Spectroscopic Properties and Thermal Stability of Er3+-Doped Germanotellurite Glasses for Broadband Fiber Amplifiers

The thermal stability and spectroscopic properties of Er₂O₃-doped TeO₂–GeO₂–ZnO–Na₂O–Y₂O₃ glasses for 1.5 μm fiber amplifiers were investigated. The thermal stability of the 75TeO₂·20ZnO· 5Na₂O glass was improved by introducing GeO₂ and Y₂O₃. The radiative transition and the nonradiative transition have a dominant influence on the ⁴I_13/2 level lifetime of Er³⁺ in high- and low-GeO₂ regions, respectively. Adding Y₂O₃ increases the ⁴I_13/2 level lifetime of Er³⁺ significantly. The Judd–Ofelt (J-O) parameter Ω₆ shows a strong correlation with the 1.5 μm emission bandwidth; and the larger the Ω₆, the wider the bandwidth.     

Mixed-Alkali Effect on Rayleigh Scattering in K2O–Na2O–MgO–SiO2 Glasses

The Rayleigh scattering of the mixed-alkali glass system K₂O–Na₂O–MgO–SiO₂ (KNMS) was investigated, both experimentally and theoretically. The lowest Rayleigh scattering coefficient (38% of that for pure SiO₂ glass) was obtained when the glass composition was 22K₂O–8Na₂O–10MgO–60SiO₂ (in mol%). These values are equal to or less than the minimum values reported for the ternary sodium silicate glass Na₂O–MgO–SiO₂. The Rayleigh scattering caused by concentration fluctuation was believed to have been reduced greatly in this KNMS glass, because the mobility of the alkali-metal ions was reduced by the mixed-alkali effect.     

Vibrational Spectra of Water- and Ammonium-Chloride-Related Residues and Upconversion Fluorescence of Er3+ in ZnCl2-Based Glasses

Chloride glasses of the ZnCl₂ and 20KCl-20BaCl₂-60ZnCl₂-0.5ErCl₃ systems were prepared using NH₄Cl as a dehydrating and chlorinating agent, under the melt-quenching method. Water- and ammonium-chloride-related residues in ZnCl₂ glasses were investigated by infrared and near-infrared absorption spectra. Water, Zn—OH, ClO, ClO₂⁻, Zn²⁺-coordinated water, free NH₃, NH₄⁺, and Zn²⁺-coordinated NH₃ were identified in ZnCl₂ glasses. 20KCl-20BaCl₂-60ZnCl₂-0.5ErCl₃ glasses prepared by melting at 500°C for 20 min, under reduced pressure, contained the smallest amounts of water, Zn—OH, and Zn²⁺-coordinated NH₃ and showed strong Er³⁺ upconversion fluorescence.     

Incorporation of Er3+ into BaTiO3

The incorporation of Er³⁺ into BaTiO₃ ceramics was investigated on samples containing 0.25, 0.5, 1, 2, 8, and 10 at.% of dopant, after sintering at 1350–1550°C in air. For Er³⁺ concentrations ≤1 at.%, dense and large-grained ceramics with low room-temperature resistivity (10²–10³Ω·cm) were obtained. The observed properties are largely independent of stoichiometry. Simultaneous substitution of Er³⁺ at both cation sites, with higher preference for the Ba site, is proposed. The behavior of heavily doped ceramics depends on stoichiometry. When Ba/Ti < 1, the electrical properties change from slightly semiconducting to insulating as Er concentration increases from 2 to 8 at.%. The ceramics have tetragonal perovskite structure and contain a large amount of Er₂Ti₂O₇ pyrochlore phase. On the other hand, when Ba/Ti > 1, the ceramics are insulating, fine-grained, and single phase. In this case, incorporation of Er³⁺ predominantly occurs at the Ti site, with oxygen vacancy compensation. Incorporation is accompanied by a significant reduction of tetragonality and by expansion of the unit cell. The different results indicate that Er³⁺ solubility at the Ba site does not exceed 1 at.%, whereas solubility at the Ti site is at least 10 at.%. However, the incorporation of Er³⁺ and the resulting properties are also strongly affected by sintering conditions.     

Effect of Neodymium:Yttrium Aluminum Garnet Laser Irradiation on Crystallization in Li2O–Al2O3–SiO2 Glass

A 355-nm neodymium:yttrium aluminum garnet laser, produced by a harmonic generator, was used for the nucleation process in photosensitive glass containing Ag⁺ and Ce³⁺ ions. The pulse width and frequency of the laser were 8 ns and 10 Hz, respectively. Heat treatment was conducted at 570°C for 1 h, following laser irradiation, to produce crystalline growth, after which a LiAlSi₃O₈ crystal phase appeared in the laser-irradiated Li₂O–Al₂O₃–SiO₂ glass. The present study compares the effect of laser-induced nucleation on glass crystallization with that of spontaneous nucleation by heat treatment.     

Energetics of La2O3–HfO2–SiO2 Glasses

A series of La₂O₃–HfO₂–SiO₂ glasses, approximately along the join 0.73SiO₂–0.27( x HfO₂–(1− x )La₂O₃), 0< x <0.3), was prepared using containerless processing techniques (aerodynamic levitation combined with laser heating in oxygen). The enthalpy of formation and enthalpy of vitrification at 25°C were obtained from drop solution calorimetry of these glasses and appropriate crystalline compounds in a molten lead borate (2PbO–B₂O₃) solvent at 702°C. The enthalpy of formation from crystalline oxides was exothermic and became less exothermic with increasing HfO₂ content. Heat contents were measured by transposed temperature drop calorimetry and depended linearly on the HfO₂ content. Differential scanning calorimetry showed that both the onset glass transition and the onset crystallization temperature of these glasses increased with increasing HfO₂ content. Upon slow cooling in air, the glasses crystallized to a mixture of baddeleyite, cristobalite, lanthanum disilicate, and hafnon.     

Dielectric Properties of Glasses in the System Nb2O5–Na2O–SiO2

The effect of niobia on the dielectric properties of glasses in the system Nb₂O₅–Na₂O–SiO₂ has been studied from 100 to 10¹⁰ cps. The dielectric constant is high even at frequencies up to 10¹⁰ cps. The Nb⁵⁺ ion, with its small ionic radius and high charge, reinforces the network and raises the dielectric constant.     

Vaporization Studies of the La2O3–Ga2O3 System

The vaporization of the samples of the compositions Ga₂O₃+ LaGaO₃, LaGaO₃+ La₄Ga₂O₉, and La₄Ga₂O₉+ La₂O₃ was investigated using Knudsen effusion mass spectrometry in the temperature range 1494–1937 K. The partial pressures of the gaseous species O₂, Ga, GaO, Ga₂O, and LaO were determined over the samples investigated. The equilibrium partial pressures were used for the calculation of the thermodynamic activities of the components at 1700 K. Gibbs energies of formation of LaGaO₃( s ) and La₄Ga₂O₉( s ) at 1700 K from the component oxides were derived from the thermodynamic activities as −46.4 ± 4.7 and −99.2 ± 7.9 kJ·mol⁻¹, respectively. The results were compared with the literature data obtained using other methods.     

Sintering and Crystallization of CaO–Al2O3–ZrO2–SiO2 Glasses Containing Different Amount of Al2O3

In this work several complementary techniques have been employed to carefully characterize the sintering and crystallization behavior of CaO–Al₂O₃–ZrO₂–SiO₂ glass powder compacts after different heat treatments. The research started from a new base glass 33.69 CaO–1.00 Al₂O₃–7.68 ZrO₂–55.43SiO₂ (mol%) to which 5 and 10 mol% Al₂O₃ were added. The glasses with higher amounts of alumina sintered at higher temperatures (953°C [lower amount] vs. 987°C [higher amount]). A combination of the linear shrinkage and viscosity data allowed to easily find the viscosity values corresponding to the beginning and the end of the sintering process. Anorthite and wollastonite crystals formed in the sintered samples, especially at lower temperatures. At higher temperatures, a new crystalline phase containing ZrO₂ (2CaO·4SiO₂·ZrO₂) appeared in all studied specimens.     

Al2O3–ZrO2–SiO2 Ternary Glasses for Molybdenum Oxidation Barriers

The wettability of binary and ternary glasses belonging to SiO₂–Al₂O₃–ZrO₂ diagram has been studied using the sessile drop technique at 1750° and 1800°C. The ternary SiO₂–Al₂O₃–ZrO₂ (90–5–5 wt%) glass has proved to be well appropriated as a molybdenum oxidation barrier coating. The addition of 5 wt% of MoO₂ slightly improves its wettablity at higher temperatures without affecting its oxidation barrier properties. The Mo comes into the glass network as a mixture of Mo⁵⁺, Mo⁴⁺, and Mo⁶⁺. After oxidation at 1000°C in oxygen atmosphere, the molybdenum remains in the glass network as Mo⁶⁺.     

La2O3-Al2O3-SiO2 Glasses for High-Power, Yb3+-Doped, 980-nm Fiber Lasers

Single-mode semiconductor pumps have failed to keep pace with the increasing power requirements of Er-doped fiber amplifiers (EDFAs), so there is a need for high-powered 980-nm sources. Yb³⁺-doped tapered fiber lasers can provide high-power output by conversion of a low-brightness, high-powered, 920-nm, multimode broad stripe laser diode to a high-brightness, 980-nm, single-mode output. The tapered fiber laser requires a fiber with high numerical aperture (NA) (>0.4), a rectangular core, and good Yb³⁺ spectroscopy for efficient operation. CVD-based fiber fabrication methods are incapable of delivering fibers with an NA > ∼0.3 or with good efficiency at 980 nm so a new method of high-NA fiber fabrication was developed. The core glass composition is critical for maintaining a high-NA fiber with good power extraction while avoiding phase separation, loss, and clustering. The SiO₂ level controlled the NA and interdiffusion between core and clad, while the Al₂O₃/La₂O₃ ratio controlled phase separation. A La₂O₃-Al₂O₃-SiO₂ glass was developed that is compatible with a pure SiO₂ cladding glass and has a laser slope efficiency of 70% at 980 nm. The optimized fiber composition yielded 450 mW of 980-nm power in a single-mode fiber.     

Properties of Sm2O3─Al2O3─SiO2 Glasses for In Vivo Applications

The compositional range for glass formation below 1600°C in the Sm₂O₃─Al₂O₃─SiO₂ system is (9–25)Sm₂O₃─(10–35)Al₂O₃─(40–75)SiO₂ (mol%). Selected properties of the Sm₂O₃─Al₂O₃─SiO₂ (SmAS) glasses were evaluated as a function of composition. The density, refractive index, microhardness, and thermal expansion coefficient increased as the Sm₂O₃ content increased from 9 to 25 mol%, the values exceeding those for fused silica. The dissolution rate in 1 N HCl and in deionized water increased with increasing Sm₂O₃ content and with increasing temperature to 70°C. The transformation temperature ( T _g ) and dilatometric softening temperature ( T _d ) of the SmAS glasses exceeded 800° and 850°C, respectively.     

Effect of Molybdenum on the Structure and on the Crystallization of SiO2–Na2O–CaO–B2O3 Glasses

Crystallization of the poorly durable Na₂MoO₄ phase able to incorporate radioactive cesium must be avoided in SiO₂–Al₂O₃–B₂O₃–Na₂O–CaO glasses developed for the immobilization of Mo-rich nuclear wastes. Increasing amounts of B₂O₃ and MoO₃ were added to a SiO₂–Na₂O–CaO glass, and crystallization tendency was studied. Na₂MoO₄ crystallization tendency decreased with the increase of B₂O₃ concentration whereas the tendency of CaMoO₄ to crystallize increased due to preferential charge compensation of BO₄⁻ entities by Na⁺ ions. ²⁹Si MAS NMR showed that molybdenum acts as a reticulating agent in glass structure. Trivalent actinides surrogate (Nd³⁺) were shown to enter into CaMoO₄ crystals formed in glasses.     

Crystallization of (Na2O–MgO)–CaO–Al2O3–SiO2 Glassy Systems Formulated from Waste Products

Aluminosilicate and silicate glass-ceramics were obtained from controlled devitrification of CaO–Al₂O₃–SiO₂ glassy systems starting from Spanish and Italian coal fly ash or Italian municipal incinerator slag mixed with other byproducts, such as glass cullet and dolomite. The nucleation mechanism and the crystallization kinetics were investigated by thermal, diffractometric, and microstructural measurements. Moreover, the experimentally observed devitrification and the identification of the crystalline phases formed were compared with the indications derived from Ginsberg, Raschin-Tschetveritkov, and Lebedeva diagrams used for petrological glass-ceramics. All the glasses showed a good crystallization tendency with the formation of dendritic pyroxene and acicular wollastonite together with feldspar and iron spinels starting from the surface. The activation energy values for crystallization ranging from 472 to 832 kJ ·mol⁻¹ were found to be close to those typical for aluminosilicate glasses; moreover, the possibility to vitrify and devitrify up to 100 wt% of slag and up to 40–50 wt% of ash mixed with glass cullet and dolomite makes the vitrification treatment a suitable disposal procedure.     

Proton Conductivity in Zr4+-Ion-Doped P2O5–SiO2 Porous Glasses

The effect of zirconium ions on glass structure and proton conductivity was investigated for sol-gel-derived P₂O₅–SiO₂ glasses. Porous glasses were prepared through hydrolysis of PO(OCH₃)₃, Zr(OC₄H₉)₄, and Si(OC₂H₅)₄. Chemical bonding of the P⁵⁺ ions was characterized using ³¹P-NMR spectra. The phosphorous ions, occurring as PO(OH)₃ in the ZrO₂-free glass, were polymerized with one or two bridging oxygen ions per PO₄ unit with increased ZrO₂ content. The chemical stability of these glasses was increased significantly on the addition of ZrO₂, but the conductivity gradually decreased from 26 to 12 mS/cm at room temperature for 10P₂O₅·7ZrO₂·83SiO₂ glass. A fuel cell was constructed using 10P₂O₅·5ZrO₂·85SiO₂ glass as the electrolyte; a power of ∼4.5 mW/cm² was attained.     

Subsolidus Phase Relationships in the System Fe2O3–Al2O3–TiO2 between 1000° and 1300°C

Subsolidus phase equilibria in the system Fe₂O₃–Al₂O₃–TiO₂ were investigated between 1000° and 1300°C. Quenched samples were examined using powder X-ray diffraction and electron probe microanalytical methods. The main features of the phase relations were: (a) the presence of an M₃O₅ solid solution series between end members Fe₂TiO₅ and Al₂TiO₅, (b) a miscibility gap along the Fe₂O₃–Al₂O₃ binary, (c) an α-M₂O₃( ss ) ternary solid-solution region based on mutual solubility between Fe₂O₃, Al₂O₃, and TiO₂, and (d) an extensive three-phase region characterized by the assemblage M₃O₅+α-M₂O₃( ss ) + Cor( ss ). A comparison of results with previously established phase relations for the Fe₂O₃–Al₂O₃–TiO₂ system shows considerable discrepancy.     

Properties of CeO2–Al2O3–SiO2 Glasses Prepared in Air

Properties of 15–30 mol% CeO₂/23 mol% Al₂O₃/62–47 mol% SiO₂ glasses prepared in air have been investigated in this study. Experimental results show that the glass transformation temperature, the dilatometric softening temperature, and the transmittance in the visible region decrease with increasing ceria content; but the thermal expansion coefficient, the bulk density, and the microhardness increase with increasing ceria content.     

Phase-Diagram Studies in the La2O3–SrO–CaO–Mn3O4 System at 1200°C in Air

The phase equilibria of the La₂O₃–SrO–CaO–Mn₃O₄ system in air at 1200°C has been studied. Under these conditions, eight univariant four-phase equilbria were observed. Quaternary phases, as well as liquid phases, were not observed. Perovskite-structure phases LaMnO₃, SrMnO₃, and CaMnO₃ did not form complete solid solutions within the system.     

Determination of CaO–SiO2–MgO–Al2O3–CrOx Liquidus

In this work, the liquidus of synthetic CaO–SiO₂–MgO–Al₂O₃–CrO _x slags is evaluated in the industrially relevant compositional domain. Equilibrium experiments are carried out at 1500°C and partial oxygen pressure ( p _O2) 10^−11.04 atm, and at 1600°C and p _O2=10^−10.16 and 10^−9.36 atm. The studied basicities (CaO/SiO₂) are 1.2 and 0.5. Al₂O₃ levels range from 0 to 30 wt%. Oversaturated liquid is sampled and phase relations are measured with quantitative electron probe microanalysis–wavelength dispersive spectroscopy (EPMA–WDS). The results are compared with the commercially available FactSage thermodynamic databases. Qualitative agreement is always obtained. Also a good quantitative agreement is found at the higher basicity, especially for the spinel liquidus. A minor but systematic deviation can be observed for the eskolaite liquidus. At the lower basicity, the calculated phase diagram deviates strongly from the experimental results, probably due to missing ternary interactions in the database.     

Effect of Sb2O3 on Thermal Properties of Glasses in Bi2O3–B2O3–SiO2 System

Glasses with compositions 50Bi₂O₃– x Sb₂O₃–10B₂O₃–(40– x ) SiO₂ ( x =0, 1, 3, 5, 8, 10) have been prepared by conventional melt quench technique. Substitution of Sb₂O₃ for SiO₂ exerted an obvious effect on properties of glasses, especially, increased glass transition temperature ( T _g) and crystalline temperature ( T _c) greatly. Results of infrared transmission spectra attributed the effect to the formation of new bridging bonds of Sb–O–B and Sb–O–Si in glass network.