Stability of the LaCl<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> and LuCl<Stack><Subscript>4</Subscript><Superscript>−</Superscript></Stack> Ions Studied by Mass Spectrometry

The enthalpy stability of the LaCl ₄ ^? and LuCl ₄ ^? ions is assessed using high-temperature mass spectrometry. The enthalpy of Cl^? detachment is determined to be Δ_rH⁰(298.15 K) = 332 ± 10 kJ/mol for LaCl ₄ ^? and 359 ± 10 kJ/mol for LuCl ₄ ^? .     

Estimating the effect of C<Stack><Subscript>2</Subscript><Superscript>−</Superscript></Stack> and C<Stack><Subscript>3</Subscript><Superscript>+</Superscript></Stack> radicals and neutral clusters on the fullerene formation

The mass spectrum of the products of arc discharge in helium between graphite electrodes has been studied for various values of the gas flow rate. As the gas flow rate increases, the intensity of C₆₀^±, C₇₀^±, C₈₄^± and C₉₀^± fullerene peaks increases and that of the C₂⁻ and C₃⁺ cluster radicals decreases, but the total decay in radicals amounts to only 21% of the total growth of fullerenes. From this it follows that a contribution to the formation of fullerenes from the neutral clusters (which are taken into account for the first time) significantly exceeds the contribution due to small radical species.     

Synthesis,electronic state,and particle size stabilization of nanoparticulate [Co(OH)<Subscript>2</Subscript>(H<Subscript>3</Subscript>O)<Stack><Subscript>δ</Subscript><Superscript>+</Superscript></Stack>]<Superscript>δ+</Superscript>

We have synthesized nanoparticulate cobalt(II) hydroxide containing Co²⁺ in tetrahedral oxygen coordination (Co _Td ²⁺ ), atypical of such systems: nano- [Co(OH)₂(H₃O) _δ ⁺ ]^δ+. The (Co _Td ²⁺ ) coordination in the hydroxide is inferred from its electronic diffuse reflectance spectrum, which shows a multiplet of strong absorption bands at 14500, 15000, and 16000 cm^?1 (⁴ A ₂(F)-⁴ T ₁(P) transition). Nanoparticulate cobalt(II) hydroxide forms in a weakly acidic medium under essentially nonequilibrium conditions due to supersaturation (by three to four orders of magnitude) with the starting reagents (CoCl₂ and LiOH) at the instant of the formation of the poorly soluble phase Co(OH)₂. Presumably, colloidal particles of nanoparticulate cobalt(II) hydroxide in a weakly acidic aqueous medium have a positive surface charge, compensated by a counter-ion (Cl^?) layer: nano-[Co(OH)₂(H₃O) _δ ⁺ ]^δ+ · δCl^?. The XRD patterns of pastes (gels) containing this hydroxide show three broad-ened lines with d = 5.31 (2θ = 16.7°), 2.77 (2θ = 32.3°), and 2.32 Å (2θ = 38.8°). According to small-angle X-ray scattering data, nano-[Co(OH)₂(H₃O) _δ ⁺ ]^δ+ has a narrow particle size distribution (1.0–2.0 nm). Synthesis and storage conditions are identified which ensure stabilization of the electronic state and particle size of nano-[Co(OH)₂(H₃O) _δ ⁺ ]^δ+ for a long time.     

Disproportionation of nonoxygenated U(V) bound in the complex with heteropoly anions P<Subscript>2</Subscript>W<Subscript>17</Subscript>O<Stack><Subscript>61</Subscript><Superscript>10−</Superscript></Stack>

The effect of experimental conditions on U^VL₂ (1–2 mM) disproportionation was studied spectrophotometrically through the U^IVL₂ accumulation (L = P₂W₁₇O ₆₁ ^10? ). In 1 M NaNO₃ solution containing 0.01 M HAc and 0.01 M NaAc, the rate of U^VL₂ disappearance is described by the equation V = k ₁[U^VL₂]. The k ₁ value is almost constant with pH decreasing from 4.5 to 1.7, but increases with increasing acetate concentration; the presence of 1 mM U^IVL₂, U(VI), or L does not affect k ₁. In the solutions of 0.1–1.0 M HClO₄ (ionic strength 1), the reaction rate is described by the equation V = 2k ₂[H⁺]^2.5[U^VL₂]². Probable disproportionation mechanism is discussed. The first stage is substitution of L by water molecules in the U^IVL₂ complex and appearance of the reactive U(V) complex with mixed coordination sphere.     

The reaction Pu(VI) + Fe(CN)<Stack><Subscript>6</Subscript><Superscript>3−</Superscript></Stack> ⇄ Pu(VII) + Fe(CN)<Stack><Subscript>6</Subscript><Superscript>4−</Superscript></Stack> in NaOH solutions

A spectrophotometric study showed that, in 5 M NaOH, Pu(VII) prepared by ozonation of Pu(VI) is reduced with excess K₄Fe(CN)₆. The Pu(VII) content can be estimated from the amount of the Fe(CN)₆³⁻ formed. In NaOH solutions of concentration exceeding 8 M, the Fe(CN)₆³⁻ ion oxidizes Pu(VI). In 10.3 M NaOH, the tenfold excess of K₃Fe(CN)₆ fully converts 1 mM Pu(VI) to the heptavalent state within 4 min (rate constant 1.3 l mol⁻¹ s⁻¹ at 20°C). With an increase in the NaOH concentration, the oxidation rate increases, and smaller excess of K₃Fe(CN)₆ is required. This oxidant is consumed not only for Pu(VI) oxidation but also in reactions with H₂O and OH⁻ ions. Pu(VII) is unstable and is slowly reduced with water and with products of decomposition of iron complexes.     

Stability of actinide(III,IV) and lanthanide(III,IV) complexes with P<Subscript>2</Subscript>W<Subscript>17</Subscript>O<Stack><Subscript>61</Subscript><Superscript>10−</Superscript></Stack> heteropolyanions

The total stability constants of Th⁴⁺, U⁴⁺, Np⁴⁺, Pu⁴⁺, Am⁴⁺, Cm⁴⁺, Ce⁴⁺, Tb⁴⁺, Pr⁴⁺, Tb³⁺, and Pr³⁺ complexes with P₂W₁₇O ₆₁ ^10? heteropolyanion in 1 M sodium salt solutions at pH ≥ 5.5 (i.e., when the anion is not protonated; so-called “absolute” constants), were determined experimentally or calculated from published data. Plots of constants vs. ionic radius of the f element were considered for solutions with ionic strength 1 (1 M acid or sodium salt solutions at pH ≥ 5.5). The correlations found confirm that the interaction of counterions in the complex is predominantly electrostatic. At the same time, different contributions of the covalent interaction for actinides and lanthanides were suggested.     

Effects of pH and concentration on ability of Cl<Superscript>−</Superscript> and NO<Stack><Subscript>3</Subscript><Superscript>−</Superscript></Stack> to intercalate into a hydrotalcite-like compound during its synthesis

In this study, we confirmed that the characteristics of anion intercalation into the interlayer of a hydrotalcite-like compound (HT) during synthesis are similar to those of the anion-exchange reaction of HTs as well as the reconstruction reaction of HTs from Mg-Al oxide. We demonstrated that (i) Cl⁻, which has a higher charge density than NO₃⁻, more easily reacted with Mg and Al species to form HT structure, resulting in greater intercalation of Cl⁻ into the HT interlayer; and (ii) for HTs with lower Mg: Al molar ratios, OH⁻, which has a higher charge density than Cl⁻ and NO₃⁻, was more likely to interact with Mg and Al species to form HT structure, blocking the intercalation of Cl⁻ and NO₃⁻. Furthermore, we showed that high concentrations of Cl⁻ and NO₃⁻ in solution regulated their intercalation into the HT interlayer. The high activity of Cl⁻ and NO₃⁻ in solution would facilitate the anions’ reactions with Mg and Al species to form HTs, resulting in a high degree of anion intercalation into the interlayer of HTs.     

Lewis and Brønsted acids in super-acid catalyst SO<Subscript>4</Subscript><Superscript>2−</Superscript>/ZrO<Subscript>2</Subscript>–SiO<Subscript>2</Subscript>

Super-acid catalyst, SO₄ ^2?/ZrO₂–SiO₂, with high zirconium loading was synthesized and the nature of the surface acid was investigated by FT-IR of pyridine adsorption. With the increasing ZrO₂ content, the Lewis and Brønsted acid sites increased and reached the maximum when Zr/Si (molar ratio) = 1.3. The sample with Zr/Si = 1.3 showed the strongest IR adsorption band in the S=O stretching region (1,300–1,400 cm^?1). Pyrosulfate and monosulfate species existed on the surface of the catalysts and the acidic strength could be enhanced by induction effect of their S=O groups. And there were two kinds of Brønsted acid sites on the surface of the catalysts.     

Luminescent properties of single-phase Ba<Subscript>2</Subscript>P<Subscript>2</Subscript>O<Subscript>7</Subscript>:Tb<Superscript>3+</Superscript>, R (R = Eu<Superscript>2+</Superscript>, Ce<Superscript>3+</Superscript>) phosphors for white LED

The Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) phosphors were synthesized by use of a co-precipitation method. Crystal phase, excitation and emission spectra of sample phosphors are analyzed by means of XRD and FL, respectively. The emission spectra of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors exhibit four linear peaks attributed to the ⁵D₄?→?⁷F_J (J?=?6–3) transition of Tb³⁺ while four broad emission bands are observed in the emission spectra of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The effects of Eu²⁺ concentration on the luminescent properties of Ba₂P₂O₇:Tb³⁺, R (R?=?Eu²⁺, Ce³⁺) are studied. Ce³⁺ affects the luminescent properties of Ba₂P₂O₇:Ce³⁺, Tb³⁺ phosphors just as the sensitizer. However, Eu²⁺ is considered both as the sensitizer and the activator in Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors. The chromaticity coordinates of Eu²⁺ and Tb³⁺ co-doped phosphors gather around the white light field with the CCT approximate to 5000 K, indicating that the luminescent property of Ba₂P₂O₇:Eu²⁺, Tb³⁺ phosphors may approach to a desired level needed for white LED application.     

Characterization of <Superscript>4</Superscript>I<Subscript>9/2</Subscript> ↔ <Superscript>4</Superscript>F<Subscript>3/2</Subscript> optical transitions in trivalent Nd<Superscript>3+</Superscript> ions in GaLaS glass

The positions of Stark levels have been determined, using a step-by-step procedure, in the ⁴I_9/2 and ⁴F_3/2 manifolds of Nd³⁺ ions from absorption and photoluminescence measurements in the 12–293 K temperature range. This data has been used to calculate the emission cross-section for which the maximum value turns out to be ～2.3 × 10^?20 cm². The radiative recombination time, calculated using Judd–Ofelt analysis, of the ⁴F_3/2 manifold is in close vicinity to the experimentally determined times that were measured by the conventional decay of PL after interruption of excitation and by QFRS. Moreover, the peak time defined by QFRS is independent of temperature. Therefore, the dominant relaxation mechanism from the ⁴F_3/2 excited manifold of Nd³⁺ ions in GaLaS glass is believed to be by radiative emission.     

Structure,electrical, and optical properties of ZnO-substituted PbO for the Er<Superscript>3+</Superscript>/Yb<Superscript>3+</Superscript> co-doped Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>–GeO<Subscript>2</Subscript>–Na<Subscript>2</Subscript>O glass system

Glasses of the 0.5Er³⁺/2.5Yb³⁺ co-doped (40Bi₂O₃–20GeO₂–(30 − x)PbO–xZnO–10Na₂O system where x = 0.0, 5, 10, 15, 20, 25, and 30 mol%) have been characterized by FT-IR spectroscopy measurements to obtain information about the influence of ZnO-substituted PbO on the local structure of the glass matrix. The density and the molar volume have been determined. The influences of the ZnO-substituted PbO on the structure of glasses have been discussed. The dc conductivity measured in the temperature range 475–700 K obeys Arrhenius law. The conductivity decreases while the activation energy for conduction increases with increase ZnO content. The optical transmittance and reflectance spectrum of the glasses have been recorded in the wavelength range 400–1100 nm. The values of the optical band gap E _opt for all types of electronic transitions and refractive index have been determined and discussed. The real and imaginary parts ε₁ and ε₂ of dielectric constant have been determined.     

Effect of Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> on the dynamics of Li<Superscript>+</Superscript> ions in Li<Subscript>2</Subscript>O·P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Lithium ion transport has been studied in bismuth lithium phosphate glasses in the frequency range 20 Hz–1 MHz and in the temperature range 423–573 K using impedance spectroscopy. The addition of Bi₂O₃ in Li₂O·P₂O₅ glass is related to the modification of the glass structure and facilitates the Li⁺ ions migration. The ac and dc conductivities, activation energy of the dc conductivity and relaxation frequency are extracted from the impedance spectra. Conductivity of the present glass system is found to be ionic in nature. The electrical response of the glasses has been studied using both conductivity and electric modulus formalisms. A single ‘master curve’ for normalized plots of all the modulus isotherms observed for a given composition indicates the temperature independence of the dynamic processes for ions in these glasses. Nearly identical values of activation energy for dc conduction and for conductivity relaxation time indicate that the ions overcome same energy barrier while conducting and relaxing.     

Cathodoluminescence properties of SiO<Subscript>2</Subscript>:Pr<Superscript>3+</Superscript>and ZnO·SiO<Subscript>2</Subscript>:Pr<Superscript>3+</Superscript> phosphor nanopowders

The successful incorporation of ZnO nanoparticles in Pr³⁺-doped SiO₂ using a sol–gel process is reported. SiO₂:Pr³⁺ gels, with or without ZnO nanoparticles, were dried at room temperature and annealed at 600 °C. On the basis of the X-ray Diffraction (XRD) results, the SiO₂ was amorphous regardless of the incorporation of Pr³⁺ and nanocrystalline ZnO or annealing at 600 °C. The particles were mostly spherical and agglomerated as confirmed by Field Emission Scanning Electron Microscopy. Thermogravimetric analysis of dried gels performed in an N₂ atmosphere indicated that stable phases were formed at ≥900 °C. Absorption bands ascribed to ³H₄-³P_{(J = 0,1,2)}, ¹I₆ and ¹D₂ in the UV–VIS region were observed from SiO₂:Pr³⁺ colloids. The red cathodoluminescent (CL) emission corresponding to the ³P₀ → ³H₆ transition of Pr³⁺ was observed at 614 nm from dried and annealed SiO₂:Pr³⁺ powder samples. This emission was increased considerably when ZnO nanoparticles were incorporated. The CL intensity was measured at an accelerating voltage of 1-5 keV and a fixed beam current of 8.5 μA. The effects of accelerating voltage on the CL intensity and the CL degradation of SiO₂:Pr³⁺ and ZnO·SiO₂:Pr³⁺ were also investigated using Auger electron spectroscopy coupled with an Ocean Optics S2000 spectrometer.     

Y<Subscript>2</Subscript>O<Subscript>2</Subscript>S:Er<Superscript>3+</Superscript>,Ce<Superscript>3+</Superscript>—A new “invisible” IR phosphor

Ce³⁺ doping of Y₂O₂S:Er³⁺ can be used to suppress the visible anti-Stokes luminescence of the phosphor under excitation in the range 0.90–0.98 μm. We take advantage of this effect to create a new, efficient “invisible” IR phosphor emitting in the range 1.5–1.6 μm.     

Probe Mössbauer Spectroscopy of BiNi<Subscript>0.96</Subscript><Superscript>57</Superscript>Fe<Subscript>0.04</Subscript>O<Subscript>3</Subscript>

This paper presents results of a ⁵⁷Fe probe Mössbauer spectroscopy study of the BiNi_0.96⁵⁷Fe_0.04O₃ nickelate. The spectra measured above its TN demonstrate that Fe³⁺ cations heterovalently substitute for Ni²⁺ nickel (←Fe³⁺), being stabilized on four sites of the nickel sublattice in the structure of BiNiO₃. Calculations in an ionic model with allowance for monopole and dipole contributions to the electric field gradient indicate that the parameters of electric hyperfine interactions between ⁵⁷Fe probe atom nuclei reflect the specifics of the local environment of the nickel in the structure of the unsubstituted BiNiO₃ nickelate. Below T^N, Mössbauer spectra transform into a complex Zeeman structure, which is analyzed in terms of first-order perturbation theory with allowance for electric quadrupole interactions as a small perturbation of the Zeeman levels of the ⁵⁷Fe hyperfine structure, as well as for specific features of the magnetic ordering of the Ni²⁺ cations in the nickelate studied.     

Excitation of the uranyl ion in oxidation of U(IV) with xenon difluoride in frozen aqueous solutions of sulfuric acid: IV. Effect of F<Superscript>−</Superscript> and UO<Stack><Subscript>2</Subscript><Superscript>2+</Superscript></Stack> ions

A specific feature of U(IV) oxidation with xenon difluoride in aqueous H₂SO₄ solutions is low-temperature chemiluminescence (CL), which in the course of warming the sample quickly cooled to 77 K is recorded starting from 165 K and reaches a maximum at about 200 K. Exothermic phase transitions, crystallization of the ice + H₂SO₄·4H₂O and ice + H₂SO₄·6.5H₂O eutectics, occur in the same temperature range. The data (temperature dependences of the chemiluminescence intensity and simultaneously recorded DTA curves) obtained in experiments with variation of the rate of mixing and cooling the solutions and of the concentrations of H₂SO₄ and F^? and UO ₂ ²⁺ ions are well explicable by the catalytic activity of the juvenile surface of H₂SO₄ crystal hydrates toward low-temperature reaction of U(IV) with XeF₂.     

Synthesis of Y<Subscript>3</Subscript>Al<Subscript>5</Subscript>O<Subscript>12</Subscript>:Ce<Superscript>3+</Superscript> phosphor in the Y<Subscript>2</Subscript>O<Subscript>3</Subscript>–Al metal–CeO<Subscript>2</Subscript> ternary system

Garnet phosphor Y₃Al₅O₁₂:Ce³⁺ is prepared in the Y₂O₃–Al metal–CeO₂ ternary system by the solid-state reaction method in the air. For the first time, metal Al is used as a source of aluminum for the reaction instead of traditional oxide Al₂O₃. It is shown that the chemical reaction can be realized at lower temperatures and without use of special reducing atmosphere. The structural and spectroscopic properties of the prepared powder phosphor are very close to those earlier reported for the Y₃Al₅O₁₂:Ce³⁺ single crystal.     

Ho<Superscript>3+</Superscript>-Doped ZrF<Subscript>4</Subscript>–BaF<Subscript>2</Subscript>–BiF<Subscript>3</Subscript> Ceramic 2-µm laser beam visualizer

A ceramic 2-µm laser beam visualizer based on Ho³⁺-doped β-BaZrF₆ is proposed. The ceramic has been prepared by crystallizing 60ZrF₄–35BaF₂–5BiF₃ glass doped with 3 wt % HoF₃. Exciting the Ho³⁺⁵I₇ level by a Tm:LiYF₄ (Tm:YLF) laser at λ = 1910 nm, we observed a strong red luminescence, due to the ⁵F₅ → ⁵I₈ transition, and a weaker, green luminescence, corresponding to the (⁵F₄, ⁵S₂) → ⁵I₈ transition. The threshold power density of the Tm:YLF laser at which a red spot was observed on a ceramic sample was 1.1 W/cm².     

Tunable luminescence and energy transfer properties in Ca<Subscript>2−x</Subscript>NaMg<Subscript>2</Subscript>V<Subscript>3</Subscript>O<Subscript>12</Subscript>:xEu<Superscript>3+</Superscript> phosphors

Novel broadband luminescence phosphors Ca_2?xNaMg₂V₃O₁₂:xEu³⁺ have been successfully prepared via the conventional high-temperature solid-state reaction. The effects of concentrations of doped Eu³⁺ and introducing Li⁺, K⁺ on the luminescent properties of phosphor were studied. X-ray diffraction, GSAS structural refinement and photoluminescence spectra were used to characterize the samples. The refinement data ensured where the doped Eu³⁺ ions occupied the lattice site in the host. Under 355 nm excitation, the emission peak of Ca₂NaMg₂V₃O₁₂:Eu³⁺ phosphors are located at 610 nm (red) ascribed to the electric dipole transition of Eu³⁺ from ⁵D₀ → ⁷F₂. In the range of 400–575 nm, Ca₂NaMg₂V₃O₁₂:Eu³⁺ phosphors have broad emission bands attributed to charge transfer of \({\text{VO}}_4^{3 - }\) group. Energy transfer mechanism, energy transfer efficiency and critical distance (R_c) of \({\text{VO}}_4^{3 - }\) → Eu³⁺ would be analyzed. The emitting color of Ca₂NaMg₂V₃O₁₂:Eu³⁺ could be tunable from blue-green to near white light.     

BaFe<Subscript>12</Subscript>O<Subscript>19</Subscript> films produced from BaFe<Subscript>2</Subscript>O<Subscript>4</Subscript>/α-Fe<Subscript>2</Subscript>O<Subscript>3</Subscript> heterostructures

BaFe₁₂O₁₉ hexaferrite films have been produced on thermally oxidized single-crystal silicon (SiO₂/Si) substrates by sequential ion-beam sputtering of BaFe₂O₄ and α-Fe₂O₃ targets in an argon-oxygen atmosphere. Their crystal structure has been studied, and the origin of the impurity phases forming during heat treatment has been identified. The results show that heat treatment may lead to the formation of eutectic melts. As a result, the hexaferrite films may contain spherulites.