Measured Lifetime Data Research Articles

Dynamic and magnetic properties of excited magnons in tetragonal fcc [formula omitted]/SiO multilayer alloys

In this paper, we investigate by numerical lattice simulations the magnetic and dynamic properties of excited magnons in d transition metal alloys FexPt1−x/SiO using Green functions and second quantification techniques. The sandwich structure consists of magnetic (FePt) and non-magnetic (SiO) layers. The corresponding quantum Heisenberg Hamiltonian includes exchange interactions, magnetocrystalline anisotropy, surface anisotropy and magnetic field. The existence of the surface magnons is demonstrated by the surface creation factor η, which is in good agreement with the measured lifetime data. Surface magnons are characterized by their excitation spectrum, susceptibility of creation, creation gap, permitted band for creation, and lifetime, which are different from volume magnons properties. The susceptibility of creation analysis is compatible with experimental values, and the calculated lifetimes are in the order of femtoseconds (fs) reproducing the analytical behavior of the measured values along the lattice symmetry axis. The surface magnons are found to be more confined in time and space than those excited in volume, indicating the presence of short-range spin correlations. Magnetization per spin versus temperature is also calculated for different iron concentrations x and found to be in excellent agreement with the measured values. Also, the response of the system to an external magnetic field is shown for xFe=0.29 with various temperature values, and it agrees well with the experience.

Incomplete activation and ionization of dopants in Si at room temperature

A new model for incomplete ionization of dopants in Si is presented, where the Fermi level of free carriers may displace with respect to the case of full activation of dopants. The curves of the ratio of free-carrier density and active-dopants density vs doping, which are calculated at partial activation of dopants with the new model, overlap exactly with the curves of the same quantity calculated at full activation of dopants with a reported model. Calculations are performed with and without reported parameterizations of the density of states and occupancy probability of the dopant band simulating incomplete ionization around the Mott concentration. With parameterizations, comparisons with Hall-mobility data show that the curves of free-carrier density calculated at partial dopant activation with the new model are more accurate than the curves of the same quantity calculated at full dopant activation with the reported model. Without parameterizations, the new model allows calculating for the same carrier species curves of majority-carrier mobility that fit measured data of minority-carrier mobility at high dopings and agree with the Klaassen mobility model for minority carriers. The consistency with the band theory of the new and reported models is discussed, and the new model is found to be the most appropriate in this respect. The free-carrier density calculated with the new model without parameterizations overlaps at high dopings with free-carrier density calculated with reported models for band-gap narrowing and allows calculating curves of Auger lifetime of majority carriers that fit measured lifetime data of minority carriers.

Experimental and Theoretical Radiative Parameters of Highly Excited Odd-parity Levels in Ir ii

Using the time-resolved laser-induced fluorescence technique, the radiative lifetimes for 15 odd-parity levels from 47,003 to 61,475 cm−1 in Ir ii were measured. To the best of our knowledge, 11 lifetime results among these levels are reported for the first time, and hence they should be a good complement to the measured lifetime data of 10 levels previously published in the literature. The pseudorelativistic Hartree–Fock including core-polarization corrections method was used to calculate the lifetimes and branching fractions (BFs) of the investigated energy levels. Combining the experimental lifetime with the theoretical BFs, the transition probabilities and oscillator strengths for 124 transitions were determined.

Triscyclometalated Iridium(III) Fluoro‐Substituted Carbene Complexes: Character of Emitting Triplet States and Excited State Dynamics

AbstractWe report the spectra of UV‐vis absorption, emission and excitation for fluoro‐substituted triscarbene iridium complexes fac‐tris(1‐(4‐fluorophenyl)‐3‐methylimidazolin‐2‐ylidene‐C,C2′) iridium(III), fac‐Ir(fpmi)3, and fac‐tris(1‐(2,4‐fluorophenyl)‐3‐methyl imidazolin‐2‐ylidene‐C,C2′ ) iridium(III), fac‐Ir(dfpmi)3. The decay of emission and transient absorption curves at 266‐nm excitation in the singlet metal‐to‐ligand charge‐transfer (MLCT) band region are recorded. Using quantum chemical calculations‐density functional theory (DFT) and time‐dependent DFT (TD‐DFT) method B3LYP, we obtained their optimized geometries, electronic structures, energies of vertical transitions and oscillator strengths. Both complexes emit in deep blue/near UV which has the highest emission energy for iridium complexes. These emission bands display vibronic structure and a small rigidochromic shift in the low‐temperature. From the measured lifetime data and the emission quantum yield, we obtain a radiative rate constant kr 2.2‐2.4 × 104 s−1 for the emitting state and assign the emitting state to 3π‐π* for these complexes. In subpicosecond transient absorption, we observed an ultrafast rise implying that crossing rate from 1MLCT to this ligand‐centered T1/T2 3π‐π* state is faster than our temporal resolution (300 fs)−1. Two components appear with time constants 0.7‐1.5 ps and 15‐47 ps and are assigned to vibrational cooling/solvation and geometry relaxation, respectively.

Fluorescence Lifetime Readouts of Troponin-C-Based Calcium FRET Sensors: A Quantitative Comparison of CFP and mTFP1 as Donor Fluorophores

We have compared the performance of two Troponin-C-based calcium FRET sensors using fluorescence lifetime read-outs. The first sensor, TN-L15, consists of a Troponin-C fragment inserted between CFP and Citrine while the second sensor, called mTFP-TnC-Cit, was realized by replacing CFP in TN-L15 with monomeric Teal Fluorescent Protein (mTFP1). Using cytosol preparations of transiently transfected mammalian cells, we have measured the fluorescence decay profiles of these sensors at controlled concentrations of calcium using time-correlated single photon counting. These data were fitted to discrete exponential decay models using global analysis to determine the FRET efficiency, fraction of donor molecules undergoing FRET and calcium affinity of these sensors. We have also studied the decay profiles of the donor fluorescent proteins alone and determined the sensitivity of the donor lifetime to temperature and emission wavelength. Live-cell fluorescence lifetime imaging (FLIM) of HEK293T cells expressing each of these sensors was also undertaken. We confirmed that donor fluorescence of mTFP-TnC-Cit fits well to a two-component decay model, while the TN-L15 lifetime data was best fitted to a constrained four-component model, which was supported by phasor analysis of the measured lifetime data. If the constrained global fitting is employed, the TN-L15 sensor can provide a larger dynamic range of lifetime readout than the mTFP-TnC-Cit sensor but the CFP donor is significantly more sensitive to changes in temperature and emission wavelength compared to mTFP and, while the mTFP-TnC-Cit solution phase data broadly agreed with measurements in live cells, this was not the case for the TN-L15 sensor. Our titration experiment also indicates that a similar precision in determination of calcium concentration can be achieved with both FRET biosensors when fitting a single exponential donor fluorescence decay model to the fluorescence decay profiles. We therefore suggest that mTFP-based probes are more suitable for FLIM experiments than CFP-based probes.

Improved Parameterization of Auger Recombination in Silicon

Accurate modeling of the intrinsic recombination in silicon is important for device simulation as well as for interpreting measured effective carrier lifetime data. In this contribution we study the injection-dependent effective carrier lifetime applying advanced surface passivation techniques based on Al2O3 or SiNx We show that in some cases the measured lifetime data significantly exceeds the previously accepted intrinsic lifetime limit proposed by Kerr and Cuevas [1]. To verify our measurements we independently perform lifetime measurements with different measurement techniques in two different laboratories. Based on effective lifetime measurements we develop an advanced parameterization of the intrinsic lifetime in crystalline silicon at 300K as a function of the doping density and the injection level, which accounts for Coulomb-enhanced Auger recombination and Coulomb-enhanced radiative recombination.

Fundamental boron–oxygen‐related carrier lifetime limit in mono‐ and multicrystalline silicon

AbstractBoron‐doped crystalline silicon is the most relevant material in today's solar cell production. Following the trend towards higher efficiencies, silicon substrate materials with high carrier lifetimes are becoming more and more important. In silicon with sufficiently low metal impurity concentrations, the carrier lifetime is ultimately limited by a metastable boron–oxygen‐related defect, which forms under minority‐carrier injection. We have analysed 49 different Czochralski‐grown silicon materials of numerous suppliers with various boron and oxygen concentrations. On the basis of our measured lifetime data, we have derived a universal empirical parameterisation predicting the stable carrier lifetime from the boron and oxygen content in the crystalline silicon material. For multicrystalline silicon it is shown that the predicted carrier lifetime can be regarded as a fundamental upper limit. Copyright © 2005 John Wiley & Sons, Ltd.

Energy transfer luminescence in (Eu 3+,Nd 3+) : tellurite glass

Here, we bring out an infrared transmitting new optical glass based on TeO 2 added with AlF 3 and LiF, containing dual rare earth ions (Eu 3+,Nd 3+) as the dopants with a purpose to examine their luminescence and also the decay times pertaining to a prominent transition of Eu 3+ ( 5D 0 → 7F 2 at 615 nm) as a function of temperature both in the presence and absence of Nd 3+ ions. The energy transfer rates ( W tr), critical distances ( R 0) and transfer efficiencies (η tr) have been evaluated based on the measured lifetime data of this glass.

Predictive systematization of line strengths for the resonance and intercombination transitions in the Be isoelectronic sequence

Measured lifetime data for the - resonance and intercombination lines in the Be isoelectronic sequence are critically evaluated, and jointly systematized using effective singlet - triplet-reduced line strengths . The data are examined together with recent theoretical predictions in the linearizing exposition and the high-Z trend is compared with the corresponding hydrogenic limit. Smoothed and interpolated predictions are presented for .

Doping of (211)B mercury cadmium telluride

We report on the electrical and electro-optical properties of n- and p-type (211)B mercury cadmium telluride grown by molecular beam epitaxy for Cd composition ∼ 0.22. Grown layers show excellent structural qualities with DCRC FWHM of 25–40 arcsec. However, in the unintentionally doped layers a complex picture of transport characteristics were observed. Indium doped layers grown on Nippon Mining substrates show excellent Hall characteristics and minority carrier lifetimes down to 1 × 1015cm−3 doping levels. But, when the net doping level falls below ∼ 2 × 1015cm−3, the measured lifetime data indicates Shockly-Read (SR) recombination centers. We believe that these SR levels are related to Hg vacancies. Also, arsenic is being investigated as a p-type dopant through a new approach called “planar doping” for MBE-HgCdTe. The obtained results are very promising. During the growth process using this method, the incorporated arsenic can be electrically activated at a temperature not exceeding 250°C.

Analysis of low doping limitation in molecular beam epitaxially grown HgCdTe(211)B epitaxial layers

We report the results of the transport properties and the recombination mechanisms of indium-doped HgCdTe(211)B (x ≈ 23.0% ± 2.0%) layers grown by molecular beam epitaxy. We have investigated the origin(s) of the background doping limitation in these layers. Molecular beam epitaxially grown layers exhibit excellent Hall characteristics down to indium levels of 2 x 1015 cm−3. Electron mobilities ranging from (2-3) x 105 cm2/v-s at 23K were obtained. Measured lifetime data fits very well with the intrinsic band-to-band recombinations. However, below 2 x 1015 cm−3 doping levels, mobility vs temperature curves starts to reflect nonuniformity in carrier distribution. Also, when we reduced the Hg vacancy concentration down to 1012 cm−3 range, by annealing at 150°C, Hall characteristics shows an increase in the nonuniformity in the epilayers. It was found that after annealed at 150°C, the obtained SR defect level has a different origin than the previously obtain Hg-vacancy related defect level.

Investigation of defect structures in deformed and helium-irradiated refractory metals by positron annihilation

The defect structures in deformed and helium-irradiated refractory metals, vanadium, niobium and tantalum have been investigated by means of positron lifetime and Doppler broadening techniques. The evolution of the defects was studied by performing isochronal annealing programmes. In all three metals after deformation a single, well defined lifetime was observed which was 30 ps to 40 ps lower than that reported for vacancies. The recovery of the deformation-induced defects however, is remarkably different for niobium and tantalum as compared to vanadium. In helium-irradiated vanadium and niobium two distinctly different defect types were observed with characteristic lifetimes of about 190 ps and 375 ps, respectively. The longer lifetime is attributed to large helium bubbles. Both metals showed a similar behaviour in the annealing studies. All measured lifetime data are consistent with the simple trapping model. The influence of oxygen impurities and oxygen resorption during the isochronal annealing procedure is discussed.

Luminescence Linewidth Broadening and Nonradiative Energy Transfer Studies of Solid UO2+2-Datura

The emission spectra and fluorescence decay curves of solid UO2+2- Datura at liquid nitrogen temperature have been measured. The linewidth of the emission peaks of UO2+2 ions in UO2+2- Datura decreases with the UO2+2 concentration. This linewidth broadening phenomenon can be explained by the existence of resonance interactions between adjacent UO2+2- Datura species. The analysis of the emission peak position of the bound ions has been used to provide a measure of the electronic factors contributing to the interaction between the uranyl ion and phosphoryl and dicarboxyl moieties on the cell wall material. An observed blue shift of the uranyl fluorescence spectrum as a function of solution pH has been ascribed to a distortion of the normally linear O-U-O bond. An inter- and intra-molecular nonradiative energy transfer model has been successfully used to interpret the measured lifetime data of UO2+2- Datura.

Dynamic interaction between functional groups in the active site of glycogen phosphorylase b

The quenching of coenzyme fluorescence in glycogen phosphorylase b is reinvestigated. Data with anionic quenchers show deviations from the original Stern-Volmer kinetics. A kinetic analysis based on measured lifetime data indicates a collisional quenching process, which is, however, not diffusion-controlled. It is proposed, that the quenching takes place primarily by enzyme-bound quencher species. The observed inhibition of the enzyme reaction by I- and IO-3 is consistent with this hypothesis. The inhibition pattern and spectral investigation refer to a true competition with the substrate, glucose-1-phosphate. So, this dynamic quenching can be regarded as an indicator of rapid conformational fluctuations which bring the two important active-site groups in contact. Effect of ligand binding on the quenching of coenzyme fluorescence should also be revaluated according to these results.