Gianluigi Ingletto

Optical spectroscopy of lanthanide ions in Al2O3–Nb2O5–TeO2 glasses

New Al 2 O 3 -Nb 2 O 5 -TeO 2 glasses doped with Er 3+ , Nd 3+ and Tm 3+ were prepared by conventional melt quenching. The absorption spectra were measured and the Judd-Ofelt parameters were extracted. Luminescence spectra in the near infrared region were measured and the values of the stimulated cross sections σ p were evaluated for selected laser transitions. The relatively high values of σ p suggest that these materials can be considered as interesting candidates for optical applications. The spectroscopic behaviour of the lanthanide ions appears to be influenced by the amount of Nb 2 O 5 and Al 2 O 3 in the glass hosts.

Fluorescence Enhancement of Aflatoxins Using Native and Substituted Cyclodextrins

Cyclodextrins have been used as fluorescence enhancers in HPLC to improve thedetection limits of aflatoxins, cancerogens which can be found in severalfoodstuffs. In this work, a screening of several cyclodextrins has been performedin order to find the factors affecting the fluorescence enhancement. Evidence for formationof a 1 : 1 AF-CD inclusion complex has been achieved by titration and competitiveexperiments with adamantanecarboxylic acid and by fluorescence quenching by KI.Stability constants of the AF-CD complexes were evaluated.

Absorption and luminescence spectroscopy of Eu3+ in lead silicate glasses

Abstract The absorption and luminiscence spectra of a lead silicate glass containing Eu3+ as impurity have been measured. The doping ion was found to occupy two classes of non-centrosymmetric sites. The intensities of the 4f6→4f6 transitions are perturbed by the interaction with low-lying charge-transfer states. The quantum yield of the luminescence from the 5D0 level of Eu3+ is usually low, probably because of the presence of a strong ion-phonon coupling.

Optical transition intensities of trivalent lanthanide ions in zinc and lead metaphosphate glasses

Abstract The Judd-Ofelt intensity parameters of the lanthanide ions Pr 3+ , Sm 3+ , Dy 3+ , Ho 3+ , Er 3+ and Tm 3+ in Zn(PO 3 ) 2 and Pb(PO 3 ) 2 glasses were evaluated from the absorption spectra. With the exception of Pr 3+ , the ω 2 parameter is significantly lower in Pb(PO 3 )2 than in Zn(PO 3 ) 2 , as previously found for the Nd 3+ ion, due to a weaker mixing with the opposite parity configurations. The monotonic dependence of ω 6 , on the number of f electrons suggests that the mechanism responsible for the spectral intensities is mainly due to static distortions. The intensity parameters are in general higher than for other common oxide glasses.

Mycotoxin Detection Plays “Cops and Robbers”: Cyclodextrin Chemosensors as Specialized Police?

As in a cops and robbers play we discover new mycotoxins and metabolites everyday and we are forced to develop new molecules quickly as chemo- or biosensors or to modify existing molecules able to recognize these new hazardous compounds. This will result in an enormous cost saving to agro-food industry through the prevention and reduction of product recalls and reduced treatment costs. Here we present a brief review of the rapid methods used to detect mycotoxins, considering usefulness and limits. Then we propose a new fast, efficient and cheap methodology, based on a combination of computer chemistry aided design and fluorescence, that can help to drive synthesis in a more efficient way.

Fluorescence line narrowing spectroscopy of Eu3+ doped sodium germanate glasses

Sodium germanate glasses of compositions (x − 0.5)Na2O–(100 − x)GeO2–0.5Eu2O3 with x = 10, 16, and 22 were studied using laser-induced fluorescence line narrowing (FLN) techniques. From the site selective luminescence spectra of Eu3+ at 20 K, the energies of the Stark components of the 7F1 and 7F2 states were obtained, and a crystal field (CF) analysis was carried out assuming a C2v site symmetry. The dependence of the CF parameters Bkq on the excitation wavenumber was similar to that observed in other oxide glasses. The behavior of the CF ratios B22/B20 and B44/B40 appears to be consistent with that calculated using the geometric model proposed by Brecher and Riseberg. The behavior of the CF strength parameter S suggests that the amount of network modifier in the glass host does not influence the CF at the Eu3+ sites. No evidence was found in the FLN spectra of the influence of 6-coordinated germanium.

Influence of some oxides on the durability of a borosilicate glass

The effects of Cs2O, SrO, U3O8 and ZnO on the durability of a borosilicate glass were evaluated with particular attention to the change in the leach rate. In the conditions we used the caesium oxide depresses the durability whereas the strontium and uranium oxides leave practically unchanged the chemical properties of the glassy matrix. The behavior of the zinc oxide is completely different: it increases the glass durability by several orders of magnitude.

Energy transfer between Tb3+ and Tm3+ in a lead silicate glass

Abstract Excitation is non-radiatively transferred from the 5D4 level of Tb3+ to excited levels of Tm3+ when the lanthanide ions are present as impurities in a 38% PbO-62% SiO2 glass. The main relaxation mechanism responsible for the transfer is 5D4(Tb)+3H6(Tm)→7F0(Tb)+3F3(Tm). The decay curves of the luminescence of the 5D4 level of Tb3+ obey the Inokuti-Hirayama model for energy transfer for an electric dipole-electric dipole interaction, in the absence of diffusion among the donors. The localization of the excitation appears to be due to the effect of the inhomogenous broadening of the electronic levels. The dipole-dipole coupling parameter is of the order 2×10-53 m6 s-1, and only weakly dependent on temperature. The nature of the interaction is attributed to the distorted geometry of the sites in which the lanthanide impurities are accommodated.

Electronic spectrum of NiII in MgWO4, ZnWO4 and CdWO4 at 4.2 K

The ligand-field spectrum of NiII has been measured in crystals of MWO4(M = Mg, Zn, Cd) from 5000 to 30 000 cm–1. Spectra were measured with light incident on the (100) and (010) faces with the electric vector parallel to all three crystallographic axes at temperatures from 300 to 4.2 K. The splittings and intensities of the bands in different polarizations are interpreted in terms of a major C2v and a minor C2 perturbation of the octahedral site. Most of the observed intensity is derived from the static low-symmetry distortion but the effect of vibronic interactions is also discussed.

Mössbauer studies of some cyclopentadienyliron derivatives

Abstract Mossbauer parameters are compared with carbonyl IR stretching frequencies for cyclopentadienyliron derivatives.