Diffusion Monte Carlo Study of the Small Mixed 3He-4He Clusters

The ground state properties of helium mixed clusters ³He_2,3,4 ⁴He₂, ³He_2,3,4 ⁴He₃, ³He_2,3,4 ⁴He₄, ³He_2,3 ⁴He₅, consisting of up to eight helium atoms are studied using variational and diffusion Monte Carlo calculations. For clusters with three and four ³He atoms released-node diffusion Monte Carlo method is used. Our calculations show that, within errorbars, clusters ³He_3,4 ⁴He₂ have the same binding energy as the cluster ³He₂ ⁴He₂, and that ³He₃ ⁴He₃ has the same binding energy as ³He₂ ⁴He₃. The clusters ³He_3,4 ⁴He₂ and ³He₃ ⁴He₃ are in states in which one or two ³He atoms are far away from the rest of the system. Other considered clusters are bound. In particular, we have shown the stability of the cluster ³He₄ ⁴He₃, which was previously considered unstable. The calculations are performed using several different interatomic potentials and the conclusions concerning stability are insensitive to the particular form of the interaction potential. We compare our results with the recent experiment and other theoretical calculations.     

Substitutions in vanadate garnets

Following the original synthesis of Durif of NaCa₂Cu₂V₃O₁₂ and later synthesis by Bayer of NaCa₂M⁺⁺V₃O₁₂ and Ca₃LiM⁺⁺V₃O₁₂, where M was Mg, Co, Ni, Cu or Zn, forty-one variations were prepared as phase-pure garnets. The general formulae of the garnets attempted were [A₂⁺⁺B⁺] M₂⁺⁺V₃O₁₂ (Type I) and A₃⁺ [B⁺M⁺⁺]V₃O₁₂ (Type II), where A⁺⁺ = Mg, Sr, Pb, Cd or Ba, M⁺⁺ = Mg, Co, Ni, Cu or Zn and B⁺ = Li, Ag, K or Rb.     

High-pressure investigations of positive ion-molecule reactions in a mixtureof H2S and CH4

The positive ion-molecule reactions in the mixtures of hydrogen sulfide and methane have been examined by means of quadrupole mass spectrometer with the high-pressure ion source. The concentration of hydrogen sulfide in mixtures ranged from 10% to 90% with 10% increment. For each mixture major bimolecular ion-molecule reactions have been identified in the total pressure range from 0.7 to 33.3 Pa. The electron energy for all measurements was fixed at 300 eV and the repeller potential was maintained at 5 V. Relative intensities of ion currents for the observed ions C⁺, CH⁺, CH₂⁺, CH₃⁺, CH₄⁺, CH₅⁺, C₂H₃⁺, C₂H₄⁺, C₂H₅⁺, S⁺, HS⁺, H₂S⁺, H₃S⁺, H₃³⁴S⁺, CHS⁺, CH₃S⁺, S₂⁺, HS₂⁺ and H₂S₂⁺ were determined as a function of total gas pressure inside the ion source collision chamber, repeller potential and concentration of methane in the mixture.     

Single phased Sr<Subscript>3</Subscript>La(PO<Subscript>4</Subscript>)<Subscript>3</Subscript>:Eu<Superscript>2+</Superscript>/Mn<Superscript>2+</Superscript> phosphors: solid state synthesis,tunable luminescence and potential applications in white light LEDs

A series of Sr₃La(PO₄)₃:Eu²⁺/Mn²⁺ phosphors were synthesized by a solid state reaction. The phase and the optical properties of the synthesized phosphors were investigated. The XRD results indicate that the doped Eu²⁺ and Mn²⁺ ions do not change the phase of Sr₃La(PO₄)₃. The peak wavelengths of Eu²⁺ single doped and Eu²⁺/Mn²⁺ codoped Sr₃La(PO₄)₃ phosphors shift to longer wavelength due to the larger crystal field splitting for Eu²⁺ and Mn²⁺. The increases of crystal field splitting for Eu²⁺ and Mn²⁺ are induced by the substitution of Sr²⁺ by Eu²⁺ and Mn²⁺ in Sr₃La(PO₄)₃ host. Due to energy transfer from Eu²⁺ to Mn²⁺ in Sr₃La(PO₄)₃:Eu²⁺/Mn²⁺ phosphors, tunable luminescence was obtained by changing the concentration of Mn²⁺. And the white light was emitted by Sr₃La(PO₄)₃:3.0 mol%Eu²⁺/4.0 mol%Mn²⁺ and Sr₃La(PO₄)₃:3.0 mol%Eu²⁺/5.0 mol%Mn²⁺ phosphors.     

Kinetics of Plutonium(IV) Reduction with 3,3'-Bis(diaziridinyl) in HNO3 Solution

3,3'-Bis(diaziridinyl), H₂N₂C₂H₂N₂H₂, is oxidized with Pu(IV) ions in excess of reductant to bis(diazirinyl), N₂C₂H₂N₂, and in excess of oxidant, to nitrogen and acetic acid. The reaction rate in the HNO₃ solution at a constant ionic strength is described by the equation -d[Pu(IV)]/dt = k[Pu(IV)]²× [H₂N₂C₂H₂N₂H₂]^{1 . 7}[H⁺]^{- 3}, where k = 28400±1400 mol^{0 . 3} l^{- 0 . 3} min^{- 1} at 35°C. The activation energy of the reaction amounts to 126±11 kJ mol^{- 1}.     

Synthesis of cobalt-aluminum spinels via EDTA chelating precursors

In this work, synthesis of nanocrystalline Co^||Co^||| _x Al_2–x O₄ (where x = 0, 0.5, 0.8, 1, 1.18 and 2) spinels by the thermal decomposition of complex precursors derived from metal nitrate salts and ethylenediaminetetraacetic acid (EDTA) has been systematically studied. Based on XRD, FTIR, DTA, TGA, SEM and TEM analyses, it has been found that the as-prepared metal organic precursors with different Co and Al contents display different thermal behavior and crystal development and particle morphology. Increment of Co content in precursors improves the degree of crystallinity of the powder. Treated at 400°C, in contrast to the well formed Co₃O₄ or Co₃O₄-like spinel structure for the powder precursors containing higher Co content, most of the powders from precursors containing lower Co content are still amorphous. Higher Co content in the precursors slightly decreases the unit cell parameters of the resulting Co^||Co^||| _x Al_2–x O₄ spinels. Prepared at 900°C, the unit cell parameters of Co^||Al₂O₄, Co^||Co^||| _0.5Al_1.5O₄, Co^||Co^|||AlO₄, Co^||Co^||| ₂O₄ are 8.1038, 8.1007, 8.0867, and 8.0834 Å, respectively. Based on this work, preparation of a series of the Co^||Co^||| _x Al_2–x O₄ spinels including black or bright blue Co^||Al₂O₄, Co^||Co^||| _0.5Al_1.5O₄, Co^||Co^|||AlO₄, Co^||Co^||| ₂O₄ from EDTA-Co(Al) complexing precursor has been established.     

Anion Exchange of Li+@C60 Salt for Improved Solubility

Anion exchange of [Li⁺@C₆₀]PF₆ ^? salt was performed to obtain three highly soluble Li⁺@C₆₀ salts, namely, the trifluoromethanesulfonate (OTf^?), bis(trifluoromethylsulfonyl)imide (NTf₂ ^?), and tetrakis{3,5-bis(trifluoromethyl)phenyl}borate (TFPB^?). We investigated the solubility of [Li⁺@C₆₀]OTf^?, [Li⁺@C₆₀]NTf₂ ^?, and [Li⁺@C₆₀]TFPB^? and found that, compared with [Li⁺@C₆₀]PF₆ ^?, the NTf₂ and TFPB salts had substantially higher solubility. X-ray crystal structure analysis of the TFPB salt revealed that the Li⁺@C₆₀ units spaced further apart because of the large anions in the crystal packing. We attribute the improved solubility of the salts to primarily the increased inter-fullerene distance of the Li⁺@C₆₀ cations.     

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.     

Realization of modulating broadband emission from Er–Tm codoped calcium boroaluminate glasses by dual-wavelength pumping

Near-infrared photoluminescence (PL) of calcium boroaluminate (CABAL) glasses codoped with Er₂O₃ and Tm₂O₃ has been investigated by dual-wavelength pumping at 795 and 476 nm. Spectrum shape of broadband emission could be modulated by controlling the power ratio of two pumping lines (P₄₇₆/P₇₉₅). The result shows that the full width at half maximum can reach ∼500 nm in the wavelength range from 1.3 to 2.0 μm by controlling P₄₇₆/P₇₉₅ = 12. The PL spectra show four characteristic peaks located at 1.46, 1.53, 1.58 and 1.80 μm, corresponding to Tm³⁺: ³H₄ → ³F₄, Er³⁺: ⁴I_13/2 → ⁴I_15/2, Tm³⁺: ¹G₄ → ³F₂ and Tm³⁺: ³F₄ → ³H₆ emissions, respectively. The energy transfer (ET) (ET1: Er³⁺: ⁴I_13/2, Tm³⁺: ³F₄ → Er³⁺: ⁴I_15/2, Tm³⁺: ³H₄ and ET2: Er³⁺: ⁴I_13/2, Tm³⁺: ³H₆ → Er³⁺: ⁴I_15/2, Tm³⁺: ³F₄) between Er³⁺ and Tm³⁺ ions play important roles in the luminescence mechanisms. In addition, a new ET process (ET: Tm³⁺: ¹G₄, Er³⁺: ⁴F_9/2 → Tm³⁺: ³F₂, Er³⁺: ⁴F_7/2) was identified. The flat broadband emission with the bandwidth of ∼500 nm could be realized by changing P₄₇₆/P₇₉₅ as a result of the radiative transitions, Tm–Tm cross-relaxation (Tm³⁺: ³H₄, ³H₆ → Tm³⁺: ³F₄, ³F₄) and Er–Tm ET processes.     

Synthesis and luminescence properties of Na+, Li+ compensated Er3+ doped CaAl4O7 phosphors

Here the green-emitting highly luminescent Er³⁺ doped, Er³⁺-Li⁺ co-doped, Er³⁺-Na⁺ co-doped CaAl₄O₇ is synthesized by Pechini method at 1000^°C. Photoluminescence (PL) of CaAl₄O₇: Er³⁺ studies have been compared with Li⁺ co-doped CaAl₄O₇: Er³⁺ and Na⁺ co-doped CaAl₄O₇: Er³⁺. Na⁺ co-doped CaAl₄O₇:Er³⁺ shows increases in luminescence intensity compared to Li⁺ co-doped CaAl₄O₇: Er³⁺ and Er³⁺ doped CaAl₄O_7. The results suggest that CaAl₄O₇:Er³⁺ phosphor can be used as efficient green-emitting phosphor in white LED. The resultant phosphor emits green color peaking at 549 nm upon 378 nm excitation. Powder X-ray diffraction (PXRD) and photoluminescence (PL) techniques have been studied to characterize the synthesized microparticles. Further, this phosphor has good thermal stability that implies its potential to act as green phosphor in white light-emitting diodes. The effect of activator (Er³⁺), Na⁺ co-doped CaAl₄O₇:Er³⁺, and Li⁺ co-doped CaAl₄O₇:Er³⁺ phosphors luminescence spectra as well as photoluminescence life time studies were studied in detail. The results show that as the concentration of Er³⁺ in CaAl₄O₇ increases, the symmetry around the Er³⁺ ion decreases due to the creation of lattice defects in the crystal. Addition of Na⁺ and Li⁺ ions in CaAl₄O₇: Er³⁺leads to a small distortion in the local symmetry of Er³⁺ ions, thereby significantly enhancing its luminescence property. Analysis of photoluminescence life time studies of the prepared samples shows a smaller concentration quenching of Er³⁺ luminescence in charge compensated Na⁺ and Li⁺ CaAl₄O₇ phosphor.

     

Synthesis and properties of laser liquids based on POCl3-TlCl3

New laser-active liquids, POCl₃-TlCl₃-Nd³⁺ and POCl₃-TlCl₃-²³⁵UO ₂ ²⁺ -Nd³⁺, were prepared. U(VI) compounds dissolve in POCl₃-TlCl₃ only in the presence of Nd, and in stable solutions [Nd³⁺]/[UO ₂ ²⁺ ] > 4. The experimental data confirm the previously found correlation between the properties of POCl₃-MCl _x -²³⁵UO ₂ ²⁺ -Nd³⁺ solutions and chemical affinity of M ^x+ for oxygen. The radiation-chemical yield of Nd³⁺ in the excited state ⁴ F _3/2 upon homogeneous excitation of POCl₃-TlCl₃-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions with uranium α-radiation increases in proportion with the Nd³⁺ concentration, is independent of the [TlCl₃]/[Nd³⁺] ratio, and is equal to 1 excited ion per 100 eV at [Nd³⁺] = 0.35 M.     

On an intermediate electronic configuration of cobalt (+III)

In a D_4h site with a strong elongation the ³A_2g term of cobalt (+III) can be stabilized with an electronic configuration intermediate between low spin (¹A_1g) and high spin (⁵E_g): d²_xzd²_yzd¹_xyd¹_z2d⁰_x2_?y2. The La₂Li_0.5Co_0.5O₄ phase, whose layer structure favours strongly such a distortion of the CoO₆ octahedra, illustrates very well this possibility for cobalt (+III). ¹A_1g → ³A_2g and ¹A_1g → ⁵E_g transitions appear as the temperature increases.     

Persistent luminescence of Zn<Subscript>2</Subscript>GeO<Subscript>4</Subscript>:Mn<Superscript>2+</Superscript>/Pr<Superscript>3+</Superscript> phosphors

Zn₂GeO₄, Zn₂GeO₄:Mn²⁺, Zn₂GeO₄:Pr³⁺ and Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphors were fabricated by a solid state reaction. The phase and luminescent properties of the fabricated phosphors were investigated. The XRD patterns show that all of the fabricated phosphors have an orthorhombic structure. The fabricated Zn₂GeO₄ shows an emission band in the range of 350–550 nm. The fabricated Zn₂GeO₄:Mn²⁺ and Zn₂GeO₄:Pr³⁺ phosphors show emission bands corresponding to Mn²⁺ and Pr³⁺ ions, respectively. The fabricated Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphor shows the emission band results from Mn²⁺ and the codoped Pr³⁺ enhances the emission intensity of Mn²⁺. Moreover, Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphor exhibits longer decay time than that of Zn₂GeO₄:Mn²⁺. The higher intensity and longer lifetime of Mn²⁺ emission are induced by the energy transfer from Pr³⁺ of various vacancies to Mn²⁺ in Zn₂GeO₄:Mn²⁺/Pr³⁺ phosphors.     

Complexation and Disproportionation of Np(V) in K10P2W17O61 Solutions

Complexation of NpO₂ ⁺ and NpO₂ ^{2 +} with unsaturated K _n P₂W₁₇O₆₁ ^{n - 1 0} (L ^x-) heteropolyanion and disproportionation of Np(V) in the presence of L ^x- were studied spectrophotometrically. The logarithms (logK) of the formation constants of NpO₂ ^VL and NpO₂ ^{V I}L are 3 and 7, respectively. The K⁺ and Na⁺ cations bind the L ^x- anions, thus decreasing the yield of the complexes. Neptunium(V) disproportionation in K₁₀P₂W₁₇O₆₁ solutions containing 1 M (HClO₄ + NaClO₄) (pH from 0 to 4) and free from NaClO₄ (pH 2-6.5) was studied. The disproportionation rate is described by the equation -d[Np(V)]/dt = k[Np(V)][L ^x-]. The pH dependence of the rate constant passes through a maximum at pH 1. The rate constant decreases with increasing [Na⁺]. The reaction is inhibited by its product, Np(IV). The Np(V) complex is not involved in disproportionation; the reactive species is NpO₂ ⁺ aqua ion, which is probably converted into NpO^{3 +}L ^x-. Then NpO^{3 +}L ^x- rapidly reacts with NpO₂ ⁺, which occurs simultaneously with, or is preceded by release of the second oxygen atom.     

Effect of carbon impurity in irradiated mixed uranium–plutonium nitride on the phase composition upon β<Superscript>−</Superscript>-decay of fission products

As shown by thermodynamic modeling, accumulation of fission products in the course of irradiation of mixed uranium–plutonium nitride containing 0.25 wt % C impurity leads to the formation of a multicomponent carbonitride solid solution containing U, Pu, Am, Np, Zr, Y, lanthanides, and also separate carbide (UMoC₂, U₂RuC₂, URu₃C_0,7, BaC₂, SrC₂) and nitride (U₂N₃) phases and intermetallic compounds U(Ru, Rh, Pd)₃. The β^?-decay of metallic radionuclides in separate carbide phases of spent nuclear fuel leads to changes in their chemical compositions. The transformation kinetics of separate dicarbide (⁸⁹SrC₂ → ⁸⁹YC₂, ⁹⁰SrC₂ → ⁹⁰YC₂ → ⁹⁰ZrC + C, ¹⁴⁰BaC₂ → ¹⁴⁰LaC₂ → ¹⁴⁰CeC₂) and complex carbide (U⁹⁹MoC₂ → UC₂ + ⁹⁹Tc) phases was calculated.     

Liquid luminophores POCl3-SiCl4-235UO 2 2+ -Nd3+

Samples of liquid luminophores POCl₃-SiCl₄-Nd³⁺, POCl₃-SiCl₄-²³⁵UO ₂ ²⁺ , and POCl₃-SiCl₄-²³⁵UO ₂ ²⁺ Nd³⁺ were prepared for the first time. The physicochemical properties and absorption spectra of the samples were compared. The solubility of Nd and U(VI) compounds in the POCl₃ SiCl₄ binary solvent was examined. The Nd³⁺ concentration attains a maximum of 0.3 mM when Nd and U(VI) trifluoroacetates are jointly dissolved at the [POCl₃]/[SiCl₄] molar ratio of 6 8. The shapes of the absorption band of the Nd ions at 860–900 nm, corresponding to the ⁴ I _9/2 → ⁴ F _3/2 electronic transition, differ significantly in POCl₃-SiCl₄-Nd³⁺ and POCl₃-SnCl₄-Nd³⁺ solutions, and in POCl₃-SiCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions the band shape also depends on the type of the Nd and U(VI) compounds introduced. The near-IR region of the absorption spectra of POCl₃-SiCl₄-²³⁵UO ₂ ²⁺ and POCl₃-SiCl₄-²³⁵UO ₂ ²⁺ -Nd³⁺ solutions contains absorption bands of the OH groups. The band intensity is analyzed in relation to the characteristics of the solutions. The Nd³⁺ luminescence lifetime τ in the luminophores synthesized was estimated at 70–20 μs.     

Synthesis and luminescence properties of Yb3+, Tm3+ and Ho3+ co-doped SrGd2(WO4)2(MoO4)2 nano-crystal

Novel up-conversion luminescent SrGd₂(WO₄)₂(MoO₄)₂: Yb³⁺/Tm³⁺/Ho³⁺ nano-crystals were synthesized by hydrothermal method. The composition ratio of rare earth had been investigated. It indicated that when C_Yb³⁺ = 10 mol% and C_Yb³⁺/C_Tm³⁺/C_Ho³⁺ = 10:1.5:2, the emission intensities were the highest. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM) and up-conversion luminescence spectra were used to characterize SrGd₂(WO₄)₂(MoO₄)₂: Yb³⁺/Tm³⁺/Ho³⁺ nano-crystals and they showed that the sample had high degree of crystallinity, the sample was tetragonal system, and the grain size of the sample was about 56 nm. Three emission peaks, including blue emission peak, green emission peak and red emission peak were observed at 477, 543 and 651 nm corresponding to ¹G₄ → ³H₆ and ¹G₄ → ³F₄ transitions of Tm³⁺, ⁵F₄ → ⁵I₈ and ⁵F₅ → ⁵I₈ transitions of Ho³⁺ respectively. All the emission peaks were observed by excitation of 980 nm semiconductor laser. The relationship between up-conversion intensity and excitation power revealed that blue emission at 477 nm was a three-photon absorption process, green emission at 543 nm and red emission at 651 nm was a two-photon absorption process. The quantum yields of the sample were near 3.2%.     

Photoelectrochemical properties of titanates with the hollandite structure

The photoelectrochemical properties and the diffuse reflection spectra of the titanates K_1.8M²⁺_0.9Ti_7.1O₁₆ (M²⁺ = Mg²⁺, Ni²⁺) and K_1.8M³⁺_1.8Ti_6.2O₁₆ (M³⁺ = Al³⁺, Cr³⁺) with the hollandite structure are reported. The white titanates K_1.8Mg_0.9Ti_7.1O₁₆ and K_1.8Al_1.8Ti_6.2O₁₆ show an optical absorption edge near 3.7 eV. These compositions can be coloured by transition-metal ions due to the occurrence of Meⁿ⁺ → Ti⁴⁺ charge-transfer transitions. When these coloured titanates were used as photo-anodes in a photoelectrochemical cell for water electrolysis, no photoresponse was observed with visible light irradiation. Possible reasons are discussed.     

Powder synthesis and white light-emitting properties of Eu3+ co-doped K2CaP2O7:Dy3+ phosphors with energy transfer between Dy3+ and Eu3+

A series of white-emitting K₂CaP₂O₇:Dy³⁺ and K₂CaP₂O₇:Dy³⁺, Eu³⁺ phosphors were synthesized via a solid-state method, and Eu³⁺ was co-doped in K₂CaP₂O₇:Dy³⁺ to improve its white light performance. The influences of preparation temperature and Dy³⁺/Eu³⁺ concentration on the crystal structure and photoluminescence characteristics were investigated. XRD results indicate that K₂CaP₂O₇:Dy³⁺ samples prepared above 700 °C matches the standard K₂CaP₂O₇ phase. Under excitation of 349 nm, K₂CaP₂O₇:Dy³⁺ phosphor exhibited characteristic emission peaks at 487 nm (blue) and 579 nm (yellow), and white emission was realized through combining these blue and yellow emissions. After co-doping Eu³⁺ ions, the co-luminescence of Dy³⁺/Eu³⁺ with energy transfer between Dy³⁺and Eu³⁺ were demonstrated. The chromaticity of white light was controlled by changing the ratio of Dy³⁺/Eu³⁺ concentrations, which lead to a warm white light. Therefore, the results indicate that K₂CaP₂O₇:Dy³⁺, Eu³⁺ powders have a potential application in w-LEDs as single-component white-emitting phosphor.