Excitation and Emission Spectra of Cs2NaLnCl6 Crystals Using Synchrotron Radiation

ABSTRACT

The visible emission and vacuum ultraviolet excitation spectra of the series Cs₂NaLnCl₆ (Ln = Y, Nd, Sm, Eu, Tb, Er, Yb) and Cs₂NaYCl₆:Ln³⁺ (Ln = Sm, Er) have been recorded using synchrotron radiation at room temperature, and in some cases at 10 K. The excitation spectra comprise features associated with charge transfer, excitation from the valence to conduction band, and impurity bands. No d–f emissions were observed for these Ln³⁺ ions, so that the emission bands comprise intraconfigurational 4f ^N –4f ^N transitions and impurity bands, whose natures are discussed. Theoretical simulations of the f–d absorption spectra have been included. The comparison with data from the synchrotron at Desy enables a comprehensive account of the ground (or vibrationally excited ground for Ln²⁺) states of the Ln³⁺ 4f ^N , Ln³⁺ 4f ^N?15d, and Ln²⁺ 4f ^N+1 configurations relative to the valence and conduction bands of Cs₂NaLnCl₆, for which the band gaps are between 6.6 and 8.1 eV.     

Excitation of the Yb II transitions terminating on the low-lying odd levels

Excitation of the transitions from the even levels of a singly charged ytterbium ion that terminate on the low-lying odd levels 4f ¹³(² F°)6s ^{2 2} F°, 4f ¹⁴(¹ S)6p ² P°, and 4f ¹³(² F°_7/2)5d6p(³ D)³[3/2]° is experimentally studied by measuring 51 excitation cross sections at an electron energy of 50 eV, and 16 optical excitation functions are determined within the electron energy range 0–200 eV. The largest magnitudes of the measured cross sections exceed 3 × 10^?17 cm².     

Excitation cross sections of thulium atom transitions terminating at 4f13(2Fo)6s6p(3Po (7/2, J2) levels with J2 = 0, 1

The excitation of odd levels of the thulium atom, spontaneous transitions from which terminate at the 4f ¹³(² F ^o)6s6p(³ P ^o) (7/2, J ₂) levels with J ₂ = 0, 1, is studied by the method of extended crossing beams. Fifty four excitation cross sections are measured at an excitation electron energy of 50 eV. Seven optical excitation functions are recorded in the electron energy range of 0–200 eV.     

Two-photon spectroscopy of ytterbium

Two-photon laser spectra of the Yb vapor have been obtained. Transitions to highly excited 4f¹⁴ 6sns¹S₀ and 4f¹⁴ 6snd ¹D₂ states are seen in direct two-photon excitation. Hybrid resonances involving 4f¹⁴ 6s6p ¹P⁰₁ and 4f¹⁴ 5d6s ³D₂ intermediate states lead to transitions to 4f¹⁴ 6sns¹S₀, 4f¹⁴ 6snp ³P⁰_2,1 and 4f¹⁴ 6snd ¹D₂ levels.     

钐原子的两步激发共振光电离光谱

采用两步激发共振光电离技术研究了Sm原子的偶宇称高激发态光谱.实验采用了两条激发路线：1)第一束激光的波长固定在478.44nm以便将Sm原子从4f⁶6s²［⁷F₁］态激发至4f⁶6s6p［⁷D₁］态,再用第二束激光使其波长从480nm扫描至530nm,将Sm原子进一步激发至待测的高激发态;2)第一束激光的波长固定在574.8 关键词： Sm原子 光谱 分步激发 共振电离     

Valence instability of uranium in U(Al1−x Gex)3

The electronic structure of U and Ge in the solid solutions U(Al_1−x Ge_x)₃ is investigated by measuring x-ray line shifts. It is shown that uranium has the mixed valence U³⁺ [Rn](5f ³)-U⁴⁺ [Rn](5f ²) over the entire composition range (0⩽x⩽1) and that the population of the uranium 5f shell increases by ∼0.28 5f electrons/U atom from UAl₃ (x=0) to UGe₃ (x=1). The electronic structure of Ge is close to the electronic structure of Ge metal over the entire composition range 0<x⩽1. No variation of the population of the Ge 4p shell is detected to within the experimental error (∼0.1 4p electrons/Ge atom) as the composition varies from x=0.2 to 1. It is established that the delocalization of a U 5f electron occurs as a result of its transition to the s or d band of the same uranium atom. Fiz. Tverd. Tela (St. Petersburg) 39, 1505–1508 (September 1997)     

Luminescence of Cs2NaScCl6:Pr3+: Effects of Changing the Elpasolite Lattice Parameter

Abstract

The luminescence spectrum of Cs₂NaScCl₆:Pr³⁺ (0.1 at.%) has been recorded at temperatures down to 10 K and assigned between 20,800 and 9900 cm^?1. Twenty‐three energy levels of the 4f² configuration Pr³⁺ ion were located and then fitted by the conventional 4f² crystal field calculation, as well as by a configuration interaction assisted crystal field (CIACF) calculation. The latter gave a much better fit. A comparison of the fit for Cs₂NaScCl₆:Pr³⁺ with fits upon the same set of energy levels in Cs₂NaYCl₆:Pr³⁺ and Cs₂NaPrCl₆, where the fifth nearest neighbor of Pr³⁺ is changed and the lattice parameter increases along this series, shows a decrease in the magnitudes of the crystal field parameters, which were also semiquantitatively simulated. Several facets of the emission spectra are interesting, including the observation of weak progressions in the totally symmetric Pr–Cl stretching vibration and the occurrences of the resonance of electronic and vibronic states. The spectra of Cs₂NaScCl₆:Pr³⁺ (1 at.%) differ considerably from those of the more dilute system and show that other species are formed rather than a complete substitution of the Sc³⁺ sites by Pr³⁺.     

On resonance processes in near-threshold excitation of the resonance lines of a Zn+ ion in electron-ion collisions

The excitation of the components of the 4p ² P ₁ ^2,3/2/0 resonance doublet of the Zn⁺ ion by monoenergetic electrons in the interval 4–10 eV is investigated by a spectroscopic method in crossed beams. Resonances are found in the energy dependences below and above the excitation thresholds of resonance lines. The subthreshold resonances are satellite of the lines investigated and are excited in the process of dielectronic recombination. The main competing process here is the electronic decay of autoionizing states, which is manifested in a resonance excitation of the ions starting at the thresholds for the excitation of the levels. Autoionizing states lying between the levels of the doublet splitting of the 4p ² P ₁ ^2,3/2/0 state decay to the 4p ² P ₁ ^2/0 level in a Koster-Kronig process. Above the excitation energy of the 4p ² P ₃ ^2/0 level the the dominant contribution to resonance excitation is from autoionizing states with configurations 3d ⁹(² D _5/2,3/2)4s ² np,(n−1)f. Pis’ma Zh. éksp. Teor. Fiz. 68, No. 8, 614–617 (25 October 1998)     

Concentration dependence of the intermediate frequency bandwidth of submillimeter heterodyne AlGaAs/GaAs nanostructures

The concentration dependence of the intermediate frequency bandwidth of heterodyne AlGaAs/GaAs detectors with 2D electron gas is measured using submillimeter spectroscopy with high time resolution at T= 4.2 K. The intermediate frequency bandwidth f_3dBfalls from 245 to 145 MHz with increasing concentration of 2D electrons n _s = (1.6-6.6) × 10[su11] cm^-2. The dependence f_3dB ≈ n _s ^- 0.04±is observed in the studied concentration range; this dependence is determined by electron scattering by the deformation potential of acoustic phonons and piezoelectric scattering.     

Quantum chemical study of the (Z)-2-penten-1-ol (HOCH2–CH = CHCH2CH3) + OH + O2 reactions

ABSTRACT

The mechanism and products of the reaction of (Z)-2-penten-1-ol [(Z)-PO21] with OH radical in the presence of O₂ have been elucidated by using high-level quantum chemical methods CCSD(T)/6-311+G(d,p)//BH&;HLYP/6-311++G(d,p). The calculations clearly indicate that addition channels contribute maximum to the total reaction and H-abstraction channels can be neglected at temperatures of 220–500 K. The rate constant for the reaction of OH radical with (Z)-PO21 at 298 K is computed to be 1.22 × 10^?10 cm³ molecule^?1 s^?1, which is in stronger agreement with the previously reported experimental values. The kinetic data obtained over the temperature range 220?500 K are used to derive an non-Arrhenius expression: k = 3.69 × 10^?13 × exp(1763.7/T) cm³ molecule^?1 s^?1. For the reaction of (Z)-PO21with OH radical in the presence of O₂, the major primary reaction products found in this study are propanal [CH₃CH₂C(O)H] and glycolaldehyde [HOCH₂C(O)H], whereas formaldehyde [HC(O)H], 2-hydroxybutanal [CH₃CH₂CH(OH)C(O)H] and the epoxide P18 are anticipated to be minor products. The calculated results are consistent with the recent experimental observations.     

The gas phase oxidation of HCOOH by Cl and NH2 radicals. Proton coupled electron transfer versus hydrogen atom transfer*

ABSTRACT

The reaction of formic acid (HCOOH) with chlorine atom and amidogen radical (NH₂) have been investigated using high level theoretical methods such BH&HLYP, MP2, QCISD, and CCSD(T) with the 6–311?+?G(2df,2p), aug-cc-pVTZ, aug-cc-pVQZ and extrapolation to CBS basis sets. The abstraction of the acidic and formyl hydrogen atoms of the acid by the two radicals has been considered, and the different reactions proceed either by a proton coupled electron transfer (pcet) and hydrogen atom transfer (hat) mechanisms. Our calculated rate constant at 298?K for the reaction with Cl is 1.14?×?10^?13?cm³?molecule^?1?s^?1 in good agreement with the experimental value 1.8?±?0.12/2.0?×?10^?13?cm³?molecule^?1?s^?1 and the reaction proceeds exclusively by abstraction of the formyl hydrogen atom, via hat mechanism, producing HOCO+ClH. The calculated rate constant, at 298?K, for the reaction with NH₂ is 1.71?×?10^?15?cm³?molecule^?1?s^?1, and the reaction goes through the abstraction of the acidic hydrogen atom, via a pcet mechanism, leading to the formation of HCOO+NH₃.     

NEW AUTOIONIZING STATES NEAR THE FIRST IONIZATION LIMIT OF RARE EARTH ELEMENT Dy

This paper describes the investigation of autoionizing states near the first ionization limit of rare-earth element Dy. The 62, 51, 97 and 25 new autoionizing states resulting from the states of 4f¹⁰(⁵I₈)6s6p(³P⁰₂)³I⁰₇, 4f⁹ (⁶H⁰)5d²(³F)(⁸G⁰)6s⁹G⁰₇, 4f⁹(⁶F⁰)5d6s^{2 7}H⁰₇ and 4f⁹5d6s^{2 7}K⁰₇, respectively, were found by using a laser resonance ionization time-of-flight mass spectrometer (LRI-TOFMS), The photoionization efficiencies for different channels were compared with each other. In addition, the Shore-Fano parameters of autoionizing states were determined by a nonlinear fitting program.     

Finestructure, hyperfine structure and isotope shift of 4f 6s7s in Er I

The isotope shift (IS) and hyperfine structure (hfs) of nine levels (31720 to 38921 cm^-1) assigned to the configuration 4 f ¹² 6 s 7 s in neutral erbium have been determined experimentally using Doppler-reduced saturation absorption spectroscopy in a gas discharge. We performed a fine structure analysis in the SL-coupling scheme of the single configuration 4 f ¹² 6 s 7 s, confirming and extending the classification of even parity Er I levels. We discriminated the different hfs contributions of the 4f¹² core and the (6 s +7 s) outer electrons of the shell in a non-relativistic JJ-coupling approach and in the relativistic effective tensor operator formalism in SL-coupling. The relativistic one-electron parameters of the hfs for ¹⁶⁷Er were fitted to the experimental data by a least squares fit procedure: [0pt] a ⁰¹ _4f =-147(3) MHz, [0pt] a ¹⁰ _6s + a ¹⁰ _7s =-1840(30) MHz, [0pt] b ⁰² _4f =6560(80) MHz. The level dependencies of the isotope shift were evaluated based on crossed second order (CSO) effects. We obtained the following results for the CSO parameters for the isotope pairs ^170-168Er: d _6s7s =-740(30) MHz, z _4f = 0(5) MHz, ( g _3,6s ( f , 6 s )+ g _{3, 7s} ( f , 7 s ))= -24(15) MHz and for ^170-166Er: d _6s7s =-1500(50) MHz, z _4f =0(10) MHz, ( g _3,6s ( f ,6 s )+ g _3,7s ( f +7 s ))=-50(29) MHz. The resulting parameters for the hfs are compared with those known for other configurations of the Er atom and ion. Received 16 May 1999 and Received in final form 31 January 2000     

Cover Picture: Contrib. Plasma Phys. 10/2014

Spatio‐temporal evolution of electron density at 6 microseconds under f = 20 kHz, ε_r = 9.0, RC = 5.0 × 10^–6 cm³ s^–1 and V_appl = 1.7 kV with 50 ppm N₂ impurities in He‐N₂ gas. (Figure 3e of the paper by M.M. Iqbal and M.M. Turner)     

Extreme ultraviolet and soft x-ray laser emission from Ni-like Nd ions

We use the energy levels, transition probabilities, and effective collision strengths for the states 1s² 2s² 2p⁶ 3s² 3p⁶ 3d¹⁰ and 1s² 2s² 2p⁶ 3s² 3p⁶ 3d⁹ 4 l (l = s, p, d, and f) of a nickel-like Nd ion to determine reduced population for 55 fine-structure levels over a wide range of electron density values (from 10²⁰ to 4 · 10²² cm ⁻³) at various electron plasma temperatures in the range of 1–2 keV. We find the gain coefficients for those transitions with the positive population inversion factor and show their dependences on the electron density.     

Autoionization cross section of lithium atoms excited by electron impact

We measure the full autoionization cross section of lithium atoms excited by electrons in the energy range from the first autoionization threshold at 56.39 to 600 eV. Data are obtained by determining the total intensity of electron spectrum of autoionization states 1sn ₁ l ₁ n ₂ l ₂ detected at the “magic” observation angle of 54.7°. The cross section behavior is characterized by a sharp increase to a maximum value of 1.7 × 10⁻¹⁸ cm² in the energy interval of 56.4–60 eV and a subsequent monotonic drop to a value of 10⁻¹⁸ cm² at 600 eV. We have discovered a “thin” cross section structure that reflects the presence of strong resonances of Li⁻ ions in the near-threshold area of excitation of the lowest energy autoionization states (1s2s2)2S, (1s2s2p)⁴ P, 1s(2s2p ³ P)² P), and 1s(2s2p ¹ P)² P. We have established that the contribution of autoionization to the absolute cross section of single ionization of lithium atoms does not exceed 4%. We perform a comparative analysis of the data with analogous data for potassium and cesium atoms.     

Cover Picture: Contrib. Plasma Phys. 9/2014

Spatio‐temporal evolution of electron density at 6 microseconds under f = 20 kHz, ε_r = 9.0, RC = 5.0 × 10^–6 cm³ s^–1 and V_appl = 1.7 kV with 50 ppm N₂ impurities in He‐N₂ gas. (Figure 3e of the paper by M.M. Iqbal and M.M. Turner)     

Collisional-radiative model for non-Maxwellian inductively coupled argon plasmas using detailed fine-structure relativistic distorted-wave cross sections

Our recently developed collisional-radiative model which included fine-structure cross sections calculated with a fully relativistic distorted-wave method [R.K. Gangwar, L. Sharma, R. Srivastava, A.D. Stauffer, J. Appl. Phys. 111, 053307 (2012)] has been extended to study non-Maxwellian inductively coupled argon plasmas. We have added more processes to our earlier collisional-radiative model by further incorporating relativistic distorted-wave electron impact cross sections from the 3p ⁵4sJ = 0, 2 metastable states, (1s ₃, 1s ₅ in Paschen’s notation) to the 3p ⁵5p (3p _i ) excited states. The population of various excited levels at different pressures in the range of 1–25 mTorr for an inductively coupled argon plasma have been calculated and compared with the recent optical absorption spectroscopy measurements as well as emission model results of Boffard et al. [Plasma Sources Sci. Technol. 19, 065001 (2010)]. We have also calculated the intensities of two emission lines, 420.1 nm (3p ₉ → 1s ₅) and 419.8 nm (3p ₅ → 1s ₄) and compared with measured intensities reported by Boffard et al. [J. Phys. D 45, 045201 (2012)]. Our results are in good agreement with the measurements.     

Atomic 6p-Tl0 centers in ferroelectric Rb2ZnCl4 crystals

Abstract

Several Tl⁰ (6s²6p ¹)-type paramagnetic centers, produced by low temperature X-ray irradiation, were observed and studied by electron spin resonance (ESR) in the orthorhombic ferroelectric phase of thallium doped Rb₂ZnCl₄ crystals. The centers were formed by electron trapping at Tl⁺ ions localized substitutionally at Rb⁺ sites. The number and properties of the observed centers account for the tripling of the unit cell in the ferroelectric phase.     

Characterization of organic–inorganic hybrid layered perovskite and intercalated compound (n-C12H25NH3)2ZnCl4

We report on some electrical properties and solid–solid phase transitions of organic–inorganic hybrid layered halide perovskite and intercalated compound (n-C₁₂H₂₅NH₃)₂ZnCl₄ which is one member of the long-chain compounds of the series (n-C_nH_2n+1NH₃)_2,(n = 8–18). The complex dielectric permittivity ?*(ω,T) and the ac conductivity σ (ω,T) were measured as functions of temperature 100 K < T < 390 K and frequency 5 kHz < f < 100 kHz. Moreover, the differential scanning calorimetery and the differential thermal analysis thermograms were performed. The analysis of our data confirms the existence of a structural phase transition at T ≈ (362?±?2) K, where the compound changes its state from intercalation to non-intercalation with a drastic increase in the c-axis by about 16.4%.

The behavior of the frequency-dependent conductivity follows the Jonscher universal power law: σ (ω, T) α?^s(?,T). The mechanism of electrical conduction in the low-temperature phase (phase II) can be described as quantum mechanical tunneling model.