Trivalent Eu Research Articles

Observation of non-Fermi liquid behavior in hole-doped Eu2Ir2O7

The Weyl semimetallic compound Eu2Ir2O7 along with its hole doped derivatives (which is achieved by substituting trivalent Eu by divalent Sr) are investigated through transport, magnetic and calorimetric studies. The metal-insulator transition (MIT) temperature is found to get substantially reduced with hole doping and for 10% Sr doping the composition is metallic down to temperature as low as 5 K. These doped compounds are found to violate the Mott-Ioffe-Regel condition for minimum electrical conductivity and show distinct signature of non-Fermi liquid behavior at low temperature. The MIT in the doped compounds does not correlate with the magnetic transition point and Anderson-Mott type disorder induced localization may be attributed to the ground state insulating phase. The observed non-Fermi liquid behavior can be understood on the basis of disorder induced distribution of spin orbit coupling parameter which is markedly different in case of Ir4+ and Ir5+ ions.

Gel-combustion assisted synthesis of eulytite-type Sr3Y(PO4)3 as a single host for narrow-band Eu3+ and broad-band Eu2+ emissions

Abstract A series of eulytite-type Sr3Y1-x(PO4)3:xEu3+ (x = 0–0.13) and Sr3-yY(PO4)3:yEu2+ (y = 0–0.10) phosphors were successfully synthesized via gel-combustion and subsequent calcination in O2 and Ar/H2 atmospheres at 1250 °C, respectively. Detailed crystal structure analysis via Rietveld refinement showed that the phosphors were crystallized in the cubic system (space group I-43d, No. 220), in which the Eu3+ and Eu2+ activators reside at the Y3+ and Sr2+ sites, respectively. The trivalent Eu3+ ions (CN = 6) exhibited typical narrow-band luminescence via intra-4f6 transitions, with the red emission at ~ 615 nm being dominant (5D0 → 7F2 transition, FWHM = 15.9 ± 0.2 nm). The divalent Eu2+ ions (CN = 6 and 9) showed broad-band luminescence ranging from light-blue to blue via 4f65d1 → 4f7 transitions (FWHM = 115 ± 2 nm). The optimal Eu3+ and Eu2+ concentrations were determined to be 10 at% (x = 0.10) and 7 at% (y = 0.07), respectively, and the mechanisms of concentration quenching were discussed. The excitation/emission properties, fluorescence decay kinetics, CIE chromaticity, and particularly the rarely addressed thermal stability of the phosphors were investigated in detail.

Enhanced luminescent properties in Eu3+-activated SrMoxW1-xO4 red-emitting phosphors for solid-state lighting and field-emission displays

We fabricated the trivalent Eu3+-activated SrMoxW1-xO4 phosphors by a high-temperature solid-state reaction technique. The prepared phosphors were characterized by X-ray diffraction patterns, field-emission scanning electron microscope images, luminescence decay curves, photoluminescence (PL) spectra, and cathodoluminescence (CL) spectra. Under the ultraviolet (UV) illumination, the emissions of Eu3+ ions with an intense peak at 615 nm were observed, indicating the Eu3+ ions occupied at the low symmetry sites without inversion in host lattices. With the addition of the Mo6+ ions, the emission intensity of the studied samples was increased and the optimum result was obtained when x = 0.9. The temperature-dependent PL emission spectra were measured to explore the thermal stability of the resultant compounds. The final products emitted visible red emissions with high color purity of 95.1%. The CL spectra revealed that the synthesized compounds also exhibited superior CL performance. These characteristics make the Eu3+-activated SrMoxW1-xO4 red-emitting phosphors a promising candidate for UV-based white light-emitting diode and field-emission display applications.

Speciation of the trivalent f-elements Eu(III) and Cm(III) in digestive media

In case radioactive materials are released into the environment, their incorporation into our digestive system would be a significant concern. Trivalent f-elements, i.e., trivalent actinides and lanthanides, could potentially represent a serious health risk due to their chemo- and radiotoxicity, nevertheless the biochemical behavior of these elements are mostly unknown even to date. This study, therefore, focuses on the chemical speciation of trivalent f-elements in the human gastrointestinal tract. To simulate the digestive system artificial digestive juices (saliva, gastric juice, pancreatic juice and bile fluid) were prepared. The chemical speciation of lanthanides (as Eu(III)) and actinides (as Cm(III)) was determined experimentally by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and the results were compared with thermodynamic modeling. The results indicate a dominant inorganic species with phosphate/carbonate in the mouth, while the aquo ion is predominantly formed with a minor contribution of the enzyme pepsin in the stomach. In the intestinal tract the most significant species are with the protein mucin. We demonstrated the first experimental results on the chemical speciation of trivalent f-elements in the digestive media by TRLFS. The results highlight a significant gap in chemical speciation between experiments and thermodynamic modeling due to the limited availability of thermodynamic stability constants particularly for organic species. Chemical speciation strongly influences the in vivo behavior of metal ions. Therefore, the results of this speciation study will help to enhance the assessment of health risks and to improve decorporation strategies after ingestion of these (radio-)toxic heavy metal ions.

NMR studies on EuNi2Si2 with trivalent Eu ion

We have performed 29Si nuclear magnetic resonance experiment to investigate microscopic magnetic properties of EuNi2Si2 with trivalent Eu ion. The temperature dependence of the nuclear spin-lattice relaxation rate 1/T1 can be explained by considering the two relaxation processes: conduction electrons and the thermally activated spins in the excited levels of J-multiplet. The temperature dependence of the Knight shift could roughly be reproduced with the spin-orbit coupling constant estimated from 1/T1.

Effects of synthesis conditions on ion exchange properties of α-zirconium phosphate for Eu and Am

Abstract Three zirconium phosphate products A, B and C, made through different synthesis routes, were investigated for their europium and americium ion exchange properties utilizing radiotracers 152Eu3+ and 241Am3+. Aim of this investigation was to see how material properties change based on different synthesis, and how does the changes effect on trivalent Eu and Am uptake and affinities on the materials. Ultimate goal of an ongoing research is to create inorganic exchanger suitable for separation of trivalent actinides and lanthanides. Powder X-ray diffraction showed that all three products had same α-zirconium phosphate crystal structure. The P:Zr ratio determined by microscope X-ray microanalysis was also the same for all products: 2.43±0.05. However, infrared absorbance, material acidity, particle morphology, and Eu and Am distribution coefficients differed significantly between products. The intensities of the strong IR absorption at approximately 960 cm−1, attributed to vibrations of the orthophosphate group, were in descending order B>C>A. Material acidity showed the same descending order B>C>A. First acidity constants pK a1 were 2.3 for product B, 3.1 for C and 3.5 for A. Unit cell volumes increased in the reverse order: B<C<A. Distribution coefficients (K D), studied for pH 0 to 3 nitric acid media, varied remarkably. For any given pH the K D descended in the order A>C>B for both Eu and Am. Separation factors, defined as K D(Eu): K D(Am), were from 4 to 41 for product A, from 5 to 15 for B, and from 3 to 7 for C. Selectivity coefficients (k M/H, M=Eu, Am) and sorption strength decreased along with increasing ZrP product acidity. Metal binding coefficients (k M) had high values, up to 109, especially in ZrP C and A, while the selectivity coefficients were low, 10−5 to 10−1, because they relate to the third power of the low pK a1. It was observed that for ZrPs there are strong interdependencies between acidity of the product, unit cell volume, IR absorption, K D, k M/H and k M. Finally, it can be concluded that the ion exchange properties of α-ZrP products can be modified considerably by varying their synthesis conditions, perhaps to tailor specific actinide/lanthanide separations.

Synthesis, Crystal Structure, and Magnetic Properties of Pyrochlore‐Type Eu2Ta2(O,N)7+δ

Pyrochlore‐type Eu2Ta2(O,N)7+δ phases were prepared by reaction of ammonia with an amorphous europium tantalum oxide precursor. 151Eu Mössbauer and EPR spectroscopy as well as magnetic susceptibility measurements point to the presence of exclusively Eu3+. For phase‐pure samples (X‐ray powder diffraction), the nitrogen content varies between 1.0 and 1.8 wt %, leading to compositions in the range Eu2Ta2O7.1N0.6 – Eu2Ta2O6.5N1.0. Pyrochlore‐type phases are structurally derived from the fluorite type with 1/8 of the anions missing, resulting in an ideal composition A2B2X7. In Eu2Ta2(O,N)7+δ the excess anions partly occupy these vacancies. The prepared phases are colorless with a direct optical bandgap of 4.3 eV and they show the typical Van Vleck paramagnetic behavior known for trivalent Eu atoms.

Synthesis and characterization of a liquid Eu precursor (EuCppm2) allowing for valence control of Eu ions doped into GaN by organometallic vapor phase epitaxy

A liquid Eu precursor, bis(normal-propyl-tetramethylcyclopentadienyl)europium has been synthesized. This precursor exists as a liquid at temperatures higher than 49 °C, has a moderately high vapor pressure, contains no oxygen in its molecular structure, and can be distilled to high purity. These properties make it ideal for doping using a chemical vapor or atomic layer deposition method, and provide a degree of control previously unavailable. As a precursor the Eu exists in the divalent valance state, however, once doped into GaN by organometallic vapor phase epitaxy, the room-temperature photoluminescence of the Eu-doped GaN exhibited the typical red emission due to the intra-4f shell transition of trivalent Eu. After variation of the growth temperature, it was found that divalent Eu could be stabilized in the GaN matrix. By tuning the Fermi level through donor doping, the ratio of Eu2+ to Eu3+ could be controlled. The change in valence state of the Eu ions was confirmed using X-ray absorption near-edge structure.

二价与三价铕共掺杂的硫酸锶荧光特性

二价与三价铕共掺杂的硫酸锶荧光特性

Luminescence Properties of Eu/Tb Activated Y 2 O 3 Phosphors Synthesized by Solid State Process

Rare-earth doped phosphors with tunable optical properties have potential applications in solid state lighting, such as display panels and fluorescent lamps. Herein, trivalent Eu 3+ , Tb 3+ activated Y 2 O 3 phosphors were synthesized by a solid state process. The phase structure was analyzed by X-ray diffraction. The results show the pure phase of Y 2 O 3 is obtained and RE ions do not exhibit any effect on the structural properties. Single RE ions activated Y 2 O 3 phosphors display their characteristic emission. With Tb 3+ doped in Y 2 O 3 , a bright green emission is obtained; when Eu 3+ is introduced into the material Y 2 O 3 : Tb 3+ , the emission color can be adjusted to white light. The calculated CIE chromaticity coordinates of RE ions activated Y 2 O 3 phosphors confirm the green and white emissions

Negative cerium anomalies in manganese (hydr)oxide precipitates due to cerium oxidation in the presence of dissolved siderophores

We present experimental results on the sorption behavior of rare earth elements and yttrium (REY) on precipitating manganese (hydr)oxide in the presence of the biogenic siderophore desferrioxamine B (DFOB). In marked contrast to inorganic systems, where preferential adsorption of HREY and depletion of LREY is commonly observed in manganese (hydr)oxide precipitates, sorption of REY in presence of the DFOB siderophore leads to HREY-depleted and LREY-enriched patterns in the precipitates. Moreover, our data indicate that surface oxidation of Ce(III) to Ce(IV) during sorption onto manganese (hydr)oxides and the resulting development of a positive Ce anomaly, which are commonly observed in inorganic experiments, are prevented in the presence of DFOB. Instead, Ce(III) is oxidized to Ce(IV) but associated with the dissolved desferrioxamine B which forms complexes with Ce(IV), that are at least twenty orders of magnitude more stable than those with Ce(III) and REY(III). The overall result is the formation of a positive Ce anomaly in the solution and a negative Ce anomaly in the Mn (hydr)oxides. The distribution of the strictly trivalent REY and Eu(III) between the manganese (hydr)oxide phase and the remaining ambient solution mimics the distribution of published stability constants for complexes of REY(III) with DFOB, i.e. the heavy REY form more stable complexes with the ligand and hence are better shielded from sorption than the LREY. Surface complexation modeling corroborates our experimental results. Negative Ce anomalies in Mn precipitates have been described from biogenic Mn oxides. Our results provide experimental evidence for the development of negative Ce anomalies in abiogenic Mn (hydr)oxide precipitates and show that the presence of the widespread siderophore desferrioxamine B during mineral precipitation results in HREY-depleted Mn (hydr)oxides with negative Ce anomalies.

Radioluminescence Properties of Europium Doped Strontium Aluminum Borate Glass

Recent topics of scintillation materials were development of halide single crystals which exhibit high energy resolution such as divalent Eu doped strontium iodide and novel solid neutron scintillators which contains high efficiency luminescent centers and Li-6 or B-10 ions which convert neutron to charged particles. One of the most traditional neutron scintillator is Ce doped Li silicate glass. On the other hand, Eu doped glass scintillators were not almost studied. We studied radioluminescence properties of Eu doped strontium aluminum borate glass (Eu 0.1% : 35 SrO – 15 Al2O3 – 50 B2O3) in order to obtain divalent Eu doped borate glass. As a result of X-ray excited luminescence, emission peaks were observed around 600 nm; they are originated from trivalent Eu. Emission peak was also observed around 400 nm; it might be originated from defect or divalent Eu. Detail of X-ray excited luminescence around 400 nm and Eu doping concentration dependence of radioluminescence spectra will be discussed on the conference.

The specific sorption of Np(V) on the corundum (α-Al2O3) surface in the presence of trivalent lanthanides Eu(III) and Gd(III): A batch sorption and XAS study

The sorption of pentavalent neptunium, Np(V), on corundum (α-Al2O3) was investigated in the absence and presence of trivalent europium or gadolinium as a competing element under CO2-free conditions. The objective of this study was to investigate how a trivalent metal ion with a higher charge than that of the neptunyl(V) ion would affect the sorption of Np(V) when allowed to adsorb on the mineral surface before the addition of Np(V). Batch sorption experiments conducted as a function of pH (pH-edges) and as a function of Np(V) concentration (isotherms) in the absence and presence of 1×10−5M Eu(III) showed no sign of Eu being able to block Np sorption sites. Surface complexation modelling using the diffuse double layer model was applied to the batch data to obtain surface complexation constants for the formed Np(V) complexes on corundum. To account for potential changes occurring in the coordination environment of the neptunium ion in the presence of a trivalent lanthanide, X-ray absorption spectroscopy (XAS) measurements were carried out on the samples containing only Np(V) and Np(V)+Gd(III). The results reveal the presence of a bidentate Np(V) edge-sharing complex on the corundum surface in the absence of Gd(III), while the coordination environment of Np(V) on the corundum surface could be changed when Gd(III) is added to the sample before the sorption of Np(V).

Energy transfer between Dy3+ and Eu3+ in Dy3+/Eu3+-codoped Gd2MoO6

Dy3+-doped and Dy3+/Eu3+-codoped Gd2MoO6 phosphors were synthesized by hydrothermal method. The results of X-ray diffraction indicate that the Gd2MoO6 phosphors have crystallized with the monoclinic structure. The emission spectra exhibit emissions at 577 nm and 488 nm that corresponded to the yellow and blue emissions, respectively. The emission intensity of these bands increases with the rise of the Dy3+ up to a particular concentration and then reduces at a higher level. The observed behaviour was explained on the basis of concentration quenching phenomena. The enhancement in the emission intensity of the Dy3+ with the addition of Eu3+ along with the red emission at 617 nm for Eu3+ was noted. The energy transfer between the two rare earth ions was studied. Codoping with the trivalent Eu ions neutralized the red emission part of the phosphor. Thus, by incorporating the adequate quantity of Eu3+ the photometric characteristics of the phosphors can be adjusted.

Application research of CdS: Eu3+ quantum dots-sensitized TiO2 nanotube solar cells

Trivalent Eu3+-doped CdS quantum dot (CdS: Eu3+ QD)-sensitized TiO2 nanotube arrays (TNTAs) solar cells are prepared by using the direct adsorption method. The influences of sensitization time, sensitization temperature, and Eu3+ ion concentrations are investigated systematically. The photo-current of the CdS: Eu3+ QDs/TiO2 nanotubes appear at the main absorption region of 320–480nm, and the maximum incident photon to the current conversion efficiency (IPCE) value is 21% at 430nm when the sensitization condition is 4% doping Eu3+ concentration, 60°C sensitization temperature, 8h sensitization time. Compared with the un-doped CdS QD-sensitized TNTAs, the conversion efficiency and IPCE of CdS: Eu3+ QDs/TNTAs are two times and three times than that of un-doped CdS QDs sensitized TNTAs. This scenario exhibits the potential applications of rare earth elements in QD-sensitized solar cells.

A case study of energy transfer mechanism from uranium to europium in ZnAl2O4 spinel host by photoluminescence spectroscopy

Zinc aluminate (ZAO), a member of spinel class of inorganic compounds has been of much interest of late due to its wide range of use in catalysis, optical, electronic and ceramic industries. When doped with several lanthanides, this material has proved to be a potential host matrix for phosphors. As lanthanides suffer from poor (direct) excitation and emission cross sections, the use of a co-dopant ion can help to circumvent this and extract better emission from a lanthanide doped ZAO system. In this connection, energy transfer mechanism from uranium to europium in the ZAO host was investigated by photoluminescence spectroscopic technique. It was seen that uranium gets stabilized in the hexavalent state as UO66− (octahedral uranate) where as the lanthanide ion, Eu is stabilized in its trivalent state in the ZAO host. In the co-doped system, an efficient energy transfer pathway from the uranate to europium ion was observed. Based upon emission and life time data a suitable mechanism was proposed for the energy transfer (quenching) process. It was proposed that after excitation by photons, the uranate ions transfer their energy to nearby 5D1 level of Eu3+ ions which non-radiatively de-excites to the corresponding lower levels of 5D0. Further this 5D0 level decays in a radiative mode to the 7F manifold giving the characteristic emission profile of trivalent Eu. It was proposed that both static and dynamic types of energy transfer mechanism were responsible for this process.

Structure and Luminescence Properties of Y\(_2\)O\(_3\): Eu\(^{3+}\) Nanophosphors

Europium trivalent (Eu\(\mbox{} ^{3+}\), 2%) doped Y\(_2\)O\(_3\) nanophosphors were synthesized by solgel method and annealed at temperature 600 \(^\circ\)C and 900 \(^\circ\)C. The phosphors were characterized by XRD, FTIR, UV-visible and PL spectroscopy. The average crystal size was in the range of 10-26 nm. FTIR spectra show that the intensities of all impurity peaks get reduce with increasing annealing temperature. The band gap was determined from the diffuse reflectance (DR) spectra using the K-M function. The photoluminescence spectra were describe by well known \(\rm ^5D_0\)-\(\rm ^7F_j\) transitions \((J=0,1,2,3,4)\) of Eu\(^{3+}\) ions.

Macroscopic and spectroscopic investigations on Eu(III) and Cm(III) sorption onto bayerite (β-Al(OH)3) and corundum (α-Al2O3)

The interaction of trivalent Cm and Eu with the aluminum hydroxide bayerite (β-Al(OH)3) and the aluminum oxide corundum (α-Al2O3) was investigated by batch sorption experiments and time resolved laser fluorescence spectroscopy (TRLFS). The experimental methods for both polymorphs show similar pH dependent sorption behavior at trace metal ion concentrations (∼10−7M), i.e. similar Eu sorption edges and nearly identical Cm speciation between pH=3 and 13. In this pH range the Cm aquo ion as well as the Cm(III) surface species surface⋯Cm(OH)x(H2O)5−x (x=0, 1, 2) can be distinguished by TRLFS. The similar sorption data point to a (surface) transformation of the thermodynamically unstable Al2O3 surface into bayerite, in agreement with the similar isoelectric points obtained for both minerals (pHIEP=8.6–8.8). The pH dependent surface charge is most likely due to the protonation/deprotonation of singly coordinated Al–OH surface groups, prevailing on the edge planes of the rod-like bayerite crystals and the surface of the colloidal Al2O3 particles. These surface groups are also believed to act as ligands for lanthanide/actinide(III) surface complexation. In contrast to the similar sorption behavior at trace metal ion concentrations, discrepancies are observed at higher Eu levels. While similar sorption edges occur up to 7×10−7M Eu for corundum, the pH edge on bayerite is gradually shifted to higher pH values in this Eu concentration range. The latter behavior may be related either to the existence of multiple sorption sites with different sorption affinities, or to the influence of an additional amorphous Al-phase, forming in the course of the bayerite synthesis.

Thermal Degradation of Nitride Phosphors

Thermal stability of phosphors for solid state lighting is usually investigated by in-situ measuring the thermal quenching behavior of the sample heated up to ~ 300oC and held at each temperature for a certain time. However, thermal quenching does not have the same meaning with thermal degradation, which thus cannot evaluate the stability of the phosphor against thermal attacks comprehensively. In this work, we attempted to study the thermal degradation of nitride phosphors (i.e., SrSi2O2N2:Eu and CaAlSiN3:Eu) by baking the powders in air or in pressued water steam at high temperatures. The degradation mechanism was discussed and clarified by carrying out the surface state analysis using various techniques. For SrSi2O2N2:Eu, the PL intensity decreased as the baking temperature rises, degrading by 10 and 30% when the samples baked at 500 and 600oC, respectively. In comparison with Ca-α-sialon:Eu2+ that retained its luminescence up to 800oC, SrSi2O2N2:Eu showed a very serious thermal degradation. By conducting the high-temperature in-situ XRD analysis and TEM observations, an impurity phase of SrSiO3 was identified additionally, as a result of the oxidation of the host SrSi2O2N2. In addition, the activator ions were also oxidized during baking in air, with divalent Eu2+ changed into trivalent Eu3. It indicates that both of the oxidation of host and activators leads to the thermal degradation of SrSi2O2N2:Eu that is an irreversible decrease of luminescence. For (Sr,Ca)AlSin3:Eu (SCASN), the moisture-induced degradation was comprehensively investigated by treating it under a severe condition of high-pressure water steam. The degradation initiated at 150oC, and the luminescence of SCASN was seen to be quenched quickly, with the powder sample being bleached after the treatment. Both of the microstructure and phase changed obviously with the oxidation, and the host turned finally into NH3, (Sr,Ca)Al2Si2O8 and Ca(OH)2. By using a variety of spectroscopic, surface and microstructure analytic techniques, the degradation mechanism was clarified and proposed to occur viathe oxidant-gas penetration mechanism through the moisture-enhanced oxidation of both the SCASN host and divalent europium.

A Novel Facile Room Temperature Chemical Lithiation for Reduction of Eu3+ in NASICON Crystal Structure

AbstractFacile and effective synthesis strategy is dramatically desirable for basic studies and practical applications of Eu2+ luminescent materials. In this work, facile chemical lithiation is used for reduction of trivalent Eu3+ ions into divalent Eu2+ ions in Eu1/3Zr2(PO4)3 crystal structure using nBu‐Li solution at room temperature. VUV/Vis luminescence properties, X‐ray absorption near edge structure (XANES), and magnetic properties were used to characterize the valence state of Eu ions in crystal structure of host lattice. The emission light color changes from orange‐red [Eu1/3Zr2(PO4)3] to blue‐green [LixEuIIxEuIII1/3–xZr2(PO4)3], and the samples are paramagnetic after this facile chemical lithiation. The ultra‐fast decay time (<50 ns) of Li0.286EuII0.286EuIII0.047Zr2(PO4)3 is attributed to the luminescence quenching effects of Eu3+ and Eu2+ co‐existing in the crystal structure. All the results indicate that this chemical lithiation method is a facile and effective method for Eu2+ luminescent materials fabrication and LixEuIIxEuIII1/3–xZr2(PO4)3 is a potential luminescent material.