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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.

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 .

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.

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.

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.

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 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; 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.

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.

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.

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.

The local strain around the cation is expressed in function of the ion displacements in the cluster. It is shown that this local strain is related to the applied uniaxial stress by “local elastic compliances” which can be different from the crystal elastic compliances. The strain Hamiltonian which represents the ion-strain interaction is given for any direction of pressure. Experimental parameters are defined, allowing to interpret the effect of the uniaxial stress on the transition between the fundamental vibronic singlet and the three lower vibronic states originating from T1 or T2 states in cubic symmetry. La deformation locale autour du cation est exprimee en fonction des deplacements desions les plus proches voisins. II est montre que cette deformation locale est reliee a la contrainte uniaxiale appliquee par des „constantes d'elasticite locales” qui peuvent etre differentes des constantes d'elasticite du cristal. L'hamiltonien de deformation qui represente I'interaction ion-deformation est donne pour une direction quelconque de la pression. Des parametres experimentaux sont definis permettant d'interpreter I'effet d'une contrainte uniaxiale sur la transition entre un singulet vibronique fondamental et les trois etats vibronique les plus bas provcnant d'etats T1 ou T2 en symetrie cubique.

Study under stress of 3T2 state of the V3+ ion in corundum (α-Al2O3) was performed at 77 K. Absorption spectra are made on 3A2(3T1)3T2 zero-phonon lines and on the 3A2(3T1) 1A1 sharp line. Under uniaxial stress, the degeneracy of vibronic levels is removed: curves show the shifts and splittings of 3A2 3T1 and 3A2 1A1 transitions as a function of the applied pressure. The strain interaction with 3T2 state only is deduced. The stress spectra cannot be quantitatively explained without taking into account a large S15* local elastic compliance. The local deformation around the V3+ ion is similar to this one around the Cr3+ or Co3+ ion. Studying the 3A2 3T2 band by the method of moments a coupling between the V3+ ion and a breathing mode A1 is found. Results of measurements cannot be interpreted by a Jahn-Teller effect with only the pure tetragonal modes. L'etude sous contrainte de l'etat 3T2 de l'ion V3+ dans le corindon (α-Al2O3) a ete effectuee a 77 K. Les mesures d'absorption ont porte sur la raie sans phonon 3A2(3T1) 3T2 et sur la raie fine 3A2(3T1) 1A1. Sous l'influence de contraintes uniaxiales la degenerescence des niveaux vibroniques est levee: differentes courbes montrent le deplacement et les splittings des transitions 3A2 3T2 et 3A2 1A1 en fonction des pressions appliquees: on en deduit l'interaction de la deformation avec 3T2 seul. Les spectres sous contrainte ne peuvent s'expliquer quantitativement que par la presence d'une forte constante d'elasticite locale S15*. La deformation locale autour de l'ion V3+ est similaire a celle qui existe autour des ions Cr3+ ou Co3+. L'etude de la bande 3A2 3T2 par la methode des moments a permis de mettre en evidence le couplage de l'ion dopant avec un mode totalement symetrique A1. Enfin les resultats des mesures ne peuvent ětre interpretes par un effet Jahn-Teller avec seulement des modes purement tetragonaux.

We have used Electron Spin Resonance to characterize the Cr 3+ clusters which grow, during various heat treatments, in a 0.8% Cr 2 O 3 -doped cordierite glass. We found useful to compare the magnetic properties of these clusters to those of powdered MgCr 2 O 4 . In MgCr 2 O 4 the room-temperature E.S.R. spectrum consists of a single exchange-narrowed dipolar line. An approximate value of the exchange field between the two sublattices at T=0 K is H e ∼2×10 6 G, explaining the disappearance of the E.S.R. signal below T N =15 K. Room-temperature E.S.R. results confirm that the Cr 3+ clusters built up during a 100 H-825°C or a 6 H-850°C heating have a MgCr 2x Al 2(1−x) O 4 composition, and precise the x value (x∼0,9). At low temperature these clusters are antiferromagnetic fine grains, with a high anisotropy field (H a ≥10 kG). After a 4 h-875°C+2 h-900°C heating, the Cr 3+ concentration in the clusters is smaller, whereas after 2 h-875°C+10 min-1050°C heating, the Cr 3+ ions are randomly distributed in MgAl 2 O 4 Etude par RPE de la formation d'amas d'ions Cr 3+ au cours de divers traitements thermiques d'un verre de cordierite dope a 0,8% en Cr 2 O 3 . Comparaison des proprietes magnetiques de ces amas a celles de MgCr 2 O 4 en poudre. Confirmation d'une composition MgCr 2x Al 2(1−x) O 4 pour les amas, avec x∼0,9, dont les grains fins formes, antiferromagnetiques, a basse temperature ont un champ d'anisotropie eleve (≥10 kG)

A correlation has been proposed by Urosevic Panic Jovanic, Zekovic and Savic between the lifetimes of Cr 3+ in various environments and the Dq parameter of ligand field theory. We show that these observed lifetimes depend on various factors such as multisite effects, reabsorption, thermal excitation or 2 E 4 T 2 mixing. The correlation between lifetimes and pressure on ruby has to consider these different effects.

Potassium niobium silicate (KNS) glasses xK2OxNb2O5(1−2x)SiO2 with x=0.167; 0.182; 0.200; 0.220 and 0.250 have been subjected to prolonged heat treatments in a wide temperature range above Tg. As a result, glasses exhibiting liquid-type phase separation phenomena have been isolated. Moreover for each glass composition, the temperature zones have been determined to produce transparent, opalescent or opaque materials which have been studied by X-ray diffraction (XRD), small-angle neutron scattering (SANS) and second harmonic generation (SHG) techniques. SANS data unambiguously point at nanostructuring of KNS glasses in the scale of 5–20 nm under appropriate heat treatments near Tg. In contrast to initial KNS glasses, nanostructured glasses exhibit SHG activity. For earliest stages of phase separation SHG-active glasses are characterized by fully amorphous XRD patterns. Further development of phase separation in glasses with increasing of their opalescence leads to diminishing SHG, and subsequently partial crystallization takes place giving opaque materials. Since relative maximum of SHG efficiency corresponds to non-crystalline nanostructured glasses, such new transparent second-order non-linear media may be of both scientific and practical interest. With regard to non-crystalline structure of nano-inhomogeneities, SHG mechanism in the glasses is supposed to be due to a combination of third-order non-linearity with a spatial modulation of linear polarizability.

Lead germanate glasses of the xPbO(1 - x)GeO2 compositions with x ranging from 0.200 to 0.625 have been synthesised and their crystallisation behaviour and vibrational properties studied by differential thermal analysis (DTA) and Raman spectroscopy. Raman spectra of the Pb5Ge3O11 ceramics also have been measured and compared to lead germanate glass spectra and literature data on beta -PbO, Ge atoms in low lead glasses are supposed to be surrounded by four to six oxygen atoms, while the high-lead glass (x = 0.625) corresponding to stoichiometry of the Pb5Ge3O11 ferroelectrics contains predominantly fourfold coordinated germanium. Structural resemblence of high-lead germanate glasses to the Pb5Ge3O11 crystal is proposed rather than to beta -PbO. The 'boson' peak range in the spectra of lead germanate glasses is discussed taking into account the similarities of the spectra of glassy and crystalline Pb5Ge3O11. (C) 2001 Elsevier Science B.V. All rights reserved.

Glasses at early stages of phase separation, while remaining amorphous, are shown to possess or not to possess second-order optical nonlinearity (SON) depending on specific features of their short-range/medium range order and nanoinhomogeneous structure characterized with IR and Raman spectroscopy, X-ray diffraction, small-angle X-ray and neutron scattering and second harmonic generation (SHG). In the present work it is demonstrated by the example of potassium titanium phosphate glasses of composition near KTiOPO4 stoichiometry. Formation of nanoinhomogeneities, structure of which is similar to the structural motif of some non-linear optical (NLO) crystal, favors SON. Heat treatment of such glasses at temperatures near glass-transition temperature Tg stimulates remarkable SON enhancement keeping transparency and amorphous state. While temperature is increasing SHG grows up to values, comparable with those of NLO crystals with rise of Bragg reflections in the X-ray diffraction pattern of the glass and decrease of its transparency. Revealing correlations between structural peculiarities of glasses and their SON argues preference of description of short- and medium-range order in glasses with composition close to boundaries of glass-forming regions from the position of quasi-crystallite models.

Polarized Raman spectra of lanthanum borogermanate (LBG) glasses of different compositions, as well as of LBG glasses obtained by the hot-extrusion technique, have been obtained. In addition, the crystallization behaviour of LBG glasses of different compositions has been studied by differential thermal analysis and X-ray diffraction. Both the Raman spectra profile and the crystallization behaviour depend on the lanthanum–boron ratio. Polarized Raman spectra of hot-extruded samples show differences from the unextruded samples. For the first time, structural changes in glasses under hot-extrusion treatment were observed by vibrational spectroscopy.