Optical transition probabilities of Er3+ in fluoride glasses

Lead-based fluoride glasses of the system PbF₂GaF₃MF₂(M = Zn or Mn) doped by trivalent erbium were prepared by melting and quenching of the appropriate fluorides under inert atmosphere. Optical spectra of the glasses with and without manganese reveal identical characteristics in the near ir region of the spectrum. In the near uv and visible part, the manganese-containing samples show higher oscillator strength, probably due to interaction between Mn²⁺ and Er³⁺. Radiative and nonradiative characteristics of the glasses were computed, using the Judd-Ofelt method. Laser transitions of the glasses were predicted.     

Ordre local dans quelques verres fluores du systeme PbF2MIItF2MIIItF3 par EXAFS

The local environment of transition metal (M_t) and lead has been studied by EXAFS for some fluoride glasses in the system PbF₂M^II_tF₂M^III_tF₃ (M^II_t = Mn²⁺, Zn²⁺; M^III_t = Fe³⁺, Ga³⁺). Theoretical phase shifts and backscattering amplitude are used after testing with crystallized fluorides of various structures. Transition metals are sixfold coordinated and M_tF distances are very close to those known in crystallized compounds. Lead has eight to nine fluorine neighbors forming a very distorted polyhedra. Radial distributions, partially corrected for phase shifts, show a very weak second peak but the second neighbors nature and the distances cannot be determined without ambiguity.     

Energy transfer between neodymium(III) and ytterbium(III) in transition-metal fluoride (TMFG) glasses

Energy transfer rates between Nd(III) and Yb(III) in glasses of the basic composition 36 PbF₂:24 ZnF₂:35 GaF₃:2 AlF₃;3 YF₃:4 LaF₃ were calculated from donor decay curves, and applied for construction of acceptor luminescence curves. The transfer rates are time dependent and the energy loss by Nd(III) is quantitatively transferred to Yb(III).     

Phase relation studies in Pb1−xM′xF2+x systems (0.0⩽x⩽1.0; M′=Nd3+, Eu3+ and Er3+)

In this communication we report the synthesis and characterization of a series of compounds with the general composition Pb_1−xM′_xF_2+x, (0.0⩽x⩽1.0; M′=Nd³⁺, Eu³⁺ and Er³⁺) to elucidate the detailed phase relations between PbF₂ and M′F₃. These three rare-earth fluorides were selected so as to delineate the effect of ionic size on the phase relations. In all the three systems, fluorite-type solid solutions are formed at the PbF₂ rich end. The solid solubility limits of NdF₃, EuF₃ and ErF₃ in the PbF₂ lattice, as observed from this study, are 30, 25 and 15 mol%, respectively. In PbF₂–NdF₃ system, beyond the fluorite-type solid solutions, NdF₃ phase is observed. However, in both PbF₂–EuF₃ and PbF₂–ErF₃ systems, certain fluorite related ordered phases, namely, a rhombohedral phase with about 40 mol% of EuF₃ or ErF₃ in PbF₂, and a tetragonal phase with 45–50 mol% of ErF₃ in PbF₂, are observed. In all the three systems, no solubility of the PbF₂ in the hexagonal or orthorhombic rare-earth fluoride lattice is observed. This is the first report on phase relation in these three systems under short annealed and slow cooled condition.     

Hyperfine interactions in MgF2:Fe2+ and ZnF2:Fe2+ by Mössbauer spectroscopy

Measurement of the magnetic hyperfine interaction in paramagnetic Fe²⁺ in ZnF₂ and MgF₂ by Mössbauer spectroscopy is reported. The results, ?275 ± 3 kOe and ?270 ± 3 kOe for ZnF₂:Fe²⁺ and MgF₂:Fe²⁺ respectively are compared with a previous analysis of hyperfine interactions in the rutile fluorides.     

直流电场诱导下镓铟基氟磷玻璃的微晶化研究

采用高温熔融法制备了20GaF3-15InF3-17CdF2-15ZnF2-20PbF2-10SnF2-3P2O5体系透明玻璃,并利用电场的诱导作用,对其微晶化进行了系统的研究。利用DSC、SEM、XRD等手段对材料进行了表征。结果表明,在热处理过程中加载一个静电场,能促进ZnF2晶粒的形成,其尺寸约为20～30 nm。而且发现,在正负电极至少有一个没有接触材料的情况下,电场也能在远低于析晶起始温度的恒温环境中起到诱导析晶作用。     

Structural and electrical studies of the PbF2-BiOF system

An investigation of the PbF₂-BiOF system at 600°C has allowed isolation of a Pb_1?xBi_xO_xF_2?x solid solution (0<x? 0.80). For x ? 0.66 the structure is of fluorite type and for 0.66 <x? 0.80 it undergoes a fluorite derived rhombohedral distortion. The transport properties of Pb_1?xBi_xO_xF_2?x are for x ? 0.50 as good as those of the best fluorides.     

Magnetic interactions in ternary cobalt oxides with cubic perovskite structure

Magnetic properties were measured on the cubic perovskite systems SrCoO_3?δ, (La_1?xSr_x)CoO₃ (0.5 ≦ x ≦ 1.0), and Sr(Co_1?xMn_x)O₃ (0 ≦ x ≦ 1.0). It is found that S²⁺ and La³⁺ ions strongly affect the spin state of the Co²⁺ ion and that the Mn⁴⁺ ion located at the octahedral site affects the spin state of Co⁴⁺ ion. The magnetic properties (T_c, T_θ, and σ) are explained by the magnetic interaction Co³⁺OCo³⁺, Co³⁺OCo⁴⁺, Co⁴⁺OCo⁴⁺, Mn⁴⁺OMn⁴⁺, and Mn⁴⁺OCo⁴⁺ in these systems.     

A neutron powder diffraction study of the κ phase in the FeWC system

The crystal structure of the κ-carbide in the FeWC system has been refined from neutron powder diffraction data using the Rietveld profile analysis method. κ-(FeWC) is isostructural with κ-(CoWC); space group $\text{P6}{}_3\text{mmc}$; unit cell dimensions a = 7.7982(2)Å, c = 7.8298(4) Å. The structure refinement indicates $\text{Fe}\text{W}$ substitution at two of the tungsten sites, and 46% vacancies at one of the carbon sites. The composition corresponds to the formula Fe_3+xW_10?xC_4?y, with x = 0.57(3) and y = 0.46(1).     

The oxygen potentials corresponding to the YBa2Cu3O6+x phase in the YBaCuO system

Phase relations in the vicinity of the YBa₂Cu₃O_6+x in the CuO-rich part of the YBaCuO system were studied by the equilibration and quenching technique. At 950°C, the system is characterized by the large number of solid four-phase combinations. The oxygen potential as a function of temperature for two four-phase combinations, i.e., YBa₂Cu₃O_6+x + BaCuO₂ + BaCu₂O₂ + Y₂BaCuO₅ and YBa₂Cu₃O_6+x + BaCu₂O₂ + Y₂BaCuO₅ + Cu₂O, were studied by means of solid state EMF measurements. At higher oxygen potentials the pair of YBa₂Cu₃O_6+x and Y₂BaCuO₅ is stable in contact with BaCuO₂. At lower oxygen pressures this pair coexists in equilibrium with BaCu₂O₂ or Cu₂O.     

Er-doped PbF2: Comparison between nanocrystals in glass-ceramics and bulk single crystals

An appropriate annealing of a GeO₂-PbO-PbF₂:ErF₃ glass leads to the formation of a glass-ceramic, composed of Pb_1−xEr_xF_2+x nanosized crystallites dispersed throughout an amorphous oxide matrix. These nanocrystallites are compared to Er³⁺-doped PbF₂ bulk single crystals. The influence of the annealing temperature on the glass-ceramics characteristics is thoroughly investigated. For several glass-ceramics resulting from different heat treatments, the quantity of crystallized PbF₂, as well as the segregation of Er³⁺ ions into the crystallites, has been studied through two methods: first, the study of the crystallographic characteristics and second, the evolution of the optical properties. It was evidenced that, for a heat treatment over 365 °C, the whole PbF₂:Er has completely crystallized and that the segregation of Er³⁺ ions into the crystallites was total. Strong interactions between Er³⁺ ions occur in the Pb_1−xEr_xF_2+x single and nanocrystals, promoting cross-relaxation processes, under 488-nm excitation, and favouring the 660- (red) and 810-nm emissions at the expense of the 550-nm (green) one.     

Long-lived emission from Eu3+:PbF2 nanocrystals distributed into sol–gel silica glass

This paper reports an optical investigation of Eu³⁺:PbF₂ nanocrystals distributed into silica glasses fabricated by sol–gel methods. The sample microstructure was investigated using scanning transmission electron microscopy. The β-cubic PbF₂ crystalline phase was identified using X-ray diffraction analysis. The observed emission bands correspond to ⁵D₀ → ⁷F_J (J = 0–4) transitions of Eu³⁺. The spectroscopic parameters for Eu³⁺ ions were determined based on excitation and emission measurements as well as luminescence decay analysis. Emission originating from ⁵D₀ state of Eu³⁺ ions in sample containing PbF₂ nanocrystals is long-lived in comparison to precursor sol–gel silica glasses.     

An infrared study of the stretching modes of the water molecules in ZnF2·4H2O

The IR spectra of ZnF₂·4H₂O and its deuterated analogues are reported at ambient and liquid-nitrogen temperatures. The OH and OD stretching and bending vibrations of the water molecules are analysed in detail. The two types of water molecules give rise to different absorption peaks in the OH and OD stretching regions in samples that contain isotopically dilute HDO groups. The strongly hydrogen-bonded water molecules H₂O(1) and H₂O(4) show four broad OH and OD stretching modes at lower frequencies, while the weaker hydrogen-bonded ones H₂O(2) and H₂O(3) give rise to four narrow bands at higher frequencies. The ν_OD frequencies of isotopically dilute HDO groups correlate very well with the known R(H---F) and R(H---O) distances in the crystals and the assignment of these modes was done on this basis. It was also found that the ratio ν_OH/ν_OD decreases with decreasing values of R(H---O) or R(H---F) in ZnF₂·4H₂O.     

Les fluoronitrures de terres rares

The reaction of rare-earth nitrides with fluorides or the pyrolysis of these fluorides in gaseous ammonia atmosphere leads, in the case of lanthanum, cerium, and gadolinium, to nitride fluorides of general formula LnN_xF_3?3x. They crystallize with a fluorite-type structure which can be described in a consistent manner in terms of a Willis model. The magnetic properties of Gd₃NF₆ have been studied.     

Mise au point dans le ternaire TlBiTe. Existence de deux phases nonstoechiometriques de type TlBiTe2

The cross section BiTeTlTe of the phase diagram TlBiTe was constructed by X-ray, microstructure, and DTA methods. Two phases were emphasized: Tl_1?xBi_1+xTe₂ with x = 0.06, and Tl_1?yBi_1+yTe₂ with y = 0.2. The first one is a nonstoichiometric representation of what so many authors studied as TlBiTe₂. The latter is a high-temperature phase which decomposes in eutectoïd reaction (415°C):

$\text{1.18{}\text{Tl}{}_{0.8}\text{Bi}{}_{1.2}\text{Te}{}_2\text{} ?}\text{Tl}{}_{0.94}\text{Bi}{}_{1.06}\text{Te}{}_2\text{+ 0.36 {}\text{BiTe}\text{}}$

.The high-temperature form undergoes a phase transformation by quenching, giving a metastable low-temperature form. The discussion includes electrical resistivity and thermoelectric measurements of each of them.     

Fluoration de telomeres polyhalogenes par le fluorure de potassium (2ème partie). Synthese d'olefines perfluorees de hauts poids moleculaires

Fluorination of chlorofluorinated telomers of general formula Cl(CFClCF₂)_nCCl₃ (n ? 7) was studied using potassium fluoride in dimethylsulfoxide as fluorinating agent. The reaction leads to a mixture of perfluorinated linear olefins having 15 to 30 carbon atoms : CF₃(CF₂)_pCFCF(CF₂)_mCF₃ (p + m = 2n?3).We perfected a method to determine molecular weights of the telomers by gel permeation chromatography (G.P.C.). The olefins obtained by fluorination are analyzed both by vapor phase chromatography (V.P.C.) and by ¹⁹F nuclear magnetic resonance (N.M.R.).     

Mise au point d'un appareillage de preparation et de manipulation de melanges anhydres HFNH3MF (M alcalin) — tension de vapeur totale au-dessus de solutions HFNH3 riches en HF

An apparatus for preparing and handling HFNH₃MF mixtures (M alkali metal) has been designed and constructed. The vacuum line made of plastic materials (PVF₂, PTFCE, PTFE) allows the purification of anhydrous hydrogen fluoride, preparation and analysis of HFNH₃ or HFNH₃MF mixtures and their handling for further study or destruction.Total vapour pressures above HFNH₃ binary mixtures rich in HF have been measured and are described as a function of ammonia concentration and temperature (?10 to +20°C).     

Zum Aufbau von PbF4 mit Strukturverfeinerung an SnF4

On the Constitution of PbF₄ with Structure Refinement of SnF₄ Colourless single crystals of SnF₄ have been prepared heating powder samples of SnF₄ in Pt-tubes (500°C, 20 d). Single crystals of PbF₄ could be synthesized by pressure fluorination of «PbF_4-x» and sublimation in autoclaves. The fluorides crystallize isostructural in space group I4/mmm with SnF₄: a = 404.42(4) pm; c = 792.41(9) pm; Z = 2 and PbF₄: a = 425.36(8) pm; c = 806.4(1) pm; Z = 2 (Guinier-de Wolff data, Cu-Kα₁). The parameters Z_F2 of both fluorides were refined from four-circle diffractometer data (Siemens AED 2) with SnF₄: R1 = 1.5%; 1623 I₀(hkl) and PbF₄: R1 = 1.0%; 777 I₀(hkl) (SHELXL-93). The structures correspond to the supposition by Hoppe and Dähne from 1962. The Madelung Part of Lattice and Molecule Energy, MAPLE and MAPME, Mean Fictive Ionic Radii, MEFIR, and Effective Coordination Numbers, ECoN, are calculated.     

Organosilicon and organophosphorus compounds with pseudohalogen groups. 1. Synthesis of alkoxydimethylsilyl cyanides and their reactions with metal fluorides

Alkoxydimethylsilyl cyanides were synthesized by the exchange reaction of the corresponding alkoxydimethylchlorosilanes with trimethylsilyl cyanide, and also by the reaction of the former compounds with HCN in the presence of triethylamine (the latter method is preferential). Reactions of silyl cyanides with SbF₃ and ZnF₂ were studied. It was found that the reaction of silyl cyanides with SBF₃ leads to the formation of Me₂SiF₂ and the corresponding alkoxydimethylfluorosilanes, which were also obtained by counter-synthesis from alkoxydimethylsilylchlorosilanes and metal fluorides (SbF₃, ZnF₂, CsF). Dimethylfluorosilyl cyanide was obtained by the reaction of silyl cyanides with ZnF₂.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 7, pp. 1593–1587, July, 1991.