The effect of host glass on optical absorption and fluorescence of Nd3+ in xNa(2)O-(30-x)K2O-70B(2)O(3) glasses

The effect of host glass composition on the optical absorption and fluorescence spectra of Nd3+ has been studied in mixed alkali borate glasses of the type xNa(2)O-(30-x)K2O-69.5B(2)O(3)-0.5Nd(2)O(3) (X = 5,10,15,20 and 25). Various spectroscopic parameters such as Racah (E-1, E-2 and E-3), spin-orbit (xi(4f)) and configuration interaction (alpha, beta) parameters have been calculated. The Judd-Ofelt intensity parameters (Omega(lambda)) have been calculated and the radiative transition probabilities (A(rad)), radiative lifetimes (tau(r)), branching ratios (beta) and integrated absorption cross sections (Sigma) have been obtained for certain excited states of the Nd3+, ion and are discussed with respect to x. From the fluorescence spectra, the effective fluorescence line widths (Deltalambda(eff)) and stimulated emission cross sections (sigma(p)) have been obtained for the three transitions F-4(3/2) --> I-4(9/2), F-4(3/2) --> I-4(11/2) and F-4(3/2) --> I-4(13/2) of Nd3+. The stimulated emission cross section (sigma(p)) values are found to be in the range (2.0-4.8) x 10(-2)0 cm(2) and they are large enough to indicate that the mixed alkali borate glasses could be potential laser host materials.

Nd3+螯合物的含氢有机溶液光谱性能研究

Tris-thenoyltrifluroacetonate of Nd3+ has been prepared and dissolved in DMF solation with very high concentration, and the contained hydrogen has not been substituted by deuterium. The absorption spectrum, emission spectrum, and fluorescence lifetime of the solution were measured. Very obvious characteristic fluorescence peaks were observed at 898 and 1058 nm. Based on Judd-Ofelt theory, three intensity parameters were obtained: Omega(2) = 4.9 x 10(-20) cm(2), Omega(4) = 5.1 x 10(-20) cm(2) and Omega(6) = 2.5 x 10(-20) cm(2). Line strengths S-cal, oscillator strengths f(cal), radiative transition probabilities A(ed), radiative lifetimes tau(r) and branch ratios beta were calculated too. The measured lifetime tau of 1058 nm peak is 460 mu s, and that of 898 nm 505 mu s. Comparison between theoretically computed radiative lifetime tau(r)(682 mu s) and the measured lifetime indicates that the non-radiative transition probability of the solution is very low and the fluorescence quantum efficiency very high. High values of three intensity parameters prove the high asymmetric surroundings of Nd3+, which is important for Nd3+ to absorb the excitation energy. Spectropic quality factor Omega(4)/Omega(6) > 1 makes radiation at 898 nm stronger than at 1058 nm.

The luminescence of Eu3+ ion in Ca2Al2SiO7

Ca2Al2SiO7:Eu3+ was prepared by the sol-gel method. Through the emission spectrum of Eu3+ ion, the fluorescence parameters such as Omega(i) (i = 2,4) and radiative transition probabilities of D-5(0)-F-7(j) were calculated. The Pb2+ ion with bigger radius has an effect on the fluorescence spectra of Eu3+ which can be explained by the structure of the matrix. Simultaneously, the energy transfers between mercury-like ions (Pb2+ and Bi3+) and Eu3+ ion were observed. The D-5(4) and D-5(2) energy levels of Eu3+ are the resonance ones for Pb2+ ion.

Theoretical investigation of LaC2 and LaC2+ clusters

LaC2 (with doublet and quartet states) and LaC2+ (with singlet and triplet states) cluster have been studied by using the B3LYP (Becke three-parameter/Lee-Yang-Parr) density functional method and the HF (Hartree-Fock) method with LANLIDZ basis set. For each cluster, four possible isomers in C-2v, C-s, C-proportional to v and D-proportional to h symmetries have been investigated. The results indicate that structures in C-s symmetry are local minima in all cases and, in most cases (particularly for high spin states), our initial guess in C-s symmetry converges to structures in C-2v symmetry. For the isomers in C-2v, C-proportional to v and D-proportional to h symmetries, local minima were found to be dependent on the method and spin state. The two clusters may also exist as linear chains. The ordering of the binding energies for the isomers in all spin states is C-s similar to C-2v < C-proportional to v < D-proportional to h. The ionization potential of LaC2 is reported as well. (C) 1998 Elsevier Science B.V.

Theoretical investigation of LaC3n+ (n = 0, 1, 2) clusters by density functional theory

LaC3n+ (n = 0, 1, 2) clusters have been studied using B3LYP (Becke 3-parameter-Lee-Yang-Parr) density functional method. The basis set is Dunning/ Huzinaga valence double zeta for carbon and [2s2p2d] for lanthanum, denoted LANL1DZ. Four isomers are presented for each cluster; two of them are edge binding isomers with C-2 upsilon symmetry, the other two are Linear chains with C-infinity upsilon symmetry. Meanwhile, two spin states for each isomer, that is, singlet and triplet for LaC3+, doublet and quartet for LaC3 and LaC32+, respectively, are also considered. Geometries, vibrational frequencies, infrared intensities, and other quantities are reported and discussed. The results indicate that at some spin states; the C-2 upsilon symmetry isomers are the dominant structures, while for the other spin states, linear isomers are energetically favored. (C) 1998 John Wiley & Sons, Inc.

Autoionizing states and their relevance in electron-ion recombination

Atomic physics plays an important role in determining the evolution stages in a wide range of laboratory and cosmic plasmas. Therefore, the main contribution to our ability to model, infer and control plasma sources is the knowledge of underlying atomic processes. Of particular importance are reliable low temperature dielectronic recombination (DR) rate coefficients. This thesis provides systematically calculated DR rate coefficients of lithium-like beryllium and sodium ions via ∆n = 0 doubly excited resonant states. The calculations are based on complex-scaled relativistic many-body perturbation theory in an all-order formulation within the single- and double-excitation coupled-cluster scheme, including radiative corrections. Comparison of DR resonance parameters (energy levels, autoionization widths, radiative transition probabilities and strengths) between our theoretical predictions and the heavy-ion storage rings experiments (CRYRING-Stockholm and TSRHeidelberg) shows good agreement. The intruder state problem is a principal obstacle for general application of the coupled-cluster formalism on doubly excited states. Thus, we have developed a technique designed to avoid the intruder state problem. It is based on a convenient partitioning of the Hilbert space and reformulation of the conventional set of pairequations. The general aspects of this development are discussed, and the effectiveness of its numerical implementation (within the non-relativistic framework) is selectively illustrated on autoionizing doubly excited states of helium.

Atomic Structures and Radiative Properties of He-like Ions in Debye Plasmas

A detailed investigation of plasma screening effects on atomic structure and transition properties are presented for He-like ions embedded in dense plasma environment. Multi-configuration Dirac-Fock calculations were carried out for these ions by considering a Debye-Huckel potential. A large-scale relativistic configuration-interaction method is adopted to calculate transition energies and transition probabilities and to allow for a systematic improvement of the calculations. Comparison of the presently calculated results with others, when available, is made.

Liouville-space R-matrix-Floquet description of atomic radiative processes involving autoionizing states in the presence of intense electromagnetic fields

A reduced-density-operator description is developed for coherent optical phenomena in many-electron atomic systems, utilizing a Liouville-space, multiple-mode Floquet–Fourier representation. The Liouville-space formulation provides a natural generalization of the ordinary Hilbert-space (Hamiltonian) R-matrix-Floquet method, which has been developed for multi-photon transitions and laser-assisted electron–atom collision processes. In these applications, the R-matrix-Floquet method has been demonstrated to be capable of providing an accurate representation of the complex, multi-level structure of many-electron atomic systems in bound, continuum, and autoionizing states. The ordinary Hilbert-space (Hamiltonian) formulation of the R-matrix-Floquet method has been implemented in highly developed computer programs, which can provide a non-perturbative treatment of the interaction of a classical, multiple-mode electromagnetic field with a quantum system. This quantum system may correspond to a many-electron, bound atomic system and a single continuum electron. However, including pseudo-states in the expansion of the many-electron atomic wave function can provide a representation of multiple continuum electrons. The 'dressed' many-electron atomic states thereby obtained can be used in a realistic non-perturbative evaluation of the transition probabilities for an extensive class of atomic collision and radiation processes in the presence of intense electromagnetic fields. In order to incorporate environmental relaxation and decoherence phenomena, we propose to utilize the ordinary Hilbert-space (Hamiltonian) R-matrix-Floquet method as a starting-point for a Liouville-space (reduced-density-operator) formulation. To illustrate how the Liouville-space R-matrix-Floquet formulation can be implemented for coherent atomic radiative processes, we discuss applications to electromagnetically induced transparency, as well as to related pump–probe optical phenomena, and also to the unified description of radiative and dielectronic recombination in electron–ion beam interactions and high-temperature plasmas.

Eu3+-activated SrMoO4 phosphors for white LEDs applications: Synthesis and structural characterization

We report the synthesis of Eu3+-activated SrMoO4 phosphors by the facile nitrate-citrate gel combustion method. Powder XRD and Rietveld refinement data confirmed that these phosphors have a monophasic scheelite-type tetragonal structure with space group I4(1)/a (No. 88). FESEM micrographs indicate the agglomerated spherical particles. FTIR spectra showed four stretching and bending vibrational modes (2A(u) and 2E(u)). UV-Visible absorption spectroscopy illustrated that the optical band gap energy (E-g) values increase with increase in Eu3+ concentration. The host SrMoO4 phosphor exhibited an intense blue emission under UV excitation (368 nm). The Eu3+-activated SrMoO4 phosphors revealed characteristic luminescence due to Eu3+ ion corresponding to D-5(1) -> F-7(J) (J = 1,2) and D-5(0) -> F-7(J) (J = 1,2,3,4) transitions upon 465 nm excitation. The electric dipole transition located at 615 nm (D-5(0) -> F-7(2)) was stronger than the magnetic dipole transition located at 592 nm (D-5(0) -> F-7(1)). Intensity parameters (Omega(2), Omega(4)) and radiative properties such as transition probabilities (A(T)), radiative lifetime (tau(rad)) and branching ratio (beta) of Eu3+-activated SrMoO4 phosphors were calculated using the Judd-Ofelt theory. Based on the CIE chromaticity diagram, these phosphors can be promising materials for the development of blue and orange-red component in white LEDs. (C) 2015 Elsevier B.V. All rights reserved.

Synthesis of Eu3+-activated BaMoO4 phosphors and their Judd-Ofelt analysis: Applications in lasers and white LEDs

Eu3+-activated BaMoO4 phosphors were synthesized by the nitrate citrate gel combustion method. The Rietveld refinement analysis confirmed that all the compounds were crystallized in the scheelite-type tetragonal structure with I4(1)/a (No. 88) space group. Photoluminescence (PL) spectra of BaMoO4 phosphor reveals broad emission peaks at 465 and 605 nm, whereas the Eu3+-activated BaMoO4 phosphors show intense 615 nm (D-5(0) -> F-7(2)) emission peak. Judd-Ofelt theory was applied to evaluate the intensity parameters (Omega(2), Omega(4)) of Eu3+-activated BaMoO4 phosphors. The transition probabilities (A(T)), radiative lifetime (tau(rad)), branching ratio (beta), stimulated emission cross-section (sigma(e)), gain bandwidth (sigma(e) x Delta lambda(eff)) and optical gain (sigma(e) x tau(rad)) were investigated by using the intensity parameters. CIE color coordinates confirmed that the BaMoO4 and Eu3+-activated BaMoO4 phosphors exhibit white and red luminescence, respectively. The obtained results revealed that the present phosphors can be a potential candidate for red lasers and white LEDs applications. (C) 2015 Elsevier B.V. All rights reserved.

Comparative study of Eu3+ -activated LnOCl (Ln=La and Gd) phosphors and their Judd-Ofelt analysis

Eu3+-activated layered LnOCl (Ln=La and Gd) phosphors were synthesized by the conventional solid-state method at relatively low temperature (700 degrees C) and shorter duration of 2 h. The structural parameters were refined by the Rietveld refinement analysis and confirmed by the high resolution transmission electron microscopy (HRTEM). Both the compounds were crystallized in the tetragonal structure with space group P4/nmm (No. 129). The homogeneity of the elements were analyzed by TEM mapping and found to be uniformly distributed. The photoluminescence spectra revealed that the intensity of D-5(0)-> F-7(2) transition (619 nm) was more intense in Eu3+-activated GdOCl compared to LaOCl. This was due to the property of Gd3+ ions to act as an intermediate sublattice to facilitate the energy transfer to Eu3+ ions. Intensity parameters and radiative properties such as transition probabilities, radiative lifetime and branching ratio were calculated using the Judd-Ofelt theory. The CIE color coordinates result revealed that the Eu3+-activated GdOCl (0.641, 0.354) phosphor was close to the commercial red phosphors like, Y2O3:Eu3+ (0.645, 0.347), (Y2OS)-S-2:Eu3+ (0.647, 0.343) and National Television System Committee (NTSC) (0.67, 0.33). The results suggest that the present GdOCl:Eu3+ compound acts as a potential candidate for red phosphor materials.

Infrared to visible upconversion fluorescence in Yb,Tm : YAG single crystal

Absorption spectrum from 400 to 2000 run and upconversion fluorescence spectra under 940 nm pumping of YAG single crystal codoped with 5 at.% Yb3+ and 4 at.% Tm3+ were studied at room temperature. The blue upconversion emission centered at 483 nm corresponds to the transition (1)G(4) -> H-3(6), the emission band around 646 nm corresponds to the transition (1)G(4) -> F-3(4) of Tm3+. Energy transfer from Yb3+ to Tm3+ is mainly nonradiative and the transfer efficiency was experimentally assessed. The line strengths, transition probabilities and radiative lifetimes of (1)G(4) level were calculated by using Judd-Ofelt theory. Gain coefficient calculated from spectra shows that the upconversion corresponding with transitions (1)G(4) -> H-3(6) in YAG doped with Yb3+ and Tm3+ is potentially useful for blue light Output. (c) 2006 Elsevier B.V. All rights reserved.

Two-electron-one-photon M1 and E2 transitions between the states of the 2p(3) and 2s(2)2p odd configurations for B-like ions with 18 <= Z <= 92

Two-electron-one-photon (TEOP) M1 and E2 transition energies, line strengths and transition probabilities between the states of the 2p(3) and 2s(2)2p odd configurations for B-like ions with 18 <= Z <= 92 have been calculated using the GRASP2K package based on the multiconfiguration Dirac-Hartree-Fock (MCDHF) method. Employing active-space techniques to expand the configuration list, we have systematically considered the valence, core-valence and core-core electron correlation effects. Breit interaction and quantum electrodynamical (QED) effects were also included to correct atomic state wavefunctions and the corresponding energies. Influences of electron correlation, Breit interaction and QED effects on transition energies and line strengths of the TEOP M1 and E2 transitions were analysed in detail. The present results were also compared with other theoretical and experimental values.

Inner-shell photoexcitation of Fe XV and Fe XVI

The configuration-interaction method as implemented in the computer code CIV3 is used to determine energy levels, electric dipole radiative transition wavelengths, oscillator strengths and transition probabilities for inner-shell excitation of transitions in Fe XV and Fe XVI. Specifically, transitions are considered of the type 1s(2) 2s(2) 2p(6) 3s(2) -1s(2) 2s(2) 2p(5) 3l3l' 3l" (l, l' and l" = s,p or d) in FeXV and 1s(2) 2s(2) 2p(6) 3s- 1s(2) 2s(2) 2p(5) 3l3l' (l and l' = s,p or d) in FeXVI, using the relativistic Breit-Pauli approach. An assessment of the accuracy of the derived atomic data is performed.

MEASUREMENT AND CALCULATION OF ABSOLUTE SINGLE AND MULTIPLE CHARGE EXCHANGE CROSS SECTIONS FOR Feq+ IONS IMPACTING H2O

Charge exchange (CE) plays a fundamental role in the collisions of solar- and stellar-wind ions with lunar and planetary exospheres, comets, and circumstellar clouds. Reported herein are absolute cross sections for single, double, triple, and quadruple CE of Feq+ (q = 5-13) ions with H2O at a collision energy of 7q keV. One measured value of the pentuple CE is also given for Fe9+ ions. An electron cyclotron resonance ion source is used to provide currents of the highly charged Fe ions. Absolute data are derived from knowledge of the target gas pressure, target path length, and incident and charge-exchanged ion currents. Experimental cross sections are compared with new results of the n-electron classical trajectory Monte Carlo approximation. The radiative and non-radiative cascades following electron transfers are approximated using scaled hydrogenic transition probabilities and scaled Auger rates. Also given are estimates of cross sections for single capture, and multiple capture followed by autoionization, as derived from the extended overbarrier model. These estimates are based on new theoretical calculations of the vertical ionization potentials of H2O up to H2O10+.