Europium Β-diketonate Research Articles

White LED based on poly(N-vinylcarbazole) and lanthanide complexes ternary co-doping system

First, binary and ternary doping system of terbium and/or europium β-diketonate complex doping in poly(N-vinylcarbazole) (PVK) was studied. Energy transfer was analyzed in such complicated doping system. In such a complicated system, inter-molecular energy transfer from PVK to Tb(DBM) 3Phen(TbDP) and Eu(DBM) 3Phen(EuDP), and from TbDP to EuDP exists. The color changed by adjusting the mixing ratio of dopants concentration and excitation wavelength. Further, in the ternary doping system, it is found that white light could be obtained by optimizing the excitation of different wavelength.

Dual role of a di-urethanesil hybrid doped with europium β-diketonate complexes containing either waterligands or a bulky chelating ligand

In the present work we report the unusual role played by a sol-gel derived di-urethane cross-linked poly(oxyethylene) (POE)/siloxane (di-urethanesil, d-Ut(600)) hybrid matrix in the immobilization of the β-diketonate aquocomplex Eu(btfac)3(H2O)2 (btfac− is 4,4,4-trifluoro-1-phenyl-2,4-butanedionate) and in the quasi preservation in the hybrid of the 5D0 quantum efficiency q(5D0) value displayed by this complex in the isolated state (0.12 versus 0.18, respectively). We demonstrate that the d-Ut(600) framework acts as an inert (although optically active) support towards Eu(btfac)3(H2O)2, enabling Eu3+ sensitization by the btfac− ligands and energy transfer between the hybrid host excited states and the lanthanide intra-4f6 levels, while the number of Eu3+-coordinated water molecules remains constant. We also provide evidence that the incorporation of the Eu(btfac)3phen (phen is 1,10-phenantroline) complex into the same hybrid matrix is disadvantageous from the 5D0 quantum efficiency standpoint, because of the severe steric hindrance that emerges between the POE chains of the host structure and the bulky phen molecules, leading to the expulsion of these ligands from the Eu3+ first coordination sphere and to their replacement by two water molecules. As a consequence, embedding of Eu(btfac)3phen in d-Ut(600) results in a significant reduction of the q(5D0) value of the isolated complex (from 0.47 to 0.16). The behaviour observed in the presence of this bidentate chelating ligand correlates well with the practically identical q(5D0) values and number of Eu3+-coordinated water molecules (ca. 2) estimated for the two hybrids.

Europium β-diketonates for red-emitting electroluminescent devices

Organic light-emitting devices were fabricated, wherein europium β-diketonates of the general formula Eu(X) 3(L) are the active emitting materials [L = 2,4,6-tri(2-pyridyl)-1,3,5-triazine (TPTZ) or 4,4′-dimethoxy-2,2′-bipyridine (dmbipy); X is the conjugate base of 4,4,4-trifluoro-1-phenyl-1,3-butanedione (HBTFA), thenoyltrifluoroacetone (HTTA), or 1,1,1,5,5,5-hexafluoro-2,4-pentanedione (HHFAC)]. Red luminescence characteristic of Eu(III) at about 614 nm was observed in each of the five devices of the general device configuration ITO/NPB/Eu(X) 3(L):CBP/BCP/AlQ/LiF/Al [ITO, indium tin oxide; NPB, 4,4′-bis[ n-(1-naphthyl)- N-phenyl-amino]biphenyl; CBP, 4,4′- N, N′-dicarbazolebiphenyl; BCP, 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline; AlQ, tris(8-hydroxy)quinoline aluminum]. Except for Eu(BTFA) 3(TPTZ), each of the other four complexes gave practically meaningful device performance. In particular, the device utilizing Eu(TTA) 3(TPTZ) exhibited a maximum brightness of 781 cd/m 2 and the highest current efficiency reported so far of 4.76 cd/A at a typical computer screen brightness (100 cd/m 2).

Luminescent characteristics of liquid-phase systems and polymer compositions containing europium β-diketonates solubilized with pluronics

The solubilization of europium β-diketonate complexes with amphiphilic polymers, ternary block copolymers of ethylene and propylene oxides (Pluronics), was shown to change luminescence intensity in such complexes. The association of europium β-diketonate complexes with Pluronics was proved by atomic force microscopy of agglomerates crystallized on mica surfaces from chloroform solutions of Pluronic F-127 in the presence and absence of the luminophores under study. In the absence of luminophores, Pluronic F-127 crystallized on a mica surface had a dendrite-like structure, while the evaporation of chloroform solutions containing both europium β-diketonates and Pluronic F-127 gave crystallized luminophore-Pluronic associates as compact islands with a characteristic size of ∼0.5 μm.

Electrical conductivity and luminescence of metal-organic nanocomposites

We presented the results of experimental study of electrical and luminescence properties of planar nanocomposites based on gold island films and layers of efficient organic luminophores — aluminum (III) 8-hydroxyquinolinate (Alq3) and europium β-diketonates [Eu(DBM)3 bath, Eu(DBM)3 phen, and Eu(DBM)3]. The mechanisms of electroluminescence of such hybrid systems are discussed and the processes of luminescence excitation in the organic component of nanocomposites are considered in detail. It is shown that the spectral characteristics of europium β-diketonates are controlled by the Eu3+ ion fluorescence. The proposed mechanisms of nanocomposite electroluminescence are confirmed by the results of measurements of cathodoluminescence spectra of organic luminophores.

Effect of temperature on the morphology of rare earth-doped microcapsules

Fluorescent microcapsules doped with europium β-diketone complex were previously fabricated by stepwise adsorption of polyelectrolytes and europium complex using the layer-by-layer (LbL) technique [Chem. Commun. (2007) 1547–1549]. In this work, the influence of thermal treatment on the morphology of rare earth-doped microcapsules was studied by atomic force microscopy (AFM). Remarkable shrinking, increase of wall thickness and decrease of surface roughness were observed after heating the rare earth-doped microcapsules until 70 °C for 30 min. Intense red light emission at 612.0 nm of the microcapsules could be clearly observed by bare eyes after thermal treatment. Diameter variation of the luminescent microcapsules induced by annealing is attributed to the molecular rearrangement of polyelectrolytes. Study on the fluorescent microcapsules with various sizes provides guidance in potential application as biological assay reagents or display elements.

The effect of temperature and solvent on the morphology of microcapsules doped with a europium β-diketonate complex

Fluorescent microcapsules doped with a europium beta-diketonate complex were fabricated for the first time by stepwise adsorption of polyelectrolytes and europium complex using the layer-by-layer technique. The influence of temperature and solvent treatment on the morphology of the microcapsules was investigated. Intense red light emission of the microcapsules could be clearly observed by fluorescence microscopy before and after treatment. Remarkable shrinking, decrease of the inner volume and increase of the wall thickness were observed using atomic force microscopy (AFM) and transmission electron microscopy (TEM) after thermal treatment. The shrinkage induced by annealing could be recovered by dissolving in ethanol solution, which was confirmed by AFM and TEM. Morphology variation of the luminescent microcapsules induced by annealing or solvent are both attributed to the molecular rearrangement of polyelectrolytes. While the shrinkage by annealing is an entropy driven process with formation of more coiled conformations of polyelectrolytes the morphology variation by ethanol might be due to the effective screening of electrostatic interaction within the polyelectrolyte multilayers and the changed interaction between hydrophobic fragments present in the polyelectrolytes.

Adducts of europium β-diketonates with nitrogen p, p′-disubstituted bipyridine and phenanthroline ligands: Synthesis, structural characterization, and luminescence studies

Europium complexes featuring fluorinated β-diketonate ligands [thenoyltrifluoroacetone (tta), 4,4,4-trifluoro-1-phenyl-1,3-butanedione (btfac), and 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate (hfac)] and nitrogen p, p′-disubstituted bipyridine and phenanthroline ligands [4,4′-dimethoxy-2,2′-bipyridine (dmbipy) and 4,7-dimethyl-1,10-phenanthroline (dmphen)] were synthesized. Their structures were determined by single crystal X-ray diffraction. Octacoordinate complexes were obtained using trifluorinated tta and btfac, while nonacoordinated complexes were produced using hexafluorinated hfac. The differences in coordination number and bond lengths of these complexes are rationalized in terms of the electronic and steric features of the ligands. UV excitation of the complexes led to red luminescence characteristic of trivalent europium ion. The high overall quantum yields observed for the europium complexes bearing hfac and dmbipy or dmphen ligands are rationalized in terms of the relatively high ligand-to-metal energy transfer efficiencies.

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.

Europium, terbium, and ytterbium 3-(3′-triethoxysilylpropyl)pentane-2,4-dionates. Synthesis and the formation of luminescent sol-gel films

3-(3′-Triethoxysilylpropyl)pentane-2,4-dione, (EtO)3SiCH2CH2CH2C[-C(O)CH3]2 (I), was synthesized from 3-allylpentane-2,4-dione, CH2 = CH-CH2-C[-C(O)CH3]2, and triethoxysilane, (EtO)3SiH, in the presence of Speier’s catalyst. The silylation occurred mainly at the terminal C atom of the allyl group. The corresponding europium(III), terbium(III), and ytterbium(III) β-diketonates were synthesized from compound I and appropriate metal isopropoxides and used to obtain transparent sol-gel films containing Eu3+, Tb3+, and Yb3+ cations. The film formation was studied by IR spectroscopy. It was found that moisture causes not only the hydrolysis and condensation of triethoxysilyl groups but also the hydration of the cation of the rare-earth metal. When the terbium complex was excited at the wavelength of one of the two peaks (230 and 308 nm) in the excitation spectrum, the cation fluoresced intensely at 491, 547, 585, and 623 nm due to the transitions 5 D 4 → 7 F 6, 5 D 4 → 7 F 5, 5 D 4 → 7 F 4, and 5 D 4 → 7 F 3, respectively. All these bands were narrow, the band at 547 nm being most intense. No emission from the organosilicon matrix at 440 nm was observed. The emission spectra of Eu3+-containing films showed, along with the bands at 593, 618, 667, and 700 nm due to the emission from the cation (5 D 0 → 7 F 1, 5 D 0 → 7 F 2, 5 D 0 → 7 F 3, and 5 D 0 → 7 F 4 transitions, respectively), an intense band at 491 nm due to the emission from the matrix.

Study on high-efficiency fluorescent microcapsules doped with europium β-diketone complex by LbL self-assembly

Rare-earth beta-diketone complex doped microcapsules with high efficiency fluorescence fabricated by the LbL technique based on electrostatic and charge-dipole interactions are reported.

Energy transfer pathways in the carbazole functionalized β-diketonate europium complexes

Two novel Eu3+ complexes Eu(CDBM)3·2H2O and Eu(CCDBM)3·2H2O have been synthesized (CDBM = 1-(4-(9-carbazol)phenyl)-3-phenyl-1,3-propanedione, CCDBM = 1-((4-(9-carbazol)methyl)phenyl)-3-phenyl-1,3-propanedione). Eu(CDBM)3·2H2O showed strong internal ligand charge transfer (ILCT) fluorescence and sensitized emission of Eu3+. Due to the charge transfer character, the fluorescence band of CDBM shifted from 403 nm in cyclohexane to 559 nm in acetonitrile. Photophysical studies demonstrated that no energy was migrated from the ILCT excited state of the ligands to Eu3+, and that Eu3+ was sensitized by the triplet state which was localized in the 1,3-diphenyl-1,3-propanedione (DBM) part. The quantum efficiencies of Eu3+ in the three complexes are in the order Eu(DBM)3·2H2O > Eu(CCDBM)3·2H2O > Eu(CDBM)3·2H2O in both solution and the solid state. The energy transfer pathways in the three Eu3+ complexes were discussed in detail. Based on the systematic photophysical studies, a new guideline for the organo-lanthanide light emitting materials has been proposed: ILCT should be avoided during molecular modification.

Electroluminescence of a device based on europium β-diketonate with phosphine oxide complex

Rare earth (RE) ions have spectroscopic characteristics to emit light in narrow lines, which makes RE complexes with organic ligands candidates for full color OLED (Organic Light Emitting Diode) applications. In particular, β-diketone rare earth (RE 3+) complexes show high fluorescence emission efficiency due to the high absorption coefficient of the β-diketone and energy transfer to the central ion. In this work, the fabrication and the electroluminescent properties of devices containing a double and triple-layer OLED using a new β-diketone complex, [Eu(bmdm) 3(tppo) 2], as transporting and emitting layers are compared and discussed. The double and triple-layer devices based on this complex present the following configurations respectively: device 1: ITO/TPD (40 nm)/[Eu(bmdm) 3(tppo) 2] (40 nm)/Al (150 nm); device 2: ITO/TPD (40 nm)/[Eu(bmdm) 3(tppo) 2] (40 nm)/Alq 3 (20 nm)/Al (150 nm) and device 3: ITO/TPD (40 nm)/bmdm-ligand (40 nm)/Al (150 nm), were TPD is ( N, N′-diphenyl- N, N′-bis(3-methylphenyl)-1,1-biphenil-4,4-diamine) and bmdm is butyl methoxy-dibenzoyl-methane. All the films were deposited by thermal evaporation carried out in a high vacuum system. These devices exhibit high intensity photo- (PL) and electro-luminescent (EL) emission. Electroluminescence spectra show emission from Eu 3+ ions attributed to the 5D 0 to 7F J ( J = 0, 1, 2, 3 and 4) transitions with the hypersensitive 5D 0 → 7F 2 transition (around 612 nm) as the most prominent one. Moreover, a transition from 5D 1 to 7F 1 is also observed around 538 nm. The OLED light emission was almost linear with the current density. The EL CIE chromaticity coordinates ( X = 0.66 and Y = 0.33) show the dominant wavelength, λ d = 609 nm, and the color gamut achieved by this device is 0.99 in the CIE color space.

Spectra of copper and europium β-diketonates in alcoholic solutions and transparent dielectrics

We have used optical and EPR spectroscopy to study the mechanisms for color center formation in nanoporous glasses, polymethylmethacrylate, and alcoholic solutions containing ?-diketonate molecules: Cu(hfac)2, Ba(hfac)2, Pr(hfac)3, and Eu(fod)3. We have observed and studied the complex structure of the absorption bands in the 300 nm region belonging to the intraligand π-π* transition. Analogous results were obtained when studying the photoluminescence spectra of 5D0 → 7F0 transitions of Eu3+ ions and the EPR spectra of Cu2+ ions in matrices doped with Cu(hfac)2. We propose a model according to which for β-diketonate molecules (except for basic diketonates), a hydrolyzed form exists that is formed during synthesis of the polycrystalline powder due to the presence of water molecules. The model allows us to explain the spectral manifestations of β-diketonates in different matrices.

Narrow bandwidth red electroluminescence from solution-processed lanthanide-doped polymer thin films

Narrow bandwidth red electroluminescence from OLED devices fabricated using a simple solution-based approach is demonstrated. A spin-casting method is employed to fabricate organic light emitting diode (OLED) devices comprising a poly( N-vinylcarbazole) (PVK) host matrix doped with a europium β-diketonate complex, Eu(dbm) 3(Phen) (dibenzoylmethanate, dbm; 1,10-phenanthroline, Phen) on glass/indium tin oxide (ITO)/3,4-polyethylene-dioxythiophene-polystyrene sulfonate (PEDOT) substrates. Saturated red europium ion emission, based on the 5D 0 → 7F 2 transition, is centered at a wavelength of 612 nm with a full width at half maximum of 3.5 nm. A maximum external quantum efficiency of 6.3 × 10 − 2 cd/A (3.1 × 10 − 2 %) and a maximum luminance of 130 cd/m 2 at 400 mA/cm 2 and 25 V is measured for ITO/PEDOT/PVK:Eu(dbm) 3(Phen)/Ca/Al devices. This measured output luminance is comparable to that of devices fabricated using more sophisticated small molecule evaporation techniques.

Synthesis In Situ, Characterization, and Photostability of Europium β-Diketone Chelates in Organically Modified Silicates (ORMOSILs)

Europium β-diketonates have desirable optical properties, and transparent inorganic materials that have been doped with these chelates seem to be promising for potential applications in luminescence-display devices, integrated optical device sources, and new visible lasers. However, these chelates may be decomposed or not dissolved in sol—gel precursor solutions and, thus, cannot be doped in gel glasses that have been prepared via traditional sol—gel processing. An in situ synthesis technique has been used for the first time to synthesize five binary and ternary coordination compounds of europium β-diketonates in transparent organically modified silicates (ORMOSILs) during heat treatment or during the process of sol-to-monolithic ORMOSIL conversion. ORMOSILs that have been doped with in situ europium β-diketonates exhibit rather-high fluorescence intensity and good monochromati-city. These materials result in enhanced red-light emission under ultraviolet excitation. The chelates that have been synthesized in situ in the ORMOSILs reveal better photostability, in comparison to that of the pure chelates that have been dissolved in ethanol solutions.

Electrophosphorescence emission in organic light-emitting diodes based on (Sm+Eu) complexes

In this work, we reported the preparation and the characterization of triple-layer electroluminescent organic devices using different blends of the samarium and europium β-diketonate complexes [Sm x Eu y (TTA) 3(TPPO) 2] ( x=0.7, 0.9; y=0.3, 0.1) as emitting layer. The organic light-emitting diode (OLED) devices contained 1-(3-methylphenyl)-1,2,3,4-tetrahydroquinoline-6-carboxyaldehyde-1,1′-diphenylhydrazone (MTCD) as hole-transporting layer and tris(8-hydroxyquinoline) aluminum (Alq 3) as electron transporting layer. The electroluminescence (EL) spectra present emission narrow bands characteristic of the Sm 3+ and Eu 3+ ions overlapped with a broad band attributed to the molecular electrophosphorescence (EP) from the triplet–singlet (T 1→S 0) transition from the TTA ligand. The intensity ratio of the peaks is determined by the bias voltage applied to the OLED and this fact, together with the ligand electrophosphorescence, allows fabrication of a voltage-tunable color light source.

Voltage color tunable OLED with (Sm,Eu)-β-diketonate complex blend

Light emission from organic electroluminescent diodes (OLEDs) in which mixed samarium and europium β-diketonate complexes, [Sm 0.7Eu 0.3(TTA) 3(TPPO) 2], was used as the emitting layer is described. The electroluminescence spectra exhibit narrow peaks arising from 4f-intraconfigurational transitions of the Sm 3+ and Eu 3+ ions and a broad emission band attributed to the electrophosphorescence of the TTA ligand. The intensity ratio of the peaks determined by the bias voltage applied to the OLED, together with the ligand electrophosphorescence, allows to obtain a voltage-tunable color light source.

Effect of ligand radicals on vibrational IR, Raman and vibronic spectra of europium β-diketonates

Vibrational IR, Raman spectra and vibronic sidebands of Eu 3+ electronic transitions of europium tris-β-diketonates Eu(β) 3·Ph (β-dipyvaloylmethane (DPM), acetylacetone (AA), benzoylacetone (BA), thenoyltrifluoroacetone (TTFA) and other β-diketones; Ph-methyl-, phenyl-, and nitro-derivatives of 1,10-phenanthroline (Phen)) as well as Eu(β) 3·Bpy and Eu(β) 3·D-Bpy (Bpy- and D-Bpy–H- and D-2,2′-bipyridine) were studied. Effect of ligand radical properties on spectra and manifestation of the reciprocal influence of non-equivalent ligands in spectra are discussed. Dependence of the spectra on electronic density distribution in both ligands as well as on the strength of MO and MN bonds at the variation of radicals of one of the ligands, β or Ph, was examined. Shape of vibronic sidebands was analysed. Behaviour of bands in the middle and far regions of IR spectra of the series Eu(β) 3·Phen and Eu(TTFA) 3·Ph was investigated. Increase of the polarising influence of Eu 3+ ions on Phen and Bpy molecules and strengthening the EuN bonds in TTFA compounds in comparison with DPM compounds were disclosed from the Raman spectra of Eu(β) 3·Phen and Eu(β) 3·Bpy, that is in accordance with properties of β-diketone radicals. Conclusion about weaker EuN bonds in europium β-diketonates with heterocyclic diimines in comparison with corresponding nitrates was derived from the spectra. Spectral data concerning the relative strength of Euligand bonds are in agreement with available X-ray data.

A luminescent tris(2-thenoyltrifluoroacetonato)europium(iii) complex covalently linked to a 1,10-phenanthroline-functionalised sol–gel glass

Lanthanide doped sol–gel glasses are an attractive type of luminescent material which can be processed at ambient temperatures. However, the solubility of the lanthanide complexes in the sol–gel matrix can be a problem and it is difficult to obtain a uniform distribution of the complexes (avoidance of cluster formation). These problems can be solved by covalently linking the lanthanide complex to the glass matrix. In this study, a strongly luminescent europium β-diketonate complex was immobilized on a 1,10-phenanthroline-functionalised silica sol–gel glass. The glass matrix was prepared by first reacting 5-amino-1,10-phenanthroline with 3-(triethoxysilyl)propyl isocyanate. The resulting compound, tetramethoxysilane (TMOS) and diethoxydimethylsilane (DEDMS) were hydrolysed and condensed at a neutral pH to a sol–gel glass. A tris(2-thenoyltrifluoroacetonato)europium(III) dihydrate complex was bound to the 1,10-phenanthroline groups on the silica gel and the coordinated water was expelled. High-resolution luminescence spectra were recorded and the radiative lifetimes were measured. It is shown that the spectroscopic behaviour of the luminescent materials is very comparable with that of the pure [Ln(tta)3(phen)] complex.