Synthesis,Optical Investigation and Biological Properties of Europium(III) Complexes with 2-(4-Chlorophenyl)-1-(2-Hydroxy-4-Methoxyphenyl)Ethan-1-one and Ancillary Ligands

Synthesis and photoluminescence behaviour of six novel europium complexes with novel β-hydroxyketone ligand, 2-(4-chlorophenyl)-1-(2-hydroxy-4-methoxyphenyl)ethan-1-one (CHME) and 2,2′-bipyridine (bipy) or neocuproine (neo) or 1,10-phenanthroline (phen) or 5,6-dimethyl-1,10-phenanthroline (dmphen) or bathophenanthroline (bathophen) were reported in solid state. The free ligand CHME and europium complexes, Eu(CHME)₃.2H₂O [1] Eu(CHME)₃.bipy [2], Eu(CHME)₃.neo [3], Eu(CHME)₃.phen [4], Eu(CHME)₃.dmphen [5] and Eu(CHME)₃.bathophen [6]were characterized by elemental analysis, FT-IR and ¹H-NMR. The photoluminescence emission spectra exhibited four characteristic peaks arising from the ⁵D₀ → ⁷F_J (J = 1–4) transitions of the europium ion in the solid state on monitoring excitation at λ_ex = 395 nm. The luminescence decay curves of these europium complexes possess single exponential behaviour indicating the presence of a single luminescent species and having only one site symmetry in the complexes. The luminescence quantum efficiency (η) and the experimental intensity parameters, Ω ₂ and Ω ₄ of europium complexes have also been calculated on the basis of emission spectra and luminescence decay curves. In addition, the antimicrobial and antioxidant activities were also studied of the investigated complexes.     

Relative Study of Luminescent Properties with Judd-Ofelt Characterization in Trivalent Europium Complexes Comprising ethyl-(4-fluorobenzoyl) Acetate

Five new europium(III) complexes Eu(p-EFBA)₃.(H₂O)₂ (C1), Eu(p-EFBA)₃.neo (C2), Eu(p-EFBA)₃.batho (C3), Eu(p-EFBA)₃.phen (C4), Eu(p-EFBA)₃.bipy (C5) have been synthesized by using ethyl-(4-fluorobenzoyl) acetate (p-EFBA) as β-ketoester ligand and neocuproine (neo), bathophenanthroline (batho), 1,10-phenanthroline (phen) and 2,2-bipyridyl (bipy) as ancillary ligands. The synthesized complexes C1-C5 were characterized by elemental analysis, nuclear magnetic resonance spectroscopy (¹H-NMR), infrared (IR) spectroscopy, thermogravimetric analysis (TG/DTG), UV-visible and photoluminescence (PL) spectroscopy. The relative study of luminescence spectra of complexes with the previously reported complexes of isomeric ligand (ortho and meta substituted ligand) indicate the higher luminescence properties of complexes as an effect of fluorine position on β-ketoester ligand. The para substituted ligand shows a remarkable effect on quantum efficiencies and Judd-Ofelt intensity parameters (Ω_2, Ω₄) of the complexes. The higher value of intensity parameter Ω₂ associated with hypersensitive ⁵D₀ → ⁷F₂ transition of europium(III) ion revealing highly polarizable ligand field. The purposed energy transfer mechanism of complexes indicates the efficient energy transfer in complexes.     

Sensitive Spectrofluorimetric Study of the Interaction between Europium(III) and 1,2-Phenylenebis(azan-1-yl-1-ylidene) bis(methan-1-yl-1-ylidene)diphenol Schiff Base

A sensitive and selective spectrofluorimetric method has been developed for the rapid determination of europium(III). This method is based on the formation of nonluminous complex between Eu(III) and a Schiff base reagent N, N′-bis (salicylidene)-1,2-phenylenediamine (PABD) and measuring the fluorescence quenching of Eu(III)-PABD complex at λ_ex/em = 390/577 nm. The fluorescence intensity complex decreased linearly by increasing the Eu(III) concentration in the range of 1.0–13.0 μM. The optimum conditions for the complex formation were determined such as a pH .0 of borate buffer. The limits of detection (LOD) and quantification (LOQ) of Eu(III) were determined and found to be 0.217 and 0.653 μM, respectively. The maximum relative standard deviation of the method for an europium(III) standard of 6.0 μM was 2.07 % (n = 6). The proposed procedures could be applied successfully for the determination of the investigated metal ion in some spiked water samples with a good precision and accuracy compared to official and reported methods as revealed by t- and F-tests.     

Photoacoustic Spectra of Sm3+, Eu3+, Dy3+ Complexes

The complexes crystals of Sm(Ac)3.4H₂O, Eu(Ac)3.4H₂O and a new complex Dy2(Ac)(NO3)4.12H₂O were synthesized and their PA spectra were determined firstly. All their PA spectra absorptions are interpreted. The fluorescence properties of Sm³⁺, Eu³⁺, Dy³⁺ and the relaxation process models were studied by their PA spectra.     

Investigation of the photoluminescence properties of composite optical resins containing high lanthanide content

Novel composite optical resins with high lanthanide content have been synthesized through a free radical copolymerization of methacrylic acid (MA), styrene (St) and Eu(DBM)₃·H₂O nanocrystals. We characterized the structure, the thermal properties, dimensions and photoluminescence properties of Eu(DBM)₃·H₂O nanocrystals. Our results indicated that the diameters of the Eu(DBM)₃·H₂O nanocrystals were within the range of 30 to 300 nm. These materials exhibited characteristic europium ion luminescence. The europium-bearing nanocrystals and were then incorporated into the copolymer systems of MA/St and luminescence functional optical resins with high lanthanide content (50 wt%) were obtained. The combination of these particles and optical resins is facile because the diameter of Eu(DBM)₃·H₂O is decreased. These copolymer-based optical resins not only possess good transparency and mechanical performance, but also exhibit an intense narrow band emission of lanthanide complexes and longer fluorescence lifetimes under UV excitation at room temperature.     

Highly luminescent europium(III) complexes with naphtoiltrifluoroacetone and dimethyl sulphoxide

The synthesis, luminescence properties, experimental determination and theoretical calculation of the emission quantum yield of Eu(NTA)₃.2L complexes, where NTA is naphtoiltri-fluroacetone and L denotes H₂O or DMSO (dimethyl sulphoxide), were reported. The compounds were characterized by elemental analysis (carbon, hydrogen and europium), thermal analysis, UV-visible absorption and photoluminescence spectroscopies. The experimental quantum yields were determined based on a method previously proposed by Bril and collaborators. The Eu(NTA)₃.2DMSO compound shows a high value for the Ω₂ intensity parameter (35.8 × 10^?20 cm²), reflecting the hypersensitive nature of the ⁵D₀ → ⁷F₂ transition and indicating that the lanthanide ion is in a highly polarizable chemical environment. The experimental quantum yield measured for that compound, 0.75, is one of the highest so far reported for solid-state europium complexes. The theoretical calculations of the quantum yield were carried out by solving an appropriate set of rate equations and by using empirical spectroscopic parameters and energy transfer rates. The theoretical results agree well with the experimental data for both complexes. The photostability of Eu(NTA)₃.2DMSO at 358K was evaluated in order to verify whether this complex can be applied as a phosphor for blue light emitting devices.     

NMR and Mössbauer Study of Al2O3–Eu2O3

Alumina–europia mixed oxides with 5 and 10 wt.% Eu₂O₃ were studied by Mössbauer spectroscopy, ²⁷Al MAS-NMR and X-ray diffraction (XRD). The samples were prepared by the sol–gel technique. The XRD patterns for the calcined samples show a broad peak around 2θ = 30° which is assigned to the Eu₂O₃; after treatment with hydrogen at 1073 K no reduction to Eu⁺² or Eu⁰ was observed. The NMR spectra show three peaks, which are assigned to the octahedral, pentahedral and tetrahedral aluminum sites; the intensity of each peak depends on the concentration of europium ions. The Mössbauer spectra of the calcined samples show a single peak near zero velocity which is attributed to the Eu⁺³; after H₂ treatment at 1073 K similar spectra were obtained, suggesting Eu⁺³ is not reducibly at this temperature.     

Effects of composition and transparency on photo and radioluminescence of Y2O3:Eu complexes

A solid state-based method using a hot reaction chamber is applied to the synthesis of Y₂O₃:Eu particles containing Eu from 0 to 5 mol%. The produced powders are studied using X-ray diffraction (XRD), scanning electron microscopy and transmission electron microscopy (TEM), as well as photoluminescence (PL) and radioluminescence tests. TEM and XRD results revealed the powder to be mono-disperse and in the form of a solid solution. The PL of Y₂O₃:Eu powder depends on both the concentration quenching effect (due to an excess of Eu concentration) and the surface luminescence effect (depicted by a higher surface area induced by the large phosphor concentration in the solution or smaller particle sizes). A ²²Na gamma source is used to compare the recorded count rates for four Y₂O₃:Eu scintillator materials with different concentrations of Eu. Each scintillator composition is examined in four forms: solid pellets with a high volume porosity and three aqueous solutions of Y₂O₃:Eu particles of the different scintillator materials at concentrations of 25, 50 and 100 mg/mL. The radioluminescence results indicated that increasing the transparency and/or the amount of Eu mol% of the scintillators increases the net average counts.     

Eu substitution and particle size control of Y2O2S for the excitation by UV light emitting diodes

Yttrium oxysulfide doped with europium (Y₂O₂S:Eu³⁺) red phosphor is used in UV light emitting diodes (LEDs) by mixing with blue and green phosphors to generate white light which are important for the application in general lighting. Here, we demonstrate the effect of shape and size and the concentration of activator (Eu) of red Y₂O₂S phosphor.     

Fluorescence quantum yield of carbon dioxide for quantitative UV laser-induced fluorescence in high-pressure flames

The fluorescence quantum yield for ultraviolet laser-induced fluorescence of CO₂ is determined for selected excitation wavelengths in the range 215–250 nm. Wavelength-resolved laser-induced fluorescence (LIF) spectra of CO₂, NO, and O₂ are measured in the burned gases of a laminar CH₄/air flame (φ=0.9 and 1.1) at 20 bar with additional NO seeded into the flow. The fluorescence spectra are fit to determine the relative contribution of the three species to infer an estimate of fluorescence quantum yield for CO₂ that ranges from 2–8×10^?6 depending on temperature and excitation wavelength with an estimated uncertainty of ±0.5×10^?6. The CO₂ fluorescence signal increases linearly with gas pressure for flames with constant CO₂ mole fraction for the 10 to 60 bar range, indicating that collisional quenching is not an important contributor to the CO₂ fluorescence quantum yield. Spectral simulation calculations are used to choose two wavelengths for excitation of CO₂, 239.34 and 242.14 nm, which minimize interference from LIF of NO and O₂. Quantitative LIF images of CO₂ are demonstrated using these two excitation wavelengths and the measured fluorescence quantum yield.     

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.     

Mössbauer studies of 151Eu in europium oxalate, europium bissalen ammonium and europium benzoate

Although a number of europium water insoluble chelates have been prepared for several decades, the covalent nature of these compounds has never been established in any quantitative fashion. Shifts in the I.R. bands and conductivity measurements of these salts were hitherto used to qualitatively compare their molecular nature. In this communique we have used temperature coefficients of ¹⁵¹Eu Mössbauer spectra to determine the Debye temperatures (θ _D) of three europium chelates: namely europium oxalate, europium bissalen ammonium (recently reported) and europium benzoate and compared their θ _D with the measured θ _D of the known ionic EuF₃. Additionally, the mean square amplitude (<x ²) of these four compounds was computed and plotted as a function of temperature giving in each case a reasonable linear plot. It was interesting to note that the θ _D of the most ionic EuF₃ was greatest (283 ± 10 K) followed by the oxalate (166 ± 15 K), then the europium bissalen ammonium (133 ± 5 K) and lastly the europium benzoate with a θ _D of (105 ± 5 K).     

Preparation, Crystal Structures and Luminescent Properties of Terbium and Europium Complexes with a New Amino-Alkenone Type Ligand

Solid complexes of terbium and europium nitrates with an amino-alkenone type ligand, 1-[2-(6-methylpyridin-2-ylamino)-5,6-dihydro-4H-pyran-3-yl]ethanone (L) have been prepared and characterized by elemental analysis, conductivity measurements, and IR spectra. The crystal and molecular structures of the complexes [TbL₂(NO₃)₃(H₂O)]·CHCl₃ (1) and [EuL₂(NO₃)₃(H₂O)]·CH₃CO₂C₂H₅ (2) have been determined by single crystal X-ray diffraction. And the coordination spheres of the complexes are similar. At the same time, the luminescent properties of the Tb³⁺ complex in solid state and in solvents were investigated at room temperature. Under the excitation of UV light, Tb(III) complex exhibited characteristic emissions but not for the Eu(III) complex. The lowest triplet state energy level of the ligand in the complex matches better to the resonance level of Tb(III) than Eu(III) ion.     

Europium-sensitized Chemiluminescence of System Tetracycline–H<Subscript>2</Subscript>O<Subscript>2</Subscript>–Fe(II)/(III) and Its Application to the Determination of Tetracycline

Chemiluminescence (CL) of the reaction system tetracycline–H₂O₂–Fe(II)/(III)–Eu(III) was used for the determination of tetracycline hydrochloride in water, pharmaceutical preparations, and honey. The CL spectrum registered for this system shows emission bands typical of Eu(III) ions, with a maximum at λ ∼ 600 nm, corresponding to the electronic transitions of ⁵D₀ → ⁷F₁ and ⁵D₀ → ⁷F₂. A strong chemiluminescence intensity characteristic of europium(III) ions in the system tetracycline–H₂O₂–Fe(II)/(III)–Eu(III), as contrasted to the emission of the system tetracycline–H₂O₂–Fe(II)/(III) without Eu(III), proves that the Eu(III) ion plays the role of a chemiluminescence sensitizer, accompanying tetracycline oxidation in the Fenton system (H₂O₂–Fe(II)/(III)). A linear dependence was observed for the integrated CL light intensity on the tetracycline concentration in the range of 2 × 10⁻⁷ to 3 × 10⁻⁵ mol l⁻¹ with the detection limit of 5 × 10⁻⁸ mol l⁻¹ in aqueous solution.     

Judd–Ofelt treatment on luminescence of europium complexes with β-diketone and bis(β-diketone)

Eu(DBM)₃2H₂O and Eu₂(DDBM)₃H₂O were synthesized by reactions between EuCl₃ and chelating regents of β-diketone (dibenzoylmethane, HDBM) and bis(β-diketone) (1,3-bis(3-phenyl-3-oxopropanoyl)benzene, H₂DDBM), respectively, and their luminescence properties were investigated by the fluorescence spectra and metastable state decay spectra. It was found that the relative intensity ratio of ⁵D₀→⁷F₂ to ⁵D₀→⁷F₁transition and the radiative lifetime shows a little change attributing to the different symmetry of europium ions, which Ω₂ of Eu complexes with β-diketone and bis(β-diketone) are 13.08 and 12.24, respectively. Moreover, it was also found that the metastable state lifetime of Eu₂(DDBM)₃H₂O is much longer than that of Eu(DBM)₃2H₂O, due to smaller water quenching and lower triplet level of ligands. The Commission Internacionale d’Éclairage (CIE) chromaticity coordinates calculated from emission spectrum are x=0.637 and y=0.343 for Eu₂(DDBM)₃H₂O, which presents high red color purity near 100%.     

Synthesis and Fluorescence Properties of Lanthanide (III) Perchlorate Complexes with Bis(benzoylmethyl) Sulfoxide

A ligand with two carbonyl groups and one sulfinyl group has been synthesized by a new method and its several lanthanide (III) complexes were synthesized and characterized by element analysis, molar conductivity, coordination titration analysis, IR, TG-DSC, ¹H NMR and UV spectra. The results indicated that the composition of these complexes is REL₅(ClO₄)₃·3H₂O (RE = La(III), Pr(III), Eu(III), Tb(III), Yb(III), L = C₆H₅COCH₂SOCH₂COC₆H₅). The fluorescent spectra illustrate that both the Tb (III) and Eu (III) complexes display characteristic metal-centered fluorescence in solid state, indicating the ligand favors energy transfer to the excitation state energy level of them. However, the Tb (III) complex displays more effective luminescence than the Eu (III) complex, which is attributed to especial effectively in transferring energy from the average triplet energy level of the ligands (T) onto the excited state (⁵D₄) of Tb (III) than that (⁵D₀) of Eu (III), showing a good antenna effect for Tb(III) luminescence. The phosphorescence spectra and the relationship between fluorescence lifetimes and fluorescence intensities were also discussed.     

Influences of compositions and ligands on photoluminescent properties of Eu(III) ions in composite europium complex/PMMA systems

Three kinds of europium complexes; Eu(phen)₂Cl₃(H₂O)₂, Eu(DN-bpy)phenCl₃(H₂O)₂ and Eu(DB-bpy)phenCl₃(H₂O)₂ (phen: 1,10-phenanthroline, DN-bpy: 4,4′-Dinonyl-2,2′-dipyridyl, DB-bpy: 4,4′-Di-tert-butyl-2,2′-dipyridyl) were prepared and then incorporated into polymethyl methacrylate (PMMA) matrix with different molar ratios of CO groups/Eu³⁺ ions. The final solid composites were formed by a self-assembly process among Eu³⁺ ion, the ligands and PMMA during the solvent evaporation process, and then the ligands re-coordinate to Eu(III). It was found that the ligands affect not only the emission properties of the pure complexes, but also the miscibility of the complexes and PMMA. More than one kind of symmetric sites of Eu³⁺ ions were formed in the composites due to the coordination of CO in PMMA to Eu³⁺ ions. The micro-environments of Eu(III) in the composites were changed with the compositions and the ligands, leading to the change in the crystalline structure, and consequently, the emission characteristics.     

The Studies of Enhanced Fluorescence in the Two Novel Ternary Rare-Earth Complex Systems

Two novel ternary rare-earth complexes SmL₅·L^’·(ClO₄)₂·7H₂O and EuL₅·L^’·(ClO₄)₂·6H₂O (the first ligand L = C₆H₅COCH₂SOCH₂COC₆H₅, the second ligand L^’ = C₆H₄OHCOO⁻) were synthesized and characterized by element analysis, molar conductivity, coordination titration analysis, IR, TG-DSC, ¹HNMR and UV spectra. The detailed luminescence studies on the rare-earth complexes showed that the ternary rare-earth complexes presented stronger fluorescence intensities, longer lifetimes, and higher fluorescence quantum efficiencies than the binary rare-earth materials. After the introduction of the second ligand salicylic acid group, the relative emission intensities and fluorescence lifetimes of the ternary complexes LnL₅·L^’·(ClO₄)₂·nH₂O (Ln = Sm, Eu; n = 7, 6) enhanced more obviously than the binary complexes LnL₅·(ClO₄)₃·2H₂O. This indicated that the presence of both organic ligand bis(benzoylmethyl) sulfoxide and the second ligand salicylic acid could sensitize fluorescence intensities of rare-earth ions, and the introduction of salicylic acid group was a benefit for the fluorescence properties of the ternary rare-earth complexes. The fluorescence spectra, fluorescence lifetime and phosphorescence spectra were also discussed.     

Quenching of Long Lifetime Emitting Fluorophores with Paramagnetic Molecules

In this work, we have studied quenching of the fluorescence of two well-known oxygen probes, 1-pyrene butyric acid (PBA) and tris(2,2’-bipyridine)ruthenium ([Ru(bpy)₃]²⁺) by reactive oxygen species (superoxide anion, nitric oxide derivative, hydrogen peroxide) and by the O₂ molecule. Both, time-resolved and steady state fluorescence measurements were performed in solution (ethanol, dimethyl sufoxide, water) and in micelles of Sodium Dodecyl Sulfate that serve as a model for membrane-containing biological structures. We have found that only the free radicals and O₂ can actively quench for the two probes, but not the diamagnetic H₂O₂. Our data correspond to the classical Stern–Volmer equation. H₂O₂ has an effect only at high molar concentrations (>0.1 M). In contrast, effective concentrations of free radicals and O₂ that lead to quenching are in millimolar range. In conclusion, our methods allows for detecting global ROS that are small free radicals without interference from the reactive hydroxyl radical. Our data suggest that the method can be used for the quantification of ROS in individual living cells based on the measurement of fluorescence lifetime of those probes.     

Ultrafast third-order optical nonlinearity of several sandwich-type phthalocyaninato and porphyrinato europium complexes

The third-order optical nonlinearity of two sandwich-type phthalocyaninato and porphyrinato europium com- plexes, including double- and triple-deckers （Eu[Pc（OC5H11）8]2, Eu2（Pc）（TPP）2, Pc=phthalocyanine, TPP=5, 10, 15, 20- tetraphenylporphyrinate）, was investigated by using the femtosecond time-resolved optical Kerr gate method at 830 nm wavelength. Their second-order hyperpolarizability is estimated to be 0.74× 10^-30esu and 3.0× 10^-3esu respectively. This exhibits an evident enhancement in comparison with 0.47×10^-30esu for one-decker Eu（Pc）（acac） （acac=acetylacetonate）, which is also measured under the same conditions. The enhancement is attributed to the introduction of lanthanide metal to the large π-conjugated system, intermacrocycle interaction and two-photon resonance etc.