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.
We applied theoretical and experimental spectroscopy tools to ad hoc silica-based "canonical" samples to characterize the influence of several dopants and of some drawing process parameters on their ...radiation sensitivities. We present in this paper, the recent advances and results occurring from our coupled approach. On the experimental side, we studied the doping influence on the response of optical fibers and showed that changing the drawing parameters has a negligible influence on the fiber response in the case of specialty fibers. We focus mainly on the defect that is observed through Electron Paramagnetic Resonance (EPR) measurements in all canonical samples. On the theoretical side, we exhibit the improvements obtained in the calculations of electronic and optical properties of defects by using Many Body Perturbation Theory through the use of the GW approximation and the resolution of the Bethe-Salpeter equation instead of the Density Functional Theory (Local Density Approximation). To continue to strengthen the link between experiment and simulation, we have performed first-principles calculations of EPR parameters of some silica-based defects. The first results allowing for an attribution of EPR signals to structural models are presented. In particular, we confirm that the E' γ center is originated by an unpaired electron in a sp 3 state at a three-fold coordinated silicon atom.
We study the performance of Optical Frequency Domain Reflectometry (OFDR) distributed temperature sensors using radiation resistant single-mode optical fibers. In situ experiments under 10 keV X-rays ...exposure up to 1 MGy( SiO 2 ) were carried out with an original setup that allows to investigate combined temperature and radiation effects on the sensors within a temperature range from 30 ° C to 250 ° C. Obtained results demonstrate that optical fiber sensors based on Rayleigh technique are almost unaffected by radiation up to the explored doses. We show that a pre-thermal treatment stabilize the sensor performance increasing the accuracy on temperature measurement from ~ 5 ° C down to ~ 0.5 ° C by reducing the packaging-related errors (such as ones related to coating modification) that could be introduced during the measurement. These results are very promising for the future integration of Rayleigh based sensors in nuclear facilities.
We report the study of a radiation resistant single mode optical fiber doped with fluorine exposed to mixed neutron and γ-radiation up to 10 17 n/cm 2 fluence and 2 MGy dose to evaluate its ...performances when used as the sensing element of a distributed Optical Frequency Domain Reflectometry (OFDR). The use of complementary spectroscopic techniques highlights some differences between the responses of solely γ-radiation (10 MGy) or mixed neutron and y (10 17 n/cm 2+ 2 MGy) irradiated samples. Those differences are linked to the defect generation rather than to structural changes of the α-SiO 2 host matrix. We show that a modification of the refractive index of ~ 10 -5 is induced at the highest investigated neutron fluence. However, the feasibility of distributed temperature measurements along the irradiated fiber is demonstrated with an accuracy of 0.1 °C over a sensing length up to ~ 130 m with the tested OBR4600 interrogator. These results are very promising for the integration of OFDR sensors in mixed neutron and gamma radiation environments.
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.
This experimental investigation is focused on a radiation induced red emission in Ge doped silica materials, elaborated with different methods and processes. The differently irradiated samples as ...well as the pristine ones were analyzed with various spectroscopic techniques, such as confocal microscopy luminescence (CML), time resolved luminescence (TRL), photoluminescence excitation (PLE) and electron paramagnetic resonance (EPR). Our data prove that irradiation induces a red luminescence related to the presence of the Ge atoms. Such emission features a photoexcitation spectrum in the UV-blue spectral range and, TRL measurements show that its decrease differs from a single exponential law with a lifetime of tens of nanoseconds. CML measurements under laser at 633nm evidenced the lack of correlation of the emission here reported with that of the Ge- or Si- non bridging oxygen hole centers. Moreover, our EPR experiments highlighted the lack of correlation between the red emitting defect with other radiation induced paramagnetic centers such as the E′Ge and Ge(2). The relation of the investigated emission with the H(II) defects, previously considered as responsible for a red emission, can not be totally excluded.
•Composite nature of the red emission in Ge-doped doped silica materials.•Experimental study with various spectroscopic techniques and on different samples.•Time resolved and stationary characterization of an new red emission.•Study of the spatial distributions of diverse red emissions in optical fibers.
A 57% SiO
2
, 3% Al
2
O
3
, 34% CaO and 6% Na
2
O glass (SCNA) has been produced in form of powders and deposited by plasma spray on titanium alloy and stainless steel substrates. The obtained ...coatings have been subjected to a patented ion-exchange treatment to introduce silver ions in the surface inducing an antibacterial behavior. Silver surface-enriched samples have been characterized by means of X-ray diffraction, SEM observation, EDS analysis, in vitro bioactivity tests, leaching tests by GFAAS (graphite furnace atomic adsorption spectroscopy) analyses, cells adhesion and proliferation, and antibacterial tests using
Staphylococcus Aureus
strain. In vitro tests results showed that the modified samples acquired an antimicrobial action against tested bacteria maintaining unaffected the biocompatibility of the glass. Furthermore the ion-exchange treatment can be successfully applied to glass-coated samples without affecting the properties of the coatings; the simplicity and reproducibility of the method make it suitable for glass or glass-ceramic coatings of different composition in order to produce coated devices for bone healing and/or prostheses, able to reduce bacterial colonization and infections risks.
Prototype samples of preforms and associated fibers have been designed and fabricated through MCVD process to investigate the role of fluorine (F) and germanium (Ge) doping elements on the radiation ...sensitivity of silica-based glasses. We characterized the behaviors of these canonical samples before, during and after 10 keV X-ray irradiation through several spectroscopic techniques, to obtain global information (in situ absorption measurements, electron paramagnetic resonance) or spatially-resolved information (confocal microscopy, absorption and luminescence on preform). These tests showed that, for the Ge-doped fiber and in the 300-900 nm range, the radiation-induced attenuation (RIA) can be explained by absorption bands associated with the following radiation-induced point defects: Ge(l); Ge-NBOHC and GeX. Other defects such as GeE' Ge(2); and Ge-ODC are generated but do not contribute in this spectral domain. For the F-doped sample, the different point defects identified, SiE', Si-NBOHC and Si-ODC(II), are unable to reproduce the RIA spectra for energies lower than 4 eV. We suggest that the radiation-induced absorption in this part of the spectrum is due to chlorine-related species, probably CI 0 radiolytic groups that absorb at around 3.5 eV. The comparison between the sensitivities of the preform and the fiber reveals the influence of the drawing process on the glass response. Its effect is strongly dose-dependent for the germanosilicate glass. The drawing process seems to be responsible for the main part of the defects generated at low doses (<1 Mrad).
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