Close Energy Levels Research Articles

Rationally investigating the influence of T1 location on electroluminescence performance of aryl amine modified phosphine oxide materials.

The correspondence between triplet location effect and host-localized triplet-triplet annihilation and triplet-polaron quenching effects was performed on the basis of a series of naphthyldiphenylamine (DPNA)-modified phosphine oxide hosts. The number and ratio of DPNA and diphenylphosphine oxide was adjusted to afford symmetrical and unsymmetrical molecular structures and different electronic environments. As designed, the first triplet (T1 ) states were successfully localized on the specific DPNA chromophores. Owing to the meso- and multi-insulating linkages, identical optical properties and comparable electrical performance was observed, including the same first singlet (S1 ) and T1 energy levels to support the similar singlet and triplet energy transfer and the close frontier molecular orbital energy levels. This established the basis of rational investigation on T1 location effect without interference from other optoelectronic factors.

Strongly enhanced atomic parity violation due to close levels of opposite parity

We present calculations of nuclear-spin-dependent and nuclear-spin-independent parity violating amplitudes in Ba, Ra, Ac+, Th and Pa. Parity nonconservation in these systems is greatly enhanced due to the presence of very close electronic energy levels of opposite parity, large nuclear charge, and strong nuclear enhancement of parity-violating effects. The presented amplitudes constitute several of the largest atomic parity-violating signals predicted so far. Experiments using these systems may be performed to determine values for the nuclear anapole moment, a P-odd T-even nuclear moment given rise to by parity-violating nuclear forces. Such measurements may prove to be valuable tools in the study of parity violation in the hadron sector. The considered spin-independent transitions could also be used to measure the ratio of weak charges for different isotopes of the same atom, the results of which would serve as a test of the standard model and also of neutron distributions. Barium, with seven stable isotopes, is particularly promising in this regard.

Regular assembly of 9-fluorenone-2,7-dicarboxylate within layered double hydroxide and its solid-state photoluminescence: a combined experiment and computational study

The assembly of an organic dye molecule incorporated into inorganic host matrices has received considerable attention for developing new types of organic–inorganic hybrid photofunctional materials. In this work, we report 9-fluorenone-2,7-dicarboxylate (FDC) assembled into Mg-Al- and Zn-Al-layered double hydroxide (LDH) systems and their solid-state photophysical properties. The detailed structure and chemical compositions of the obtained composites were characterized by X-ray diffraction, elemental analysis, thermogravimetry and differential thermal analysis (TG-DTA), infrared spectra (IR) and 13C nuclear magnetic resonance (NMR), which show that the positively-charged LDH layer can delocalize the electronic density of the anionic FDC to some extent. Moreover, FDC/LDH systems exhibit a blue-shift photoemission and enhanced fluorescence lifetime compared with those of the pristine FDC sample, and the FDC/LDH thin films exhibit well-defined polarized luminescence with the fluorescence anisotropy of 0.15–0.25. In addition, a periodic density functional theoretical (DFT) calculation was employed to calculate the geometric and electronic structures of the FDC/LDH systems. It was found that the FDC/LDH can be regarded as energy transfer systems from the interlayer organic chromophore to the inorganic host layer due to close energy levels between two components. Therefore, based on the combination of experimental and theoretical studies on the chromophore assembled LDH systems, this work not only gives a detailed investigation on the relationship between the layered host–guest structures and photoluminescence properties, but also provides a new insight into the energy-transfer performance of guest dye molecules confined between the 2D inorganic host matrix.

Modulation cancellation method for isotope ^18O/^16O ratio measurements in water

The application of an innovative spectroscopic balancing technique to measure the isotope 18O/16O ratio in water vapor is reported. Quartz enhanced photoacoustic spectroscopy has been employed as the absorption sensing technique. Two isotope absorption lines with the same quantum numbers, with very close lower energy levels, have been selected to limit the sensitivity to temperature variations and guarantee identical broadening as well as relaxation properties. The sensitivity in measuring the deviation from a standard sample δ18O is 1.4‰, in 200 sec of integration time.

Enhancement of electrochemical ion/electron-transfer reaction at solid|liquid interface by polymer coating on solid surface

Controlling the ion/electron-transfer reaction at the electrode|electrolyte (solid/liquid) interface is a necessary and vitally important point for improving the operation of various electrochemical devices. In this paper, we propose a polymer coating technique which enhances the Li + ion-transfer reaction at the LiCoO 2|electrolyte interface, and confirm the effects of the polymer coating by cyclic voltammetry (CV) and AC impedance techniques. The results from the experiments indicated that the application of an F-introduced polymer on the LiCoO 2 (LCO) surface decreased the activation barrier for Li + ion transfer. Besides the electrochemical studies, the present computational results indicated that the Li + exchange process between two states, which are both solved with ethylene carbonate (EC) and coordinated with an F-introduced polymer, might occur due to the close energy levels of Li + stability. Accordingly, we inferred that the transition state of this exchange process promotes the observed decrease in activation energy for the interfacial Li +-transfer reaction.

Large magnetic polarization of Ti 4+ ions in FeTiO 3

Nominal valence states of Ti ions in FeTiO 3 are generally considered to be Ti 4+. However, due to the close energy levels between Fe 2+ and Ti 4+ states, there are some possibilities of intervalence charge transfer from Fe 2+ to Ti 4+. In order to clarify the real electronic structures of Ti ions in FeTiO 3, we performed resonant photoemission spectroscopy (RPES) and X-ray magnetic circular dichroism (XMCD) across the Ti 2p→3d excitation. The RPES spectra clearly indicated the partial density of states derived from the Ti 3d states on the valence band. The Ti 3d states appearing at the top of the valence bands were overlapped with the Fe 3d states. Moreover, the XMCD spectra at Ti L 2,3 edges suggested large magnetic polarization of Ti ions in FeTiO 3 in spite of nonmagnetic natures of Ti 4+ ions in common sense. The Ti ions in FeTiO 3 seemed to have some 3d electron densities caused by the electron transfer from the Fe 3d t 2g↓ states.

Evaluating Densities and Energy Levels of Impurities with Close Energy Levels in Semiconductor from Temperature Dependence of Majority-Carrier Concentration

By modifying the graphic method proposed in Jpn. J. Appl. Phys. 35 (1996) L555, the author aims to evaluate the densities and energy levels of impurities with two kinds of close energy levels. Using the temperature dependence of the majority-carrier concentration n(T), the function n(T) exp (E ref/kT)/kT is defined, where k is the Boltzmann constant and E ref is a newly introduced parameter. The densities and energy levels of the impurities can be evaluated from the peaks of this function. Even in Si with two donors (Sb and P), it is found that the densities and energy levels of the two donors can be evaluated accurately.

Interpretation of Anomalous Ultraviolet Transitions of Fe II Observed in Laboratory Fourier Transform Spectra and Stellar HST and IUE Spectra

We discuss LS-forbidden Delta S = 2 transitions of Fe Pi that appear as strong lines in ultraviolet stellar and laboratory spectra. The lines occur because of indirect lever mixing-two close energy levels, w(2)P(3/2) and x(6)P(3/2), are mixed through a third level acting as a catalyst. In transition multiplets, that involve either the w(2)P(3/2) or the x(6)P(3/2) level the normal component is accompanied by a close, parasite component. These components are well resolved in laboratory Fourier transform spectra, from which accurate intensity ratios can be measured. Spectra of the HgMn star chi Lupi, recorded with the Hubble Space Telescope, show the normal and the parasite components resolved for the first time in stellar spectra. These have been used together with laboratory spectra to derive oscillator strengths for four multiplets and the mixing coefficients for the two interacting energy levels. We also provide improved spectroscopic data for all Fe Pi multiplets that include the w(2)P(3/2) and x(6)P(3/2) levels. The level mixing involves the UV 191 multiplet of Fe Pi around 1780 Angstrom, which is shown to have one parasite component. This multiplet is known to be a prominent emission feature in spectra of various objects, e.g., cool star chromospheres and symbiotic stars. As an example, we show IUE spectra of the eclipsing binary 32 Cyg, which provides perfect conditions for fluorescence experiments, and discuss possible excitation mechanisms of UV 191. Based on second-order perturbation theory and multiconfiguration Hartree-Fock calculations, an atomic three-level model is constructed. This model explains the contradiction found when applying first-order perturbation theory, viz., two close energy levels perturbing each other without causing a repulsion. (Less)

Size dependence of the carrier ground state of small semiconductor particles

By calculating the carrier density distribution and the effective one-particle potential self-consistently, we investigate the size dependence of the carrier ground state of small spherical semiconductor particles with the doping level fixed. The particles are assumed to be in an insulating medium or in the vacuum. The prominent peak just inside the carrier-deficient surface layer in the carrier density profile persists regardless of the particle size, while, with increasing size, the oscillatory density-profile feature inside the prominent peak becomes less and less conspicuous and reduces to nearly constant density to achieve charge neutrality. The remarkable variation of the potential bending with increase of the size depends upon where the newly occupied carrier states have their probability density concentrated. This variation of the potential bending often involves the energy intersection of two close energy levels with different angular momenta l.

Characteristics of the propagation of electron waves in coupled-quantum-well waveguides in a transverse electrostatic field.

We investigate how the presence of a transverse electrostatic field influences the propagation properties of guided electron waves in coupled-quantum-well waveguides. The basis eigenstates of electrons in the uncoupled quantum well in the presence of a transverse electric field are calculated by using the Airy-function approach and the transfer-matrix method. By decomposing the eigenfunctions of electrons in the coupled double quantum wells in terms of the basis eigenfunctions of the individual wells, the expression for the mode-amplitude functions (MAF) for various bare states in the wells is presented. By setting up appropriate initial boundary conditions one can simulate different electron-injection conditions for the system and study how the electron waves evolve among the various states. By varying the bias, different configurations of electron-state structure can be formed. When a pair of matching states are produced in the wells, the electron-wave transfer takes place mainly between these matching bare states. The particular patterns of the transfer depend on the injection conditions and the energy of the incident electron. The variation of the magnitude of the MAF's can have a sinusoidal-like oscillation or the profile of a rapid decay (growth) from unity (zero) to a plateau imposed upon a small-amplitude oscillation. When all the bare states are mismatched the transfer of electron waves may still occur between two states with close energy levels in the channels. We also show the influence of multimodes on the variation of the magnitude of MAF. This leads to some oscillations imposed on the original sinusoidal-like function and causes incomplete transfer between pairs of states in the channels. Therefore, the pattern of the electron-wave transfer in channels may be controlled and modified by applying a transverse electrostatic field in the coupled-quantum-well waveguide.

A method for discriminating several deep-level centres from capacitance versus time transients

The study of deep centres induced by irradiation of charged particles in semiconductors is difficult due to the large number of different centres created. These centres may have close energy levels, so that the free-carrier emission processes observed by the capacitance transients are a combination of the contributions of several centres. In this study, we have used a set of isothermal relaxation measurements covering a broad temperature range for excitation. For each experiment, the emission rates of the accessible levels are obtained by a statistical analysis of the experimental data. The method is written in GLOP code with which, on the basis of a suggested fitting model, the relevant parameters are evaluated. Moreover, it gives the physicist a guideline for comparing several models (differing for example in the number of deep centres). The method has been applied to the study of the base material of silicon solar cells irradiated by low-energy protons.

The decay of 73As

The relative intensities of the gamma and X rays of 73As have been measured with a Si(Li) spectrometer and the information used for the calculation of conversion coefficients. These are compared with theoretical values.Sufficiently precise gamma energy measurements have been made to remove an ambiguity in the ordering of two close energy levels.