Evaluation of the lanthanide compression by spectra of europium and terbium compounds

Comparison of the luminescence spectra of europium and terbium compounds was suggested for direct evaluation of the influence of compression of the lanthanide wavefunctions in transition from europium to terbium—‘lanthanide compression’. It is possible because the types of symmetry of the states of the Stark components of europium ⁷F_J energy levels determined previously could be used for assignment of corresponding components of Tb³⁺ energy levels. This procedure can lower the ambiguity of calculations of the crystal field parameters for terbium compounds.     

Spectroscopic Study of the Photophysical Properties of Rare Earth Ions Encapsulated: Water Soluble Functional Calixresorcin[4]Arene

Abstract

A novel macrocyclic compound-water soluble functional calixresorcin[4]arenes—tetra para sulfo-phenylmethyl-calixresorcin[4]arenes was synthesized for the first time. the photophysical properties of terbium and europium ions encapsulated in the macrocyclic ligand were studied in detail. the triplet state energy of the calixresorcin[4]arene was determined to be 24400 cm^?1 by the low temperature phosphorescence spectrum and it was found that it can sensitize both terbium ion and europium ion. the possible energy transfer process between the functional calixresorcin[4]arene and the encapsulated Tb³⁺ and Eu³⁺ was discussed. the luminescence quantum efficiency of Tb³⁺- calixresorcin[4]arene was calculated.     

The sensitivity of the lehn cryptand—europium and terbium (III) complexes to anions compared to a coordinatively saturated systems

Titrations of the Lehn cryptand [Ln⊂bpy.bpy.bpy]³⁺ complexes of both europium (III) and terbium (III) with fluoride and phosphate ions indicate that these anions displace water from the solvation sphere. In the case of the europium complex an enhancement of luminescence intensity is observed, whilst with the terbium complex a reduction in the emission intensity occurs. Described are the preparations of analogous, coordinatively saturated complexes that are inert to the influence of these anions.     

Investigation of the luminescence properties and thermal stability of dysprosium,terbium, and europium ions singly- and co-doped strontium yttrium borate phosphors

A series of trivalent rare-earth element ions (europium, terbium, dysprosium) singly- and co-doped strontium yttrium borate phosphors was synthesized via the sol–gel method. The phase formation, luminescence properties, decay times, and energy transfer behaviors from terbium ions to europium ions, the thermal stability, and the Commission Internationale de L’Eclairage coordinates were investigated. Under the excitation of ultraviolet light, the singly doped phosphors exhibited green emission of terbium ions, white emission of dysprosium ions, and red emission of europium ions, respectively. For the terbium and europium ions co-doped strontium yttrium borate samples, a white emission can be realized by blending the doping concentration of terbium and europium ions. The critical distance between terbium and europium ions has been calculated to be about 14.52?Å and the energy transfer from terbium to europium occurred through the dipole–quadrupole interaction. At 150°C, the emission intensity of terbium and europium in the 12?mol% terbium and 14?mol% europium co-doped strontium yttrium borate sample was maintained at about 74% and 87% of their corresponding initial values, respectively, and the dysprosium ions singly doped strontium yttrium borate sample showed about 70% of its initial emission intensity at room temperature. The above results suggested that europium, terbium, dysprosium ions singly- and co-doped strontium yttrium borate phosphors have potential applications as ultraviolet-convertible phosphors.     

邻苯二甲酸—邻菲罗啉—铕—铽络合体系的荧光性能研究

波长为３６５ｎｍ的紫外光激发下均可发出特征荧光的邻苯二甲酸－邻菲罗啉－铕和铽固体络合物以机械研磨和化学作用两种方式进行混合，研究了这两系列混合络合物的荧光光谱和红外光谱。结果表明，由于铕、铽之间存在相互影响，其荧光强度变化较大，而荧光发射峰位基本不变。经化学混合后铽对铕的荧光强度有极强的敏化作用，铕对铽具有很强的猝灭作用，并用红外光谱对上述四种络合物体系的结构进行了表征     

Luminescent europium(III) and terbium(III) nicotinate complexes covalently linked to a 1,10-phenanthroline functionalised sol-gel glass

Sol-gel glasses with covalently linked lanthanide complexes are luminescent materials which can be processed at ambient temperatures, which have a good solubility and uniform distribution of the complexes in the host matrix. In this study, a luminescent terbium(III) complex was covalently coupled to an organic-inorganic hybrid material prepared by the sol-gel process. This was realised by use of nicotinate groups as the ligands for the terbium(III) ion. The [Tb(C₅H₄NCO₂)₃(phen)(H₂O)₂] complex was immobilised on the sol-gel glass matrix and showed a green photoluminescence upon irradiation with ultraviolet light. The nicotinate groups act as an antenna to absorb the incident light and channel the excitation energy to the terbium(III) ion. The sol-gel glass was also prepared for the corresponding europium(III) complex. In this case, excitation of the europium(III) ion was possible via both the nicotinate ligands and the 1,10-phenanthroline ligands. High-resolution luminescence and excitation spectra were recorded and the radiative lifetimes were measured.     

Ionic distribution and polymer conformation, near phase separation, in sodium polyacrylate/divalent cations mixtures: small angle X-ray and neutron scattering

Anomalous small angle X-ray scattering experiments show that before demixion in sodium polyacrylate/cobalt and sodium polyacrylate/calcium mixtures all the divalent counterions are in the close vicinity of the polyacrylate chain. The present results are consistent with previous UV/VIS spectroscopy, which have shown that all cobalt ions are chemically associated with acrylate groups. The chemical association dehydrates the acrylate monomers. However, the hydrophobicity of the complexed monomers is not strong enough to induce a collapse of the polymer chain at small spatial scale before the demixion. Indeed, the scattered intensity (X-ray and neutron scattering) decreases with the scattering vector q as q^-x with for q > 0.1 nm ^-1 which indicates that the local conformation of the chain is Gaussian. Received 21 January 1999     

The photoluminescent properties of europium and terbium ions co-doped one-dimensional gadolinium orthophosphate nanorods and microcrystals

The europium/terbium ion-doped gadolinium orthophosphate nanorods and microcrystals phosphors were synthesized by the hydrothermal reaction and solid-phase reaction, respectively. The structures, morphologies, and luminescent behaviors were compared. The microcrystals can obtain higher quantum efficiency compared with nanorods because of the different structures (monoclinic and hexagonal). In the ultraviolet-visible region, the gadolinium ions absorbed energy then transferred to europium and terbium ions. The energy transfer from terbium to europium existed both in microcrystals and in nanorods, and it was confirmed that the energy transfer efficiency from terbium to europium in nanorods is higher than that in microcrystals.     

Phosphor material evaluation for use in medical imaging radiation detectors by the noise-equivalent-quanta (NEQ) method

This study presents a method to evaluate the imaging performance of phosphor materials used in medical imaging systems. The advantage of the method is that phosphor evaluation is performed independently of the optical detectors (films, photocathodes, photodiodes) used in radiation detectors to capture phosphor light. The method is based on the noise-equivalent-quanta (NEQ) concept, which provides an index of the signal-to-noise ratio (SNR) associated with the diagnostic value of a medical image. NEQ was expressed as a function of the phosphor’s emitted light wavelength, light energy flux, and modulation transfer function (MTF). All these parameters are related to intrinsic phosphor properties such as effective atomic number, density, activator ion. The method was tested on three yttrium-based phosphors, two of them activated with europium (Eu³⁺) and one with terbium (Tb³⁺). Results showed that europium-activated phosphors (Y₂O₂S:Eu, Y₂O₃:Eu) exhibited improved SNR, whereas the terbium phosphor (Y₂O₂S:Tb) had better MTF. Received: 11 August 1998 / Revised version: 4 January 1999 / Published online: 10 March 1999     

Thermoluminescent analysis of CaSO4:Tb,Eu crystal powder for dosimetric purposes

The motivation of this work was to produce crystals of CaSO₄ doped with an unusual combination of RE elements such as terbium (Tb) and europium (Eu) in different concentrations, and analyze its thermoluminescent (TL) properties. The crystals were produced by the slow evaporation route using calcium carbonate (CaCO₃) as precursor, and incorporating the dopants (Tb₂O₃ and Eu₂O₃) in a solution of sulfuric acid, that is evaporated and collected again, leaving just CaSO₄:Tb,Eu crystal powder. The terbium and europium ions were incorporated in concentration ratios of 1:1, 2:1 and 5:1 (weight proportions). X-ray diffraction analyses showed that samples of doped CaSO₄ exhibit only a single phase corresponding to the crystal structure of anhydrite. The radioluminescence confirmed the presence of Tb³⁺ and Eu²⁺ in the crystal matrix. The CaSO₄:Tb,Eu crystal powders showed TL emission glow curves with three peaks centered around 170 °C, 270 °C and 340 °C, after irradiation with a ⁹⁰Sr/⁹⁰Y source. Thermoluminescent (TL) characteristics such as linearity, reproducibility and fading were evaluated. Samples produced with concentration ratio of 2:1 of Tb and Eu showed the highest TL intensity. The produced CaSO₄:Tb,Eu samples present TL properties useful for dosimetric purposes.     

Magnetization and AC susceptibility of TbxY1-xCo2 compounds

Magnetization and ac susceptibility measurements have been performed on Tb_xY_1-xCo₂ compounds. Samples with x > 0.1 order ferromagnetically below room temperature. The cobalt magnetic moments in these compounds are induced by the internal magnetic field exerted by the terbium moments on the cobalt atoms. The ac susceptibility measurements indicate a change from second order to first order in the ferromagnetic transition for samples with x-values equal or smaller than 0.5.     

Europium precipitation in monocrystalline RbCl and RbBr monitored by optical techniques

In the present paper optical absorption and photoluminescence data dealing with the different precipitated phases of divalent europium ions in rubidium chloride and rubidium bromide single crystals are presented. The europium precipitation processes which occur in these crystals in the low-temperature region (25–100°C) are quite different to those which occur at ≈ 200°C. In fact, the annealing at 70°C produces europium precipitation into a second phase precipitate which appears to be related with the Suzuki phase. However, the aging at 200°C produces the nucleation of at least two metastable precipitates from which grows the stable phase EuX₂. The optical data reported in this paper, together with those previously reported for the different precipitated phases of Eu²⁺ in the sodium and potassium halide series, give a complete picture of the different Eu-second phase precipitates which nucleate in the alkali halides.     

混合固态铕铽配合物的荧光研究

由邻苯二甲酸氢钾,２,２’－联吡啶分别与ＥｕＣｌ３和ＴｂＣｌ３在乙醇水溶液中反应,合成了铕配合物Ｅｕ２Ｌ３Ｌ’和铽配合物Ｔｂ２Ｌ３Ｌ’（Ｌ＝邻苯二甲酸根,Ｌ’＝２,２’联吡啶）;以不同摩尔比混合两种配合物,经机械研磨,得混合固体铕铽配合物。测试了配合物的荧光光谱及红外光谱,结果表明,与单一铕配合物和铽配合物相比,混合固态配合物无论是荧光发射峰位还是荧光强度均发生了明显变化,铽对铕的荧光强度有敏化作     

Surface and bulk phenomena in the process of hydride formation in thin films of rare earth metals: Comparison between terbium and europium

Work function changes ΔΦ caused by H₂ interaction with thin terbium and europium films deposited on glass under UHV conditions were correlated with hydrogen uptake and electrical resistance R, measured in situ. For both metals, the course of ΔΦ(H/Me) at room temperature confirms the change in charge-transfer direction on the surface during hydride formation. As a result, the hydrogen adsorbate's nature is changed from positively polarized (precursor state) to negatively polarized adspecies. The hydrogen behavior is significantly different at low temperature due to the formation of the surface ordered low-temperature phase (α′) with positively polarized hydrogen adspecies. This phase, strongly inhibiting penetration of hydrogen into the bulk, is stable up to 100 K for terbium and 160 K for europium. Increasing temperature above these values resulted in additional large absorption of hydrogen. Moreover, differences in the course of R(H/Me) are clearly noticeable between the investigated metals. The resistance of thin TbH_x (x ∼ 3) films in our experiments did not exceed 1 kΩ, however transition of thin metallic europium film into EuH_y (y ∼ 2) increased the resistance up to 10 MΩ. This dissimilarity in electrical behavior can be explained by the coexistence of two factors which are different for the two metals in question: the phase relation of hydrides and the response of thin film to stress generated during hydride formation.     

Synthesis and Luminescence of a Novel Conjugated Europium Complex with 6-Aniline Carbonyl 2-Pyridine Carboxylic Acid

A novel organic ligand, 6-aniline carbonyl 2-pyridine carboxylic acid (HAP), and the corresponding europium complex, tris(6-aniline carbonyl 2-pyridine carboxylato) europium (III) (Eu-AP) have been designed and synthesized. The results showed that Eu-AP was a conjugated complex, emitting strong red luminescence. The lifetimes of ⁵D₀ of Eu³⁺ in the complex were examined using time-resolved spectroscopic analysis, and the lifetime value was 0.55 ± 0.01 ms for solid Eu(AP)₃. Thermogravimetric analysis showed that the europium complex had good thermal stability.     

Photophysical Properties of Luminescent Quaternary Lanthanide Molecular Hybrid Systems with Chemical Bonds from the Cooperative Design and Assembly of Structure and Function

Two long chain aliphatic acyl chlorides (dodecanoyl chloride (C₁₀H₁₉OCl, abbreviated as DC) and stearoyl chloride (C₁₈H₃₅Ocl, abbreviated as SC)) were modified by means of the amidation reaction with crosslinking molecules (N-aminopropyl-triethoxylsiliane, (APES, H₂N(CH₂)₃Si(OC₂H₅)₃)) and afford two kinds of structural molecular bridge DC (SC)− APES with double reactivity. Subsequently, according to the principle of coordination chemistry, ternary lanthanide (terbium and europium) molecular complex systems with two molecular bridges DC (SC)− APES and 1,10-phenanthroline (phen) of were successfully assembled. Then the modified molecular bridges behave as structural ligands to form the covalent bond Si− O network with matrix precursor (tetraethoxysilane, TEOS) through a sol-gel process (cohydrolysis and copolycondensation process), resulting in a novel quaternary molecular hybrid material (so called as phen-Tb(Eu)−DC(SC)− APES) with strong chemical bonds (N− Tb(Eu)− O coordination bonds and Si− O covalent bonds). And phen behaves as functional ligand to sensitize the luminescence of terbium or europium ions through the effective intramolecular energy transfer process, which gives rise to the characteristic emission of metal ion.     

UV-induced photoluminescence and thermally stimulated luminescence of CaSO4:Eu and CaF2:Tb3+ phosphors

Ultraviolet radiation induced changes in photoluminescence (PL) and thermally stimulated luminescence (TSL) of europium activated calcium sulphate (CaSO₄:Eu³⁺, Eu²⁺) and terbium doped calcium fluoride (CaF₂:Tb³⁺) phosphors have been studied. PL measurements suggest conversion of Eu³⁺ to Eu²⁺ on 254 nm irradiation corresponding to charge transfer band of Eu³⁺ ions and reduction of Eu²⁺ ions with 365 nm illumination representing a f–d transition of Eu²⁺ ions. Similar studies carried out on CaF₂:Tb³⁺ phosphor, however, do not show any significant wavelength specific changes. The integrated TSL output appears to be rate-dependent for both phosphors. The wavelength dependent changes in TSL output observed for CaSO₄:Eu phosphor have been correlated with those obtained in PL studies. The changes in TSL and PL characteristics of CaF₂:Tb³⁺ phosphor have been explained on the basis of stabilisation of traps based on matrix specific charge similarities.     

Enhanced piezoelectric properties of sodium bismuth titanate (Na0.5Bi4.5Ti4O15) ceramics with B‐site cobalt modification

The piezoelectric properties of the cobalt‐modified sodium bismuth titanate (Na_0.5Bi_4.5Ti₄O₁₅, NBT) piezoelectric ceramics were investigated. The piezoelectric properties of NBT ceramics were significantly enhanced by cobalt modification. The Curie temperature T_C and piezoelectric constant d₃₃ for the 0.3 wt% cobalt‐modified NBT ceramics (NBT‐C3) were found to be 663 °C and 30 pC/N, respectively. Thermal annealing studies presented that the cobalt‐modified NBT ceramics possess stable piezoelectric properties, demonstrating that the cobalt‐modified NBT‐based ceramics are promising candidates for high temperature piezoelectric applications. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Effect of C-H bonds on the quenching of luminescent lanthanide chelates

The quenching of europium(III) and terbium(III) chelate luminescence by high-energy C-H vibrational manifolds was studied with two types of stable chelates, i.e., a seven-dentate phenylethynylpyridine derivative and a nine-dentate terpyridine derivative. The replacement of C-H bonds by C-D bonds in the chelating parts of the ligands had a clear positive effect on Eu³⁺ luminescence but a negligible effect on Tb²⁺ luminescence. In aqueous solution, however, the positive effect was undetectable, if the chelating ligand did not create complete shielding of the ion against aqueous quenching. In chelates, where the coordination of water molecules to the inner sphere is prevented, the residual quenching through C-H vibrational quanta can be avoided by replacement of all C-H bonds in the vicinity of the emitting ion by C-D bonds.     

Electrical conductivity of molten mixtures of potassium and sodium fluorides with calcium fluoride

The electrical conductivity of molten mixtures of calcium fluoride with sodium and potassium fluorides was investigated by impedance spectroscopy. The calcium fluoride additions to alkali metal fluoride melts decrease their electrical conductivity. Small additions of potassium and sodium fluorides to CaF₂ do not change its conductivity essentially.