Fernando Aparecido Sigoli

Luminescent properties and lattice defects correlation on zinc oxide

Abstract The ZnO luminescent properties are strongly influenced by the preparation method and they are principally related to electronic and crystalline structures. This work reports about the correlation among luminescence properties of ZnO, obtained from zinc hydroxycarbonate, and crystalline lattice defects, microstrain, as function of thermal treatment. The crystallite size increase and the qualitative microstrain, obtained by Williamson–Hall plots, decrease as function of temperature. The evolution of electronic defects is analyzed by luminescence spectroscopy based on energy of the electronic transitions. From excitation spectrum, it is verified two bands around 377 nm and 405 nm attributed to the transitions between valence–conduction bands and valence band to interstitial zinc level, respectively. The emission spectra of sample treated at 600°C shows large band at 670 nm. However, the green emission around 530 nm is observed for samples treated at 900°C. The intensities of excitation and emission bands are associated with the increase of the electronic defects that depend on the strain lattice decrease. The lowest strain lattice results on the best green luminescent properties of zinc oxide.

Europium(III)-containing zinc oxide from Pechini method

ZnO:Eu3+ (0.1 and 3 at%) with average particle size of 500 nm were prepared by the Pechini method. Photoluminescence spectroscopy evidences that there is no energy transfer between ZnO and Eu3+ ion. The emission spectrum at 77 K shows that Eu3+ ions occupy at least three different sites in ZnO:Eu 3 at% sample. The experimental intensity parameter Ω2 indicates that Eu3+ ions in the sample doped with 3 at% occupy sites where 4f-configurational levels can better mix with opposite-parity states than those in the sample doped with 0.1 at%.

Morphological evolution of zinc oxide originating from zinc hydroxide carbonate

Instituto de Quimica Universidade Estadual Paulista-UNESP, PO Box 355, 14801-970 Araraquara, SP

Phase separation in pyrex glass by hydrothermal treatment: evidence from micro-Raman spectroscopy

In this work, we investigated the formation of porous silica matrix obtained by hydrothermal treatment under saturated steam condition from Pyrex® glass. This investigation was carried out by scanning electron microscopy (SEM), infrared spectroscopy (IR), X-ray powder diffractometry (XRD) and Raman microscopy. We observed the presence of connected and homogeneously distributed pores in a non-crystalline silica phase and a detectable interface between silica and remnant glass phases resulting in a framework similar to asymmetric membranes. The results indicate that the process of phase separation takes place at lower temperature than that of glass-transition on the surface of the glass phase. Essential reaction between water and silica at supercritical condition together with the formation and leaching of soluble phase contribute to obtain porous silica matrix.

Ion-Exchange Properties of Imidazolium-Grafted SBA-15 toward AuCl4– Anions and Their Conversion into Supported Gold Nanoparticles

Imidazolium groups were successfully prepared and grafted on the surface of SBA-15 mesoporous silica. The ion-exchange properties of the functionalized porous solid (SBA-15/R(+)Cl(-)) toward AuCl(4)(-) anions were evaluated through an ion-exchange isotherm. The calculated values of the equilibrium constant (log β = 4.47) and the effective ion-exchange capacity (t(Q) = 0.79 mmol g(-1)) indicate that the AuCl(4)(-) species can be loaded and strongly retained on the functionalized surface as counterions of the imidazolium groups. Subsequently, solids containing different amounts of AuCl(4)(-) ions were submitted to a chemical reduction process with NaBH(4), converting the anionic gold species into supported gold nanoparticles. The plasmon resonance bands, the X-ray diffraction patterns, and transmission electron microscopy images of the supported gold nanoparticles before and after thermal treatment at 973 K indicate that the metal nanostructures are highly dispersed and stabilized by the host environment.

Luminescence of Eu(III) β-diketone complex supported on functionalized macroporous silica matrix ☆

Abstract This work reports on the photoluminescent properties of the complex diaquatris(thenoyltrifluoroacetonate) europium(III), which was adsorbed or supported on tubes of modified surface silica matrix. The luminescence data and the experimental intensity parameter results evidence the existence of high interactions between the complex [Eu(tta) 3 (H 2 O) 2 ] and the modified surface matrix. The anchored complex on macroporous silica shows higher intensity parameter values suggesting that the Eu–O bond becomes more covalent than the adsorbed one. Therefore, the hypersensitive character of the 5 D 0 → 7 F 2 transition increases evidencing a high contribution of the dynamic coupling mechanism possibly due to highly polarizable chemical environments occupied by europium(III) ion. The lifetimes of the complex on silica matrices were measured.

Determination of Judd-Ofelt Intensity Parameters of Pure Samarium(III) Complexes

This work reports an alternative aproach to obtain the Judd-Ofelt intensity parameters of Sm(III) complexes with the general formula: [Sm(tta)3(L)n], with L = H2O, triphenylphosphine oxide (tppo), 2,2′-bipyridine (bipy) and 1,10-phenantroline (phen); n = 2 for H2O and tppo and n = 1 for phen and bipy, using the absorption spectra of rare earth complexes where the powders are dispersed in KBr pellets. This approach can be applied to other complexes of rare earth ions that have spin allowed transitions and it is validated by comparing the emission spectra of the complexes with those dispersed in KBr pellets.

Fast detection of paracetamol on a gold nanoparticle–chitosan substrate by SERS

A fast method for detecting pharmaceutical drugs, such as paracetamol, by surface-enhanced Raman spectroscopy (SERS) using a gold nanoparticle substrate was studied. Gold nanoparticles were synthesized using chitosan (AuNP–chitosan) as a reductant and capping agent and subsequently deposited on glass slides as a thin film. The SERS performance of AuNP–chitosan films was evaluated using methylene blue (MB, 10−6 mol L−1) as a SERS probe molecule. The method is based on drop-drying an analyte solution (paracetamol, 10−3 mol L−1) onto a substrate surface and subsequently analyzing by Raman spectroscopy. The spectra were obtained in 10 seconds with two accumulations and exhibit a high signal-to-noise ratio. This preliminary study supports the AuNP–chitosan substrate as a SERS sensor, for a convenient analytical method for detection of paracetamol and other pharmaceutical drug molecules.

Preparation of supported AuPd nanoalloys mediated by ionic liquid-like functionalized SBA-15: structural correlations concerning its catalytic activity

Noble metal nanoalloys are very important in catalysis, sensing, electrochemistry, and plasmonics. Based on the importance of these materials and in order to overcome the synthetic limitations for the in situ synthesis of supported nanoalloys in porous supports, we extended a synthetic protocol to achieve supported AuPd nanoalloys within SBA-15 pores modified with an ionic liquid-like alkoxysilane. The synthesized materials form very small nanoparticles with non-passivated surfaces, which are highly active as heterogeneous catalysts for the reduction of 4-nitrophenol. The anion exchange ability of the functionalized SBA-15 was used to adsorb Au and Pd anionic complexes. The adsorbed species were then reduced and converted into supported monometallic nanoparticles or nanoalloys. Nitrogen physisorption isotherms showed that the synthetic process does not damage the mesoporous support nor block the pores. TEM/EDS and UV-vis analyses were used to prove alloy formation in the bimetallic materials through the concomitant presence of Au and Pd in the same particles and through the disappearance of the gold plasmon band as the palladium content increased. Finally, the catalytic activity of the materials increased as the palladium content increased, showing that it is possible to control the catalytic performance by tuning the material composition during the anion exchange step.

Non-stabilized europium-doped lanthanum oxyfluoride and fluoride nanoparticles well dispersed in thin silica films

Well dispersed non-stabilized lanthanum oxyfluoride and fluoride nanoparticles were prepared in situ in thin silica films from rapid thermal decomposition of lanthanum tris-trifluoroacetate under nitrogen atmosphere. The thin silica films were obtained from sol–gel method and spin-coating. The spectroscopic properties of the non-stabilized nanoparticles as well the nanoparticles dispersed into thin silica films were studied in order to apply the system in future photonic applications such as erbium(III)-doped waveguide amplifiers. The non-stabilized nanoparticles were characterized by XRD, FT-IR, Transmission Electron Microscopy, Confocal Raman Spectroscopy and steady-state and time-resolved Luminescence Spectroscopy and these characterizations were used as a starting point to characterize the nanoparticles dispersed into the films. According to the temperature of the thermal treatments, the non-stabilized nanoparticles may present Eu(III)-doped LaOF in tetragonal and rhombohedral phases as well as a mixed phase of Eu(III)-doped LaF3 and LaOF. The tetragonal LaOF phase has C4v La(III) point symmetry and is more symmetric than the rhombohedral LaOF phase, where the La(III) ion has C3v symmetry, consequently tetragonal LaOF presented lower Ω2 values than rhombohedral LaOF. Theoretical calculations of Judd–Ofelt intensity parameters were also performed and were in good agreement with the experimental values. The samples containing the mixed phase of LaF3 and LaOF presented lower values of intensity parameters than pure LaOF phases. The samples containing the mixed phase presented higher values of emission lifetimes and quantum efficiencies. Confocal Raman spectroscopy of these samples complements the luminescence studies and indicates which LaOF phase is present in the mixed phase of LaF3 and LaOF. The rapid thermal decomposition of the precursor tris-trifluoroacetate on thin silica films results in well-dispersed 10 nm nanoparticles. The mixed phase of LaF3 and LaOF phases is also present in thin films. The luminescence of the Eu(III) and Er(III)/Yb(III)-doped LaF3/LaOF nanoparticles containing thin silica films presented broad emission bands suggesting that in the future the systems may be applied as erbium(III)-doped waveguide amplifiers.