Oscar L. Malta

Spectroscopic properties of a new light-converting device Eu(thenoyltrifluoroacetonate)3 2(dibenzyl sulfoxide). A theoretical analysis based on structural data obtained from a sparkle model

Abstract We report the synthesis, characterization and spectroscopic properties of the compound Eu(thenoyltrifluoroacetonate), 2(dibenzyl sulfoxide) which is highly luminescent under UV excitation. Experimental and theoretical results on ligand field parameters, 4f-4f intensities and intramolecular energy transfer processes are described. The characteristic emission spectrum of the Eu 3+ ion shows a very high intensity for the hypersensitive 5 D 0 → 7 F 2 transition, pointing to a highly polarizable chemical environment around the Eu 3+ ion. No emission at low temperature from the organic part of the compound is observed, in contrast to the case of the analog compound with Gd 3+ , indicating that energy transfer from the ligands to the Eu 3+ ion is quite efficient. Lifetime measurements confirm that the Eu 3+ luminescence has a higher efficiency than in the case of the hydrated compound (two water molecules in the place of the dibenzyl sulphoxides). The theoretical calculations are based on an optimized coordination geometry and electronic structure obtained from the SMLC/AM1 (Sparkle Model for the calculation of lanthanide complexes within the Austin Model 1), recently introduced in the literature, and ligand field and 4f-4f intensity models previously developed. A comparison with experiment is made. Considerably high values of intramolecular energy transfer rates are predicted.

Intensity parameters of 4f—4f transitions in the Eu(dipivaloylmethanate)3 1, 10-phenanthroline complex

Abstract We present and discuss experimental and theoretical relevant intensity parameters of 4f—4f transitions in the Eu(dipivaloylmethanate) 3 1, 10-phenanthroline complex which is a highly luminescent material under UV excitation. The theoretical analysis is based on the crystallographic data of the compound and on a theoretical scheme which takes into account the forced electric dipole and dynamic coupling mechanisms as developed in previous work. The good agreement found between theory and experiment provides support to the model used and indicates that, at least in the present case, further contributions to the intensities beyond the second-order theory are of no relevance.

Experimental and theoretical emission quantum yield in the compound Eu(thenoyltrifluoroacetonate)3.2(dibenzyl sulfoxide)

Abstract We report the experimental determination and a theoretical calculation of the 4f–4f emission quantum yield in the Eu(thenoyltrifluoroacetonate)3.2(dibenzyl sulfoxide) compound. The experimental procedure for determining the quantum yields is based on a method previously proposed by Bril and coworkers. The theoretical calculations are carried out by solving an appropriate set of rate equations and by using spectroscopic parameters and energy transfer rates recently reported for this compound. For the sake of comparison, the hydrated compound (two water molecules in the place of the dibenzyl sulfoxide) is also studied. Good agreement between theory and experiment is obtained, provided that the lifetime of the lowest triplet level of the donor ligand is ≥10−5 s at room temperature.

Influence of the N-[methylpyridyl]acetamide ligands on the photoluminescent properties of Eu(III)-perchlorate complexes

Abstract This work reports the synthesis, characterization and spectroscopic studies of Eu(III)-perchlorate complexes with amide ligands derived from N -[ x -methylpyridyl]acetamide where x =3, 4 and 6. The Eu(ClO 4 ) 3 3( x -mpa) complexes were characterized by elemental analyses, molar conductance, TG analyses and vibrational spectroscopy. Raman and infrared data show that the perchlorate ion, (ClO 4 − ), is bonded to Eu(III) as a monodentate ligand and that in these three complexes water molecules are not coordinated to the rare earth ion. The profiles of the emission spectra of the complexes with 3- and 4-mpa ligands are very similar but they differ from the complex containing 6-mpa ligand. This spectroscopic behavior can be rationalized in terms of the Ω λ ( λ =2 and 4) and R 02 experimental intensity parameters. The values of Ω 2 (∼6.5×10 −20 cm 2 ) in these complexes are smaller than in Eu(III)-TTA compounds ( Ω 2 ∼35.0×10 −20 cm 2 ), indicating that in the former case the rare earth ion is in a chemical environment less polarizable. Lifetime and emission quantum efficiency measurements for the emitting level 5 D 0 were carried out and the results are discussed.

Enhancement of Pr3+ luminescence in PbO–GeO2 glasses containing silver nanoparticles

Pr3+-doped PbO–GeO2 (PGO) glasses containing silver nanoparticles (NPs) were prepared and their spectroscopic characteristics were studied. The PGO samples and the nucleation of silver NP were obtained melting the starting oxide powders, quenching and annealing. Transmission electron microscopy was used to characterize the NP size distribution. Isolated silver particles with average diameter of 2 nm and aggregates with dimensions smaller than 100 nm were observed. Optical absorption and luminescence experiments were performed to investigate the properties of the composite system. Enhancement of the Pr3+ ions’ luminescence was observed due to the presence of the silver NP.

Theoretical analysis of the fluorescence yield of rare earth ions in glasses containing small metallic particles

We examine the fluorescence yield of rare earth ions in glasses containing a uniform volumetric distribution of metallic particles with small specific volume. The role of energy transfer between the ions and the particles is discussed. Depending on the particle size and the ion emission quantum efficiency, quenching or enhancement of the fluorescence is predicted.

Intermolecular energy transfer and photostability of luminescence-tuneable multicolour PMMA films doped with lanthanide–β-diketonate complexes

It is reported in this work the preparation, characterisation and photoluminescence study of poly(methylmethacrylate) (PMMA) thin films co-doped with [Eu(tta)3(H2O)2] and [Tb(acac)3(H2O)3] complexes. Both the composition and excitation wavelength may be tailored to fine-tune the emission properties of these Ln3+–β-diketonate doped polymer films, exhibiting green and red primary colours, as well as intermediate colours. In addition to the ligand–Ln3+ intramolecular energy transfer, it is observed an unprecedented intermolecular energy transfer process from the 5D4 emitting level of the Tb3+ ion to the excited triplet state T1 of the tta ligand coordinated to the Eu3+ ion. The PMMA polymer matrix acts as a co-sensitizer and enhances the overall luminescence intensity of the polymer films. Furthermore, it provides considerable UV protection for the luminescent species and improves the photostability of the doped system.

Luminescence investigation of the Sm(III)-β-diketonates with sulfoxides, phosphine oxides and amides ligands

Abstract In this paper we report on a photoluminescent investigation of complexes involving Sm 3+ -β-diketonates with sulfoxides, phosphine oxides and amides ligands. In the synthesis of the coordination compounds we used samarium tris(thenoyltrifluoroacetonate) dihydrated precursor with the following ligands (L): DBSO and PTSO sulfoxides; TPPO phosphine oxide and (PHA) N -phenylacetamide. They have shown high orange luminescence characteristic of the Sm 3+ ion. The emission spectra of the Sm 3+ -complexes present narrow bands arising from the 4 G 5/2 → 6 H J ( J =5/2, 7/2, 9/2, 11/2) transitions with the hypersensitive 4 G 5/2 → 6 H 9/2 transition as a prominent group. It is observed an efficient intramolecular energy transfer from the triplet state (T) of the ligands to the emitting 4 G 5/2 state of the Sm 3+ ion. The experimental intensity parameters ( η Sm and η Eu ) for the Sm and Eu complexes have been determined and compared. The lifetimes ( τ ) of the emitting level 4 G 5/2 of the Sm-complexes are approximately 10 times higher than in the precursor compound [Sm(TTA) 3 ·(H 2 O) 2 ] indicating that radiative processes are operative in all the compounds due to the absence of multiphonon relaxation by coupling with the OH oscillators.

Overlap polarizability of a chemical bond: a scale of covalency and application to lanthanide compounds

We introduce the concept of overlap polarizability of a single directional chemical bond and propose an expression for this quantity. The concept of ionic specific valence is also introduced, as a consequence of a relation, involving the bond force constant, between the overlap polarizability and the square of the overlap charge. It is proposed that the overlap polarizability can be used to define an ordinal scale of covalency. When applied to lanthanide compounds, each pair lanthanide-ligating atom being regarded as a diatomic-like molecule, these concepts lead to a remarkable result in which an expression for the charge factors, appearing in the simple overlap model for the ligand field, can be obtained when these factors are identified with the ionic specific valences of the ligating atoms. An ordinal scale of covalency for a few representative lanthanide compounds correlates well with the nephelauxetic effect.

Theoretical intensities of 4f-4f transitions between stark levels of the Eu3+ ion in crystals

Abstract We report a theoretical calculation of the intensities of the 4f-4f transitions between Stark levels of the Eu 3+ ion in KY 3 F 10 , LiYF 4 and LaOCl hosts. A ligand field Hamiltonian, described by a simple overlap model, is initially applied to oxychlorides, oxybromides and fluorides doped with the Eu 3+ ion. Since for the even rank ligand field parameters, there is a significant improvement with respect to the crude electrostatic approximation, this model is also used in the evaluation of the odd rank parameters required in the intensity calculations. The average energy denominator method used by Bebb and Gold to treat multi-photon ionization processes in hydrogen and rare gas atoms is used here as an alternative procedure to evaluate the electric dipole matrix elements. The results are in good agreement with those given by the standard Judd-Ofelt theory. Only the forced electric dipole mechanism up to second order and the dynamic coupling are taken into account. Emphasis is given to the fact that these two mechanisms should contribute with the same sign to the B λtp intensity parameters, in contrast with theoretical calculations currently found in the literature. Comparison with experimental values points to the neglect of higher order corrections to these two mechanisms, and the use of a still incomplete representation of the ligand field as the reason for the discrepancies between theory and experiment.