Oxidation State Of Europium Research Articles

Decoration of graphene films with europium oxide through the R.F. sputtering technique

ABSTRACTThe present work is aimed to study a comparison among synthesized graphene films, deposited on copper substrates and commercial graphene films; both decorated with Eu2O3 particles, with the purpose of promoting photoluminescence. The decoration procedure was achieved using the radio frequency sputtering (R.F. Sputtering) technique for the deposition of Eu2O3 on synthesized or commercial graphene films. The SEM obtained images, show differences in morphology when commercial and synthesized graphene films are compared. Our results indicate that the type of surface is the main factor that accounts for the europium oxide spatial distribution that ultimately leads to luminescence enhancing. The x-ray photoelectron spectroscopy (XPS) analyses, showed the trivalent oxidation state of europium and the atomic content of Europium for both; the commercial graphene film and synthesized one, where the first one presented the higher europium concentration. Analysis by Raman spectroscopy reveals that graphene films become disordered after the decoration is achieved. The main Raman bands of the commercial graphene films undergo a remarkable red shift, as a consequence of the presence of europium oxide It was observed that the interaction of Eu2O3 with the sp2 levels of graphene, improves the red photoluminescence of the samples grown on both, commercial and prepared graphene films.

Spectroscopic Characterization of the 3+ and 2+ Oxidation States of Europium in a Macrocyclic Tetraglycinate Complex.

The 3+ and 2+ oxidation states of europium have drastically different magnetic and spectroscopic properties. Electrochemical measurements are often used to probe EuIII/II oxidation state changes, but a full suite of spectroscopic characterization is necessary to demonstrate conversion between these two oxidation states in solution. Here, we report the facile conversion of an europium(III) tetraglycinate complex into its EuII analogue. We present electrochemical, luminescence, electron paramagnetic resonance, UV-visible, and NMR spectroscopic data demonstrating complete reversibility from the reduction and oxidation of the 3+ and 2+ oxidation states, respectively. The EuII-containing analogue has kinetic stability within the range of clinically approved GdIII-containing complexes using an acid-catalyzed dissociation experiment. Additionally, we demonstrate that the 3+ and 2+ oxidation states provide redox-responsive behavior through chemical-exchange saturation transfer or proton relaxation, respectively. These results will be applicable to a wide range of redox-responsive contrast agents and Eu-containing complexes.

Europium valence control in the hydrothermal synthesis of apatites and borosilicates

The solid-state chemistry of novel metal silicate and borosilicate crystals containing Eu2+ and Eu3+ in high temperature hydrothermal fluids was investigated. It was found that europium ions could be readily incorporated into a number of crystals using a variety of simple glass-based feedstocks. The hydrothermal growth reactions were performed at nearly 600 °C in 1–5 M NaOH mineralizer fluids, and this was found to be a versatile route to both europium ion oxidation states with Eu acting as either a fundamental structural building block or a dopant ion. Several new single crystals were identified including two new apatites as well as a new europium borosilicate. The apatites crystallize in space group P63/m with a = 9.4619(13) Å and c = 7.0054(14) Å for Eu10(SiO4)6O2, and a = 9.4413(13) Å and c = 6.9087(14) Å for NaEu9(SiO4)6O2. The new borosilicate, Eu2SiB2O8, crystallizes in space group Pbcn with a = 13.310(3) Å, b = 4.4247(9) Å and c = 9.2394(18) Å. The investigation of Eu-doped borosilicates demonstrated the strong blue emission generated from 370 nm excitation that was expected for the Eu2+ doped materials, as well as the less intense orange-red emission expected for the Eu3+ dopants. The hydrothermal reactions naturally facilitated a degree of europium reduction in Eu:Ba3Si2B6O16. It was found that the oxidation states of europium in the final product could be further controlled by using hydrazine as a reducing reagent.

The oxidation state of europium in silicate melts as a function of oxygen fugacity, composition and temperature

Europium LIII-edge X-ray absorption near edge structure (XANES) spectra were recorded for a series of synthetic glasses and melts equilibrated over a range of oxygen fugacities (fO2s, from −14 to +6 logarithmic units relative to the quartz–fayalite–magnetite, QFM, buffer) and temperatures (1250–1500°C). Eu3+/ΣEu (where ΣEu=Eu2++Eu3+) values were determined from the spectra with a precision of ±0.015. Eu3+/ΣEu varies systematically with fO2 from 0 to 1 over the range studied, increases with decreasing melt polymerisation and temperature, and can be described by the empirical equation: Eu3+/ΣEu=11+10−0.25logfO2−6410/T−14.2Λ+10.1, where Λ is the optical basicity of the melt and T is the temperature in K. Eu3+/ΣEu in glasses and melts equilibrated at the same conditions are in excellent agreement for Fe-free systems. For Fe-bearing compositions the reaction Eu2++Fe3+=Eu3++Fe2+ occurs during quenching to a glass and the high temperature value of Eu3+/ΣEu is not preserved on cooling; in situ measurements are essential for determining Eu3+/ΣEu in natural melts.

Stability of divalent/trivalent oxidation state of europium in some Sr-based inorganic compounds

This work investigates the stability of Eu2+ and Eu3+ in some Sr-based inorganic compounds. Generally reducing condition is adopted in order to obtain Eu2+, however, the Eu doped SrAl2O4/SrLaAlO4 case indicates that for some compounds Eu3+ is stabilized even in reducing atmosphere. Bond valence method is applied to explain this phenomenon and it reveals that crystal structure also determines the valence state of europium cations along with reducing/oxidizing condition. An analysis of other Eu doped Sr-based materials is performed which shows the relationship between Eu2+/Eu3+ stability and the Global Instability Index (GII). This research provides a guideline for synthesizing specific novel Eu2+/Eu3+ phosphors.

The oxidation state of europium in halide glasses

The luminescent properties of divalent europium ions can be exploited to produce storage phosphors for x-ray imaging applications. The relatively high cost and limited availability of divalent europium halides makes it desirable to synthesize them from the readily available trivalent salts. In this work, samples of pure EuCl3 and fluoride glass melts doped with EuCl3 were processed at 700–800 °C in an inert atmosphere furnace. The Eu oxidation state in the resulting materials was determined using fluorescence and Mössbauer spectroscopy. Heat treatment of pure EuCl3 for 10 min at 710 °C resulted in a material comprising approximately equal amounts of Eu2+ and Eu3+. Glasses made using mixtures of EuCl2 and EuCl3 in the starting material contained both oxidation states. This paper describes the sample preparation and analysis and discusses the results in the context of chemical equilibria in the melts.

Preparation and Electrical Properties of Eu(II)xNb(IV)O2+x

Abstract Nonstoichiometric compounds, EuxNbO2+x, were prepared. A cubic tungsten bronze type structure was found in the single phase region of EuxNbO2+x (0.5≤x≤1.0). Magnetic susceptibility measurements showed that the oxidation state of europium in the bronzes was bivalent. The EuxNbO2+x was a metallic conductor in the temperature range 4.2–300 K. Thermoelectromotive force measurements (100–350 K) indicated that the charge carriers were electrons and that the effective mass of the electrons increased with decreasing x in EuxNbO2+x.

Oxidation states of europium in zeolites

Rare-earth metal ions have proven to be particularly useful in zeolite catalysis, both as stabilizing ions and by virtue of their redox chemistry. In the research reported here, the europium Moessbauer spectra of hydrated and dehydrated euorpium-exchanged zeolites A, Y, and ZSM-5 have been studied. Eu(OH)/sub 2/.H/sub 2/O, used to ion exchange Eu/sup 2 +/ into the zeolites, immediately oxidizes to an Eu/sup 3 +/ complex in a deoxygenated aqueous solution. This same reaction occurs in the solid state for Eu(OH)/sub 2/.H/sub 2/O. An investigation into the role of europium in the thermolytic decomposition of water has been made, and the redox changes from the 3+ to the 2+ oxidation states of europium in zeolites Y and ZSM-5 have been confirmed by EPR. The Moessbauer isomer shifts are sufficiently sensitive to detect the difference in the chemical environment of Eu/sup 3 +/ as a consequence of oxidation by chlorine and oxygen. No evidence of Eu/sup 4 +/ has been found in an isomer shift range of +- 35 mm/s. Metal ions produced by dissolving europium metal in liquid ammonia can be exchanged into the zeolites to give an Eu/sup 2 +/ species as indicated by Moessbauer spectroscopy.

The oxidation state of europium in niobates and tantalates having the tetragonal tungsten-bronze structure

Europium-151 Mössbauer spectroscopy has been used to study the oxidation states and magnetic properties of europium in 15 mixed metal niobates and tantalates having the tetragonal tungsten-bronze structure. All the compounds featured substantial concentrations of Eu(III) in addition to the expected Eu(II) and this was shown to account for the low magnetic susceptibilities of the compounds. There was no evidence of electron charge hopping, at least on the Mössbauer timescale (∼ nsec) and no evidence of magnetic ordering of Eu(II) down to 4.2°K. The significance of these results is briefly discussed.

The defect model and oxidation state of europium and molybdenum in EuxMoO4

The defect model and oxidation state of europium and molybdenum in EuxMoO4

The oxidation state of europium as an indicator of oxygen fugacity

The distribution of Eu between plagioclase feldspar and magmatic liquid has been determined experimentally for basaltic and andesitic systems as a function of temperature and oxygen fugacity at one atmosphere total pressure. Using the approach of Philpotts the ratios Eu 2+ Eu 3+ in plagioclase and coexisting magmatic liquid have been calculated. These ratios appear to be simply related to oxygen fugacity for the bulk compositions studied here. Using published trace element distribution data for natural rocks oxygen fugacities may be calculated from these experimental results. For terrestrial basalts calculated oxygen fugacities average 10 −7 with little dispersion from this value. Andesites average 10 −8.1 with considerable dispersion, while dacites and rhyodacites average 10 −9.1, also with considerable dispersion. Oxygen fugacities for lunar ferrobasalts cluster tightly around 10 −12.7. Data on achondritic meteorites are limited, but calculations indicate oxygen fugacities of two-to-five orders of magnitude lower than lunar ferrobasalts.

EPR measurement of the effect of glass composition on the oxidation states of europium

The techniques of electron paramagnetic resonance (EPR) were used to measure the concentration ratio of Eu 2+ to Eu 3+ in quenched silicate liquids as a function of their compositions. The compositional end members were CaAl 2Si 2O 8 and either MSiO 3 or M 2Si0 4, M = Mg, (Ca 0.5, Mg 0.5), and Ca. All of the liquids were quenched from 1650 ± 25°C, 10 −6.9±0.6 atm of oxygen, and 10 −6.1±0.6 atm total pressure. For a particular choice of M, the ratio of Eu 2+ to Eu 3+ increased as much as a factor of 24 with increasing atomic ratio (Al + Si)/(O); for a constant value of (Al + Si)/(O), the ratio of Eu 2+ to Eu 3+ increased in the order Mg > ( Ca 0.5, Mg 0.5) > Ca. In order to interpret the compositional dependence of the redox equilibrium of Eu in a systematic manner, the concept of a solvent coefficient was introduced.

Measurement of the effects of temperature and partial pressure of oxygen on the oxidation states of europium in silicate glasses

The techniques of electron paramagnetic resonance (EPR) were used to measure the concentration ratio of Eu 2+ to Eu 3+ in quenched CaMgSi 2O 6, Ca 3Si 3O 12, and CaAl 2Si 2O 8 liquids as functions of partial pressure of oxygen and temperature. The redox equilibrium of the Eu ions was described by the reaction 4 Eu 3+ + 20 2− = 4 Eu 2+ + O 2. The reduction of Eu 3+ to Eu 2+ was endothermic, and for CaMgSi 2O 6 and Ca 3Al 2Si 3O 12 liquids the mean value of ΔH 0 and the standard deviation from that mean were 25 ± 7 kcal/mole. The magnitude of the Eu anomaly in the distribution coefficients is discussed in terms of the compositions of the solid and liquid phases.

Oxidation States of Europium in the Alkaline Earth Oxide and Sulfide Phosphors

Emission and absorption spectra of the alkaline earth sulfides activated with europium and fired in a neutral atmosphere have been re‐investigated. The emission and absorption spectra of the alkaline earth oxides, also activated with Eu, and fired in a neutral or a reducing atmosphere have been obtained. The sulfides show both band emission and band absorption, as does fired in hydrogen. The other hydrogen‐fired oxides have band absorption, except for and give either mixed band and line emission or only line emission. The nitrogen‐fired oxides, except give line emission and little, if any, selective absorption. emits a broad line spectrum for both the nitrogen‐and hydrogen‐fired samples and shows no absorption peaks. Emission and absorption spectra have been correlated with the oxidation state of the activator in the several phosphors, the line emissions being associated with the presence of and the band emissions with .