Dependence Of Energy Transfer Efficiency Research Articles

Förster Energy Transfer in Arrays of Epitaxial CdSe/ZnSe Quantum Dots Involving Bright and Dark Excitons

Using time-resolved photoluminescence (PL) spectroscopy, we establish the presence of the Forster energy transfer mechanism between two arrays of epitaxial CdSe/ZnSe quantum dots (QDs) of different sizes. The mechanism operates through dipole–dipole interaction between ground excitonic states of the smaller QDs and excited states of the larger QDs. The dependence of energy transfer efficiency on the width of barrier separating the QD insets is shown to be in line with the Forster mechanism. The temperature dependence of the PL decay times and PL intensity suggests the involvement of dark excitons in the energy transfer process.

Ферстеровский резонансный перенос энергии с участием светлых и темных экситонов в массивах эпитаксиальных квантовых точек CdSe/ZnSe

AbstractUsing time-resolved photoluminescence (PL) spectroscopy, we establish the presence of the Förster energy transfer mechanism between two arrays of epitaxial CdSe/ZnSe quantum dots (QDs) of different sizes. The mechanism operates through dipole–dipole interaction between ground excitonic states of the smaller QDs and excited states of the larger QDs. The dependence of energy transfer efficiency on the width of barrier separating the QD insets is shown to be in line with the Förster mechanism. The temperature dependence of the PL decay times and PL intensity suggests the involvement of dark excitons in the energy transfer process.

Excitation-Energy Transfer Paths from Tryptophans to Coordinated Copper Ions in Engineered Azurins: a Source of Observables for Monitoring Protein Structural Changes

Abstract The intrinsic fluorescence of recombinant proteins offers a powerful tool to detect and characterize structural changes induced by chemical or biological stimuli. We show that metal-ion binding to a hexahistidine tail can significantly broaden the range of such structurally sensitive fluorescence observables. Bipositive metal-ions as Cu2+, Ni2+ and Zn2+ bind 6xHis-tag azurin and its 6xHis-tagged R129W and W48A-R129W mutants with good efficiency and, thereby, quench their intrinsic fluorescence. Due to a much more favourable spectral overlap, the 6xHis-tag/Cu2+ complex(es) are the most efficient quenchers of both W48 and W129 emissions. Based on simple Förster-type dependence of energy-transfer efficiency on donor/acceptor distance, we can trace several excitation-energy transfer paths across the protein structure. Unexpected lifetime components in the azurin 6xHis-tag/Cu2+ complex emission decays reveal underneath complexity in the conformational landscape of these systems. The new tryptophan emission quenching paths provide additional signals for detecting and identifying protein structural changes.

The features of energy transfer to the emission centers in ZnWO4 and ZnWO4:Mo

The process of energy transfer to the emission centers is studied in ZnWO4 and ZnWO4:Mo single crystals in the temperature range 10–300K. A numerical simulation describing the process is presented; the temperature dependence of energy transfer efficiency to the intrinsic emission centers in ZnWO4 is shown to be defined by the modification of Onsager sphere radius. A competitive role of radiative relaxation channel related to the impurity of molybdenum is studied in ZnWO4:Mo. It is shown that below 60K the energy transfer to the MoO6 emission centers by free charge carriers terminates due to the self-trapping of holes at WO6 complexes.

Color tunable phosphor CaMoO4:Eu3+,Li+ via energy transfer of MoO42−–Eu3+ dependent on morphology and doping concentration

The cooling rate and the solubility of molybdate in molten salt play crucial roles on the microscopic morphologies and photoluminescence (PL) properties of the phosphor CaMoO4:Eu3+,Li+. Undoped CaMoO4 exhibits self-activated green PL with a broad emission band which is assigned to the spin forbidden 3T1,2–1A1 transition of the MoO42− complex. The strong UV absorption of undoped CaMoO4 is originated from the charge transfer from O2− ligands to the central Mo6+ ions inside MoO42− group. The emission of the phosphor CaMoO4:Eu3+,Li+ obtained by molten salt synthesis (MSS) at 900°C is composed of a broad green emission from MoO42− and a group of sharp red emission peaks from f–f transitions of Eu3+. Efficient energy transfer from MoO42− to Eu3+ is responsible for the increased red PL of the phosphor. The dependence of energy transfer efficiency on the processing conditions and doping concentration has been investigated.

Efficiency enhancement of organic light emitting diode via surface energy transfer between exciton and surface plasmon

Organic light emitting diodes (OLEDs) with surface plasmon (SP) enhanced emission have been fabricated. Gold nanoclusters (GNCs) deposited using thermal evaporation technique has been used for localization of surface plasmons. Size of GNCs and distance of GNCs from the emissive layer have been optimized using steady state and time resolved photoluminescence (PL) results. 3.2 Times enhancement in PL intensity and 2.8 times enhancement in electroluminescence intensity of OLED have been obtained when GNCs of size 9.3 nm has been introduced at a distance of 5 nm from emissive layer. Distance dependence of energy transfer efficiency between exciton and SPs was found to be of 1/ R 4 type, which is typically the dependence for dipole-surface energy transfer.

Infrared emission properties and energy transfer in ZnO–SiO 2:Yb 3+ composites

Intense near-infrared emission at 1 μm has been obtained in ZnO–SiO 2:Yb 3+ composites via a facile sol–gel method upon broadband ultraviolet light excitation. Systematic optical measurements including static and time-resolved photoluminescence have been performed to elucidate the energy transfer from ZnO quantum dots to Yb 3+ ions. The dependence of energy transfer efficiency on Yb 3+ concentration has been investigated in detail. Codoping with Li + ions leads to about twice enhancement of the near-infrared luminescence intensity around 1 μm at room temperature. The enhancement in the luminescence intensity could be mostly attributed to the modification of the local symmetry around Yb 3+ ions by codoping with Li + ions.

Broadband downconversion from oxygen-deficient centers to Yb^3+ in germanate glasses

We report broadband downconversion from ultraviolet to near-infrared in Yb3+-doped oxygen-deficient SrO-Al2O3-GeO2 glasses. Oxygen-deficient centers are introduced in germanate glasses by adding metal Al instead of corresponding oxide (Al2O3). Tunable luminescence related to these defects is observed. Conversion of broadband ultraviolet light to blue-green tunable luminescence and to near-infrared emission is detected in glasses. The energy transfer efficiency increases with increasing Yb2O3 concentration. The dependence of energy transfer efficiency on wavelength is also discussed.

Nucleic Acid Base Analog FRET-Pair Facilitating Detailed Structural Measurements in Nucleic Acid Containing Systems

We present the first nucleobase analog fluorescence resonance energy transfer (FRET)-pair. The pair consists of tC(O), 1,3-diaza-2-oxophenoxazine, as an energy donor and the newly developed tC(nitro), 7-nitro-1,3-diaza-2-oxophenothiazine, as an energy acceptor. The FRET-pair successfully monitors distances covering up to more than one turn of the DNA duplex. Importantly, we show that the rigid stacking of the two base analogs, and consequently excellent control of their exact positions and orientations, results in a high control of the orientation factor and hence very distinct FRET changes as the number of bases separating tC(O) and tC(nitro) is varied. A set of DNA strands containing the FRET-pair at wisely chosen locations will, thus, make it possible to accurately distinguish distance- from orientation-changes using FRET. In combination with the good nucleobase analog properties, this points toward detailed studies of the inherent dynamics of nucleic acid structures. Moreover, the placement of FRET-pair chromophores inside the base stack will be a great advantage in studies where other (biomacro)molecules interact with the nucleic acid. Lastly, our study gives possibly the first truly solid experimental support to the dependence of energy transfer efficiency on orientation of involved transition dipoles as predicted by the Forster theory.

Energy-harvesting characteristics of PZT-5A under gunfire shock

The energy-harvesting behaviors of a ring-shaped PZT-5A element exposed to gunfire shock are investigated for military applications such as an in-flight power source for electronic fuze. A laboratory test using a pneumatic shock machine up to 3000 g's and a gunfire test accompanied by the acceleration of 65,000 g's have been performed. The PZT-5A element subjected to gunfire shock has worked in its strong-depolarization region, thereby generating the electric energy whose quantity is about 140.4 times larger than that measured in its linear operation region. The experimental studies on the PZT-5A element under dynamic load have demonstrated three physico-electric characteristics: the dependence of piezoelectric constant on load-rate, the shock-aging of piezoelectric effect, and the dependence of energy-transfer efficiency on the change in normalized impulse.

Statistical Theory of Collisional Energy Transfer in Molecular Collisions.trans-Stilbene Deactivation by Argon, Carbon Dioxide, andn-Heptane

Recent advances in experimental techniques have made it possible to measure the full conditional probability density P(E, E') of the energy transfer between two colliding molecules in the gas phase, one of which is highly energized and the other in thermal equilibrium at a given temperature. Data have now become available for trans-stilbene deactivation by the three bath gas molecules Ar, CO2, and n-heptane (C7H16). The initial energies of trans-stilbene are set to 10 000, 20 000, 30 000, and 40 000 cm (-1). The results show that exceptionally large amounts of energy are transferred in each collision. By application of our partially ergodic collision theory (PECT), we find that the energy transfer efficiency betaE ranges from a rather normal value of 0.15 for n-heptane at the highest excitation energy to 0.93-nearly in the ergodic collision limit-for the argon bath gas at high excitation energy. Generally, the PECT produces a good fit of the data except for the nearly elastic peak in the case of n-heptane, where PECT produces a rounded and downshifted peak in contrast to a sharply defined elastic maximum of the monoexponential functional fit produced from the original experimental data obtained by kinetically controlled selective ionization in the work of the group of Luther in Göttingen. This problem is analyzed and found to be related partly to the lack of treatment of glancing collisions in the theory with a remaining uncertainty due to the weak dependence of energy transfer efficiency on nearly elastic collisions. A summary of the present state of understanding shows that collisional activation and deactivation of reactant molecules is more efficient and more statistical than has been previously realized.

Shock spectra of piano hammers

It has been suggested [I. Bork, Appl. Acoust. 30 (in press)] that an effective way to characterize the frequency dependence of energy transfer efficiency from a piano hammer to a string is by means of the shock spectrum, which describes the vibration amplitudes of a simple oscillating system with a resonance frequency f, either during (initial shock spectrum) or after (residual shock spectrum) an impact. Shock spectra of piano hammers striking a string segment have been recorded by means of a force transducer and an FFT analyzer. Initial results indicate that as the hammer speed increases, the shock spectrum broadens and its maximum shifts systematically upward in frequency (fmax is nearly proportional to the square root of speed for most hammers). In a carefully voiced piano, fmax increases from bass to treble but does not double each octave. Experimental results are compared to various hammer models that include a nonlinear spring characteristic.

Excitation energy transfer between J-aggregates of cyanine dyes arranged in a layer structure

Luminescence and excitation energy transfer of organic dye molecules in monolayer assemblies have been studied. Three cyanine dyes: 5,6,5′,6′-dibenzo-1, 1′-diethyl-2, 2′-cyanine chloride (dye I), 5,5′-dichloro-3, 3′-diethyl-9-phenyl-thiacar-bocyanine chloride (dye II), 3,3′-dimethyl-9-phenyl-4,5,4′,5′-naphthothiacarbocyanine chloride (dye III) are organized into the J-aggregate which consists of large arrays of densely packed chromophores and is characterized by an intense absorption band (J band) and a sharp resonance fluorescence. Sensitization of resonance fluorescence of the acceptor aggregate (dye II, dye III) by the donor aggregate (dye I) is evident in the monolayer assemblies in which donor and acceptor layers are in direct contact with one another. Dependence of energy transfer efficiency on the layer separation has yielded an empirical formula of exponential decay type. Excitation energy transfer between the J-aggregates is also observed when both donor (dye I) and acceptor (dye II) aggregates are incorporated into the same layer plane of the monolayer assembly.

The Energy Transfer Between Ce3+ and Tb3+ Ions in LaOBr : Ce3 + , Tb3+

The energy transfer between Ce3+ and Tb3+ ions in , Tb3+ was systematically studied. The emission spectra of Ce3+ and Tb3+ in , Tb3+ have been measured with excitation at 355 and 250 nm. At the same time, the fluorescence lifetime and time‐resolved spectra in nanosecond scale, for a series of samples doped with different concentrations, were measured. The temperature dependence of energy transfer efficiency and probability of energy transfer from Ce3+ to Tb3+ was studied. It was found that energy is transferred, not only from Ce3+ to Tb3+, but also from Tb3+ to Ce3+. A model of energy transfer is proposed.

Self-trapping on a dimer: Time-dependent solutions of a discrete nonlinear Schrödinger equation.

From the discrete nonlinear Schr\"odinger equation describing transport on a dimer we derive and solve a closed nonlinear equation for the site-occupation probability difference. Our results, which are directly relevant to specific experiments such as neutron scattering in physically realizable dimers, exhibit a transition from "free" to "self-trapped" behavior and illustrate features expected in extended systems, including soliton/polaron bandwidth reduction and the dependence of energy-transfer efficiency on initial conditions.

Low-temperature (4–77°K) spectroscopy of anacystis; temperature dependence of energy transfer efficiency

From the absorption spectra, emission and excitation spectra of chlorophyll a (Chl a) and phycocyanin fluorescence measured (from 4 to 77°K) at different wavelengths, we confirmed that a large portion of Chl a (Chl a 670, Chl a 678 and Chl a 705), in Anacystis, is in System I, and that System II is composed mainly of phycocyanin and of some Chl a 670 and Chl a 678. Our data also confirmed the following correspondence between absorption and fluorescence bands: phycocyanin (with bands at 580, 625 and 634–637 nm) and allophycocyanin (approx. 650 nm) are responsible for the broad fluorescence band at 653–655 nm and Chl a 670 for F680 (when Chl a 678 is preferentially extracted). (Date in ref. 20 show that Chl a 678 is responsible for F685.) The ratio of f715 to f685 +f695 was greater in System I than in System II. The efficiency of energy transfer from Chl a 670 to Chl a 678, that approaches 100% even at 4°K, was found to be independent of temperature. However, transfer efficiency from phycocyanin to Chl a was temperature dependent; it was lower at 4 than at 77°K. The quantum yield of Chl a fluorescence (λexcitation= 435nm) was higher (by a factor of 4) at 4 than at 77°K. The estimated quantum yield of fluorescence in Anacystis at 4°K is only 6% (λexcitation= 560nm) and approx. 3% (λexcitation= 436nm).

Low-temperature (4–77°K) spectroscopy of chlorella; temperature dependence of energy transfer efficiency

From the absorption spectra and the excitation spectra of chlorophyll a fluorescence measured (4–77°K) at different wavelengths (685–760 nm) and their comparison with the emission spectra published elsewhere 23, we confirm that both the Pigment Systems (I and II) contain chlorophyll b, chlorophyll a 670 and chlorophyll a 678. But System II is relatively enriched in chlorophyll b and System I in chlorophyll a 685–715. Moreover, our data suggest the following correspondence between absorption and fluorescence bands: chlorophyll a 678 is responsible for F687, “Trap II” for F698 and chlorophyll a 685–715 for F725. The efficiencies of energy transfer from chlorophyll b to chlorophyll a and from chlorophyll a 670 to chlorophyll a 678 that approach 100 % even at 4°K were found to be independent of temperature (4–295°K). However, transfer efficiencies from chlorophyll a to the suggested trap of System II may be temperature dependent.