Investigation of the formation of nanostructures of Ln(III) salts with phosphate and carbonate anions using Eu(III) chelates as luminescent markers

The monitoring of variations in the luminescence intensity (I _lum) of nanostructures of Eu(MBTA)₃phen (MBTA is p-methoxybenzoyl trifluoroacetonate) complexes formed in aqueous solutions upon the introduction of anions is proposed as a method of analyzing the composition of Eu(III), Gd(III) and Lu(III) phosphate complexes in solutions with [PO ₄ ^3? ] < [Ln]. It is found that low-lability binuclear complexes, which rearrange within an hour or longer, are formed in these solutions. It is shown that the lability of Ln(III) carbonate complexes exceeds the lability of Ln(III) complexes with PO ₄ ^3? . An analysis of the dependence of I _lum of the solution on the concentration of Eu(III) ions and on the time from the instant of the solution preparation shows that, in aqueous solutions where the concentration of anions is higher than the concentration of Ln(III) ions, nanostructures of Eu(III) phosphate and carbonate salts are formed in the range of Ln(III) concentrations 0.5–5 μM at concentrations of anions on the order of 10 μM and at concentrations of exceeding 100 μM. The rearrangement of these nanostructures to nanostructures of Eu(MBTA)₃phen complexes is studied.     

Energy transfer from Eu(III) and Tb(III) complexes to dyes in their mixed nanostructures. I

The formation of nanostructures that consist of complexes of β-diketones with 1,10-phenanthroline and involve dyes of the polymethine, triphenylmethane, oxazine, and xanthene series is observed in aqueous solutions. It is found that nanostructures of complexes of Ln(III) ions and dyes are reliably observed at concentrations of Ln complexes from 0.5 to 5 μM and at dye concentrations above 5 nM. Nanostructures of complexes Eu(MBTA)₃phen, Eu(NTA)₃phen, Eu(PTA)₃phen, Tb(PTA)₃phen, Gd(MBTA)₃phen, and Lu(MBTA)₃phen with dyes are studied, where MBTA is n-methoxybenzoyltrifluoroacetone, NTA is naphthoyltrifluoroacetone, PTA is pivaloyltrifluoroacetone, and phen is 1,10-phenanthroline. It is shown that nanostructures formed can contain dye molecules not only inside a nanostructure of Ln complexes but also on its outer shell. It is proved that, at a dye concentration in the solution of the order of nanomole or higher, the formation of mixed nanostructures of Eu complexes and dyes whose S ₁ level is below the ⁵ D ₀ level of Eu(III) leads to the quenching of the luminescence of Eu(III) and gives rise to the sensitized luminescence of dyes. The energy transfer efficiency from Eu(III) ions to dye molecules is determined by the ability of these molecules to incorporate into nanostructures of Eu complexes. The effect of the formation of nanostructures on the shape and position of the spectra of luminescence and absorption of dyes is studied. Comparison of the sensitized luminescence intensities of Nile blue in structures of Eu, Lu, and Gd complexes shows that the greater part of the excitation energy of Eu complexes is transferred directly from ions to dye molecules according to the inductive-resonance energy transfer mechanism rather than by means of energy migration over singlet levels of organic ligands in complexes of a nanostructure.     

Luminescent Properties of Zeolite Modified by Eu(III) and Tb(III) Complexes

The luminescence of the sorbates of the Eu(III) and Tb(III) complexes on the CaA-type zeolite with derivatives of aliphatic and aromatic carbonic acids has been studied. It is shown that the luminescent materials obtained can be used as light regulators and transformers which absorb energy in the UV spectral region and transform it into visible radiation.     

Luminescent Eu(III) and Tb(III) Complexes: Developing Lanthanide Luminescent-Based Devices

This mini review gives some highlights of the work recently carried out in our research group in Dublin on the developments of lanthanide luminescent devices, where the future goal is to produce devices that can operate as sensors. A few examples demonstrate our design principles for targeting both anion and cations that are of biological or pharmaceutical relevance, where the recognition occurs in aqueous competitive media. We also discuss the possibility of developing mixed f-d metal complexes and conjugates that can be employed as novel supramolecular architectures.     

Luminescence Characteristics of the Sorbates of Eu(III) and Tb(III) Complexes with Diphenacylphosphinic Acid on Zeolite

The possibility of obtaining new luminescent materials based on the CaA zeolite modified by complex compounds of Eu(Tb) with diphenacylphosphinic acid has been shown. The optimal sorption conditions have been established and the luminescent characteristics of the sorbates have been determined.     

The influence of the solution preparation method on the co-luminescence intensity of chelates of Eu(III) ions and estimation of the size of arising nanostructures

The luminescence intensity of Eu(III) ions (I ^Eu) in 3: 1 aqueous solutions of thenoyltrifluoroacetone, n-methoxybenzoylacetone, and dibenzoylmethane with 1,10-phenanthroline is studied in the presence and the absence of La(III), Gd(III), and Nd(III) ions. It is found that, in binary solutions of Eu(III) with La and Gd, the intensity I ^Eu, as well as the influence of chelates of La and Gd on I ^Eu, is considerably greater if these ions are introduced into the solutions of β-diketones and 1,10-phenanthroline simultaneously and homogeneously than when they are introduced into these solutions successively. This result is explained by the difference in the distribution of different Ln chelates over nanostructures. The average size of the structures arising is estimated.     

Photo- and electroluminescence of Eu(III) and Tb(III) coordination compounds in thin polyvinylcarbazole films

Organic thin-film structures based on Eu(III), Tb(III), and polyvinylcarbazole coordination compounds are synthesized. Their photo- and electroluminescent properties and volt-ampere and volt-brightness characteristics are investigated.     

Eu(III) and Tb(III) luminescent lanthanide systems derived from DTPA-bisamide and DTTA-based ligands incorporating bipyridine antenna

Four new polycarboxylate ligands H₃Lⁿ have been synthesized by the attachment of two or one 2,2′-bipyridine subunits onto a diethylenetriamine pentacarboxylic acid (DTPA-bisamide derivatives: H₃L¹, H₃L²) or a diethylenetriamine tricarboxylic acid (DTTA derivatives: H₃L³, H₃L⁴) core. The neutral Eu^III and Tb^III complexes of these chelates have been prepared and studied from their UV-vis and luminescence data. The main photophysical characteristics of these complexes, i.e. the absorption and luminescence spectra, the metal-centred lifetimes and the overall luminescence yields (Φ) were measured in buffered aqueous solutions. In addition the role played by non-radiative paths (vibrational energy transfer involving coordinated water molecules, involvement of ligand-to-metal charge-transfer excited states, or metal→ligand back-transfer) was investigated. In all complexes, we found that the bidentate bipyridine chromophore is not coordinated to the lanthanide ion, allowing one (LnL¹, LnL²) or two (LnL³, LnL⁴) water molecules to penetrate the first coordination sphere of the metal. Although the bipyridine chromophore behaves as remote (from the binding site) light-harvesting unit for the lanthanide ion in these systems, a sizeable sensitization of the Eu- and Tb-centred luminescence can be effective (LnL², LnL³, Φ=16-19% in aerated D₂O solutions). Our photophysical investigations show that overall non-radiative deactivation is not dependant of thermally activated non-radiative channels but the efficiency of the ligand→Ln intramolecular energy transfer has to be taken into account to explain the obtained results.     

Intermolecular energy transfer between lanthanide complexes. 8. Tb(III) donor and Eu(III) acceptor complexes of citric acid

Intermolecular energy transfer between the citric acid complexes of Tb(III) and Eu(III) has been used to evaluate the conditions under which the formation of polynuclear species might take place. The luminescence was followed both as a function of pH (ranging between 2 and 12), and metal/ligand ratio (working at ratios of 1:1, 1:2, 1:3, 1:5, and 1:10). Consideration of the luminescence results permitted a conclusion that all equilibria could be explained if only Ln(CIT) and Ln(CIT)₂ complexes existed under the conditions used. At the 1:1 metal/ligand ratio, extensive complex association was noted upon ionization of two of the citrate carboxyl protons. Since little hydroxide ion exists at these pH values, it would appear that the citrate ligand prefers to bind multiple metal centers while still in the bidentate bonding mode. However, upon ionization of the final carboxyl group, the associated complexes broke apart into monomeric species. At all higher ratios, the complexes were found to be monomeric at all pH values, thus indicating that the binding of two citrate ligands by a lanthanide ion (regardless of the bonding mode of the ligand) is also capable of preventing the formation of polynuclear species.     

A new Eu(III)/Tb(III) binuclear coordination compound with crown ethers and bridging 4,4′-dipyridyl

A new Eu(III)/Tb(III) binuclear coordination compound with red and yellow emissions in solution and solid state, respectively, has been prepared. The lanthanide (Ln) ions are coordinated to crown ethers (C) and bridged by a dipyridyl (dipy) ligand. Ln/C and Ln/C/dipy complexes were also synthesized as precursors for the bimetallic compounds. The homo- and heterobimetallic Ln(III) complexes were characterized by elemental analysis as well as infra-red, absorption (UV-visible) and emission spectroscopies. The heterobimetallic complex geometry was predicted using the Sparkle/AM1 model and suggested to a chemical environment of very low symmetry around the lanthanide ions (C₁), in agreement with the luminescence spectrum. The Eu(III) and Tb(III) complexes display intense red and green emissions, respectively, in the solid state at room temperature.     

A Mechanism of the influence of Gd(III) and other Ln(III) ions on sensitized luminescence of Eu(III) and Tb(III) ions in aqueous and ethanol solutions: The role of hydroxyl bridges

We studied sensitization of Eu(III) and Tb(III) ions by molecules of 1,10-phenanthroline and 2,2-bipyridil in D₂O and d ₆-ethanol and the influence of Nd(III), Pr(III), Sm(III), Gd(III), and Ho(III) ions on the luminescence intensity I _lum and lifetime τ_lum of Eu(III) and Tb(III) in solutions. The stability constants of complexes of Eu(III) and Gd(III) with 2,2′-bipyridil are measured by spectrophotometric and luminescence methods. It is shown that luminescence of Eu(III) is quenched by Gd(III) ions at the ion concentration equal to 10^?2–10^?1 M, which is caused by competing between these ions for a sensitizer. At the concentration of Ln(III) ions equal to 10^?6?10^?3 M, the sensitized luminescence of Eu(III) and Tb(III) was quenched and τ_lum decreased in the presence of Nd(III) ions, whereas in the presence of Gd(III) the luminescence intensity increased. It is proved that a bridge that connects the two ions upon energy transfer is formed by hydroxyl groups. The intensity of luminescence of Eu(III) and Tb(III) in aqueous solutions and its lifetime decreased in the presence of hydroxyl groups, while upon addition of Gd(III) to these solutions these quantities were restored. We also found that the addition of Gd(III) to deoxygenated ethanol solutions of 2,2′-bipyridil and Eu(III) slows down photochemical and thermal reactions between bipyridil and Eu(III), resulting in the increase in the luminescence intensity of Eu(III).     

Energy transfer from Eu(III) complexes to dyes in their mixed nanostructures. II

The effects of the concentration of a number of dyes in an aqueous solution and of the method of formation of mixed nanostructures of dyes and Eu(MBTA)₃phen (MBTA is p-methoxybenzoyltrifluoroacetone; phen is 1,10-phenanthroline) complexes that form these structures on the luminescence decay kinetics of Eu(III) ions are studied. It is shown that, in the concentration range 5–50 nM of Nile blue, the concentration dependences of the luminescence decay and of the decrease in τ _lum of Eu(III) nearly coincide and are nearly linear. The dependence of the ratio of I _lum of Eu(III) to the intensity of the sensitized delayed fluorescence of Nile blue on the delay time of the probe pulse is analyzed; it is found that the majority of dye molecules incorporated in nanostructures of Eu(MBTA)₃phen complexes emit sensitized delayed fluorescence with times 1–50 μs. Analysis of the effect of the structure of nanostructures on the quenching of I _lum of Eu(III) by the dye at different concentrations of Eu(III) shows that nanostructures of Eu(MBTA)₃phen and Eu(NTA)₃phen (NTA is 2-naphthoyltrifluoroacetone) complexes appear in the aqueous solution at a concentration of Eu(III) of 0.1 μM (the MBTA or NTA concentration is 50 μM, and the concentration of phen is 17 μM) and exist in the solution at the Eu(III) concentrations up to ～5 μM. This confirms the conclusion on the occurrence range of nanostructures of Ln complexes previously made based on the analysis of columinescence in these structures.     

Radiolytic formation of Ce(IV) in aqueous solutions of Ce(III) chelates with aminopolycarboxylic acids

Gamma -radiolysis of alkaline solutions of Ce(III) chelates with aminopolycarboxylic acids of different sizes like ethylenediaminetetraacetic acid (EDTA), nitrilotriacetic acid (NTA) and iminodiacetic acid (IDA) revealed that OH radicals selectively attack the ligands probably due to a molecular kinetic effect rather than a steric one. The low G (CH₂O) values are ascribed to the reaction of CH₂O with H₂O₂.     

Europium(III) Concentration Effect on the Spectroscopic and Photoluminescent Properties of BaMoO4:Eu

BaMoO₄:Eu (BEMO) powders were synthesized by the polymeric precursor method (PPM), heat treated at 800 °C for 2 h in a heating rate of 5 °C/min and characterized by powder X-ray diffraction patterns (XRD), Fourier Transform Infra-Red (FTIR) and Raman spectroscopy, besides room temperature Photoluminescence (PL) measurements. The emission spectra of BEMO samples under excitation of 394 nm present the characteristic Eu³⁺ transitions. The relative intensities of the Eu³⁺ emissions increase as the concentration of this ion increases from 0.01 to 0.075 mol, but the luminescence is drastically quenched for the Ba_0.855Eu_0.145MoO₄ sample. The one exponential decay curves of the Eu^{3+ 5}D₀→⁷F₂ transition, λ _exc = 394 nm and λ _em = 614 nm, provided the decay times of around 0.54 ms for all samples. It was observed a broadening of the Bragg reflections and Raman bands when the Eu⁺³ concentration increases as a consequence of a more disordered material. The presence of MoO₃ and Eu₂Mo₂O₇ as additional phases in the BEMO samples where observed when the Eu³⁺ concentration was 14.5 mol%.     

The nature of the effect of Gd(III) on fluorescence of Ln(III) chelates in water solutions

The intensity of fluorescence of Eu(III) and Sm(III) ions sensitized by molecules of n-benzoyltrifluoroacetone and 1,10-phenanthroline introduced in a water solution in a ratio of 3: 1 is studied as a function of the ion concentration in the solution. The comparison of the fluorescence decay curves of Eu(III) and Sm(III) in D₂O and H₂O (pH≥7) solutions containing 10^?4 M of n-Cl-BTFA and 3×10^?5 M of 1,10-phen and the values of τ_fl of Sm(III) in themselves (51–90 μs) are indicative of an insignificant content of water molecules in the first coordination sphere of ions. The effect of other ions on I _fl and τ_fl of Eu(III) ions is studied under these conditions. The intensity of fluorescence of Eu(III) in solutions of 10^?4 M Cl-BTFA and 3×10^?5 H 1,10-phen is found to increase by 1–2 orders of magnitude in the presence of Y(III) and Gd(III) ions, and the magnitude of this effect is unaffected by deoxygenation of the solution. The introduction of a third ion Nd(III) in the solution is shown to attenuate the influence of Gd(III) on I _fl of Eu(III) for Nd(III) concentrations commensurable with the Eu(III) concentration in the solution. The strength of the influence of Gd(III) ions on I _fl of Eu(III) is found to depend on the method of preparation of the solution. The analysis of the results obtained testifies that inhomogeneities consisting of chelates of lanthanide ions displaced from the water structure appear in water. The presence of these inhomogeneities results in efficient energy transfer from ligands of Gd(III) chelates to Eu(III) chelates, which is the reason for the increasing I _fl of Eu(III). The possibility of using data on the enhancement of I _fl of Eu(III) in the presence of Gd(III) and on the reduction of τ_fl of Eu(III) in the presence of Nd(III) for estimating dimensions and structures of displaced systems is discussed.     

Determination of Dy(III) in the presence of Tb(III) using time-resolved luminescence

We have measured the relative luminescence quantum yields and luminescence lifetimes of Tb(III) and Dy(III) ions in complexes with pyrazole-5-carboxylic acids. Based on study of the time-resolved luminescence spectra of Tb(III) and Dy(III) complexes with 3-(6-benzodioxanyl)pyrazole-5-carboxylic acid, we have demonstrated the possibility in principle of determining Dy(III) in the presence of Tb(III) by separating the short-lived component of the luminescence of dysprosium, despite the practically complete overlap of the analytical bands of dysprosium by the terbium bands. This method was used to determine Dy(III) in luminescent materials: scandium borates doped with terbium and dysprosium. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 74, No. 3, pp. 327–331, May–June, 2007.     

三价铕离子配合物的激光光谱研究

利用高灵敏度的时间辨激光光谱技术研究了在配位场作用下Ｅｕ＾３＾＋的直接激发与发特性。Ｅｕ＾３＾＋的直接激发光谱（特别是７Ｆ０－５Ｄ０的超灵敏跃迁）及其发射光谱随不同的配合物的变化，同时观测到与配位对称性及配位强度有联系的７Ｆ１－５Ｄ０磁偶极跃 迁的分裂。在对７Ｆ０－５Ｄ０跃迁共振与非共振的１０ｐｓ激光脉冲的激励下，都可以立即观察到５Ｄ０－７ＦＪ（Ｊ＝２，３，４）的发射，说明Ｅｕ＾３＾＋的５Ｄ０能态     

Luminescence and circularly polarized luminescence of macrocyclic Eu(III) and Tb(III) complexes embedded in xerogel and sol–gel SiO2 glasses

Luminescence, time-resolved luminescence, circularly polarized luminescence (CPL) and decay profiles of Ln(III)(15-crownether-5) (Ln=Ce, Sm, Eu, Tb) and Tb(III)-(R),(S)-cyclen derivative complexes doped in xerogel and sol–gel silica glasses are measured at temperatures down to 10 K to characterize luminescence properties and the electronic structure in the excited states. Luminescence spectral profiles and calculation of crystal field parameters (B₀⁽²⁾,B₂⁽²⁾) in the ⁵D₀→⁷F_J(J=1,2) transition give evidence of the fact that the pentagonal and planar structure of Eu(III) (15-crownether-5) does hold in xerogel and sol–gel glasses prepared at temperatures below 100°C. As annealing temperatures are increased from 80°C to 750°C, Eu(III) complexes in sol–gel glasses are found to decompose gradually to SiO₂:Eu³⁺. Tb(III)-(R) and (S)-cyclen derivative complexes in xerogel reveal at room temperature and 10 K sharp CPL spectra with luminescence dissymmetry factors g_lum=−0.1 and 0.1, respectively. These complexes doped in sol–gel glasses represent luminescence characteristics of rare earth ions encapsulated in the nano-porous host.