Shell Transitions Research Articles

Excited electronic structure of methylcyanoacetylene probed by VUV Fourier-transform absorption spectroscopy

High resolution photoabsorption spectrum of gas-phase methylcyanoacetylene (CH3C3N) has been recorded from 44500 to 130000cm−1 at room temperature with a vacuum ultraviolet Fourier-transform spectrometer on the DESIRS synchrotron beamline (SOLEIL). The absolute photoabsorption cross section in this range is reported for the first time. Valence shell transitions and Rydberg series converging to the ground state X˜+E2 of the cation as well as series converging to electronically excited states (A˜+A12 and C˜+) are observed and assigned. Time-dependent density-functional-theory calculations have been performed to support the assignment of the experimental spectrum in the low energy range. A tentative scaling of the previously measured CH3C3N+ ion yield by Lamarre et al. [17] is proposed, based on the comparison of the absorption data above the first ionization potential with the observed autoionization structures.

Direct detection of the (229)Th nuclear clock transition.

Today's most precise time and frequency measurements are performed with optical atomic clocks. However, it has been proposed that they could potentially be outperformed by a nuclear clock, which employs a nuclear transition instead of an atomic shell transition. There is only one known nuclear state that could serve as a nuclear clock using currently available technology, namely, the isomeric first excited state of (229)Th (denoted (229m)Th). Here we report the direct detection of this nuclear state, which is further confirmation of the existence of the isomer and lays the foundation for precise studies of its decay parameters. On the basis of this direct detection, the isomeric energy is constrained to between 6.3 and 18.3 electronvolts, and the half-life is found to be longer than 60 seconds for (229m)Th(2+). More precise determinations appear to be within reach, and would pave the way to the development of a nuclear frequency standard.

Visible to infrared low temperature photoluminescence of rare earth doped bismuth germanate crystals

In this paper, the influence of a series of rare earth (Eu, Tm, Nd) and Cr ion doping on the optical properties of BGO was investigated by means of photoluminescence (PL) from visible to IR region in the 10–300K temperature range using different types of detectors, namely, photomultiplier tube (PMT), InGaAs (IGA), and Si. Several samples were investigated having dopants concentrations of 0.3wt%Nd, 0.4wt%Tm, 0.06wt% Cr and 3ppm Eu. The PL spectra of the samples showed different luminescence behaviour which is assigned to the 4f intra shell transition from rare earth ions. The temperature dependence of the PL from rare earth doped BGO crystals is also examined.

Excitation mechanisms of Er optical centers in GaN epilayers

We report direct evidence of two mechanisms responsible for the excitation of optically active Er3+ ions in GaN epilayers grown by metal-organic chemical vapor deposition. These mechanisms, resonant excitation via the higher-lying inner 4f shell transitions and band-to-band excitation of the semiconductor host, lead to narrow emission lines from isolated and the defect-related Er optical centers. However, these centers have different photoluminescence spectra, local defect environments, decay dynamics, and excitation cross sections. The photoluminescence at 1.54 μm from the isolated Er optical center which can be excited by either mechanism has the same decay dynamics, but possesses a much higher excitation cross-section under band-to-band excitation. In contrast, the photoluminescence at 1.54 μm from the defect-related Er optical center can only be observed through band-to-band excitation but has the largest excitation cross-section. These results explain the difficulty in achieving gain in Er doped GaN and indicate approaches for realization of optical amplification, and possibly lasing, at room temperature.

K-Shell Excitation and Ionization of a Gas-Phase Protein: Interplay between Electronic Structure and Protein Folding

Understanding the correlation between proteins’ tertiary and electronic structures is a great challenge, which could possibly lead to a more efficient prediction of protein functions in living organisms. Here, we report an experimental study of the interplay between electronic and tertiary protein structure, by probing resonant core excitation and ionization over a number of charge-state selected precursors of electrically charged proteins. The dependence of the core ionization energies on the protein charge state shows that the ionization of a protonated protein is strongly correlated to its tertiary structure, which influences its effective Coulomb field. On the other hand, the electronic core-to-valence shell transition energies are not markedly affected by the unfolding of the protein, from compact to totally elongated structures, suggesting that frontier protein orbitals remain strongly localized. Nevertheless, the unfolding of a protein seems to influence the cross section ratio between different resonant electronic transitions.

Photoluminescence and Judd–Ofelt analysis of Eu3+ doped LaAlO3 nanophosphors for WLEDs

Europium doped lanthanum aluminate nanophosphors were synthesized by a combustion process using Oxalyl di-hydrazide as fuel. The nanophosphors calcined at 900 °C for 3 h were characterized by PXRD, FTIR spectroscopy, SEM and TEM. The average crystallite size determined by TEM and Scherrer's method was found to be in the range 20–50 nm. The characteristic emission peaks (λexi - 395 nm) recorded at ∼ 591, 616, 646 and 696 nm (5D0→7Fj=0,1,2,3) may be attributed to the 4f–4f intra shell transitions of Eu3+ ions. The estimated CIE chromaticity co-ordinates were calculated from emission spectra, were close to the national television standard committee value of red emission. Correlated color temperature was found to be 1929 K.

Influence of Co and Dy Doping on the Optical and Magnetic Properties of ZnO Nanoparticles for DMS Application

Dysprosium-(Dy) and cobalt (Co)-doped zinc oxide (ZnO) nanoparticles with various concentrations have been synthesized by simple chemical precipitation method. X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy-dispersive X-ray (EDAX) measurements were conducted respectively for the structural, morphological, and compositional investigation of the sample. XRD analysis indicated that diffraction peaks of all the samples can be indexed to the hexagonal wurtzite structure of ZnO. No secondary phases including Co and Dy ions were detected in the samples even for the highest doping concentrations of Dy. Average particle size is found to be 25–34 nm. Scanning electron microscope and transmission electron microscope analysis revealed that the dopant atoms of Co and Dy are homogeneously distributed in ZnO wurtzite structure. The samples were characterized by EDAX to confirm the expected stoichiometry. In the photoluminescence spectra, Dy co-doped samples show a violet emission along with a broad yellow emission due to the4F9/2–6H15/2 inner shell transitions of Dy3+ ion. The photoluminescence (PL) enhancement process in Dy co-doped ZnO:Co is mainly due to Dy as a sensibilizer which could effectively enhance the luminescence intensity. Absorption spectra of dysprosium- (Dy) and cobalt (Co)-doped ZnO nanoparticles exhibited enhanced optical absorption in visible region. Magnetization measurements have shown that the particles have room temperature ferromagnetic behavior with relatively high coercive fields which are decreasing with the increase of doping concentration. The analysis of optical and magnetic properties shows that Co- and Dy-doped ZnO nanoparticles are a promising material for DMS application and have potential applications in optoelectronic devices.

Visible to infrared low temperature luminescence of Er3+, Nd3+ and Sm3+ in CaSnO3 phosphors

Novel stannate phosphor, orthorhombic CaSnO3 phosphors doped with Er3+, Nd3+ and Sm3+ have been synthesized by a conventional solid-state method under N2+H2 gas flow. Visible and near-infrared photoluminescence (PL) properties were investigated as function of laser power and temperature. It was observed that all dopant ions are well incorporated in CaSnO3 and are responsible for the optical emission in the temperature range of 10–300K. PL peaks at 490, 546, 656, 696, 894, 1065, and 1344nm were observed for the CaSnO3:Nd3+ phosphor and associated to f–f transition of Nd3+ ion. Emissions at 564, 600–607, 646–656 and 714nm were detected for the CaSnO3:Sm3+. The strongest one, observed at 600nm, was associated to 4G5/2→6H7/2 of Sm3. Emission lines at 528, 548, 662 at 852nm were also seen for CaSnO3:Er3+ and correspond to Er3+ intra-4fn shell transitions. In addition, at low temperatures, a stark splitting of the 4f electron energy levels of the Er3+ ions were observed in infrared region (1520–1558nm) and assigned to the transition between the 4I13/2 state and the 4I15/2 state. Finally, our results show that the rare earth doped CaSnO3 has remarkable potential for applications as optical material since it exhibits efficient and sharp emissions due to rare earth ions.

Charge exchange produced emission of carbon in the extreme ultraviolet spectral region

We used a time-reolving high-resolution grating spectrometer to study extreme ultraviolet emission from plasmas in the National Spherical Tokamak Experiment (NSTX). The NSTX spectral range from 150-250 Å is typically dominated by emission from M-shell iron lines, L- shell transitions of oxygen, or K-shell lines of lithium. However, we also observed several intense emission lines, which we now attribute to transitions in C V and C VI. Collisional-radiative modeling shows that electron-impact excitation is far too weak to account for the features we observed. Instead, these lines appear to be produced by charge exchange with neutral hydrogen.

Unique properties of photoluminescence excitation spectra in a Eu-doped GaN epitaxial film

We have investigated the temperature dependence of photoluminescence-excitation (PLE) spectra of Eu3+ emission due to the intra-4f shell transitions in a Eu-doped GaN epitaxial film from the viewpoint of the energy transfer process by carriers and excitons from the host GaN to Eu3+ ions. It was found that the excitonic band of the PLE spectrum disappears in a low temperature region below ∼140 K in spite of the fact that the optical transitions of the A and B excitons are clearly observed in a reflectance spectrum. The excitonic PLE band becomes remarkable with an increase in temperature. This fact indicates that carriers originating from the thermal dissociation of photogenerated excitons contribute to the Eu3+ emission. In other words, excitons play no role in the energy transfer process. Furthermore, the PLE spectrum at room temperature exhibits an oscillatory structure resulting from longitudinal-optical phonon emission in a hot carrier relaxation process.

Energy levels, transition rates, oscillator strengths and lifetimes in Ne-like, Ni-like, and Cu-like uranium ions

We present the fine-structure energy levels, wavelengths, oscillator strengths, transition energies, and transition rates of optically allowed inner-shell transitions of Ne-, Ni-, and Cu-like uranium ions by using the multiconfiguration Dirac–Fock method with the fully relativistic GRASP2 code (partly improved by us). In order to compare these results, we have performed other independent calculations with a fully relativistic Flexible Atomic Code (FAC). We have determined extensive configuration interaction wavefunctions to calculate the level energies of the inner-shell excited states of these three uranium ionic states. Overall, our calculated energy levels, wavelengths, transition rates, and oscillator strengths within the levels of selected configurations show better agreement with the available experimental and other theoretical results. Furthermore, we report radiative lifetimes of all the excited states of these three uranium ions. We also present many unpublished data about energy values, wavelengths, transitions rates, and oscillator strengths for inner-shell transitions. We believe that our calculated inner shell transition energies are of interest for the analysis of uranium x-ray spectra.

Zn2TiO4:Eu3+ nanophosphor: Self explosive route and its near UV excited photoluminescence properties for WLEDs

A simple and low-cost solution combustion method was used to prepare Eu3+ (1–11mol%) doped Zn2TiO4 nanophosphors at 500°C using zinc nitrates as precursors and oxalyl di-hydrazide (ODH) as fuel. The final product was calcined at 1100°C for 3h and then characterized by powder X-ray diffraction (PXRD), fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and UV–visible absorption (UV–Vis). The PXRD patterns of the sample calcined at 1100°C show pure cubic phase. The crystallite size was estimated using Scherrer’s method and found to be in the range 20–25nm and the same was confirmed by TEM studies. Effects of Eu3+ (1–11mol%) cations on the luminescence properties of Zn2TiO4 nanoparticles were studied. The samples exhibit intense red emission upon 395nm near ultra violet (NUV) excitation. The characteristic emission peaks recorded at ∼578, 592, 613 and 654nm may be attributed to the 4f–4f intra shell transitions (5D0→7Fj=0,1,2,3) of Eu3+ cations. The CIE chromaticity co-ordinates and CCT were calculated from emission spectra and the values (x, y) were very close to NTSC standard values for red emission and CCT was close to Plankian locus. Therefore, the present phosphor may be highly useful for display applications.

Structural characterization and EXAFS wavelet analysis of Yb doped ZnO by wet chemistry route

Lanthanide doped ZnO are interesting materials for optical and electrical applications. The wide band gap of this semiconductor makes it transparent in the visible range (Egap=3.2eV), allowing a sharp emission from intra shell transition from the lanthanides. From the electrical side, ZnO is a widely used material in varistors and its electrical properties can be tailored by the inclusion of lanthanides. Both applications are influenced by the location of the lanthanides, grain boundaries or lattice inclusion. Yb doped ZnO samples obtained by wet chemistry route were annealed at different temperatures and characterized by Transmission Electron Microscopy (TEM), X-ray Diffraction (XRD), Rietveld refinement of XRD data, and X-ray Absorption Fine Structure (XAFS). These techniques allowed to follow the changes occurred in the matrix and the Yb environment. The use of the Cauchy continuous wavelet transform allowed identifying a second coordination shell composed of Zn atoms, supporting the observations from XRD Rietveld refinement and XAFS fittings. The information obtained confirmed the incorporation of Yb in Oh sites of the wurtzite structure without Yb2O3 clustering in the lattice.

Spectral content of buried Ag foils at 10(16) W/cm(2) laser illumination.

Sources of 5-12 keV thermal Heα x-rays are readily generated by laser irradiation of mid-Z foils at intensities >10(14) W/cm(2), and are widely used as probes for inertial confinement fusion and high-energy-density experiments. Higher energy 17-50 keV x-ray sources are efficiently produced from "cold" Kα emission using short pulse, petawatt lasers at intensities >10(18) W/cm(2) [H.-S. Park, B. R. Maddox et al., "High-resolution 17-75 keV backlighters for high energy density experiments," Phys. Plasmas 15(7), 072705 (2008); B. R. Maddox, H. S. Park, B. A. Remington et al., "Absolute measurements of x-ray backlighter sources at energies above 10 keV," Phys. Plasmas 18(5), 056709 (2011)]. However, when long pulse (>1 ns) lasers are used with Z > 30 elements, the spectrum contains contributions from both K shell transitions and from ionized atomic states. Here we show that by sandwiching a silver foil between layers of high-density carbon, the ratio of Kα:Heα in the x-ray spectrum is significant increased over directly illuminated Ag foils, with narrower lines from K-shell transitions. Additionally, the emission volume is more localized for the sandwiched target, producing a more planar x-ray sheet. This technique may be useful for generating probes requiring spectral purity and a limited spatial extent, for example, in incoherent x-ray Thomson scattering experiments.

3차원 솔리드-평면 쉘 변환요소의 강성행렬 추정

A structural model consists of many types of finite elements, such as truss, beam, plate, shell and solid element, and so on. With the aid of commercial computer programs, field engineers comfortably use these finite elements at the same time for the modelling and analysis of real structure in their new projects. However, it is still difficult to model the connections and interfaces between different types of finite elements because of mutually ill-matched node numbers and degrees of freedom(d.o.f). To settle these problems, Many researchers studied and proposed various solution methods in literatures on FEA(Finite Element Analysis) and the use of transition elements is considered as one of the solutions. This pater presents an isoparametric formulation for three dimensional transition finite element, especially the solid-flat shell transition element. The proposed solid-flat shell transition element is composed of the solid element with 8 nodes, 3 d.o.f and the flat shell element with 4 nodes, 6 d.o.f for the simple formula derivation and the usefulness of practical applications. Basic theories for solid element and flat shell element are studied at first and a possible method for realizing the solid-flat shell transition element is suggested. On the basis of these theoretical backgrounds, the formula which calculates the stiffness matrix of the solid-flat shell transition element is derived in detail and an algorithm available for computer programming is investigated lastly.

Exposing the role of electron correlation in strong-field double ionization: X-ray transient absorption of orbital alignment in Xe+ and Xe2+.

Orbital alignment measurements and theory are used to examine the role of electron correlation during atomic strong-field double ionization (795 nm, (1-5) × 10(14) W cm(-2)). High-order harmonic, transient absorption spectroscopy is used to measure the angular distributions of singly and doubly tunnel-ionized xenon atomic states via 4d core to 5p valence shell transitions between 55 and 60 eV. The experimental MJ alignment distributions are compared to results of a rate-equation model based on sequential ionization, previously developed for coherent electron motion, and now applied to account for the alignment prepared by tunneling ionization. The hole generated in the (2)P3/2 state of Xe(+) is measured to be entirely composed of |MJ| = 1/2, in agreement with theory. The result is a higher degree of alignment than previously reported. Because the model neglects effects of electron-ion recollision, the theory predicts a high degree of alignment in both spin-parallel (triplet) and antiparallel (singlet) terms of Xe(2+). However, the alignment generated with linearly polarized light is observed to be spin-state dependent. The measured alignments for triplet spin states ((3)P2 has |MJ| = [0 : 1 : 2] of [27±6 : 45±11 : 29±0] and (3)P1 has |MJ| = [0 : 1] of [56±2 : 44±2]) are in good agreement with the expectations of theory, which are [33 : 53 : 14] and [66 : 33], respectively. The results validate the rate equation model for sequential tunnel ionization. However, the alignment extracted for a singlet state is greatly diminished: (1)D2 is measured to be [18±1 : 39±2 : 43 ± 2] compared to theoretical expectation of [60 : 39 : 1] for |MJ| = [0 : 1 : 2]. The poor agreement with the sequential ionization model suggests that the alignment of (1)D2 is strongly influenced by the high propensity for the liberated first electron to return to and recollide with its parent atomic orbital. Therefore, although the influence of electron recollision appears minor in the triplet states and suggests sequential ionization, electron correlation between the ionic core and the first ionized electron cannot be ignored in the singlet state. Singlet states are likely to be generated through nonsequential double ionization over the intensity range where the experiments are performed.

Sensitization effect of Al co-doping on Nd-related photoluminescence in TiO2 matrix

Nd and Al co-doped anatase phase TiO2 thin films were prepared on silicon substrates by laser ablation and post annealing. These thin films exhibited intense light emissions due to intra-4f shell transitions in the Nd3+ ions at room temperature. Furthermore, the intensity and line shape of the Nd3+-related luminescence were affected by the Al co-doping. The emission dynamics measurements showed that a slight Al co-doping led to an improvement of the Nd3+-emission lifetime. Our results indicated that Al is an effective sensitizer of enhancing Nd3+-related emission in the TiO2 matrix.

Ionization photophysics and spectroscopy of cyanoacetylene.

Photoionization of cyanoacetylene was studied using synchrotron radiation over the non-dissociative ionization excitation range 11-15.6 eV, with photoelectron-photoion coincidence techniques. The absolute ionization cross-section and spectroscopic aspects of the parent ion were recorded. The adiabatic ionization energy of cyanoacetylene was measured as 11.573 ± 0.010 eV. A detailed analysis of photoelectron spectra of HC3N involves new aspects and new assignments of the vibrational components to excitation of the A(2)Σ(+) and B(2)Π states of the cation. Some of the structured autoionization features observed in the 11.94 to 15.5 eV region of the total ion yield (TIY) spectrum were assigned to two Rydberg series converging to the B(2)Π state of HC3N(+). A number of the measured TIY features are suggested to be vibrational components of Rydberg series converging to the C(2)Σ(+) state of HC3N(+) at ≈17.6 eV and others to valence shell transitions of cyanoacetylene in the 11.6-15 eV region. The results of quantum chemical calculations of the cation electronic state geometries, vibrational frequencies and energies, as well as of the C-H dissociation potential energy profiles of the ground and electronic excited states of the ion, are compared with experimental observations. Ionization quantum yields are evaluated and discussed and the problem of adequate calibration of photoionization cross-sections is raised.

Sputtering‐assisted metal‐organic chemical vapor deposition of Yb‐doped ZnO for photonic conversion in Si solar cells

AbstractWe have grown Yb‐doped ZnO (ZnO:Yb) on c‐plane sapphire substrates by sputtering‐assisted metal‐organic chemical vapor deposition (SA‐MOCVD). X‐ray diffraction (XRD) revealed that these ZnO:Yb films exhibit a c‐axis orientation and that the lattice constant increases with Yb concentration. After annealing the samples at 600 °C for 0.5 h in O2, they showed a clear 980 nm emission due to the intra‐4f shell transitions of 2F5/2–2F7/2in Yb3+ ions. It turns out that Yb lu‐minescent centers with different local structures coexist, which exhibit different energy transfer processes from the ZnO host. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Stability of a Cylindrical Shell Made of a Shape-Memory Alloy

A method for solving the problem of the stability of a cylindrical shell made of a shape memory alloy is proposed. The alloy undergoes the direct martensitic transformation under uniform axial compression, torsional moment, and uniform external pressure. It is shown that the additional structural changes that occur during buckling considerably reduce the critical loads for thin-walled shells. It is also important to allow for the additional phase transition in medium-thickness shells.