Preparation of Small-Particle-Size, Semiconductor CdS-Doped Silica Glasses by the Sol–Gel Process

The sol–gel process has been applied successfully to the preparation of small-particle-size CdS-doped silica glasses with a significant quantum size effect. Gels prepared through the hydrolysis of a complex solution of Si(OC₂H₅)₄ and Cd(CH₃COO)₂·2H₂O were heated at 500°C, then reacted with H₂S gas to form fine, hexagonal, CdS-microcrystal-doped glasses. The optical absorption edge is blue shifted by ∼0.4 eV compared with the bulk absorption value of CdS crystal. This result is interpreted in terms of a quantum-confinement effect of small crystal size.     

Preparation of Cerium-Activated Silica Glasses: Phosphorus and Aluminum Codoping Effects on Absorption and Fluorescence Properties

Cerium-activated silica (SiO₂) glasses were prepared by plasma torch chemical vapor deposition (CVD). In Ce-doped SiO₂ glasses, most Ce exists as Ce⁴⁺ ions; the remaining small amount of Ce³⁺ ions exhibits a broad fluorescence spectrum with a large Stokes shift, ∼9600 cm^-1, from the excitation spectrum peak of 324 nm. Aluminum and phosphorus codoping considerably increases the Ce³⁺ ratio and shifts the peaks of both spectra to shorter wavelengths. P codoping is the more effective way to achieve this result and in some cases produces an absorption spectrum similar to that of a Ce-doped phosphate glass. These findings are consistent with the solvatiorn shell model for codoping, as previously proposed. To codope P, a soot remelting method was devised to deal with the highly volatile P₂O₅.     

Positron Lifetime Study of the Crystal Evolution and Defect Formation Processes in a Scintillating Glass

The crystal evolution and defect formation in scintillating glasses as a consequence of thermal annealing were studied by annihilation lifetime spectroscopy and UV-Vis absorption spectroscopy. The annihilation lifetime spectra and UV-Vis spectra were recorded on glass 50SiO₂–45ZnO–5BaF₂ before and after annealing at 580°C for 16, 32, and 48 h, respectively. The results show that the three lifetime components (τ₁, τ₂, and τ₃) and the corresponding intensities ( I ₁, I ₂, and I ₃) change systematically with increasing annealing time. This reflects the crystal evolution and defect formation in the glass matrix. The continued crystal evolution was also revealed by the UV-Vis spectra, as the absorption edge of the material shifted to a lower energy with prolonged annealing.     

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.     

Corrosion of Lead Glasses in Acid Media: I, Leaching Kinetics

The leaching kinetics of lead glasses (25 to 35 mol% PbO-75 to 65 mol% SiO₂; some with K₂O and A1₂O₃, additions) were determined in 10% acetic acid. Except for a ternary glass (SiO₂-PbO-K₂O) which had a linear dependence on time, all compositions exhibited a linear dependence on the square root of time for the amount of Pb and K removed. Increasing the SiO₂: PbO ratio or the Al₂O₃ content improved the durability whereas adding K₂O to a binary PbO-Si0₂ glass greatly increased the corrosion rate. Activation energies for the rates of Pb and K removal were determined for three compositions and it was deduced that the diffusion of H⁺ controlled the leaching for binary and 4-component glasses whereas dissolution of the silica network was rate-controlling for the ternary.     

Microstructure and Properties of Co2+: ZnAl2O4/SiO2 Nanocomposite Glasses Prepared by Sol–Gel Method

Transparent bulk Co²⁺: ZnAl₂O₄/SiO₂ nanocomposites containing nanocrystalline Co²⁺: ZnAl₂O₄ dispersed in silica glass matrix were obtained by the sol–gel method. The gels of composition 89SiO₂–6Al₂O₃–5ZnO− x CoO ( x =0.2, 0.4, 0.6, 0.8, 1.0) (mol%) were prepared at room temperature by using two different aluminum salts, aluminum nitrate and aluminum alkoxide (aluminum-iso-propoxide, Al(OPrⁱ)₃), as starting materials. The transparent gels were converted to the crystalline phase of gahnite by heating above 900°C. The microstructural evolution of gels was characterized. The effect of Co²⁺ concentration on spectroscopic properties was also discussed. Co²⁺: ZnAl₂O₄ nanocrystals dispersed in the SiO₂-based glass are formed at lower heat-treatment temperature and shorter heating time by using Al(OPrⁱ)₃ as raw material.     

Preparation and Physical Properties of Radiofrequency-Sputtered Amorphous Films in the System AlPO4–TiO2

Amorphous films in the system AlPO₄–TiO₂ were prepared by an rf-sputtering method, and their physical properties, such as density, refractive index, and thermal expansion coefficient, and the infrared absorption spectra were measured. The thermal expansion coefficient increased linearly with increasing TiO₂ content. The results of the molar refractivity and the infrared absorption spectra indicated that the coordination number of titanium ions in these films is higher than that in SiO₂–TiO₂ glasses with a negative thermal expansion, in which Ti⁴⁺ ions are tetrahedrally coordinated. In order to confirm the coordination state of the titanium ions in these amorphous films, titanium K -band emission spectra were obtained by X-ray emission spectroscopy, revealing sixfold coordination. The higher coordination state of Ti⁴⁺ was considered to account for these amorphous films not exhibiting negative thermal expansion, as in the SiO₂–TiO₂ system.     

Infrared Absorption Spectrum of Silicon Dioxide

The absorption spectra of fused silica and α-quartz were investigated in the 2600 to 50 cm⁻¹ wave number region. Only part of the absorption frequency bands of the crystal quartz appeared in the fused state and some of them were shifted to higher wave numbers. The principal absorption frequencies in the fused silica were at 1126, 809, 452, and 200 cm⁻¹ It is proposed that the infrared spectrum of the fused silica results from two vibrating units, of point group T_d and D_{3 h} , simultaneously. In the vitreous state, some of the Si-O-Si bonds are disrupted allowing random orientation of the tetrahedral SiO₄ groups (point group T_d). As a consequence of the formation of nonbridging oxygen, the force constant will be increased, as indicated by the shift of the vibrational frequencies to higher values. For every nonbridging oxygen atom formed, the silicon atom previously connected to it would be left with a positive hole. The point group D _{3 h} is due to such a silicon atom and its v ₃ and v ₄ modes coincide with the v ₃ and v ₄ modes of the T_d point group.     

Tm3+-Doped Gallium–Germanium–Bismuth–Lead Glasses as 1.47 μm Fiber Amplifier Materials

We report the spectroscopic properties of Tm³⁺-doped and Tm³⁺/Ho³⁺-codoped [Ga₂O₃–GeO₂–Bi₂O₃–PbO (PbF₂)] glasses for S-band optical amplifications. The Judd–Ofelt intensity parameters have been determined based on the measured absorption spectra. It is found that PbF₂-modified glasses exhibit a lower Ω₂ value, and the addition of PbF₂ caused the chemical bond associated with Tm³⁺ ions to be more ionic. The PbF₂-free glasses have large peak emission cross-sections in the range of 2.15–2.18 × 10⁻²¹ cm². Meanwhile, the studied glasses exhibit broad 1.47 μm emission with the full width at half-maximum of 119–126 nm. The results indicate that these glasses are useful host material for broadband S-band fiber amplifiers.     

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.     

Optical Properties of Dysprosium-Doped Low-Phonon-Energy Glasses for a Potential 1.3 μm Optical Amplifier

Dysprosium-doped glasses were prepared in the system of gallium-based sulfide, tellurite, zirconium-baed and indium-based fluorides and their optical properties were studied. From the absorption cross sections of five f-f bands, three Judd-Ofelt parameters, ω _t ( t = 2, 4, 6), of Dy³⁺ ion were determined. The compositional variaton of the ω₂value showed the order sulfide > tellurite > fluorozirconate > fluoroindate, whereas the ω₆ value showed the opposite tendency. Compositional variaton of the fluorescence intensity ratio of the (⁴F_9/2⁶H_13/2)/(⁴F_9/2)→⁶H_15/2) is explained by the ratio of ω₂/ω₆ of doped Dy³⁺. The emission probabilities A and the branching ratio β from ⁶H_9/2 and ⁶F_11/2 levels, which are the doublet initial level of the 1.3 μm luminescence, were calculated for the glasses, and it was found that both values showed a tendency similar to that of ω₂ against the glass composition. In the sulfide glass, A was 2.6 × 10³S^-1 and β was 93%, both the highest in all of the glasses investigated. By 1.06 μm pumping of a Nd: YAG laser, the sulfide glass showed strong 1.3 μm emission and the lifetime was 25 μs, resulting in a quantum efficiency of 7%. This value is higher than that of the Pr³⁺:¹G₄ level in ZBLAN glass with β= 60%.     

Evidence for 6-Coordinated Zirconium in Inactive Nuclear Waste Glasses

In inactive glasses used as models for French nuclear waste forms, Zr K - and L _2,3-edge X-ray absorption spectroscopy spectra indicate that Zr is only 6-coordinated, with d (Zr-O) distances of 2.08 ± 0.01 Å and with a small radial disorder. Beyond, the first coordination shell, next-nearest Si neighbors occur at about 3.4 Å. These distances exclude the presence of ^[7]Zr and/or ^[8]Zr and suggest ^[6]Zr-O-Si angles close to 130°, indicating corner-shared ZrO₆ and SiO₄ polyhedra. This structural configuration is similar to those observed in some crystalline zirconosilicates and is in agreement with the stability of Zr in borosilicate melts and glasses.     

Phase Equilibrium in a Portion of the Ternary System Ba OA-I2,O3,-SiO2,

Phase-equilibrium relations on the liquidus surface in the system Ba0-A1₂O₃-SiO₂ have been investigated by the quenching method. The compositions investigated within the ternary area were those containing less than 30%, A1₂O₃ and more than 20% SiO₂ by weight. Petrographic and X-ray techniques were employed in the determination of the crystalline phases.
The crystal phases that separate from melts within the area investigated are barium orthosilicate (2BaO. SiO₂,), barium metasilicate (BaO 2SO₂,), solid solutions, sanbornite (BaO 2SiO₂), tridymite and cristobalite (SO₂), mullite (3A1₂O₃ 2SiO₂), and celsian (BaO A1₂O3_.2SiO₂). Diagrams show the isotherms and indices of refraction of the glasses.
Five quintuple points and eleven boundary curves have been determined within = .5yo compositional variations. The liquidus-surface temperatures have been obtained within limits of ± 125°C.     

Synthesis of Amorphous Silica Nanosheets and Their Photoluminescence

We demonstrate the synthesis of silica nanosheets (SiONSs) by exfoliation and oxidation with layered polysilane, (SiH) _n . The resulting silica was produced in the form of amorphous nanosheets with a uniform thickness of 0.68 nm, which was constructed of six-membered rings of SiO₄ tetrahedra. The thickness is an order magnitude smaller than previously reported silica nanoparticles prepared by a variety of other methods. Strong photoluminescence (PL) was observed, and the PL spectra had maxima at 2.7 and 3.1 eV. This strong emission may be because of the defect center of oxygen deficiency in the sheets. The SiONSs may have potential applications in future integrated optical devices.     

Yb:Niobosilicate Glass with High-Emission Cross Section

The emission cross section for the ² F _5/2–² F _7/2 transition of Yb³⁺ has been determined from absorption and emission measurements of niobosilicate glasses at room temperature. Using systematic variations in the spectroscopic properties, relative to composition, a glass host with emission cross sections of >2.00 pm² and fluorescence lifetimes of >0.8 ms is obtained. This glass has advantages over some laser glasses that have been reported in other published papers.     

Properties and Network Constitution of rf-Sputtered Amorphous Films in the System Silicon Dioxide–Aluminum Orthophosphate

Amorphous films in the system SiO₂–AlPO₄ were prepared by means of the rf-sputtering method, and their physical properties, such as density, refractive index, and temperature coefficient of Young's modulus, and infrared spectra were measured. Also, the K α X-ray emission spectra of silicon and aluminum were measured in order to investigate the coordination state of these cations in the amorphous films. The density and the refractive index were close to those of amorphous SiO₂ and AlPO₄ and the compositional dependence showed a small deviation from linearity. The temperature coefficients of Young's modulus were positive for all of the samples. The infrared absorption spectra of all of the samples were similar to those of SiO₂ glass and amorphous AlPO₄ film, and there was no evidence of the presence of P═O bonds. The coordination states of silicon and aluminum ions in the present amorphous films were the same as those in fused silica and AlPO₄ crystal, respectively. The results of the properties, infrared absorption spectra, and X-ray emission spectra suggest that SiO₄ tetrahedrons and AlO₄–PO₄ connecting tetrahedral dimers constitute the network of the present amorphous films. A small deviation of the physical properties from an additive rule was thought to result from the difference in the bond character between the newly formed Si–O–Al and Si–O–P bonds and the bonds in the end members, Si–O–Si and Al–O–P.     

Optimization of Properties of Photoconductive Oxide Glasses

Using as a base the Cd0-B₂O₃-Si0₂ photoconducting glass previously found, various systematic substitutions and additions were made to determine their influence on the photoresponse of these glasses. Complete substitution of GeO₂ for SiO₂ led to the highest photocurrents observed in these glasses and to a shift of the spectral response into the visible region.     

Formation of Small-Sized CdSxSe1-x Crystals in Sol-Gel-Derived SiO2 Glasses

Silica glasses doped with small-sized CdS_x-Se_1-x crystals were prepared by the sol-gel method. Gels synthesized by the hydrolysis of Si(OC₂H₅)₄, in the presence of CdSeO₄ with NH₄SCN dissolved in HNO₃ or NH₄OH, were heated in H₂-N₂ atmosphere. The pH value of solutions for CdSeO⁴ and NH⁴SCN primarily determined the fraction of anions in CdS^xSe^1-x crystals. The anion content in crystals was dependent on the pH value of the solvent and/or heat-treatment temperature, and the sulfur fraction changed from 0.1 to 0.6. The optical absorption spectra were red-shifted as the selenium content and the crystal size increased, and the emission spectra showed a sharp band near the absorption edge position and a broad tail extending into the long wavelength. The optical band gap energies increased reciprocally proportional to the square of the crystal size.     

Glass-Ceramic Formation in the ZnO-P2O5 System and the Effect of Silica as a Nucleating Agent

Crystallization of a series of ZnO-P₂O₅ based glasses was investigated. ZnO-P₂O₅-CaO glasses could be converted most readily to glass-ceramics and crystallization of these led to formation of alpha-Zn₂P₂O₇, alpha-CaZn₂(PO₄)₂, and ß-CaZn₂(PO₄)₂ phases. A further phase has been tentatively identified as monoclinic (Zn,Ca)₂P₂O₇. The most promising glass-ceramic composition Z15 (59.4ZnO·33P₂O₅·6.6CaO·1SiO₂) crystallized to alpha-Zn₂P₂O₇ and ß-CaZn₂(PO₄)₂, the latter phase being stabilized by the presence of SiO₂ which also encouraged volume nucleation giving a fine-scale (submicrometer) microstructure.     

Preparation by a Sol-Gel Process of Borosilicate Glasses Containing Microcrystals of Tellurium and Zinc Telluride

Borosilicate glasses, 5B₂O₃· 95SiO₂ (mol%), containing TeO₂ and ZnO nominally equivalent to 10 wt% Te and ZnTe were prepared by a solgel method from Si(OC₂H₅)₄, B(OCH₃)₃, H₆TeO₆, and Zn(NO₃)₂. A study by electron spectroscopy for chemical analysis (ESCA) showed that glasses heated at high temperature (450°C) in air contained both Te⁶⁺ and Te⁴⁺ ions on the surface layer, but that mainly Te⁴⁺ ions occurred inside the bulk glass. When solgel-derived borosilicate glasses containing the TeO₂ compound were reduced at elevated temperature in a hydrogen atmosphere, Te crystallites ranging in size from 4 to 15 nm were produced at a lower temperature, between 200° and 250°C. The absorption edge moved from the infrared to the visible wavelength region as the particle size decreased to about 4 nm. For glasses containing both TeO₂ and ZnO, ZnTe crystallites formed at high temperature—over 300°C—and existed along with the Te phase.