Luminescence of europium trifluoroacetates

The luminescence spectral characteristics of mixed-ligand europium trifluoroacetates with nitrogen- and phosphorus-containing neutral ligands were studied at different temperatures. For several trifluoroacetates, the intensity of luminescence increased with temperature. The diffuse reflectance data were analyzed, and a mechanism of thermal luminescence buildup was suggested. Original Russian Text ? I.V. Kalinovskaya, A.N. Zadorozhnaya, A.G. Mirochnik, V.E. Karasev, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 6, pp. 1175–1177.     

Fluorescence properties of mixed-ligand europium carboxylates

Mixed-ligand binuclear and mononuclear europium carboxylate complexes with nitrogen-and phosphorus-containing neutral ligands have been studied by luminescence and X-ray photoelectron spectroscopy. The coordination of neutral ligands through the nitrogen donor atom leads to an increase in electron density at the Eu³⁺ atom. In groups of carboxylates of the same type, the coordination of neutral donor ligands leads to an increase in the relative intensity of the ⁵ D ₀-⁷ F ₄ electric dipole transition. Analysis of the luminescence excitation spectra points to the presence of two excitation energy transfer channels for mixed-ligand europium trifluoroacetate and toluate complexes and of one channel for europium cinnamate complexes with neutral ligands.     

Photochemical properties of mixed-ligand complexes europium carboxylates

The photochemical behavior of mixed-ligand complexes of europium carboxylates with nitrogen-and phosphorus-containing neutral ligands of island and dimer types, Eu(L)₃ · xD · nH₂O and [Eu(L)₃ · xD]₂ · nH₂O (L is the trifluoroacetate, toluate, or cinnamate anion), was studied. During UV irradiation of the complexes of europium carboxylates with 1,10-phenanthroline and 2,2′-dipyridyl, a luminescence buildup was observed. EPR measurements demonstrated that the observed buildup of luminescence from europium occurs in parallel with the increase of the concentration of radical anions formed from neutral ligands.     

Carboxylato-bis-dibenzoylmethanates of europium(III): Luminescence and magnetic properties

The luminescent and magnetic properties of europium(III) carboxylates, determined from the structure of Stark and Zeeman sublevels, are studied. It is found that the values of the λ_lum energy gap between the ground state ⁷ F ₀ and ⁷ F ₁ term in the luminescence spectra and λ_magn obtained from magnetochemical measurements correlate well.     

Luminescence and magnetic properties of europium(III) nitrate complex with 1,10-phenanthroline

Luminescent and magnetic properties of the europium nitrate complex with 1,10-phenanthroline synthesized in the traditional way by precipitation from water-ethanol medium and by the method of mechanical activation were investigated. Correlations between luminescent and magnetic properties of the complex compounds were revealed. The higher value of molar magnetic susceptibility ??_m was shown to be typical for the highly dispersed europium compound obtained by mechanochemistry method due to the presence of the paramagnetic ion Eu²⁺.     

Luminescent and magnetic properties of europium compounds with cinnamic acid

The temperature dependences of the molar magnetic susceptibility of luminescent europium compounds with cinnamic acid [Eu(Cin)₃] _n and Eu(Cin)₃ · 2D · H₂O (where Cin is the cinnamic acid anion and D is phen (1,10-phenanthroline) or dipy (2,2-dipyridyl)) were studied at temperatures from 300 to 2 K. The molar magnetic susceptibility of the compounds increased in the series Eu(Cin)₃ · 2dipy · H₂O < Eu(Cin)₃ · 2phen · H₂O < [Eu(Cin)₃] _n . The energy distances λ_lum between the ⁷ F ₀ ground level and the ⁷ F ₁ state in the luminescence spectra correlated well with λ_magn obtained from magnetochemical data.     

Mechanochemical synthesis of mixed-ligand europium β-diketonates with nitrogen-containing neutral ligands

The solid-phase reaction between europium salts of β-diketones and nitrogen-containing neutral ligands in a planetary mill produces luminescent mixed-ligand compounds Eu(β-dic)₃ · D, where β-dic stands for dibenzoylmethane (DBM), benzoylacetone (BA), thenoyltrifluoroacetone (TTA), or benzoyltrifluoroacetone (BTFA); and D stands for 1,10-phenanethroline (Phen), 2,2-dipyridyl (Dipy), or diphenylguanidine (DPG). The mechanosynthesis and yield of lanthanide β-diketonates are studied as affected by the treatment parameters and the nature of the reagents. Powder X-ray diffraction demonstrates a staged course of the mechanochemical synthesis. Examination of formation-rate curves shows that grinding/stirring is the rate-controlling stage of the process. Thermogravimetric analysis (TGA) shows that the mechanosynthesis can proceed in the self-propagation mode. The relative luminescence intensity is determined as a function of treatment time. Particles of the mechanically activated mixture have sizes of 10–100 μm.     

Mössbauer study of mixed-ligand complexes of europium(III)

A series of europium(III) mixed complexes was prepared containing 1,10-phenanthroline or 2,2-bipyridine as neutral ligand and simple inorganic anions or benzoate and its derivatives as ionic ligands. The Mössbauer spectra of the products indicated that both types of ligands were directly coordinated to the central europium(III) atom. The Mössbauer isomer shift values reflected both electron shifting and steric effects of the substituents on the ligand. The quadrupole splitting values pointed to the similar symmetry of the electron shell of the europium in almost all complexes with analogous composition. The IR spectra provided evidence of the binding mode of the carboxylate groups in the complexes containing benzoate or its derivatives. The x-ray photoelectron spectra of the compounds demonstrated the effects of electrophilic and nucleophilic substituents on the electron binding energies in the europium, oxygen, and nitrogen orbitals.     

Luminescence studies of the thermal dehydration of europium trifluoride

The thermal dehydration of hydrated europium trifluoride has been followed by high-resolution luminescence spectroscopy and thermogravimetric analysis. For EuF₃ precipitated by aqueous HF, it was determined that the bound water of hydration actually existed in two forms, which were removable at low (100–250°C) and high (350–550°C) temperatures. Calcination of this material at still higher temperatures produced anhydrous EuF₃ contaminated by EuOF. Precipitation of EuF₃ by NH₄F resulted in the occlusion of variable amounts of ammonium fluoride, but in these materials only the low-temperature water was contained. Extensive ethanol washing of the NH₄F-precipitated EuF₃ led to removal of the ammonium fluoride, but this hydrated material was not found to contain the high-temperature water. Neither material prepared by NH₄F precipitation exhibited any tendency towards EuOF formation. It would thus appear that the EuOF compound is formed only during the loss of the high-temperature water, and if this water is not present in the sample then one may form anhydrous EuF₃ free from EuOF contamination.     

Synthesis, structural and magnetic properties of diphenoxo-bridged binuclear mixed-ligand Cu(II) complexes

The copper(II) complexes [Cu₂(phen)₂(HL¹)₂] (ClO₄)₂ (1) and [Cu₂(phen)₂(HL²)₂] (ClO₄)₂ (2) synthesized from two potentially tridentate ligands N-(2-hydroxybenzyl) propanolamine (H₂L¹) and N-(5-methyl-2-hydroxybenzyl) propanolamine (H₂L²) have centrosymmetric bis(μ₂-phenoxo)-bridged dicopper(II) structures. Variable temperature magnetic measurements have revealed the existence of relatively weak antiferromagnetic interactions (1: 2J=−212.5, 2: 2J=−337.0 cm⁻¹) with respect to the bridging angles (1: θ=101.47(18)°, 2: θ=102.79(12)°). The results suggest that the distortion index of the Cu(II) atoms (1: τ=0.73, 2: τ=0.53) may be the major factor governing the spin coupling between the copper(II) centers of these diphenoxo-bridged binuclear complexes. The coordination moieties of complex 1 are connected into a 1D linear structure via intermolecular hydrogen bonds between alkoxyl, amine, and perchlorate groups.     

Luminescence determination of europium microquantities after its preconcentration on polyurethane foam

Sorption of the mixed-ligand complexes of europium(III) with thenoyltrifluoroacetone (TTA) and 1,10-phenanthroline (Phen) on polyurethane foam (PUF) has been studied by a luminescence method. The optimum conditions of sorption have been found. The sorbate composition on PUF has been determined (the Eu:TTA:Phen ratio was 1:3:1). Luminescence spectra of the europium complexes in solution and on PUF at 77 K have been investigated. It was concluded that the character of the Eu³⁺ coordination both in solution and on the sorbent is the same. Stability constants for the complexes in solution (lg K = 8.4) and on the sorbent (lg K = 5.5) have been calculated. The decrease of the stability of the complex on PUF is explained by the deformation of the complex molecule in the sorbent phase. Sorption coefficients for europium (245) and scandium (2.35) and the coefficient of selectivity for europium in Sc₂O₃ (102.3) have been determined. A method for the sorption-luminescence determination of europium in Sc₂O₃ with a lower limit of contents determined of 1 × 10⁻⁶⁰% has been developed.     

Luminescence studies of europium chelates with increasing benzene ring substituents ligand-doped polymer

The luminescence properties of four europium chelates with increasing benzene ring substituents ligand in poly(methylmethacrylate) (PMMA) have been investigated by fluorescence emission spectra and lifetime measurements. According to the fluorescence emission spectra, the Judd-Ofelt parameters Omega2, Omega4 of europium chelates-doped PMMA have been calculated and the radiative properties were also presented. It showed that the increase of benzene ring substituents in ligand can increase the metastable state lifetime tau(m), the luminescence quantum yield eta and the stimulated emission cross-section sigma of 5D0-->7F2 transition.     

Synthesis and spectral properties of europium phthalocyanine complexes

Methods for the synthesis of europium complexes with phthalocyanine and thenoyltrifluoroacetonate (tta) or ferrocenoyltrifluoroacetonate (fta) ligands are discussed. The spectral characteristics of the complexes PcEu(tta)(ttaH) and PcEu(fta)(ftaH) (Pc is phthalocyanine) are studied.     

Luminescence of ytterbium(III) in mixed-ligand compounds with cinnamic acid and neutral phosphorus-containing ligands

The luminescence spectral characteristics of mixed-ligand compounds of ytterbium(III) with cinnamic acid and neutral phosphorus-containing ligands were studied by luminescence spectroscopy. The intensity of luminescence of the compounds was determined. The highest intensity of luminescence was found for the ytterbium(III) compound with triphenylphosphine oxide.     

DNA binding and photocleavage properties of two mixed-ligand oxovanadium complexes

An oxovanadium complex [VO(satsc)(bipy)] (1) (satsc = salicylaldehyde thiosemicarbazone, bipy = 2,2′-bipyridine) and its dibromo derivative [VO(3,5-dibrsatsc)(bipy)] (2) (3,5-dibrsatsc = 3,5-dibromosalicylaldehyde thiosemicarbazone) have been synthesized and characterized by elemental analysis, IR, ES-MS and ¹H NMR. The interaction of these two complexes with calf-thymus DNA (CT-DNA) was studied using UV/Vis, fluorescence spectroscopic titration, viscosity measurements and thermal denaturation. The results suggest that complexes 1 and 2 interact with CT-DNA by intercalative modes. The DNA-binding affinity of complex 1 is larger than that of complex 2. In addition, their photocleavage reactions with pBR322 supercoiled plasmid DNA were investigated by gel electrophoresis experiments. Both complexes exhibit significant DNA cleavage activity, and complex 1 showed greater cleaving efficiency than complex 2.     

The preparation and fluorescence properties of europium nanoparticles

A new structured metallic nanomaterial of europium nanoparticle was prepared using tannic acid as the reductive agent,and nanoeuropium protein conjugates were synthesized by the method of lipoic acid modification on the surface of nanoparticle,which opens a new field of application of lanthanides in nanotechniques.Their properties were also characterized by UV-vis absorption spectroscopy,transmission electron microscopy (TEM),and fluorescence spectroscopy.The europium nanoparticle and its protein conjugates solution were stable and water-soluble.The fluorescence intensity of the composite europium nanoparticles was significantly increased in the presence of trace protein,and was linear proportional to the concentration of proteins under optimum conditions.According to this,a fluorimetric method for the determination of protein was developed in this paper.     

Luminescence of europium(III) β-diketonate complexes in a Nafion membrane

EuL₃ · phen complex compounds (L is benzoylacetone, dibenzoylmethane, or thenoyltrifluoroacetone; phen is 1,10-phenanthroline) were synthesized in a perfluorosulfonic membrane. The results of adsorption measurements suggest that the complexes experience steric hindrances in the membrane pores. The luminescence from intercalates is sensitized due to the increase in the degree of population of the ⁵ D ₀ excited state of europium(III) caused by the transfer of energy from the ligands. Depending on the type of β-diketonate ligand, the adsorption of water on the modified membrane can enhance or suppress the luminescence from the complex.