0000000000353519
AUTHOR
Aldo Magistris
Lithium ion conducting PVdF-HFP composite gel electrolytes based on N-methoxyethyl-N-methylpyrrolidinium bis(trifluoromethanesulfonyl)-imide ionic liquid
Blends of PVDF-HFP and ionic liquids (ILs) are interesting for application as electrolytes in plastic Li batteries. They combine the advantages of the gel polymer electrolytes (GPEs) swollen by conventional organic liquid electrolytes with the nonflammability, and high thermal and electrochemical stability of ILs. In this work we prepare and characterize PVDF-HFP composite membranes swollen with a solution of LiTFSI in ether-functionalized pyrrolidinium-imide (PYRA12O1). The membranes are filled in with two different types of silica: i) mesoporous SiO2 (SBA-15) and a commercial nano-size one (HiSilTM T700). The ionic conductivity and the electrochemical properties of the gel electrolytes ar…
Optical properties and photosensitivity of vacuum synthesized Ge-doped sol-gel amorphous SiO/sub 2/
We report optical and electron paramagnetic resonance investigations of gamma ray irradiation effects in sol-gel Ge-doped amorphous SiO/sub 2/. The studied materials have Ge-doping levels up to 10/sup 4/ molar part per million and were densified by two routes differing for the atmosphere: O/sub 2/+N/sub 2/ or vacuum. The obtained results evidence that irradiation affects matrix sites inducing paramagnetic defects. Furthermore, the comparison between the two densification procedures shows that vacuum atmosphere induces higher radiation sensitivity.
Effect of oxygen deficiency on the radiation sensitivity of sol-gel Ge-doped amorphous SiO2
We report experimental investigation by electron paramagnetic resonance (EPR) measurements of room temperature γ-ray irradiation effects in sol-gel Ge doped amorphous SiO2. We used materials with Ge content from 10 up to 104 part per million (ppm) mol obtained with different preparations. These latter gave rise to samples characterized by different extents of oxygen deficiency, estimated from the absorption band at ~5.15 eV of the Ge oxygen deficient centers (GeODC(II)). The irradiation at doses up to ~400 kGy induces the E'-Ge, Ge(1) and Ge(2) paramagnetic centers around g ~ 2 with concentrations depending on Ge and on GeODC(II) content. We found correlation between Ge(2) and GeODC(II) con…
Hydrogen-Related Paramagnetic Centers in Ge-Doped Sol-Gel Silica Induced by γ-Ray Irradiation
We have studied the generation mechanisms of H(II) paramagnetic centers in Ge-doped silica by investigating up to 104 mol ppm sol-gel Ge-doped silica materials. We have considered materials with the same concentrations of Ge but that are produced by two different densification routes that give rise to different concentrations of Ge-related oxygen deficient centers (GeODC(II)). These centers are characterized by an optical absorption band at ∼5.2 eV (B2 β band) and two related emissions at ∼3.2 eV and ∼4.3 eV. The GeODC(II) content was estimated by absorption and emission measurements. The H(II) centers were induced by room temperature γ-ray irradiation and their concentration was determined…
Luminescence activity of surface and interior Ge-oxygen deficient centers in silica
We report a comparative study on the optical activity of surface and interior Ge–oxygen deficient centers in pressed porous and sol–gel Ge-doped silica, respectively. The experimental approach is based on the temperature dependence of the two photoluminescence bands at 4.2 (singlet–singlet emission, S1! S0) and 3.1 eV (triplet–singlet emission, T1! S0), excited within the absorption band at about 5 eV. Our data show that the phonon assisted intersystem crossing process, linking the two excited electronic states, more effective for surface than for interior centers in the temperature range 5–300 K. For both centers, a distribution of the activation energies of the process is found. Based on th…
Structural inhomogeneity of Ge-doped amorphous SiO2 probed by photoluminescence lifetime measurements under synchrotron radiation.
We report a study of the photoluminescence (PL) time decay of the B-type center, characterized by an optical absorption band peaked at similar to 5.2 eV and two related PL bands peaked at similar to 3.2 eV and similar to 4.3 eV, in sol-gel Ge-doped a- SiO2 under excitation by synchrotron radiation. Measurements were carried out by excitation in UV and in vacuum-UV (VUV), and were performed in the temperature range from 8 K up to 300 K in order to isolate the effects of the intersystem-crossing process, proposed to link the two emission bands of the center. Repeating the time decay measurement at several emission energies falling inside the 4.3 eV band, we have observed a variation of the PL…
Twofold coordinated Ge defects induced by gamma-ray irradiation in Ge-doped SiO2
We report an experimental study by photoluminescence, optical absorption and Electron Paramagnetic Resonance measurements on the effects of exposure of Ge-doped amorphous SiO2 to gamma ray radiation at room temperature. We have evidenced that irradiation at doses of the order of 1 MGy is able to generate Ge-related defects, recognizable from their optical properties as twofold coordinated Ge centers. Until now, such centers, responsible for photosensitivity of Ge-doped SiO2, have been induced only in synthesis procedures of materials. The found result evidences a role played by gamma radiation in generating photosensitive defects and could furnish a novel basis for photosensitive pattern wr…