Severino Alves

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.

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.

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.

Emission quantum yield of europium (III) mixed complexes with thenoyltrifluoroacetonate and some aromatic ligands

Abstract We report the experimental determination and theoretical calculation of the 4f–4f emission quantum yield (q) and 5D0 excited state lifetime in the Eu (TTA)3.nL compounds (where TTA=thenoyltrifluoroacetonate, L denotes 1,10-phenantroline orp-tolyl sulfoxide and n=1 or 2). The experimental q values for these compounds vary significantly by changing the L ligand. The relation between the emission quantum yield and photophysical characteristics of the compounds is discussed. The calculations are carried out by using theoretical models for ligand–rare earth ion energy transfer processes and numerical solutions of the rate equations. Pathways for the intramolecular energy transfer process between the ligands and the rare earth ion are proposed. The theoretical results agree well with the experimental data for the compounds analyzed.

A novel fluorinated Eu(III) β-diketone complex as thin film for optical device applications

Abstract We discuss the synthesis and spectroscopic characteristics of a thin film (∼30–90 nm) based on lanthanide europium (III) complexes as the emitter layers, to shift the UV portion of light spectrum into the visible region. The complex presents high quantum efficiency (∼65%), is highly volatile and thermodynamically stable. In addition, the thin film is used as an alternative antireflection coating on a silicon solar cell, allowing for an improvement of about 21% on cell efficiency. The high absorption and luminescence properties in the UV–visible region and its compatibility with device fabrication processes make this material of great potential for use in advanced optical device technologies.

Modeling, Structural, and Spectroscopic Studies of Lanthanide-Organic Frameworks

In this paper, we report the hydrothermal synthesis of three lanthanide-organic framework materials using as primary building blocks the metallic centers Eu(3+), Tb(3+), and Gd(3+) and residues of mellitic acid: [Ln(2)(MELL)(H(2)O)(6)] (where Ln(3+) = Eu(3+), Tb(3+), and Gd(3); hereafter designated as (1), (2) and (3)). Structural characterization encompasses single-crystal X-ray diffraction studies, thermal analysis, and vibrational spectroscopy, plus detailed investigations on the experimental and predicted (using the Sparkle/AM1 model) photophysical luminescent properties. Crystallographic investigations showed that the compounds are all isostructural, crystallizing in the orthorhombic space group Pnnm and structurally identical to the lanthanum 3D material reported by the group of Williams. (2) is highly photoluminescent, as confirmed by the measured quantum yield and lifetime (37% and 0.74 ms, respectively). The intensity parameters (Omega(2), Omega(4), and Omega(6)) of (1) were first calculated using the Sparkle/AM1 structures and then employed in the calculation of the rates of energy transfer (W(ET)) and back-transfer (W(BT)). Intensity parameters were used to predict the radiative decay rate. The calculated quantum yield derived from the Sparkle/AM1 structures was approximately 16%, and the experimental value was 8%. We attribute the registered differences to the fact that the theoretical model does not consider the vibronic coupling with O-H oscillators from coordinated water molecules. These results clearly attest for the efficacy of the theoretical models employed in all calculations and open a new window of interesting possibilities for the design in silico of novel and highly efficient lanthanide-organic frameworks.

Doped polymers with Ln(III) complexes: simulation and control of light colors

Complexes of Eu(III) and Tb(III) were dispersed in polystyrene for the purpose of generating the primary red and green light colors, and simulating of the secondary yellow color. The polymer was doped with one or both complexes. Under ultraviolet excitation, the Eu(III) and Tb(III) complex-doped polymers, both solid state light emitters, generate the red and green colors, respectively. The Eu(III) and Tb(III) mixed complexes in the polymer present the characteristic emissions of the lanthanide ions, simulating the secondary yellow light color.

Lanthanide complexes dispersed in enamel: a promising new material for photonic devices

Abstract A lanthanide-thin-film based dosimeter with high sensitivity and selectivity to UV cumulative measurements was developed. The dosimeter is based on nitrocellulose–enamel and has been designed in order to present useful responses covering the three main UV regions related to skin damage effects: UV-A (365 nm), UV-B (315 nm), UV-C (290 nm).The active part of the system is a thin layer of commercial nitrocellulose enamel ultrasound-mixed with lanthanide complex powder. We have monitored the Eu (III) emission ( 5 D 0 → 7 F 2 ) and the Tb (III) emission ( 5 D 4 → 7 F 5 ) as a function of UV exposure time and a luminescence decrease of the Eu (III) emission was observed. Since this effect is irreversible, a memory effect is associated to the system allowing dosimetry measurements. For the red (600 nm), green (540 nm) and blue (430 nm) excitation the luminescence remained the same, which reinforces the UV selectivity of the dosimeter proposed. We may also adjust the dosimeter sensitivity by controlling the amount of powder mixed with the enamel.

New Homotrinuclear Lanthanide Complexes: Synthesis, Characterization and Spectroscopic Study

This work presents the synthesis and spectroscopic study of new homotrinuclear (TRI) systems for photonics applications. The luminescence spectroscopy shows characteristics transitions of Eu(III) and Tb(III) ions. For the Gd(III) complexes, the triplets states were determined by phosphorescence measurement. The complexes’ coordination geometries were calculated using the Sparkle/AM1 model. For the europium systems, the Sparkle/AM1 geometries were used to calculate all details involved in the energy transfer process, and the theoretical quantum yields were determined. From an energy diagram, that estimates triplet levels, it was possible to understand some experimental phenomenon, such as weak luminescence for precursor complex (without heterocyclics ligands), and ligands emission in terbium complexes. Some of these observations can also be explained by the Jablonski diagrams that describe, based on theoretical calculations, all luminescent process. The synthesized complexes showed high values of quantum yield in ethanolic environment: 50% for EuTRIDipy, 26% EuTRITerpy, and 56% for EuTRIPhen complexes.

CdTe quantum dots conjugated to concanavalin A as potential fluorescent molecular probes for saccharides detection in Candida albicans

Semiconductor colloidal quantum dots (QDs) have been applied in biological analysis due to their unique optical properties and their versatility to be conjugated to biomolecules, such as lectins and antibodies, acquiring specificity to label a variety of targets. Concanavalin A (Con A) lectin binds specifically to α-d-mannose and α-d-glucose regions of saccharides that are usually expressed on membranes of mammalian cells and on cell walls of microbials. Candida albicans is the most common fungal opportunistic pathogen present in humans. Therefore, in this work, this fungus was chosen as a model for understanding cells and biofilm-forming organisms. Here, we report an efficient bioconjugation process to bind CdTe (Cadmium Telluride) QDs to Con A, and applied the bioconjugates to label saccharide structures on the cellular surface of C. albicans suspensions and biofilms. By accomplishing hemagglutination experiments and circular dichroism, we observed that the Con A structure and biochemical properties were preserved after the bioconjugation. Fluorescence microscopy images of yeasts and hyphae cells, as well as biofilms, incubated with QDs-(Con A) showed a bright orange fluorescence profile, indicating that the cell walls were specifically labeled. Furthermore, flow cytometry measurements confirmed that over 93% of the yeast cells were successfully labeled by QD-(Con A) complex. In contrast, non-conjugated QDs or QDs-(inhibited Con A) do not label any kind of biological system tested, indicating that the bioconjugation was specific and efficient. The staining pattern of the cells and biofilms demonstrate that QDs were effectively bioconjugated to Con A with specific labeling of saccharide-rich structures on C. albicans. Consequently, this work opens new possibilities to monitor glucose and mannose molecules through fluorescence techniques, which can help to optimize phototherapy protocols for this kind of fungus.