Triplet-triplet transitions in zinc-like ions

Theoretical oscillator strengths are reported for the lines of the 4s4p ³ P-4s4d ³ D transition in some ions of the zinc isoelectronic sequence, which are of interest in fusion plasma research. The calculations have been performed with the relativistic quantum defect orbital (RQDO) method. A core-polarization to the dipole transitions moment has also been included in the formalism. A comparative study with other theoretical results and the scarce experimental measurements has also been carried out. Systematic trends of individual oscillator strengths along the isoelectronic sequence are also shown in a graphical form.     

A test of the R-centroid method

The R-centroid method is shown to be exact when the molecular dipole transition moment, D(R), varies linearly with internuclear distance R, but may fail to give accurate results in the region of a maximum in D(R). Using individual line strengths computed for the X¹Σ⁺—A¹Σ⁺ system in LiH in which D(R) goes through a maximum, it is shown that good results can still be obtained if only the strongest transitions are used in the R-centroid analysis.     

M1 transition probabilities between fine structure components2L J (L ≥ 1)

Spontaneous emission transition probabilities of the magnetic dipole transitions between states of ground state configurations consisting of onenl electron (or a hole) outside a closed shell have been calculated by using relativistic terms of order α² Z ² and using hydrogenic orbitals to calculate the required overlap integrals. The line strengths calculated for the Boron and Fluorine isoelectronic sequences are in excellent agreement with the calculations involving Dirac wavefunctions for all ions uptoZ=60. The maximum difference at the highest value ofZ=92 is about 6%. Our calculated lifetimes for the state 2p ^{5 2} P _1/2 for Fluorine-like Mg IV and Fe XVIII are 5.03 s and 51.7 µs respectively which are in excellent accord with corresponding values 5.00 s and 51.0 µs calculated by using sophisticated configuration interaction wavefunctions within the Breit-Pauli approximation. Our calculated value of lifetime for Thalium-like Pb II is 40.0 ms which is in good accord with the experimental value of 41.2 ms. New results are presented for the highly ionized ions in the Al-like and Cl-like isoelectronic sequences. The present analysis can be exploited for all the ions in the isoelectronic sequences of elements of groups III A, III B VII A of the periodic table.     

Allowed transitions and intercombination lines in B II

Systematic multiconfiguration results are reported for the 2s ^{2 1} S ₀ → 2s2p ³ P ₁ intercombination line in B II. Both Breit-Pauli and fully relativistic calculations have been performed. The two methods are compared and the results are found to be in good agreement. Length and velocity forms of the oscillator strengths of related allowed transitions are also reported. The latter are used as a check on accuracy along with term energy separation. Fine-structure splitting is also reported but shown not to be a check on accuracy in the Breit-Pauli approximation.     

Fluorescence of europium(III) in a flouride glass containing zirconium

Europium(III) incorporated in a new zirconium barium flouride glass shows 14 luminescent transitions (at 300 K) from ⁵D_J (J= 0,1,2,3) to ⁷F_J (_J = 0,1,2,3,4) which are compared with Judd-Ofelt parameters for induced electric dipolar radiation, as well as for calculated magnetic dipolar transition probabilities.     

Transition probabilities of europium(III) in zirconium and beryllium fluoride glasses,phosphate glass,and pentaphosphate crystals

Eigenvectors of Eu³⁺ were obtained by a least-squares fitting procedure to the measured transitions from the two lowestJ levels to a multitude of excited levels up to 41 000 cm^?1. The Judd-Ofelt parametersΩ_t(t = 2, 4, 6) were obtained by comparison between theU^(t) calculated from the eigenvectors, and the observed oscillator strengths. Radiative transition probabilities and branching ratios were evaluated for the excited states⁵D_J(J = 0, 1, 2, 3) and⁵L₆ to⁷F_J. The agreement between the calculated and observed lifetimes and branching ratios is better in oxide glasses than in the pentaphosphate crystal and fluoride glasses. This can be understood on the basis of the higher variety of sites and hence, better averaging.     

On the line intensity ratios of prominent Si II,Si III,and Si IV multiplets

Line intensities of singly, doubly and triply ionized silicon (Si II, Si III, and Si IV, respectively) belonging to the prominent higher multiplets, are of interest in laboratory and astrophysical plasma diagnostics. We measured these line intensities in the emission spectra of pulsed helium discharge. The Si II line intensity ratios in the 3s3p²²D–3s²4p²P^o, 3s²3d²D–3s²4f²F^o, and 3s²4p²P^o–3s²4d²D transitions, the Si III line intensity ratios in the 3s3d³D–3s4p³P^o, 3s4p³P^o–3s4d³D, 3s4p³P^o–3s5s³S, 3s4s³S–3s4p³P^o, and 3s4f³F^o–3s5g³G transitions, and the Si IV line intensity ratios in the 4p²P^o–4d²D and 4p²P^o–5s²S transitions were obtained in a helium plasma at an electron temperature of about 17,000 ± 2000 K. Line shapes were recorded using a spectrograph and an ICCD camera as a highly-sensitive detection system. The silicon atoms were evaporated from a Pyrex discharge tube designed for the purpose. They represent impurities in the optically thin helium plasma at the silicon ionic wavelengths investigated. The line intensity ratios obtained were compared with those available in the literature, and with values calculated on the basis of available transition probabilities. The experimental data corresponded well with line intensity ratios calculated using the transition probabilities obtained from a Multi Configuration Hartree–Fock approximation for Si III and Si IV spectra. We recommend corrections of some Si II transition probabilities.     

Two-photon induced fluorescence and resonance-enhanced ionization of sulfur atoms

Two-photon induced fluorescence and resonance-enhanced photoionization have been observed in atomic sulfur originating from both the ³P_2,1,0 and the ¹D₂ states. Sulfur atoms are generated by the sequential multiphoton dissociation of CS₂ at probing wavelengths. The two-photon absorption process involves the 3 ³P_2,1,0 → 4 ³P_2,0,1 or the 3 ¹D₂ → 4 ¹F₃ transitions with resolution of the individual J″ → J′ transitions in most cases. Intensities of the 3³P_J″ → 4 ³P_J′ transitions have been compared with Hartree-Fock calculated transition probabilities from the analogous transitions in atomic oxygen. Photoionization is observed in a three-photon (two to resonance) ionization originating from the ³P_2,1,0 and the ¹D₂ states. Induced fluorescence is observed at 167 and 180 nm which is dipole-allowed radiation from the intermediate ³S⁰₁ and ¹D⁰₂ states, respectively.     

Calculations on transitions in singly- and doubly-excited C IV

Wavelengths for transitions in the quartet spectrum of C IV are calculated and compared with recent experimental measurements. Transition probabilities and radiative lifetimes are also predicted for several of the lowest 1s 2snl ⁴ L and 1s2pnl ⁴ L levels up toL=4. In addition, wavelengths and transition probabilities for some recently observed C IV doublet transitions to then=4 level are presented.     

Relativistic effects in transitions of highly ionized heavy atoms

Wavelenghts, oscillator strengths, and lifetimes of KL shell heavy ions such as Fe²⁰⁺, Br³⁰⁺, etc. are predicted, including both relativistic and correlation effects. In such ions the distinction between “normal” electric dipole (El) and spin—orbit allowed electric dipole transitions (SOAEl) disappears and the Z-dependence of oscillator strengths is very different from the predictions of non-relativistic orbital theories. The feasibility of observing these ions in heavy ion accelerators is indicated. The results have implications for relativistic many-electron theory, ESCA, X-ray spectra, and molecular total energies.     

Allowed transitions in silicon isoelectronic ions

Dipole‐allowed transitions have been studied for the first few members of the Si isoelectronic sequence. Transition energies, oscillator strengths, transition probabilities and quantum defect values have been estimated for the low‐ and high‐lying excited states of s and d symmetries up to the principal quantum number n=7 for these 3p open shell ions from P⁺ to Cr¹⁰⁺. Time‐dependent coupled Hartree–Fock (TDCHF) theory has been utilized to calculate such transition properties. Most of the results for transition energies, oscillator strengths, and transition probabilities for higher excited states are new. The transition energies for low‐lying excited states agree well with experimental data wherever available. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001     

Emission spectra of Cs2NaTbCl6 and Cs2NaYCl6: Tb3+

The emission spectra of microcrystalline Cs₂NaTbCl₆ and Cs₂Na(Y_0.99Tb_0.01)Cl₆ have been measured at room temperature and at 77 K. The crystal structures of these compounds are face-centered cubic and the terbium (III) ions lie at sites of octahedral (O_h) symmetry surrounded by six chloride ions. Emission is observed from both the ⁵D₃ and ⁵D₄ excited states of Tb³⁺. Assignments have been made for nearly all of the magnetic-dipole transitions split out of the Tb³⁺⁷F₆, ⁷F₅, ⁷F₄, ⁷F₃, ⁷F₂, ⁷F₁ ← ⁵D₄ and ⁷F₄, ⁷F₂ ← ⁵D₃ transitions. These assignments are based on the calculated transition energies and relative magnetic-dipole strengths and intensities obtained from a weak-field crystal-field analysis of octahedral TbCl₆^3? units. Magnetic-dipole lines dominate the spectra for transitions of ΔJ = ±1 free-ion parentage, whereas both magnetic-dipole lines and vibronically induced electric-dipole lines contribute significantly to the emission intensities of the ΔJ = 0, ±2 transitions. The crystal-field sub-levels of both ⁵D₃ and ⁵D₄ appear to reach a Boltzmann thermal equilibrium prior to emission. Emission from ⁵D₃ is partially quenched in going from low temperature to high temperature and in going from Cs₂NaYCl₆: Tb³⁺ (1%) to Cs₂NaTbCl₆.This study has led to the identification and assignment of nearly all of the pure magnetic-dipole transitions split out of the Tb³⁺⁷F₆, ⁷F₅, ⁷F₄, ⁷F₃, ⁷F₂, ⁷F₁ ← ⁵D₄ and ⁷F₄, ⁷F₂ ← ⁵D₃ transitions in crystal-line Cs₂NaTbCl₆. The assignments were based on calculated transition energies and relative magnetic-dipole strengths (and intensities) obtained from a (weak-field) crystal-field analysis of octahedral (O_h) TbCl₆^3? clusters. Excellent agreement between the calculated and observed relative intensities of the magnetic-dipole lines was achieved by assuming a Boltzmann equilibrated set of crystal-field sub-levels for both the ⁵D₄ and ⁵D₃ emitting states. Furthermore, the experimental results suggest that ⁵D₄ ← ⁵D₃ relaxation is temperature-dependent.The energy levels calculated and displayed in table 1 appear to be qualitatively correct and are in semiquantitative agreement with the emission results (as interpreted in section 4). Calculated and observed transition energies for the assigned magnetic-dipole transitions generally agree to within 0.2%.One of the most remarkable features of the emission spectra obtained on Cs₂NaTbCl₆ is the absence of any vibrational structure in the ΔJ = ± 1 transitions (⁷F₆, ⁷F₃ ← ⁵D₄ and ⁷F₄, ⁷F₂ ← ⁵D₃), and the presence of extensive vibrational structure in the ΔJ = O, ±2 transitions (⁷F₆, ⁷F₄, ⁷F₂ ← ⁵D₄). If other than OO vibronic transitions do contribute to the ΔJ = ±1 emissions, their intensities must be at least two or three orders-of-magnitude weaker than the OO magnetic-dipole lines. Vibronically induced electric-dipole transitions appear, however, to make substantial contributions to the ⁷F₆, ⁷F₄, ⁷F₂ ← ⁵D₄ emission spectra. A clear-cut theoretical explanation for the absence of vibrational structure in the ΔJ = ±1 transitions is not readily apparent. We are presently examining this problem in greater detail.     

Forbidden electric quadrupole transitions between even OIII levels

The relativistic CI method is used to determine transition probabilities for electric quadrupole transitions between the 1s ² 2s ² 2p ² (³ P ₀,³ P ₂,¹ D ₂) and 1s ² 2p ^{4 3} P ₂ even levels of OIII. The variation of the results with the number of configurations used is discussed, both for the Coulomb and the Babushkin (length) gauge.     

Absorption spectra of dysprosium compounds in nonaqueous solutions. Spectral intensity analysis

Absorption spectra of dysprosium compounds were measured in amides and D₂O within the 5500–35000 cm^?1 region and in alcohols within the 7000–34300 cm^?1 region. The oscillator strengths of f-f absorptions bands below 35000 cm^?1 were determined. The intensities of the Dy³⁺ ground state absorption were analyzed according to the Judd-Ofelt theory of forced electric dipole transitions.A good fit to the measurements was obtained with the intensity parameter given in Tables 4–6. The polarizability effect on the intensity of the f-f transition with high value matrix elements U⁽⁴⁾ and U⁽⁶⁾ were considered.     

Absorption and emission spectral studies of Eu3+-doped PbO-PbF2 glass system

Judd-Ofelt parameters obtained from the absorption spectra of Eu³⁺ ions doped in PbO-PbF₂ glasses are intermediate between the values for fluoride and phosphate glass matrices. Eu³⁺ ions are coordinated to both oxide and fluoride ions. The calculated transition probabilities (As^-1) for the laser transition⁵D_o→⁷F₂ are 171 and 170 for 30PbO-70PbF₂ and 70PbO-30PbF₂ glasses respectively and are significantly lower compared to phosphate glasses. The calculated (β_R cal) and experimental (β_Rexpt) branching ratios for this transition show good agreement. The emission spectra display high energy transitions in the 440–570 nm region, a characteristic of parent matrices with low energy phonons such as the tellurite, germanate and fluoride glasses. The electron-phonon coupling strengths deduced from the excitation spectra of Eu³⁺ are 10.2 x 10⁻³ and 9.5 x l0⁻³ for 30PbO-70PbF₂ and 70PbO-30PbF₂ glasses respectively. The relative emission intensities of the low energy transitions to high energy transitions and the ratios of the most intense transitions⁵D₀→⁷F₂/⁵D₀→⁷F₇ significantly vary for the two glasses providing evidence for clustering of Eu³⁺ ions with increase in its concentration and increasing PbO content.     

Novel Eu-doped lead telluroborate glasses for red laser source applications

We report the absorption, luminescence and decay analysis of Eu³⁺-doped lead telluroborate (PTBEu) glasses for different Eu³⁺ concentrations ranging from 0.1 to 2.0 mol%. Judd-Ofelt intensity parameters obtained from ⁵D₀→⁷F_J=0-6 emission transitions of Eu³⁺ were used to calculate the radiative transition probabilities, luminescence branching ratios and radiative decay times. The luminescence spectra and decay times were measured at 464 nm excitation. The optical band gap energies are also determined. The luminescence intensity ratio, color purity and emission cross-section values support that the PTBEu20 glass is a suitable candidate for red laser source applications.     

Ab initio transition probabilities,band strengths and lifetimes for the lowest-lying vibrational states of Li+3

By calculating the dipole moments at 65 discrete points on a dipole moment hypersurface and by fitting a power series analytical function to these points, we have determined the ab initio transition probabilities, band strengths and lifetimes for the ten lowest-lying states of ⁷Li⁺₃ (⁶Li⁺₃). Of these, the fourth and tenth states were found to have long lifetimes of the order 4907 s(3344 s) and 1648 s(1093 s) respectively which is in accordance with the fact that transitions from these states to the ground state are dipole forbidden.     

Relativistic oscillator strengths for excited state transitions in some ions of the silver isoelectronic sequence

The relativistic quantum defect orbital method has been applied to the study of fine structure 5p ² P-nd ² D and 5p ² P-ns ² S (n5) transitions (some of them involving highly excited upper levels) in the silver isoelectronic sequence. The resulting oscillator strengths are analyzed in terms of other relativistic results and some available experimental data.     

Doubly excited states of highly stripped ions: a time dependent perturbation approach

Doubly excited singlet states have been calculated for the astrophysically important highly stripped He like ions Al^{11 +}, Si^{12 +}, P^{13 +}, S^{14 +} and Cl^{15 +} for the transitions 2s ²: ¹ S ^e, 2p ²: ¹ D ^e, 2snp: ¹ P ⁰, 2snd: ¹ D ^e and 2pnd: ¹F⁰ for n45. The transition energies are obtained from the position of resonances in the oscillations of the two electron charge cloud under an external harmonic perturbation. Linearised version of a suitably constructed variational functional is used for obtaining the response properties of the system. Most of the results are new. Agreement with the only few existing experimental data along this line is very reasonable. Analytic representations of the doubly excited states are obtained and the Coulomb repulsion integral in these states are estimated for checking the consistency of the wavefunctions. The doubly excited state wavefunctions so obtained may be used for evaluating other physical properties connected with transitions.