Luigi Stagi

Optical and structural characterization of cerium doped LYSO sol-gel polycrystal films: potential application as scintillator panel for X-ray imaging†

The optical and structural properties of sol–gel prepared polycrystalline films of Cerium doped Lutetium and Yttrium oxyorthosilicates (Ce:LYSO) are investigated by means of optical spectroscopy, XRD diffraction and Raman spectroscopy. The sol–gel samples are compared to commercially available Ce-doped LYSO single crystals, and a detailed study of the emission properties from the different cerium sites is performed. The main result is that the polycrystalline films do show very good radioluminescence properties for possible applications as X-ray scintillating panels. The structural characterization indicates that the sol–gel polycrystals have similar phase composition to commercial monocrystals; concerning the excitation and emission properties, the same radiative recombination channels are observed in the polycrystals and commercial monocrystals with a slightly faster decay time in the first case. In addition, low temperature measurements (8 K) indicate the presence of a non-radiative cross-relaxation mechanism among cerium ions in the sol–gel grown samples in the two possible crystallographic sites. The results indicate the possibility to develop sol–gel synthesized polycrystalline thin films as scintillating materials in the X-ray energy range.

Luminescence enhancement by energy transfer in melamine-Y2O3:Tb3+ nanohybrids

The phenomenon of luminescence enhancement was studied in melamine-Y2O3:Tb hybrids. Terbium doped Y2O3 mesoporous nanowires were synthesized by hydrothermal method. X-ray diffraction patterns and Raman scattering spectra testified the realization of a cubic crystal phase. Organic-inorganic melamine-Y2O3:Tb3+ hybrid system was successfully obtained by vapour deposition method. Vibration Raman active modes of the organic counterpart were investigated in order to verify the achievement of hybrid system. Photoluminescence excitation and photoluminescence spectra, preformed in the region between 250 and 350 nm, suggest a strong interaction among melamine and Terbium ions. In particular, a remarkable improvement of 5D4→ FJ Rare Earth emission (at about 542 nm) of about 102 fold was observed and attributed to an efficient organic-Tb energy transfer. The energy transfer mechanism was studied by the use of time resolved photoluminescence measurements. The melamine lifetime undergoes to a significant decrease when ...

A facile strategy for new organic white LED hybrid devices: design, features and engineering

A facile and ecofriendly strategy to design and engineer new organic white LEDs is tested. The hybrid system was implemented by combining a commercial blue LED, with emission at 405 nm, with a hybrid transparent organic film (polycarbonate, PMMA, PVC) containing two selected organic dyes. The emitting molecules, a home-designed push–pull based coumarin and DCM ([2-[2-[4-(dimethylamino)phenyl]ethenyl]-6-methyl-4H-pyran-4-ylidene]-propanedinitrile), were selected for their optical features and appropriately mixed to obtain white light, perceptible by the naked eye, through the metamerism effect. The proposed strategy shows the critical parameters to account for in the selection of organic dyes, bearing in mind the preservation of the dye emission properties from the solution to the solid state. To this purpose, the contributions of dynamic and static quenching effects were analyzed in detail, to single out the optimum concentrations to assure the compliance with the respective sphere of interaction and guarantee high optical performances. Different new hybrid white-emitting LEDs, with tunable color rendering index (from warm to cold CCT), high energy efficiency (quantum yield larger than 90%), and high photostability, were produced to prove the proposed strategy.

Surface effects and phase stability in metal oxides nanoparticles under visible irradiation

The light induced phase transformation between stable phases of metal oxides nanoparticles is analyzed. The surrounding atmosphere as well as the defect density at the surface play a fundamental role. It has been found that in oxygen poor chamber atmosphere the phase transformation is favored, while the phase transition cannot be achieved if the defects at the surface are properly passivated. The phase transition is activated by intragap irradiation, able to activate the F- center at the surface connected to oxygen vacancies, and promoting the activation of the surface and the nucleation of neighboring crystallites. The phase transition was studied in Titanium oxide (TiO2) and in Iron oxide (Fe2O3): Maghemite is subjected to a phase transformation to α−Fe2O3 (hematite), Anatase nanoparticles converts to Rutile. The general mechanism of the phase transition and, more in general, the possibility to optically control the surface activity of metal oxides is discussed.

Vibrational and optical characterization of s-triazine derivatives

The optical and electron properties of three different s-triazine derivatives are investigated to ascertain the role of the donor acceptor character in amine-triazine systems depending on the bridging radical of the ammine group. The three derivatives were obtained starting from three different ammine compounds allowing to achieve a structure with a triazine core, surrounded by three ammine group and terminated with cyano or methyl or oxy-methyl functional group. Experimental optical data were interpreted in view of the electronic insights gathered by means of density functional theory simulations on base compounds. As compared to the reference electron donating triazine core, the resulting compounds show different donor acceptor character, from electron accepting to electron donating feature. Among the analyzed derivatives, the cyano terminated ammino-triazine compound shows the most promising optical features for photonics and lighting applications.

Structure Solution of NaYO2 Compound Prepared by Soft Chemistry from X-Ray Diffraction Powder Data.

Structure Solution of NaYO2 Compound Prepared by Soft Chemistry from X-Ray Diffraction Powder Data. Luigi Stagi, P. Carlo Ricci, Daniele Chiriu, Emilio Napolitano, Stefano Enzo*. Department of Physics, Università di Cagliari sp 8 Km 0,700, 09042 Monserrato (Ca) (Italy) European Commission -DG Joint Research Centre-Institute for Energy and Transport, Westerduinweg 3, NL-1755 Petten, The Netherlands. Department of Chemistry and Pharmacy, via Vienna n. 2, I-07100 Sassari (Italy) enzo@uniss.it