Electronic Transition Probabilities Research Articles

Electronic states and spectra of BiTe

NIR/VIS emission spectra of the bismuth telluride radical, BiTe, were measured in the 3600–20 000 cm −1 region with a Fourier-transform spectrometer. BiTe was produced by reaction of bismuth and tellurium vapors and excited by energy transfer from metastable oxygen O 2( a 1Δ g) in a fast-flow system. The spectrum of BiTe was found to be markedly different from those of the previously studied BiO, BiS and BiSe radicals. The A 2 4Π 1/2 → X 1 2Π 1/2 transition which forms the most prominent and extended band system in these molecules was not observed for BiTe, and the X 2 2Π 3/2 → X 1 2Π 1/2 fine structure transition shows up with a different structure and at much lower wavenumbers than in the spectra of the lighter bismuth chalcogenides. The only common feature is the C 1 4Σ − 1/2 → X 1 2Π 1/2 system which is found in the range 16 500–19 000 cm −1 similar to the three other molecules. Besides the X 2 → X 1 and C 1 → X 1 systems, seven other transitions show up by short Δ ν = 0 sequences only. With help of the data derived from the analyses of the X 2 → X 1 and C 1 → X 1 systems and theoretical predictions of electronic and vibrational energies and transition probabilities of the strongest transitions of BiTe by Lingott et al. [7] the spectra were assigned to the transitions C 1 4Σ − 1/2 → X 2 2Π 3/2, C 1 4Σ − 1/2 → A 2 4Π 1/2, A 4 4Π 1/2 → A 2 4Π 1/2, A 4 4Π 1/2 → X 2 2Π 3/2, B 1 2Π 1/2 → A 2 4Π 1/2, B 1 2Π 1/2 → A 1 4Π 3/2, and B 2 2Π 3/2 → X 2 2Π 3/2.

Internal friction of duralumin in a DC magnetic field

As a result of an experimental study of the low-frequency (10 Hz) internal friction of D16 duralumin in dc magnetic fields with an induction 0 ≤ B ≤ 0.9 T at a temperature of 20°C, a maximum in the field dependence of the internal friction is detected in a field B ≈ 0.45 T. A numerical analysis of the experimental data is carried out using the Friedel amplitude dependence of the internal friction, which takes into account thermal displacements of dislocations in a crystal with impurities. The Friedel amplitude dependence is modified using the concept of the influence of a magnetic field on the probability of singlet-triplet electron transitions in the dislocation core-paramagnetic center (defect) system. Duralumin is used as an example to show that the modified Friedel dependence provides satisfactory agreement of the calculated data and the experimental data. It is concluded that the sensitivity of the low-frequency internal friction of D16 duralumin to a dc magnetic field measured at 20°C is due to the fact that mobile dislocations overcome impurity atoms of paramagnetic elements, in particular, titanium, because of thermal fluctuations. Internal friction can be used to determine the numerical values of the parameters characterizing the mechanical properties of metallic paramagnets in a dc magnetic field.

First-principles study on electronic structure and optical properties of anatase TiO2 codoped with nitrogen and iron

The crystal structure, electronic structure and optical properties of nitrogen and iron codoped anatase TiO2 were studied by using the plane-wave ultrasoft pesudopotentials method based on density functional theory. The calculated results show that the octahedral dipole moments in nitrogen and iron codoped TiO2 increase due to the changes in lattice parameters, bond length and charge of atoms, which is very effective for the separation of photoexcited electron-hole pairs and the improvement of the photocatalytic activity of TiO2. Some impurity energy levels of codoped TiO2 are below the conduction band minimum, and others are above the valence band maximum. The distance between them is narrowed, which results in the redshift of the optical absorption edges to visible-light region. These impurity energy levels can reduce the recombination rate of photoexcited carriers and improve the photocatalytic efficiency of TiO2. Compared with that of Fe doped TiO2, for the codoped TiO2, the density of states peak of impurity energy levels above the valence band maximum increase apparently, which increases the electronic transition probability from the impurity energy levels to the conduction band, and improves the solar energy utilization. If the impurity level is not taken into account, compared with that of pure TiO2, the CB edge position and the VB edge position of codoped TiO2 is only slightly changed, it means that the strong redox capacity of codoping photocatalysts is still excellent.

Structure and spectroscopy of NaNd(SP)4 chelate: a new type of lanthanide luminophore

Lanthanide β-diketones and their derivatives are extensively studied coordination compounds, due to their luminescent properties and many possible applications. The tetrakisNd(III) complex with phosphorylated sulfonylamides derivatives of β-diketones was synthesized. The X-ray diffraction showed that the compound of formula {[Na[Ln(SP)4]}n (SP = C6H5S(O)2NP(O)(OCH3)2; Ln = Nd(III) crystallize in the monoclinic P21/c space group with the following unit-cell parameters: a = 22.006(4)A, b = 11.075(2)A, c = 22.334(5)A, and β = 118.71(3)°. The molecular structure of the investigated compound is polymeric. The lanthanide ions as well as the sodium ions are coordinated by sulfonyl and phosphoryl groups of the ligand, and because of the bridging behavior, link different units of the polymer. High-resolution absorption, emission, and excitation spectra of neodymium crystals were measured at 298, 77, and 4K temperatures. The sensitized emission of [Na[Nd(III)(L)4]}n chelate in the IR range of the spectrum was recorded. This kind of the compounds can be used in organic light emitting diodes in compact display technology. The spectral characteristic of the compound is controlled by donor–acceptor properties and electron-hole transporting chemical groups. Those factors affect the energy level location, energy transfer (ET), electron–phonon coupling, and finally the luminescence quantum yield. The optical behavior of the title compound was characterised by crystal field (CF), correlation crystal field (CCF), and electron transition probability calculations. X-ray structural data and the nephelauxetic effect check the role of the character of the bonding. The IR spectra were used to analyze the vibronic components in electronic transitions. The role of ligands, singlet and triplet states in energy transfer, are discussed. The ET mechanism and emission quenching pathways are proposed. Some spectroscopic parameters will be compared with earlier reported NaNdWo4 × H2O (Wo = CCl3 CONPO(OCH3)2).

Quantum Transition of Two-Level System in a Parabolic Quantum Dot

The time evolution of the quantum mechanical state of an electron is calculated by using variational method of Pekar type on the condition of electric-LO phonon strong coupling in a parabolic quantum dot. We obtained the eigen energies of the ground state and the first-excited state, the eigen functions of the ground state and the first-excited state this system in a quantum dot may be employed as a two-level quantum system-qubit. The supposition electron is in system’s ground state in the initial time, the electron transit from the ground state to the excited state in presence of an electric field F along the x axis. The results indicate that the electron transition probability and the oscillation period increase with decreasing the electron-LO-phonon coupling constant, increasing the electric field and the confinement length.

Enhanced electronic transition probabilities and line intensities of Er + 3 ion in a (W, La)-tellurite glass as revealed from Judd–Ofelt analysis

A series of tellurite glasses containing dispersed Er 2WO 6 nanocrystals of different concentration was prepared, and the optical properties of the best luminescent sample (1 g mol% of Er 2O 3) were investigated by Judd–Ofelt theory. The intensity parameters Ω 2 ( = 8.410 × 1 0 − 20 cm 2 ) , Ω 4 ( = 4.833 × 1 0 − 20 cm 2 ) , Ω 6 ( = 2.027 × 1 0 − 20 cm 2 ) of the Er +3 ion in the glass were determined and then used to calculate parameters such as the radiative transition probabilities ( A r ), radiative life-times ( τ f ), fluorescence branching ratios ( β c ) and the integrated emission cross-section ( Σ σ ) of different transitions. The experimental optical constant and the calculated oscillator strength values ( P ) suggest that the Er +3 ions in the glass can most effectively be excited by 4 I 15 / 2 → 4 F 7 / 2 (489 nm) and 4 I 15 / 2 → 2 H 11 / 2 (522 nm), 4 I 15 / 2 → 4 F 9 / 2 (653 nm) and 4 I 15 / 2 → 4 I 13 / 2 (1533 nm) transitions while the spontaneous emission rate ( A r ) values show that strong visible emissions should occur respectively through ( 4 F 9 / 2 → 4 I 15 / 2 ) and ( 4 S 3 / 2 → 4 I 15 / 2 ) transitions and strong NIR emissions through ( 4 I 13 / 2 → 4 I 15 / 2 ), ( 4 S 3 / 2 → 4 I 11 / 2 ), ( 4 F 9 / 2 → 4 I 13 / 2 ), ( 4 I 11 / 2 → 4 I 15 / 2 ), ( 4 S 3 / 2 → 4 I 13 / 2 ) transitions. The spectroscopic parameters show that the glass is a superior photonic material compared to other known Er +3 doped glass and crystals.

Stochastic Dynamics of Release Unit in a Cardiac Cell in Electron-Conformational Model

To further understand the role of stochastic dynamics of ryanodine receptor (RyR) channels on spark generating process we studied the stochastic RyR's cluster gating in calcium release unit (RU) in cardiomyocytes under steady-state conditions. We apply a simple biophysically-reasonable electron-conformational (EC) model [Moskvin ea, PBMB, 2006] for the RyR channel. Single RyR channels are characterized by fast electronic and slow classical conformational degrees of freedom. The RyR gating implies calcium induced electronic transitions between two branches of a conformational potential, a conformational Langevin dynamics, thermoactivated transitions and quantum tunneling. The sarcoplasmic (SR) load is incorporated into the model through the effective conformational strain.We examined different model dependencies of the electronic transition probability on the calcium ion concentration and effective temperature in dyadic space to reproduce all the features observed in lipid bilayer experiments. The 11 × 11 RyR cluster was build into a simple RU dynamic unit. Model simulations performed in frames of a diabatic approximation with a conformational inter-RyR coupling have revealed different gating regimes with a single RyR channel openings generating a Ca2+ synapse (quark) and a cooperative cluster mode, due to a step-by-step opening of a fraction of coupled RyR channels. We have found and analyzed the spark generating openings of groups of channels, providing for a sufficient release. The SR overload was shown to lead to the autooscillation regime with nearly periodical openings-closings of RyR-channels.The RU functioning was examined under different rates of SR load and different strength of the inter-RyR coupling. The EC model was shown to provide an adequate description of the cardiomyocite RU dynamics with valid prediction abilities.Supported by RFBR Grants 05-04-48352, 07-04-96126.

Local, global and electronic structure of supported gold nanoclusters determined by EXAFS, XRD and XPS methods

We analyze gold nanoclusters as supported catalysts by extended X-ray absorption fine structure, X-ray diffraction and X-ray photoelectron spectroscopy in order to determine their local, global and electronic structure. The present study points out a strong deformation of the local structure of the metal due to its interaction with oxide supports. We determine the particle size distribution and microstrain functions of the Au nanoclusters by X-ray diffraction method. Based on X-ray absorption fine structure spectroscopy analysis we show that the entire local structure of the investigated systems is strongly distorted regarding the average Au–Au coordination number. The distances between atoms are practically the same as standard Au foil. The strong metal–support interaction is confirmed by the change in shape of the electron transition probability densities that appear in the Au L III-edge. From XPS investigations we find electronic states corresponding to gold as well as to the oxide supports.

Theoretical analysis of cascade levels forming in SrTiO3

The possibility of forming cascading energy levels in SrTiO3 by doping Bi and Cu as an example is analyzed by using the density-functional-theory based first principles calculations of the electronic structure. The results show that both Bi doping and Cu doping can introduce a defect level in the forbidden band，and Co-doping of Bi and Cu can introduce two defect levels in the forbidden band. Electrons at the top of valence band can transit to the bottom of conduction band through a cascade transition process. Using the nonradiative transition model，we point out that the probability of electronic transition from the valence band to the conduction band through a cascade transition is much higher than that of direct transition from the valence band to the conduction band. The cascade transitions can effectively increase the carrier concentration in the conduction band.

Non-Condon vibronic coupling of coherent molecular vibration in MEH-PPV induced by a visible few-cycle pulse laser

Vibrational real-time spectra of poly-[2-methoxy-5-(2′-ethyl-hexyloxy)-p-phenylene vinylene] (MEH-PPV) were measured in a 5 fs pump–probe experiment simultaneously at 128 probe wavelengths with a multichannel detection system. The spectral dependence of the coherent vibrational amplitudes obtained from the Fourier transform (FT) on the probe wavelength detected was found to be given by the sum of the ground-state absorption spectrum and its first and second derivatives. This indicates that the change of the transition probability caused by a wave packet motion can be explained as induced by both the non-Condon effect (non-Condon (NC) mechanism) and the time-dependent Franck–Condon factor (Frank-Condon (FC) mechanism). The FC mechanism can contribute to the first and second derivatives' dependence. On the other hand, the NC mechanism is dominant in the zeroth-order derivative. This result proves that the 11Bu exciton is strongly coupled with the excited 1Ag state, which is known to be essential in third-order optical nonlinearity. The amounts of shift of the absorption peaks and changes in the bandwidth due to the wave packet motions were determined for the four most prominent modes in the FT power spectra. The shift due to the FC mechanism was about 1.3–1.1% of the peak transition energy and the broadening of the vibronic transition due to the NC mechanism was about 8.0–7.6% of the bandwidth for the four modes. A novel ultrafast optical switch utilizing the modulation of electronic transition probability by molecular vibration through vibronic coupling and the interference of the wave packets is proposed.

The changes of macroscopic features and microscopic structures of water under influence of magnetic field

Influences of magnetic field on microscopic structures and macroscopic properties of water are studied by the spectrum techniques of infrared, Raman, visible, ultraviolet lights and X-ray. From these investigations, we know that the magnetic fields change the distribution of molecules and electrons, cause displacements and polarization of molecules and atoms, result in changes of dipole-moment transition and vibrational states of molecules and variation of transition probability of electrons, but does not alter the constitution of molecules and atoms. These are helpful in seeking the mechanism of magnetization of water. Meanwhile, we also measure the changed rules of the surface tension force, soaking effect or angle of contact, viscosity, rheology features, refraction index, dielectric constant and electric conductivity of magnetized water relative to that of pure water. The results show that the magnetic fields increase the soaking degree and hydrophobicity of water to materials, depress its surface-tension force, diminish the viscosity of war, enhance the feature of plastic flowing of water, and increase the refraction index, dielectric constant and electric conductivity of water after magnetization. These changes are caused by the above changes of microscopic structures under the action of magnetic field. Therefore, our studies are significant in science and has practical value of applications.

Approximate method for calculation of electron transition probability for simple outer-sphere electrochemical reactions

The probability of an elementary act in an outer-sphere electrochemical electron transfer reaction is calculated with arbitrary values of the parameter of reactant-electrode electron interaction for diabatic freeenergy surfaces of the parabolic form. The dependence of effective transmission coefficient on the Landau-Zener parameter is found. Interpolation formulas are obtained that describe this dependence and allow calculating the electron transition probability using the results of quantum chemical calculations of the electronic matrix element as a function of distance.

Material metrics for laser cooling of solids

The material metrics for optimal laser cooling of ion-doped solids are derived using atomic and molecular dynamics properties of the constituents. The anti-Stokes process is modeled as an optical phonon coupling of the bound electron, followed by a photon absorption. The transition dipole moment is estimated using a simplified charge-displacement model and the Judd--Ofelt theory of rare-earth ions both suggesting that transitions with high-energy gaps and similar angular momentum states should be used. The electron-phonon coupling is interpreted as a derivative of electronic energy with respect to displacement of the nearest neighboring ligands whose stretching mode frequency is approximated using the molecular data. The Debye-Gaussian model is used for the phonon density of states of diatomic crystal. Then, the Fermi golden rule is used for photon-induced, phonon-assisted electronic transition probability and applied to the cooling rate equation by defining a phonon-assisted transition dipole moment. Based on the material metrics, an example blend is investigated for its cooling performance and a general guide is proposed for selection of better performing laser cooling hosts. Furthermore, the cooling rate limits are discussed and three distinct characteristic times are identified with the photon-induced, phonon-assisted transition time controlling the rate. The metrics guide the selection of host materials for optimal cooling, and predict a noticeable increase in the absorption rate when using a blend of cation atoms.

Luminescence features of nonbridging oxygen hole centres in silica probed by site-selective excitation with tunable laser

Time-resolved photoluminescence at 1.9 eV associated with the nonbridging oxygen hole centre (NBOHC) in silica was investigated under excitation with a ns pulsed laser system, tunable in the visible range. Mapping of the excitation/emission pattern evidences the site-selective excitation of the resonant zero phonon line (ZPL) transition due to its weak coupling with the stretching mode of dangling oxygen. Decay of ZPL follows an exponential law with lifetime of 15.3 μs, which provides a precise measure of the electronic transition probability of a single NBOHC.

Classification of Dynamic Vibronic Couplings in Vibrational Real-Time Spectra of a Thiophene Derivative by Few-Cycle Pulses

Pump-probe spectroscopy was performed with a few cycle pulses of 6.7 fs duration. The electronic transition intensity modulation was induced by molecular vibration in a quinoid thiophene molecule in solution. The real-time vibrational features were analyzed in terms of dependence of vibrational amplitude and phase on probe photon energy. The electronic transition probability is modulated by molecular vibration via vibronic coupling. Changes in the spectral shape and intensity of the time-resolved spectrum were studied by tracking characteristic spectral features including the peak frequency and intensity, spectral bandwidth, and band-integrated intensity. From the analysis the modulation mechanisms were classified into two groups: (1) Condon type and (2) non-Condon type. The features of the wave packet motions were also classified into zeroth-order derivatives due to quasi-pure non-Condon type and first- and second-order derivative types due to the displacement of the potential minimum and the potential curvature change associated with the relevant vibronic transition, respectively.

Space-time contours to treat intense field-dressed molecular states. II. Applications

This second article in the two back-to-back articles presents a numerical application to support and strengthen two theoretical findings extensively discussed in the previous article (article I). In I, we found that introducing the space-time contours enables to distinguish between N, the number of nuclear Schrodinger equations to be solved, and L, the number of field-free states that become populated by the external field (in the ordinary, perturbative approaches this distinction is not apparent). In the numerical study we show, employing the electronic transition probability matrix P(s,t) [which closely is related to the transformation matrix omega(s,t)--see Eqs. (21) and (25) in I], that the N=L case is rare and in most cases we have N<L. Since the perturbative approach can be shown to follow when N=L (see Sec. III C in I) the numerical study implies that in most cases the perturbative approach is not reliable. The second issue that is studied is related to the diabatization process. It is shown, numerically, that the N<L case, in general, does not lead to field-dressed diabatic potentials which are single valued. However, if N is chosen to be identical to the number of field-free states that yield field-free single-valued diabatic potentials in a given spatial region then the corresponding N field-dressed states also yield single-valued (field-dressed) diabatic potentials. This result is independent of L. The numerical study is carried out for an eigenvalue problem based on the Mathieu equation.

Luminescence Enhancement Mechanism of ZnGa2O4 Phosphor Screen with an In2O3 Buffer Layer

The luminescence enhancement mechanism of a white phosphor screen with an buffer layer was studied by growing with optimal sputtering parameters and varying the deposition conditions of . A film with better crystallization and smaller grains was obtained when it was deposited on . These qualities revealed that the resistivity of the phosphor screen was correlated with the surface roughness and resistivity of the buffer layer. The photoluminescence spectra of the phosphor screen revealed that the ligand field of the Ga luminescence center was not modified when the deposition parameters were varied; however, the emission intensities were altered due to the electron-transition probability in the Ga energy levels changing with the crystallization of phosphor. A significantly enhanced emission from the phosphor screen was observed by improving the crystallization, surface morphology, and resistivity of the prepared phosphor film with the buffer layer.

Enhanced Lasing Properties of Dissymmetric Eu(III) Complex with Bidentate Phosphine Ligands

The luminescent and lasing properties of Eu(III) complexes were enhanced by using an dissymmetric Eu(III) complex. The photophysical properties (the emission spectral shapes, the emission lifetimes, the emission quantum yields, and the stimulated emission cross section (SEC)) were found to be dependent on the geometrical structures of Eu(III) complexes. The geometrical structures of Eu(III) complexes were determined by X-ray single crystal analyses. The symmetrical group of Eu(hfa)3(BIPHEPO) (tris(hexafluoroacetylacetonato)europium(III) 1,1'-biphenyl-2,2'-diylbis(diphenylphosphine oxide)) was found to be C1, which was more dissymmetric than Eu(hfa)3(TPPO)2 (tris(hexafluoroacetylacetonato)europium(III) 1,2-phenylenebis(diphenylphosphine oxide): C2 symmetry) and Eu(hfa)3(OPPO)2 (tris(hexafluoroacetylacetonato)europium(III) 1,2-phenylenebis(diphenylphosphine oxide): C2 symmetry). The analytical data were supported by Judd-Ofelt analysis. The most dissymmetrical Eu(III) complex, Eu(hfa)3(BIPHEPO), showed large electron transition probability and large SEC (4.64 x 10(-20) cm2). The SEC of Eu(hfa)3(BIPHEPO) was superior to even the values of Nd-glass laser for practical use (1.6-4.5 x 10(-20) cm2). The lasing properties of Eu(III) complexes in polymer thin film were measured by photopumping of a Nd:YAG laser (355 nm). The threshold energy of lasing oscillation was found to be 0.05 mJ. The increasing rate of the lasing intensity of Eu(hfa)3(BIPHEPO) as a function of the excitation energy was much larger than that of Eu(hfa)3(TPPO)2 and Eu(hfa)3(OPPO)2. The dissymmetrical structure of Eu(hfa)3(BIPHEPO) promoted the enhancement of the lasing property.

Judd-Ofelt analysis of spectroscopic property of Er3+ in congruent and near-stoichiometric Zn∕Er-codoped LiNbO3 crystals

Congruent LiNbO3 crystals doped with 5.5∕1, 6∕0.15, and 7∕0.8mol%∕mol% of Zn∕Er were thermally treated at 1120°C over 101h using vapor transport equilibration (VTE) technique. Unpolarized visible and infrared absorption spectra of the VTE-treated and corresponding as-grown crystals were recorded at room temperature. It is shown that VTE treatment has brought these crystals closer to stoichiometric composition. X-ray powder diffraction and optical absorption results show that the VTE treatment induces the crystalline phase transformation with respect to Er3+ from the original Er3+:LiNbO3 to the ErNbO4 in all crystals studied. The formation of the ErNbO4 phase results in substantial absorption changes that include the drop of the transparency in the visible region, the reduction of Er3+ absorption, and the Zn-doping-level-dependent changes in spectral shape and peaking position at 0.98 and 1.5μm regions. Based upon the measured absorption spectra, the influences of Zn-doping level and VTE treatment on the Er3+ spectroscopic properties were studied by using the Judd-Ofelt (JO) theory. The results show that the VTE treatment has a little effect on the fluorescence branch ratio, while a large effect on the JO parameters, oscillator strength, and electron transition probability. The Zn doping level affects the JO parameters, oscillator strength, and transition probabilities of some individual manifolds. In addition, the VTE treatment leads to the increases of the theoretical radiative lifetimes of almost all manifolds considered. For the emission at 1.5μm, the lifetime increase is as much as 30% and the theoretical results are in well agreement with the experimental data. The VTE-induced lifetime increase is qualitatively explained.

High pressure fluorescence studies of Sm3+-doped K–Ba–Al phosphate glass

Pressure-induced fluorescence spectra and decay curves for the 4G5/2 level of Sm3+ ions in P2O5+K 2O+BaO+Al 2O 3 glass have been studied up to 24.4 GPa at room temperature. The study reveals that 4G5/2→6H J (J=9/2, 7/2 and 5/2) emission band positions are shifted to lower energy (red shift) in the order of 2.4, 2.6 and 2.7 cm−1 per GPa, respectively. The increase in Stark level splittings has also been noticed with increasing pressure for the emission bands mentioned above. The decay profiles show increased non-exponential behaviour at higher pressures accompanied by a shortening of lifetimes. The non-exponential decay curves were fitted to the Inokuti–Hirayama model. The decrease in the lifetime with an increase in pressure is caused by an increase in the electronic transition probabilities. This is a result of the increased crystal-field strength around Sm3+ ions. The original results obtained after the release of pressure confirm that no structural hysteresis takes place around the Sm3+ ions.