O<Subscript>2</Subscript> photodesorption from AuO<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> and Au<Subscript>2</Subscript>O<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack>

Using time-resolved photoelectron spectroscopy, the decay channels of AuO₂⁻ and Au₂O₂⁻ following photoexcitation with 3.1-eV photons have been studied. For AuO₂⁻, a state with a rather long lifetime of 30 ps has been identified. Its decay path could not be determined but photodesorption can be excluded. For Au₂O₂⁻, the spectra indicate O₂ desorption after 3.1-eV photoexcitation on a time scale of 1 ps. While comparing these results on Au _n O₂⁻ with analogous data on Ag _n O₂⁻ clusters, a discernible pattern emerges: for dissociatively bound O₂(AuO₂⁻, Ag₃O₂⁻), there are long-living excited states which do not decay by oxygen desorption, while for molecular chemisorption (Au₂O₂⁻, Ag₂O₂⁻, Ag₄O₂⁻, Ag₈O₂⁻), the 3.1-eV photoexcitation triggers fast O₂ desorption with a high quantum yield.     

Potential energy of <Superscript>∞</Superscript>H<Stack><Subscript>2</Subscript><Superscript>-</Superscript></Stack>(<Superscript>2</Superscript>∑<Stack><Subscript>u</Subscript><Superscript>+</Superscript></Stack> in the bound-state region

An accurate calculation of the lowest negative electronic state of H ₂ ^- (fixed nuclei) is reported using the CCSD(T) method and doubly augmented cc-pv5z basis set. Comparison has been made with the reference data by Senekowitsch et al. [Chem. Phys. Lett. 111 (1984) 211]. Owing to larger size of the basisset and inclusion of triple excitations, no vertical shift in this work is necessary to reproduce the asymptotics of H + H ^-. In addition, the effect of basis-set truncation is estimated, based on the complete-basis-set extrapolation method. The contribution of correlated electron-proton motion to the electron-energy curve for H₂ ^– dynamics is pointed out.Dedicated to Prof. Jií Horáek on the occasion of his 60th birthday.     

<Superscript>10</Superscript>B–<Superscript>11</Superscript>B isotope substitution and superconductivity in ZrB<Subscript>12</Subscript>

The specific heat of the ZrB₁₂ compound in the normal and superconducting states (T _C ≈ 6 K) has been studied in the 1.9–7 K temperature range for high-quality single crystals with different relative contents of boron isotopes. For Zr¹⁰B₁₂, Zr^natB₁₂, and Zr¹¹B₁₂ dodecaborides, the electron density of states and the electronphonon coupling constant, λ_e-ph ∼ 0.4, are found. The dependence of the thermodynamic and upper critical fields, as well as of the Ginzburg-Landau parameter (κ = 0.8–1.14) on temperature and isotope composition is determined. The results suggest the existence of the magnetic field induced phase transition at T* = 4–5 K, which is not related to the transition from type-I to type-II superconductivity. The possibilities of the existence of two-gap superconductivity and a structural phase transition at T* in zirconium dodecaboride are discussed.     

Visualization of 2-μm radiation by BiF<Subscript>3</Subscript>:Ho<Superscript>3+</Superscript> and BiF<Subscript>3</Subscript>:Ho<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> ceramics

A series of ceramic samples of the compositions BiF₃:1%Ho³⁺, BiF₃:4%Ho³⁺, BiF₃:1%Ho³⁺ + 1%Yb³⁺, and BiF₃:1%Ho³⁺ + 3%Yb³⁺ is synthesized and the conversion of Tm:YLF laser radiation (λ = 1908 nm) is studied. The luminescence spectra exhibit bands in the regions of 490, 545, and 650 nm. The kinetic measurements of the afterglow of the green and red bands show that the population of the ⁵S₂ and ⁵F₄ states in the BiF₃:1%Ho³⁺ samples occurs due to successive absorption of excitation photons, while the ⁵F₅ level of Ho³⁺ is populated due to the ion–ion interaction. Codoping with Yb³⁺ leads to a decrease in the visualization threshold power density to 2 W/cm².     

Photoluminescence of sol–gel-derived Y<Subscript>2</Subscript>O<Subscript>3</Subscript>:Eu<Superscript>3+</Superscript> thin-film phosphors with Mg<Superscript>2+</Superscript> and Al<Superscript>3+</Superscript> co-doping

Red-light-emitting Y₂O₃:Eu³⁺ thin-film phosphors were synthesized using a sol–gel process. The effect of Mg²⁺ and Al³⁺ co-dopants on the Y₂O₃:Eu³⁺ thin-film phosphor photoluminescence (PL) property was investigated. At a certain concentration, both Mg²⁺ and Al³⁺ co-dopants were found to further enhance the PL emission intensity of Y₂O₃:Eu³⁺ thin-film phosphors. The optimum PL emission intensity was observed in Y₂O₃:12%Eu³⁺, 7%Mg²⁺ and Y₂O₃:12%Eu³⁺, 2%Al³⁺ phosphor films. From our results, the enhancement of the emission intensity by the Mg²⁺ and Al³⁺ co-dopants is explained in terms of the creation of defect states near the Y(4d+5s) conduction band, which overlap with the Eu³⁺ charge-transfer state (CTS). The overlapping leads to CTS broadening and consequently induces higher absorption and hence an increase of the emission intensity. From X-ray diffraction results, we have found that there is no additional phase formed in the co-doped phosphor films. PACS 68.55.Ln; 78.55.-m; 81.20.Fw     

Hyperfine Interactions in Pb<Superscript>3+</Superscript>F<Stack><Subscript>8</Subscript><Superscript>−</Superscript></Stack>F<Stack><Subscript>a</Subscript><Superscript>−</Superscript></Stack> clusters in fluorite crystals

The parameters of hyperfine interactions in Pb³⁺F ₈ ^? F _a ^? tetragonal clusters of MeF₂ crystals (Me=Ca, Sr, Ba) are interpreted. The contributions of the spin polarization to the parameters of the proper hyperfine interaction and additional (ligand) hyperfine interactions are calculated in the approximation of weak binding between a charge-compensating ion F _a ^? and a cubic fragment in the tetragonal cluster. It is demonstrated that correct inclusion of the contributions from the spin polarization to the ligand isotropic hyperfine interaction for the F _a ^? ion leads to anomalously large parameters of this interaction for MeF₂ crystals. These results are in agreement with experimental data.     

“Alpha decays” of <Stack><Subscript>Λ</Subscript><Superscript>10</Superscript></Stack>Be and <Stack><Subscript>Λ</Subscript><Superscript>10</Superscript></Stack>B hypernuclei: Phenomenological analysis and role of nuclear structure

Hypernuclei are used to study the baryon-baryon weak interaction and associated effective weak Hamiltonian. We will show how the proper choice of hypernucleus can be used to pick out components of the effective weak Hamiltonian. It is well known that removing one nucleon from ⁹Be or ⁹B results in ⁸Be* with a subsequent αα decay. Through this unique process, it would be possible to identify final states of the residual nucleus. So, due to these specific properties of the core nuclei ⁹Be and ⁹B, it may be possible to measure the branching fractions Γ _ααi ^n(p) for the exclusive decays of the _Λ ¹⁰ Be ( _Λ ¹⁰ B) hypernuclei.     

Analysis of the vector form factors f<Superscript>+</Superscript><Subscript>Kπ</Subscript>(Q<Superscript>2</Superscript>) and f<Superscript>-</Superscript><Subscript>Kπ</Subscript>(Q<Superscript>2</Superscript>) with light-cone QCD sum rules

In this article, we calculate the vector form factors f⁺ _Kπ(Q²) and f^- _Kπ(Q²) within the framework of the light-cone QCD sum rule approach. The numerical values of f⁺ _Kπ(Q²) are compatible with existing theoretical calculations, and the central value of f⁺ _Kπ(0) (f⁺ _Kπ(0)=0.97) is in excellent agreement with the values from chiral perturbation theory and lattice QCD. The values of |f^- _Kπ(0)| are very large compared to the theoretical calculations and experimental data, and they cannot give any reliable prediction. At large momentum transfer with Q² > 5 GeV², the form factors f⁺ _Kπ(Q²) and |f^- _Kπ(Q²)| can either show the asymptotic behavior of or decrease more quickly than ; more experimental data are needed to select the ideal sum rules. PACS 12.38.Lg; 12.38.Bx; 12.15.Hh     

Analysis of Ω<Subscript>c</Subscript><Superscript>*</Superscript>(css) and Ω<Subscript>b</Subscript><Superscript>*</Superscript>(bss) with QCD sum rules

In this article, we calculate the masses and residues of the heavy baryons Ω_c ^*(css) and Ω_b ^*(bss) with spin–parity with the QCD sum rules. The numerical values are compatible with the experimental data and other theoretical estimations. PACS 14.20.Lq, 14.20.Mr     

Conserved vector current and decays τ<Superscript>−</Superscript> → η(η′)π<Superscript>−</Superscript>π<Superscript>0</Superscript>ν<Subscript>τ</Subscript>

We use experimental data on e ⁺ e ^? → (η′)π⁺π^? and conservation of vector current to estimate the branching fractions of τ^? decay to η(η′)π^?π⁰ν_τ. The obtained values are compared to the experimental results.     

Visible up-conversion and NIR luminescence studies of LiAl<Subscript>5</Subscript>O<Subscript>8</Subscript>:Er phosphor co-doped with Yb<Superscript>3+</Superscript> and Zn<Superscript>2+</Superscript>

The frequency up-conversion, an efficient laser emission and amplification in Er³⁺:LiAl₅O₈ phosphors co-doped with Yb³⁺ and Zn²⁺ phosphor powders in the 520–560, 640–680 nm regions and at ∼1.5 μm, respectively, have been reported. The emission corresponds to the ²H_11/2, ⁴S_3/2→⁴I_15/2, ⁴F_9/2→⁴I_15/2 and ⁴I_13/2→⁴I_15/2 transitions upon direct excitation into the intermediated ⁴I_11/2 level using ∼980 nm radiation from a CW laser. Possible mechanisms involved for the up-conversion processes based on the energy level matching scheme, the pump-power dependence and the dynamical behaviour have been discussed. The effect of the addition of Yb³⁺ and Zn²⁺ for the amplification in the 1.5 μm eye-safe telecommunication window has been elaborated and characterized in detail.     

EIT Ground State Cooling Scheme of <Superscript>171</Superscript>Yb<Superscript>+</Superscript> Based on the <Superscript>2</Superscript>S<Subscript>1/2</Subscript>→<Superscript>2</Superscript>P<Subscript>1/2</Subscript> Cooling Transition

We propose a method for EIT ground state cooling of ¹⁷¹Yb+ ion, which involves three light fields with detuning on a MHz scale. The steady-state mean vibrational quantum number is calculated to be less than 0.005. Efficient cooling is achievable in a motional-mode frequency range of 2π · (1.5 ± 0.5 MHz).     

Calix[4]arene Based Dual Fluorescent Sensor for Al<Superscript>3+</Superscript> and S<Subscript>2</Subscript>O<Subscript>7</Subscript><Superscript>2−</Superscript>

Specific functionalized calix[4]arene based fluorescent chemosensor was synthesized for cations and anions binding efficiency examination. Receptor C4MA displayed strong affinity for Al³⁺and S₂O₇ ^2? with enhanced fluorescence intensity. The selective response of C4MA was investigated in the presence of different co-existing competing ions. The limit of detection (LOD) of Al³⁺and S₂O₇ ^2? was calculated as 2.8?×?10^?6 M and 2.6?×?10^?7 M respectively. Sensor C4MA forms (1:1) stoichiometric complex with both Al³⁺ and S₂O₇ ^2? and their binding constants were calculated as 12.1?×?10⁴ and 8.3?×?10³ respectively. Complexes were also characterized through FT-IR spectroscopy.

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Graphical Abstract ?

     

110 W ceramic Nd<Superscript>3+</Superscript> : Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript> laser

A high-power, continuous-wave 0.6% Nd³⁺-doped ceramic Y₃Al₅O₁₂ (Nd:YAG) laser has been developed. 110 W laser output at 1064 nm was obtained, with a slope efficiency of about 41%. The M² factor was found to be around 6. The laser performance of the ceramic laser material was found to compare favorably with that obtained with single crystal Nd:YAG. PACS 42.55.-f; 42.55.Xi; 42.70.Hj     

Visible upconversion and infrared luminescence investigations of Al<Subscript>2</Subscript>O<Subscript>3</Subscript> powders doped with Er<Superscript>3+</Superscript>, Yb<Superscript>3+</Superscript> and Zn<Superscript>2+</Superscript> ions

Alumina (Al₂O₃) powders doped with Er³⁺, Yb³⁺ and Zn²⁺ ions have been prepared by a low-temperature combustion synthesis technique. The phase purity and crystalline structure of the combustion products are confirmed by powder X-ray diffraction. An efficient frequency upconversion in the visible region and the emission in the infrared (IR) region respectively corresponding to the ²H_11/2, ⁴S_3/2→⁴I_15/2, ⁴F_9/2→⁴I_15/2 and ⁴I_13/2→⁴I_15/2 transitions upon direct excitation with a CW laser lasing at ∼980 nm are discussed. The enhancement observed in the intensity of the upconversion emission bands in the visible region and the emission band in the IR region due to the presence of Yb³⁺ and Zn²⁺ in Er³⁺:Al₂O₃ powders is reported and explained in detail.     

Optimizing after-glow luminescent parameters of Sr<Subscript>4</Subscript>Al<Subscript>14</Subscript>O<Subscript>25</Subscript>:Eu<Superscript>2+</Superscript>, Dy<Superscript>3+</Superscript>, by sol–gel method and combustion process

Strontium aluminates are viewed as a promising persistent luminescent materials. There are many researches on strontium aluminates, including SrAl₂O₄, Sr₄Al₁₄O₂₅. Between these two phases, Sr₄Al₁₄O₂₅ shows much better properties than SrAl₂O₄. The traditional way to synthesize Sr₄Al₁₄O₂₅ is the solid state reaction. However, it exists few problems, especially non-homogeneous product. As a result, there are two methods chosen to make homogeneous precursor. One is sol–gel method, the other is combustion with Urea as a fuel. Boric acid is added as a flux in both method. In this study, combustion process is found to be a better way for synthesizing Sr₄Al₁₄O₂₅. We change the temperature, synthetic method. The samples are finely grinded and used for XRD analysis, photoluminescence measurement, and after-glow decay curve to figure out the optimizing luminescent parameters.     

<Superscript>57</Superscript>Fe emission Mössbauer spectroscopy following dilute implantation of <Superscript>57</Superscript>Mn into In <Subscript>2</Subscript>O<Subscript>3</Subscript>

Emission Mössbauer spectroscopy has been utilised to characterize dilute ⁵⁷Fe impurities in In ₂O₃ following implantation of ⁵⁷Mn (T _1/2 = 1.5 min.) at the ISOLDE facility at CERN. From stoichiometry considerations, one would expect Fe to adopt the valence state 3 + , substituting In ³⁺, however the spectra are dominated by spectral lines due to paramagnetic Fe²⁺. Using first principle calculations in the framework of density functional theory (DFT), the density of states of dilute Fe and the hyperfine parameters have been determined. The hybridization between the 3d-band of Fe and the 2p band of oxygen induces a spin-polarized hole on the O site close to the Fe site, which is found to be the cause of the Fe²⁺ state in In ₂O₃. Comparison of experimental data to calculated hyperfine parameters suggests that Fe predominantly enters the 8b site rather than the 24d site of the cation site in the Bixbyite structure of In ₂O₃. A gradual transition from an amorphous to a crystalline state is observed with increasing implantation/annealing temperature.     

Hydrothermal synthesis,characterization, and luminescence of Ca<Subscript>2</Subscript>B<Subscript>2</Subscript>O<Subscript>5</Subscript>:RE (RE = Eu<Superscript>3+</Superscript>, Tb<Superscript>3+</Superscript>, Dy<Superscript>3+</Superscript>) nanofibers

Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers were synthesized by the hydrothermal reaction method. The structural refinement was conducted on the base of the X-ray powder diffraction (XRD) measurements. The surface properties of the Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers were investigated by the measurements such as the scanning electron microscope (SEM), transmission electron microscope (TEM), and the energy dispersive spectrum (EDS). The nanofiber has a diameter of about 100 nm and a length of several micrometers. The luminescence properties such as photoluminescence excitation (PLE) and emission spectra (PL), decay lifetime, color coordinates, and the absolute internal quantum efficiency (QE) were reported. Ca₂B₂O₅:Eu³⁺ nanofibers show the red luminescence with CIE coordinates of (x = 0.41, y = 0.51) and the luminescence lifetime of 0.63 ms. The luminescence of Ca₂B₂O₅:Tb³⁺ nanofibers is green color (x = 0.29, y = 0.53) with the lifetime of 2.13 ms. However, Dy³⁺-doped Ca₂B₂O₅ nanofibers present a single-phase white-color phosphor with the fluorescence decay of 3.05 ms. Upon near-UV excitation, the absolute quantum efficiency is measured to be 65, 35, and 37 % for Eu³⁺-, Tb³⁺-, Dy³⁺-doped Ca₂B₂O₅ nanofibers, respectively. It is suggested that Ca₂B₂O₅:RE (RE = Eu³⁺, Tb³⁺, Dy³⁺) nanofibers could be an efficient phosphor for lighting and display.     

<Superscript>151</Superscript>Eu Mössbauer study of multiferroic Eu<Subscript>0.75</Subscript>Y<Subscript>0.25</Subscript>MnO<Subscript>3</Subscript>

We are herewith reporting the ¹⁵¹Eu Mössbauer spectra collected on a polycrystalline powder sample of Eu_0.75Y_0.25MnO₃ from 15 K to room temperature. All the spectra consist of a single line, whose shape and related sample thickness are dependent on the temperature T. The thermal trend of the mean square displacement of Eu ion, obtained from the spectra analysis, clearly reveals a large low-temperature anharmonicity and in concomitance with the onset of the magnetic ordering consists in a linear strong decrease interrupted by two narrow wells at 29.5 K and 40 K. This behavior is interpreted in connection with the transfer of spectral weight from the 120 cm^-1 optical phonon to the electromagnonic modes. The T-trend of the central shift shows that Eu³⁺ electronic ground state in the magnetically ordered phase differs from the one in the paramagnetic state. Finally, the temperature dependence of the hyperfine field under T _N gives a contribution to interpret some controversial features regarding the phase-diagram.