}1} as determined by hole burning and femtosecond pump-probe spectroscopies, is weakly dependent on pressure and temperature, both of which significantly affect the B800-B850 energy gap. The resilience is theoretically explained in terms of a modified Foerster theory with the spectral overlap provided by the B800 fluorescence origin band and weak vibronic absorption bands of B850. Possible explanations for the additional sub-picosecond relaxation channel of B800 observed with excitation on the blue side of B800 are given. Data from pressure and temperature dependent studies show that the B800 and B850 bacteriochlorophyll a (BChl a) molecules are weakly and strongly excitonically coupled, respectively, which is consistent with the X-ray structure of LH2. The B875 BChl a molecules are also strongly coupled. It is concluded that electron-exchange, in addition to electrostatic interactions, is important for understanding the strong coupling of the B850 and B875 rings. The large linear pressure shifts of {approximately}{minus}0.6 cm{sup {minus}1}/MPa associated with B850 and B875 can serve as important benchmarks for electronic structure calculations.

  6. The exciton excitations and relaxation processes in low-dimensional semiconductor heterostructures with quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Aleshkin, V. Ya.; Gavrilenko, L. V.; Gaponova, D. M., E-mail: dmg@ipmras.ru; Krasil’nik, Z. F.; Kryzhkov, D. I. [Russian Academy of Sciences, Institute for Physics of Microstructures (Russian Federation)

    2016-12-15

    The processes associated with the transfer of excitonic excitations between tunnel-uncoupled quantum wells (QW) and the influence of the local electric field were investigated in AlGaAs/GaAs heterostructures by the method of photoluminescence excitation (PLE) spectroscopy at low (4.2 K) temperature. The variation in the intensity of photoluminescence (PL) from the wider QW under resonant excitation of excitonic transition in the adjacent narrow QW has been observed. The difference in the PL maximum position and intensity of the wider QW under resonance excitation of the narrow one is explained by the influence of quantum-confined Stark effect on the process of exciton recombination.

  7. Exciton dynamics in solid-state green fluorescent protein

    Science.gov (United States)

    Dietrich, Christof P.; Siegert, Marie; Betzold, Simon; Ohmer, Jürgen; Fischer, Utz; Höfling, Sven

    2017-01-01

    We study the decay characteristics of Frenkel excitons in solid-state enhanced green fluorescent protein (eGFP) dried from solution. We further monitor the changes of the radiative exciton decay over time by crossing the phase transition from the solved to the solid state. Complex interactions between protonated and deprotonated states in solid-state eGFP can be identified from temperature-dependent and time-resolved fluorescence experiments that further allow the determination of activation energies for each identified process.

  8. Optical Studies of Excitonic Effects at Two-Dimensional Nanostructure Interfaces

    Science.gov (United States)

    Ajayi, Obafunso Ademilolu

    Atomically thin two-dimensional nanomaterials such as graphene and transition metal dichalcogenides (TMDCs) have seen a rapid growth of exploration since the isolation of monolayer graphene. These materials provide a rich field of study for physics and optoelectronics applications. Many applications seek to combine a two dimensional (2D) material with another nanomaterial, either another two dimensional material or a zero (0D) or one dimensional (1D) material. The work in this thesis explores the consequences of these interactions from 0D to 2D. We begin in Chapter 2 with a study of energy transfer at 0D-2D interfaces with quantum dots and graphene. In our work we seek to maximize the rate of energy transfer by reducing the distance between the materials. We observe an interplay with the distance-dependence and surface effects from our halogen terminated quantum dots that affect our observed energy transfer. In Chapter 3 we study supercapacitance in composite graphene oxide-carbon nanotube electrodes. At this 2D-1D interface we observe a compounding effect between graphene oxide and carbon nanotubes. Carbon nanotubes increase the accessible surface area of the supercapacitors and improve conductivity by forming a conductive pathway through electrodes. In Chapter 4 we investigate effective means of improving sample quality in TMDCs and discover the importance of the monolayer interface. We observe a drastic improvement in photoluminescence when encapsulating our TMDCs with Boron Nitride. We measure spectral linewidths approaching the intrinsic limit due to this 2D-2D interface. We also effectively reduce excess charge and thus the trion-exciton ratio in our samples through substrate surface passivation. In Chapter 5 we briefly discuss our investigations on chemical doping, heterostructures and interlayer decoupling in ReS2. We observe an increase in intensity for p-doped MoS2 samples. We investigated the charge transfer exciton previously identified in

  9. Energy transfer from the host to Er{sup 3+} dopants in semiconductor SnO{sub 2} nanocrystals segregated in sol-gel silica glasses

    Energy Technology Data Exchange (ETDEWEB)

    Castillo, Javier del [Universidad de La Laguna, Departamento Fisica Basica (Spain)], E-mail: fjvargas@ull.es; Rodriguez, V. D. [Universidad de La Laguna, Departamento Fisica Fundamental y Experimental, Electronica y Sistemas (Spain)], E-mail: vrguez@ull.es; Yanes, A. C. [Universidad de La Laguna, Departamento Fisica Basica (Spain); Mendez-Ramos, J. [Universidad de La Laguna, Departamento Fisica Fundamental y Experimental, Electronica y Sistemas (Spain)

    2008-03-15

    Undoped and Er{sup 3+}-doped glass-ceramics of composition (100-x)SiO{sub 2}-xSnO{sub 2}, with x = 5 or 10 and with 0.4 or 0.8 mol% of Er{sup 3+} ions, were synthesised by thermal treatment of precursor sol-gel glasses. Structural studies were developed by X-Ray Diffraction. Wide band gap SnO{sub 2} semiconductor quantum-dots embedded in the insulator SiO{sub 2} glass are obtained. The mean radius of the SnO{sub 2} nanocrystals, ranging from 2 to 3.2 nm, is comparable to the exciton Bohr radius. The luminescence properties have been analysed as a function of sample composition and thermal treatment. The results show that Er{sup 3+} ions are partially partitioned into the nanocrystalline phase. An efficient UV excitation of the Er{sup 3+} ions by energy transfer from the SnO{sub 2} nanocrystal host is observed. The Er{sup 3+} ions located in the SnO{sub 2} nanocrystals are selectively excited by this energy transfer mechanism. On the other hand, emission from the Er{sup 3+} ions remaining in the silica glassy phase is obtained by direct excitation of these ions.

  10. Exploiting energy transfer in hybrid metal and semiconductor nanoparticle systems for biosensing and energy harvesting

    Energy Technology Data Exchange (ETDEWEB)

    Mayilo, Sergiy

    2009-06-19

    In this work, gold and semiconductor nanoparticles are used as building blocks for nanostructures, in which energy transfer is investigated. Fluorescence quenching by gold nanoparticles is investigated and used to develop novel immunoassays for medically relevant molecules. The influence of gold nanoparticles on radiative and non-radiative rates of Cy3 and Cy3B dyes is studied here. A competitive, homogeneous immunoassay for digoxigenin and digoxin, a drug used to cure heart diseases, is developed. The assay has a limit of detection of 0.5 nM in buffer and 50 nM in serum. Time resolved spectroscopy reveals that the quenching is due to energy transfer with an efficiency of 70%. A homogeneous sandwich immunoassay for cardiac troponin T, an indicator of damage to the heart muscle, is developed. Gold nanoparticles and fluorophores are functionalized with anti-troponin T antibodies. In the presence of troponin T the nanoparticles and fluorophores form a sandwich structure, in which the dye fluorescence is quenched by a gold nanoparticle. The limit of detection of the immunoassay in buffer is 0.02 nM and 0.11 nM in serum. Energy transfer is demonstrated in clusters of CdTe nanocrystals assembled using three methods. In the first method, clusters of differently-sized water soluble CdTe nanocrystals capped by negatively charged mercaptoacid stabilizers are produced through electrostatic interactions with positively charged Ca{sup 2+} cations. The two other methods employ covalent binding through dithiols and thiolated DNA as linkers between nanocrystals. Energy transfer from smaller nanocrystals to larger nanocrystals in aggregates is demonstrated by means of steady-state and time-resolved photoluminescence spectroscopy, paving the way for nanocrystal-based light harvesting structures in solution. Multi-shell onion-like CdSe/ZnS/CdSe/ZnS nanocrystals are presented. The shade of the white light can be controlled by annealing the particles. Evidence for intra

  11. Excitonic insulator transition in the conjugated polymer polyacene

    NARCIS (Netherlands)

    Rice, MJ; Gartstein, YN

    2004-01-01

    According to molecular orbital theory, the symmetrically positioned one-dimensional (I-D) conduction and valence bands of polyacene touch at the X point. Clearly, the exciton binding energy of this semimetal exceeds the band gap so that polyacene should be a textbook case of a semimetal undergoing a

  12. Energy transfer rate in double-layer graphene systems: Linear regime

    Energy Technology Data Exchange (ETDEWEB)

    Bahrami, B., E-mail: b_bahrami@sbu.ac.ir [Department of Physics, Shahid Beheshti University, G. C., Evin, 1983963113, Tehran (Iran, Islamic Republic of); Vazifehshenas, T., E-mail: t-vazifeh@sbu.ac.ir [Department of Physics, Shahid Beheshti University, G. C., Evin, 1983963113, Tehran (Iran, Islamic Republic of)

    2012-10-15

    We theoretically investigate the energy transfer phenomenon in a double-layer graphene (DLG) system. We use the balance equation approach in linear regime and random phase approximation screening function to obtain energy transfer rates at different electron temperatures, densities and interlayer spacings. We find that the rate of energy transfer in the DLG is qualitatively similar to that obtained in the double-layer two-dimensional electron gas but its values are an order of magnitude greater. Also, at large electron temperature differences between two graphene layers, the electron density dependence of energy transfer is significantly different, particularly in case of unequal electron densities.

  13. Long-Range Plasmon Assisted Energy Transfer Between Two Fluorescent Emitters

    CERN Document Server

    Bouchet, D; Carminati, R; De Wilde, Y; Krachmalnicoff, V

    2016-01-01

    We demonstrate plasmon assisted energy transfer between two fluorophores located at distances up to $7\\; \\mu$m on the top of a thin silver film. Thanks to the strong confinement and large propagation length of surface plasmon polaritons, the range of the energy transfer is almost two orders of magnitude larger than the values reported in the literature so far. The parameters driving the energy transfer range are thoroughly characterized and are in very good agreement with theoretically expected values. This work shows the potential of plasmonic structures for efficient long-range energy transfer and opens rich perspectives for the study of collective emission phenomena.

  14. Rapid Detection of Enterotoxigenic Clostridium perfringens by Real-Time Fluorescence Resonance Energy Transfer PCR

    National Research Council Canada - National Science Library

    dela Cruz, Wilfred P; Gozum, Mary M.A; Lineberry, Sarah F; Stassen, Sarah D; Daughtry, Marianne; Stassen, Nicholas A; Jones, Morris S; Johnson, Oswald L

    2006-01-01

    ...) produced by some strains during sporulation. We developed a quantitative real-time PCR assay based on fluorescence resonance energy transfer hybridization chemistry that targets the C. perfringens...

  15. Excitation and temperature dependent exciton-carrier transport in CVD diamond: Diffusion coefficient, recombination lifetime and diffusion length

    Energy Technology Data Exchange (ETDEWEB)

    Ščajev, Patrik, E-mail: patrik.scajev@ff.vu.lt

    2017-04-01

    Time-resolved induced absorption (IA) and light induced transient grating (LITG) techniques were applied for the investigation of nonequilibrium exciton-carrier diffusion and recombination processes in a high-purity CVD diamond. Injection range from 10{sup 15} to 10{sup 20} cm{sup −3} carrier density was achieved by combining one photon and two photon excitations. The measurements were performed in the 10–750 K temperature range. The LITG diffusion coefficient peaked at 44 cm{sup 2}/s value at room temperature under low injection conditions. At lower temperatures it transferred to much lower exciton diffusion coefficient. A strong decrease of diffusion coefficient under higher injection conditions was explained by exciton formation with a low diffusion coefficient and many body effects, as polyexciton and electron-hole droplet formation. High temperature phonon-limited diffusion coefficient was weakly injection dependent. Low excitation carrier lifetime was about 700 ns above 200 K. At lower temperatures, the decay time reduced by two orders of magnitude, which was explained by the formation of biexcitons. At lowest temperatures, an increase of the carrier recombination rate at high injection was attributed to Auger recombinations of polyexcitons and electron-hole droplets. While at high temperatures, the increase of the recombination rate with 490 meV activation energy was observed. The combination of IA and LITG measurements provided effective diffusion lengths in a 0.3–50 µm range, being strongly dependent on the excess carrier density and temperature.

  16. Accelerating FRET between Near-Infrared Emitting Quantum Dots Using a Molecular J-Aggregate as an Exciton Bridge.

    Science.gov (United States)

    Wang, Chen; Weiss, Emily A

    2017-09-13

    Fast energy transfer (EnT) among quantum dots (QDs) with near-infrared (NIR) emission is essential for fully exploiting their light harvesting and photon downconversion (multiexciton generation) abilities. This paper demonstrates a relayed EnT mechanism that accelerates the migration of NIR excitons between PbS QDs by a factor of 20 from that of one-step EnT through a polyelectrolyte and even a factor of ∼2 from that of one-step EnT between QDs in direct contact, by employing a J-aggregate (J-agg) of a cyanine dye as an exciton bridge. The donor QDs, acceptor QDs, and J-agg are electrostatically assembled into a sandwich structure with layer-by-layer deposition. Estimates of EnT rate and yield from transient and steady-state absorption and photoluminescence spectroscopies show that the rate-limiting step in the relay is EnT from the donor QD to the J-agg, while EnT from the J-agg to the acceptor QD occurs in J-agg with more intermolecular order. This work demonstrates the viability of relayed EnT through a molecular bridge as a strategy for accelerating long-distance exciton migration in assemblies of QDs, in particular in the near-infrared.

  17. Theory of optical absorption by interlayer excitons in transition metal dichalcogenide heterobilayers

    Energy Technology Data Exchange (ETDEWEB)

    Wu, Fengcheng; Lovorn, Timothy; MacDonald, A. H.

    2018-01-01

    We present a theory of optical absorption by interlayer excitons in a heterobilayer formed from transition metal dichalcogenides. The theory accounts for the presence of small relative rotations that produce a momentum shift between electron and hole bands located in different layers, and a moire pattern in real space. Because of the momentum shift, the optically active interlayer excitons are located at the moire Brillouin zone's corners, instead of at its center, and would have elliptical optical selection rules if the individual layers were translationally invariant. We show that the exciton moire potential energy restores circular optical selection rules by coupling excitons with different center of mass momenta. A variety of interlayer excitons with both senses of circular optical activity, and energies that are tunable by twist angle, are present at each valley. The lowest energy exciton states are generally localized near the exciton potential energy minima. We discuss the possibility of using the moire pattern to achieve scalable two-dimensional arrays of nearly identical quantum dots.

  18. Self-trapped exciton and core-valence luminescence in BaF{sub 2} nanoparticles

    Energy Technology Data Exchange (ETDEWEB)

    Vistovskyy, V. V., E-mail: vistvv@gmail.com; Zhyshkovych, A. V.; Chornodolskyy, Ya. M.; Voloshinovskii, A. S. [Ivan Franko National University of Lviv, 8 Kyryla i Mefodiya, 79005 Lviv (Ukraine); Myagkota, O. S. [Lviv Polytechnic National University, 12S. Bandera, 79013 Lviv (Ukraine); Gloskovskii, A. [Deutsches Elektronen-Synchrotron DESY, 22607 Hamburg (Germany); Gektin, A. V. [Institute for Scintillation Materials, NAS of Ukraine 60 Lenina Ave, 61001 Kharkiv (Ukraine); Vasil' ev, A. N. [Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University, 119991 Moscow (Russian Federation); Rodnyi, P. A. [Saint-Petersburg State Polytechnical University, 29, Polytekhnicheskaya, 195251 Saint-Petersburg (Russian Federation)

    2013-11-21

    The influence of the BaF{sub 2} nanoparticle size on the intensity of the self-trapped exciton luminescence and the radiative core-valence transitions is studied by the luminescence spectroscopy methods using synchrotron radiation. The decrease of the self-trapped exciton emission intensity at energies of exciting photons in the range of optical exciton creation (hν ≤ E{sub g}) is less sensitive to the reduction of the nanoparticle sizes than in the case of band-to-band excitation, where excitons are formed by the recombination way. The intensity of the core-valence luminescence shows considerably weaker dependence on the nanoparticle sizes in comparison with the intensity of self-trapped exciton luminescence. The revealed regularities are explained by considering the relationship between nanoparticle size and photoelectron or photohole thermalization length as well as the size of electronic excitations.

  19. Fractal dimension method for exciton in cylindrical GaAs/AlxGa1‑xAs core-shell-cap nanowires

    Science.gov (United States)

    Sun, Hui; Wu, Zhenhua; Tian, Qiang

    2017-11-01

    By use of the fractal dimension method, the binding energies of heavy-hole exciton and light-hole exciton in cylindrical GaAs/AlxGa1‑xAs core-shell-cap nanowire are explored. In this study, the exciton is confined in GaAs shell of the GaAs/AlxGa1‑xAs core-shell-cap nanowire for a given aluminum concentration of x=0.3. The numerical results of heavy-hole exciton binding energy, light-hole exciton binding energy and fractal dimension parameter are worked out as functions of shell width and core radius. It has been shown by the calculated results that heavy-hole exciton binding energy and light-hole exciton binding energy firstly increase and then decrease as the shell width increases. When the core radius increases, both the heavy-hole exciton binding energy and light-hole exciton binding energy increase gradually. Exciton problems in GaAs shell of the cylindrical GaAs/AlxGa1‑xAs core-shell-cap nanowire are solved in a simple manner to avoid complex and lengthy calculations by using the fractal dimension method.

  20. Plasmon-Exciton-Polariton Lasing

    CERN Document Server

    Ramezani, Mohammad; Fernández-Domínguez, Antonio I; Feist, Johannes; Rodriguez, Said Rahimzadeh-Kalaleh; Garcia-Vidal, Francisco J; Gómez-Rivas, Jaime

    2016-01-01

    Strong coupling of Frenkel excitons with surface plasmons leads to the formation of bosonic quasi-particles known as plasmon-exciton-polaritons (PEPs).Localized surface plasmons in nanoparticles are lossy due to radiative and nonradiative decays, which has hampered the realization of polariton lasing in a plasmonic system, i.e., PEP lasing. These losses can be reduced in collective plasmonic resonances supported by arrays of nanoparticles. Here we demonstrate PEP lasing in arrays of silver nanoparticles by showing the emergence of a threshold in the photoluminescence accompanied by both a superlinear increase of the emission and spectral narrowing. We also observe a reduction of the threshold by increasing the coupling between the molecular excitons and the resonances supported by the array despite the reduction of the quantum efficiency of the emitters. The coexistence of bright and dark collective modes in this plasmonic system allows for a 90?-change of polarization in the emission beyond the threshold.

  1. Definition and determination of the triplet-triplet energy transfer reaction coordinate

    Energy Technology Data Exchange (ETDEWEB)

    Zapata, Felipe; Marazzi, Marco; Castaño, Obis; Frutos, Luis Manuel, E-mail: luisma.frutos@uah.es [Departamento de Química Física, Universidad de Alcalá, 28871 Alcalá de Henares, Madrid (Spain); Acuña, A. Ulises [Instituto de Química Física “Rocasolano”, C.S.I.C., Serrano 119, 28006 Madrid (Spain)

    2014-01-21

    A definition of the triplet-triplet energy transfer reaction coordinate within the very weak electronic coupling limit is proposed, and a novel theoretical formalism is developed for its quantitative determination in terms of internal coordinates The present formalism permits (i) the separation of donor and acceptor contributions to the reaction coordinate, (ii) the identification of the intrinsic role of donor and acceptor in the triplet energy transfer process, and (iii) the quantification of the effect of every internal coordinate on the transfer process. This formalism is general and can be applied to classical as well as to nonvertical triplet energy transfer processes. The utility of the novel formalism is demonstrated here by its application to the paradigm of nonvertical triplet-triplet energy transfer involving cis-stilbene as acceptor molecule. In this way the effect of each internal molecular coordinate in promoting the transfer rate, from triplet donors in the low and high-energy limit, could be analyzed in detail.

  2. Definition and determination of the triplet-triplet energy transfer reaction coordinate

    Science.gov (United States)

    Zapata, Felipe; Marazzi, Marco; Castaño, Obis; Acuña, A. Ulises; Frutos, Luis Manuel

    2014-01-01

    A definition of the triplet-triplet energy transfer reaction coordinate within the very weak electronic coupling limit is proposed, and a novel theoretical formalism is developed for its quantitative determination in terms of internal coordinates The present formalism permits (i) the separation of donor and acceptor contributions to the reaction coordinate, (ii) the identification of the intrinsic role of donor and acceptor in the triplet energy transfer process, and (iii) the quantification of the effect of every internal coordinate on the transfer process. This formalism is general and can be applied to classical as well as to nonvertical triplet energy transfer processes. The utility of the novel formalism is demonstrated here by its application to the paradigm of nonvertical triplet-triplet energy transfer involving cis-stilbene as acceptor molecule. In this way the effect of each internal molecular coordinate in promoting the transfer rate, from triplet donors in the low and high-energy limit, could be analyzed in detail.

  3. Interaction mechanism for energy transfer from Ce to Tb ions in silica

    Energy Technology Data Exchange (ETDEWEB)

    Seed Ahmed, H.A.A. [Department of Physics, University of the Free State, Bloemfontein (South Africa); Department of Physics, University of Khartoum, Khartoum (Sudan); Chae, W.S. [Korea Basic Science Institute (KBSI), Gangneung (Korea, Republic of); Ntwaeaborwa, O.M. [Department of Physics, University of the Free State, Bloemfontein (South Africa); Kroon, R.E., E-mail: KroonRE@ufs.ac.za [Department of Physics, University of the Free State, Bloemfontein (South Africa)

    2016-01-01

    Energy transfer phenomena can play an important role in the development of luminescent materials. In this study, numerical simulations based on theoretical models of non-radiative energy transfer are compared to experimental results for Ce, Tb co-doped silica. Energy transfer from the donor (Ce) to the acceptor (Tb) resulted in a decrease in the Ce luminescence intensity and lifetime. The decrease in intensity corresponded best with the energy transfer models based on the exchange interaction and the dipole-dipole interaction. The critical transfer distance obtained from the fitting using both these models is around 2 nm. Since the exchange interaction requires a distance shorter than 1 nm to occur, the mechanism most likely to account for the energy transfer is concluded to be the dipole–dipole interaction. This is supported by an analysis of the lifetime data.

  4. Interwell excitons in GaAs superlattices

    DEFF Research Database (Denmark)

    Birkedal, Dan; Sayed, Karim El; Sanders, G.

    1997-01-01

    The formation of spatially indirect excitons in superlattices with narrow minibands is investigated experimentally. The interwell exciton is similar to the first Wannier-Stark localized exciton of an electrically biased superlattice. However, in the present case the localization is mediated by th...

  5. Single-collision studies of energy transfer and chemical reaction

    Energy Technology Data Exchange (ETDEWEB)

    Valentini, J.J. [Columbia Univ., New York, NY (United States)

    1993-12-01

    The research focus in this group is state-to-state dynamics of reaction and energy transfer in collisions of free radicals such as H, OH, and CH{sub 3} with H{sub 2}, alkanes, alcohols and other hydrogen-containing molecules. The motivation for the work is the desire to provide a detailed understanding of the chemical dynamics of prototype reactions that are important in the production and utilization of energy sources, most importantly in combustion. The work is primarily experimental, but with an important and growing theoretical/computational component. The focus of this research program is now on reactions in which at least one of the reactants and one of the products is polyatomic. The objective is to determine how the high dimensionality of the reactants and products differentiates such reactions from atom + diatom reactions of the same kinematics and energetics. The experiments use highly time-resolved laser spectroscopic methods to prepare reactant states and analyze the states of the products on a single-collision time scale. The primary spectroscopic tool for product state analysis is coherent anti-Stokes Raman scattering (CARS) spectroscopy. CARS is used because of its generality and because the extraction of quantum state populations from CARS spectra is straightforward. The combination of the generality and easy analysis of CARS makes possible absolute cross section measurements (both state-to-state and total), a particularly valuable capability for characterizing reactive and inelastic collisions. Reactant free radicals are produced by laser photolysis of appropriate precursors. For reactant vibrational excitation stimulated Raman techniques are being developed and implemented.

  6. Ion Transfer Battery: Storing Energy by Transferring Ions across Liquid-Liquid Interfaces

    OpenAIRE

    Peljo, Pekka Eero; Bichon, Marie; Girault, Hubert

    2016-01-01

    A battery utilizing the Galvani potential difference between aqueous and organic phases is demonstrated. The battery consists of two organic redox electrolytes separated by an immiscible aqueous phase. The charge is stored by transferring a salt from the aqueous phase into organic phases in ion transfer coupled electron transfer reactions.

  7. Fluorescence Resonance Energy Transfer Systems in Supramolecular Macrocyclic Chemistry.

    Science.gov (United States)

    Lou, Xin-Yue; Song, Nan; Yang, Ying-Wei

    2017-09-29

    The fabrication of smart materials is gradually becoming a research focus in nanotechnology and materials science. An important criterion of smart materials is the capacity of stimuli-responsiveness, while another lies in selective recognition. Accordingly, supramolecular host-guest chemistry has proven a promising support for building intelligent, responsive systems; hence, synthetic macrocyclic hosts, such as calixarenes, cucurbiturils, cyclodextrins, and pillararenes, have been used as ideal building blocks. Meanwhile, manipulating and harnessing light artificially is always an intensive attempt for scientists in order to meet the urgent demands of technological developments. Fluorescence resonance energy transfer (FRET), known as a well-studied luminescent activity and also a powerful tool in spectroscopic area, has been investigated from various facets, of which the application range has been broadly expanded. In this review, the innovative collaboration between FRET and supramolecular macrocyclic chemistry will be presented and depicted with typical examples. Facilitated by the dynamic features of supramolecular macrocyclic motifs, a large variety of FRET systems have been designed and organized, resulting in promising optical materials with potential for applications in protein assembly, enzyme assays, diagnosis, drug delivery monitoring, sensing, photosynthesis mimicking and chemical encryption.

  8. Fluorescence Resonance Energy Transfer Systems in Supramolecular Macrocyclic Chemistry

    Directory of Open Access Journals (Sweden)

    Xin-Yue Lou

    2017-09-01

    Full Text Available The fabrication of smart materials is gradually becoming a research focus in nanotechnology and materials science. An important criterion of smart materials is the capacity of stimuli-responsiveness, while another lies in selective recognition. Accordingly, supramolecular host-guest chemistry has proven a promising support for building intelligent, responsive systems; hence, synthetic macrocyclic hosts, such as calixarenes, cucurbiturils, cyclodextrins, and pillararenes, have been used as ideal building blocks. Meanwhile, manipulating and harnessing light artificially is always an intensive attempt for scientists in order to meet the urgent demands of technological developments. Fluorescence resonance energy transfer (FRET, known as a well-studied luminescent activity and also a powerful tool in spectroscopic area, has been investigated from various facets, of which the application range has been broadly expanded. In this review, the innovative collaboration between FRET and supramolecular macrocyclic chemistry will be presented and depicted with typical examples. Facilitated by the dynamic features of supramolecular macrocyclic motifs, a large variety of FRET systems have been designed and organized, resulting in promising optical materials with potential for applications in protein assembly, enzyme assays, diagnosis, drug delivery monitoring, sensing, photosynthesis mimicking and chemical encryption.

  9. A New Efficient Method for Calculation of Frenkel Exciton Parameters in Molecular Aggregates

    CERN Document Server

    Plötz, Per-Arno; Kühn, Oliver

    2013-01-01

    The Frenkel exciton Hamiltonian is at the heart of many simulations of excitation energy transfer in molecular aggregates. It separates the aggregate into Coulomb-coupled monomers. Here it is shown that the respective parameters, i.e. monomeric excitation energies and Coulomb couplings between transition densities, can be efficiently calculated using time-dependent tight-binding-based density functional theory (TD-DFTB). Specifically, Coulomb couplings are expressed in terms of self-consistently determined Mulliken transition charges. The determination of the sign of the coupling requires an additional super-molecule calculation. The approach is applied to two dimer systems. First, formaldehyde oxime for which a detailed comparison with standard DFT using the B3LYP and the PBE functionals is provided. Second, the Coulomb coupling is explored in dependence on the intermolecular coordinates for a perylene bisimide dimer. This provides structural evidence for the previously observed biphasic aggregation behavior...

  10. Bosonic cascades of indirect excitons

    Science.gov (United States)

    Nalitov, A. V.; De Liberato, S.; Lagoudakis, P.; Savvidis, P. G.; Kavokin, A. V.

    2017-08-01

    Recently, the concept of the terahertz bosonic cascade laser (BCL) based on a parabolic quantum well (PQW) embedded in a microcavity was proposed. We refine this proposal by suggesting transitions between indirect exciton (IX) states as a source of terahertz emission. We explicitly propose a structure containing a narrow-square QW and a wide-parabolic QW for the realisation of a bosonic cascade. Advantages of this type of structures are in large dipole matrix elements for terahertz transitions and in long exciton radiative lifetimes which are crucial for realisation of threshold and quantum efficiency BCLs.

  11. Efficient near-field wireless energy transfer using adiabatic system variations

    Energy Technology Data Exchange (ETDEWEB)

    Hamam, Rafif E.; Karalis, Aristeidis; Joannopoulos, John D.; Soljacic, Marin

    2017-11-28

    Disclosed is a method for transferring energy wirelessly including transferring energy wirelessly from a first resonator structure to an intermediate resonator structure, wherein the coupling rate between the first resonator structure and the intermediate resonator structure is .kappa..sub.1B, transferring energy wirelessly from the intermediate resonator structure to a second resonator structure, wherein the coupling rate between the intermediate resonator structure and the second resonator structure is .kappa..sub.B2, and during the wireless energy transfers, adjusting at least one of the coupling rates .kappa..sub.1B and .kappa..sub.B2 to reduce energy accumulation in the intermediate resonator structure and improve wireless energy transfer from the first resonator structure to the second resonator structure through the intermediate resonator structure.

  12. Composite Boson Description of a Low-Density Gas of Excitons

    Science.gov (United States)

    Golomedov, A. E.; Lozovik, Yu. E.; Astrakharchik, G. E.; Boronat, J.

    2017-12-01

    Ground-state properties of a fermionic Coulomb gas are calculated using the fixed-node diffusion Monte Carlo method. The validity of the composite boson description is tested for different densities. We extract the exciton-exciton s-wave scattering length by solving the four-body problem in a harmonic trap and mapping the energy to that of two trapped bosons. The equation of state is consistent with the Bogoliubov theory for composite bosons interacting with the obtained s-wave scattering length. The perturbative expansion at low density has contributions physically coming from (a) exciton binding energy, (b) mean-field Gross-Pitaevskii interaction between excitons, and (c) quantum depletion of the excitonic condensate (Lee-Huang-Yang terms for composite bosons). In addition, for low densities we find a good agreement with the Bogoliubov bosonic theory for the condensate fraction of excitons. The equation of state in the opposite limit of large density is found to be well described by the perturbative theory including (a) mixture of two ideal Fermi gases and (b) exchange energy. We find that for low densities both energetic and coherent properties are correctly described by the picture of composite bosons (excitons).

  13. Modeling the efficiency of Förster resonant energy transfer from energy relay dyes in dye-sensitized solar cells

    KAUST Repository

    Hoke, Eric T.

    2010-02-11

    Förster resonant energy transfer can improve the spectral breadth, absorption and energy conversion efficiency of dye sensitized solar cells. In this design, unattached relay dyes absorb the high energy photons and transfer the excitation to sensitizing dye molecules by Förster resonant energy transfer. We use an analytic theory to calculate the excitation transfer efficiency from the relay dye to the sensitizing dye accounting for dynamic quenching and relay dye diffusion. We present calculations for pores of cylindrical and spherical geometry and examine the effects of the Förster radius, the pore size, sensitizing dye surface concentration, collisional quenching rate, and relay dye lifetime. We find that the excitation transfer efficiency can easily exceed 90% for appropriately chosen dyes and propose two different strategies for selecting dyes to achieve record power conversion efficiencies. © 2010 Optical Society of America.

  14. Tunable negligible-loss energy transfer between dipolar-coupled magnetic disks by stimulated vortex gyration

    OpenAIRE

    Hyunsung Jung; Ki-Suk Lee; Dae-Eun Jeong; Youn-Seok Choi; Young-Sang Yu; Dong-Soo Han; Andreas Vogel; Lars Bocklage; Guido Meier; Mi-Young Im; Peter Fischer; Sang-Koog Kim

    2011-01-01

    A wide variety of coupled harmonic oscillators exist in nature. Coupling between different oscillators allows for the possibility of mutual energy transfer between them and the information-signal propagation. Low-energy input signals and their transport with negligible energy loss are the key technological factors in the design of information-signal processing devices. Here, utilizing the concept of coupled oscillators, we experimentally demonstrated a robust new mechanism for energy transfer...

  15. Tunable energy transfer between dipolar-coupled magnetic disks by stimulated vortex gyration

    OpenAIRE

    Jung, Hyunsung; Lee, Ki-Suk; Jeong, Dae-Eun; Choi, Youn-Seok; Yu, Young-Sang; Han, Dong-Soo; Vogel, Andreas; Bocklage, Lars; Meier, Guido; Im, Mi-Young; Fischer, Peter; Kim, Sang-Koog

    2010-01-01

    A wide variety of coupled harmonic oscillators exist in nature1. Coupling between different oscillators allows for the possibility of mutual energy transfer between them2-4 and the information-signal propagation5,6. Low-energy input signals and their transport with low-energy dissipation are the key technical factors in the design of information processing devices7. Here, utilizing the concept of coupled oscillators, we experimentally demonstrated a robust new mechanism for energy transfer be...

  16. Electrical control of the exciton-biexciton splitting in self-assembled InGaAs quantum dots

    Energy Technology Data Exchange (ETDEWEB)

    Kaniber, M; Huck, M F; Mueller, K; Clark, E C; Bichler, M; Finley, J J [Walter Schottky Institut, Technische Universitaet Muenchen, Am Coulombwall 4, 85748 Garching (Germany); Troiani, F [S3, Instituto Nanoscienze-CNR, 41125 Modena (Italy); Krenner, H J, E-mail: kaniber@wsi.tum.de [Lehrstuhl fuer Experimentalphysik 1 and Augsburg Center for Innovative Technologies (ACIT), Universitaet Augsburg, Universiaetsstr. 1, 86159 Augsburg (Germany)

    2011-08-12

    The authors demonstrate how lateral electric fields can be used to precisely control the exciton-biexciton splitting in InGaAs quantum dots. By defining split-gate electrodes on the sample surface, optical studies show how the exciton transition can be tuned into resonance with the biexciton by exploiting the characteristically dissimilar DC Stark shifts. The results are compared to model calculations of the relative energies of the exciton and biexciton, demonstrating that the tuning can be traced to a dominance of hole-hole repulsion in the presence of a lateral field. Cascaded decay of the exciton-biexciton system enables the generation of entangled photon pairs without the need to suppress the fine structure splitting of the exciton. Our results demonstrate how the exciton-biexciton system can be electrically controlled.

  17. High resolution IR diode laser study of collisional energy transfer between highly vibrationally excited monofluorobenzene and CO2: the effect of donor fluorination on strong collision energy transfer.

    Science.gov (United States)

    Kim, Kilyoung; Johnson, Alan M; Powell, Amber L; Mitchell, Deborah G; Sevy, Eric T

    2014-12-21

    Collisional energy transfer between vibrational ground state CO2 and highly vibrationally excited monofluorobenzene (MFB) was studied using narrow bandwidth (0.0003 cm(-1)) IR diode laser absorption spectroscopy. Highly vibrationally excited MFB with E' = ∼41,000 cm(-1) was prepared by 248 nm UV excitation followed by rapid radiationless internal conversion to the electronic ground state (S1→S0*). The amount of vibrational energy transferred from hot MFB into rotations and translations of CO2 via collisions was measured by probing the scattered CO2 using the IR diode laser. The absolute state specific energy transfer rate constants and scattering probabilities for single collisions between hot MFB and CO2 were measured and used to determine the energy transfer probability distribution function, P(E,E'), in the large ΔE region. P(E,E') was then fit to a bi-exponential function and extrapolated to the low ΔE region. P(E,E') and the biexponential fit data were used to determine the partitioning between weak and strong collisions as well as investigate molecular properties responsible for large collisional energy transfer events. Fermi's Golden rule was used to model the shape of P(E,E') and identify which donor vibrational motions are primarily responsible for energy transfer. In general, the results suggest that low-frequency MFB vibrational modes are primarily responsible for strong collisions, and govern the shape and magnitude of P(E,E'). Where deviations from this general trend occur, vibrational modes with large negative anharmonicity constants are more efficient energy gateways than modes with similar frequency, while vibrational modes with large positive anharmonicity constants are less efficient at energy transfer than modes of similar frequency.

  18. Travelling energy systems: knowledge transfer for energy efficiency and conservation from European to Australian building projects

    Energy Technology Data Exchange (ETDEWEB)

    Glad, Wiktoria (Tema Technology and Social Change, Linkoeping Univ. (Sweden); Inst. for Sustainable Futures, Univ. of Technology, Sydney (Australia))

    2009-07-01

    Energy efficiency and conservation in the Australian built environment have not yet been implemented to any great extent. Despite favourable prerequisites, such as vast windswept unpopulated areas suitable for wind power and many hours of direct sunlight in most populated areas, electricity is mainly generated by burning brown coal and buildings are poorly equipped for hot summers and cool winters. Australia urgently needs to convert to alternative energy sources and implement energy efficiency measures, since its carbon dioxide emissions per capita are among the highest in the world. In a recent major redevelopment in Sydney, the Carlton and United Brewery (CUB) site knowledge of energy efficiency and conservation measures used in European buildings was transferred and implemented in local designs and infrastructure. This knowledge came mainly from urban planning and developments in London, but also from high-profile architectural firms based in Paris and Germany. The arrival of this knowledge in Australia led to phases when the knowledge was translated and enacted in local spaces and the constituent ideas were transformed into action. The present research is based on ten months of ethnographic fieldwork in which the planning and design of the CUB site was observed. The results of the study identify barriers to and opportunities for energy system knowledge transfer between different cultures and local spaces. Substantial time must be spent overcoming cultural barriers, so the involved parties can start talking the same language. This is not only true for stakeholders operating in different continents, but for stakeholders operating in different local arenas in the same country.

  19. Imaging and Manipulating Energy Transfer Among Quantum Dots at Individual Dot Resolution.

    Science.gov (United States)

    Nguyen, Duc; Nguyen, Huy A; Lyding, Joseph W; Gruebele, Martin

    2017-06-27

    Many processes of interest in quantum dots involve charge or energy transfer from one dot to another. Energy transfer in films of quantum dots as well as between linked quantum dots has been demonstrated by luminescence shift, and the ultrafast time-dependence of energy transfer processes has been resolved. Bandgap variation among dots (energy disorder) and dot separation are known to play an important role in how energy diffuses. Thus, it would be very useful if energy transfer could be visualized directly on a dot-by-dot basis among small clusters or within films of quantum dots. To that effect, we report single molecule optical absorption detected by scanning tunneling microscopy (SMA-STM) to image energy pooling from donor into acceptor dots on a dot-by-dot basis. We show that we can manipulate groups of quantum dots by pruning away the dominant acceptor dot, and switching the energy transfer path to a different acceptor dot. Our experimental data agrees well with a simple Monte Carlo lattice model of energy transfer, similar to models in the literature, in which excitation energy is transferred preferentially from dots with a larger bandgap to dots with a smaller bandgap.

  20. Exploiting Structured Environments for Efficient Energy Transfer: The Phonon Antenna Mechanism.

    Science.gov (United States)

    Rey, Marco Del; Chin, Alex W; Huelga, Susana F; Plenio, Martin B

    2013-03-21

    A nontrivial interplay between quantum coherence and dissipative environment-driven dynamics is becoming increasingly recognized as the key for efficient energy transport in photosynthetic pigment-protein complexes, and converting these biologically inspired insights into a set of design principles that can be implemented in artificial light-harvesting systems has become an active research field. Here we identify a specific design principle, the phonon antenna, by which interpigment coherence is able to modify and optimize the way that excitations spectrally sample their local environmental fluctuations. We provide numerical simulations that suggest that the Fenna-Matthews-Olson complex of green sulfur bacteria has an excitonic structure that is close to such an optimal operating point, and place the phonon antenna concept into a broader context that leads us to conjecture that this general design principle might well be exploited in other biomolecular systems.

  1. Predicting Excitonic Gaps of Semiconducting Single Walled Carbon Nanotubes From a Field Theoretic Analysis

    OpenAIRE

    Konik, Robert M.; Sfeir, Matthew Y.; Misewich, James A.

    2014-01-01

    We demonstrate that a non-perturbative framework for the treatment of the excitations of single walled carbon nanotubes based upon a field theoretic reduction is able to accurately describe experiment observations of the absolute values of excitonic energies. This theoretical framework yields a simple scaling function from which the excitonic energies can be read off. This scaling function is primarily determined by a single parameter, the charge Luttinger parameter of the tube, which is in t...

  2. Effect of exciton oscillator strength on upconversion photoluminescence in GaAs/AlAs multiple quantum wells

    Energy Technology Data Exchange (ETDEWEB)

    Kojima, Osamu, E-mail: kojima@phoenix.kobe-u.ac.jp; Okumura, Shouhei; Kita, Takashi [Department of Electrical and Electronic Engineering, Graduate School of Engineering, Kobe University, 1-1 Rokkodai, Nada, Kobe 657-8501 (Japan); Akahane, Kouichi [National Institute of Information and Communications Technology, 4-2-1 Nukui-kitamachi, Koganei, Tokyo 184-8795 (Japan)

    2014-11-03

    We report upconversion photoluminescence (UCPL) in GaAs/AlAs multiple quantum wells. UCPL from the AlAs barrier is caused by the resonant excitation of the excitons in the GaAs well. When the quantum well has sufficient miniband width, UCPL is hardly observed because of the small exciton oscillator strength. The excitation-energy and excitation-density dependences of UCPL intensity show the exciton resonant profile and a linear increase, respectively. These results demonstrate that the observed UCPL caused by the saturated two-step excitation process requires a large number of excitons.

  3. Study made of transfer of heat energy through metal joints in vacuum environment

    Science.gov (United States)

    Elliot, D. H.

    1967-01-01

    Heat energy transfer is concentrated closely around a melted joint and the temperature drop across it decreases rapidly as the bolt and nut are tightened to a minimum torque level. Flat metal surfaces pressed together display a cyclical improvement in heat energy transfer as the interface pressure is increased.

  4. The 2H(e, e' p)n reaction at large energy transfers

    NARCIS (Netherlands)

    Willering, Hendrik Willem

    2003-01-01

    At the ELSA accelerator facillity in Bonn, Germany, we have measured the deutron "breakup" reaction 2H(e,e' p)n at four-momentum transfers around Q2 = -0 .20(GeV/c)2 with an electron beam energy of E0 = 1.6 GeV. The cross section has been determined for energy transfers extending from the

  5. A study of polaritonic transparency in couplers made from excitonic materials

    Energy Technology Data Exchange (ETDEWEB)

    Singh, Mahi R.; Racknor, Chris [Department of Physics and Astronomy, Western University, London, Ontario N6A 3K7 (Canada)

    2015-03-14

    We have studied light matter interaction in quantum dot and exciton-polaritonic coupler hybrid systems. The coupler is made by embedding two slabs of an excitonic material (CdS) into a host excitonic material (ZnO). An ensemble of non-interacting quantum dots is doped in the coupler. The bound exciton polariton states are calculated in the coupler using the transfer matrix method in the presence of the coupling between the external light (photons) and excitons. These bound exciton-polaritons interact with the excitons present in the quantum dots and the coupler is acting as a reservoir. The Schrödinger equation method has been used to calculate the absorption coefficient in quantum dots. It is found that when the distance between two slabs (CdS) is greater than decay length of evanescent waves the absorption spectrum has two peaks and one minimum. The minimum corresponds to a transparent state in the system. However, when the distance between the slabs is smaller than the decay length of evanescent waves, the absorption spectra has three peaks and two transparent states. In other words, one transparent state can be switched to two transparent states when the distance between the two layers is modified. This could be achieved by applying stress and strain fields. It is also found that transparent states can be switched on and off by applying an external control laser field.

  6. Investigation of Exciton Recombination Zone in Quantum Dot Light-Emitting Diodes Using a Fluorescent Probe.

    Science.gov (United States)

    Huang, Xiaoyu; Zhang, Heng; Xu, Dingxin; Wen, Feng; Chen, Shuming

    2017-08-23

    Exciton recombination zone, where the photons are generated, can greatly affect the performance, such as the efficiency and color purity, of the quantum dot (QD) light-emitting diodes (QLEDs). To probe the exciton recombination zone, 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) is doped into the charge transport layer as a fluorescent sensor; by monitoring the Förster resonant energy transfer (FRET) between QD and DCJTB, the location of the recombination zone can be determined. It is found that the electron transport layer (ETL) has a great impact on the recombination zone. For example, in QLEDs with ZnMgO ETL, the recombination zone is near the interface of the QD/hole transport layer (HTL) and is shifted to the interface of the QD/ETL as the driving voltage is increased, whereas in devices with 1,3,5-tris(2-N-phenylbenzimidazolyl) benzene (TPBi) ETL, the recombination zone is close to the interface of the QD/ETL and moved to the interface of the QD/HTL with the increase in the driving voltage. Our results can also clarify the light emission mechanism in QLEDs. In devices with ZnMgO ETL, the emission is dominated by the direct charge recombination, whereas in devices with TPBi ETL, the emission is contributed by both FRET and direct charge recombination. Our studies suggest that fluorescent probe can be a powerful tool for investigating the exciton recombination zone, light emission mechanism, and other fundamental processes in QLEDs.

  7. Momentum and Energy Transfer in an Ionospheric Critical Ionization Velocity Experiment

    OpenAIRE

    Bolin, O.; Brenning, N.; Swenson, C. M.; Primdahl, Fritz

    1995-01-01

    We present new data from the subpayload of the GRIT II ionospheric active injection experiment. The analysis made possible by these data provides a good understanding of the momentum transfer between the injected ions and the ambient ionosphere. It resolves the conflict between the two competing models for the energy transfer from the newly created ions to hot electrons, while also giving a natural coupling between the energy and momentum transfer processes.

  8. Exciton dynamics in molecular aggregates

    NARCIS (Netherlands)

    Augulis, R.; Pugžlys, A.; Loosdrecht, P.H.M. van; Pugzlys, A

    2006-01-01

    The fundamental aspects of exciton dynamics in double-wall cylindrical aggregates of cyanine dyes are studied by means of frequency resolved femtosecond pump-probe spectroscopy. The collective excitations of the aggregates, resulting from intermolecular dipole-dipole interactions have the

  9. Magnetic exciton dispersion in praseodymium

    DEFF Research Database (Denmark)

    Rainford, B. D.; Houmann, Jens Christian Gylden

    1971-01-01

    Measurements of the dispersion of magnetic excitons have been made in a single crystal of praseodymium metal using inelastic neutron scattering. A preliminary analysis of the data yields the first detailed information about the exchange interactions and the crystal field splittings in the light...

  10. Excitons in tubular molecular aggregates

    NARCIS (Netherlands)

    Didraga, C; Knoester, J

    2004-01-01

    We present a brief overview of recent work on the optical properties of molecular aggregates with a tubular (cylindrical) shape. The exciton states responsible for these properties can be distinguished with regard to a transverse wave number, which directly relates to optical selection rules and

  11. Rotational Energy Transfer of N2 Determined Using a New Ab Initio Potential Energy Surface

    Science.gov (United States)

    Huo, Winifred M.; Stallcop, James R.; Partridge, Harry; Langhoff, Stephen R. (Technical Monitor)

    1997-01-01

    A new N2-N2 rigid-rotor surface has been determined using extensive Ab Initio quantum chemistry calculations together with recent experimental data for the second virial coefficient. Rotational energy transfer is studied using the new potential energy surface (PES) employing the close coupling method below 200 cm(exp -1) and coupled state approximation above that. Comparing with a previous calculation based on the PES of van der Avoird et al.,3 it is found that the new PES generally gives larger cross sections for large (delta)J transitions, but for small (delta)J transitions the cross sections are either comparable or smaller. Correlation between the differences in the cross sections and the two PES will be attempted. The computed cross sections will also be compared with available experimental data.

  12. Excitons into one-axis crystals of zinc phosphide (Zn3P2

    Directory of Open Access Journals (Sweden)

    D.M. Stepanchikov

    2009-01-01

    Full Text Available Theoretical study of excitons spectra is offered in this report as for Zn3P2 crystals. Spectra are got in the zero approach of the theory of perturbations with consideration of both the anisotropy of the dispersion law and the selection rules. The existence of two exciton series was found, which corresponds to two valence bands (hh, lh and the conductivity band (c. It is noteworthy that anisotropy of the dispersion law plus the existence of crystalline packets (layers normal to the main optical axis, both will permit the consideration of two-dimensional excitons too. The high temperature displaying of these 2D-exciton effects is not eliminated even into bulk crystals. The calculated values of the binding energies as well as the oscillator's strength for the optical transitions are given for a volume (3D and for two-dimensional (2D excitons. The model of energy exciton transitions and four-level scheme of stimulated exciton radiation for receiving laser effect are offered.

  13. Strong excitonic interactions in the oxygen K-edge of perovskite oxides

    Energy Technology Data Exchange (ETDEWEB)

    Tomita, Kota; Miyata, Tomohiro [Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505 (Japan); Olovsson, Weine [Department of Physics, Chemistry and Biology (IFM), Linköping University, SE-581 83 Linköping (Sweden); Mizoguchi, Teruyasu, E-mail: teru@iis.u-tokyo.ac.jp [Institute of Industrial Science, The University of Tokyo, 4-6-1 Komaba, Meguro, Tokyo 153-8505 (Japan)

    2017-07-15

    Excitonic interactions of the oxygen K-edge electron energy-loss near-edge structure (ELNES) of perovskite oxides, CaTiO{sub 3}, SrTiO{sub 3}, and BaTiO{sub 3}, together with reference oxides, MgO, CaO, SrO, BaO, and TiO{sub 2}, were investigated using a first-principles Bethe–Salpeter equation calculation. Although the transition energy of oxygen K-edge is high, strong excitonic interactions were present in the oxygen K-edge ELNES of the perovskite oxides, whereas the excitonic interactions were negligible in the oxygen K-edge ELNES of the reference compounds. Detailed investigation of the electronic structure suggests that the strong excitonic interaction in the oxygen K-edge ELNES of the perovskite oxides is caused by the directionally confined, low-dimensional electronic structure at the Ti–O–Ti bonds. - Highlights: • Excitonic interaction in oxygen-K edge is investigated. • Strong excitonic interaction is found in the oxygen-K edge of perovskite oxides. • The strong excitonic interaction is ascribed to the low-dimensional and confined electronic structure.

  14. Low temperature exciton-exciton annihilation in amphi-PIPE J-aggregates

    Directory of Open Access Journals (Sweden)

    C. Spitz

    2006-01-01

    Full Text Available The mobility of optically excited excitons on J-aggregates can be demonstrated by the phenomena of exciton-exciton annihilation. In this intensity-dependent process the collision of two excitons results in their annihilation and hence in a shortening of the mean excitation lifetime. By measuring the intensity-dependent fluorescent lifetime in contrast to the predicted immobilization of the excitons at low temperature we could prove the excellent mobility of the excitons at a temperature (4K, which is far below their expected freezing point.

  15. Energy transfers in large-scale and small-scale dynamos

    Science.gov (United States)

    Samtaney, Ravi; Kumar, Rohit; Verma, Mahendra

    2015-11-01

    We present the energy transfers, mainly energy fluxes and shell-to-shell energy transfers in small-scale dynamo (SSD) and large-scale dynamo (LSD) using numerical simulations of MHD turbulence for Pm = 20 (SSD) and for Pm = 0.2 on 10243 grid. For SSD, we demonstrate that the magnetic energy growth is caused by nonlocal energy transfers from the large-scale or forcing-scale velocity field to small-scale magnetic field. The peak of these energy transfers move towards lower wavenumbers as dynamo evolves, which is the reason for the growth of the magnetic fields at the large scales. The energy transfers U2U (velocity to velocity) and B2B (magnetic to magnetic) are forward and local. For LSD, we show that the magnetic energy growth takes place via energy transfers from large-scale velocity field to large-scale magnetic field. We observe forward U2U and B2B energy flux, similar to SSD.

  16. Förster Resonance Energy Transfer between Core/Shell Quantum Dots and Bacteriorhodopsin

    Directory of Open Access Journals (Sweden)

    Mark H. Griep

    2012-01-01

    Full Text Available An energy transfer relationship between core-shell CdSe/ZnS quantum dots (QDs and the optical protein bacteriorhodopsin (bR is shown, demonstrating a distance-dependent energy transfer with 88.2% and 51.1% of the QD energy being transferred to the bR monomer at separation distances of 3.5 nm and 8.5 nm, respectively. Fluorescence lifetime measurements isolate nonradiative energy transfer, other than optical absorptive mechanisms, with the effective QD excited state lifetime reducing from 18.0 ns to 13.3 ns with bR integration, demonstrating the Förster resonance energy transfer contributes to 26.1% of the transferred QD energy at the 3.5 nm separation distance. The established direct energy transfer mechanism holds the potential to enhance the bR spectral range and sensitivity of energies that the protein can utilize, increasing its subsequent photocurrent generation, a significant potential expansion of the applicability of bR in solar cell, biosensing, biocomputing, optoelectronic, and imaging technologies.

  17. Picosecond dynamics of internal exciton transitions in CdSe nanorods

    DEFF Research Database (Denmark)

    Cooke, D. G.; Jepsen, Peter Uhd; Lek, Jun Yan

    2013-01-01

    . The onset of exciton-LO phonon coupling appears as a bleach in the optical conductivity spectra at the LO phonon energy for times > 1 ps after excitation. Simulations show a suppressed exciton temperature due to thermally excited hole states being rapidly captured onto ligands or unpassivated surface states......The picosecond dynamics of excitons in colloidal CdSe nanorods are directly measured via their 1s to 2p-like internal transitions by ultrabroadband terahertz spectroscopy. Broadened absorption peaks from both the longitudinal and transverse states are observed at 8.5 and 11 THz, respectively...

  18. Resonant exciton-phonon coupling in ZnO nanorods at room temperature

    Directory of Open Access Journals (Sweden)

    Soumee Chakraborty

    2011-09-01

    Full Text Available Vibronic and optoelectronic properties, along with detailed studies of exciton-phonon coupling at room temperature (RT for random and aligned ZnO nanorods are reported. Excitation energy dependent Raman studies are performed for detailed analysis of multi-phonon processes in the nanorods. We report here the origin of coupling between free exciton and its associated phonon replicas, including its higher order modes, in the photoluminescence spectra at RT. Resonance of excitonic electron and resonating first order zone center LO phonon, invoked strongly by Frolich interaction, are made responsible for the observed phenomenon.

  19. Particle-in-a-bos model of one-dimensional excitons in conjugated polymers

    DEFF Research Database (Denmark)

    Pedersen, T.G.; Johansen, P.M.; Pedersen, H.C.

    2000-01-01

    A simple two-particle model of excitons in conjugated polymers is proposed as an alternative to usual highly computationally demanding quantum chemical methods. In the two-particle model, the exciton is described as an electron-hole pair interacting via Coulomb forces and confined to the polymer...... of these cases an approximate solution for the general case is obtained. As an application of the model the influence of a static electric field on the electron-hole overlap integral and exciton energy is considered....

  20. Linear energy transfer incorporated intensity modulated proton therapy optimization

    Science.gov (United States)

    Cao, Wenhua; Khabazian, Azin; Yepes, Pablo P.; Lim, Gino; Poenisch, Falk; Grosshans, David R.; Mohan, Radhe

    2018-01-01

    The purpose of this study was to investigate the feasibility of incorporating linear energy transfer (LET) into the optimization of intensity modulated proton therapy (IMPT) plans. Because increased LET correlates with increased biological effectiveness of protons, high LETs in target volumes and low LETs in critical structures and normal tissues are preferred in an IMPT plan. However, if not explicitly incorporated into the optimization criteria, different IMPT plans may yield similar physical dose distributions but greatly different LET, specifically dose-averaged LET, distributions. Conventionally, the IMPT optimization criteria (or cost function) only includes dose-based objectives in which the relative biological effectiveness (RBE) is assumed to have a constant value of 1.1. In this study, we added LET-based objectives for maximizing LET in target volumes and minimizing LET in critical structures and normal tissues. Due to the fractional programming nature of the resulting model, we used a variable reformulation approach so that the optimization process is computationally equivalent to conventional IMPT optimization. In this study, five brain tumor patients who had been treated with proton therapy at our institution were selected. Two plans were created for each patient based on the proposed LET-incorporated optimization (LETOpt) and the conventional dose-based optimization (DoseOpt). The optimized plans were compared in terms of both dose (assuming a constant RBE of 1.1 as adopted in clinical practice) and LET. Both optimization approaches were able to generate comparable dose distributions. The LET-incorporated optimization achieved not only pronounced reduction of LET values in critical organs, such as brainstem and optic chiasm, but also increased LET in target volumes, compared to the conventional dose-based optimization. However, on occasion, there was a need to tradeoff the acceptability of dose and LET distributions. Our conclusion is that the

  1. Linear energy transfer incorporated intensity modulated proton therapy optimization.

    Science.gov (United States)

    Cao, Wenhua; Khabazian, Azin; Yepes, Pablo P; Lim, Gino J; Poenisch, Falk; Grosshans, David R; Mohan, Radhe

    2017-11-13

    The purpose of this study was to investigate the feasibility of incorporating linear energy transfer (LET) into the optimization of intensity modulated proton therapy (IMPT) plans. Because increased LET correlates with increased biological effectiveness of protons, high LETs in target volumes and low LETs in critical structures and normal tissues are preferred in an IMPT plan. However, if not explicitly incorporated into the optimization criteria, different IMPT plans may yield similar physical dose distributions but greatly different LET, specifically dose-averaged LET, distributions. Conventionally, the IMPT optimization criteria (or cost function) only includes dose-based objectives in which the relative biological effectiveness (RBE) is assumed to have a constant value of 1.1. In this study, we added LET-based objectives for maximizing LET in target volumes and minimizing LET in critical structures and normal tissues. Due to the fractional programming nature of the resulting model, we used a variable reformulation approach so that the optimization process is computationally equivalent to conventional IMPT optimization. In this study, five brain tumor patients who had been treated with proton therapy at our institution were selected. Two plans were created for each patient based on the proposed LET-incorporated optimization (LETOpt) and the conventional dose-based optimization (DoseOpt). The optimized plans were compared in terms of both dose (assuming a constant RBE of 1.1 as adopted in clinical practice) and LET. Both optimization approaches were able to generate comparable dose distributions. The LET-incorporated optimization achieved not only pronounced reduction of LET values in critical organs, such as brainstem and optic chiasm, but also increased LET in the target volumes, compared to the conventional dose-based optimization. However, on occasion, there was a need to tradeoff the acceptability of dose and LET distributions. Our conclusion is that the

  2. Biomolecular interactions probed by fluorescence resonance energy transfer

    Science.gov (United States)

    Lange, Daniela Charlotte

    2000-09-01

    This thesis describes how a physical phenomenon, Fluorescence Resonance Energy Transfer (FRET), can be exploited for the study of interactions between biomolecules. The physical basis of this phenomenon is discussed and it is described how some of its characteristics can be exploited in measurement. A recently introduced method, photobleaching FRET microscopy, was implemented and its image analysis refined to suit our biological context. Further, a new technique is proposed, which combines FRET with confocal laser scanning microscopy to optimize resolution and to allow for 3D-studies in living cells. The first part of this thesis presents the application of FRET to the study of oligomerization of G-protein coupled receptors (GPCRs), which was performed at the Fraser Laboratories at McGill University in Montreal. It is demonstrated how FRET microscopy allowed us to circumvent problems of traditional biochemical approaches and provided the first direct evidence for GPCR oligomerization in intact cells. We found that somatostatin receptors (SSTRs) functionally interact by forming oligomers with their own kind, with different SSTR isoforms, and even with distantly related GPCRs, such as dopamine receptors, the latter of which is breaking with the dogma that GPCRs would only pair up with their own kind. The high sensitivity of the FRET technique allowed us to characterize these interactions under more physiological conditions, which lead to the observation that oligomerization is induced by receptor agonist. We further studied the differential effects of agonists and antagonists on receptor oligomerization, leading to a model for the molecular mechanism underlying agonist/antagonist function and receptor activation. The second part was carried out at the Neurobiology Laboratory of the VA Medical Center in Newington, CT. The objective was to further our understanding of Niemann- Pick type C disease, which is characterized by a defect in intracellular cholesterol

  3. Nanoscale heat transfer and thermoelectrics for alternative energy

    Science.gov (United States)

    Robinson, Richard

    2011-03-01

    In the area of alternative energy, thermoelectrics have experienced an unprecedented growth in popularity because of their ability to convert waste heat into electricity. Wired in reverse, thermoelectrics can act as refrigeration devices, where they are promising because they are small in size and lightweight, have no moving parts, and have rapid on/off cycles. However, due to their low efficiencies bulk thermoelectrics have historically been a niche market. Only in the last decade has thermoelectric efficiency exceeded ~ 20 % due to fabrication of nanostructured materials. Nanoscale materials have this advantage because electronic and acoustic confinement effects can greatly increase thermoelectric efficiency beyond bulk values. In this talk, I will introduce our work in the area of nanoscale heat transfer with the goal of more efficient thermoelectrics. I will discuss our experiments and methods to study acoustic confinement in nanostructures and present some of our new nanostructured thermoelectric materials. To study acoustic confinement we are building a nanoscale phonon spectrometer. The instrument can excite phonon modes in nanostructures in the ~ 100 s of GHz. Ballistic phonons from the generator are used to probe acoustic confinement and surface scattering effects. Transmission studies using this device will help optimize materials and morphologies for more efficient nanomaterial-based thermoelectrics. For materials, our group has synthesized nano-layer superlattices of Na x Co O2 . Sodium cobaltate was recently discovered to have a high Seebeck coeficent and is being studied as an oxide thermoelectric material. The thickness of our nano-layers ranges from 5 nm to 300 nm while the lengths can be varied between 10 μ m and 4 mm. Typical aspect ratios are 40 nm: 4 mm, or 1:100,000. Thermoelectric characterization of samples with tilted multiple-grains along the measurement axis indicate a thermoelectric efficiency on par with current polycrystalline samples

  4. Analysis on spatial transfer model of energy development layout and the ecological footprint affection

    Science.gov (United States)

    Wei, Xiaoxia; Zhang, Jinfang

    2017-01-01

    Consider the global energy interconnection, the global is concentrating on carrying out clean energy alternative, which is mainly focusing on using the clean energy to take place of fossil energy, and change the global energy layout and ecological atmosphere condition. This research gives the energy spatial transfer model of energy development layout to analyse the global energy development layout condition and ecological affection. And it is a fast and direct method to analyse its energy usage process and environmental affection. The paper also gives out a system dynamics model of energy spatial transfer shows, which electric power transmission is better than original energy usage and transportation. It also gives the comparison of different parameters. The energy spatial transfer can affect the environment directly. Consider its three environmental factors, including energy saving, climate changing and conventional pollutant emission reduction, synthetic combine with the spatial transfer model, it can get the environmental change parameters, which showed that with the clean energy wide usage, the ecological footprint affection will be affected significantly.

  5. Technology transfer for the US Department of Energy's Energy Storage Program: Volume 2, Appendices

    Energy Technology Data Exchange (ETDEWEB)

    Bruneau, C.L.; Fassbender, L.L.

    1988-10-01

    This document contains the appendices to Technology Transfer Recommendations for the US Department of Energy's Storage Program (PNL-6484, Vol. 1). These appendices are a list of projects, publications, and presentations connected with the Energy Storage (STOR) program. In Volume 1, the technology transfer activities of the STOR program are examined and mechanisms for increasing the effectiveness of those activities are recommended.

  6. Excitonic Quasimolecules Formed by Spatially Separated Electrons and Holes in a Ge/Si Heterostructure with Germanium Quantum Dots

    Science.gov (United States)

    Pokutnyi, S. I.

    2017-05-01

    It is shown that in a Ge/Si nanostructure with germanium quantum dots, two Ge quantum dots act as an excitonic quasimolecule, where the excitons (formed by spatially separated electrons and holes) are localized above the surfaces of the quantum dots. A substantial increase in binding energy is observed for the singlet ground state of the excitonic quasimolecule in the nanosystem, compared with the binding energy of a biexciton in a silicon single crystal. It is established that the major contribution to the binding energy of the quasimolecule comes from the electron-hole exchange interaction energy, which is considerably greater than the contribution from the electron-hole Coulomb interaction.

  7. Photoinduced energy and electron transfer in rubrene-benzoquinone and rubrene-porphyrin systems

    KAUST Repository

    Khan, Jafar Iqbal

    2014-11-01

    Excited-state electron and energy transfer from singlet excited rubrene (Ru) to benzoquinone (BQ) and tetra-(4-aminophenyl) porphyrin (TAPP) were investigated by steady-state absorption and emission, time-resolved transient absorption, and femtosecond (fs)-nanosecond (ns) fluorescence spectroscopy. The low reduction potential of BQ provides the high probability of electron transfer from the excited Ru to BQ. Steady-state and time-resolved results confirm such an excited electron transfer scenario. On the other hand, strong spectral overlap between the emission of Ru and absorption of TAPP suggests that energy transfer is a possible deactivation pathway of the Ru excited state.

  8. Real-space investigation of energy transfer in heterogeneous molecular dimers

    Science.gov (United States)

    Imada, Hiroshi; Miwa, Kuniyuki; Imai-Imada, Miyabi; Kawahara, Shota; Kimura, Kensuke; Kim, Yousoo

    2016-10-01

    Given its central role in photosynthesis and artificial energy-harvesting devices, energy transfer has been widely studied using optical spectroscopy to monitor excitation dynamics and probe the molecular-level control of energy transfer between coupled molecules. However, the spatial resolution of conventional optical spectroscopy is limited to a few hundred nanometres and thus cannot reveal the nanoscale spatial features associated with such processes. In contrast, scanning tunnelling luminescence spectroscopy has revealed the energy dynamics associated with phenomena ranging from single-molecule electroluminescence, absorption of localized plasmons and quantum interference effects to energy delocalization and intervalley electron scattering with submolecular spatial resolution in real space. Here we apply this technique to individual molecular dimers that comprise a magnesium phthalocyanine and a free-base phthalocyanine (MgPc and H2Pc) and find that locally exciting MgPc with the tunnelling current of the scanning tunnelling microscope generates a luminescence signal from a nearby H2Pc molecule as a result of resonance energy transfer from the former to the latter. A reciprocating resonance energy transfer is observed when exciting the second singlet state (S2) of H2Pc, which results in energy transfer to the first singlet state (S1) of MgPc and final funnelling to the S1 state of H2Pc. We also show that tautomerization of H2Pc changes the energy transfer characteristics within the dimer system, which essentially makes H2Pc a single-molecule energy transfer valve device that manifests itself by blinking resonance energy transfer behaviour.

  9. Hole, impurity and exciton states in a spherical quantum dot

    Directory of Open Access Journals (Sweden)

    V.I. Boichuk

    2010-01-01

    Full Text Available The 3x3 kp hole Hamiltonian for the wave-function envelopes (effective mass Hamiltonian was used for calculation of discrete states of the hole and acceptor hydrogenic impurity in a spherical Si/SiO2 nanoheterostructure as a function of the quantum dot radius by neglecting the corrugation of constant-energy surfaces. A study was conducted in the case of finite potential well at the separation boundary of the nanoheterosystem. The dependence of the hole energy spectrum on polarization charges, which arise at the separation boundary of the media, and on the dielectric permittivity, was defined. Using the exact electron and hole solutions, the exciton wave-function was constructed and the exciton ground-state energy was defined. The theoretical results have been compared with experimental data.

  10. Chirality and energy transfer amplified circularly polarized luminescence in composite nanohelix

    Science.gov (United States)

    Yang, Dong; Duan, Pengfei; Zhang, Li; Liu, Minghua

    2017-06-01

    Transfer of both chirality and energy information plays an important role in biological systems. Here we show a chiral donor π-gelator and assembled it with an achiral π-acceptor to see how chirality and energy can be transferred in a composite donor-acceptor system. It is found that the individual chiral gelator can self-assemble into nanohelix. In the presence of the achiral acceptor, the self-assembly can also proceed and lead to the formation of the composite nanohelix. In the composite nanohelix, an energy transfer is realized. Interestingly, in the composite nanohelix, the achiral acceptor can both capture the supramolecular chirality and collect the circularly polarized energy from the chiral donor, showing both supramolecular chirality and energy transfer amplified circularly polarized luminescence (ETACPL).

  11. Introducing novel amorphous carbon nanoparticles as energy acceptors into a chemiluminescence resonance energy transfer immunoassay system.

    Science.gov (United States)

    Wang, Zhenxing; Gao, Hongfei; Fu, Zhifeng

    2013-11-21

    A novel chemiluminescence resonance energy transfer (CRET) system for competitive immunoassay of biomolecules was developed by using novel amorphous carbon nanoparticles (CNPs) prepared from candle soot as energy acceptors. The CNPs were firstly prepared to bind with the antigen (Ag) for obtaining the nanocomposite CNP-Ag, and this obtained CNP-Ag was then reacted with the horseradish peroxidase-labeled antibody (HRP-Ab) to assemble the CRET system. The luminol catalyzed by HRP serving as the energy donor for CNPs triggered the CRET phenomenon between luminol and CNPs, which led to the chemiluminescence signal decrease. Due to the competitive immunoreaction of the target antigen and the CNP-Ag, a part of the CNP-Ag was replaced from the HRP-Ab, and then resulted in a weaker interaction between luminol and CNPs. Thus the competitive immunoreaction led to a higher chemiluminescence emission. This CNP-based CRET system was successfully applied to detect the human IgG as a model analyte, and a linear range of 10-200 ng mL(-1) and a detection limit of 1.9 ng mL(-1) (S/N = 3) were obtained. The results for real sample analysis demonstrated its application potential in some important areas such as clinical diagnosis.

  12. Peculiarities in the energy transfer by waves on strained strings

    Science.gov (United States)

    Butikov, Eugene I.

    2013-12-01

    Localization of elastic potential energy associated with waves in a stretched string is discussed. The influence of nonlinear coupling between transverse and longitudinal waves on the density of energy is investigated by considering the examples of stationary traveling and standing waves. Misunderstandings about different expressions for the density of potential energy encountered in the literature are clarified. The common statement regarding the relationship between the densities of kinetic and potential energies in a transverse wave is criticized.

  13. Local strain-induced band gap fluctuations and exciton localization in aged WS2 monolayers

    Science.gov (United States)

    Krustok, J.; Kaupmees, R.; Jaaniso, R.; Kiisk, V.; Sildos, I.; Li, B.; Gong, Y.

    2017-06-01

    Optical properties of aged WS2 monolayers grown by CVD method on Si/SiO2 substrates are studied using temperature dependent photoluminescence and reflectance contrast spectroscopy. Aged WS2 monolayers have a typical surface roughness about 0.5 nm and, in addition, a high density of nanoparticles (nanocaps) with the base diameter about 30 nm and average height of 7 nm. The A-exciton of aged monolayer has a peak position at 1.951 eV while in as-grown monolayer the peak is at about 24 meV higher energy at room temperature. This red-shift is explained using local tensile strain concept, where strain value of 2.1% was calculated for these nanocap regions. Strained nanocaps have lower band gap energy and excitons will funnel into these regions. At T=10K a double exciton and trion peaks were revealed. The separation between double peaks is about 20 meV and the origin of higher energy peaks is related to the optical band gap energy fluctuations caused by random distribution of local tensile strain due to increased surface roughness. In addition, a wide defect related exciton band XD was found at about 1.93 eV in all aged monolayers. It is shown that the theory of localized excitons describes well the temperature dependence of peak position and halfwidth of the A-exciton band. The possible origin of nanocaps is also discussed.

  14. Spectroscopic evidence of resonance energy transfer mechanism from PbS QDs to bulk silicon

    Directory of Open Access Journals (Sweden)

    Bernechea M.

    2013-06-01

    Full Text Available In this work, we study the efficiency of the resonance energy transfer from PbS quantum dots to bulk silicon. We present spectroscopic evidence that resonance energy transfer from PbS quantum dots to bulk silicon can be an efficient process for separation distances below 12 nm. Temperature measurements are also presented for PbS quantum dots deposited on glass and silicon with 5 nm and 20nm spacer thicknesses substrates. Our findings show that the resonance energy transfer efficiency remains constant over the 50K to 300K temperature range.

  15. Thickness and local field effects on energy transfer rate in coupled quantum wells system: Linear regime

    Energy Technology Data Exchange (ETDEWEB)

    Vazifehshenas, T.; Bahrami, B. [Department of Physics, Shahid Beheshti University, G.C., Evin, 1983963113 Tehran (Iran, Islamic Republic of); Salavati-fard, T., E-mail: taha@udel.edu [Department of Physics and Astronomy, University of Delaware, Newark, DE 19716 (United States)

    2012-12-15

    We investigate theoretically the dependence of energy transfer rate in Double-Quantum-Well system on the well thickness by using the balance equation formalism. Also, by including the local field correction in our calculations through the zero- and finite-temperature Hubbard approximations, we study the effect of the short-range interactions on the energy transfer phenomenon. Calculations consider both the static and dynamic screening approximations. Our numerical results predict that the energy transfer rate increases considerably by increasing the layers' thicknesses and by taking into account the short-range interactions, as well.

  16. Energy Transfer Process of Eu3+ Ions Doped in Tellurite Glass

    Science.gov (United States)

    Hong, Tran Thi; Dung, Phan Tien; Quang, Vu Xuan

    2016-05-01

    Tellurite glass doped with different concentrations of Eu3+ ions has been prepared by the conventional melting process. Photoluminescence, Raman spectra, phonon side-band spectra, and Judd-Ofelt analysis were carried out. Some spectroscopic parameters were estimated to predict the luminescence efficiency of the materials. The energy transfer between the rare-earth ions was observed, and a model for its cross-relaxation was proposed and quantitatively estimated. The charged intrinsic defects in the form of nonbridging oxygen (NBO) were determined, and the energy transfer between NBO and rare-earth ions observed. The energy-transfer-induced Eu3+ photoluminescence enhancement in tellurite glass is studied.

  17. Coherent exciton-polariton devices

    Science.gov (United States)

    Fraser, Michael D.

    2017-09-01

    The Bose-Einstein condensate of exciton-polaritons has emerged as a unique, coherent system for the study of non-equilibrium, macroscopically coherent Bose gases, while the full confinement of this coherent state to a semiconductor chip has also generated considerable interest in developing novel applications employing the polariton condensate, possibly even at room temperature. Such devices include low-threshold lasers, precision inertial sensors, and circuits based on superfluidity with ultra-fast non-linear elements. While the demonstration and development of such devices are at an early stage, rapid progress is being made. In this review, an overview of the exciton-polariton condensate system and the established and emerging material systems and fabrication techniques are presented, followed by a critical, in-depth assessment of the ability of the coherent polariton system to deliver on its promise of devices offering either new functionality and/or room-temperature operation.

  18. Shape similarity of charge-transfer (CT) excitation energy curves in a series of donor-acceptor complexes and its description with a transferable energy of CT orbital

    Science.gov (United States)

    Gritsenko, O. V.

    2017-08-01

    A simple nature of charge-transfer (CT) in the prototype complexes Dp -F2 (Dp =NH3 , H2O) manifests itself in a very close shape of their CT excitation energy curves ωCT (R) along the donor-acceptor separation R. It affords a simple orbital description in terms of the CT orbitals (CTOs) obtained with a transformation of the virtual orbitals of the standard local density approximation (LDA). The transferable energy of the relevant CTO as a function of R closely approximates the common shape of ωCT (R) , while the height of the individual curve is determined with the ionization potential of Dp .

  19. Measuring distances within unfolded biopolymers using fluorescence resonance energy transfer: The effect of polymer chain dynamics on the observed fluorescence resonance energy transfer efficiency

    Science.gov (United States)

    Makarov, Dmitrii E.; Plaxco, Kevin W.

    2009-01-01

    Recent years have seen a number of investigations in which distances within unfolded proteins, polypeptides, and other biopolymers are probed via fluorescence resonance energy transfer, a method that relies on the strong distance dependence of energy transfer between a pair of dyes attached to the molecule of interest. In order to interpret the results of such experiments it is commonly assumed that intramolecular diffusion is negligible during the excited state lifetime. Here we explore the conditions under which this “frozen chain” approximation fails, leading to significantly underestimated donor-acceptor distances, and describe a means of correcting for polymer dynamics in order to estimate these distances more accurately. PMID:19725638

  20. Role of impurities in determining the exciton diffusion length in organic semiconductors

    Energy Technology Data Exchange (ETDEWEB)

    Curtin, Ian J.; Holmes, Russell J. [Department of Chemical Engineering and Materials Science, University of Minnesota, Minneapolis, Minnesota 55455 (United States); Blaylock, D. Wayne [Engineering and Process Sciences, Core R& D, The Dow Chemical Company, Midland, Michigan 48674 (United States)

    2016-04-18

    The design and performance of organic photovoltaic cells is dictated, in part, by the magnitude of the exciton diffusion length (L{sub D}). Despite the importance of this parameter, there have been few investigations connecting L{sub D} and materials purity. Here, we investigate L{sub D} for the organic small molecule N,N′-bis(naphthalen-1-yl)-N,N′-bis(phenyl)-benzidine as native impurities are systematically removed from the material. Thin films deposited from the as-synthesized material yield a value for L{sub D}, as measured by photoluminescence quenching, of (3.9 ± 0.5) nm with a corresponding photoluminescence efficiency (η{sub PL}) of (25 ± 1)% and thin film purity of (97.1 ± 1.2)%, measured by high performance liquid chromatography. After purification by thermal gradient sublimation, the value of L{sub D} is increased to (4.7 ± 0.5) nm with a corresponding η{sub PL} of (33 ± 1)% and purity of (98.3 ± 0.8)%. Interestingly, a similar behavior is also observed as a function of the deposition boat temperature. Films deposited from the purified material at a high temperature give L{sub D} = (5.3 ± 0.8) nm with η{sub PL} = (37 ± 1)% for films with a purity of (99.0 ± 0.3)% purity. Using a model of diffusion by Förster energy transfer, the variation of L{sub D} with purity is predicted as a function of η{sub PL} and is in good agreement with measurements. The removal of impurities acts to decrease the non-radiative exciton decay rate and increase the radiative decay rate, leading to increases in both the diffusivity and exciton lifetime. The results of this work highlight the role of impurities in determining L{sub D}, while also providing insight into the degree of materials purification necessary to achieve optimized exciton transport.

  1. Construction of energy transfer systems within nanosized polymer micelles and their fluorescence modulation properties.

    Science.gov (United States)

    Chen, Jian; Zeng, Fang; Wu, Shuizhu

    2010-04-06

    The nanoparticle-based fluorescence resonance energy transfer (FRET) systems have recently attracted considerable attention due to some of their advantages; however, these systems are structurally more complicated than that of small molecule systems, and the energy transfer behavior for particle systems has been seldom investigated. In this study, we synthesized a series of ABC triblock copolymers that contain hydrophilic poly(ethylene oxide) (PEO), hydrophobic poly(styrene) (PS) and photochromic poly(2-(3-(3',3'-dimethyl-6-nitrospiro(indoline-2',2-[2H-1]benzopyran)-1'-yl)propanoylo-xy)ethyl methacrylate) (PSPMA) blocks by using the sequential two-step atom transfer radical polymerization (ATRP). The amphiphilic micelles made from these copolymers can incorporate a hydrophobic fluorescent dye, the nitrobenzoxadiazolyl derivative (NBD), thus forming a water dispersible energy transfer system with the fluorescent dye NBD as the donor and spiropyran moieties as the potential acceptor. The spectral properties of NBD/triblock copolymers with varied PS block lengths and PSPMA block lengths have been investigated; the results indicate that the length of PS block in triblock copolymers can affect the energy transfer efficiency of the micelle-based fluorescence modulation system, the micelles with moderate PS block length are preferable for forming FRET system with higher energy transfer efficiency, and short PSPMA blocks (less than 5 repetition units) are enough for efficient energy transfer.

  2. Mechanisms of energy conversion and transfer in bioluminescence. Progress report, August 15, 1976--November 14, 1977. [Renilla (anthozoa)

    Energy Technology Data Exchange (ETDEWEB)

    Cormier, M.J.

    1977-01-01

    Progress is reported on the following studies: isolation of luciferase and green fluorescent protein (GFP) from Renilla; chemical properties and chemical reactions of luciferase and GFP; and analogy of energy transfer in bioluminescence to energy transfer in photosynthesis. (HLW)

  3. Halogenation of SiC for band-gap engineering and excitonic functionalization

    OpenAIRE

    Drissi, L.B.; Ramadan, F. Z.; Lounis, S.

    2017-01-01

    The optical excitation spectra and excitonic resonances are investigated in systematically functionalized SiC with Fluorine and/or Chlorine utilizing density functional theory in combination with many-body perturbation theory. The latter is required for a realistic description of the energy band-gaps as well as for the theoretical realization of excitons. Structural, electronic and optical properties are scrutinized and show the high stability of the predicted two-dimensional materials. Their...

  4. Exciton-mediated Raman scattering in CdS quantum dot

    Science.gov (United States)

    Guo, Xiaotong; Liu, Cuihong

    2017-09-01

    A theoretical calculation of the differential cross section (DCS) is presented for the exciton-mediated Stokes Raman scattering in CdS quantum dot within the frame work of effective mass approximation at T = 0 K. Numerical calculations reveal that the excitonic effects cause blue shifts in Raman spectroscopy. The magnitude of the Raman shift depends on the quantum confinement, the Coulomb interaction, and the incident photon energy.

  5. Electroluminescence from charge transfer states in Donor/Acceptor solar cells

    DEFF Research Database (Denmark)

    Sherafatipour, Golenaz; Madsen, Morten

    Charge photocurrent generation is a key process in solar energy conversion systems. Effective dissociation of the photo-generated electron-hole pairs (excitons) has a strong influence on the efficiency of the organic solar cells. Charge dissociation takes place at the donor/acceptor interface via...... charge transfer (CT) excitons, which is Coulombically bound interfacial electron- hole pairs residing at the donor/acceptor heterojunctions. The CT state represents an intermediate state between the exciton dissociation and recombination back to the ground state. Since the recombination of photo-generated...... charges is a major limitation for the efficiency of the organic solar cells, a thorough understanding of this loss mechanism is crucial to improve the performance of the devices. Furthermore, examining this interfacial state is of great importance in order to maximize open-circuit voltage and photocurrent...

  6. Numerical Simulations of the Kinetic Energy Transfer in the Bath of a BOF Converter

    Science.gov (United States)

    Zhou, Xiaobin; Ersson, Mikael; Zhong, Liangcai; Jönsson, Pär

    2016-02-01

    The paper focuses on the fundamental aspects of the kinetic energy transfer from a top and bottom gas injection to the bath of the basic oxygen furnace (BOF) by applying a mathematical model. The analyses revealed that the energy transfer is less efficient when top lance height is lowered or the flowrate is increased in the top blowing operations. However, an inverse trend was found that the kinetic energy transfer is increased when the bottom flowrate is increased for the current bottom blowing operation conditions. The kinetic energy transfer index results indicated that the energy transfer for the bottom blowing is much more efficient than that of the top blowing operations. To understand the effects of the upper buoyant phase on the energy dissipation of the bulk liquid in the bath, different mass and physical properties of slag and foam were considered in the bottom blowing simulations. The slag on top of the bath is found to dissipate by 6.6, 9.4, and 11.2 pct for slag mass values of 5, 9, and 15 t compared to the case without slag atop the surface of the bath, respectively. The results showed that the kinetic energy transfer is not largely influenced by the viscosity of the upper slag or the foaming phases.

  7. A model for energy transfer in collisions of atoms with highly excited molecules.

    Science.gov (United States)

    Houston, Paul L; Conte, Riccardo; Bowman, Joel M

    2015-05-21

    A model for energy transfer in the collision between an atom and a highly excited target molecule has been developed on the basis of classical mechanics and turning point analysis. The predictions of the model have been tested against the results of trajectory calculations for collisions of five different target molecules with argon or helium under a variety of temperatures, collision energies, and initial rotational levels. The model predicts selected moments of the joint probability distribution, P(Jf,ΔE) with an R(2) ≈ 0.90. The calculation is efficient, in most cases taking less than one CPU-hour. The model provides several insights into the energy transfer process. The joint probability distribution is strongly dependent on rotational energy transfer and conservation laws and less dependent on vibrational energy transfer. There are two mechanisms for rotational excitation, one due to motion normal to the intermolecular potential and one due to motion tangential to it and perpendicular to the line of centers. Energy transfer is found to depend strongly on the intermolecular potential and only weakly on the intramolecular potential. Highly efficient collisions are a natural consequence of the energy transfer and arise due to collisions at "sweet spots" in the space of impact parameter and molecular orientation.

  8. Exciton circular dichroism in channelrhodopsin.

    Science.gov (United States)

    Pescitelli, Gennaro; Kato, Hideaki E; Oishi, Satomi; Ito, Jumpei; Maturana, Andrés Daniel; Nureki, Osamu; Woody, Robert W

    2014-10-16

    Channelrhodopsins (ChRs) are of great interest currently because of their important applications in optogenetics, the photostimulation of neurons. The absorption and circular dichroism (CD) spectra of C1C2, a chimera of ChR1 and ChR2 of Chlamydomonas reinhardtii, have been studied experimentally and theoretically. The visible absorption spectrum of C1C2 shows vibronic fine structure in the 470 nm band, consistent with the relatively nonpolar binding site. The CD spectrum has a negative band at 492 nm (Δε(max) = -6.17 M(-1) cm(-1)) and a positive band at 434 nm (Δε(max) = +6.65 M(-1) cm(-1)), indicating exciton coupling within the C1C2 dimer. Time-dependent density functional theory (TDDFT) calculations are reported for three models of the C1C2 chromophore: (1) the isolated protonated retinal Schiff base (retPSB); (2) an ion pair, including the retPSB chromophore, two carboxylate side chains (Asp 292, Glu 162), modeled by acetate, and a water molecule; and (3) a hybrid quantum mechanical/molecular mechanical (QM/MM) model depicting the binding pocket, in which the QM part consists of the same ion pair as that in (2) and the MM part consists of the protein residues surrounding the ion pair within 10 Å. For each of these models, the CD of both the monomer and the dimer was calculated with TDDFT. For the dimer, DeVoe polarizability theory and exciton calculations were also performed. The exciton calculations were supplemented by calculations of the coupling of the retinal transition with aromatic and peptide group transitions. For the dimer, all three methods and three models give a long-wavelength C2-axis-polarized band, negative in CD, and a short-wavelength band polarized perpendicular to the C2 axis with positive CD, differing in wavelength by 1-5 nm. Only the retPSB model gives an exciton couplet that agrees qualitatively with experiment. The other two models give a predominantly or solely positive band. We further analyze an N-terminal truncated mutant

  9. Bispectral experimental estimation of the nonlinear energy transfer in two-dimensional plasma turbulence

    DEFF Research Database (Denmark)

    Manz, P.; Ramisch, M.; Stroth, U.

    2008-01-01

    -wave turbulence. The density fluctuations, which at the realistic collisionality are advected as a passive scalar with the vorticity, show power transfer from large to small scales, while the spectral power in potential fluctuations, which represents the energy, is transferred as an inverse cascade to larger...

  10. Ultrafast energy transfer in chlorosomes from the green photosynthetic bacterium Chloroflexus aurantiacus

    Energy Technology Data Exchange (ETDEWEB)

    Savikhin, S.; Struve, W.S. [Ames Lab., IA (United States)]|[Iowa State Univ., Ames, IA (United States); Zhu, Y.; Blankenship, R.E. [Arizona State Univ., Tempe, AZ (United States)

    1996-02-29

    Energy transfers between the bacteriochlorophyll c and a antennae in light-harvesting chlorosomes from the green bacterium Chloroflexus aurantiacus have been studied in two-color pump-probe experiments with improved sensitivity and wavelength versatility. The BChl c {yields} BChl a energy transfers are well simulated with biexponential kinetics, with lifetimes of 2-3 and 11 ps. They do not exhibit an appreciable subpicosecond component. In the context of a kinetic model for chlorosomes, these lifetimes suggest that both internal BChl c processes and the BChl c {yields} BChl a energy-transfer step contribute materially to the empirical rod-to-baseplate energy-transfer kinetics. 11 refs., 2 figs., 1 tab.

  11. Local Measurement of Fuel Energy Deposition and Heat Transfer Environment During Fuel Lifetime Using Controlled Calorimetry

    Energy Technology Data Exchange (ETDEWEB)

    Don W. Miller; Andrew Kauffmann; Eric Kreidler; Dongxu Li; Hanying Liu; Daniel Mills; Thomas D. Radcliff; Joseph Talnagi

    2001-12-31

    A comprehensive description of the accomplishments of the DOE grant titled, ''Local Measurement of Fuel Energy Deposition and Heat Transfer Environment During Fuel Lifetime using Controlled Calorimetry''.

  12. Energy Link Optimization in a Wireless Power Transfer Grid under Energy Autonomy Based on the Improved Genetic Algorithm

    Directory of Open Access Journals (Sweden)

    Zhihao Zhao

    2016-08-01

    Full Text Available In this paper, an optimization method is proposed for the energy link in a wireless power transfer grid, which is a regional smart microgrid comprised of distributed devices equipped with wireless power transfer technology in a certain area. The relevant optimization model of the energy link is established by considering the wireless power transfer characteristics and the grid characteristics brought in by the device repeaters. Then, a concentration adaptive genetic algorithm (CAGA is proposed to optimize the energy link. The algorithm avoided the unification trend by introducing the concentration mechanism and a new crossover method named forward order crossover, as well as the adaptive parameter mechanism, which are utilized together to keep the diversity of the optimization solution groups. The results show that CAGA is feasible and competitive for the energy link optimization in different situations. This proposed algorithm performs better than its counterparts in the global convergence ability and the algorithm robustness.

  13. Tuning the Exciton Binding Energies in Single Self-Assembled InGaAs/GaAs Quantum Dots by Piezoelectric-Induced Biaxial Stress

    NARCIS (Netherlands)

    Ding, F.; Singh, R.; Plumhof, J.D.; Zander, T.; K?ápek, V.; Chen, Y.H.; Benyoucef, M.; Zwiller, V.; Dörr, K.; Bester, G.; Rastelli, A.; Schmidt, O.G.

    2010-01-01

    We study the effect of an external biaxial stress on the light emission of single InGaAs/GaAs(001) quantum dots placed onto piezoelectric actuators. With increasing compression, the emission blueshifts and the binding energies of the positive trion (X+) and biexciton (XX) relative to the neutral

  14. Effect of energy transfer from atomic electron shell to an α particle emitted by decaying nucleus

    Energy Technology Data Exchange (ETDEWEB)

    Igashov, S. Yu., E-mail: igashov@theor.mephi.ru [All-Russian Research Institute of Automatics (Russian Federation); Tchuvil’sky, Yu. M. [Moscow State University, Skobeltsyn Institute of Nuclear Physics (Russian Federation)

    2016-12-15

    The process of energy transfer from the electron shell of an atom to an α particle propagating through the shell is formulated mathematically. Using the decay of the {sup 226}Ra nucleus as an example, it is demonstrated that this phenomenon increases the α-decay intensity in contrast with other known effects of similar type. Moreover, the α decay of the nucleus is more strongly affected by the energy transfer than by all other effects taken together.

  15. Intra/Inter-Particle Energy Transfer of Luminescence Nanocrystals for Biomedical Applications

    Directory of Open Access Journals (Sweden)

    Ching-Ping Liu

    2012-01-01

    Full Text Available Elaborate design of energy transfer systems in luminescent nanocrystals revealed tremendous advantages in nanotechnology, especially in biosensing and drug delivery systems. Recently, upconversion nanoparticles have been discussed as promising probes as labels in biological assays and imaging. This article reviews the works performed in the recent years using quantum dot- and rare-earth doped nanoparticle-based energy transfer systems for biomedical applications.

  16. Energy transfer between a nanosystem and its host fluid: A multiscale factorization approach

    Science.gov (United States)

    Sereda, Yuriy V.; Espinosa-Duran, John M.; Ortoleva, Peter J.

    2014-02-01

    Energy transfer between a macromolecule or supramolecular assembly and a host medium is considered from the perspective of Newton's equations and Lie-Trotter factorization. The development starts by demonstrating that the energy of the molecule evolves slowly relative to the time scale of atomic collisions-vibrations. The energy is envisioned to be a coarse-grained variable that coevolves with the rapidly fluctuating atomistic degrees of freedom. Lie-Trotter factorization is shown to be a natural framework for expressing this coevolution. A mathematical formalism and workflow for efficient multiscale simulation of energy transfer is presented. Lactoferrin and human papilloma virus capsid-like structure are used for validation.

  17. Elucidating energy and electron transfer dynamics within molecular assemblies for solar energy conversion

    Science.gov (United States)

    Morseth, Zachary Aaron

    The use of sunlight to make chemical fuels (i.e. solar fuels) is an attractive approach in the quest to develop sustainable energy sources. Using nature as a guide, assemblies for artificial photosynthesis will need to perform multiple functions. They will need to be able to harvest light across a broad region of the solar spectrum, transport excited-state energy to charge-separation sites, and then transport and store redox equivalents for use in the catalytic reactions that produce chemical fuels. This multifunctional behavior will require the assimilation of multiple components into a single macromolecular system. A wide variety of different architectures including porphyrin arrays, peptides, dendrimers, and polymers have been explored, with each design posing unique challenges. Polymer assemblies are attractive due to their relative ease of production and facile synthetic modification. However, their disordered nature gives rise to stochastic dynamics not present in more ordered assemblies. The rational design of assemblies requires a detailed understanding of the energy and electron transfer events that follow light absorption, which can occur on timescales ranging from femtoseconds to hundreds of microseconds, necessitating the use of sophisticated techniques. We have used a combination of time-resolved absorption and emission spectroscopies with observation times that span nine orders of magnitude to follow the excited-state evolution within single-site and polymer-based molecular assemblies. We complement experimental observations with electronic structure calculations, molecular dynamics simulations, and kinetic modeling to develop a microscopic view of these dynamics. This thesis provides an overview of work on single-site molecular assemblies and polymers decorated with pendant chromophores, both in solution and on surfaces. This work was made possible through extensive collaboration with Dr. Kirk Schanze's and Dr. John Reynolds' research groups who

  18. Probing Exciton Diffusion and Dissociation in Single-Walled Carbon Nanotube-C60 Heterojunctions

    Energy Technology Data Exchange (ETDEWEB)

    Dowgiallo, Anne-Marie; Mistry, Kevin S.; Johnson, Justin C.; Reid, Obadiah G.; Blackburn, Jeffrey L.

    2016-05-19

    The efficiency of thin-film organic photovoltaic (OPV) devices relies heavily upon the transport of excitons to type-II heterojunction interfaces, where there is sufficient driving force for exciton dissociation and ultimately the formation of charge carriers. Semiconducting single-walled carbon nanotubes (SWCNTs) are strong near-infrared absorbers that form type-II heterojunctions with fullerenes such as C60. Although the efficiencies of SWCNT-fullerene OPV devices have climbed over the past few years, questions remain regarding the fundamental factors that currently limit their performance. In this study, we determine the exciton diffusion length in the C60 layer of SWCNT-C60 bilayer active layers using femtosecond transient absorption measurements. We demonstrate that hole transfer from photoexcited C60 molecules to SWCNTs can be tracked by the growth of narrow spectroscopic signatures of holes in the SWCNT 'reporter layer'. In bilayers with thick C60 layers, the SWCNT charge-related signatures display a slow rise over hundreds of picoseconds, reflecting exciton diffusion through the C60 layer to the interface. A model based on exciton diffusion with a Beer-Lambert excitation profile, as well as Monte Carlo simulations, gives the best fit to the data as a function of C60 layer thickness using an exciton diffusion length of approximately 5 nm.

  19. Dynamical patterns of phase transformations from self-trapping of quantum excitons

    Energy Technology Data Exchange (ETDEWEB)

    Yi, Tianyou [South University of Science and Technology of China, Shenzhen, Guangdong 518055 (China); Kirova, Natasha, E-mail: kirova@lps.u-psud.fr [CNRS, LPS, UMR 8626, Univeristé Paris-sud, Orsay 91405 (France); International Institute of Physics, UFRN, 59078-400 Natal, RN (Brazil); Brazovskii, Serguei [CNRS, LPTMS, UMR 8502, Univeristé Paris-sud, Orsay 91405 (France); International Institute of Physics, UFRN, 59078-400 Natal, RN (Brazil)

    2015-03-01

    Phase transitions induced by short optical pulses is a new mainstream in studies of cooperative electronic states. Its special realization in systems with neutral-ionic transformations stands out in a way that the optical pumping goes to excitons rather than to electronic bands. We present a semi-phenomenological modeling of spacio-temporal effects applicable to any system where the optical excitons are coupled to a symmetry breaking order parameter. In our scenario, after a short initial pulse of photons, a quasi-condensate of excitons appears as a macroscopic quantum state which then evolves interacting with other degrees of freedom prone to instability. This coupling leads to self-trapping of excitons; that locally enhances their density which can surpass a critical value to trigger the phase transformation, even if the mean density is below the required threshold. The system is stratified in domains which evolve through dynamical phase transitions and may persist even after the initiating excitons have recombined. We recover dynamic interplays of fields such as the excitons' wave function, electronic charge transfer and polarization, lattice dimerization.

  20. Excitonic Coherence in Semiconductor Nanostructures Measured by Speckle Analysis

    DEFF Research Database (Denmark)

    Langbein, Wolfgang; Hvam, Jørn Märcher

    1999-01-01

    are determined separately, thus distinguishing lifetime from pure dephasing. In particular, the secondary emission of excitons in semiconductor quantum wells is investigated. Here, the combination of static disorder and inelastic scattering leads to a partially coherent emission. The temperature dependence...... is well explained by phonon scattering. Spin-relaxation is found to be dominated by disorder, and is preserving the coherence, while phonon-assisted energy-relaxation is foundto destroy the coherence....

  1. Excitonic condensation in quasi-two-dimensional systems

    Energy Technology Data Exchange (ETDEWEB)

    Crisan, M. [Department of Theoretical Physics, University of Cluj, 400084 Cluj-Napoca (Romania)]. E-mail: mcrisan@phys.ubbcluj.ro; Tifrea, I. [Department of Theoretical Physics, University of Cluj, 400084 Cluj-Napoca (Romania); Department of Physics and Astronomy, University of Iowa, Iowa City, IA 52242 (United States)

    2005-10-17

    We present a low energy model for the Bose-Einstein condensation in a quasi-two-dimensional excitonic gas. Using the flow equations of the renormalization group and a {phi}{sup 4} model with the dynamical critical exponent z=2 we calculate the temperature dependence of the critical density, coherence length, magnetic susceptibility, and specific heat. The model can be relevant for the macroscopic coherence observed in GaAs/AlGaAs coupled quantum wells.

  2. Non-contact pumping of light emitters via non-radiative energy transfer

    Science.gov (United States)

    Klimov, Victor I.; Achermann, Marc

    2010-01-05

    A light emitting device is disclosed including a primary light source having a defined emission photon energy output, and, a light emitting material situated near to said primary light source, said light emitting material having an absorption onset equal to or less in photon energy than the emission photon energy output of the primary light source whereby non-radiative energy transfer from said primary light source to said light emitting material can occur yielding light emission from said light emitting material.

  3. Numerical simulations of energy transfer in two collisionless interpenetrating plasmas

    Directory of Open Access Journals (Sweden)

    Davis S.

    2013-11-01

    Full Text Available Ion stream instabilities are essential for collisionless shock formation as seen in astrophysics. Weakly relativistic shocks are considered as candidates for sources of high energy cosmic rays. Laboratory experiments may provide a better understanding of this phenomenon. High intensity short pulse laser systems are opening possibilities for efficient ion acceleration to high energies. Their collision with a secondary target could be used for collisionless shock formation. In this paper, using particle-in-cell simulations we are studying interaction of a sub-relativistic, laser created proton beam with a secondary gas target. We show that the ion bunch initiates strong electron heating accompanied by the Weibel-like filamentation and ion energy losses. The energy repartition between ions, electrons and magnetic fields are investigated. This yields insight on the processes occurring in the interstellar medium (ISM and gamma-ray burst afterglows.

  4. Time Resolved Energy Transfer and Photodissociation of Vibrationally Excited Molecules

    National Research Council Canada - National Science Library

    Crim, F. F

    2007-01-01

    ...) in solution and in the gas phase. This second experiment is one of the few direct comparisons of intramolecular vibrational energy flow in a solvated molecule with that in the same molecule isolated in a gas...

  5. On the Concentration Dependence of Metallic Nano-Particles in Enhanced Forster Resonance Energy Transfer

    Science.gov (United States)

    Hoa, N. M.; Nhung, T. H.; Thao, T. T.; Theu, L. T.; Viet, N. A.

    2017-06-01

    The enhanced Forster resonance energy transfer is obtained in recent experiments. One of the most important experimental facts is the observed strong enhancement of donor fluorescence with increasing concentration of metallic nanoparticle acceptors in the first stage. We propose three types of energy transfer mechanisms (Forster FRET, surface SET, and Coulomb CET) and predict simple relations for their dependencies on the concentration of metallic nano-particles. The competition of these mechanisms leads to the transfer intensity dependence on the concentration dependence of metallic nano-particles. Using these assumptions, we expect and argue about the compatibility between the experimental results.

  6. Photonic Crystal Architecture for Room-Temperature Equilibrium Bose-Einstein Condensation of Exciton Polaritons

    Science.gov (United States)

    Jiang, Jian-Hua; John, Sajeev

    2014-07-01

    We describe photonic crystal microcavities with very strong light-matter interaction to realize room-temperature, equilibrium, exciton-polariton Bose-Einstein condensation (BEC). This goal is achieved through a careful balance between strong light trapping in a photonic band gap (PBG) and large exciton density enabled by a multiple quantum-well (QW) structure with a moderate dielectric constant. This approach enables the formation of a long-lived, dense 10-μm-1-cm- scale cloud of exciton polaritons with vacuum Rabi splitting that is roughly 7% of the bare exciton-recombination energy. We introduce a woodpile photonic crystal made of Cd0.6 Mg0.4Te with a 3D PBG of 9.2% (gap-to-central-frequency ratio) that strongly focuses a planar guided optical field on CdTe QWs in the cavity. For 3-nm QWs with 5-nm barrier width, the exciton-photon coupling can be as large as ℏΩ=55 meV (i.e., a vacuum Rabi splitting of 2ℏΩ=110 meV). The exciton-recombination energy of 1.65 eV corresponds to an optical wavelength of 750 nm. For N =106 QWs embedded in the cavity, the collective exciton-photon coupling per QW (ℏΩ/√N =5.4 meV) is much larger than the state-of-the-art value of 3.3 meV, for the CdTe Fabry-Pérot microcavity. The maximum BEC temperature is limited by the depth of the dispersion minimum for the lower polariton branch, over which the polariton has a small effective mass of approximately 10-5m0, where m0 is the electron mass in vacuum. By detuning the bare exciton-recombination energy above the planar guided optical mode, a larger dispersion depth is achieved, enabling room-temperature BEC. The BEC transition temperature ranges as high as 500 K when the polariton density per QW is increased to (11aB)-2, where aB≃3.5 nm is the exciton Bohr radius and the exciton-cavity detuning is increased to 30 meV. A high-quality PBG can suppress exciton radiative decay and enhance the polariton lifetime to beyond 150 ps at room temperature, sufficient for thermal

  7. Photonic Crystal Architecture for Room-Temperature Equilibrium Bose-Einstein Condensation of Exciton Polaritons

    Directory of Open Access Journals (Sweden)

    Jian-Hua Jiang

    2014-08-01

    Full Text Available We describe photonic crystal microcavities with very strong light-matter interaction to realize room-temperature, equilibrium, exciton-polariton Bose-Einstein condensation (BEC. This goal is achieved through a careful balance between strong light trapping in a photonic band gap (PBG and large exciton density enabled by a multiple quantum-well (QW structure with a moderate dielectric constant. This approach enables the formation of a long-lived, dense 10-μm-1-cm- scale cloud of exciton polaritons with vacuum Rabi splitting that is roughly 7% of the bare exciton-recombination energy. We introduce a woodpile photonic crystal made of Cd_{0.6}  Mg_{0.4}Te with a 3D PBG of 9.2% (gap-to-central-frequency ratio that strongly focuses a planar guided optical field on CdTe QWs in the cavity. For 3-nm QWs with 5-nm barrier width, the exciton-photon coupling can be as large as ℏΩ=55  meV (i.e., a vacuum Rabi splitting of 2ℏΩ=110  meV. The exciton-recombination energy of 1.65 eV corresponds to an optical wavelength of 750 nm. For N=106 QWs embedded in the cavity, the collective exciton-photon coupling per QW (ℏΩ/sqrt[N]=5.4  meV is much larger than the state-of-the-art value of 3.3 meV, for the CdTe Fabry-Pérot microcavity. The maximum BEC temperature is limited by the depth of the dispersion minimum for the lower polariton branch, over which the polariton has a small effective mass of approximately 10^{−5}m_{0}, where m_{0} is the electron mass in vacuum. By detuning the bare exciton-recombination energy above the planar guided optical mode, a larger dispersion depth is achieved, enabling room-temperature BEC. The BEC transition temperature ranges as high as 500 K when the polariton density per QW is increased to (11a_{B}^{−2}, where a_{B}≃3.5  nm is the exciton Bohr radius and the exciton-cavity detuning is increased to 30 meV. A high-quality PBG can suppress exciton radiative decay and enhance the polariton

  8. [Mechanism of intermolecular energy transfer and reception of ultralow action by chemical and biological systems].

    Science.gov (United States)

    Gall', L N; Gall', N R

    2009-01-01

    A novel concept of intermolecular energy transfer and reception of the ultralow action in living systems is proposed. The concept is based on the methods of nonlinear mathematical physics used in description of energy movement along molecular chains and on quantum mechanical ideas concerning signal formation in anisotropic media. A concept of a molecular cell as an indivisible structural unit and a constituent of a biological (chemical) system has been put forward and substantiated, which manifests collective features of the unity of molecules, physical fields, and energetically strained bound water media in processes of energy transfer and reception. Both intermolecular energy transfer and amplification of the ultralow action has been shown to be the components of a unified energy process in a living system, and the physical basis of both processes is the unity of molecules and water-field media in a molecular cell.

  9. Fluorescence resonance energy transfer between conjugated molecules infiltrated in three-dimensional opal photonic crystals

    Energy Technology Data Exchange (ETDEWEB)

    Zou, Lu; Sui, Ning; Wang, Ying-Hui, E-mail: yinghui_wang@jlu.edu.cn; Qian, Cheng; Ma, Yu-Guang; Zhang, Han-Zhuang, E-mail: zhanghz@jlu.edu.cn

    2015-02-15

    Fluorescence resonance energy transfer (FRET) from Coumarin 6 (C-6) to Sulforhodamine B (S-B) infiltrated into opal PMMA (poly-methyl-methacrylate) photonic crystals (PCs) has been studied in detail. The intrinsic mesh micro-porous structure of opal PCs could increase the luminescent efficiency through inhibiting the intermolecular interaction. Meanwhile, its structure of periodically varying refractive indices could also modify the FRET through affecting the luminescence characteristics of energy donor or energy acceptor. The results demonstrate that the FRET efficiency between conjugated dyes was easily modified by opal PCs. - Highlights: • We investigate the fluorescence resonance energy transfer between two kinds of dyes. • These two kinds of dyes are infiltrated in PMMA opal photonic crystals. • The structure of opal PCs could improve the luminescent characteristics. • The structure of opal PCs could improve the energy transfer characteristics.

  10. Highly Efficient Deep Blue Organic Light-Emitting Diodes Based on Imidazole: Significantly Enhanced Performance by Effective Energy Transfer with Negligible Efficiency Roll-off.

    Science.gov (United States)

    Shan, Tong; Liu, Yulong; Tang, Xiangyang; Bai, Qing; Gao, Yu; Gao, Zhao; Li, Jinyu; Deng, Jian; Yang, Bing; Lu, Ping; Ma, Yuguang

    2016-10-26

    Great efforts have been devoted to develop efficient deep blue organic light-emitting diodes (OLEDs) materials meeting the standards of European Broadcasting Union (EBU) standard with Commission International de L'Eclairage (CIE) coordinates of (0.15, 0.06) for flat-panel displays and solid-state lightings. However, high-performance deep blue OLEDs are still rare for applications. Herein, two efficient deep blue emitters, PIMNA and PyINA, are designed and synthesized by coupling naphthalene with phenanthreneimidazole and pyreneimidazole, respectively. The balanced ambipolar transporting natures of them are demonstrated by single-carrier devices. Their nondoped OLEDs show deep blue emissions with extremely small CIEy of 0.034 for PIMNA and 0.084 for PyINA, with negligible efficiency roll-off. To take advantage of high photoluminescence quantum efficiency of PIMNA and large fraction of singlet exciton formation of PyINA, doped devices are fabricated by dispersing PyINA into PIMNA. A significantly improved maximum external quantum efficiency (EQE) of 5.05% is obtained through very effective energy transfer with CIE coordinates of (0.156, 0.060), and the EQE remains 4.67% at 1000 cd m(-2), which is among the best of deep blue OLEDs reported matching stringent EBU standard well.

  11. Syntrophic growth with direct interspecies electron transfer as the primary mechanism for energy exchange

    DEFF Research Database (Denmark)

    Shrestha, Pravin Malla; Rotaru, Amelia-Elena; Aklujkar, Muktak

    2013-01-01

    Direct interspecies electron transfer (DIET) through biological electrical connections is an alternative to interspecies H2 transfer as a mechanism for electron exchange in syntrophic cultures. However, it has not previously been determined whether electrons received via DIET yield energy to supp...... dehydrogenase, the pilus-associated c-type cytochrome OmcS and pili consistent with electron transfer via DIET. These results suggest that electrons transferred via DIET can serve as the sole energy source to support anaerobic respiration....... to support cell growth. In order to investigate this, co-cultures of Geobacter metallireducens, which can transfer electrons to wild-type G. sulfurreducens via DIET, were established with a citrate synthase-deficient G. sulfurreducens strain that can receive electrons for respiration through DIET only...

  12. Experimental Study of RF Energy Transfer System in Indoor Environment

    Science.gov (United States)

    Adami, S.-E.; Proynov, P. P.; Stark, B. H.; Hilton, G. S.; Craddock, I. J.

    2014-11-01

    This paper presents a multi-transmitter, 2.43 GHz Radio-Frequency (RF) wireless power transfer (WPT) system for powering on-body devices. It is shown that under typical indoor conditions, the received power range spans several orders of magnitude from microwatts to milliwatts. A body-worn dual-polarised rectenna (rectifying antenna) is presented, designed for situations where the dominant polarization is unpredictable, as is the case for the on-body sensors. Power management circuitry is demonstrated that optimally loads the rectenna even under highly intermittent conditions, and boosts the voltage to charge an on-board storage capacitor.

  13. Manipulating Energy Transfer in Conjugated Polymers using Radical Mediators

    Science.gov (United States)

    Wilcox, Daniel; Mukherjee, Sanjoy; Boudouris, Bryan

    Previous efforts have demonstrated that polymers containing open-shell moieties can be used to improve the performance of organic electronic devices (e.g., organic field-effect transistors (OFETs) and photovoltaic devices). However, the exact mechanism of how these redox-active radical polymers improve the performance of these next-generation devices has yet to be described in full. Here, we take the first steps towards elucidating this full picture by demonstrating that the galvinoxyl radical can be used as an electron acceptor for a common electron-donating macromolecule. First, galvinoxyl was used as a fluorescence quencher for poly(3-hexylthiophene) (P3HT) with quenching performance on par with that of oft-used fullerene derivatives. This effect was caused by photoinduced electron transfer between the two materials. Additionally, the galvinoxyl radical was used as an active layer dopant for P3HT OFETs. By increasing the P3HT carrier density through spontaneous electron transfer, the behavior of the device was changed from that of an intrinsic semiconductor to that of a highly-doped semiconductor. Thus, these initial studies lay the foundation for a paradigm where open-shell entities are used to dope conjugated polymer semiconductors for high-performance device applications.

  14. Spatial dependence of magnetopause energy transfer: Cluster measurements verifying global simulations

    Directory of Open Access Journals (Sweden)

    M. Palmroth

    2011-05-01

    Full Text Available We investigate the spatial variation of magnetopause energy conversion and transfer using Cluster spacecraft observations of two magnetopause crossing events as well as using a global magnetohydrodynamic (MHD simulation GUMICS-4. These two events, (16 January 2001, and 26 January 2001 are similar in all other aspects except for the sign of the interplanetary magnetic field (IMF y-component that has earlier been found to control the spatial dependence of energy transfer. In simulations of the two events using observed solar wind parameters as input, we find that the GUMICS-4 energy transfer agrees with the Cluster observations spatially and is about 30 % lower in magnitude. According to the simulation, most of the the energy transfer takes place in the plane of the IMF (as previous modelling results have suggested, and the locations of the load and generator regions on the magnetopause are controlled by the IMF orientation. Assuming that the model results are as well in accordance with the in situ observations also on other parts of the magnetopause, we are able to pin down the total energy transfer during the two Cluster magnetopause crossings. Here, we estimate that the instantaneous total power transferring through the magnetopause during the two events is at least 1500–2000 GW, agreeing with ε scaled using the mean magnetopause area in the simulation. Hence the combination of the simulation results and the Cluster observations indicate that the ε parameter is probably underestimated by a factor of 2–3.

  15. Excitons and polaritons in planar heterostructures in external electric and magnetic fields: A multi-sub-level approach

    Science.gov (United States)

    Wilkes, J.; Muljarov, E. A.

    2017-08-01

    Excitons and microcavity polaritons that possess a macroscopic dipole alignment are attractive systems to study. This is due to an enhancement of collective many body effects and an ability to electrostatically control their transport and internal structure. Here, we present an overview of a rigorous calculation of spatially-indirect exciton states in semiconductor coupled quantum wells in externally applied electric and magnetic fields. We also treat dipolaritons that form when such structures are positioned at the antinode of a resonant cavity mode. Our approach is general and can be applied to various planar solid state heterostructures inside optical resonators. It offers a thorough description of the properties of excitons and polaritons that are important for modelling their respective fluids. In particular, we calculate the exciton Bohr radius, binding energy, optical lifetime and magnetic field induced enhancement of the effective mass. We also describe electric and magnetic field control of the exciton and polariton dipole moment and brightness.

  16. Remote Electric Power Transfer Between Spacecrafts by Infrared Beamed Energy

    Science.gov (United States)

    Chertok, Boris E.; Evdokimov, Roman A.; Legostaev, Victor P.; Lopota, Vitaliy A.; Sokolov, Boris A.; Tugaenko, Vjacheslav Yu.

    2011-11-01

    High efficient wireless electric energy transmission (WET) technology between spacecrafts by laser channel is proposed. WET systems could be used for remote power supplying of different consumers in space. First of all, there are autonomous technology modules for microgravity experiments, micro and nano satellites, different equipment for explorations of planetary surfaces, space transport vehicles with electric rocket propulsion systems. The main components of the WET technology consist of radiation sources on the base of semiconductor IR laser diodes; systems for narrow laser beam creation; special photovoltaic receivers for conversion of monochromatic IR radiation with high energy density to electric power. The multistage space experiment for WET technology testing is described. During this experiment energy will be transmitted from International Space Station to another spacecrafts like cargo transport vehicles (Progress or/and ATV) and micro satellites.

  17. Solar-pumped electronic-to-vibrational energy transfer lasers

    Science.gov (United States)

    Harries, W. L.; Wilson, J. W.

    1981-01-01

    The possibility of using solar-pumped lasers as solar energy converters is examined. The absorbing media considered are halogens or halogen compounds, which are dissociated to yield excited atoms, which then hand over energy to a molecular lasing medium. Estimates of the temperature effects for a Br2-CO2-He system with He as the cooling gas are given. High temperatures can cause the lower energy levels of the CO2 laser transition to be filled. The inverted populations are calculated and lasing should be possible. However, the efficiency is less than 0.001. Examination of other halogen-molecular lasant combinations (where the rate coefficients are known) indicate efficiencies in all cases of less than 0.005.

  18. Probing resonant energy transfer in collisions of ammonia with Rydberg helium atoms by microwave spectroscopy

    Science.gov (United States)

    Zhelyazkova, V.; Hogan, S. D.

    2017-12-01

    We present the results of experiments demonstrating the spectroscopic detection of Förster resonance energy transfer from NH3 in the X1A1 ground electronic state to helium atoms in 1sns 3S1 Rydberg levels, where n = 37 and n = 40. For these values of n, the 1sns 3S1 → 1snp 3PJ transitions in helium lie close to resonance with the ground-state inversion transitions in NH3 and can be tuned through resonance using electric fields of less than 10 V/cm. In the experiments, energy transfer was detected by direct state-selective electric field ionization of the 3S1 and 3PJ Rydberg levels and by monitoring the population of the 3DJ levels following pulsed microwave transfer from the 3PJ levels. Detection by microwave spectroscopic methods represents a highly state selective, low-background approach to probing the collisional energy transfer process and the environment in which the atom-molecule interactions occur. The experimentally observed electric-field dependence of the resonant energy transfer process, probed both by direct electric field ionization and by microwave transfer, agrees well with the results of calculations performed using a simple theoretical model of the energy transfer process. For measurements performed in zero electric field with atoms prepared in the 1s40s 3S1 level, the transition from a regime in which a single energy transfer channel can be isolated for detection to one in which multiple collision channels begin to play a role has been identified as the NH3 density was increased.

  19. Quantum Monte Carlo Characterization of Excited States and Energy-Level Alignment at Oligomer/Quantum-Dot Interfaces

    Science.gov (United States)

    Kanai, Yosuke; Dubois, Jonathan L.; Lee, Donghwa

    2012-02-01

    Charge separation of excitons in materials is one of the most important physical processes that need to take place in excitonic solar cells and in photocatalytic devices. Heterogeneous interfaces with the so-called type-II character are often employed for inducing the exciton dissociation through interfacial charge transfer. As the simplest criterion for designing such an interface, the energy alignment of the quasi-particle states is often discussed in literature, together with the exciton binding energy of electron-donating materials. Therefore, accurate characterization of the interfacial energy-level alignment and the exciton binding energy using first principles calculations is important for making systematic progresses in designing better materials for solar energy conversion. However, Density Functional Theory calculations need to be employed with caution in this context. First principles calculations such as Many-Body Perturbation Theory and Quantum Monte Carlo are promising alternatives for accurate characterization, but much more work is needed in this area to assess how well these methods perform in practice. In this talk, we will discuss our preliminary results using diffusion Quantum Monte Carlo on calculating the excited states and energy-level alignment of popular Oligomer/Quantum-Dot interfaces.

  20. Transient terahertz spectroscopy of excitons and unbound carriers in quasi two-dimensional electron-hole gases

    Energy Technology Data Exchange (ETDEWEB)

    Kaindl, Robert A.; Hagele, D.; Carnahan, M. A.; Chemla, D. S.

    2008-09-11

    We report a comprehensive experimental study and detailed model analysis of the terahertz (THz) dielectric response and density kinetics of excitons and unbound electron-hole pairs in GaAs quantum wells. A compact expression is given, in absolute units, for the complex-valued THz dielectric function of intra-excitonic transitions between the 1s and higher-energy exciton and continuum levels. It closely describes the THz spectra of resonantly generated excitons. Exciton ionization and formation are further explored, where the THz response exhibits both intra-excitonic and Drude features. Utilizing a two-component dielectric function, we derive the underlying exciton and unbound pair densities. In the ionized state, excellent agreement is found with the Saha thermodynamic equilibrium, which provides experimental verification of the two-component analysis and density scaling. During exciton formation, in turn, the pair kinetics is quantitatively described by a Saha equilibrium that follows the carrier cooling dynamics. The THz-derived kinetics is, moreover, consistent with time-resolved luminescence measured for comparison. Our study establishes a basis for tracking pair densities via transient THz spectroscopy of photoexcited quasi-2D electron-hole gases.