Decomposition Process of Carboxylate MOF HKUST-1 Unveiled at the Atomic Scale Level

HKUST-1 is a metal-organic framework (MOF) which plays a significant role both in applicative and basic fields of research, thanks to its outstanding properties of adsorption and catalysis but also because it is a reference material for the study of many general properties of MOFs. Its metallic group comprises a pair of Cu2+ ions chelated by four carboxylate bridges, forming a structure known as paddle-wheel unit, which is the heart of the material. However, previous studies have well established that the paddle-wheel is incline to hydrolysis. In fact, the prolonged exposure of the material to moisture promotes the hydrolysis of Cu-O bonds in the paddle-wheels, so breaking the crystalline n…

Resonance Raman of oxygen dangling bonds in amorphous silicon dioxide

We investigate the origin of a resonance Raman band induced by ionizing radiation in amorphous silicon dioxide (silica glass), which can be detected under ultraviolet laser excitation. A silica sample, rich of oxygen-excess related defects, was prepared by treating some length of a pure-silica-core multimode fiber in an O2 atmosphere (at high temperature and pressure) and by irradiating it with X-rays at 10 MGy(SiO2) dose. A micro-Raman study revealed a gaussian band peaking at 896 cm−1 with a full width at half maximum of 32 cm−1, which could be detected by exciting the sample with the 325-nm line of a HeCd laser. This spectral feature is absent in the Raman spectra performed with the 442-…

Ge-doped silica nanoparticles: production and characterisation

Silica nanoparticles were produced from germanosilicate glasses by KrF laser irradiation. The samples were investigated by cathodoluminescence and scanning electron microscopy, providing the presence of nanoparticles with size from tens up to hundreds of nanometers. The emission of the Germanium lone pair center is preserved in the nanoparticles and atomic force microscopy revealed the presence of no spherical particles with a size smaller than ~4 nm. The absorption coefficient enhancement induced by Ge doping is reputed fundamental to facilitate the nanoparticles production. This procedure can be applied to other co-doped silica materials to tune the nanoparticles features.

Structural properties of core and surface of silica nanoparticles investigated by Raman spectroscopy

We studied the experimental Raman spectra of various commercial silica nanoparticles of average diameter from 7 to 40 nm and specific surface from 50 to 380 m^2/g. We found that the peculiarities of the particles Raman spectra systematically depend on their specific surface. In detail, the peak position of the R band at about 440 cm ^-1 shifts towards high wavenumbers following an almost linear dependence on the specific surface. Similarly, the amplitudes of the D1 and D2 bands, at about 495 and 605 cm ^-1, respectively, increase linearly with the same quantity. Our results are interpreted in the frame of the shell model for the nanoparticles clarifying that the network of the core of the n…

Facile and novel synthesis of Graphene oxide/Silica nanohybrids with tunable properties

X-ray irradiation effects on fluorine-doped germanosilicate optical fibers

International audience; We report an experimental investigation on the effects of fluorine codoping on the radiation response of Ge-doped Optical Fibers (OFs) obtained by three different drawing conditions. The OFs were irradiated with 10 keV X-rays up to 300 Mrad and studied by online Radiation-Induced-Attenuation (RIA) measurements. Confocal Micro- Luminescence (CML) and Electron Paramagnetic Resonance (EPR) were also employed to investigate the permanent radiation-induced-defects. The variation of the Germanium-Lone-Pair-Center (GLPC) and Non-Bridging- Oxygen-Hole-Centers (NBOHC) concentration with the radiation dose is investigated by CML, whereas the ones of the induced Ge(1), Ge(2) an…

Raman and IR investigation of silica nanoparticles structure

Abstract In the present investigation we report experimental data regarding the Raman and Infra-Red (IR) absorption activities of commercial silica nanoparticles. We compared the data of the nanoparticles with the ones acquired in the same experimental conditions for commercial bulk silica. By this comparison we highlighted that the variability of the spectral features of the matrix related Raman and IR bands in the nanoparticles is above the one observed for the bulk systems before any treatments. Furthermore, by studying nanoparticles with different sizes (diameters from 40 to 7 nm) and applying the shell-model we can suggest that the core network of the nanoparticles is close to the one …

Evidence of different red emissions in irradiated germanosilicate materials

International audience; 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 …

Evolution of Photo-induced defects in Ge-doped fiber/preform: influence of the drawing

International audience; We have studied the generation mechanisms of two different radiation-induced point defects, the Ge(1) and Ge(2) centers, in a germanosilicate fiber and in its original preform. The samples have been investigated before and after X-ray irradiation using the confocal microscopy luminescence and the electron paramagnetic resonance techniques. Our experimental results show the higher radiation sensitivity of the fiber as compared to the perform and suggest a relation between Ge(1) and Ge(2) generation. To explain our data we have used different models, finding that the destruction probability of the Ge(1) and Ge(2) defects is larger in fiber than in preform, whereas the …

Interstitial O2 distribution in amorphous SiO2 nanoparticles determined by Raman an Photoluminescence spectroscopy

The O2 content and emission properties in silica nanoparticles after thermal treatments in oxygen rich atmosphere have been investigated by Raman and photoluminescence measurements. The nanoparticles have different sizes with average diameter ranging from 7 up to 40 nm. It is found that O2 concentration in nanoparticles monotonically increases with nanoparticles size. This finding is independent on the measurement technique and evidences that oxygen molecules are not present in all the nanoparticles volume. This dependence is interpreted on the basis of a structural model for nanoparticles consisting of a core region able to host the oxygen molecules and a surface shell of fixed size and fr…

Steady-State X-Ray Radiation-Induced Attenuation in Canonical Optical Fibers

The so-called canonical optical fibers (OFs) are samples especially designed to highlight the impact of some manufacturing process parameters on the radiation responses. Thanks to the results obtained on these samples, it is thus possible to define new procedures to better control the behaviors of OFs in radiation environments. In this article, we characterized the responses, under steady-state X-rays, of canonical samples representative of the most common fiber types differing by their core-dopants: pure silica, Ge, Al, and P. Their radiation-induced attenuation (RIA) spectra were measured online at both room temperature (RT) and liquid nitrogen temperature (LNT), in the energy range [~0.6…

Optical and morphological properties of infrared emitting functionalized silica nanoparticles

Abstract The loading process of functionalized silica nanoparticles was investigated in order to obtain nanoparticles having functional groups on their surface and Near-Infrared (NIR) emission properties. The NIR emission induced by O 2 loading was studied in silica nanoparticles, produced by pyrogenic and microemulsion methods, with size ranging from 20 to 120 nm. Loading was carried out by thermal treatments in O 2 atmosphere up to 400 °C and 90 bar. The effects of the thermal treatments on the NIR emission and on the structural properties were studied by luminescence and Raman techniques, whereas the morphological features were investigated by Transmission Electron Microscopy and Atomic …

Laser wavelength effects on the refractive index change of waveguides written by femtosecond pulses in silica glasses

We investigate the influence of two fs-laser wavelengths (343 and 800 nm) on the induced refractive index change (Δn) of waveguides written in silica materials. Results show that Δn is higher for waveguides photo-inscribed with UV photons.

Structural properties of core and surface of silica nanoparticles investigated by Raman spectroscopy

We studied the experimental Raman spectra of various commercial silica nanoparticles of average diameter from 7 to 40 nm and specific surface from 50 to 380 m2/g. We found that the peculiarities of the particles Raman spectra systematically depend on their specific surface. In detail, the peak position of the R band at about 440 cm−1 shifts towards high wavenumbers following an almost linear dependence on the specific surface. Similarly, the amplitudes of the D1 and D2 bands, at about 495 and 605 cm−1, respectively, increase linearly with the same quantity. Our results are interpreted in the frame of the shell model for the nanoparticles clarifying that the network of the core of the nanopa…

Near infrared emitting silica nanoparticles: O2 diffusion properties and excited state relaxation

A rapid and eco-friendly route to synthesize graphene-doped silica nanohybrids

International audience; In the present study, the possibility to synthesize graphene oxide (GO)-based nanohybrids with pure and O2-doped silica nanoparticles by a rapid and easy hydrothermal process has been explored. The nanohybrids were prepared by varying the type of silica nanoparticles (average diameter 7 nm or 40 nm) and the silica/GO weight ratio. All the materials were fully characterized by spectroscopic and morphological techniques.The experimental results revealed that it is possible to tune the characteristics of the obtained nanohybrids, such as morphology and amount of ester/ether linkages upon varying the preparation parameters, together with the nanosilica's typology and the…

Investigation by raman spectroscopy of the decomposition process of HKUST-1 upon exposure to air

We report an experimental investigation by Raman spectroscopy of the decomposition process of Metal-Organic Framework (MOF) HKUST-1 upon exposure to air moisture (T=300 K, 70% relative humidity). The data collected here are compared with the indications obtained from a model of the process of decomposition of this material proposed in literature. In agreement with that model, the reported Raman measurements indicate that for exposure times longer than 20 days relevant irreversible processes take place, which are related to the occurrence of the hydrolysis of Cu-O bonds. These processes induce small but detectable variations of the peak positions and intensities of the main Raman bands of th…

O2-Loading Treatment of Ge-Doped Silica Fibers: A Radiation Hardening Process

International audience; The effects of a high-pressure O2-loading treatment on the radiation response of Ge-doped optical fibers (OFs) were investigated. We found that the incorporation of high concentration of interstitial molecular oxygen remarkably enhances the resistance to ionizing radiation of Ge-doped OFs in the UV-Visible domain and, at the same time, improves the transmission of UV light in the unirradiated OF sample. By comparison with previously reported results, the O2-loading treatment turned out to increase the radiation resistance of Ge-doped OFs more efficiently than F or Ce codoping. The understanding of such amelioration relies in basic radiation-induced mechanisms that we…

β-ray irradiation effects on silica nanoparticles

By electron paramagnetic resonance (EPR) measurements, we examine the amplitude of the signal typically due to a combination of NBOHC (Non Bridging Hole Center) and POR (Peroxy Radical) defects induced by β-ray irradiation (from 1.2 to 1200 MGy) in silica nanoparticles with diameter ranging from 7 to 20 nm. Our data indicate that the signal line-shapes recorded at different doses is quite independent from the particles sizes and from the dose. Furthermore, for each considered nanoparticles size, the concentration of defects is also almost constant with respect to dose, and it does not change significantly if measured after 2 or 9 months from the irradiation. By contrast, we observed that th…

EPR on Radiation-Induced Defects in SiO2

Continuous-wave electron paramagnetic resonance (EPR) spectroscopy has been the technique of choice for the studies of radiation-induced defects in silica (SiO2) for 60 years, and has recently been expanded to include more sophisticated techniques such as high-frequency EPR, pulse electron nuclear double resonance (ENDOR), and pulse electron spin echo envelope modulation (ESEEM) spectroscopy. Structural models of radiation-induced defects obtained from single-crystal EPR analyses of crystalline SiO2 (alfa-quartz) are often applicable to their respective analogues in amorphous silica (a-SiO2), although significant differences are common.

Diffusion and outgassing of O2 in amorphous SiO2 silica nanoparticles with specific surface properties

Silica nanoparticles with hydrophilic and hydrophobic surface and average diameter of 12 and 40 nm are investigated to study the surface group influence on the diffusion process of molecular oxygen. The O2 diffusion kinetics and molecular solubility are determined by Raman/Photoluminescence measurements. Thermal treatments up to 127°C in controlled atmosphere show that the surface chemistry of nanoparticles is not changed, the equilibrium emission of O2 depends on nanoparticles surface properties, whereas the dynamics of diffusion is surface independent suggesting that surface groups could only affect overall content or detectability of interstitial molecules. The post loading outgassing in…

Structural and thermal stability of graphene oxide-silica nanoparticles nanocomposites

Abstract The investigation of the thermal stability up to 400 °C of Graphene Oxide (GO) and GO-silica nanoparticles (n-SiO2) composites prepared by direct mixture of GO and n-SiO2 is reported. Using Scanning Electron Microscopy, X-ray Photoelectron Spectroscopy, Energy Dispersive X-ray analysis, Atomic Force Microscopy, Raman and Infrared absorption measurements a thorough characterization of the prepared materials is carried out. By deepening the changes induced in the 2D Raman spectral region of GO at about 2900 cm−1 the comprehension of an interplay, driven by the thermally induced changes of the material, between inter-valley and intra-valley vibrational transitions is elucidated. This …

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…

Irradiation induced Germanium Lone Pair Centers in Ge-doped Sol-gel SiO2: luminescence lifetime and temperature dependence

We studied the temperature dependence of the emission profile and of the lifetime, measured at 4.3 eV, related to the germanium lone pair centers (GLPC) induced by gamma ray at 5 MGy in a Ge-doped silica sample and in an analogous sample irradiated at 10 MGy, in which by a successive thermal treatment up to 415 °C the induced GLPC has been modified (named residual GLPC in the following). The measurements were recorded in the temperature range 10-300 K using an excitation of ∼5.2 eV. The data show that the energy level scheme of the induced and the residual GLPC is very similar to that of the native defects generated during the synthesis, and the intersystem crossing process (ISC) of the ind…

Properties of HO2• radicals induced by γ-ray irradiation in silica nanoparticles

Abstract We report an experimental investigation on the effects of γ -ray irradiation in several types of silica nanoparticles previously loaded with O 2 molecules. They differ in specific surface and average diameter. By electron paramagnetic resonance (EPR) measurements we observe the generation of about 10 18 HO 2 • /cm 3 interstitial radicals. These radicals are induced by reaction of interstitial O 2 molecules with radiolytic H atoms, as previously suggested for O 2 -loaded bulk a-SiO 2 samples. However, at variance with respect to bulk materials, our experimental evidences suggest a different generation process of HO 2 • radical. In fact, by a detailed study of samples exposed to D 2 …

Electron Irradiation Effects on Single‐Layer MoS 2 Obtained by Gold‐Assisted Exfoliation

International audience; Mechanical exfoliation assisted by gold is applied to obtain good quality large lateral size single-layer MoS2. The effects of 2.5 MeV electron irradiation are investigated at room temperature on structural and electronic features by Raman and microluminescence spectroscopy. The exciton recombination emission in the direct bandgap of single-layer MoS2 is affected during irradiation starting from the minimum explored dose of 1 kGy. At higher doses, Raman bands show no relevant modifications whereas the exciton emission is quenched, suggesting that irradiation-induced point defects affect exciton dynamics.

Effects of Pressure, Thermal Treatment, and O2 Loading in MCM41, MSU-H, and MSU-F Mesoporous Silica Systems Probed by Raman Spectroscopy

We present a Raman study of the effects induced by pressure, thermal treatments, and O2 loading in MCM41, MSU-H, and MSU-F representative mesoporous silica. We compared the starting powders with the mechanically pressed tablets produced applying pressures of ∼0.2 and ∼0.45 GPa. The spectra of the three untreated tablets evidence that the main value of the Si-O-Si angle decreases and that in the MCM41 and the MSU-H Si-O-Si hydrolysis occurs, whereas such a process is absent or much less efficient in the MSU-F. Despite their different networks, the three powders tend to crystallize in cristobalite when treatments are at 1000 °C. The MCM41 and MSU-H tablets exhibit behavior similar to their st…

Isolation of the CH3˙ rotor in a thermally stable inert matrix: first characterization of the gradual transition from classical to quantum behaviour at low temperatures

International audience; Matrix isolation is a method which plays a key role in isolating and characterizing highly reactive molecularradicals. 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–SiO2matrix. This host is found to exhibit a comparable inertness with respect to that of most conventionalnoble gas matrices but it is characterized by a peculiar thermal stability. The latter property is related to thecovalent nature of the host material a…

Raman investigation of the drawing effects on Ge-doped fibers

International audience; We have investigated the Raman activity of various germanosilicate fibers and their associated preforms. Our data indicate an enhancement in small rings' (3-member rings) concentration in the silica-based matrix of the fibers during the drawing process. The generation of such rings appears compatible with an increase of the sample density and fictive temperature. The data regarding the drawing effects on the fiber stress appear less clear, and it is possible to suggest that in some cases the drawing could lower the tensile stress. Finally we have also provided evidence that changing the drawing conditions within the usual range of application leads to no significant …

Properties and generation by irradiation of germanium point defects in Ge-doped silica

Ge doped amorphous silicon dioxide (Ge doped silica) has attracted the attention of researchers for more than 50 years. This material is used in many different technological fields from electronics, to telecommunication, to optics. In particular, it is widely used for the production of optical fibers and linear and nonlinear optical devices. The optical fibers, which allow to transmit optical signals with high speed avoiding interferences, are constituted by two regions with different refractive index values: core (inner part) and cladding (external part). To increase the refractive index of the core with respect to that of cladding, Ge doping of silica is commonly used. Moreover, in the Ge…

Structure of the FeBTC Metal–Organic Framework: A Model Based on the Local Environment Study

The local environment of iron in FeBTC, a metal organic framework commercially known as Basolite F300, is investigated combining XANES and EXAFS studies of the iron K-edge. The building block of the FeBTC can be described as an iron acetate moiety. Dehydration induces a change in the coordination of the first shell while preserving the network. We propose that the local structure around Fe atoms does not undergo a rearrangement, thus, leading to the formation of an open site. The analysis conveys that the FeBTC is a disordered network of locally ordered blocks.

Phosphorous doping and drawing effects on the Raman spectroscopic properties of O=P bond in silica-based fiber and preform.

International audience; We report an experimental study of the doping and drawing effects on the Raman activities of phosphorus (P)-doped silica-based optical fiber and its related preform. Our data reveal a high sensitivity level in the full width at half maximum value of the 1330 cm−1 (O = P) Raman band to the P-doping level. Its increase with the P doping level does not clash with an increase in the disorder of the O = P surrendering matrix. In addition, we observe that in the central core region of the sample (higher doping level), the drawing process decreases the relative band amplitude. We tentatively suggest that this phenomenon is due to the change in the first derivate of the bond…

Diffusion and outgassing of O<inf>2</inf> in amorphous SiO<inf>2</inf> silica nanoparticles with specific surface properties

Coupled irradiation-temperature effects on induced point defects in germanosilicate optical fibers

International audience; We investigated the combined effects of temperature and X-rays exposures on the nature of point defects generated in Ge-doped multimode optical fibers. Electron paramagnetic resonance (EPR) results on samples X-ray irradiated at 5 kGy(SiO2), employing different temperatures and dose rates, are reported and discussed. The data highlight the generation of the Ge(1), Ge(2), E0 Ge and E0 Si defects. For the Ge(1) and Ge(2), we observed a decrease in the induced defect concentrations for irradiation temperatures higher than *450 K, whereas the E0 defects feature an opposite tendency. The comparison with previous post-irradiation thermal treatments reveals peculiar effects…

Spectral properties and lifetime of green emission in γ-ray irradiated bismuth-doped silica photonic crystal fibers

Abstract We report an experimental investigation focused on the green emission detected in γ-ray irradiated Bismuth-doped photonic crystal fibers. Our photoluminescence spectra, recorded at room temperature, provide evidence for the presence of two emission bands both located at ~ 530 nm (2.34 eV). One emission is detected only in the Bi-doped core while the other, is detected in the cladding. These two emissions feature different excitation spectra and a fast and a slow decay lifetime. The origin of the fast emission decay, about ten nanoseconds, is tentatively attributed to a silica intrinsic defect, whereas the slow component, having lifetime of about 2 μs and featuring anti-stokes emiss…

Aging of MCM41, MSU-H and MSU-F mesoporous systems investigated through the Raman spectroscopy

Here we report an experimental investigation, based on the Raman spectroscopy, on the aging of some mesoporous silica based systems. In details, we studied the aging in air of the MCM41, the MSU-H and the MSU-F materials by acquiring the Raman spectra of as received and of mechanically pressed, at 0.2 and 0.45 GPa, powders. Our data evidenced that the starting powders of the MCM41 and of the MSU-H undergo structural modification when they are exposed to the ambient atmosphere, such modification consisting in the decrease of the D2 Raman band (originated by the three member rings). At variance the powders of the MSU-F appear to be stable. Furthermore, by pressing the starting powders to prod…

O2 trapping in silica nano-structures with high specific surfaces

We report an experimental investigation regarding the entrapping of O2 molecules inside various silica nano– structured systems having specific surfaces from 50 to 1000 m2/g. By recording Raman spectra and Near Infrared O2 emission we studied the O2 content per mass unit. Our data show that the internal voids of these nanostructured systems can trap O2 molecules diffusing from the surrounding air or from a pure O2 atmosphere, whereas the concentration of O2 that can be trapped in the silica near–surface layer is at least one order of magnitude lower. This low ability is consistently observed in non–porous and porous silica nanoparticles and in mesoporous silica systems. Furthermore, we obse…

X-ray irradiation effects on a multistep Ge-doped silica fiber produced using different drawing conditions

International audience; We report an experimental study based on confocal microscopy luminescence (CML) and electron paramagnetic resonance (EPR) measurements to investigate the effects of the X-ray (from 50 krad to 200 Mrad) on three specific multistep Ge doped fibers obtained from the same preform by changing some of the drawing conditions (tension and speed). CML data show that, both before and after the irradiation, Germanium Lone Pair Center (GLPC) concentrations are similarly distributed along the diameters of the three fibers and they are partially reduced by irradiation. The irradiation induces also the Non Bridging Oxygen Hole Center (NBOHC) investigated by CML and other paramagnet…

Concentration growth and thermal stability of gamma-ray induced germanium lone pair center in Ge-doped sol–gel a-SiO2

Abstract We report an experimental study of the concentration growth by γ-ray irradiation of germanium lone pair center (GLPC) in 10 4 part per million molar Ge-doped sol–gel silica. The data show that γ-ray induced GLPC concentration increases linearly up to ∼5 MGy and then it seems to reach a limit value. In addition to the dose dependence, we have studied the thermal stability of the radiation induced GLPC in ambient atmosphere up to 415 °C. We found that the concentration of this latter GLPC starts to decrease at ∼300 °C, at variance to native GLPC, suggesting that the annealing is related to irradiation products. After the thermal treatments the photoluminescence (PL) activity of the γ…

Influence of fluorine on the fiber resistance studied through the nonbridging oxygen hole center related luminescence

The distribution of Non-Bridging Oxygen Hole Centers (NBOHCs) in fluorine doped optical fibers was investigated by confocal microluminescence spectroscopy, monitoring their characteristic 1.9 eV luminescence band. The results show that these defects are generated by the fiber drawing and their concentration further increases after c irradiation. The NBOHC concentration profile along the fiber provides evidence for an exponential decay with the fluorine content. This finding agrees with the role of fluorine in the fiber resistance and is discussed, from the microscopic point of view, by looking at the conversion mechanisms from strained bonds acting as precursors.

Irradiation temperature effects on the induced point defects in Ge-doped optical fibers

We present an experimental investigation on the combined effects of temperature and irradiation on Ge-doped optical fibers. Our samples were X-ray (10 keV) irradiated up to 5 kGy with a dose rate of 50 Gy(SiO2)/s changing the irradiation temperature in the range 233-573 K. After irradiation we performed electron paramagnetic resonance (EPR) and confocal microscopy luminescence (CML) measurements. The recorded data prove the generation of different Ge related paramagnetic point defects and of a red emission, different from that of the Ge/Si Non-Bridging Oxygen Hole center. Furthermore, by comparing the behaviour of the EPR signal of the Ge(1) as a function of the irradiation temperature with…

Influence of the manufacturing process on the radiation sensitivity of fluorine-doped silica-based optical fibers

International audience; In this work, we analyze the origins of the observed differences between the radiation sensitivities of fluorine-doped optical fibers made with different fabrication processes. We used several experimental techniques, coupling in situ radiation-induced absorption measurements with post mortem confocal microscopy luminescence measurements. Our data showed that the silica intrinsic defects are generated both from precursor sites and from strained regular Si-O-Si linkages. Our work also provides evidence for the preponderant role of the chlorine in determining the optical losses at about 3.5 eV. The results show that the manufacturing process of these fibers strongly af…

Comparison of gamma and beta-ray irradiation effects in sol-gel Ge-doped SiO2

O2 Loaded Germanosilicate Optical Fibers: Experimental In Situ Investigation and Ab Initio Simulation Study of GLPC Evolution under Irradiation

International audience; In this work we present a combined experimental and ab initio simulation investigation concerning the Germanium Lone Pair Center (GLPC), its interaction with molecular oxygen (O2), and evolution under irradiation. First, O2 loading has been applied here to Ge-doped optical fibers to reduce the concentration of GLPC point defects. Next, by means of cathodoluminescence in situ experiments, we found evidence that the 10 keV electron irradiation of the treated optical fibers induces the generation of GLPC centers, while in nonloaded optical fibers, the irradiation causes the bleaching of the pre-existing GLPC. Ab initio calculations were performed to investigate the reac…

Concentration growth and thermal stability of gamma-ray induced Germanium lone pair center in Ge-doped sol-gel SiO2

Gamma and x-ray irradiation effects on different Ge and Ge/F doped optical fibers

International audience; We performed electron paramagnetic resonance (EPR) measurements on γ and X ray irradiated Ge doped and Ge/F co-doped optical fibers. We considered three different drawing conditions (speed and tension), and for each type of drawing, we studied Ge and Ge/F doped samples having Ge doping level above 4% by weight. The EPR data recorded for the γ ray irradiated fibers confirm that all the samples exhibit a very close radiation response regardless of the drawing conditions corresponding to values used for the production of specialty fibers. Furthermore, as for the X irradiated materials, in the γ ray irradiated F co-doped fibers, we observed that the Ge(1) and the Ge(2) d…

Pulsed X‐Ray Radiation Responses of Solarization‐Resistant Optical Fibers

International audience; The transient radiation‐induced attenuation (RIA) of two different versions of pure‐silica‐core (PSC) multimode optical fibers (so‐called “solarization‐resistant” fibers) exposed to nanosecond 1 MeV X‐ray pulses are investigated. On‐line RIA spectra measurements at both room temperature (RT) and liquid nitrogen temperatures (LNT) in the range 1–3.5 eV are performed. Following the RIA kinetics, the properties of the metastable defects that are bleached just after the pulse are discussed. The spectral decomposition of the RIA is performed using known Gaussian bands associated to point defects absorbing in this spectral range. For both fiber types, the generation and th…

Combined Temperature Radiation Effects and Influence of Drawing Conditions on Phosphorous‐Doped Optical Fibers

International audience; This work focuses on the effects of high dose ionizing radiation, up to 10 MGy(SiO2), on P‐doped multimode optical fibers (OF) at different irradiation temperatures. The investigation is based on two complementary experimental techniques: radiation‐induced attenuation (RIA) measurements and electron paramagnetic resonance (EPR). The latter technique allows measuring the P1, P2, metastable‐POHC and stable‐POHC defects. Three OF samples are drawn from the same preform to evaluate the influence of changing their drawing conditions of the OFs on the radiation responses. This first study is performed under X‐rays at room temperature. The results are compared with the ones…

Micro-Raman investigation of X or gamma irradiated Ge doped fibers

International audience; Micro-Raman spectra have been recorded on Ge doped optical fibers before and after 10 keV-X or c-ray irradiation up to doses of 1 MGy (X-ray) or 7.8 MGy (-ray). Our data provide evidence that, at such dose levels, the glass matrix is not modified in a detectable way. We observed that varying the Ge doping levels from 0 to about 11 wt.%, X or radiation sensitivity of the overall matrix remains unchanged. Such results are observed for fibers obtained with drawing conditions within the usual range used for the fabrication of specialty fibers as radiation-tolerant waveguides. Our data support the potentiality of fiberbased sensors using glass properties, e.g. Raman sc…

Study of silica-based intrinsically emitting nanoparticles produced by an excimer laser

International audience; We report an experimental study demonstrating the feasibility to produce both pure and Ge-doped silica nanoparticles (size ranging from tens up to hundreds of nanometers) using nanosecond pulsed KrF laser ablation of bulk glass. In particular, pure silica nanoparticles were produced using a laser pulse energy of 400 mJ on pure silica, whereas Ge-doped nanoparticles were obtained using 33 and 165 mJ per pulse on germanosilicate glass. The difference in the required energy is attributed to the Ge doping, which modifies the optical properties of the silica by facilitating energy absorption processes such as multiphoton absorption or by introducing absorbing point defect…

Comparison of γ and β-ray irradiation effects in sol-gel Ge-doped SiO<inf>2</inf>

We report an experimental study on the comparison between the γ or β ray induced Ge related point defects in Ge doped silica. Silica samples doped with ∼2.2 1017 Ge atoms/cm3 produced with the sol-gel technique have been irradiated. The effects of the irradiation have been investigated by optical absorption, photoluminescence and electron paramagnetic resonance spectroscopy in order to evaluate the generation and the dependence on dose of the Ge(1), E'Ge, Germanium Lone Pair Center (GLPC) and H(II) point defects. No relevant differences between the concentrations of γ or β ray induced Ge(1) and E'Ge point defects have been observed. In addition, it is found that both irradiations are able t…

Formation of optically active oxygen deficient centers in Ge-doped SiO2 by γ- and β-ray irradiation

Abstract We report an experimental study on the comparison between the γ- or β-ray induced Ge related point defects in Ge-doped silica. Silica samples doped with ∼2.2 1017 Ge atoms/cm3 produced with the sol–gel technique have been irradiated with γ-ray or with β-ray. The effects of the irradiation have been investigated by optical absorption, photoluminescence and electron paramagnetic resonance spectroscopy in order to evaluate the generation and the dependence on dose of the Ge(1), E’Ge, GLPC (Germanium lone pair center) and H(II) point defects. No relevant differences between the concentrations of γ- or β-ray induced Ge(1) and E’Ge point defects have been observed and, in addition, it ha…

Emissive titanium dioxide nanoparticles synthesized py pulsed laser ablation in liquid phase

The remarkable applications of TiO2 nanomaterials, including, e.g. photocatalysis and dye-sensitized solar cells, have inspired in the last two decades an extensive amount of research aimed at understanding the properties of these materials. Photoluminescence is scarcely used to probe the electronic properties of TiO2, because neither bulk or nanosized TiO2 commonly display room-temperature emission. In particular, the fundamental luminescence due to the recombination of the self-trapped exciton in anatase TiO2 is typically observed only at low temperatures. We report the synthesis of luminescent titanium dioxide nanoparticles (NPs) by pulsed laser ablation of titanium in aqueous solution. …

Dependence of the emission properties of the germanium lone pair center on Ge doping of silica

We present an experimental investigation regarding the changes induced by the Ge doping level on the emission profile of the germanium lone pair center (GLPC) in Ge doped silica. The investigated samples have been produced by the sol-gel method and by plasma-activated chemical vapor deposition and have doping levels up to 20% by weight. The recorded photoluminescence spectra show that the GLPC emission profile is the same when the Ge content is lower than ∼ 1% by weight, whereas it changes for higher doping levels. We have also performed Raman scattering measurements that show the decrease of the D1 Raman band at 490 cm( - 1) when the Ge content is higher than 1% by weight. The data suggest…

Entrapping of O2 Molecules in Nanostructured Silica Probed by Photoluminescence

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 800cm-1) ratio decreases with increasing the specific surface both for the as received and the loaded samples. By performing a thermal treatment (600 °C for 2h) 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…

Phase change and O2 loading in mesoporous silica MCM41, MSU-H and MSU-F

Refractive index change dependence on Ge(1) defects inγ-irradiated Ge-doped silica

We present an experimental study regarding the effects of the $\ensuremath{\gamma}$ radiation on silica glass doped with Ge up to $10\text{ }000$ ppm molar produced by the sol-gel technique. We have determined the irradiation-induced changes in the refractive index $(\ensuremath{\Delta}n)$ as a function of the oxygen deficiency of the samples, evaluated from the ratio between the germanium lone pair centers (GLPC) and the Ge content. $\ensuremath{\Delta}n$ at 1500 nm have been estimated using optical-absorption spectra in the range 1.5--6 eV. We have found that $\ensuremath{\Delta}n$ is independent of Ge differences for GLPC/Ge values $l{10}^{\ensuremath{-}4}$, while it depends on Ge for la…

Near‐IR Radiation‐Induced Attenuation of Aluminosilicate Optical Fibers

The X-ray radiation-induced attenuation (RIA) growth kinetics are studied online in different single-mode aluminosilicate optical fibers in the near-IR (NIR) domain to evaluate their potential in terms of dosimetry. The optical fibers differ by Al contents, core sizes, drawing parameters, and also by a preform deposition process. The data show no dependence of the RIA on all these parameters, a positive result for the design of point or distributed radiation detectors exploiting RIA to monitor the dose. The RIA growth rate is unchanged for dose rates changing from 0.073 to 6.25 Gy(SiO2) s−1, and the RIA linearly increases with the dose up to 2 kGy(SiO2). Small but noticeable RIA changes are…

Overview of radiation induced point defects in silica-based optical fibers

International audience; Silica-based optical fibers, fiber-based devices and optical fiber sensors are today integrated in a variety of harsh environments associated with radiation constraints. Under irradiation, the macroscopic properties of the optical fibers are modified through three main basic mechanisms: the radiation induced attenuation, the radiation induced emission and the radiation induced refractive index change. Depending on the fiber profile of use, these phenomena differently contribute to the degradation of the fiber performances and then have to be either mitigated for radiation tolerant systems or exploited to design radiation detectors and dosimeters. Considering the stro…

Thermally induced structural modifications and O2 trapping in highly porous silica nanoparticles

Abstract In this work we investigate by Raman spectroscopy the effect of isochronal (2 h) thermal treatments in air in the temperature range 200–1000 °C of amorphous silicon dioxide porous nanoparticles with diameters ranging from 5 up to 15 nm and specific surface 590–690 m2/g. Our results indicate that the amorphous structure changes similarly to other porous systems previously investigated, in fact superficial SiOH groups are removed, Si–O–Si linkages are created and the ring statistic is modified, furthermore these data evidence that the three membered rings do not contribute significantly to the Raman signal detected at about 495 cm−1. In addition, after annealing at 900 and 1000 °C we…

Ultraviolet-visible light-induced solarisation in silica-based optical fibres for indoor solar applications

Abstract The transmission performances of pure- and doped-silica (a-SiO2) optical fibres are compared during the exposure to a high-power broadband light source approximating the solar spectrum. From the Gaussian decomposition of the attenuation spectra, we found that Al- and P-doped fibres show a fast solarisation effect which leads to transmission degradation in the ultraviolet-visible range. Similarly, Ge-doped fibres undergo photoinduced colour-centre formation which, however, does not prevent visible-light propagation. One of the two tested pure-silica fibres results completely unaffected by light exposure whereas the other shows an absorption band probably due to the presence of chlor…

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…

Effect of irradiation temperature on the radiation induced attenuation of Ge-doped fibers

International audience; The UV-visible radiation induced attenuation (RIA) was studied in Ge-doped optical fibers, during X-ray (10 keV) irradiations at different temperatures. By comparing the spectra recorded in dissimilarly irradiated samples we evidenced the impact of the irradiation temperature. In details, we highlighted that, from a certain dose, increasing the temperature the RIA decreases for wavelengths lower than 470 nm, whereas at higher wavelengths the RIA depends only on the dose. Such findings suggest that it is possible to distinguish the irradiation temperature by comparing the signal at two different wavelengths. From the microscopic point of view, it appears that the RIA …

Transient Radiation Responses of Optical Fibers: Influence of MCVD Process Parameters

International audience; A dedicated set of fibers elaborated via the Modified Chemical Vapor Deposition (MCVD) technique is used to study the influence of composition and drawing parameters on their responses to an X-ray pulse representative of the radiation environments associated with Megajoule class lasers. These canonical fibers were designed to highlight the impact of these parameters on the amplitude and kinetics of the transient pulsed X-ray Radiation Induced Attenuation (RIA) at room temperature. From preforms differing by their core composition, three optical fibers were elaborated by varying the tension and speed during the drawing process. No or only slight RIA change results fro…

Alpha and deuteron irradiation effects on silica nanoparticles

We present an experimental investigation focused on the effects of alpha and deuteron irradiation on different silica nanoparticles. The study has been devoted also to characterize the induced point defects and the eventual structural modifications to evaluate the effects of the different irradiation source in comparison with the bulk materials. After irradiation up to about 10^16 ions cm^-2, we performed electron paramagnetic resonance (EPR), photoluminescence (PL), infrared (IR) absorption, Raman, and atomic force microscopy (AFM) measurements. We found that the two types of irradiation qualitatively induce comparable effects. Furthermore, irradiation generates the socalled twofold coordi…

Coupled theoretical and experimental studies for the radiation hardening of silica-based optical fibers

International audience; 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 ${rm SiE}^prime$ defect that is observed through Electron Paramagnetic Resonance (EPR) measurements in all cano…

Irradiation temperature influence on the in-situ measured radiation induced attenuation of Ge-doped fibers

International audience; We report an experimental investigation on the radiation induced attenuation (RIA) in the ultraviolet-visible domain for Ge-doped optical fibers, during X-rays (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 explai…

Near-IR- and UV-femtosecond laser waveguide inscription in silica glasses

The influence of laser parameters on silica based waveguide inscription is investigated by using femtosecond laser pulses at 1030 nm (near-IR) and at 343 nm (UV). Negative phase contrast microscopy technique is used to measure the refractive index contrast for different photo-inscribed waveguides and shows the effects of both laser wavelength and scanning speed. In particular, UV photons have a higher efficiency in the waveguide production process as also confirmed by the lower optical losses at 1550 nm in these waveguides. These measurements are combined with micro-Raman and photoluminescence techniques, highlighting that laser exposure induces both structural modification of the silica an…

Resonance Raman of oxygen dangling bonds in amorphous silicon dioxide

We investigate the origin of a resonance Raman band induced by ionizing radiation in amorphous silicon dioxide (silica glass), which can be detected under ultraviolet laser excitation. A silica sample, rich of oxygen-excess related defects, was prepared by treating some length of a pure-silica-core multimode fiber in an O2 atmosphere (at high temperature and pressure) and by irradiating it with X-rays at 10 MGy(SiO2) dose. A micro-Raman study revealed a gaussian band peaking at 896 cm−1 with a full width at half maximum of 32 cm−1, which could be detected by exciting the sample with the 325-nm line of a HeCd laser. This spectral feature is absent in the Raman spectra performed with the 442-…

Influence of Drawing Conditions on the Properties and Radiation Sensitivities of Pure-Silica-Core Optical Fibers

International audience; The structure and radiation sensitivities of three different pure-silica-core fluorine-doped-cladding optical fibers, made from the same original preform, were investigated by several experimental techniques. The fibers were obtained by changing the drawing speed and tension in the typical ranges of values used for the radiation-tolerant waveguides. The Raman spectroscopy revealed no significant difference among the fibers before irradiation. At variance, the comparison between the fibers and their associated preform highlighted an increase in the amplitude of the D2 band that is related to the concentration of 3 member rings. Moreover, in the zones where the D2 incr…

Silica nanoparticle core structure examined by the E?Si? center 29Si strong hyperfine interaction

Abstract β-Ray irradiation up to 1.2 GGy was employed to induce E′Si γ defects and to study the structure of silica nanoparticles with diameters from 7 up to 20 nm. Defect concentration and their 29 Si strong hyperfine doublet were investigated through electron paramagnetic resonance measurements. Our data indicate that stable defects are located in the nanoparticle core. Furthermore, the E′Si γ hyperfine interaction evidences that the core structure is denser than bulk silica and independent from the particle size. Finally, we put in evidence that the core structure is stable and unaffected by the irradiation in the investigated dose range maintaining the specific features of nanoparticles.

Influence of Ge doping level on the EPR signal of Ge(1), Ge(2) and E'Ge defects in Ge-doped silica

Abstract We present an experimental investigation on the Ge doping level dependence of the Electron Paramagnetic Resonance (EPR) signal spectral features of the Ge(1), Ge(2) and E'Ge defects induced in Ge doped silica. We have studied samples produced by sol–gel or PCVD techniques and doped with different amounts of Ge up to 20% by weight. The samples were gamma or beta ray irradiated and successively they were thermally treated to isolate the EPR signals of the different point defects. The data show that the EPR line shapes of the Ge(1) and the Ge(2) centers are progressively modified for doping level higher than 1%, whereas the line shape of the E'Ge defect appears independent from the do…

Radiation Response of Ce-Codoped Germanosilicate and Phosphosilicate Optical Fibers

We report an experimental investigation on the effects of Ce-codoping in determining the radiation response of germanosilicate and phosphosilicate Optical Fibers (OFs) in the UV-Visible domain and up to doses of $1~\hbox{MGy}({\rm SiO}_{2})$ . We show that the addition of Ce strongly impacts the Radiation Induced Attenuation (RIA) of both types of fibers. In the first case the radiation induced losses increase, whereas in the second one decrease. By combining the online RIA measurements with the Electron Paramagnetic Resonance (EPR) ones, we are able to infer the basic microscopic mechanisms taking place under irradiation, which involve the cerium codopant and some of the known Ge-related o…

Ge-doping dependence of gamma-ray induced germanium lone pair centers in Ge-doped silica

We report an experimental study on the y irradiation effects in Ge-doped sol-gel silica samples doped with Ge from 10 2 up to 10 4 part per million molar. The samples were exposed to the radiation generated by a 60 Co source up to an accumulated dose value of 10 MGy. Our data evidence that the γ irradiation significantly increases the number of Germanium Lone Pair Centers (GLPC). Such defects are induced with a concentration that depends on the Ge content of the employed material in those samples where no optical activity related to -s GLPC was detected before irradiation. Furthermore an increase of the GLPC concentration was detected also in a sample that already contains this defect after…

Transient and Steady-State Radiation Response of Phosphosilicate Optical Fibers: Influence of H2 Loading

The radiation response of a phosphorus-doped multimode optical fiber is investigated under both transient (pulsed X-rays) and steady-state ( $\gamma $ - and X-rays) irradiations. The influence of a H2 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…

The relevance of point defects in studying silica-based materials from bulk to nanosystems

The macroscopic properties of silica can be modified by the presence of local microscopic modifications at the scale of the basic molecular units (point defects). Such defects can be generated during the production of glass, devices, or by the environments where the latter have to operate, impacting on the devices’ performance. For these reasons, the identification of defects, their generation processes, and the knowledge of their electrical and optical features are relevant for microelectronics and optoelectronics. The aim of this manuscript is to report some examples of how defects can be generated, how they can impact device performance, and how a defect species or a physical phenomenon …