Energy transfer in Li6Gd(BO3)3

The synthesis and structure of the new one-dimensional material Li₆Gd(BO₃)₃ are described. The Gd³⁺ fluorescence is studied from 300 to 1.5 K after selective pulsed excitation into the ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ manifold. Above 40 K the fluorescence decays indicate fast diffusion of the energy among intrinsic and perturbed Gd³⁺ ions, and trapping by impurities. Below 40 K the energy transfer takes place dominantly towards perturbed Gd³⁺ ions and is diffusion limited. This behaviour is discussed in relation with the quasi one-dimensional crystal structure.     

A study of valency changes of vanadium ions in Al2O3 by γ irradiation

The effect of γ irradiation at 300 K on the concentrations of vanadium ions V³⁺, V⁴⁺ and V²⁺ in Al₂O₃ has been studied quantitatively, using three techniques: optical absorption (V³⁺), low temperature thermal conductivity measurements (V⁴⁺) and EPR (V²⁺). Several single crystals of Al₂O₃ doped with vanadium in a large range of concentration $\text{(2.8 × 10}{}^{18}\text{? 1.3 × 10}{}^{20}\text{at.}\text{cm}{}^3\text{)}$ have been measured. The evolution of the respective concentrations by γ irradiation as a function of the total vanadium content C is quite different in the two regions $\text{C< 1.2 × 10}{}^{19}\text{at.}\text{cm}{}^3$ and C larger than this value. A consistent analysis of the results has nevertheless been achieved, leading to the determination of the absolute concentrations of the three ions in the as-received and γ irradiated states for all samples with $\text{C<4.2 × 10}{}^{19}\text{at.}\text{cm}{}^3$ (room temperature annealing is observed above this value). The concentrations of V⁴⁺ and V²⁺ ions are always small, but V⁴⁺ ions are more stable: they are present in the as-received state at a level of 1% of the total concentration and a maximum value of $\text{/}\text{?}\text{2.3 × 10}{}^{18}\text{at.}\text{cm}{}^3$ is observed in the γ irradiated state; on the other hand there are less than 4.7 × 10¹⁵V²⁺ ions per cm³ in the as-received state and the maximum value is only $\text{4.2 × 10}{}^{17}\text{at.}\text{cm}{}^3$. Charge transfer between V ions only is not sufficient to explain the experimental results and other defects must be involved in the γ irradiation effect.     

Transverse spin correlation function of the one-dimensional spin-12 XY model

The transverse spin pair correlation function p^x_n=<S^x_mS^x_m+n>=<S^x_mS^x_m+n> is calculated exactly in the thermodynamic limit of the system described by the one-dimensional, isotropic, spin-$\text{1}\text{2}$, XY Hamiltonian

$\text{H=?2J}\text{∑}\text{l=1}\text{N}\text{(S}{}^{\mathrm{x}}{}_{\mathrm{l}}\text{S}{}^{\mathrm{x}}{}_{\mathrm{l+1}}\text{+S}{}^{\mathrm{y}}{}_{\mathrm{l}}\text{S}{}^{\mathrm{y}}{}_{\mathrm{l+1}}\text{)}$

. It is found that at absolute zero temperature (T = 0), the correlation function ρ^x_n for n ≥ 0 is given by

$\text{ρ}{}^{\mathrm{x}}{}_{\mathrm{2p}}\text{=}\text{1}\text{4}\text{2}\text{π}{}^{\mathrm{2p}}\text{Π}\text{j=1}\text{p?1}\text{4j}{}^2\text{4j}{}^2\text{?1}{}^{\mathrm{2p?2j}}\text{if}\text{n=2p}$

,

$\text{ρ}{}^{\mathrm{x}}{}_{\mathrm{2p+1}}\text{=±}\text{1}\text{4}\text{2}\text{π}{}^{\mathrm{2p+1}}\text{Π}\text{j=1}\text{p}\text{4j}{}^2\text{4j}{}^2\text{?1}{}^{\mathrm{2p+2j}}\text{if}\text{n=2p+1}$

, where the plus sign applies when J is positive and the minus sign applies when J is negative. From these the asymptotic behavior as n → ∞ of |?^x_n| at T = 0 is derived to be $\text{|ρ}{}^{\mathrm{x}}{}_{\mathrm{n}}\text{| ～}\text{a}\text{n}$ with a = 0.147088?. For finite temperatures, ρ^x_n is calculated numerically. By using the results for ?^x_n, the transverse inverse correlation length and the wavenumber dependent transverse spin pair correlation function are also calculated exactly.     

Effects of defects on the quantum efficiency of Eu2+ -doped aluminates with the magnetoplumbite-type crystal structure

The luminescence of SrAl₁₂O₁₉ : Eu²⁺ phosphors can be quenched by substitution of a small amount of Mg for Al, or by preparing samples with excess Al₂O₃. It is most probable that oxygen vacancies near the Eu²⁺ activator ions act as the radiationless sinks of the excitation energy. In CaAl₁₂O₁₉ : Eu²⁺ the quenching of the luminescence by the introduction of defects is much less effective, so that less oxygen vacancies are supposed to be formed. In view of the fact that the stability of CaAl₁₂O₁₉, with respect to less oxygen containing phases, is higher than that of SrAl₁₂O₁₉, this is a reasonable assumption. The homogeneity range of $\text{La}{}_{\mathrm{1?x}}\text{Al}{}_{\mathrm{<mtext>11</mtext><mtext>2</mtext><mtext>3\; +\; x</mtext>}}\text{O}{}_{19}\text{: Eu}{}^{\mathrm{2+}}$ is at such values of x that a large number of Al vacancies exist. Quenching of its luminescence by the introduction of oxygen vacancies was not observed. In LaMgAl₁₁O₁₉ : Eu²⁺ phosphors Al³⁺ interstitials rather than oxygen defects seem to play a dominate role in achieving charge neutrality.     

Ni2+ emission in MgO,KMgF3, KZnF3 and MgF2

The emission of Ni²⁺ ions in MgO, KMgF₃, KZnF₃ and MgF₂ crystals has been investigated. The fine structure on the bands at about 20 000 cm^-1 and 13 000 cm^-1 has been studied in detail and from this and the excitation spectra these bands are assigned to ${}^1\text{T}{}_{\mathrm{2g}}\text{→}{}^3\text{A}{}_{\mathrm{2g}}$ and ${}^1\text{T}{}_{\mathrm{2g}}\text{→}{}^3\text{T}{}_{\mathrm{2g}}$ transitions respectively.     

A j-forbidden isomeric transition in 204At

An isomeric 587.3 keV transition was investigated using several target-ion combinations: ¹⁹⁷Au+¹²C, ¹⁹³Ir+¹⁶O and ¹⁹⁶Pt+¹⁵N. From the measured excitation functions for the ${}^{193}\text{Ir}\text{(}{}^{16}\text{O, x}\text{n}\text{)}{}^{\mathrm{<mtext>209–</mtext><mtext>x</mtext>}}$ At reaction it follows that this transition belongs to ²⁰⁴At. The isomeric level is ascribed to the 10^? state of the configuration π(h_{$\text{9}\text{2}$})³_{$\text{9}\text{2}$}ν(i_{$\text{13}\text{2}$})^?1.     

Etude d'un groupement (Ru3O12)13− en presence de degenerescence orbitale et de couplage spin-orbite

A trinuclear cluster (Ru₃O₁₂)^13? occurs in the Ba₄NbRu₃O₁₂, and Ba₄TaRu₃O₁₂ compounds where the oxydation states of ruthénium are +III and +IV. The exchange interaction between magnetic sites is described by a Hamiltonian, which takes account of the orbital degeneracy of the ${}^2\text{T}{}_{\mathrm{<mtext>2</mtext><mtext>g</mtext>}}\text{(}\text{Ru}{}^{\mathrm{3+}}\text{)}\text{and}{}^3\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>g</mtext>}}\text{(}\text{Ru}{}^{\mathrm{4+}}\text{)}$ terms. For these ions, the spin-orbit coupling is the dominant effect and it appears that the low temperature magnetic susceptibility depends essentially on the orbital reduction factor and the distortion of the coordination octahedra. There is apparently no first order perturbation of the ground state due to the interaction between magnetic ions.     

Multiphonon relaxation rate from pumped level to upper laser level in YAG:Nd

The rise time of the near-infrared fluorescence intensity has been measured in YAG:Nd³⁺ at room temperature under the excitation by 10 ns duration pulses at 514.5 nm using a time-correlated single photon counting method. The result reveals that the relaxation rate from the pumped level (${}^2\text{K}{}_{\mathrm{<mtext>13</mtext><mtext>2</mtext>}}$ + ${}^2\text{G}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ + ${}^4\text{G}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}\text{)}$ to the upper level laser level $\text{(}{}^4\text{F}{}_{\mathrm{<mtext>sol3</mtext><mtext>2</mtext>}}\text{)}$ is larger than 10⁸s^?1, which is in contrast with the previously reported values of (1.6 ～ 2) × 10⁶s^?1. An experiment to search for the visible emission in YAG:Nd³⁺ gives support to the present value.     

The γ-decay of the g92 analogue state in 59Cu

An investigation of the γ-decay of the $\text{1}\text{g}{}_{\mathrm{<mtext>9</mtext><mtext>2</mtext>}}$ analogue state in ⁵⁹Cu has been performed using the ⁵⁸Ni(p, γ)⁵⁹Cu reaction. The (p, γ) excitation function has been taken in the range E_p = 3450–3650 keV. The decay schemes of the (p, γ) resonances at E_p = 3483, 3532 and 3547 keV, measured with Ge(Li) detectors, lead to eight new levels in ⁵⁹Cu with excitation energies between 1.8 and 4.7 MeV and to spin assignments of several states. The spins of the first two resonances are found to be ($\text{1}\text{2}$, $\text{3}\text{2}$) and ($\text{5}\text{2}$). The spin of the E_p = 3547 keV resonan is, from angular distributions, uniquely determined to be $\text{J}{}^{\mathrm{\pi }}\text{=}\text{9}\text{2}{}^{\mathrm{+}}$ and this state is found to be the unfragmented analogue state of the $\text{E}{}^1\text{= 3.062}\text{MeV}$, $\text{J}{}^{\mathrm{\pi }}\text{=}\text{9}\text{2}{}^{\mathrm{+}}$ parent state in ⁵⁹Ni. The measured complete decay scheme of this resonance shows that its isovector M1 decay is in disagreement with all existing theoretical predictions.     

Dye laser site selection spectroscopy on U6+ luminescent molecular centers in LiF-U3O8 crystals

The polarized excitation and emission spectra of the U⁶⁺ molecular centers giving the most intense emission lines at 18 940 cm^?1 and 19 285 cm^?1 are presented and analyzed in detáil. From the polarization experiments, it is shown that the symmetry of the centers is C_4v and that the symmetries of the observed electronic states are Γ₂, Γ₁ and Γ₅. Finally, an electronic model is proposed which associates the emission and excitation lines of the U⁶⁺ centers in the visible region to transitions between the fundamental state $\text{Γ}{}_1\text{(6p}{}^6\text{,}{}^1\text{S)}$ and the states of the excited configuration $\text{6p}{}^5\text{(}{}^2\text{P}\text{3}\text{2}\text{) 7s}$.     

Absorption spectra of Ni2+ in (NH4)2Mg(SO4)2·6H2O and Co2+ in Na2Zn(SO4)2·4H2O

Optical absorption spectra of Ni²⁺ in (NH₄)₂Mg(SO₄)₂·6H₂O and Co²⁺ in Na₂Zn(SO₄)₂·4H₂O single crystals have been studied at room and liquid nitrogen temperatures. From the nature and position of the observed bands, a successful interpretation could be made assuming octahedral symmetry for both the ions in the crystals. The splitting observed for ${}^3\text{T}{}_{\mathrm{1g}}\text{(F)}$ band in Ni²⁺ and ${}^4\text{T}{}_{\mathrm{2g}}\text{(F)}$ band in Co²⁺ at liquid nitrogen temperature have been explained as due to spin-orbit interaction. The extra band observed at 16,325 cm^-1 in the case of Ni²⁺ at low temperature has been interpreted to be the superposition of vibrational mode of SO^2-₄ radical on ${}^3\text{T}{}_{\mathrm{1g}}\text{(F)}$ band. The observed band positions in both the crystals have been fitted with four parameters B, C, Dq and ζ.     

The mechanism of 5D3−5D4 cross-relaxation in Y3Al5O12: Tb3+

The ${}^5\text{D}{}_3\text{?}{}^5\text{D}{}_3$ cross-relaxation of YAG:Tb³⁺ has investigated by analysis of the ⁵D₃ decay curve as a function of Tb³⁺ concentration. This technique is a more sensitive test of the mechanism than relative intensity measurements alone. It is shown that the relaxation is predominantly dipole-dipole in character (R₀ ～ 1.3nm), and insensitive to temperature. The population of the ⁵D₄ state following high energy excitation occurs almost entirely via cross-relaxation from the ⁵D₃ state.     

The decay process 11ΛB → π− + 11C

The branching ratios are calculated for ¹¹_ΛB decay to the ¹¹C ground and excited states below 8 MeV for two possible spin values of ¹¹_ΛB. It is found that the decay rate to the ¹¹C^★ state at E^★ = 6.48 MeV is comparable in magnitude to that leading to the ¹¹C ground state if $\text{J(}{}^{11}{}_{\mathrm{\Lambda }}\text{B}\text{) =}\text{5}\text{2}$ is assumed. This result, unlike the branching ratios calculated for the $\text{J(}{}^{11}{}_{\mathrm{\Lambda }}\text{B}\text{) =}\text{7}\text{2}$ case, is in accord with experiment and lends support to the assumption that $\text{J =}\text{5}\text{2}$ holds for ¹¹_ΛB. The necessity of the reinterpretation of some of the so-called ¹³_ΛC events in terms of ${}^{11}{}_{\mathrm{\Lambda }}\text{B}\text{→ π}{}^{\mathrm{?}}\text{+}{}^{11}\text{C}{}^1$ is indicated.     

Electric dipole transition cross sections and effective site symmetry of Eu3+ in pseudocentric K5Eu(MoO4)4

The fluorescence and absorption spectra of Eu³⁺ in K₅Eu(MoO₄)₄ have been measured at 300 K and 77 K. The fluorescence lifetime of the ⁵D₀ state is 1.4 ms at 300 K. The largest cross section $\text{σ(}{}^5\text{D}{}_0\text{→}{}^7\text{F}{}_2\text{(4)) = 1.3 × 10}{}^{\mathrm{?21}}\text{cm}{}^2$ and the removal of degeneracies require to replace the nearest neighbour D_3d symmetry of Eu³⁺ by the effective symmetries C₁, C₂ and C_s of the whole unit cell. It is shown that C₁ dominates because of the statistical distribution of K⁺ and Eu³⁺. The corresponding inhomogeneous broadening is observed at 77 K.     

In-beam γ-ray studies of complex band structures and of isomeric states in 152, 153Dy nuclei

The high-spin level structures of ¹⁵²Dy and ¹⁵³Dy were studied experimentally with ^{154, 155}Gd(α xnγ) in-beam reactions, and for ¹⁵²Dy also with ${}^{\mathrm{144,\; 146}}\text{Nd}\text{(}{}^{12}\text{C, x}\text{n}\text{γ)}$ reactions. The experiments included measurements of singles γ-ray and conversion-electron spectra, γ-ray angular distributions and E_γ-t and E_γ-E_γ-t coincidences. A multiplicity filter set-up was used to study the feeding and decay of isomeric states in ¹⁵²Dy. In ¹⁵²Dy about twenty so far unknown levels were found, including two high-spin isomeric states with $\text{T}{}_{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}\text{≈ 60}\text{and}\text{≈ 13}\text{ns}$ at excitation energies E_x ≈ 5.04 and 6.08 MeV, respectively. These states are compared with recent calculations on yrast traps. The level scheme of ¹⁵³Dy contains 28 levels up to E_x = 4.1 MeV and $\text{J}{}^{\mathrm{\pi }}\text{= (}\text{37}\text{2}{}^{\mathrm{+}}\text{)}$. Band structures in both nuclei are discussed in comparison with other N = 86 and N = 87 isotones.     

Study of particle and γ decays of the Ex = 12.00 MeV 63+ level in 24Mg

Direct coincidence observation of α- and γ-decays of the E_x = 12.0 MeV level populated in the ${}^{12}\text{C}\text{(}{}^{16}\text{O}\text{, α)}{}^{24}\text{Mg}$ reaction has been used to show that both 6⁺ and 3^? levels exist near this excitation energy. Comparison of the present work with previous radiative capture studies permits the conclusion that the 6₃⁺ level in ²⁴Mg decays primarily by γ-emission, in agreement with recent shell-model calculations using an (sd)⁸ basis. Absolute E2 and M1 strengths deduced from the data are not, however, in good quantitative agreement with the predictions of the shell model.     

The dipole moment of thioformaldehyde in its singlet and triplet π1 − n excited states

Laser-induced fluorescence excitation has been used to measure Stark splittings of selected lines in the $\text{A}\text{?}{}^1\text{A}{}_2\text{-}\text{X}\text{?}{}^1\text{A}{}_1$ and $\text{a}\text{?}{}^3\text{A}{}_2\text{-}\text{X}\text{?}{}^1\text{A}{}_2$ band systems of H₂CS in electric fields up to 13 kV/cm. The derived excited state a-axis dipole moments are 0.820 ± 0.007 D for the 4¹ level of the ¹A₂ state; 0.838 ± 0.008 D for the zeroth vibrational level of ¹A₂; and 0.534 ± 0.015 D for the zeroth vibrational level of the ³A₂ state. These results are compared with the corresponding values of H₂CO, and interpreted in terms of the changing localization of the π and $\text{π}{}^1$ orbitals accompanying electronic excitation.     

Proton particle states in the region around 13250Sn82

The decay of ¹³³Sn leading to levels in ¹³³₅₁Sb₈₂, which has one proton outside the closed shell, has been observed at the OSIRIS isotope separator on-line facility. The half-life is 1.47±0.04 sec and the $\text{d}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$. level is found at an excitation of 963 keV. The decay of $\text{18±1}\text{sec}{}^{135}\text{Te}$ to one-particle and three-particle levels in ^135₅₃I₈₂ has also been studied.     

Mise en évidence d'un échange électronique entre Fe2+ ET Fe3+ dans les oxydes rhomboédriques AFe2O4 par spectroscopie mossbauer DU57Fe

The ABB'O₄ rhomboedral oxides containing exclusively either Fe²⁺(InFeGe_0,5Zn_0,5O₄) or Fe³⁺(LuMg-FeO₄ and LuMnFeO₄) are investigated with Mössbauer spectroscopy, in their paramagnetic state.A similar study is made on two mixed oxides containing iron under its two oxidation states, with the $\text{Fe}{}^{\mathrm{2+}}\text{Fe}{}^{\mathrm{3+}}\text{= 2}$ and 1 (InFe_1,5Ga_0,5O₄ and InFe₂O₄) atomic ratio.Comparing the results, we have come to the conclusion that a fast electronic exchange between Fe²⁺ and Fe³⁺ takes place at room temperature. In this structure, point Fe²⁺ and Fe³⁺ are distributed on the same crystallographic site with the point symmetry C_3v. We show that neighbouring effects lower this local symmetry.     

Spin-parity assignments to high-spin states of 41K and 41Ca

Yrast states of ⁴¹K and ⁴¹Ca have been investigated with the ²⁶Mg(¹⁸O, p2nγ)⁴¹K and ²⁶Mg(¹⁸O, 3nγ)⁴¹Ca reactions at a beam energy of 34 MeV. Gamma-gamma coincidence, γ-ray angular distribution and linear polarization measurements were performed with a Ge(Li)-NaI(Tl) Compton suppression spectrometer and a three-crystal Ge(Li) Compton polarimeter. Unambiguous spin-parity assignments of $\text{J}{}^{\mathrm{\pi }}\text{=}\text{7}\text{2}{}^{\mathrm{+}}$, $\text{11}\text{2}{}^{\mathrm{+}}$, $\text{11}\text{2}{}^{\mathrm{?}}$, $\text{13}\text{2}{}^{\mathrm{+}}$, $\text{15}\text{2}{}^{\mathrm{?}}$ and $\text{19}\text{2}{}^{\mathrm{?}}$ to the ⁴¹K levels at E_x = 1.68, 2.53, 2.76, 2.77, 4.27 and 4.98 MeV and of $\text{9}\text{2}{}^{\mathrm{+}}\text{,}\text{11}\text{2}{}^{\mathrm{+}}\text{and}\text{15}\text{2}{}^{\mathrm{+}}$to the ⁴¹Ca levels at E_x = 3.20, 3.37 and 3.83 MeV, respectively, have been obtained. Excitation energies, branching ratios, multipole mixing ratios and transition strengths are reported. The main features of the ⁴¹K and ⁴¹Ca level and decay schemes are reproduced in a 2p-1h and 3p-2h shell-model calculation.