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Padova, Italy

Belmokhtar S.,Abdelmalek Essaadi University | Bouajaj A.,Abdelmalek Essaadi University | Britel M.,Abdelmalek Essaadi University | Normani S.,CNR Institute for Photonics and Nanotechnologies | And 6 more authors.
Journal of Materials and Environmental Science | Year: 2016

The aim of this paper is to study the possibility to improve the efficiency of solar cells by using downconversion of high energy photons into low energy ones thanks to the Tb3+/Yb3+ energy transfert mechanism in 70SiO2-30HfO2 glass-ceramic waveguides. The preparation of the waveguides by a sol-gel method is first presented. Then results of compositional and optical (Photoluminescence) characterization are given. The result found is that the transfer efficiency is about 38% for the sample with the highest concentration of rare earths (5%). Source

Belmokhtar S.,Abdelmalek Essaadi University | Bouajaj A.,Abdelmalek Essaadi University | Britel M.,Abdelmalek Essaadi University | Normani S.,CNR Institute for Photonics and Nanotechnologies | And 6 more authors.
Lecture Notes in Electrical Engineering | Year: 2016

A down-conversion layer placed on the front side of silicon solar cells waveguides has the potential to cute one high-energy photon into two low energy photons. This paper examines the Tb3+/Yb3+ energy transfer efficiency in a 70SiO2–30HfO2 glass and glass-ceramics waveguide in order to convert absorbed photons at 488 nm in photons at 980 nm. The evaluation of the transfer efficiency between Tb3+ and Yb3+ is obtained by comparing the luminescence decay of Tb with and without Yb co-doping ions. A transfer efficiency of 25 % obtained with glass-ceramic sample and 6 % with glass sample proving that glass-ceramic can be a viable system to fulfil our requirements. © Springer International Publishing Switzerland 2016. Source

Kappes M.S.,University of Vienna | Gruber K.,University of Vienna | Gruber K.,Johannes Kepler University | Frigerio S.,University of Vienna | And 5 more authors.
Geomorphology | Year: 2012

Many regions worldwide are threatened by multiple natural hazards with the potential to cause high damages and losses. However, the modeling of multiple hazards in a joint analysis scheme is still in the early stages of development as a range of serious challenges emerges in the multihazard context such as differing modeling approaches in use for contrasting hazards; the time- and data-demanding conduct of each single preparative, intermediate and analysis step; and the clear visualization of the modeling outcome. Under consideration of these difficulties, a regional multihazard exposure analysis concept is developed for five natural hazards: debris flows, rock falls, shallow landslides, avalanches, and river floods, complemented by a visualization scheme to present the modeling outcome. An automation of the two schemes resulted in a beta version of the MultiRISK modeling and the MultiRISK visualization software tool forming together the MultiRISK platform. To test the analysis scheme and the software implementation of MultiRISK a case study is performed in the Barcelonnette basin in France with a worst-case parameterization of the models on the basis of extensive literature reviews. Experiences from this case study offered many insights into the multihazard topic and even more questions, e.g. with respect to coherent multihazard model parameterization, validation or the comparability and interpretation of single-hazard modeling results, respectively. Although analysis schemes can be proposed and software tools can be provided to facilitate many steps, a well-conceived and reflective approach to multihazard settings is essential. The worst-case analysis based on literature values apparently leads to an overestimation of the susceptible areas and the number of exposed elements. Nevertheless, depending on the data situation of an area, especially in areas without any information on past events, this approach may offer the determination of general hazard distributions, overlaps, and areas of potential risk without data-demanding calibration. © 2012 Elsevier B.V. Source

Peruzzo V.,Cso Stati Uniti | Lanza A.,University of Bern | Nestola F.,University of Padua | Vigato P.A.,Cso Stati Uniti | Tamburini S.,Cso Stati Uniti
Inorganica Chimica Acta | Year: 2014

The [1+1] Schiff base macrocyclic ligands H2LA and H3LB, synthesized by condensation of 3,3′-(3- oxapentane-1,5-diyldioxy)bis(2-hydroxybenzaldehyde) (H2L′) with 1,5-diamino-3-azamethylpentane (A′) and N,N-bis(2-aminoethyl)-2- hydroxybenzylamine·3HCl (HB′·3HCl), respectively, and their related polyamines H2RA and H3RB, which exhibit enhanced stability toward hydrolysis and greater flexibility, give rise to a wide series of mono-Ln and heterodinuclear-LnNa complexes. The crystal structure of [LuNa(RB)(OH)]2, determined by single-crystal X-ray diffraction, indicates the preference of the lutetium(III) ion and of the sodium(I) ion for the Schiff base and the crown-ether like chambers, respectively. To test the flexibility of reduced ligands and the possibility to encapsulate different lanthanide(III) ions in the coordinating moiety, [LuNa(RB)(CH3COO)]·2iPrOH, [LuNa(L B)(Cl)], [LaNa(RB)(Cl)] and [LaNa(LB)(Cl)] are mixed with different lanthanide(III) salts to detect metalation, demetalation, transmetalation and/or site migration processes by ESI mass spectrometry and NMR spectroscopy. In particular the role of the metals and of the coordinating moiety in directing these processes is discussed. Furthermore, the possibility to use these complexes as probe for selective recognition of alkali and alkaline earth metal ions is tested by ESI mass spectrometry on [LuNa(R B)(CH3COO)]·2iPrOH and by the 23Na NMR shift on [YbNa(RB)(CH3COO)]. The partial or total transmetalation of the sodium(I) ion represents a relevant result capable to open interesting scientific opportunities. © 2014 Elsevier B.V. All rights reserved. Source

Belmokhtar S.,Abdelmalek Essaadi University | Bouajaj A.,Abdelmalek Essaadi University | Britel M.R.,Abdelmalek Essaadi University | Normani S.,CNR Institute for Photonics and Nanotechnologies | And 8 more authors.
Proceedings of 2015 IEEE International Renewable and Sustainable Energy Conference, IRSEC 2015 | Year: 2015

The efficiency of semiconductor solar cells may be improved by inserting in the front or rear of the solar cell an optically active layer doped with rare earth ions which acts as «down-converter» (DC) or «up-converter» (UC). This is just one of the possibilities that involve several structures and geometries such as waveguide configuration and radiation trapping systems. Among these systems glass ceramics play a crucial role especially because they combine the optical properties of glasses with the spectroscopic properties of the crystals activated by luminescent species. In this work we will give a short review regarding the research already performed by the team in the field of down-conversion process. We will focus the attemption on the cooperative energy transfer between donor and acceptor ions taking as example the interaction among one Tb3+ ion and two Yb3+ ions allowing to cut one high energy photon at wavelength shorter than 488 nm into two low energy photons around 980 nm. The choice of the matrix is another crucial point to obtain an efficient down conversion processes with rare earth ions; we demonstrated that the Tb3+/Yb3+ energy transfer efficiency in a 70SiO2-30HfO2 glass-ceramic waveguide is effective. © 2015 IEEE. Source

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