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The first nonlinear optic nanocomposite based on a low-melting vitreous matrix and a ferrielectric crystal has been obtained. The matrix consists of lead-borate glass and the filler is single-phase powder of ferrielectric KNbSi2O7. The quadratic optical nonlinearity of composites was studied depending on temperature and time of dissolution of crystals in the glass matrix. Conditions for producing transparent nanocomposites that generate the second optic harmonic are identified.

In this study, we report the results of an in situ X-ray absorption spectroscopy investigation of the La2O3–B2O3–GeO2 (LBG) glass compressed in a diamond anvil cell until 17 GPa at ambient temperature. A pressure-induced coordination change of germanium from fourfold to sixfold is shown here. The analysis of Ge K-edge X-ray absorption near-edge structure spectra supports a model of mixing of fourfold and sixfold coordinated Ge sites during the compression/decompression cycle. This transformation proves to be irreversible: about 25% of sixfold coordinated Ge still exists at ambient pressure. This phenomenon underlines a polymorphism property of the LBG glass, whose origin lies in the complexity of composition.

Amorphous nanoheterogeneities of the size less than 100 A have been formed in glasses of the Li2O–Nb2O5–SiO2 (LNS) and Li2O–ZnO–Nb2O5–SiO2 (LZNS) systems at the initial stage of phase separation and examined by transmission electron microscopy, small-angle X-ray and neutron scattering. Both LNS and LZNS nanoheterogeneous glasses exhibit second harmonic generation (SHG) even when they are characterized by fully amorphous X-ray diffraction (XRD) patterns. Chemical differentiation and ordering of glass structure during heat treatments at appropriate temperatures higher Tg lead to drastic increase of SHG efficiency of LNS glasses contrary to LZNS ones in the frame of amorphous state of samples. Following heat treatments of nanostructured glasses result in crystallization of ferroelectric LiNbO3 and non-polar LiZnNbO4 in the LNS and LZNS glasses, respectively. Taking into account similar polarizability of atoms in LNS and LZNS glasses, the origin of the principal difference in the second-order optical non-linearity of amorphous LNS and LZNS samples is proposed to connect predominantly with the internal structure of formed nanoheterogeneities and with their polarity. Most probably, amorphous nanoheterogeneities in glasses may be characterized with crystal-like structure of polar (LiNbO3) phase initiating remarkable SHG efficiency or non-polar (LiZnNbO4) phase, which do not initiate SHG activity. It gives an opportunity to vary SHG efficiency of glasses in a wide rage without remarkable change of their transparency by chemical differentiation process at the initial stage of phase separation when growth of nanoheterogeneities is ‘frozen’. At higher temperatures, LiNbO3 crystals identified by XRD precipitate in LNS glasses initiating even more increase of SHG efficiency but visually observable transparency is impaired.

Glass isotropy could be broken by using the electric field of the 355 nm wavelength delivered by a nanosecond YAG: Nd 3+ laser. In this way, pulsed laser-induced birefringence was obtained in the La 2 O 3 –B 2 O 3 –GeO 2 (LBG) glassy system. Buried lines behaving like waveguides were written in glasses using this laser irradiation process. Micro Raman spectra performed in irradiated points of glasses revealed a rotation of the light polarization in agreement with previous results obtained on thermally-poled LBG glasses. However, no orientation effects of irradiated points related to the direction of the laser wave polarization (UV poling) could be clearly evidenced as suggested in our last paper. The interaction of the glass with the electromagnetic field of the UV laser beam can be more probably described by mechanisms based on a densification process.

Raman amplification presents a huge potential for optical communications. x PbO–(1 − x )GeO 2 glasses (with x = 0, 10%, 20%, 30% and 40% mol) are studied. The association of lead oxide and germanate is thought to be a suitable candidate for Raman amplification regarding to its high scattering level and the large plateau existing on its Raman scattering spectra. The estimated optimal composition is 0.36PbO–0.64GeO 2 .

Luminescence characteristics of Er 3+ -activated, Yb 3+ -sensitised GeO 2 –Na 2 O–Nb 2 O 5 heavy metal germanate glasses have been investigated in the context of searching active media for laser devices. Optical absorption, emission spectra and decay time measurements have been performed at room temperature on these materials. Intense 1540 nm infrared fluorescence and visible emission bands at 533, 554, and 660 nm were observed under continuous wave excitation at 980 nm. An efficient energy transfer from Yb 3+ to Er 3+ ions, increasing as a function of Yb 3+ concentration, favours the Er 3+ 1.54 μm eye-safe laser emission in these materials. The power dependence study of the upconverted emissions gives evidence of a bi-photonic process. Moreover, the Yb 3+ codoping enhances the up-conversion efficiency. Decay time measurements have been examined in the purpose of elucidating the possible mechanisms involved in this process. The experimental results are in good agreement with an effective Yb 3+ -to-Er 3+ nonradiative energy transfer.

Raman scattering, optical absorption and photoluminescence studies have been performed on Er3+-doped Na2O–Nb2O5–GeO2 germanate-based glasses. The main bands in the Raman spectra involve vibrational modes associated with the germanium oxide network. Judd–Ofelt intensity parameters were determined and then used to calculate the radiative transition rates and excited-state radiative lifetimes. Green and red up-conversion luminescence was observed at room temperature under 800 nm laser line excitation. The emission intensities have a quadratic dependence on the excitation pump power, indicating a two-step up-conversion mechanism. The intensity of the 660 nm red band shows an increase relative to the 554 nm green band with increasing Er3+ content. Combined with the time-resolved luminescence data of the emitting states, we suggest from these results that the up-conversion process is attributed to a competitive situation of excited-state absorption and energy transfer between excited ions accompanied by multiphonon relaxation. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Resume Introduction Nous rapportons deux cas de patients ayant developpe une sarcoidose avec adenopathies diffuses pour lesquels l’interrogatoire a mis en evidence des applications repetees de talc au niveau de zones cutanees irritees. Cas clinique Une lecture attentive des prelevements histologiques en microscopie optique a permis, sous lumiere polarisee intense, l’observation d’une accumulation de particules birefringentes au sein de vaisseaux au contact des zones granulomateuses. L’etude par microscopie electronique apres microdissection des zones concernees a prouve que les particules accumulees correspondaient a de la silice et des silicates pouvant provenir du talc applique. Conclusion Le role d’un empoussierement mineral dans la survenue d’une sarcoidose est discute. Certains cas pourraient etre en rapport avec des applications cutaneo-muqueuses de poudre minerale sur des plaies avec transport a distance de particules de silice et silicates responsables des reactions granulomateuses. A propos de ces deux observations nous discutons le fait que certaines sarcoidoses pourraient etre en rapport avec des empoussierements aeriens ou cutaneo-muqueux souvent sous-estimes sur un terrain genetique favorable.

Crystallisation behaviour of glasses in the K2O-TiO2-P2O5 (KTP) has been studied by DTA, XRD, EM and SHG techniques to isolate composition ranges where bulk precipitation of ferroelectric phase KTiOPO4 occurs. It was found that bulk crystallisation of KTiOPO4 at temperatures slightly exceeding Tg is initiated by addition of SiO2. Controlled heat treatment leads to formation of optically non-linear KTiOPO4 nano-particles in KTP glasses (like amorphous nanostructuring in KNS glasses) in initial stages of phase separation and produces nanoscaled modulation of polarisability and SHG effect. The results are compared to the xK2O xNb2O5(1-2x)SiO2 (KNS) systems.

UV assisted photoelectron emission measurements are carried out using a xenon lamp as the excitation source. Free-standing diamond surfaces treated at diverse experimental conditions give rise to varying photocurrent intensities. In order to gain a better understanding of these phenomena, different surfaces are prepared: as-grown, hydrogenated, oxidized and annealed. The hydrogenated film is obtained from optimised treatment in hydrogen plasma. The highest emission photocurrent is obtained with the hydrogenated diamond film in agreement with in situ surface conductivity values. Moreover, in situ photoelectric measurements performed in a vacuum chamber demonstrate that the emission photocurrent increases when the sample is exposed to air. Indeed, it is now agreed that the formation of an adsorbate layer on hydrogenated surfaces leads to a decrease of the work function. Two electrons emission thresholds are observed: the highest energy emission is close to the bandgap value (5.5 eV) and the lowest is located near 4.5 eV corresponding to defect levels in the bandgap. Both emissions are dependent on the surface coverage but the main striking result is the increase of the intensity of the 4.5 eV emission for hydrogenated diamonds in contact with air. Optical absorption experiments are compared with the photoconductivity measurements. Laser excited photoluminescence at 514 nm revealed defects corresponding to a 690 nm broad band emission sensitive to the surface coverage.

The spectral-luminescent properties of silica gel glasses coactivated by Ce4+ and Eu3+ ions are investigated. The structure of the glasses is studied using x-ray powder diffraction and small-angle neutron scattering. The inference is drawn that Ce4+-Eu3+ centers with high-symmetry Eu(III) oxo complexes, which are formed in the glasses, have nanocrystalline nature. These centers are characterized by a weak vibronic interaction of Eu3+ ions with the matrix. The size of nanocrystallites formed under the synthesis conditions and at coactivator concentrations used is approximately equal to 10 nm.

In order to describe the rare earth environment in an aluminoborosilicate nuclear glass and its evolution with water leaching, Eu 3+ was used as a luminescent structural probe. Two types of Eu 3+ environments were observed in the glass as well as in the gels (originating from leached glass). A study of the B 2 crystal field parameters allows one to identify one site as a silicate type. We showed moreover that the second site is modified with leaching from a borate to an aluminate site. Asymmetry ratio from photoluminescence and Mossbauer analyses demonstrated a decrease of the average distortion of the Eu 3+ sites in the gels. Indeed, gel can be described as an amorphous matrix but less disordered than glass. Another important result is that the lanthanide environment is not influenced by the leaching mode.

We studied the influence of germanium atom introduction into the silica network and the influence of heat treatements on the glass structure by doing Raman and infra-red spectra of vitreous germanium doped silica (5% wt GeO 2 , 95% wt SiO 2 ). Germanium incorporates into the network by substituting Si atoms and consequently, we observed band shifts and broadening of defect peaks D 1 and D 2 . The peak positions are directly correlated with the structural state characterized by the glass fictive temperature T F of the different samples.

The Amaldi 10 Parallel Session C3 on Advanced Gravitational Wave detectors gave an overview of the status and several specific challenges and solutions relevant to the instruments planned for a mid-decade start of observation. Invited overview talks for the Virgo, LIGO, and KAGRA instruments were complemented by more detailed discussions in presentations and posters of some instrument features and designs. © 2014 Springer Science+Business Media New York.

Site distribution of Eu 3+ ions was studied by site selective spectroscopy in an aluminoborosilicate nuclear glass and in its leached form called gel. Spectroscopic studies allow one to detect two types of site distributions in the glass as well as in two gels. One is attributed to a silicate environment while for the other one an aluminate environment is suspected. Tunable dye-laser excitation spectra show that bandwidths are narrower in gels than in glass so that the site distribution is narrower in gels. Moreover, site symmetry is higher in gels than in the glass.

In this study, we investigate the photoelectric emission from CVD diamond films. These diamond samples present NEA properties due to their as-grown surfaces terminated with hydrogen atoms. Photocathodes are characterised by UV pulsed laser-induced photoelectric measurements and photoelectric threshold measurements because the photoelectric emission is strongly dependant on the electron affinity of the diamond surface. Photoelectric threshold measurements show the existence of a sub-bandgap signal associated to a defect-band level for both samples, with the lowest value obtained for the highest defect-density diamond film. Moreover, the quantum efficiency of undoped diamond is measured at 213 nm as a function of the CH4 concentration. The highest quantum efficiency value is measured for the highest defect-density diamond film. Surface bonds modifications occurring during a prolonged laser irradiation are responsible for the decrease in the photoemissive performances of diamond films. # 2000 Elsevier Science B.V. All rights reserved.

Steady -state luminescence, polarization spectroscopy and laser-induced time-resolved spectroscopy techniques have been applied to Eu 3+ -doped synthetic ZrSiO 4 . Eu 3+ is used as a structural probe of nonequivalent centers. The structure of the three main sites analyzed and discussed.

The methods of small angle synchrotron radiation scattering, vibration spectroscopy, and second harmonic generation are applied to glasses of the K2O-TiO2-P2O5 system near the stoichiometry of potassium titanyl-phosphate to demonstrate that at the initial stage of phase separation, while glass remains x-ray amorphous and clear, it can possess quadratic optical nonlinearity. The emergence of nonlinearity is facilitated by the formation of nanoheterogeneities in glass whose structure resembles the structural pattern of a nonlinear-optical crystal. Acorrelation established between the structural specifics of x-ray amorphous glass and its quadratic optical nonlinearly suggests the advisability of describing the short-range and medium-range orders of glasses at the glass-formation boundary in the context of quasicrystallite models.

The quartz-cristobalite transformation in heated natural chert (flint) rock composed of micro- and ŗypto-quartz was investigated in the temperature interval of 1000–1300°C by micro-Raman spectroscopy, FT-IR spectroscopy, X-ray diffraction and Scanning Electron Microscopy. A small amount of crystobalite was first observed in the chert after heating at 1000°C for 1 h and the transformation was almost completed after heating at 1300°C for 24 h. On the other hand, cristobalite was not detected in well-crystallized pure quartz after heating under the same conditions. The transformation occurs as a solid state nucleation and crystal growth of cristobalite replacing quartz at high-temperatures. The chert rock is naturally rich in crystal defects and boundaries which serve as nucleation sites and enable an earlier quartz-cristobalite transformation.

Time-resolved luminescence allows the differences between rare-earth elements and manganese accommodation in apatites to be distinguished. The valence state and exact crystal site of incorporated cations are interpreted from the spectral characteristics. Contrary to the apriory incorporated cations, the adsorbed species can be revealed only after high temperature diffusion.

The nanostructure and nonlinear optical properties of high-niobium glasses in the (1 - x)KNbO3-xSiO2 system with an SiO2 content x = 0.05-0.35 have been studied by small-angle neutron scattering (SANS), electron microscopy (EM), and second-optical-harmonic generation (SHG). Vitreous samples are manufactured by the methods of fast melt cooling (pressing with metal plates and quenching between rotating rolls). Glasses with x < 0.12 have been established to form a micro-inhomogeneous structure in the form of silica-enriched regions at the cooling rates used. According to SANS data, quenched glasses with x > 0.2 are homogeneous, but form a silica-enriched nanostructure after thermal treatments. At temperatures below ∼T g + 50 C, silica-enriched regions manifest a very slight tendency to grow, whereas, according to SANS and X-ray diffraction data, their chemical composition is observed to shift appreciably towards SiO2 with thermal treatment. The obtained data on an inhomogeneous structure allows us to clarify the complicated character of the previously revealed dependence T g (x). Nano-inhomogeneous transparent samples produce a weak SHG signal, which indicates the quasi-periodic modulation of the chemical composition and, correspondingly, polarizability, in the volume of glass. The nonlinear optical phase KNbO3 precipitates at later stages of crystallization, when a glass loses its transparency. In this case, the SHG signal is amplified by several orders of magnitude. © 2013 Pleiades Publishing, Ltd.

International audience; We report on Brillouin and in situ small angle X-ray scattering (SAXS) analyses of topological heterogeneity in compressed sodium borosilicate glasses. SAXS intensity extrapolated to very low angular regimes, I(q = 0), is related to compressibility. From Brillouin scattering and analyses of the elastic properties of the glass, the Landau-Placzek ratio is determined and taken as a direct reflection of the amplitude of frozen-in density fluctuations. It is demonstrated that with increasing fictive pressure, topological (mid- and long-range) homogeneity of the glass increases significantly. Heating and cooling as well as isothermal scans were performed to follow the evolution of density fluctuations upon pressure recovery. For a sample with a fictive pressure p(f) of 470 MPa, complete recovery to pf = 0.1 MPa was observed to occur close to the glass transition temperature. The values of fictive and apparent fictive temperature, respectively, as obtained via the intersection method from plots of I(q = 0) vs. temperature were found in good agreement with previous calorimetric analyses. Isothermal scans suggest that mid- and long-range recovery govern macroscopic density relaxation. (C) 2011 American Institute of Physics. [doi:10.1063/1.3593399]

In this paper, type II interfaces between semiconductors and their photoluminescence (PL) properties are presented. In these interfaces, the PL arises from the recombination of electrons and holes separated by the interface. This spatial separation lowers the wave function overlap of the electrons and holes compared to that of a direct band gap semiconductor and results in a larger PL decay time. Despite the spatial separation of the carriers, the interface PL peak intensity is high and broad. The similarity between these properties and those of the porous silicon (PS) more intense PL peak, the so-called slow band (S band), suggest a model for explaining the origin of this PS PL band. In this model, the radiative recombinations at the origin of the band S occur across the Si/Si oxide interface, i.e. it involves energy levels within the silicon oxide layer. This model takes into account the quantum confinement and the energy threshold above which PS PL is observed.

CdS doped amorphous silica was prepared by the sol-gel method. The CdS concentration in weight varied from 5% to 20%. The samples were characterized by four different and complementary techniques: X-ray diffraction (XRD), high resolution transmission electron microscopy (HRTEM), low frequency inelastic Raman scattering (LOFIRS) and small angle X-ray scattering (SAXS). These observations show that the size of the nanocrystals does not depend on the CdS concentration.

International audience; Density and concentration fluctuations have been investigated in a 3 mol % GeO2 doped silica glass as a function of the fictive temperature (the temperature at which the structure of the supercooled liquid has been frozen-in to form the glass) by small angle x-ray scattering measurements. The fluctuations increase in a way is quite similar to that observed for pure silica glass as a result of density fluctuation fictive temperature dependence. Fluctuations have also been studied in glasses containing different amounts of GeO2 up to 21 mol % GeO2. The fluctuations are shown to increase very strongly with germanium amount as a result of strong concentration fluctuation increase. This observation is in agreement with already observed excess losses in light scattering measurements.

Simplified inactive rare-earths doped nuclear waste glasses have been obtained by molecular dynamics (MD) simulation in order to investigate the local structure around the rare-earth by luminescence studies. MD calculations were performed with modified Born–Mayer–Huggins potentials and three body angular terms representing Coulomb and covalent interactions. Atomic positions within the glasses are then determined. Simulations of luminescence spectra were then obtained by calculation of the ligand field parameters affecting each luminescent ion. Considering the C 2 v symmetry, it is possible to calculate the radiative transition probabilities between the emitter level, 5 D 0 , and the splitted receptor levels, 7 F J ( J = 0–3) for each Eu 3+ ion. The simulated emission spectra are obtained by convolution of all the Eu 3+ ions contributions. A comparison with the experimental data issue from fluorescence line narrowing and microluminescence spectroscopies allowed us not only to validate the simulation of luminescence spectra from simulated environments, but also to confirm the presence and the identification of two major Eu 3+ sites distribution in the nuclear glasses thanks to spectra-structure correlations.

Nucleation process of an aluminosilicate precursor of a glass-ceramic SiO2Al2O3Li2O is studied when a low concentration of Cr2O3 is added to the usual nucleating elements ZrO2 and TiO2. For annealing at 770 and 720°C, low frequency inelastic scattering (LoFIS) and transmission electron microscopy (TEM) characterize diameter of nuclei up to 6 nm while electron paramagnetic resonance and laser spectroscopy determine the environment of the chromium ions during the nucleation process. It is shown that chromium ions strongly modify the nucleation but do not enter in the nuclei. An enhancement of the number of nuclei and a simultaneous reduction of their size is postulated.

Sodium tetraborate (100 – x)(Na2B4O7.10H2O)­­ ­­­­­– xV2O5, (x = 0 to 20 mole %) has been elaborated by splat cooling technique. Raman Measurements on the doped and non polish samples reveal the presence of the of α-NaVO3 crystal on the superficial layer. After polishing, Raman spectra characteristic of glasses are obtained with two main bands located at 555 and 1097 cm-1 in the undoped glass and four bands at 241, 381, 776 and 938 cm-1 for the vanadium oxyde doped glasses. The volume devitrification of these glasses occurs at 750° C and the β-NaVO3 crystalline phase is identified by Raman scattering.

We report on two patients with sarcoidosis with disseminated nodes, who used talc on irritated cutaneous areas.A histologic examination with intense polarised light showed up cristalline bi-refringent particles within vessels in contact with granulomatous areas. Microdissection followed by an electronic microscopy study and microanalysis was realised. In situ microanalysis allowed us to identify bi-refringent particles with a size of roughly 0.25microm as silica or silicate coming possibly from talc. We consequently studied a brand name talc. The diffraction spectrum showed that this product not only contained talc but also chlorite and quartz. Electron microscopy examination showed particles of all sizes even smaller than 0.25microm. These infra-microscopic particles, visible in a vessel only when agglomerated, could be invisible under optic microscopy (resolution: roughly 0.5microm) inside the granuloma even though they are responsible for it. Moreover, at this level of size of particles, they may escape mineralogic analyses which use methods involving the destruction of organic material, the mineral residue collecting on cellulose filter with a diameter generally of 0.45microm.Two recent epidemiologic studies confirm the possible role of mineral exposure in sarcoidosis. Some sarcoidosis could be caused by mineral overload on genetically predisposed patients. Some cases could be related to mineral powder application. Among different types of mineral exposure, applications of cosmetic products may induce disseminated granulomatous reaction on genetically predisposed patients. Such applications have to be considered in epidemiologic studies.

International audience; Radiation effects in oxide glass as external β-irradiation has been investigated by Raman spectroscopy, Cr3+ luminescence and EPR spectroscopy to analyze microstructure evolution. Comparison between simplified and complex glasses (high-level nuclear waste glass analogue) was undertaken. Migration and segregation of sodium have been confirmed on simplified irradiated glasses by a polymerization increase and dissolved oxygen presence. Densification under irradiation has also been demonstrated with the increase of three-membered silicate rings in silicate glass and the decrease of the average Si–O–Si angle in the borosilicate glass. In both glasses, Cr3+ crystal field was increased, suggesting a Cr–O length decrease. The complex borosilicate glass responds differently: densification effect and Na segregation were not detected. Under β-irradiation, electron-trapping processes on Cr6+ occurred, forming Cr4+ and Cr5+ species.

Two types of borosilicate leached SON68-type glasses were studied, one doped with uranium and the other with rare-earth element (Nd, Eu). Photoluminescence and cathodoluminescence properties of U doped samples have been correlated to microscopic features of the corroded glass. Nuclear analysis, Electronic Microprobe and Scanning Electron Microscope investigations revealed the heterogeneous composition of the gels with differentiated phases. Enriched U phases (crystallised or not) and phosphorus precipitated phases in rare earth gel have been detected.

International audience; The in situ elastic and plastic behaviors of sodium aluminosilicate glasses with different degrees of depolymerization were analyzed using Brillouin spectroscopy. The observed elastic anomaly progressively vanished with depolymerization. The densification process appears to be different from that observed in pure silica glass. In the plastic regime of densified glasses hysteresis loops were observed and related to modification of the local silicon environment facilitated by the addition of sodium.

Micro-Raman spectra are performed at different radial positions in order to determine the fictive temperature distribution in pure silica optical fibers. As-received and annealed optical fibers are compared and Raman results reveal a large decrease in the fictive temperature after annealing. The fictive temperature gradient between the core and the edge of the optical fiber can be eliminated after annealing and the spectroscopic decoupling between stress and the fictive temperature variation is discussed. The micro-Raman is a good probe in determining the spatial distribution of the fictive temperature in the micrometer length scale.

INTRODUCTION Spontaneous pneumomediastinum is a little known cause of chest pain in young adults. The prognosis is invariably good. CASE REPORT The authors report two cases of spontaneous pneumomediastinum with different aetiologies developing in young adults. The first occurred during strenuous sport and the second during an asthma attack. CONCLUSION The discussion stresses the frequency of this condition in young men, its pathogenesis and natural history. In particular the authors draw on the current scientific data to explain the absence of predisposing factors and the extreme rarity of relapse of this benign disorder. Poor acquaintance with this clinical entity may lead to unnecessary diagnostic and therapeutic actions. The authors suggest a guideline for the management of this disorder.

The Letter proposes a model to explain the PL mechanism in porous silicon. It was inspired by type II semiconductor interface PL behaviour. In this model, the PS radiative recombinations involve energy levels in the silicon oxide layer. This model takes into account quantum confinement and the energy threshold above which PS PL is observed.

Low-frequency Raman scattering was observed from different silica aerogels obtained from hydrolysis of tetramethoxysilane in alkaline conditions. It is deduced that the diameter of cylindrical chains of the network is 50 or 70 AA, depending on the origin of the aerogel. These experimental results are interpreted on the basis of Raman scattering from fractal vibrations in spherical structural units for base-catalysed aerogels.