Temperature Dependence Of Energy Transfer Research Articles

Abnormal anti-quenching and controllable multi-transitions of Bi3+ luminescence by temperature in a yellow-emitting LuVO4 :Bi3+ phosphor for UV-converted white LEDs.

Phosphors with an efficient yellow-emitting color play a crucial role in phosphor-converted white LEDs (pc-WLEDs), but popular yellow phosphors such as YAG:Ce or Eu(2+) -doped (oxy)nitrides cannot smoothly meet this seemingly simple requirement due to their strong absorptions in the visible range. Herein, we report a novel yellow-emitting LuVO(4) :Bi(3+) phosphor that can solve this shortcoming. The emission from LuVO(4) :Bi(3+) shows a peak at 576 nm with a quantum efficiency (QE) of up to 68 %, good resistance to thermal quenching (T(50 %) =573 K), and no severe thermal degradation after heating-cooling cycles upon UV excitation. The yellow emission, as verified by X-ray photoelectron spectra (XPS), originates from the ((3)P(0),(3)P(1))→(1) S0 transitions of Bi(3+). Increasing the temperature from 10 to 300 K produces a temperature-dependent energy-transfer process between VO(4)(3-) groups and Bi(3+), and further heating of the samples to 573 K intensifies the emission. However, it subsequently weakens, accompanied by blueshifts of the emission peaks. This abnormal anti-thermal quenching can be ascribed to temperature-dependent energy transfer from VO(4)(3-) groups to Bi(3+), a population redistribution between the excited states of (3)P(0) and (3)P(1) upon thermal stimulation, and discharge of electrons trapped in defects with a trap depth of 359 K. Device fabrication with the as-prepared phosphor LuVO(4) :Bi(3+) has proved that it can act as a good yellow phosphor for pc-WLEDs.

Measurement and model calculation of the temperature dependence of ligand-to-metal energy transfer rates in lanthanide complexes

Temperature dependent transient curves of excited levels of a model Eu3+ complex have been measured for the first time. A coincidence between the temperature dependent rise time of the 5D0 emitting level and decay time of the 5D1 excited level in the [Eu(tta)3(H2O)2] complex has been found, which unambiguously proves the T1→5D1→5D0 sensitization pathway. A theoretical approach for the temperature dependent energy transfer rates has been successfully applied to the rationalization of the experimental data.

Understanding energy transfer in Ce doped Li6Gd(BO3)3: A study of millisecond decay kinetics in 77–300 K range

Large size, transparent and crack-free single crystals of pure and 0.1mol% Ce doped Li6Gd(BO3)3 have been grown using the Czochralski technique. The photoluminescence and decay kinetics in millisecond range were investigated in the 77–300K temperature range. In the case of Ce doped single crystals a broad emission band at 400nm corresponding to 5d→4f transitions of Ce3+ centers has been observed near room temperature. This emission band splits into two peaks at 386nm and 414nm below 200K. The temperature dependence of Ce3+ emission corresponding to excitation bands at 312 and 345nm were studied. It was observed that for an excitation at 345nm (corresponding to the Ce3+ ions alone) the emission intensity decreases with increasing temperatures while it remains constant for the excitation of Ce3+ at 312nm that coincides with the Gd3+ energy level at the same wavelength. This suggests the participation of a temperature dependent energy transfer mechanism between Gd3+ and Ce3+ ions in the Li6Gd(BO3)3 matrix. The mechanism has been explained by studying the temperature dependence of Gd3+ emission at 312nm in the doped and undoped crystals.

Luminescence and energy transfer in Lu3Al5O12 scintillators co-doped with Ce3+ and Pr3+

Lu3Al5O12:Ce3+ (LuAG:Ce) is a scintillator with a fast response time. The light yield is lower than theoretically expected and to increase the light yield co-doping with Pr3+ is investigated. To better understand the energy flow to the Ce3+ ion, first low temperature emission and excitation spectra of Pr3+ doped LuAG were investigated, allowing the accurate determination of the zero-phonon lines for the 5d states of Pr3+ in LuAG and the temperature dependent energy transfer from the Self Trapped Exciton to Pr3+. In addition VUV excitation and soft X-ray excited emission spectra of the co-doped LuAG:Ce,Pr were studied. The results show that energy transfer from Pr3+ to Ce3+ occurs but it is followed by back transfer to the 4f states of Pr3+.

Direct hole and delayed electron capture on a picosecond timescale by Eu2+ centers in CaGa2S4 monitored by synchroscan with horizontal blanking

A Eu2+ concentration and temperature dependent energy transfer study from the host lattice to Eu2+ luminescence centers in Ca(1–x)EuxGa2S4 (x = 0.001 to 0.05) was performed with a special streak camera that combines the high timing resolution of a conventional synchroscan operation (<2 ps) with the ability to study long lived states (10 ns − 1 ms) typical for rare earth and transition metal ions. Two transfer mechanisms from the CaGa2S4 host lattice to the Eu2+ ions were identified. A fast transfer process (<4 ps) is interpreted as sequential hole-electron capture by the Eu2+ ions, and slower process (>1 ns) is interpreted as the sequential capture of a hole and an electron by Eu2+ but with the electron first entering an intermediate state trapped near Eu3+. Energy transfer via a self-trapped excitonic (STE) state is unlikely because of the absence of an anti-correlation between the STE decay-time and the Eu2+ rise-time as well as between the STE emission intensity and the Eu2+ intensity. All rise-time spectra were successfully fitted with a model representing the above transfer mechanisms.

Photoluminescence investigations on a novel green-emitting phosphor Ba3Sc(BO3)3:Tb3+ using synchrotron vacuum ultraviolet radiation

Vacuum ultraviolet (VUV) spectroscopic properties of undoped and Tb3+-doped Ba3Sc(BO3)3 were investigated by using synchrotron radiation. The Tb3+-doped Ba3Sc(BO3)3 sample crystallized in a flower-like shape even was synthesized at 1100 °C. Upon VUV excitation, Ba3Sc(BO3)3 exhibited an intrinsic broad UV emission centered at 336 nm, which results from radiative annihilation of self-trapped exciton (STE) that may presumably be associated with band-gap excitations or molecular transitions within the BO33− group. The maximum host absorption for Ba3Sc(BO3)3 was found at about 180 nm. Upon doping of Tb3+ ions into Ba3Sc(BO3)3, an efficient energy transfer from the host excitations to Tb3+via STE emission was observed, showing host sensitization of Tb3+ occurs. The energy transfer from host to Tb3+via STE emission in Ba3Sc(BO3)3:Tb3+ was studied as a function of temperature and Tb3+ doping concentration. It has been demonstrated that the energy transfer efficiency was increased with either increasing temperature or Tb3+ doping concentration. In the case of temperature dependent energy transfer, the energy transfer from the STE to Tb3+ is thermally activated, probably due to exciton mobility, while in the case of concentration dependent energy transfer, the energy transfer from the STE to Tb3+ is promoted due to a closer distance between the STE and Tb3+ at high Tb3+ concentration.

Polarization Portraits of Single Multichromophoric Systems: Visualizing Conformation and Energy Transfer

A novel technique, two-dimensional (2D) polarization single-molecule imaging, is presented. It is based on measurements and analysis of fluorescence intensity as a function of excitation and emission polarization angles. The technique allows recording of full information on the steady-state polarization properties of fluorescent objects. It is particularly suitable for application to single multichromophoric systems (molecules or nanoparticles) with energy transfer (ET) between different chromophores (e.g., single fluorescent pi-conjugated polymer chains). The 2D polarization data simultaneously provide information on the conformation of the system and the efficiency of its internal excitation ET. The technique is used to characterize single chains and different kinds of chain aggregates of different conjugated polymers at different temperatures. The 2D polarization measurements reveal a dramatic difference in ET taking place in these systems. Clear temperature dependence of ET is observed for individual aggregates as well as for their statistical ensembles. Also, a dependence on solvent and aggregate size is shown. Additionally, extensive "traditional one-dimensional" polarization results on the polarization anisotropy of fluorescence excitation and emission are presented. These results and findings are discussed in relation to internal organization of the nano-objects under study.

Conversion of near-ultraviolet radiation into visible and infrared emissions through energy transfer in Yb2O3 doped SrO–TiO2–SiO2 glasses

We demonstrated the conversion of near-ultraviolet radiation of 250–350 nm into visible emission of 450–600 nm and near-infrared emission of 970–1100 nm in the Yb2O3 doped transparent 40SrO-20TiO2-40SiO2 glasses. The observed broad visible emission band centered at 510 nm is associated with silicon-oxygen-related defects in the glassy matrix, and the near-infrared emission originated from the Yb3+ F25/2→F27/2 transition is due to the energy transfer from silicon-oxygen-related defects to Yb3+. The energy transfer process was studied by both the steady state spectra and the time-resolved spectra of Yb3+ at 15 K. The temperature dependent energy transfer rate was calculated. The Yb2O3 concentration dependent energy transfer efficiency has also been evaluated, and the maximum value is 56% for 12 mol % Yb2O3 doped glass.

Temperature Dependent Energy Transfer Measurements Reveal Flexibility in the Upper 50 kDa Domain of Myosin V

Our previous work has demonstrated that labeling myosin V in the upper 50 kDa domain with the biarsenical dye FlAsH can serve as an acceptor for fluorescence resonance energy transfer studies with mant labeled nucleotides and IAEDANS actin. These FRET studies suggest that myosin V can adopt a conformation in which the nucleotide binding pocket and the actin binding cleft are in a closed conformation. Our studies suggest the upper 50 kDa domain may be highly flexible in certain nucleotide-states which allows tight binding to nucleotide and actin. Molecular geometric simulations demonstrate the upper 50 kDa domain is most flexible in the myosin V.ADP state, consistent with this state having a high affinity for ADP and actin. Currently, we examined the temperature dependence of the FRET signal between mantADP and MV FlAsH. We found that at low temperature (4-15°C) a high FRET state dominates (closed pocket) while at high temperature (30-37°C) a low FRET state dominates (open pocket). This transition is reversible suggesting a temperature-dependent conformational change. We also found that FlAsH labeled G440A MV, a non-hydrolyzable mutant, has a similar temperature-dependent transition in the presence of mantATP. In contrast, the transition does not occur in the presence of mantADP.BeFx or with the non-hydrolyzable E44A MV mutant in the presence of mantATP. Our results suggest coordination of the gamma-phosphate of ATP rigidifies the upper 50 kDa domain which results in a weak actin affinity state (open actin binding cleft and closed nucleotide binding pocket). However, upon phosphate release the upper 50kDa domain becomes more flexible which allows myosin to adopt a conformation in which it has a high affinity for both nucleotide and actin (closed nucleotide binding pocket and actin binding cleft).

Temperature-dependent energy transfer in photo-sensitized luminescence of rare earth complexes

We have fabricated polymer thin films containing bis(triphenylphosphineoxide)-tris(hexafluoroacetylacetonato) terbium(III) [Tb(HFA) 3(TPPO) 2] as a thermo-sensor. The thermo-sensitivity of the thin film containing the Tb(III) complex was found to be 13.5%/°C. The emission intensity ratio normalized according to that at 0 °C observed for Tb(HFA) 3(TPPO) 2 in the thin film was not affected by pressure. The thermo-sensing thin film is expected to be useful in measuring surface-temperatures of bodies in wind-tunnel experiments.

Temperature dependent energy transfer in Ar–O3 collisions

The energy transfer between argon atoms and ozone complexes O3*, excited in the region of the dissociation threshold, is calculated for fixed temperatures (100 K< or =T < or =2500 K) using classical trajectories. The internal energy of ozone is resolved in terms of vibrational and rotational energies. For all temperatures, energy flows from O3* to Ar. The vibrational energy transfer, relative to k(B)T, is very small below 500 K, but gradually increases towards high temperatures. The relative rotational energy transfer, on the other hand, monotonously decreases with T; around 1100 K it falls below the relative vibrational energy transfer. Thermally averaged cross sections for vibrational and rotational energy transfers are also calculated. The implications for the stabilization of ozone complexes in the energy transfer model are discussed.

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

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.

Optical bistability in Yb3+:YCa4O(BO3)3 crystal

Abstract A hysteresis cycle has been observed in 15 mol.% Yb 3+ :YCa 4 O(BO 3 ) 3 by varying infrared excitation power while recording Yb 3+ cooperative luminescence. The sample was mounted in a cryostat maintained at 12.5 K. Two mechanisms have been considered to explain this optical bistability: Yb 3+ pair interaction and effects of heating by the laser excitation. The former process, which should involve a large transition displacement, has not been identified. On the other hand, a monitoring of the sample temperature by Yb 3+ infrared emission showed that thermal effects cannot be neglected. However, a simple model of thermal equilibrium is unable to reproduce the hysteresis. This suggests that other processes should be taken into account, like temperature-dependent energy transfer towards traps.

The temperature dependence of energy transfer between the Tm 3F 4 and Ho 5I 7 manifolds of Tm-sensitized Ho luminescence in YAG and YLF

The temperature dependence of the energy transfer process between the Tm 3F 4 and Ho 5I 7 manifolds in Tm : Ho doped laser materials is investigated. Decay data of luminescence in Tm : Ho : YAG and Tm : Ho : YLF in the temperature range 243–323 K are analyzed to extract energy transfer rates and elucidate the theoretical description of the energy distribution between Tm and Ho ions in solid host materials.

Fluorescence heterogeneity of tryptophans in Na,K-ATPase: evidences for temperature-dependent energy transfer

The intrinsic fluorescence emission kinetics of Na,K-ATPase, a large membrane protein containing 16 tryptophan residues, was studied by time-resolved techniques. The lifetime distributions recovered by the Maximum Entropy Method exhibit a strong dependence on the emission wavelength at temperatures between 37°C and −70°C. From the `blue' edge of the fluorescence emission spectrum up to the maximum of emission, the lifetime distribution at room temperature is the result of four broad peaks which cover the time range 0.3–7 ns. With increasing emission wavelength, these peaks move to longer lifetimes and the peak at shorter times are suppressed at the red edge, while the longest component (6–7 ns) becomes dominant. With decreasing temperature, the number of lifetime components is reduced for the benefit of the long one. At cryogenic temperatures, the emission decay in the red-edge of the fluorescence spectrum consists of one major slow component (6–7 ns) and a fast one (0.5 ns) associated with a negative pre-exponential term. This is a characteristic feature of an excited-state reaction. The temperature dependence of this fast component and the fluorescence anisotropy decay at low temperature in the red-edge, indicate that this excited state reaction may be accounted for a unidirectional inter-tryptophan fluorescence energy transfer from `blue' populations of donors to `red' populations of acceptors. This is also illustrated by the time-resolved emission spectra. In the blue edge of the fluorescence emission spectrum, moreover, the time course of the anisotropy decay suggests the existence of homo-transfer of excitation energy involving `blue' tryptophan residues. The steady-state anisotropy excitation spectrum in vitrified solvent agrees with this suggestion. These different energy transfer mechanisms may be used as structural probes to detect more accurately conformational changes of the protein elicited by effectors and ion binding or release.

Temperature and energy gap dependence of energy transfer between rare-earth ions in solids

In this paper we develop a model to explain the temperature dependence of energy transfer between rare-earth ions for situations in which the energy gap is small. When the gap is large, and many phonons are required the transfer rate follows the well-known exponential law. When just a few phonons are required, however, the temperature dependence may be quite different, and may even be more efficient at low temperatures; this is shown to be the case of Er to Ho transfer in YAG. We show that for small energy gaps, the redistribution of the ions with temperature may be a driving factor in the transfer. As the number of phonons increases, this redistribution becomes less important and the exponential law emerges.

Excited State Energy Transfer Pathways in Photosynthetic Reaction Centers. 1. Structural Symmetry Effects

Ultrafast excited state energy transfer to the primary electron donor or special pair in photosynthetic reaction centers has been measured following excitation of the lowest electronic state of the other chromophores. This was achieved by observing the rise time and induced anisotropy in the spontaneous fluorescence from the special pair using fluorescence up-conversion at 85 K. Very fast energy transfer is observed when exciting either of the bacteriochlorophyll monomers. Energy transfer from the bacteriopheophytins, which are considerably further from the special pair than the bacteriochlorophyll monomers, is about 50% slower. The rate, distance, and temperature dependence of energy transfer in both cases are very different from what is predicted by conventional Förster dipole−dipole theory. By working at low temperature and with the reaction center mutant (M)L214H (the beta mutant), which assembles with a bacteriochlorophyll monomer in place of a bacteriopheophytin in the HL binding site (the location of the primary electron acceptor), it is possible to selectively initiate the energy transfer process on the functional and nonfunctional sides of the reaction center. The observed rates of energy transfer to the special pair are found to be similar. Thus energy transfer rates are comparable on the functional and nonfunctional sides, while electron transfer rates differ by at least 2 orders of magnitude. This suggests that the dominant source of functional asymmetry for electron transfer involves differences in the association of the functional-side chromophores with their environment (e.g. free and reorganization energy differences), rather than differences in electronic coupling.

Radiation inactivation of proteins: temperature-dependent inter-protomeric energy transfer in ox liver catalase.

The radiation-inactivation method is widely used to determine the oligomeric structure of enzymes without need for solubilization or purification. We have used purified ox liver catalase, a tetrameric enzyme in solution, to study energy transfer between associated promoters responsible for oligomer inactivation. However, after freeze-drying the tetramer dissociates into an asymmetric dimer. In the present paper we compare both the radiation-inactivation size (obtained by following the activity decay) and the target size (obtained by measuring the amount of remaining protein by SDS/PAGE) of catalase under various states of aggregation and temperature. At -78 degrees C, only one promoter was fragmented after being hit by a gamma-ray and, as expected, this protomer was also inactivated. This result was obtained when either catalase was in tetrameric or in dimeric forms. However, at 38 degrees C, even though a single monomer was fragmented as at -78 degrees C, the whole dimer was inactivated. This result suggests that, at the higher temperature, there is a transfer of energy from the fragmented protomer to the other associated protomer, causing inactivation of the whole dimer. The inactivation of oligomeric enzymes is a two-step mechanism involving: (1) fragmentation of the hit monomer, followed by (2) temperature-dependent energy transfer from the fragmented towards the associated protomer. Thus we conclude that the radiation-inactivation size reflects the transfer of absorbed energy inside the oligomer which causes inactivation of one or several monomers.

Simulations of the temperature dependence of energy transfer in the PSI core antenna

In order to understand the organization of the PSI core antenna and to interpret results obtained from studies of the temperature and wavelength dependence of energy transfer and trapping in the PSI particles, we have constructed a model for PSI in which spectral heterogeneity is considered via a self-consistent approach based on Forster transport. The temperature dependence of the absorption and emission spectra of the individual Chl molecules in the protein matrix is calculated based on a model Hamiltonian which includes a phonon contribution. Time and wavelength resolved kinetics of PSI at different temperatures are investigated by means of two-dimensional lattice models. We conclude that wavelength-dependent fluorescence decay kinetics result only when two or more bottlenecks exist in the energy transfer and trapping process. A single trap or several pseudo-traps with spectrally identical environments do not lead to wavelength dependent decays. Simple funnel arrangements of the spectral types can be ruled out. At least one pigment with energy lower than the photochemical trap located close to the reaction center is required to produce the trends of the fluorescence lifetimes observed experimentally. The remainder of the core antenna is consistent with a random arrangement of spectral types.

Temperature dependence of energy transfer from the long wavelength antenna BChl-896 to the reaction center in Rhodospirillum rubrum, Rhodobacter sphaeroides (w.t. and M21 mutant) from 77 to 177K, studied by picosecond absorption spectroscopy

Decay of the bacteriochlorophyll excited state was measured in membranes of the purple bacteria Rhodospirillum (R.) rubrum, Rhodobacter (Rb.) sphaeroides wild type and Rb. sphaeroides mutant M21 using low intensity picosecond absorption spectroscopy. The excitation and probing pulses were chosen in the far red wing of the long wavelength absorption band, such that predominantly the minor antenna species B896 was excited. The decay of B896 was studied between 77 and 177K under conditions that the traps were active. In all species the B896 excited state decay is almost temperature independent between 100 and 177K, and probably between 100 and 300 K. In this temperature range the decay rates for the various species are very similar and close to 40 ps. Below 100 K this rate remains temperature independent in Rb. sphaeroides w. t. and M21, while in R. rubrum a steep decrease sets in. An analysis of this data with the theory of nuclear tunneling indicates an activation energy for the final transfer step from B896 to the special pair of 70cm(-1) for R. rubrum and 30cm(-1) or less for Rb. sphaeroides.