Electronic Transition Probabilities Research Articles

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.

Stochastic simulations of electrochemical electron transfer reactions

The rate of electron transfer reaction has been investigated by stochastic molecular dynamics. The electronic transition probability was calculated from the Landau–Zener formula, and the coupling strength was varied over a wide region, covering both the adiabatic and the non-adiabatic regime. For low coupling, the results of first order perturbation theory are recovered, for high coupling Kramers theory is valid, and the simulations bridge these two regions.

Fast electronic relaxation in metal nanoclusters via excitation of coherent shape deformations

Electron-phonon relaxation in size-quantized systems may become inhibited when the spacing of discrete electron energy levels exceeds the magnitude of the phonon frequency. We show, however, that nanoclusters can support a fast nonradiative relaxation channel which derives from their distinctive ability to undergo Jahn-Teller shape deformations. Such a deformation represents a collective and coherent vibrational excitation and enables electronic transitions to occur without a multiphonon bottleneck. We analyze this mechanism for a metal cluster within the analytical framework of a three-dimensional potential well undergoing a spheroidal distortion. An expression for the time evolution of the distortion parameter is derived, the electronic level crossing condition formulated, and the probability of electronic transition at a level crossing is evaluated. An application to electron-hole recombination in a closed-shell aluminum cluster with 40 electrons shows that the short $(\ensuremath{\sim}250\phantom{\rule{0.3em}{0ex}}\mathrm{fs})$ excitation lifetime observed in recent pump-probe experiments can be explained by the proposed mechanism.

Damping of multiphoton Rabi oscillations and multiphoton Purcell effect

Damping of multiphoton Rabi oscillations due to a finite lifetime of photons is investigated using an algebraic method of the solution of the master equation. The time dependence of the probability of electron transitions between atomic levels is evaluated. In a regime of weak atom–photon coupling (a coupling constant smaller than the photon decay rate), the spontaneous emission of many photons from a single electron transition due to the interaction with a resonant light is found. Thus, a multiphoton counterpart of the Purcell effect is predicted.

Cathodoluminescence of a White ZnGa2O4 ∕ ZnO Phosphor Screen

This paper investigates the cathodoluminescence of a white ∕ITO∕glass phosphor screen. The effect of a ZnO buffer layer and annealing temperature on the luminescence property of a phosphor screen are discussed as well. The films were prepared by the radio frequency magnetron sputtering with optimal deposition parameters. The preferred growth plane for the ZnO buffer layer was found to be (002). The phosphor layer, when deposited on top of ZnO, was amorphous even when it was annealed at . However, when the annealing temperature was above , the was polycrystalline, and an apparent cathodoluminescence of the phosphor screen was observed. The ligand field and electron transition probability in the Ga d orbit were altered because of the lattice mismatch between the and ZnO films and the thermal treatment. The lowest resistivity and optimal luminescence of a white ∕ITO∕glass phosphor screen was obtained by annealing at .

Influence of vapor transport equilibration on spectroscopic properties of Er:LiNbO3 crystal heavily codoped with MgO

Z -cut MgO heavily codoped (6mol%) Er(0.4mol%):LiNbO3 crystals were thermally treated at 1110 and 1120°C over 100, 120, and 220h using vapor transport equilibration (VTE) technique. Visible and infrared-absorption and x-ray powder diffraction have been used to characterize their spectral, spectroscopic, and crystalline phase characteristics in comparison with the as-grown crystal. The experimental results show that VTE treatment results in the reduction of background absorption and 4–5-nm blueshift of the optical-absorption edge, qualitatively showing that these crystals have been brought closer to stoichiometric composition. The VTE procedure also results in remarkable Er3+ absorption changes. These spectroscopic changes imply that the VTE treatment may result in the formation of ErNbO4 precipitates in all VTE crystals. In addition, the VTE treatment also results in substantial spectral changes with respect to OH− absorption. These OH− spectral changes are explained from the viewpoint of VTE-induced site-occupancy alterations of intrinsic and extrinsic defects. Based upon the measured absorption spectra, the influences of VTE treatment on the Er3+ spectroscopic parameters were studied by using the Judd–Ofelt (JO) theory. The theoretical results show that VTE treatment has a little influence on the branch ratio, and a substantial influence on JO parameters and electron transition probability because of the phase transformation with respect to Er3+. The VTE treatment results in the increase of the JO parameters by more than 50% and theoretical radiative lifetime by 50%–120%.

High-pressure fluorescence study of Sm3+-doped borate and fluoroborate glasses

Fluorescence spectra and decay properties of the G5∕24 level of the Sm3+ ions have been measured in two glass systems of lithium borate and lithium fluoroborate glasses as a function of pressure up to 27.2 and 25.9 GPa, respectively, at room temperature. With an increase in pressure continuous redshifts of the G5∕24→HJ6 (J=9∕2,7∕2, and 5∕2) multiplet transitions as well as progressive increases in the magnitude of the splittings for these transitions are observed. Decay curves in both the systems exhibit perfect single exponential behavior at ambient pressure and become nonexponential at higher pressures accompanied by a moderate decrease in lifetimes. The nonexponential decay curves fit well to the Inokuti–Hirayama [M. Inokuti and F. Hirayama, J. Chem. Phys. 43, 1978 (1965)] model for S=6, indicating that the interaction for cross relaxation is of dipole-dipole type. The decrease in lifetime of the G5∕24 level in both the systems with pressure is explained as resulting from the increase in the crystal-field strength felt by the Sm3+ ions due to volume reduction accompanied by a simultaneous increase in the electronic transition probabilities.

Light-induced absorption and its relaxation under illumination of continuous wave ultraviolet light in Mn-doped near-stoichiometric LiNbO3

The steady-state light-induced absorption and the temporal relaxation behavior under illumination of cw ultraviolet light in Mn-doped near-stoichiometric LiNbO3 with different crystal compositions are investigated. The ultraviolet-light-induced absorption has been assigned to small polarons NbLi4+ by measuring the absorption spectra at room temperature. The dependences of relaxation behaviors (time constant and stretching factor) of light-induced absorption on various illumination conditions (intensity, polarization) and temperature are presented, which are very different from those observed in Fe-doped LiNbO3 illuminated with highly intense light pulse, though the temporal relaxation follows the same stretched-exponential decay behavior in both cases. The results are explained reasonably by using the model of distance-dependent electron transition probabilities between localized deep traps and small polarons without any additional assumptions, and discussed to tailor doped near-stoichiometric LiNbO3 crystals for two-color holographic recording with cw laser light.

Laser-induced resonant electron transitions in a structure with three quantum dots

The effect of a resonance laser pulse on the quantum dynamics of electrons in a system of three semiconductor boxlike quantum dots is theoretically analyzed. It is shown that, in an asymmetric structure, the electron transfer between the two outer dots can be described in terms of a two-level scheme with diagonal transitions. The energies of the operating electron levels and the matrix elements for the corresponding electron transitions are found in the high-barrier approximation. The parameters of the laser pulse corresponding to the highest probability of resonance electron transitions between the ground states of two quantum dots are determined.

Electric Field Effects on Photoconductivity and Electronic Absorption Spectra of Photogeneration Sites in Amorphous Molecular Semiconductors

Field dependences of photogeneration quantum yields of charge carriers in films of amorphous molecular semiconductors at high external electric field strengths cannot be always explained in terms of the Onsager or the Poole–Frenkel model, which do not consider the effect of an electric field on basic parameters of these materials. It is assumed that an external electric field shifts the electron density in molecules from its equilibrium distribution, thus altering the probability of electronic transitions. The assumption has been verified in studying the effect of an external electric field on the absorption spectra of poly(N-epoxypropylcarbazole) films doped with a merocyanine dye. Correlation between the theoretical and experimental results has been obtained.

Electron transfer between semiconductor quantum dots via laser-induced resonance transitions

The effect of a resonant laser pulse on the quantum dynamics of an electron in a system of two semiconductor quantum dots (QDs) is studied theoretically. The pulse characteristics (frequency, amplitude, and duration) corresponding to the highest probability of electron transition from the ground state of one QD to the ground state of the other QD are determined with regard to possible difference in the QD sizes. A specific model with QDs of near cubic shape is considered.

Collisional transport of electrons in disturbed magnetic field

A path integral method is applied to a statistical analysis of electron transport described as a Langevin equation in a disturbed magnetic field line structure; in particular, the transition probability of electrons strongly tied to field lines is considered. When the effect of the Coulomb collisions is interpreted as the Gaussian white noise in configuration space, the radial transport of electrons in the chaotic field line structure is different from Brownian diffusion with the diffusion coefficient of field lines, even if a sufficiently small diffusion coefficient of the collisions is considered.

Spectroscopic studies on chromotropic mixed-ligand copper(II) complexes containing o-hydroxy benzoyl derivatives and dinitrogen bases

Synthesis of chromotropic copper(II) mixed ligand complexes of o-hydroxy benzoyl derivatives (L 1) and dinitrogen bases (L 2), general formula Cu n (L 1)(L 2) n X n ; where n=1 or 2, L 1=4,6-diacetyl-resorcinol (H 2DACR), o-hydroxy benzaldhyde (HOHBZ) or o-hydroxy acetophenone (HOHAP), L 2= N, N, N′, N′-tetramethylethylenediamine (Me 4en), 1,10-phenanthroline (phen) or bipyridine (bipy) and X=ClO 4 −, NO 3 − or Br − have been reported. Spectral, magnetic and molar conductance measurements as well as analytical data of these complexes show either mononuclear structure for OHBZ and OHAP or binuclear structure for DACR complexes. The IR stretching vibration frequencies of CuN and CuO are linearly correlated with the d–d absorption frequencies. The d–d absorption bands of Me 4en-complexes in weak donor solvents suggest square-planar, distorted octahedral and distorted trigonal bipyramid geometries for the perchlorate, nitrate and bromide complexes, respectively. However, an octahedral structure is identified for the complexes in strong donor solvents. Perchlorate complexes show a remarkable color change from violet to green as the donor ability of the axial ligand increases, whereas bromide complexes are mainly affected by the Lewis acidity of the axial ligand. Specific and non-specific interactions of solvent molecules with the complexes are investigated using the unified solvation model. Calculations of the electronic transition probability ( f) of the d–d band along with molecular orbital calculations of ligands have been carried out and correlated with the experimental data.

Spectroscopy of forbidden transitions in ions of astrophysical interest

The spectroscopic study of forbidden transitions in ions of astrophysical interest has been performed using an extension of the well-established relativistic quantum defect orbital (RQDO) method. The method has so far proved to be a very useful tool for predicting a large body of electron transition probabilities, and other related properties. The RQDO method has been applied to the study of E2 transitions in the spectra of ions relevant in astrophysics, such as Ti XII, Fe XVI, Co XVII and Ni XVIII.

Path integral approach for electron transport in disturbed magnetic field lines

A path integral method is developed to investigate statistical property of an electron transport described as a Langevin equation in a statically disturbed magnetic field line structure; especially a transition probability of electrons strongly tied to field lines is considered. The path integral method has advantages that (1) it does not include intrinsically a growing numerical error of an orbit, which is caused by evolution of the Langevin equation under a finite calculation accuracy in a chaotic field line structure, and (2) it gives a method of understanding the qualitative content of the Langevin equation and assists to expect statistical property of the transport. Monte Carlo calculations of the electron distributions under both effects of chaotic field lines and collisions are demonstrated to comprehend the above advantages through some examples. The mathematical techniques are useful to study statistical properties of various phenomena described as Langevin equations in general. By using parallel generators of random numbers, the Monte Carlo scheme to calculate a transition probability can be suitable for a parallel computation.

Tunneling magnetoresistance of phase-separated manganites

A simple model of phase separation is used to study the magnetoresistance of manganites in the nonmetallic state. It is assumed that the phase separation corresponds to the emergence of small ferromagnetic metallic droplets (ferrons) in a nonconducting antiferromagnetic or paramagnetic medium, with the metallic phase concentration being far from the percolation threshold. The charge transfer is accomplished by way of electron jumps between droplets. The magnetoresistance in such a system is defined both by the variation of the volume of the metal phase and by the dependence of the probabilities of electron transitions on the magnitude of the magnetic field. It is demonstrated that, in the region of low magnetic fields, the magnetoresistance is quadratic with respect to the field and decreases with temperature by the T −n law, where n takes values from 1 to 5 depending on the correlation between the parameters. In the high-field limit, the magnetoresistance increases abruptly with the volume of the metal phase. The crossover of the field dependence from quadratic to a stronger one may be accompanied by the emergence of a platean in the magnetoresistance. The correlation between the obtained results and the available experimental data is discussed.

Intensities of Vibronic Transitions for the Main Bands Observed in the Electronic Spectrum of Atmospherically Relevant Nitric Oxide

Absorption oscillator strengths for the γ(A2Σ+−X2Π), δ(C2Π−X2Π), and ε(D2Σ+−X2Π) bands of NO, which are relevant to the study of atmospheric processes are reported. We have calculated both electronic and vibronic transition probabilities with the molecular-adapted quantum defect orbital (MQDO) method, which has proved, in previous applications, to be an adequate theoretical tool in the context of Rydberg spectra. The results appear to be in good accord with the available experimental values and, with some exceptions, conform fairly well with theoretical data derived from rather more sophisticated methods.

Coherent and incoherent photon-assisted electron tunneling in optoelectronic molecular devices in soft solids

An electron in a bath with slow degrees of freedom (such as soft solids, e.g., proteins) is driven by a strong time-dependent electric field. In this molecular device, the electron dynamics are characterized by quasicoherent oscillations with slow square-root decay even at room temperatures. The frequency of the oscillations and the equilibrium distribution are found essentially to depend on the field intensity and the medium parameters. The applied field effectively changes the relaxation time of the environment from fast to slow and vice versa. The quasicoherence allows for the prevention of overheating in the microdevice. It is also shown that the applied field is capable of changing the character of the electron dynamics from quasicoherence to incoherent decay. The electron transition probability strongly depends upon the applied voltage (bias) and at some values of the field parameters, this voltage can quickly switch the coherent transfer over to incoherent transfer and vice versa. Despite the slow electron transfer in the incoherence region, the equilibrium distribution can favor either products or reactants, depending upon the field intensity. In the incoherent regime, the electron localization is possible. All these features can be exploited in microcomputers or quantum computers.

Calculation of the probability of nonradiative electronic transitions from deep centers in GaAs in the one-coordinate approximation

A study was made of the experimental optical bands of radiative VGaSAs and VGaSnGa complexes in GaAs in a wide temperature range. Parameters of the one-coordinate model of the centers were determined. The configuration-coordinate diagram of the VGaSAs complex was constructed. Using parameters of the one-coordinate model of the VGaSAs complex as the base, the field dependences of emission rates were calculated. The calculation results were compared with the experimental data. A conclusion was made that the one-coordinate model can be used for the description of the field dependence of the rate of hole emission from the VGaSAs center.

Two-dimensional Penning ionization electron spectroscopy of CO/He*(23S)

Two-dimensional Penning ionization electron spectrum (2D-PIES) of CO by collision with He*(23S) was observed. Collision energy dependence of partial ionization cross-sections was reproduced theoretically by trajectory calculation with anisotropic potential energy surface. In order to obtain the potential energy surfaces for exit channel, ionic ground and excited states were calculated for CO+–He. By adding up the electron transition probabilities for the specific electron energy calculated by the difference between potential energies for the entrance and the exit channels at each trajectory step, the collision-energy-resolved Penning ionization electron spectrum (CERPIES) was obtained. The CERPIESs at various collision energies were then converted into calculated 2D-PIES.