Ieda L. V. Rosa

Monoterpenes oxidation in the presence of Y zeolite-entrapped manganese(III) tetra(4-N-benzylpyridyl)porphyrin

Abstract Under homogeneous conditions and as a Y zeolite supported complex, manganese(III) tetra(4- N -benzylpyridyl)porphyrin (MnTBzPyP) is an active catalyst in the epoxidation of ( R )-(+)-limonene and α-pinene, and in the hydroxylation of carvacrol and thymol, using H 2 O 2 /ammonium acetate, at room temperature and atmospheric pressure. A combined study on the characterization and catalytic performance of MnTBzPyP–NaY suggests that its preparation led to a successful inclusion of MnTBzPyP inside the zeolite during the hydrothermal synthesis. Unfortunately, irreversible catalyst deactivation occurs in the presence of H 2 O 2 . Changes in the crystalline structure of MnTBzPyP–NaY during the oxidative transformations are accompanied by leaching of the porphyrin complex to the reaction solution, accounting for the nearly complete loss of activity when the catalyst is re-used. Higher substrate conversions were achieved with the zeolite-impregnated complex. The iron analogue is inactive, under the applied reaction conditions.

On the photoluminescence behavior of samarium-doped strontium titanate nanostructures under UV light. A structural and electronic understanding

A combined experimental and theoretical investigation on the photoluminescence properties of SrTiO(3) (ST) and SrSm(0.01)Ti(0.99)O(3) (ST_Sm) nanostructures is presented in this work. The nanocrystalline powders were prepared by the polymeric precursor method, and the order-disorder behavior of this material was investigated by means of X-ray diffraction (XRD), spectral absorbance (UV-vis), transmission electron microscopy (TEM) images, electron paramagnetic resonance (EPR) and photoluminescence (PL) experimental techniques. The decrease in the broad PL emission band of ST and ST_Sm powders measured at room temperature indicates an increase in the structural order as the annealing temperature increases, i.e. characteristic samarium peaks intensify as the structural order increases in ST_Sm samples. The interactions of the network clusters that form the ST and ST_Sm structures were evaluated by means of the ab initio periodic method at the density functional theory (DFT) level with the hybrid nonlocal B3LYP approximation. The symmetry-breaking process that leads to the presence of non-ideal [TiO(6)] and [SrO(12)] clusters, as well as the relationship between these clusters, provides favorable structural and electronic conditions for the appearance of PL phenomena.

Luminescent properties of Eu3+ β-diketonate complexes supported on Langmuir—Blodgett films

Abstract In this work we report the results for dihexadecylphosphate (dhp)-Eu 3+ incorporated monolayers transferred to hydrophobic silanized quartz plates. The transfer was followed by luminescence and photophysical measurements. The monolayers were then dipped in a 10 -5 M aqueous solution of benzoyltrifluoroacetone (bfa) at pH ≈ 6.5. The emissions related to the 5 D 0 → 7 F 1,2 transitions in Eu 3+ , when excited at 335 nm, were observed even for one Langmuir—Blodgett monolayer deposited on each side of the plate. It was also noticed that these emissions increased by about a factor of two in intensity after the monolayers were dipped in the bfa solution.

Rietveld refinement and optical properties of SrWO4:Eu3+ powders prepared by the non-hydrolytic sol-gel method

We investigated the effect of annealing time on the structure and optical properties of SrWO4:Eu3+ powders prepared by the non-hydrolytic sol-gel method and heat treated at 800 °C for 2, 4, 8 and 16 h. Thermogravimetric and differential thermal analyses revealed that SrWO4:Eu3+ powders were obtained at about 800 °C. X-ray diffraction patterns and Rietveld refinement data confirmed that all powders had a scheelite-type tetragonal structure. Micro-Raman and Fourier transform infrared spectra indicated structural order at short range and anti-symmetric stretching vibrations of O–W–O bonds associated with tetrahedral [WO4] clusters. Optical properties were investigated by ultraviolet-visible (UV-vis) diffuse reflectance, and photoluminescence (PL) data which provided the evolution of quantum efficiency (η) and lifetime (τ). UV-vis spectroscopy evidenced intermediate energy levels within the band gap of SrWO4:Eu3+ powders. PL properties validated that the Eu3+ electric-dipole (5D0→7F2) transition in PL emission spectra was dominant which proved that Eu3+ ions were positioned in a site without an inversion center. [(5D0→7F2)/(5D0→7F1)] band ratios showed that Eu3+ ions were located in a low symmetry environment. The PL emission, η and τ proved the dependence on the annealing time in the behavior of SrWO4:Eu3+ powders with a higher relative emission PL intensity as well as higher η and τ values related to other samples when heat treated at 800 °C for 8 h.

Luminescence of a new Tm3+ β-diketonate compound

Abstract This work reports the results for the synthesis, characterization and photophysical properties of a new Tm(ppa) 3 ·2H 2 O complex (ppa=3-phenyl-2,4-pentanedionate). Its characterization was carried out by EDTA titration and TGA analysis, which indicates the presence of the tris-β-diketonate complex with two water molecules completing the metal coordination sphere. The photophysical analyses of the Tm(ppa) 3 ·2H 2 O complex were carried out at room (25°C) and liquid nitrogen (77 K) temperatures. Excitation and absorption spectra showed a broad band centered at ∼335 nm which is ascribed to the complex, since the ppa absorbance maximum is centered at 296 nm. The emission spectra ( λ ex =335 nm) presented the characteristic bands of Tm 3+ due to the 1 G 4 → 3 H 6 (478 nm), 1 G 4 → 3 F 4 (650 nm), 1 G 4 → 3 H 5 (770 nm) and 3 H 4 → 3 H 6 (790 nm) transitions. A pyridine adduct was also prepared but no spectral features could be observed in it. The Gd(ppa) 3 ·2H 2 O was synthesized in order to determine the triplet state of the ppa.

Study of Structural and Photoluminescent Properties of Ca8Eu2(PO4)6O2

In this work it is presented for the first time the nanostructured hydroxyapatites doped with 0.5, 1.0 and 2.0 wt% of Eu3+ prepared at room temperature by the mechanical alloying technique. X-ray diffraction powder (XRD), infrared (IR) and Raman scattering spectroscopy, scanning electron microscopy (SEM), microhardness measurements as well as luminescent data of Eu3+ were used to investigate the structural and optical properties of these nanomaterials. The electrical and dielectrical analyses were used with the intention of having a better comprehension about the electromagnetic fields in pure and doped hydroxyapatites.

Structural, optical, and magnetic properties of NiMoO4 nanorods prepared by microwave sintering.

We report on the structural, optical, and magnetic properties of α,β-NiMoO4 nanorods synthesized by annealing the NiMoO4:nH2O precursor at 600°C for 10 minutes in a domestic microwave. The crystalline structure properties of α,β-NiMoO4 were investigated using X-ray diffraction (XRD), Fourier transform infrared (FTIR), and Raman (FT-Raman) spectroscopies. The particle morphologies and size distributions were identified by field emission microscopy (FE-SEM). Experimental data were obtained by magnetization measurements for different applied magnetic fields. Optical properties were analyzed by ultraviolet-visible (UV-vis) and photoluminescence (PL) measurements. Our results revealed that the oxygen atoms occupy different positions and are very disturbed in the lattice and exhibit a particular characteristic related to differences in the length of the chemical bonds (Ni-O and Mo-O) of the cluster structure or defect densities in the crystalline α,β-NiMoO4 nanorods, which are the key to a deeper understanding of the exploitable physical and chemical properties in this study.

SiO2–GeO2 Soot Preform as a Core for Eu2O3 Nanocoating: Synthesis and Photophysical Study

Nowadays solid state chemists have the possibility of work with low temperature strategies to obtain solid state materials with appropriate physical and chemical properties for useful technological applications. Photonic core shell materials having a core and shell domains composed by a variety of compounds have been synthesized by different methods. In this work we used silica-germania soot prepared by vapor-phase axial deposition as a core where a nanoshell of Eu2O3 was deposited. A new sol-gel like method was used to obtain the Eu2O3 nanoshell coating the SiO2–GeO2 particles, which was prepared by the polymeric precursor method. The photophysical properties of Eu3+ were used to obtain information about the rare earth surrounding in the SiO2–GeO2@Eu2O3 material during the sintering process. The sintering process was followed by the luminescence spectra of Eu3+ and all the samples present the characteristic emission related to the 5D0→7FJ (J = 0, 1, 2, 3 and 4). The ratios of the 5D0→7F2/5D0→7F1 emission intensity for the SiO2–GeO2@Eu2O3 systems were calculated and it was observed an increase in its values, indicating a low symmetry around the Eu3+ as the temperature increases.

Eu3+ and Tb3+ organophosphonates: synthesis, characterization and luminescent properties

Abstract This paper reports the results for the synthesis, characterization and photophysical properties of EuH(O 3 PR) 2 and TbH(O 3 PR) 2 (R=CH 3 or C 6 H 5 ). The Eu 3+ luminescence data revealed highly red emissive materials where the characteristic transitions 5 D 0 → 7 F J ( J =1, 2, 3, and 4) of Eu 3+ were observed when they were excited at 378 nm. The lifetime ( λ EXC =378 nm) for EuH(O 3 PC 6 H 5 ) 2 ( λ EM =614.5 nm) is 1.95 ms and for EuH(O 3 PCH 3 ) 2 ( λ EM =610.5 nm) is 1.75 ms. Tb 3+ compounds presented a highly green luminescence when excited at 368 nm due to the Tb 3+ 5 D 4 → 7 F J ( J =6, 5, 4, and 3) transitions. The Tb 3+ lifetime ( λ EXC =368 nm, λ EM =544 nm) for TbH(O 3 PC 6 H 5 ) 2 is 2.59 and 2.88 ms for TbH(O 3 PCH 3 ) 2 . The emission spectra of the solids resulting from TGA/DTA showed a Eu 3+ 5 D 0 → 7 F 1 transition more intense than the 5 D 0 → 7 F 2 one. The decrease in the 0→2/0→1 ratio from 2.92 to 0.503 for EuH(O 3 PCH 3 ) 2 and from 3.19 to 0.881 for EuH(O 3 PC 6 H 5 ) 2 , is consistent with a higher symmetry around Eu 3+ .

α-Ag2–2xZnxWO4 (0 ≤ x ≤ 0.25) Solid Solutions: Structure, Morphology, and Optical Properties

A theoretical study was elaborated to support the experimental results of the Zn-doped α-Ag2WO4. Theses α-Ag2-2xZnxWO4 (0 ≤ x ≤ 0.25) solid solutions were obtained by coprecipitation method. X-ray diffraction data indicated that all α-Ag2-2xZnxWO4 (0 ≤ x ≤ 0.25) microcrystals presented an orthorhombic structure. The experimental values of the micro-Raman frequencies were in reasonable agreement with both previously reported and calculated results. Microscopy images showed that the replacement of Ag+ by Zn2+ promoted a reduction in the average crystal size and modifications in the morphology, from rod-like with hexagonal shape to roll-like with a curved surface. A theoretical methodology based on the surfaces calculations and Wulff constructions was applied to study the particle shapes transformations and the surface energy variations in α-Ag2-2xZnxWO4 (0 ≤ x ≤ 0.25) system. The decrease in the band gap value (from 3.18 to 3.08 eV) and the red shift in photoluminescence with the Zn2+ addition were associated with intermediary energy levels between the valence and conduction bands. First-principles calculations with density functional theory associated with B3LYP hybrid functional were conducted. The calculated band structures revealed an indirect band gap for the α-Ag2-2xZnxWO4 models. The electronic properties of α-Ag2WO4 and α-Ag2-2xZnxWO4 microcrystals were linked to distortion effects and oxygen vacancies (VOx) present in the clusters, respectively. Finally, photoluminescence properties of α-Ag2WO4 and α-Ag2-2xZnxWO4 microcrystals were explained by means of distortional effects and oxygen vacancies (VOx) in [AgOy] (y = 2, 4, 6, and 7) and [WO6] clusters, respectively, causing a red shift. Calculations revealed that the substitution for Ag+ with Zn2+ occurred randomly in the α-Ag2WO4 lattice, and it was more favorable on the Ag4 site, where the local coordination of Ag+ cations was four.