Luminescent Europium Research Articles

Composition-Thermometric Properties Correlations in Homodinuclear Eu3+ Luminescent Complexes.

A family of homodinuclear Ln3+ (Ln3+ = Gd3+, Eu3+) luminescent complexes with the general formula [Ln2(β-diketonato)6(N-oxide)y] has been developed to study the effect of the β-diketonato and N-oxide ligands on their thermometric properties. The investigated complexes are [Ln2(tta)6(pyrzMO)2] (Ln = Eu (1·C7H8), Gd (5)), [Ln2(dbm)6(pyrzMO)2] (Ln = Eu (2), Gd (6)), [Ln2(bta)6(pyrzMO)2] (Ln = Eu (3), Gd (7)), [Ln2(hfac)6(pyrzMO)3] (Ln = Eu (4), Gd (8)) (pyrzMO = pyrazine N-oxide, Htta = thenoyltrifluoroacetone, Hdbm = dibenzoylmethane, Hbta = benzoyltrifluoroacetone, Hhfac = hexafluoroacetylacetone, C7H8 = toluene), and their 4,4′-bipyridine N-oxide (bipyMO) analogues. Europium complexes emit a bright red light under UV radiation at room temperature, whose intensity displays a strong temperature (T) dependence between 223 and 373 K. This remarkable variation is exploited to develop a series of luminescent thermometers by using the integrated intensity of the 5D0 → 7F2 europium transition as the thermometric parameter (Δ). The effect of different β-diketonato and N-oxide ligands is investigated with particular regard to the shape of thermometer calibration (Δ vs T) and relative thermal sensitivity curves: i.e.. the change in Δ per degree of temperature variation usually indicated as Sr (% K–1). The thermometric properties are determined by the presence of two nonradiative deactivation channels, back energy transfer (BEnT) from Eu3+ to the ligand triplet levels and ligand to metal charge transfer (LMCT). In the complexes bearing tta and dbm ligands, whose triplet energy is ca. 20000 cm–1, both deactivation channels are active in the same temperature range, and both contribute to determine the thermometric properties. Conversely, with bta and hfac ligands the response of the europium luminescence to temperature variation is ruled by LMCT channels since the high triplet energy (>21400 cm–1) makes BEnT ineffective in the investigated temperature range.

Hollow molecularly imprinted fluorescent sensor using europium complex as functional monomer for the detection of trace 2,4,6-trichlorophenol in real water samples

As an important environmental indicator, 2,4,6-trichlorophenol (2,4,6-TCP) was proved extremely harmful to human body. In this article, hollow molecularly imprinted fluorescent polymers (@MIPs) for the selective detection of 2,4,6-TCP were devised and fabricated by sacrificial skeleton method based on SiO2 nanoparticles. As the most innovation, highly luminescent europium complex Eu(MAA)3phen played the role of both fluorophores and functional monomers of the MIPs. The obtained @MIPs showed monodispersity and the average particle size was around 130nm. It had a linear fluorescent response within the concentration range 10-100nmolL-1 with the correlation coefficient calculated as 0.99625, and the limit of detection was identified as 2.41nmolL-1. The results show that Eu(MAA)3phen as a fluorophore has high luminescent properties, and as a functional monomer, it can improve the selectivity and anti-interference performance of MIPs. Furthermore, the hollow structure made it possible that the imprinted specific recognition sites distributed on both inner and outer surfaces of @MIPs. The experimental results showed that these @MIPs could be employed to the selective detection of chlorophenols under low concentration. And this work will provide a reference for further optimization of fluorescent imprinted sensors.

A turn-off luminescent europium probe for efficient and sensitive detection of some low molecular weight polycyclic aromatic hydrocarbons in seawater

Eu(III)-(CCA)2 complex probe was applied for the direct detection of polycyclic aromatic hydrocarbons PAHs naphthalene, anthracene, acenaphthene or fluorene in seawater samples were collected from Suez Bay. The low limit of detection and the quantification limit were calculated for all compounds under study. The selectivity of the probe was characterized through studying the effect of some interfering ions. The results obtained from fluorimetric method using Eu(III)-(CCA)2 probe was validated through using gas chromatography and arecoverymethod. The developed Eu(III)-(CCA)2 probe has the ability for detecting PAHs in rapid and straightforward procedure even in presence of interfering metal ions. The data indicated that the Eu(III)-(CCA)2 probe is suitable for direct and efficient determination of PAHs compounds from seawater.

Luminescence properties of a nanotheranostics based on a multifunctional Fe3O4/Au/Eu[1-(2-naphthoyl)-3,3,3-trifluoroacetone]3 nanocomposite

Abstract The multifunctional Fe3O4/Au/Eu [1-(2-Naphthoyl)-3,3,3-trifluoroacetone]3 nanocomposite (NC) composed of luminescent europium(III) complex with 1-(2-naphthoyl)-3,3,3- trifluoroacetone (NTA) ligands (Eu(NTA)3), superparamagnetic Fe3O4 and plasmonic gold nanoparticles (FAEu(NTA)3) is developed for theranostic application. The FAEu(NTA)3 NC has been functionalized by 3-(mercaptopropyl)trimethoxysilane/3-(triethoxysilyl)-propylamine (MCPMS/TESPA) and conjugated with IgG antibody. This study was focused on luminescent properties and evaluation of the temperature dependent luminescence of FAEu(NTA)3 NC. The in vitro fluorescent imaging test of the prostate cancer PC3 cells incubated with FAEu(NTA)3 NC has been also presented.

New highly luminescent europium(Ⅲ) complex covalently bonded with titania-based host via using a terpyridine carboxylate derivative linker for fluorescence sensing

Herein the novel luminescent europium(Ⅲ) hybrid material (denoted as Eu(tta)3cptpy-TiO2) was designed and synthesized. With the coordination interaction between europium(Ⅲ) ions and the organic ligands, the as-synthesized Eu(tta)3(H2O)(EtOH) complex was covalently grafted to the titania host backbone. The materials were characterized by FT-IR and Raman spectra, 13C SSNMR, X-ray diffraction, SEM, XPS, thermogravimetric analysis and photoluminescence spectra. The results reveal that Eu(tta)3cptpy-TiO2 possesses the combined superior properties of the complex and the inorganic matrix, which not only realized better thermal stability but also obtained more excellent luminescence performance than that of the complex. Moreover, this material performs reasonably long lifetime of 1.02 ms because of the efficient energy transfer from the ligands or titania host to Eu3+ ion. Furthermore, the application in detecting organic solvents and metal ions was investigated systematically. Meanwhile, Eu(tta)3cptpy-TiO2 presents superior detection for nitrobenzene molecule and Fe3+ ion. In addition, the limit of detection (LOD) of Eu(tta)3cptpy-TiO2 for nitrobenzene molecule and Fe3+ ion can be counted as 6.162 × 10−5 M and 2.371 × 10−5 M, respectively. The results demonstrate that Eu(tta)3cptpy-TiO2 bears potential for highly sensitive sensing of nitrobenzene and Fe3+ ion.

Coordination Environment-Controlled Photoinduced Electron Transfer Quenching in Luminescent Europium Complexes.

The quenching of sensitized Eu(III) luminescence by photoinduced electron transfer from the excited light-harvesting antenna to Eu(III) was investigated. A series of complexes incorporating different metal binding sites and thus having varying Eu(III)/Eu(II) reduction potentials were prepared. The complexes were fully characterized using a combination of single-crystal X-ray crystallography and paramagnetic 1H NMR spectroscopy, the results of which support the structural similarity of the complexes. The redox and photophysical behavior of the Eu(III) center and the light-harvesting antenna were studied using cyclic voltammetry and steady-state and time-resolved emission spectroscopy on the nanosecond and millisecond time scales. The contribution of photoinduced electron transfer to the overall reduction of the Eu(III) luminescence quantum yield was found to be comparable and, in many cases, larger than the quenching caused by well-established processes such as coupling to X-H oscillators. These results suggest that the elimination or mitigation of photoinduced electron transfer could substantially improve the emissive properties of the widely used Eu(III)-based emitters.

Luminescent europium(III)-organic framework for visual and on-site detection of hydrogen peroxide via a tablet computer

A luminescent metal-organic framework of type Eu(III)-MOF has been fabricated for visual and on-site fluorometric determination of hydrogen peroxide (H2O2) via atabletcomputer. The maximum excitation and emission peaks of type Eu(III)-MOF were found at λex = 290nm and λem = 615nm, respectively. The average length of Eu-MOF is 1.21 ± 0.07μm. In the presence of the target H2O2, Fe2+ is transmitted into Fe3+ via Fenton reaction, leading to a fluorescence quenching of Eu-MOF. Therefore, visible color change occurred from bright red into colorless. Interestingly, by means of tablet computer's digital camera and ImageJ software, fluorescent signals were captured and transduced into digital parameters, resulting ina linear relationship between fluorescence intensity and the concentration of H2O2. As a result, the determination of H2O2 without the aid of complicated instruments is achieved in therange 2.0μM to 0.2mM with a detection limit of1.02μM. Our approach has beensuccessfully applied to quantify H2O2 in serum, urine, and waste water with good recovery and precision (< 2.5% RSD). Besides, our assay has beenexploited for visual detection of H2O2 released from HepG2 cells with the advantages of portability and accuracy. Moreover, the strategy displays acceptable selectivity and stability. Hence, our assay provides an alternative practical method for on-site determination of H2O2 without the need for instruments. Graphical abstract Schematic representation of the synthesis procedure of a luminescent Eu-MOF, which has been successfully applied for on-site detection of H2O2 via Fenton reaction and imaging analysis technique. The method exhibits handheld and accuracy for H2O2 determination, holding the potential for biochemical and clinical applications in remote regions.

Red luminescence and UV light generation of europium doped zinc oxide thin films for optoelectronic applications

In the present work, the Europium doped Zinc Oxide (ZnO: Eu) thin films were elaborated using spray pyrolysis technique. We are interested in investigating the structural properties, photoluminescence (PL) and third harmonic generation (THG) of the elaborated films. The structural properties of as-prepared thin films were characterized by X-ray diffraction (XRD). It confirms that all deposited thin films of Europium doped Zinc Oxide are crystallized in the hexagonal wurtzite structure. Both undoped and doped europium thin films show strong preferred c-axis orientation. Photoluminescence (PL) emission from Europium doped Zinc Oxide thin films, under excitation by 266 nm, shows characteristic transitions of Europium (5D0 → 7F0, 5D0 → 7F1, 5D0 → 7F2, etc.). It reveals the good incorporation of Eu3+ ions in the ZnO host. Additionally, the 5D0 → 7F2 is the most intense transition usually observed for Eu3+ embedded in materials of Zinc Oxide lattice. The dependence of third-order nonlinear susceptibility on doping rate was evaluated. The highest nonlinear susceptibility χ 3 is obtained for the 5% Europium doped ZnO sample.

New Heteroligand Europium and Gadolinium Formate Triazole Dicarboxylates: Synthesis, Structures, and Luminescence Properties

Complexes {(NMe2H2)[Ln(TDA)(HCOO)] ∙ 0.5H2O)} are prepared by the solvothermal synthesis in a water–dimethylformamide (1 : 1) system from a mixture of 1,2,3-triazole-4,5-dicarboxylic acid (H3TDA), NaOH, and Ln(NO3)3 (Ln = Eu, Gd). The crystal structure of the europium complex is determined by X-ray structure analysis (CIF file CCDC no. 1939689). This compound is shown to be the ionic metal-organic framework, where the cavities in the anionic structure of [Eu(TDA)(HCOO)]– are partially occupied by the dimethylammonium cations and water molecules. The study of the luminescence spectra of the gadolinium derivative gives the energy of the triplet level of the H3TDA ligand (~25 300 cm–1), the value of which makes it possible to efficiently sensitize the luminescence of rare-earth metal ions, in particular, Eu3+. The decay kinetics and the emission and excitation spectra of the heterometallic derivatives {(NMe2H2)[Gd1 – xEux(TDA)(HCOO)] ∙ 0.5H2O)} are studied. The dilution of europium with gadolinium results in a substantial decrease in the concentration quenching of the europium luminescence and an increase in the observed lifetimes of the excited state of Eu3+.

A luminescent europium hairpin for DNA photosensing in the visible, based on trimetallic bis-intercalators

Luminescence monitoring of DNA intercalator complexes is important for assessing their localisation and targeting: We report herein a luminescent hetero-trimetallic complex with europium as a luminescent reporter and two attached platinum acetylide terpyridyl units as the DNA recognition units. The ligand, based on a bisamide derivative of diethylenetriaminepentaacetic acid functionalized with two ethynyl groups, provides a backbone to anchor two platinum terpyridyl units, Pt-tpy, leading to the hairpin-shaped heterometallic complex 1. We also prepared a related mono-nuclear platinum complex 2 to compare its intercalation properties with 1. Linear dichroism, UV–visible and melting experiments show the ability of both complexes to interact with calf thymus DNA, with linear dichroism confirming intercalation and demonstrating the expected greater DNA stiffening by the bis-intercalator 1. Importantly, the tri-metallic complex 1 shows a three-fold enhancement in europium luminescence upon addition of calf thymus DNA; other mono-intercalator lanthanide designs have commonly shown a decrease in emission on binding. The ability of the complex to monitor DNA interactions gives the potential use as a luminescence switch in sensing experiments and highlights the design of heterometallic bis-intercalator complexes as an effective approach for DNA-responsive sensitisation of a lanthanide luminescence signal.

Effect of gadolinium on europium luminescence and its in-situ valence conversion in SrBPO5 host

Gadolinium/europium-activated strontium borophosphate (SrBPO5) phosphors were synthesized through solid-state reaction route in air atmosphere. Morphology and particle size were analyzed using scanning electron microscopy (SEM). Both europium and gadolinium were observed to emit strongly in this host. Interestingly, photoluminescence (PL) of both Eu2+ and Eu3+ was also observed. In the co-activated SrBPO5: Eu, Gd phosphors, the PL intensity of Eu3+ was enhanced significantly with simultaneous quenching of Eu2+ luminescence. The excitation and emission profiles of europium indicated the valence conversion (VC) of Eu2+ to Eu3+ in the presence of gadolinium. In addition to the VC, the luminescence of Eu3+ was also enhanced due to the energy transfer (ET) from Gd3+ to Eu3+. The ET was maximum for SrBPO5: Eu0.01, Gd0.075 phosphor at a critical distance of 2.76 Å. The co-activated phosphors exhibited a high color rendering index for Eu3+, suggesting it to be an efficient orange-red phosphor. PL lifetime decay studies suggested a single site occupancy for Eu2+ though the number of sites for Gd3+ and Eu3+ varied depending on their concentrations. The time-resolved emission spectroscopy (TRES) revealed different emission profiles for Eu3+ in varying time domains corroborating its different site occupancies. Strong thermoluminescence (TSL) was observed from these phosphors, though Eu2+ and Eu3+ PL were quenched following γ-irradiation. The calculated trap parameters and dose-response of γ-irradiated Eu, Gd-coactivated phosphor, suggested it to be a good thermoluminescent phosphor.

Modeling the Kinetics of Luminescence in the 1,4-Dimethylnaphthalene Endoperoxide/Eu(fod)3 System

A study was made of the kinetics of the luminescence of europium(III) β-diketonate complex [Eu(fod)3] in the presence of in situ generated O2(1Δg) at thermal decomposition of the 1,4-dimethylnaphthalene endoperoxide. A scheme was proposed in which the luminescence of Eu(III) (λmax = 615 nm) is determined by the stepwise oxidation of the ligands of the complex, resulting in electronically excited heptafluoro-2-oxo-pentanal and the subsequent transfer of energy to the central cation.

Variation of a Halide Anion as Efficient Way to Control the Spectral-Brightness Characteristics of Divalent Europium Luminescence in Condensed Medium

The blue or green visible to the naked eye chemiluminescence of the divalent europium ions, generated by the acceptance of energy from triplet-excited isobutyraldehyde—a product of the oxidation of diisobutylaluminium hydride by oxygen in tetrahydrofuran—was found and studied.

Europium luminescence in silver and gold nanoparticles co-embedded phosphate glasses: Judd-Ofelt calculation

Some europium ions (Eu3+) activated magnesium-zinc-sulfophosphate glasses with the silver (Ag) and gold (Au) nanoparticles (NPs) co-embedment were prepared via the melt-quenching method. The as-prepared samples were characterised using different analytical techniques to determine the effect of various Au NPs contents (0.05, 0.10, 0.15, 0.20, 0.25, and 0.30 g) on their spectroscopic characteristics. Furthermore, the Judd-Ofelt theory was used to evaluate the intensity parameters and radiative properties of the glasses. These glasses showed very high optical gain (in the range of 5.10 × 10−25 to 15.87 × 10−25 cm2 s−1) and branching ratio (from 8.27 to 61.6%). The glass prepared with Au NPs of 0.25 g revealed the highest optical gain (15.7 × 10−25 cm2 s−1) and gain bandwidth (9.55 × 10−22 cm2) for the 5D0→7F2 transition. The observed significant increase in the stimulated emission cross-section of the glasses indicated their prospect towards the photonic device fabrication. The achieved improvement in the photoluminescence emission intensity for the 5D0→7F2 transition was largely credited to the energy transfer between the Eu3+ and NPs inside the glasses. The high colour purity (for red colour coordinate) of the glasses obtained from the CIE chromaticity diagram suggested their potential for the development of efficient red laser.

Preparation of PVA Fluorescent Gel and Luminescence of Europium Sensitized by Terbium (III).

Polyvinyl alcohol (PVA) gel has a very wide range of applications in agriculture, military, industry, and other fields. As a widely used water-soluble polymer, PVA has good mechanical properties, excellent spinnability, good hydrophilicity, remarkable physical and chemical stability, good film formation, is non-polluting, and exhibits good natural degradation and biocompatibility. It is an ideal gel preparation material. Incorporation of rare-earth elements into PVA polymers can be used to prepare rare-earth luminescent gel materials. Results show that the luminescent efficiency of complexes is mainly related to their structure, ligand substituents, synergists, and the electronic configuration of doped rare-earth ions. Fluorescent gel films were prepared by adding europium, terbium, and europium/terbium co-doped into PVA, and their fluorescence properties were compared and analyzed. It was found that, in addition to the above factors, the sensitization of terbium to europium, and the fluorescence-quenching effect of hydroxyl groups, will influence the fluorescence properties. This has opened a new route for the application of rare-earth materials and may have value in the field of new materials.

Synthesis and Luminescent Properties of Europium Doped Zirconia Nanoparticles

This paper reports a tunable luminescence of europium (Eu 3+) doped zirconia (ZrO2) nanoparticles as a function of hydrothermal temperature, europium concentrations, time and pH value. The nano-sized Eu doped ZrO2 (Eu:ZrO2) particle was synthesized by hydrothermal method at the temperature of 200 °C and time up to 48 h. The nano-sized Eu:ZrO2 particles have a diameter of about 10 nm. The luminescent properties of nano-sized Eu:ZrO2 particle was enhanced in the sample when high temperature, high Eu 3+ concentration and prolonging hydrothermal time were used at pH 7. These results suggest the use of Eu:ZrO2 nanoparticles followed by thermal annealing in tuning the luminescence of Eu:ZrO2 nanoparticles which have potential applications as phosphors in solid state lighting.

Effect of the Counterion on Circularly Polarized Luminescence of Europium(III) and Samarium(III) Complexes.

Each enantiopure europium(III) and samarium(III) nitrate and triflate complex of the ligand L, with L = N,N′-bis(2-pyridylmethylidene)-1,2-(R,R + S,S)-cyclohexanediamine ([LnL(tta)2]·NO3 and [LnL(tta)2(H2O)]·CF3SO3, where tta = 2-thenoyltrifluoroacetylacetonate) has been synthesized and characterized from a spectroscopic point of view, using a chiroptical technique such as electronic circular dichroism (ECD) and circularly polarized luminescence (CPL). In all cases, both ligands are capable of sensitizing the luminescence of both metal ions upon absorption of light around 280 and 350 nm. Despite small differences in the total luminescence (TL) and ECD spectra, the CPL activity of the complexes is strongly influenced by a concurrent effect of the solvent and counterion. This particularly applies to europium(III) complexes where the CPL spectra in acetonitrile can be described as a weighed linear combination of the CPL spectra in dichloromethane and methanol, which show nearly opposite signatures when their ligand stereochemistries are the same. This phenomenon could be related to the presence of equilibria interconverting solvated, anion-coordinated complexes and isomers differing by the relative orientation of the tta ligands. The difference between some bond lengths (M–N bonds, in particular) in the different species could be at the basis of such an unusual CPL activity.

Photoluminescent report on red light emitting europium(III) complexes with heterocyclic acid

Five luminescent europium (III) carboxylate complexes have been synthesized by using ligand 3-isopropylpyrazole-5-carboxylic acid as primary ligand and 4,4’-dimethyl-2,2’-bipyridyl, 2,2’-bipyridyl, 5,6-dimethyl-1,10-phenanthroline and 1,10-phenanthroline as secondary ligands and characterized through various techniques. These complexes exhibit excellent thermal stability and characteristic europium centered photoemission spectra under the excitation of ultraviolet light. Luminescence decay curves, Judd–Ofelt analysis, internal quantum efficiency and energy transfer mechanism have also been discussed. The color coordinates and color purity are calculated to investigate red emission of the complexes. The study results reveal that these complexes can be potentially used as red light emitting materials in various optoelectronic devices.

Sensitive Label-Free Thermal Stability Assay for Protein Denaturation and Protein-Ligand Interaction Studies.

In modern biochemistry, protein stability and ligand interactions are of high interest. These properties are often studied with methods requiring labeled biomolecules, as the existing methods utilizing luminescent external probes suffer from low sensitivity. Currently available label-free technologies, e.g., thermal shift assays, circular dichroism, and differential scanning calorimetry, enable studies on protein unfolding and protein–ligand interactions (PLI). Unfortunately, the required micromolar protein concentration increases the costs and predisposes these methods for spontaneous protein aggregation. Here, we report a time-resolved luminescence method for protein unfolding and PLI detection with nanomolar sensitivity. The Protein-Probe method is based on highly luminescent europium chelate-conjugated probe, which is the key component in sensing the hydrophobic regions exposed to solution after protein unfolding. With the same Eu-probe, we also demonstrate ligand-interaction induced thermal stabilization with model proteins. The developed Protein-Probe method provides a sensitive approach overcoming the problems of the current label-free methodologies.

Chiroptical Spectroscopic Studies on Lanthanide Complexes with Valinamide Derivatives in Solution.

Ligands based on 2,2'-bipyridine and valinamide moieties induce circularly polarized luminescence in their europium complexes. Both the R and S enantiomers of the complexes were successfully obtained. Single-crystal X-ray analysis of the racemic crystal confirmed that the ligand is coordinated to the europium ion in a tetradentate fashion. The π-electronic system of the ligand is co-planar with the valinamide moiety, and acts as an efficient photoantenna to sensitize europium luminescence by UV excitation. The luminescence quantum yield (QY) of europium in the valinamide-containing complex was 44 % in acetonitrile. The glum value to evaluate the circularly polarized luminescence was relatively high at |0.13| estimated from their magnetic dipole transitions around 593 nm. For comparison, we prepared hexadentate europium complexes in the S- and R-forms derived from two bipyridine moieties linked by ethylenediamines. The determined QYs were 18 % (S) and 16 % (R), and the glum value |0.12| for the hexadentate complexes. The photophysical properties of the gadolinium complexes of the ligands were also evaluated.