Differential scanning calorimetry, x-ray diffraction and F-19 nuclear magnetic resonance investigations of the crystallization of InF3-based glasses

Results of differential scanning calometry (DSC), x-ray diffraction (XRD), and F-19 nuclear magnetic resonance (NMR) of InF3-based glasses, treated at different temperatures, ranging from glass transition temperature (T-g) to crystallization temperature (T-c), are reported. The main features of the experimental results are as follows. DSC analysis emphasizes several steps in the crystallization process. Heat treatment at temperatures above T-g enhances the nucleation of the first growing phases but has little influence on the following ones. XRD results show that several crystalline phases are formed, with solid state transitions when heated above 680 K, the F-19 NMR results show that the spin-lattice relaxation, for the glass samples heat treated above 638 K, is described by two time constants. For samples treated below this temperature a single time constant T-1 was observed. Measurements of the F-19 spin-lattice relaxation time (T-1), as a function of temperature,made possible the identification of the mobile fluoride ions. The activation energy, for the ionic motion, in samples treated at crystallization temperature was found to be 0.18 +/- 0.01 eV. (C) 1998 American Institute of Physics.

New glasses in the system InF3-BaF2-ErPO4

New glasses have been obtained in the system InF3-BaF2-ErPO4. Glass compositions with up to 30% mol Er3+ were shown to exist and characterized by thermal analysis, x-ray: diffraction, IR absorption and electronic spectroscopy. The systems with high Er3+ content were studied recording IR and visible emission spectral characteristics. A specially elaborated technique allowed the preparation of a high purity phosphate precursor ErPO4. X-ray identification of the crystalline phases appearing during thermal treatment have been carried out and parameters of a mixed fluoride Ba4In3-nErnF17 calculated.

Nonresonant third-order nonlinearity of antimony glasses at telecom wavelengths

We report measurements of the nonresonant nonlinear refractive index n(2) in antimony glasses at telecom wavelengths. The measurements were performed using the Z-scan technique with a 130 fs pulsed laser operating at five wavelengths in the range of 1400-1600 nm. Values of n(2)approximate to 10(-15) cm(2)/W were measured and a negligible two-photon absorption coefficient (< 0.003 cm/GW) was estimated for all glasses compositions. The samples present a good figure of merit for ultrafast all-optical switching. (c) 2006 American Institute of Physics.

Thermo-optical characterization of tellurite glasses by thermal lens, thermal relaxation calorimetry and interferometric methods

In this work the thermal lens, thermal relaxation calorimetry and interferometric methods are applied to investigate the thermo-optical properties of tellurite glasses (in mol%: 80TeO(2)-20 Li2O(TeLi), 80TeO(2)-15Li(2)O-5TiO(2) (TeLiTi-5) and 80TeO(2)-10Li(2)O-10TiO(2) (TeLiTi-10)). Thermal diffusivity, thermal conductivity, specific heat and the temperature coefficients of refractive index, optical path length, thermal expansion and electronic polarizability were determined. The use of three independent methods was useful for a complete characterization of the studied tellurite glasses. In addition, our results showed that the thermal expansion coefficient and the temperature coefficient of the optical path length (dS/dT) were significantly modified with the introduction of titanium, which may be relevant for the application of these glasses in the photonic area. (c) 2006 Elsevier B.V. All rights reserved.

Characterization of tin oxide based sol-gel coatings on borosilicate glasses by X-ray reflectivity

The X-ray reflectivity technique was applied in the study of tin oxide films deposited by sol-gel dip-coating on borosilicate glasses. The influence of the withdrawal speed and temperature of thermal treatment on the film structure was analyzed. We have compared the thermal evolution of the density and the shrinkage of the films with these properties measured for the monolithic xerogel by helium picnometry and thermomechanical analysis. In agreement with the Landau-Levich model, the layer thickness increases by increasing the withdrawal speed. Nevertheless, it decreases with the increase of the thermal treatment temperature, due to the densification process. The values of apparent density are smaller than the skeletal density, which shows that the films are porous. The comparison between the film and the monolith indicates that shrinkage during firing is anisotropic, occurring essentially perpendicular to the coating surface.

Antimony oxide based glasses

Glass formation has been investigated in binary systems based on antimony oxide as the main glass former: (100-x)Sb2O3-xWO3, (5 < x < 65), (100 - x)Sb2O3-xSbPO(4), (5 < x < 80) and (100 - x)Sb2O3-x[Sb(PO3)(3)](n), (10 < x < 40). Ternary systems derived from the Sb2O3-WO3 binary glass have also been studied: Sb2O3-WO3-BaF2 Sb2O3-WO3-NaF and Sb2O3-WO3-[Sb(PO3)(3)](n). Glass transition temperature ranges from 280 degreesC to 380 degreesC. 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 WO3 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. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Spectroscopic properties of Yb3+ doped PbO-Bi2O3-Ga2O3 glasses for IR laser applications

PbO-Bi2O3-Ga2O3 glasses doped with different concentrations of Yb3+ are presented. The spectroscopic properties and laser parameters are calculated and a comparison between different results obtained when calculating the Yb3+ emission cross-section with the reciprocity method and with the Fuchtbauer-Ladenburg formula is presented. The behavior of the near-infrared luminescence is described theoretically by a rate equation and compared with the experimental results. This host doped with Yb3+ is a promising material for laser action at 1019 nm, with properties similar to other known glasses used as active laser media; the emission cross-section of 1.1 x 10(-20) cm(2), the high absorption cross-section (of 2.0 x 10(-20) cm(2)) and a minimum pump intensity of 2.4 kW/cm(2) are interesting properties for short pulse generation. (C) 2005 Elsevier B.V. All rights reserved.

Efficient plasmonic coupling between Er3+:(Ag/Au) in tellurite glasses

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Er3+-doped germanate glasses for active waveguides prepared by Ag+/K+ <-> Na+ ion-exchange

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Tungstate fluorophosphate glasses as optical limiters

Nonlinear absorption measurements were performed on fluorophosphate glasses with high concentrations of tungsten oxide. Large two-photon absorption coefficients, alpha(2), were determined at 660 nm using nanosecond laser pulses. It was observed that alpha(2) increases for increasing tungsten oxide concentrations and, hence, the optical limiting performance of this glass composition can be controlled. (C) 2002 American Institute of Physics.

Photoexpansion and photorefraction in oxysulphide glasses

Oxysulphide glasses have been prepared in the pseudo binary system GeS(2.6)-Ga(2)O(3). The effect of addition of gallium oxide has been evaluated in term of thermal and optical properties. Structural behavior has been studied using Raman spectroscopy. Samples have been exposed above band gap energy (3.52 eV) varying power density and exposure time. Giant photoexpansion and photorefraction is obtained for samples containing 20% of Ga(2)O(3). (C) 2009 Elsevier B.V. All rights reserved.

Effect of the ytterbium concentration on the upconversion luminescence of Yb3+/Er3+ co-doped PbO-GeO2-Ga2O3 glasses

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Er(3+) doped phosphoniobate glasses and planar waveguides: structural and optical properties

Phosphoniobate glasses with composition (mol%) (100-x) NaPO(3)-xNb(2)O(5) ( x varying from 11 to 33) were prepared and characterized by means of thermal analysis, Fourier transform infrared spectroscopy, Raman scattering and (31)P nuclear magnetic resonance. The addition of Nb(2)O(5) to the polyphosphate base glass leads to depolymerization of the metaphosphate structure. Different colors were observed and assigned as indicating the presence of Nb(4+) ions, as confirmed by electron paramagnetic resonance measurements. The color was observed to depend on the glass composition and melting temperature as well. Er(3+) containing samples were also prepared. Strong emission in the 1550 nm region was observed. The Er(3+4)I(15/2) emission quantum efficiency was observed to be 90% and the quenching concentration was observed to be 1.1 mol%( 1.45 x 10(20) ions cm(-3)). Planar waveguides were prepared by Na(+)-K(+)-Ag(+) ion exchange with Er(3+) containing samples. Optical parameters of the waveguides were measured at 632.8, 543.5 and 1550 nm by the prism coupling technique as a function of the ion exchange time and Ag(+) concentration. The optimized planar waveguides show a diffusion depth of 5.9 mu m and one propagating mode at 1550 nm.

Structural and spectroscopic study of oxyfluoride glasses and glass-ceramics using europium ion as a structural probe

Transparent oxyfluoride glasses and beta-PbF(2) nanocrystals containing glass-ceramics were prepared with varying Eu(3+) content (0.3, 0.4, 0.5 and 0.6%). The effect of Eu(3+) content on the preparation of glass-ceramics was investigated. From differential scanning calorimetry, the T(x)-T(g)(T(x)-temperature of the onset of crystallization; T(g)-glass transition temperature) parameter for glasses has shown slight variation, and an exothermic peak near T(g) called the ceramization temperature (T(c)) has been observed. Heat treatments were performed at this temperature to obtain transparent glass-ceramics containing beta-PbF(2) nanocrystals, identified by x-ray diffraction. Heat treatments for different periods of time were performed and were observed to be very important in the control of the crystal size and of the crystallization rate. Based upon the absorption spectra, the scattering level due to the presence of beta-PbF(2) nanocrystals in the glass-ceramics was observed to be similar to that for the mother glasses. Detailed analysis of emission spectra and decay time measurements led to the identification of Eu(3+) ions as the beta-PbF(2) crystalline phase. Excitation spectra at 70 K show the interaction of Eu(3+) ions with the fluorogermanate network.

Tm and Tm-Tb-doped germanate glasses for S-band amplifiers

The mechanism involved in the Tm(3+)((3)F(4)) -> Tb(3+)((7)F(0,1,2)) energy transfer as a function of the Tb concentration was investigated in Tm:Tb-doped germanate (GLKZ) glass. The experimental transfer rate was determined from the best fit of the (3)F(4) luminescence decay due to the Tm -> Tb energy transfer using the Burshtein model. The result showed that the 1700 nm emission from (3)F(4) can be completely quenched by 0.8 mol% of Tb(3+). As a consequence, the (7)F(3) state of Tb(3+) interacts with the (3)H(4) upper excited state of TM(3+) slighting decreasing its population. The effective amplification coefficient beta(cm(-1)) that depends on the population density difference Delta n = n((3)H(4))-n((3)F(4)) involved in the optical transition of Tm(3+) (S-band) was calculated by solving the rate equations of the system for continuous pumping with laser at 792 nm, using the Runge-Kutta numerical method including terms of fourth order. The population density inversion An as a function of Tb(3+) concentration was calculated by computational simulation for three pumping intensities, 0.2, 2.2 and 4.4 kWcm(-2). These calculations were performed using the experimental Tm -> Tb transfer rates and the optical constants of the Tm (0.1 mol%) system. It was demonstrated that 0.2 mol% of Tb(3+) propitiates best population density inversion of Tin(3+) maximizing the amplification coefficient of Tm-doped (0.1 mol%) GLKZ glass when operating as laser intensity amplification at 1.47 mu m. (C) 2007 Elsevier B.V. All rights reserved.