Terms Of Energy Transfer Research Articles

Ultrafast excited state dynamics of spirilloxanthin in solution and bound to core antenna complexes: Identification of the S* and T1 states

Ultrafast excited state dynamics of spirilloxanthin in solution and bound to the light-harvesting core antenna complexes from Rhodospirillum rubrum S1 were investigated by means of femtosecond pump-probe spectroscopic measurements. The previously proposed S∗ state of spirilloxanthin was clearly observed both in solution and bound to the light-harvesting core antenna complexes, while the lowest triplet excited state appeared only with spirilloxanthin bound to the protein complexes. Ultrafast formation of triplet spirilloxanthin bound to the protein complexes was observed upon excitation of either spirilloxanthin or bacteriochlorophyll-a. The anomalous reaction of the ultrafast triplet formation is discussed in terms of ultrafast energy transfer between spirilloxanthin and bacteriochlorophyll-a.

Analysis of charge, momentum and energy transfer by an impinging sub-keV electron beam on a conductor via Monte Carlo simulation including secondary-electron generation

In this work, a Monte Carlo simulation code for the electron-beam propagation was developed using the Mott’s elastic scattering cross section and the Penn’s dielectric function to account for beam scatterings and energy losses. Additional steps were introduced to compute the electron density profile, the momentum distribution, and the kinetic energy deposited inside the target material due to the penetration of the beam. Details of the simulation were outlined and backscattering results were validated against available data in the literature. Various parameters that govern the simulation were discussed extensively. It was shown that the electron deposition distributions were highly non-uniform. The electron density inside the target was modified significantly due to the beam and it depleted at a few nanometers below the surface while charge accumulation occurred deeper below the surface. On the other hand, the electron momentum deposited within the workpiece showed sign of increasing average electron velocity in all directions. In terms of the kinetic energy transfer, the energy distribution reached maximum at a few nanometers below the surface. Results between gold (a conductor) and silicon (an insulator) were compared as well, and they differed in magnitude and local deposition distributions, although the overall trends of the deposition distributions were similar.

Structural, thermal, and optical properties of Pr3+/Yb3+ co-doped oxyhalide tellurite glasses and its nano-crystalline parts

Nano-crystalized glass-ceramics and ceramics co-doped with Pr3+/Yb3+ have been successfully prepared by heat treatment of the precursor oxyhalide glass sample synthesized by melt-quench method. Thermal measurement of glass sample shows its glass transition temperature (Tg), and onset crystallization temperature (Tc). Formation of nano-crystals was verified by X-ray diffraction patterns and transmission electron microscopy (TEM) images. Values of optical band gap (Eopt) were found to be 2.85 eV and 1.54 eV for direct and indirect transitions, respectively. Up and downconversion emission spectra recorded with 976 and 532 nm laser wavelengths show emission from Pr3+ ions. Emission of Pr3+ enhances approximately thirty times when Yb3+ ion is added with the matrix. The Stark splitting and the intensity of different emission bands increase effectively when we approach to ceramic via glass-ceramic sample. Intense upconversion emission observed by naked eyes has been quantified in terms of standard chromaticity diagram (CIE). Power dependence study shows that the upconversion of NIR radiation to visible takes place mainly via photon avalanche (PA) process. Upconversion mechanisms have been discussed in terms of excited state absorption (ESA) and energy transfer (ET) processes.

Isokinetic behavior in the gas phase hydrogenation of nitroarenes over Au/TiO2: application of the selective energy transfer model

The gas phase selective hydrogenation of a series of nitroarenes (nitrobenzene, p-chloronitrobenzene, p-bromonitrobenzene, p-nitroaniline, p-nitrotoluene, p-nitrophenol and p-nitroanisole) has been examined over Au/TiO2 (0.3 % w/w Au, mean Au particle size = 3.9 nm). Compensation behavior is demonstrated with an associated isokinetic temperature (Tiso) of 558 ± 32 K. We account for this response in terms of the selective energy transfer (SET) model where the occurrence of resonance between catalyst and reactant vibrations generates the activated complex. An analysis of the stepwise variation of the activation energies has identified a critical vibrational frequency of 853 cm−1, which is close (±2 cm−1) to the reference value for nitro-group (in-plane symmetric O–N–O bending and stretching) vibrations. Application of SET suggests activation of weakly adsorbed nitroarene (at the support or metal/support interface) by excitation of the nitro-group via IR radiation from a strongly adsorbed surface nitroarene component. The excited nitroarene is then attacked by reactive hydrogen supplied by the Au sites to generate the respective aromatic amine with 100 % selectivity. Agreement of the SET predicted Tiso with the experimental value requires the incorporation of a term due to C–N torsional entropy resulting from distortion of the O–N–O plane.

Mechanism of quantum dot luminescence excitation within implanted SiO2:Si:C films

Results of the investigation of photoluminescence (PL) mechanisms for silicon dioxide films implanted with ions of silicon (100 keV; 7 × 1016 cm−2) and carbon (50 keV; 7 × 1015–1.5 × 1017 cm−2) are presented. The spectral, kinetic and thermal activation properties of the quantum dots (Si, C and SiC) formed by a subsequent annealing were studied by means of time-resolved luminescence spectroscopy under selective synchrotron radiation excitation. Independent quantum dot PL excitation channels involving energy transfer from the SiO2 matrix point defects and excitons were discovered. A resonant mechanism of the energy transfer from the matrix point defects (E′ and ODC) is shown to provide the fastest PL decay of nanosecond order. The critical distances (6–9 nm) of energy transport between the bulk defects and nanoclusters were determined in terms of the Inokuti–Hirayama model. An exchange interaction mechanism is realized between the surface defects (Es′-centres) and the luminescent nanoparticles. The peculiarities of an anomalous PL temperature dependence are explained in terms of a nonradiative energy transfer from the matrix excitons. It is established that resonant transfer to the luminescence centre triplet state is realized in the case of self-trapped excitons. In contrast, the PL excitation via free excitons includes the stages of energy transfer to the singlet state, thermally activated singlet–triplet conversion and radiative recombination.

Plasmonic solar water splitting

The study of the optoelectronic effects of plasmonic metal nanoparticles on semiconductors has led to compelling evidence for plasmon-enhanced water splitting. We review the relevant physics, device geometries, and research progress in this area. We focus on localized surface plasmons and their effects on semiconductors, particularly in terms of energy transfer, scattering, and hot electron transfer.

Synthesis and characterization of charge-transporting π-stacked polybenzofulvene derivatives

Two new benzofulvene derivatives bearing two or three methoxy substituents on the benzene ring were synthesized and induced to polymerize spontaneously in order to investigate the photophysical and electronic properties of the corresponding polymers. The photophysical features of the newly synthesized polymers suggested a high degree of π-stacking both in the solid state and in diluted solutions, and the large Stokes shift was interpreted in terms of an efficient energy transfer within the excimer. Absorption and emission features in the solid state were found to be similar to those in diluted solutions and the stable PL quantum yield was considered a promising feature with regard to the potential applications of the polymers in light emitting devices. Finally, the remarkable hole mobility shown by poly-4,5,6-MO-BF3k along with the enhancing effect of the methoxy substituents in the charge mobility opens up new routes to the development of materials potentially useful in optoelectronics.

Scale-by-scale energy budgets which account for the coherent motion

Scale-by-scale energy budget equations are written for flows where coherent structures may be prominent. Both general and locally isotropic formulations are provided. In particular, the contribution to the production, diffusion and energy transfer terms associated with the coherent motion is highlighted. Preliminary results are presented in the intermediate wake of a circular cylinder for phase-averaged second-and third-order structure functions. The experimental data provide adequate support for the scale-by-scale budgets.

Report 86

The absorbed dose, the mean value of the energy imparted by ionizing radiation to a volume of interest divided by the mass of that volume, is often a very effective way to describe radiation exposures. For example, in radiation therapy and industrial radiation processing, the absorbed dose is usually adequate for predicting the results of the irradiation. However, in situations in which the heterogeneity of the energy deposition or of the target structure results in individual targets (often assumed to be a cell or a cell nucleus) receiving energy depositions that are dramatically different from the mean value, the absorbed dose does not provide sufficient information needed to fully understand the consequences of irradiation or for the use of radiation-response models. In some cases, such as microbeam irradiations, heterogeneous exposures have been created intentionally in order to study mechanisms of response to ionizing radiation. In other situations, such as background-radiation exposure, the heterogeneity occurs as a result of the low level of radiation exposure or of a small local concentration of a radioactive material. When the energy deposition is heterogeneous, the conventional description in terms of absorbed dose can be misleading because it suggests that neighboring structures will incur the same amount of damage, and that the amount received by an individual target can be decreased to as low a value as desired. In fact, the individual targets can receive highly variable energy depositions, with a mean and variance determined by the physical properties of the radiation and the target. Reliance on the mean values rather than the spectrum of individual energy depositions can lead to inappropriate conclusions about the relationship between energy deposited and the initiation of biological response. Even with the same amount of deposited energy, the spectrum of initial damage products depends on radiation quality (sometimes specified in terms of the linear energy transfer). However, the complex combinations of biomolecular processes occurring following irradiation make it unlikely that any single-parameter description of the radiation interaction will be satisfactory for understanding biological processes. This Report recommends that, in cases in which energy deposition is likely to be heterogeneous, a detailed description of the radiation field, with an appropriate description of the irradiated system, should be given. The complete description of the radiation is the energy distribution of the particle radiance as a function of time and particle type. However, simplified descriptions such as the distribution of fluence rate, the probability density of lineal energy, and the event rate, or even the absorbed dose rate and radiation quality are appropriate descriptions of the irradiation in many cases.

Theoretical study of adsorption of lithium atom on carbon nanotube

We investigate the adsorption of lithium atoms on the surface of the (12,0) single wall carbon nanotube (SWCNT) by using ab initio quantum chemical calculations. The adsorption of one lithium atom on the inside of this SWCNT is favored compared to the outside. We check this feature by charge transfer and regional chemical potential density. The adsorption of multiple lithium atoms on the interior of the SWCNT is studied in terms of adsorption energy and charge transfer. We show that repulsive force between lithium atoms destabilizes a system for the large number of lithium atoms.

Bright white upconversion luminescence from Er 3+–Tm 3+–Yb 3+ doped CaSnO 3 powders

Bright white upconversion luminescence from Er 3+–Tm 3+–Yb 3+ doped CaSnO 3 powders is obtained under the diode laser excitation of 980 nm. It is composed of three primary colors of red, green and blue emissions, which originate from the transitions of 4F 9/2 → 4I 15/2, ( 2H 11/2, 4S 3/2) → 4I 15/2 of Er 3+ ions and 1G 4 → 3H 6 of Tm 3+ ions, respectively. The efficient upconversion emission is attributed to the energy transfer between Yb 3+ and Er 3+ or Tm 3+ions. Moreover, it is observed that Tm 3+ acts as the quenching center for the green upconversion luminescence from Er 3+ ions, and the sensitizer for the red and blue luminescence when the Tm 3+ doping content is less than 0.3 mol%. This is interpreted in terms of the efficient energy transfer between Tm 3+ and Er 3+ ions. The calculated color coordinates fall within the white region in the standard 1931 CIE chromaticity diagram, indicating the potential applications of Er 3+–Tm 3+–Yb 3+ doped CaSnO 3 in the field of displaying and lasers, etc.

How Water, Carbon, and Energy Drive Critical Zone Evolution: The Jemez–Santa Catalina Critical Zone Observatory

The structure of the critical zone (CZ) is a result of tectonic, lithogenic, and climatic forcings that shape the landscape across geologic time scales. The CZ structure can be probed to measure contemporary rates of regolith production and hillslope evolution, and its fluids and solids can be sampled to determine how structure affects CZ function as a living filter for hydrologic and biogeochemical cycles. Substantial uncertainty remains regarding how variability in climate and lithology influence CZ structure and function across both short (e.g., hydrologic event) and long (e.g., landscape evolution) time scales. We are addressing this issue using a theoretical framework that quantifies system inputs in terms of environmental energy and mass transfer (EEMT, MJ m−2 yr−1) in the recently established Jemez River Basin (JRB)–Santa Catalina Mountains (SCM) Critical Zone Observatory (CZO). We postulate that C and water fluxes, as embodied in EEMT, drive CZ evolution and that quantifying system inputs in this way leads to predictions of nonlinear and threshold effects in CZ structure formation. We are testing this hypothesis in the JRB‐SCM CZO, which comprises a pair of observatories—in northern New Mexico within the Rio Grande basin (JRB) and in southern Arizona within the Colorado River basin (SCM). The JRB‐SCM CZO spans gradients in climate, lithology, and biota representative of much variation found in the larger U.S Southwest. Our approach includes in situ monitoring of zero‐order basins nested within larger CZO watersheds and measurement–modeling iterations. The initial data collected at the ecosystem, pedon, and catchment scales indicates a strong role of coupled C and water flux in regulating chemical denudation of catchments in the JRB site.

Mn, Cr-co-doped MgAl 2O 4 phosphors for white LEDs

The Mn-, Cr-doped and Mn, Cr-co-doped MgAl 2O 4 powders have been synthesized via a gel–solid reaction method. Energy transfer from Mn 2+ to Cr 3+ has been observed for the first time in the co-doped MgAl 2O 4 phosphors. When excited with blue light with a wavelength of 450 nm at room temperature, both green emission from Mn 2+ around 520 nm and red emission from Cr 3+ around 675and 693 nm were generated. Moreover, the color of the emission can be modified by controlling the doping concentrations of Mn 2+ and Cr 3+. Therefore, MgAl 2O 4: Mn 2+, Cr 3+ could be used as a single-phased phosphor for white LED with a blue LED chip. The energy transfer in terms of Mn 2+ to Cr 3+ is determined by means of radiation and reabsorption.

Effect of Aggregation on the Photophysical Properties of Three Fluorene–Phenylene-Based Cationic Conjugated Polyelectrolytes

The effect of aggregation on the photophysical properties of three cationic poly{9,9-bis[N,N-(trimethylammonium)hexyl] fluorene-co-l,4-phenylene} polymers with average chain lengths of ∼6, 12, and 100 repeat units (PFP-NR3(6(I),12(Br),100(Br))) has been studied by steady-state and time-resolved fluorescence techniques. Conjugated polyelectrolytes are known to aggregate in solution and for these PFP-NR3 polymers this causes a decrease in the fluorescence quantum yield. The use of acetonitrile as a cosolvent leads to the breakup of aggregates of PFP-NR3 in water; for PFP-NR3(6(I)), this results in an ∼10-fold increase in fluorescence quantum yield, a ca. 2-fold increase in the molar extinction coefficient at 380 nm, and an increase in the emission lifetime, as compared with polymer behavior in water. Fluorescence anisotropy also decreases with increasing aggregation, and this is attributed to increased fluorescence depolarization by interchain energy transfer in aggregate PFP-NR3 clusters. Förster resonance energy transfer along the polymer chain is expected to be very fast, with a calculated FRET rate constant of 7.3 × 10(12) s(-1) and a Förster distance of 2.83 nm (cf. the polymer repeat unit separation of 0.840 nm) for PFP-NR3(100(Br)). The complex polymer excited-state decay kinetics in aggregated PFP-NR3 systems have been successfully modeled in terms of intrachain energy transfer via migration and trapping at interchain aggregate trap sites, with model parameters in good agreement with data from picosecond time-resolved studies and the calculated theoretical Förster energy-transfer rates.

New understanding of the role of cerebrospinal fluid: Offsetting of arterial and brain pulsation and self-dissipation of cerebrospinal fluid pulsatile flow energy

Many theories have been postulated to date regarding the mechanisms involved in the absorption of the intracranial arterial blood flow energy in the intracranial space, but it is as yet nor clearly defined. The blood flow energy that is transmitted from the heart formulates the cerebrospinal fluid (CSF) pulsatile flow, and is known to constitute the major energy of the CSF flow, while the bulk flow carries only small energy. The intracranial space that is enclosed in a solid cranium and is an isolate system as in the Monroe–Kellie doctrine, and the authors propose to re-analyze the Monroe–Kellie doctrine concept in terms of energy transfer and dissipation of the Windkessel effect. We propose that the large blood flow energy that initiates in the heart is transferred in order of precedence to the arteries, arterioles, brain parenchyma, and finally to CSF within the cranium, in which the energy is confined and unable to be transferred, so that the final transfer of energy to the CSF pulsatile flow is self-dissipated in terms of direction and chronology in CSF pulsatile flow. In order for the CSF pulsatile flow that is transferred from arterial blood flow energy to be dissipated in the intracranial space, this cannot be explained with bulk flow energy in any perspective, since the pulsatile flow kinetic energy is greater than the bulk flow kinetic energy by at least a 100-fold. The pulsatile flow energy within the closed intracranial space cannot be transferred and is confined, as postulated by the Monroe–Kellie doctrine, and therefore the authors propound that the pulsatile flow dissipates by itself. The dissipation of the CSF pulsatile flow kinetic energy will be in all directions in a diffuse and random manner, and is offset by the CSF flow energy vector due to the CSF mixing process. Such energy dissipation will lead to maintenance of low CSF flow energy, which will result in maintaining low intracranial pressure (ICP), and sufficient brain perfusion. It is our opinion that our hypothesis will be able to explain the decreasing offsetting effect of arterial pulsation in chronic obstructive hydrocephalus, and the mechanisms for the ventricular dilatation in communicating hydrocephalus without changes in the mean ICP, and therefore highly justifying our hypothesis.

Operant responding following exposure to HZE particles and its relationship to particle energy and linear energy transfer

On exploratory class missions astronauts will be exposed to a variety of heavy particles (HZE particles) which differ in terms of particle energy and particle linear energy transfer. The present experiments were designed to evaluate how these physical characteristics of different particles affect cognitive performance, specifically operant responding. Following exposure to 28Si, 48Ti, 12C and 16O particles at the NASA Space Radiation Laboratory rats were tested for their ability to respond appropriately to changes in reinforcement schedules using an operant task. The results showed that the effectiveness of different particles in disrupting cognitive performance, defined as the lowest dose that produced a performance decrement, varied as a function of the energy of the specific particle: for comparisons between different energies of the same particle ( e.g., 56Fe) the effectiveness of the particle was directly proportional to particle linear energy transfer, whereas for comparisons between different particles ( e.g., 56Fe and 16O) effectiveness was inversely proportional to particle linear energy transfer. The results are discussed in terms of the mechanisms that influence the effectiveness of different particles and energies and in terms of their implications for analyzing the possible risks to astronauts of decrements in cognitive performance following exposure to HZE particles on long-duration exploratory class missions.

Quantitative analysis of energy transfer between fluorescent proteins in CFP–GBP–YFP and its response to Ca2+

This article reports the full characterisation of the optical properties of a biosynthesised protein consisting of fused cyan fluorescent protein, glucose binding protein and yellow fluorescent protein. The cyan and yellow fluorescent proteins act as donors and acceptors for intramolecular fluorescence resonance energy transfer. Absorption, fluorescence, excitation and fluorescence decays of the compound protein were measured and compared with those of free fluorescent proteins. Signatures of energy transfer were identified in the spectral intensities and fluorescence decays. A model describing the fluorescence properties including energy transfer in terms of rate equations is presented and all relevant parameters are extracted from the measurements. The compound protein changes conformation on binding with calcium ions. This is reflected in a change of energy transfer efficiency between the fluorescent proteins. We track the conformational change and the kinetics of the calcium binding reaction from fluorescence intensity and decay measurements and interpret the results in light of the rate equation model. This visualisation of change in protein conformation has the potential to serve as an analytical tool in the study of protein structure changes in real time, in the development of biosensor proteins and in characterizing protein-drug interactions.

Unusual enhancement of triplet carotenoid formation in pigmentprotein complexes as revealed by femtosecond pump-probe spectroscopy

Ultrafast excited state dynamics of carotenoids in solution and bound to pigment-protein complexes have been investigated by means of femtosecond pump-probe spectroscopic measurements. Ultrafast triplet formation of carotenoids bound to pigmentprotein complexes was observed upon excitation of both carotenoids and bacteriochlorophyll. The anomalous reaction of triplet formation of carotenoids bound to pigment-protein complexes is discussed in terms of ultrafast triplet-triplet excitation energy transfer between carotenoid and bacteriochlorophyll.

Electronic Energy Transfer and Quantum-Coherence in π-Conjugated Polymers

Electronic energy transfer (EET) has been the subject of intense research because of its significant contribution to the photophysical properties of various material systems. For π-conjugated polymers, it has long been accepted that a classical hopping mechanism is dominant in the energy transfer dynamics because of a weak electronic coupling. However, recent research reveals that conjugated polymers, in fact, can have an electronic coupling strong enough to preserve quantum-coherence. In this review, we summarize the main photophysical features of conjugated polymers. We discuss how electronic excited states evolve on various time scales from femtoseconds to hundreds of picoseconds in terms of exciton relaxation, localization, and electronic energy transfer. The Förster energy transfer model and modifications needed for describing energy transfer in conjugated polymers are described. We discuss how chain conformation and its disorder influence EET and the time scale of the evolution of electronic excited states, and demonstrate how quantum coherence contributes to energy transfer dynamics. Recent research on exciton diffusion in various kinds of polymers is summarized.

Gd3+ Sensitized Enhanced Green Luminescence in Gd:Tb(Sal)3Phen Complex in PVA

Ternary and tertiary complexes of Tb(Sal)(3)Phen and Gd:Tb(Sal)(3)Phen were synthesized and characterized in PVA polymer. The structural properties of these systems were evaluated on the basis of NMR and FT-IR techniques. The absorption, excitation and emissive properties of the Tb(3+) ion were improved when coordinated with Sal and Phen ligands. Photoluminescence properties of the complexes in solution, crystals and dispersed in PVA film were explored in steady state and in time domain. Selective excitations (487, 355, 310 and 266 nm) of Tb(3+), Sal and Gd(3+) ions reveal an intramolecular energy transfer process. The emission of Gd:Tb(Sal)(3)Phen complex in PVA indicates the contribution of Gd(3+) ion to enhance the emission intensity of Tb(3+) ion. On the basis of these investigations, photophysics was widely discussed in terms of energy transfer and encapsulation effect.