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Glasses were prepared in the pseudo-binary system (1 − x)AgPO3–xWO3 (0≤ × ≤ 0.6 mol%). The structural evolution of the vitreous network was studied as a function of composition by thermal analysis, Fourier Transform Infrared spectroscopy (FTIR), Raman scattering, high resolution 31P solid state NMR and XANES at the W-L1 absorption edge. For compositions with x ranging from 0 to 0.5 a pronounced increase in the glass transition temperature is observed, suggesting a significant increase in the glass network connectivity. At the same time Raman spectra indicate that tungsten atoms are linked to non-bridging oxygen atoms (W–O- or W=O bonded species) whereas the 31P MAS-NMR spectra indicate the successive formation of new P–O–W linkages. The formation of some anionic tungsten sites (if these are revealed by the presence of W–O terminal bonds) implies an increase in the average degree of polymerization of the phosphate network, which is consistent with the compositional evolution of the 31P MAS-NMR spectra at low x values. For higher x-values, the Raman spectra indicate the presence of W–O–W linkages. W-L1 XANES data indicate that at least 90% of tungsten atoms are octahedrally coordinated.

Vitreous samples were prepared in the binary system NaPO 3 –MoO 3 and their characteristic temperatures were determined by Differential Scanning Calorimetry. Glasses with high amounts of MoO 3 (>45 mol%) exhibit an intense crystallization peak and the composition 50 NaPO 3 –50 MoO 3 was chosen for the crystallization study. Two different methods based on thermal analyzes were used to determine the mechanism of crystallization in these molybdenum–phosphate glasses. In the first procedure, thermal analyses by DTA were performed on samples with different grain sizes and the crystallization tendency deduced in function of superficial area. The second method used the classical non-isothermal crystallization study: DSC measurements were performed under several heating rates to access activation energy for crystallization and Avrami parameter n . Critical cooling rate was calculated and compared with experimental data obtained from DTA analysis upon cooling.

To study the influence of Ga addition on photoinduced effect, GaGeS glasses with constant atomic ratio S/Ge = 2.6 have been prepared. Using Raman spectroscopy, we have reported the effect of Ga on the structural behavior of these glasses. An increase of the glass transition temperature Tg, the linear refractive index and the density have been observed with increasing gallium content. The photoinduced phenomena have been examined through the influence of time exposure and power density, when exposed to above light bandgap (3.53 eV). The correlation between photoinduced phenomena and Ga content in such glasses are shown hereby.

Boehmite-GPTS (GPTS-glycidoxypropyltrimethoxysilane) hybrids (BGS) have been prepared by the sol-gel methodology. Spectroscopic properties and structural features have been evaluated from the initial sols to xerogels as a function of composition. Eu 3+ -containing BGS samples were also prepared, and the Eu 3+ 5 DO state emission quantum efficiency was observed to depend on the boehmite-siloxane interactions. Boehmite-siloxane heterocondensation was inferred from vibrational spectroscopy and 13 C, 29 Si, and 27 Al nuclear magnetic resonance results. Unreacted epoxi groups could be identified in the final material being an important characteristic for the future applications. Good optical quality and mechanical properties lead to the preparation of thin films deposited on glass substrates by dip and spin-coating. Refractive index could be tuned by the relative boehmite and GPTS content. Waveguide properties have also been studied by m-lines spectroscopy and guided modes together with attenuation measurements suggest potential application of the prepared films in integrated optics.

The spray-pyrolysis (SP) synthesis technique has been employed to obtain SiO 2 :Eu 3+ and γ-AlOOH:Eu 3+ . It was possible to obtain sub-micrometric spherical particles of SiO 2 with luminescent Eu 3+ ions bonded to the silica surface or embedded in amorphous silica beads, by controlling the synthesis and annealing process. Boehmite γ-AlOOH doped with Eu 3+ nanoparticles were synthesized by SP at moderate temperature (200 °C) with Eu 3+ ions bonded to the surface hydroxyls of the boehmite nanocrystals. Luminescent nano-composites were obtained by controlled reaction of γ-AlOOH:Eu 3+ nanocrystals with ASN (asparagine). In these nano-composites, the Eu 3+ are held at the surface of the boehmite nanocrystals and partially shielded from interactions with additional luminescence quenchers (hydroxyl groups, water molecules).

Planar waveguides were prepared by Ag + /K + ↔ Na + ion-exchange on Er +3 -doped GeO 2 –ZnO–Na 2 O–Li 2 O glasses obtained by a melting–casting method. Optical parameters of the waveguides were measured at 543.5, 632.8, and 1550 nm by m-line technique as a function of the Ag + ion-exchange time. The optimized planar waveguides show an effective diffusion depth ( d ) of 2.95 μm and well confined propagating TE 0 and TM 0 modes at 1550 nm. Spectroscopic properties as photoluminescence emission and emission decay time were evaluated for the erbium-doped planar waveguide, indicating that Ag + ↔ Na + ion-exchange enhance the photoluminescence emissions in the green and infrared regions from erbium ions. The glass system studied is promising to be applied as optical amplifiers in the C-telecom band. Green emission sensitized by Ag + was also observed.

Er3+-doped glass-ceramic SiO2–ZrO2 optical planar waveguides were prepared by the sol–gel route using different SiO2:ZrO2 molar ratios (90:10, 85:15, 80:20 and 75:25). Multilayered films were deposited onto Si(1 0 0) substrates by the dip-coating technique. Structural characterization was performed using vibrational spectroscopy and X-ray diffraction. Some optical properties, densification and surface morphology of these films were investigated as a function of the SiO2:ZrO2 ratio, annealing temperature and time. Optical properties such as refractive index, number of propagating modes and attenuation coefficient were measured at 632.8, 543.5 and 1550 nm, by the prism coupling technique. Uniform surface morphology with roughness less than 0.5 nm. Low losses, less than 0.9 dB/cm at 612.8 nm in the TE0 mode, were measured for the planar waveguides containing up to 25 mol% zirconium oxide. Luminescence of Er3+ in the near infrared was observed for the active nanocomposite.

Energy-transfer excited upconversion luminescence in Ho 3+ /Yb 3+ - and Tb 3+ /Yb 3+ -codoped PbGeO 3 –PbF 2 –CdF 2 glass and glass–ceramic under infrared excitation is investigated. In Ho 3+ /Yb 3+ -codoped samples, green (545 nm), red (652 nm), and near-infrared (754 nm) upconversion emission corresponding to the 5 S 2 ( 5 F 4 ) → 5 I 8 , 5 F 5 → 5 I 8 , and 5 S 2 ( 5 F 4 ) → 5 I 7 transitions, respectively, was observed. Blue (490 nm) emission assigned to the 5 F 2,3 → 5 I 8 transition was also detected. In the Tb 3+ /Yb 3+ -codoped system, bright UV–visible emission around 384, 415, 438, 473–490, 545, 587, and 623 nm, identified as due to the 5 D 3 ( 5 G 6 ) → 7 F J ( J = 6, 5, 4) and 5 D 4 → 7 F J ( J = 6, 5, 4, 3) transitions, was measured. The comparison of the upconversion process in glass ceramic and its glassy precursor revealed that the former samples present much higher upconversion efficiencies. The dependence of the upconversion emission upon pump power, and doping contents was also examined. The results indicated that successive energy-transfer between ytterbium and holmium ions and cooperative energy-transfer between ytterbium and terbium ions followed by excited-state absorption are the dominant upconversion excitation mechanisms herein involved. The viability of using the samples for three-dimensional solid-state color displays is also discussed.

Glasses in the binary system (100 x)SbPO4–xWO3 (20 6 x 6 60, x in mol%) have been prepared and characterized. Differential thermal analysis (DTA) shows that the glass transition temperature, Tg, increases from 412 � C, for samples containing 20 mol% of WO3, to 481 � C observed for glass containing 60 mol%. Sample containing 40 mol% in WO3 were observed to be the most stable against devitrification. The structural organization of the glasses has been studied by using Fourier transform infra-red (FTIR), Raman, 31 P Magic angle spinning (MAS) and spin echo nuclear magnetic resonance (NMR) spectroscopies. Results suggest two distinct networks comprising the glass structure, one with high SbPO4 content and the other characteristic of the highest WO3 content samples. The glasses present photochromic properties. Colour changes are observed for samples after exposure to ultraviolet or visible laser light. XANES, at L1 absorption edge of tungsten, suggests partial reduction from W 6+ to W 5+ species during the laser irradiation. The photochromic effects and the colour changes, promoted by laser excitation, are reversible and easily removed by heat for during 1 h at 150 � C. Subsequent ‘write/erase’ cycles can be done without degradation of the glasses. � 2007 Elsevier B.V. All rights reserved. PACS: 61.43.Fs; 61.66.Fn; 82.47.Jk

In this paper we investigate the energy transfer processes in Tm 3+ /Er 3+ doped telluride glass pumped at the commercial diode laser pump wavelength ∼800 nm. Tailoring the rare-earths content in the glass matrix, seven main energy transfer channels within the doping range considered were identified. A 6-fold enhancement of the Er 3+ visible frequency upconversion fluorescence at ∼660 nm is observed due to the inclusion of Tm 3+ ions. This is evidence of the relevant contribution of the route Er 1 ( 4 I 11/2 ) + Er 2 ( 4 I 13/2 ) → Er 1 ( 4 I 15/2 ) + Er 2 ( 4 F 9/2 ) to the process. Energy migration among pumped 4 I 9/2 level reducing the efficiency of the upconversion emission rate ( 3 H 11/2 , 4 S 3/2 , and 4 F 9/2 ) is observed for Er 3+ above 1.5 wt%. The rate equations regarding the observed energy transfer routes are determined and a qualitative analysis of the observed processes is reported.

Sodium phosphoniobate glasses with the composition (mol%) 75NaPO 3 -25Nb 2 O 5 and containing 2 mol% Yb 3+ and x mol% Er 3+ (0.01 ≤ x ≤ 2) were prepared using the conventional melting/casting process. Er 3+ emission at 1.5 μm and infrared-to-visible upconversion emission, upon excitation at 976 nm, are evaluated as a function of the Er 3+ concentration. For the lowest Er 3+ content, 1.5 μm emission quantum efficiency was 90%. Increasing the Er 3+ concentration up to 2 mol%, the emission quantum efficiency was observed to decrease to 37% due to concentration quenching. The green and red upconversion emission intensity ratio was studied as a function of Yb 3+ co-doping and the Er 3+ Er 3+ energy transfer processes.

Changes occurring in absorption coefficients when glasses in the SbPO 4 –WO 3 binary system were irradiated by light, at the edge of the absorption band, were measured in real time. These glasses present good thermal and optical properties and photoinduced changes in the absorption coefficients are reversible by heat treatment around 150 °C. Subsequent recording/erasing cycles could be made without sample degradation. The sensitivity of the induced optical changes was studied for different wavelengths, light powers and energy of light dose exposures, and for different compositions of the glasses. The changes in the absorption coefficients of the glass samples were accompanied by a color change from yellow to blue, and were also characterized by visible spectroscopy. The color changes occurred through the entire volume of the glass (∼2 mm thickness) for the Ar-ion laser lines at the edge of the absorption band.

X-ray absorption spectroscopy was used to study the local environment of tungsten atoms in NaPO 3 –BaF 2 –WO 3 glasses and the results were compared with crystalline references Na 2 WO 4 and WO 3 . XANES measurements at the W-L 1 edge allowed to determine a distorted octahedral environment of tungsten atoms in these glasses similar to the local order of tungsten in monoclinic WO 3 . Extended X-ray absorption fine structure (EXAFS) has been used as a local probe to monitor the effect of WO 3 concentration on the tungsten environment. Based on an analysis of the EXAFS data, we proposed a three-shell model of oxygen atoms around tungsten as in monoclinic WO 3 . With increasing WO 3 concentration, it was found that R 2 decreases from 1.96 to 1.92 A whereas R 3 increases from 2.07 to 2.12 A.

Two series of glasses with composition (mol%) 70PbGeO3–15PbF2–15CdF2, the first one with different Tm3+ contents (0.2, 0.4, 0.6 and 0.8 mol%) and the second one with 0.2 mol% Tm3+ and different Ho3+ contents (0.1, 0.5, 1.0 and 1.5 mol%), have been prepared and some of their spectroscopic properties studied. Absorption in the visible-near infrared and emission in the near infrared region of the electromagnetic spectrum have been obtained. Concerning emission at the 1.4–1.5 μm region, optimization of rare earth ions content leads to 0.2 and 0.5 mol% for Tm3+ and Ho3+, respectively. We discuss potential application of these compositions.

Monodisperse latex spheres were obtained by a surfactant free styrene polymerization method and used to obtain colloidal crystals by controlled centrifugation settling. Silica inverse opals were then prepared by using the colloidal crystals as templates and TEOS/ethanol solution. The inverse opals were infiltrated with Rhodamine 6G and laserlike emission was observed at 590 nm under 532 nm pump wavelength. The data show line narrowing of the dye fluorescence and a laser threshold of ∼0.1 mJ/pulse. Local-field effects and light scattering due to structural defects are the main mechanisms contributing to generation of the laser-action observed.

A new class of tungstate fluorophosphate glasses was identified in the NaPO 3 –BaF 2 –WO 3 ternary system. The variation of several physical properties was determined with respect to chemical composition. Characteristic temperatures, density and refractive index increase as tungsten oxide content increases. The optical transmission range and specially the energy bandgap depend of the WO 3 amount. No crystallization could be observed for the most WO 3 concentrated vitreous samples (⩾20% molar). Color and optical properties of the glasses depend of the melting time because of the presence of reduced tungsten species like W 5+ and W 4+ . In addition, photodarkening is observed in tungsten rich glass samples under UV laser illumination and this phenomenon can be reversible by heat treatment near the glass transition temperature.

70SiO2–30HfO2 mol% planar waveguides, doped with Er3+ with concentrations ranging from 0.3 to 2 mol% were prepared by sol–gel route, using dip-coating deposition on vitreous-SiO2 substrates. Infrared-to-visible upconversion emission, upon excitation at 980 nm, has been observed for all the samples. The upconversion results in green, red and blue emissions. The investigation of the upconversion dynamic as a function of the Er3+ concentration and excitation power, show that processes such as excited state absorption and energy transfer upconversion are effective.

Irreversible photoexpansion effect has been observed in amorphous Ga10Ge25S65 glasses when its surface was exposed to light with energy greater than the band gap, 3.52 eV. A volume change of about 5% was reached in bulk samples by controlling illumination time and the laser power density. To understand the atomic scale processes of the photoexpansion effect, extended X-ray absorption fine structure (EXAFS) spectroscopy has been used as a local probe of the germanium environment in the glass samples before and after illumination. Modifications are observed in the average coordination shell around Ge atoms in the illuminated sample compared to the non-illuminated one. For the non-illuminated sample, the Ge coordination shell is described by a distorted tetrahedron of sulfur atoms at around 2.20 A. After illumination, the EXAFS signal can be explained by introducing an additional contribution to this average environment. Based on an analysis of the EXAFS data we proposed a two-shell model of 0.5 oxygen atoms at 2.01 A and 3.6 sulfur atoms at a 2.20 A. The existence of Ge–O bonds in the glass after illumination was confirmed by infrared measurements.

Glass formation has been investigated in binary systems based on antimony oxide as the main glass former: (100 - x)Sb 2 O 3-x WO 3 , (5 < x < 65), (100 - x)Sb 2 O 3-x SbPO 4 , (5 < x < 80) and (100 - x)Sb 2 O 3-x [Sb(PO 3 ) 3 ] n , (10 < x < 40). Ternary systems derived from the Sb 2 O 3 -WO 3 binary glass have also been studied: Sb 2 O 3 -WO 3 -BaF 2 , Sb 2 O 3 -WO 3 -NaF and Sb 2 O 3 -WO 3 -[Sb(PO 3 ) 3 ] n . Glass transition temperature ranges from 280°C to 380°C. It increases as the concentration in tungsten oxide or antimony phosphate increases. Refractive index is larger than 2. Tungsten-containing glasses are yellow in transmission and turn green at the largest WO 3 content. Optical transmission and temperatures of glass transition, T g , onset of the crystallization, T x , and maximum of crystallization, T p , have been measured using differential scanning calorimetry (DSC). These glasses have potential photonic applications.

We report photoinduced photo-darkening in SbPO 4 –WO 3 glass by exposure to 532 nm light with a power density of 143 mW/cm 2 . The time of exposure was varied between 0 and 256 min following which visible photo-darkening, peaking at 850 nm was observed. Spectrophotometer measurement of absorption was performed for both treated and untreated regions of the sample. Time exposure to below band-gap light results in a single exponent Gaussian absorption function over an exceptionally wide range of wavelengths (500 nm–1600 nm), with a 1/ e width of 647.5 nm. Kramers–Kronig transform of the change in the absorption indicates a negative local change in the refractive index. The dispersed refractive index change at 1550 nm, ∆ n , is calculated to be ∼−5 × 10 − 8 . The peak absorption increases with time of exposure and the photo-darkening remains irreversible at room temperature.

The understanding of the kinetics of devitrification of a glass is important for anticipating its stability in a particular purpose, such as fiber-drawing processes. The crystallization kinetics of (BaF 2 ) 16 (ZnF 2 ) 20 (SrF 2 ) 20 (NaF) 2 (GaF 3 ) 5 (InF 3 ) 36 (GdF 3 ) 1 glass prepared by quenching were studied by differential scanning calorimetry (DSC). Avrami's exponent ( n ) obtained by a non-isothermal method was 4.3 for a solid and 2.4 for a powdered sample. According to the classical interpretation of n , these magnitudes correspond to an interface-controlled crystal growth and a diffusion-controlled crystal growth, respectively. The activation energies for crystallization ( E ) was 62±1 kJ/mol for solid glass and 245±2 kJ/mol for powdered glass. These results are discussed in terms of glass particle size.

Alkali niobium tellurite glasses have been prepared and some of their properties measured by differential scanning calorimetry and Raman scattering. The vitreous domain was established in the pseudo ternary phases diagram for the system TeO2–Nb2O5–(0.5K2O–0.5Li2O). Raman scattering shows that for samples in the TeO2 rich part of the phase diagram the vitreous structure is composed essentially of (TeO4) units connected by the vertices, as in the α-TeO2 crystal. The addition of alkali and niobium oxides causes depolymerization to occur with structures composed essentially of (TeO3) and (NbO6) units. Samples with the composition (mol%) 80TeO2–10Nb2O5–5K2O–5Li2O, stable against crystallization, were prepared containing up to 10% mol Nd3+. The addition of this oxide increases the rigidity of the vitreous network shifting characteristic temperatures to higher temperatures. For the 10% Nd3+ sample amorphous phase separation is assumed to exist from the observation of two glass transition temperatures. Spectroscopic properties such as Judd–Ofelt Ωλ intensity parameters, radiative emission probabilities, and induced emission cross sections were calculated. From these results and also from the emission quenching observed as a function of Nd3+ concentration, we suggest that these glasses could be utilized in optical amplifying devices.

Glasses with composition 60PbGeO 3 –10PbF 2 –30CdF 2 (mol%) have been obtained in the bulk form with a high stability against crystallization. After doping them with 0.5 mol% of Er 3+ or Eu 3+ and appropriate heat treatment transparent glass ceramics could be obtained. Electronic spectroscopy, X-ray diffraction and transmission electron microscopy measurements have been made. β-PbF 2 : Er 3+ /Eu 3+ single crystals, 5–10 nm in size, are detected in the otherwise transparent composite medium, the size of the particles and absence of clustering allowing for the increased transparency of the final materials.

Crystallization of binary InF3MF2 and GaF3MF2 (where M  Ba, Sr and Ca) glasses was studied. Characteristic temperatures and kinetic parameters E (activation energy) and n (Avrami exponent) were obtained. Stability against devitrification is discussed in terms of the above cited parameters and also of some others parameters proposed in literature. Optical properties (IR and upconversion emissions) are reported in different crystallized samples containing Nd3+. The main observation is that up conversion emission presents an enhanced sensibility to crystallization when compared to conventional emission.

Glasses with compositions (1 − x )ZrF 4 − x LnF 3 , 0.2 ≤ x ≤ 0.4 and Ln = La or La, Eu have been synthesized and investigated using differential scanning calorimetry, X-ray diffraction, Raman scattering and Eu 3+ optical spectroscopy. Single-phase polycrystalline lanthanum fluorozirconates with ratio equal to 1, 2 and 3 have been investigated using the same techniques for comparison. The crystalline phases LnZrF 7 , LnZr 2 F 11 , LT-LnZr 3 F 15 (orthorhombic) and HT-LnZr 3 F 15 (trigonal) have been characterized in the recrystallized glasses and in samples spontaneously crystallized from the melt. Another phase has also been observed but remains undefined. The Raman scattering spectra of the vitreous samples are related to the vibration modes of [ZrF 6 ] isolated octahedra, and of [ZrF 7 ] and [ZrF 8 ] structural units with bridging fluorine ions. The Eu 3+ fluorescence data are related to a predominant local environment of the lanthanide ions in the glasses similar to that of the lanthanide in LnZrF 7 .

In this work, tantalum alkali-phosphate glasses were prepared in the ternary system 0.9[(100 − x)NaPO3 − xTa2O5] − 0.1K2O with x varying from 0 to 20. The thermal properties as a function of Ta2O5 content were investigated by Differential Scanning Calorimetry and Differential Thermal Analysis in order to understand the influence of composition on glass transition temperatures and crystallization behaviors. Increasing Ta2O5 content leads to a drastic and linear increase of glass transition temperatures in agreement with the increasing viscosity of the melt observed during the synthesis. In addition, Ta2O5 incorporation results in high thermal stability against devitrification, suggesting the intermediary role of tantalum in the alkali-phosphate network. Comparison of powder and bulk thermal analyzes also pointed out a dominant surface crystallization mechanism for these glass samples. UV–visible absorption measurements proved the high visible transparency of the samples and a decrease of the optical bandgap energy with tantalum addition, suggesting an increase of the glass network covalency. Finally, vibrational spectroscopies performed by FTIR and Raman support the hypothesis of tantalum insertion inside the phosphate tetrahedral network with TaO6 units cross-linking the metaphosphate and pyrophosphate units. Thus, the intermediary behavior of tantalum increases the network connectivity with higher rigidity, glass transition temperatures and thermal stabilities against devitrification.