The radiation response of a phosphorus-doped multimode optical fiber is investigated under both transient (pulsed X-rays) and steady-state (γ- and X-rays) irradiations. The influence of a H 2 ...preloading on the fiber radiation-induced attenuation (RIA) in the 300-2000-nm wavelength range has been characterized. To better understand the impact of this treatment, online behaviors of fiber samples containing different amounts of gas are compared from glass saturation (100%) to less than 1%. In addition to these in situ experiments, additional postirradiation spectroscopic techniques have been performed such as electron paramagnetic resonance or luminescence measurements to identify the different point defects responsible for the induced losses and their H 2 dependence. All our data at room temperature (RT) highlight a strong positive impact of H 2 , even at very low concentrations, on the RIA. Hydrogen quickly passivates (t <; 1 s) most of the defects responsible for the visible-near-IR RIA, mainly phosphorus oxygen hole centers (POHC) and P1 defects. However, 1 year after the H 2 loading at RT or when operating at liquid nitrogen temperature, the RIA levels of the not-treated and H 2 -loaded fiber become comparable. The obtained results provide a better understanding of the potential and limitations of H 2 -loading treatment to design radiation-hardened fiber links.
An ethylenediamine (EDA) and octadecylamine (-C
18
) hyaluronic acid (HA) derivative, named HA-EDA-C
18
, has been used for the production of interpenetrated composite biomaterials with silk fibroin. ...The peculiar ionic strength sensibility of this HA derivative allows the production of porous matrices without the need for chemical crosslinking. Scaffolds have been produced through a salt leaching procedure by exploiting the properties of silk fibroin and HA-EDA-C
18
to physically crosslink when forced through a syringe loaded with NaCl. The porosity of the sponges, comprised between 70-80%, was dependent on the amount of each polymer and NaCl size distribution. Moreover, through FT-IR analysis, it has been evaluated how the blend composition influences the conformational changes of fibroin. This study demonstrates that HA-EDA-C
18
induces the transition of silk fibroin to its β-sheet conformation. Moreover, the HA-EDA-C
18
weight fraction in composite sponges regulates the scaffold susceptibility to protease and hyaluronidase. FT-IR analysis and enzymatic hydrolysis studies suggest that the homogeneous interpenetration of polymers occurs.
In vitro
studies indicate that the presence of fibroin improves the viability and attachment of bovine chondrocytes.
A functionalized HA derivative (HA-EDA-C
18
) was processed with silk fibroin
via
a salt leaching procedure to produce stable porous scaffolds for biomedical applications. The HA derivative was able to induce β-sheet transitions on fibroin.
We studied the emission of the O2 molecules embedded in fumed silica (amorphous silicon dioxide) nanoparticles differing for diameters and specific surface. By using a 1064 nm laser as a source we ...recorded both the O2 emission and the Raman signal of silica. Our experimental data show that the O2 emission/Raman signal (at 800 cm–1) ratio decreases with increasing the specific surface for both the as-received and the loaded samples. By performing a thermal treatment (600 °C for 2 h) we modified the structure and the water content of the smallest nanoparticles without observing any significant change in the O2 emission/Raman signal ratio. Our data are explained by a shell model showing that the O2 emission is essentially due to the molecules entrapped in the core of the nanoparticles, whereas the contribution due to the surface shell, having a thickness of about 1 nm, is negligible because of its high content of Si–OH groups that introduce nonradiative relaxation channels or because of the very low content of molecules trapped in this thin region.
The O2 diffusion process in silica nanoparticles is experimentally studied in samples of average radius of primary particles ranging from 3.5 to 20 nm and specific surface ranging from 50 to 380 ...(m2/g). The investigation is done in the temperature range from 98 to 177 °C at O2 pressure ranging from 0.2 to 66 bar by measuring the interstitial O2 concentration by Raman and photoluminescence techniques. The kinetics of diffusion can be described by the Fick’s equation with an effective diffusion coefficient depending on the temperature, O2 pressure, and particles size. In particular, the dependence of the diffusion coefficient on the pressure and nanoparticles size is more pronounced at lower temperatures and is connected to morphological and physical factors.
We report an experimental investigation on the radiation-induced attenuation (RIA) in the ultraviolet-visible domain for Ge-doped optical fibers, during X-ray (10 keV) exposure at different ...temperatures. The objective is to characterize the impact of the irradiation temperature on the RIA levels and kinetics. Our data highlight that for dose exceeding 1 kGy(SiO2) the RIA spectrum changes with the irradiation temperature. In particular, for wavelengths below 470 nm the RIA depends both on the dose and on the irradiation temperature, whereas at higher wavelengths the RIA depends only on the dose. From the microscopic point of view the origin of this behavior is explained by a larger impact of the irradiation temperature on the Ge(1) defects generation mechanism with respect to the one of GeX defects, which appears as poorly temperature sensitive in the tested range. This finding prevents us from easily establishing a conclusive relation between the generation mechanisms of these two types of defects. The lower content of radiation induced Ge(1), in fiber irradiated at higher temperature, is supported by the electron paramagnetic resonance (EPR) results acquired after the irradiation. In situ RIA and postmortem EPR data show a significant correspondence of the Ge(1) growth as a function of the dose. Confocal microscopy luminescence experiments indicate that the non-bridging oxygen hole center concentration is higher at 473 K in comparison with those observed at 300 and 373 K.
The near infrared singlet emission and photoluminescence lifetime of O2 molecules embedded in silica nanoparticles are studied from room temperature down to 10K. The area of the photoluminescence ...band under infrared excitation decreases for temperature above 100K and the lifetime is shortened. These observations provide evidence of a thermally activated relaxation channel with activation energy of about 40meV. This relaxation mechanism adds to the already known temperature independent electronic-to-vibrational coupling involving high energy vibrational modes of the host matrix or its impurities. The thermally activated process is suggested to consist in the breakage of the O2 molecule weak bonds with walls of the matrix interstices with ensuing molecular motion and collisional exchange of energy.
•The temperature dependence of the oxygen singlet emission is studied.•The excited singlet relaxation shows a temperature dependence.•Nonradiative relaxation mechanisms have activation energy of 40meV.
Matrix isolation is a method which plays a key role in isolating and characterizing highly reactive molecular radicals. However, the isolation matrices, usually composed of noble gases or small ...diamagnetic molecules, are stable only at very low temperatures, as they begin to desegregate even above a few tens of Kelvin. Here we report on the successful isolation of CH3˙ radicals in the cages of a nearly inert clathrate-SiO2 matrix. This host is found to exhibit a comparable inertness with respect to that of most conventional noble gas matrices but it is characterized by a peculiar thermal stability. The latter property is related to the covalent nature of the host material and gives the opportunity to study the confined radicals from a few degrees of Kelvin up to at least room temperature. Thanks to this advantage we were able to explore with continuity for the first time the CH3˙ rotor properties by electron paramagnetic resonance spectroscopy, starting from the quantum rotations which are observable only at the lowest temperatures (T ≈ 4 K), going through the gradual transition to the classical motion (4 K < T < 30 K), and ending with the properties of the fully classical rotor (T > 30 K). The method of isolation presented here is found to be very effective and promising, as it is expected to be applicable to a large variety of different molecular radicals.
We report an experimental study on the photoluminescence band peaked at 2.7eV (blue band) induced by thermal treatments in nanometric amorphous SiO2. In particular the emission dependence on the ...nanometric particles size as a function of their mean diameter from 7nm up to 40nm is investigated. We found that the emission amplitude increases on decreasing the particle diameter, showing a strong correlation between the blue band and the nanometric nature of the particles. By Raman spectroscopy measurements it is evidenced that the SiO2 nanoparticles matrix is significantly affected by the reduction of size. Basing on the shell-like model, these findings are interpreted assuming that the defects responsible for the photoluminescence are localized on a surface shell of the particles and not simply on their surface. In addition it is found that the generation efficiency of these defects depends on the structural properties of the SiO2 matrix in the surface shell.
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