Production and properties of high purity TeO2–ZnO–Na2O–Bi2O3 and TeO2–WO3–La2O3–MoO3 glasses

High-purity TeO₂–ZnO–Na₂O–Bi₂O₃ and TeO₂–WO₃–La₂O₃–MoO₃ glasses were produced by melting the high-purity oxides mixtures in platinum or gold crucible at 800 °C in hermetic chamber in the purified oxygen atmosphere. The content of limiting impurities in the produced initial oxides and glasses, the optical properties as well as the stability to crystallization were investigated. The optical fibers were produced from high-purity tellurite glasses with losses at the level of several hundreds of dB/km.The total content of 3d-transition metals in the glasses was not more than 1 ppm wt and content of hydroxyl groups corresponded to the absorption level of 0.001–0.002 cm⁻¹ at ∼3 μm. The absorption band, monotonically increasing with the increase in MoO₃ content, was observed in dry TeO₂–WO₃–La₂O₃–MoO₃ glasses with the maximum at about 3.7 μm.     

Effect of substituting Al2O3 and ZrO2 on thermal and optical properties of high refractive index La2O3–TiO2 glass system prepared by containerless processing

La₄Ti₉O₂₄ glass and La₂O₃–TiO₂–Al₂O₃ and La₂O₃–TiO₂–ZrO₂ glass systems were prepared by containerless processing. The thermal stability and refractive indices of these glasses were investigated. It was found that these glasses had high refractive indices over 2.29 and high glass transition temperatures. The effects of substituting Al₂O₃ or ZrO₂ for La₂O₃ or TiO₂ in La₄Ti₉O₂₄ glass on the refractive index is discussed by analyzing the optical parameters of the glasses. The high refractive index of these glasses was due to their large oxygen packing densities and significant electronic polarizabilities of oxygen ions. The substitution of Al₂O₃ and ZrO₂ was effective for the refractive indices and wavelength dispersions.     

Raman spectroscopic study of structure of WO3La2O3B2O3 glasses with no color and crystallization of LaBWO6

Glasses with the nominal compositions of xWO₃25La₂O₃(75 − x)B₂O₃ (mol%) with x = 15, 25, and 50 were prepared using a conventional melt quenching method, and their structure and crystallization behavior were examined from Raman scattering spectra and X-ray diffraction analyses. The glasses are colorless in the visible light region and give the optical band gap energy of 3.49-3.61 eV. The glass transition and crystallization temperatures and the thermal stability against crystallization decrease with increasing WO₃ content. The strong Raman bands at 840 and 940-960 cm⁻¹ suggest that the main coordination state of W⁶⁺ ions in the glasses is isolated (WO₄)²⁻ tetrahedral units. The formation of WO₆ octahedral units is also suggested in the glasses with high WO₃ contents. The main crystallization mechanism in the glasses is the surface crystallization, and the glass of 50WO₃25La₂O₃25B₂O₃ shows the crystallization of LaBWO₆ single phase. The present study proposes that WO₃La₂O₃B₂O₃ glasses and crystallized glasses are very interesting as optical functional materials.     

Low-loss,high-purity (TeO<Subscript>2</Subscript>)<Subscript>0.75</Subscript>(WO<Subscript>3</Subscript>)<Subscript>0.25</Subscript> glass

By melting a mixture of high-purity oxides in a platinum crucible under flowing purified oxygen, we have prepared (TeO₂)_0.75(WO₃)_0.25 glass with a total content of 3d transition metals (Fe, Ni, Co, Cu, Mn, Cr, and V) within 0.4 ppm by weight, a concentration of scattering centers larger than 300 nm in size below 10² cm⁻³, and an absorption coefficient for OH groups (λ ∼ 3 μm) of 0.008 cm⁻¹. The absorption loss in the glass has been determined to be 115 dB/km at λ = 1.06 μm, 86 dB/km at λ = 1.56 μm, and 100 dB/km at λ = 1.97 μm. From reported specific absorptions of impurities in fluorozirconate glasses and the impurity composition of the glass studied here, the absorption loss at λ ∼ 2 μm has been estimated at ≤100 dB/km. The glass has been drawn into a glass-polymer fiber, and the optical loss spectrum of the fiber has been measured.     

Observation of surface plasmon resonance of silver particles and enhanced third-order optical nonlinearities in AgCl doped Bi2O3-B2O3-SiO2 ternary glasses

Bi₂O₃-B₂O₃-SiO₂ ternary glasses embedded with Ag nanoparticles were prepared by introducing AgCl into the bismuthate glasses using conventional melt quenching method and characterized by several experimental techniques. Scanning electron microscopic studies indicated the formation of Ag contained nanoclusters which crack and become regular with increase of AgCl content in these composites. Optical absorption spectra of the nanocomposites showed the presence of absorption band of surface plasmon resonance (SPR) due to Ag nanoparticles at ∼600 nm. Z-scan measurement with femtosecond laser was used to investigate third-order optical nonlinearities of the nanocomposites. The results show that the nonlinear refraction γ was dramatically increased up to 30 times by the appearance of Ag nanoparticles when excited within its SPR region, while nonlinear absorption due to two-photon absorption exhibited opposite tendency or even saturated behavior. The calculation of figure of merit suggests that the Ag particle embedded Bi₂O₃-B₂O₃-SiO₂ glass composites are promising candidates for optoelectronic devices.     

Natural Fe3O4 nanoparticles embedded zinc–tellurite glasses: Polarizability and optical properties

Modifying the optical behavior of zinc–tellurite glass by embedding magnetic nanoparticles has implication in nanophotonics. A series of zinc–tellurite glasses containing natural Fe₃O₄ nanoparticles with composition (80 − x)TeO₂·xFe₃O₄·20ZnO (0 ≤ x ≤ 2) in mol% are synthesized by melt quenching method and their optical properties are investigated using FTIR and UV–vis–NIR spectroscopies. Lorentz–Lorenz relations are exploited to determine the refractive index, molar refraction and electronic polarizability. The sharp absorption peaks of FTIR spectra show a shift from 667 cm⁻¹ to 671 cm⁻¹ in the presence of nanoparticles that increase the non-bridging oxygen, confirmed by the intensity change of the TeO₃ peak at 752 cm⁻¹. A new peak around 461 cm⁻¹ is also observed which is attributed to the band characteristic of covalent Fe–O linkages. A decrease in the Urbach energy as much as 0.122 eV and the optical energy band gap with the increase of Fe₃O₄ concentration (0.5–1.0 mol%) is evidenced. Electronic polarizability of the glasses increases with increasing Fe₃O₄ nanoparticles concentration up to 1 mol%. Interestingly, the polarizability tends to decrease with the further increase of Fe₃O₄ concentration at 2 mol%. The role of magnetic nanoparticles in influencing the structural and optical behavior are examined and understood.     

Optical bistability for ZnO–Nb2O5–TeO2 glasses

We examined the optical nonlinear properties of ZnO–Nb₂O₅–TeO₂. The absorption and Raman spectra were measured, the third-order nonlinear susceptibility was determined by degenerated four wave mixing technique. The magnitude of χ⁽³⁾ is about 1.0 × 10⁻¹² esu, larger than that of silica glasses, and the optical bistability was observed in a Fabry–Perot cavity.     

Extinction coefficient of Ni2+ in (TeO2)0.78(WO3)0.22 glass

The absorption spectra of (TeO₂)_0.78(WO₃)_0.22 glasses containing 0.01–1.0 wt % NiO have been measured at wavelengths from 450 to 2700 nm, and the spectral dependence of the extinction coefficient of Ni²⁺ in the glasses has been obtained. In the absorption bands centered at 810 and 1320 nm, the extinction coefficient is 20.2 ± 0.8 cm⁻¹ (870 ± 35 dB/(km ppmw)). According to the spectral range of its absorption and its extinction coefficient, nickel is a strongly absorbing impurity in tellurite glasses. The present results can be used to formulate sound nickel concentration limits in tellurite glasses for fiber-optic applications.     

Optical absorption studies for TeO2-P2O5 and Bi2O3-TeO2-P2O5 glasses

A range of TeO₂-P₂O₅ and Bi₂O₃-TeO₂-P₂O₅ glass systems were prepared. The optical absorption spectra were measured in the spectral range 300–800 nm and it was found that the fundamental absorption of these glasses is dependent on the glass composition. The optical energy gap of binary glasses increases with increasing TeO₂ content while the addition of Bi₂O₃ to TeO₂-P₂O₅ decreases the optical energy gap. The absorption edges of these glasses arise from direct forbidden transitions and occur at photon energies in the range of 2.17 to 2.97 eV for TeO₂-P₂O₅ glasses and 2.63 to 2.32 eV for Bi₂O₃-TeO₂-P₂O₅ glasses depending on their composition.     

Low-temperature sintering characteristics of nano-sized BaNd2Ti5O14 and Bi2O3–B2O3–ZnO–SiO2 glass powders prepared by gas-phase reactions

Nano-sized BaNd₂Ti₅O₁₄ (BNT) powders were prepared by spray pyrolysis from solutions containing ethylenediaminetetraacetic acid and citric acid. Treatment at temperatures ≥900 °C and subsequent milling resulted in nanoparticle powders with orthorhombic crystal structures. The mean particle size of the powder post-treated at 1000 °C was 160 nm. Nano-sized Bi₂O₃–B₂O₃–ZnO–SiO₂ glass powder with 33 nm average particle size was prepared by flame spray pyrolysis and used as a sintering agent for the BNT. BNT pellets sintered at 1100 °C without the glass had porous structures and fine grain sizes. Those similarly sintered with the glass had denser structures and larger grains.     

Fabrication of Yb3+/Er3+ codoped Bi2O3–WO3–TeO2 pedestal type waveguide for optical amplifiers

We report, for the first time to our knowledge, experimental results on pedestal waveguides produced with Yb³⁺/Er³⁺ codoped Bi₂O₃–WO₃–TeO₂ thin films deposited by RF Sputtering for photonic applications. Thin films were deposited using Ar/O₂ plasma at 5 mTorr pressure and RF power of 40 W on substrates of silicon wafers. The definition of the pedestal waveguide structure was made using conventional optical lithography followed by plasma etching. Propagation losses around 2.0 dB/cm and 2.5 dB/cm were obtained at 633 and 1050 nm, respectively, for waveguides in the 20–100 μm width range. Single-mode propagation was measured for waveguides width up to 10 μm and 12 μm, at 633 nm and 1050 nm, respectively; for larger waveguides widths multi-mode propagation was obtained. Internal gain of 5.6 dB at 1530 nm, under 980 nm excitation, was measured for 1.5 cm waveguide length (∼3.7 dB/cm). The present results show the possibility of using Yb³⁺/Er³⁺ codoped Bi₂O₃–WO₃–TeO₂ pedestal waveguide for optical amplifiers.     

Solid-state field-assisted silver diffusion in (TeO2)0.6(WO3)0.25(La2O3)0.05(Na2O)0.1 glass

Silver-doped layers have been produced in (TeO₂)_0.6(WO₃)_0.25(La₂O₃)_0.05(Na₂O)_0.1 (TWLN) glass by solid-state field-assisted diffusion. The silver concentration profile in the glass has been determined by secondary ion mass spectrometry (SIMS) and Rutherford backscattering spectrometry (RBS). The Matano-Boltzmann method applied to thermally activated diffusion indicates that the silver diffusion coefficient in the glass is a weak function of silver concentration. We carried out modeling of silver concentration profiles in the doped layer of the TWLN glass after solid-state field-assisted diffusion. Good agreement of the theoretical fit and experimental data suggests that the model chosen can be used to describe solid-state field-assisted diffusion of silver ions in TWLN glasses. Using RBS data, we have quantitatively estimated the surface density of silver atoms after field-assisted diffusion. Combining SIMS and RBS, we were able to assess the absolute silver concentration depth profile. Our results demonstrate that field-assisted diffusion, a simple and effective procedure for doping optical glasses, can be used to produce planar waveguide structures based on the tellurite glass studied here.     

New oxyhalide glasses involving Sb2O3

A family of oxyhalide glasses involving Sb₂O₃ and various R_mX_n halides (R = monovalent or divalent cation; X = F, Cl, Br or I) has been prepared. The thermal, mechanical and optical properties of the glasses are reported. Easy to prepare and to shape (windows, fibers,), chemically stable, they are transparent from about 0.43 μm up to 6.50 μm. The special case of vitreous Sb₂O₃ is also discussed.     

Influence of modifier oxides on some physical properties of antimony borate glass system doped with V2O5

Three series of glasses, of the composition 20 MO (M = Ca, Pb, Zn)–40 Sb₂O₃–(40 − x) B₂O₃:xV₂O₅, with six values of x ranging from 0 to 1 mol% were prepared. The samples were characterized by X-ray diffraction, scanning electron microscopy, EDS and differential scanning calorimetric techniques. The comparison of DSC data among the three series has indicated high glass forming ability for ZnO mixed glasses. Dielectric properties over a range of frequency and temperature, optical absorption, ESR spectra at room temperature and IR spectra have been investigated. The variations observed in all these properties due to different modifiers as a function of the concentration of V₂O₅ have been analyzed in the light of different oxidation states and environment of vanadyl ions in these glasses. The analysis of these results indicated that the ZnO mixed glasses are more stable against devetrification and possess high insulating strength when compared with PbO and CaO mixed glasses.     

Spectroscopy and frequency upconversion of Er ions in fluorotellurite glasses

In this work we report the optical properties and upconversion luminescence of Er³⁺ ions in TeO₂–WO₃–PbO–BaF₂ and TeO₂–TiO₂–Nb₂O₅–BaF₂ fluorotellurite glasses and their comparison with those of TeO₂–TiO₂–Nb₂O₅ glass. The optical properties of Er³⁺ ions have been established in terms of absorption and emission spectra and lifetime measurements. The 1.5 μm emission cross-section has been determined from the line shape of the emission spectrum and the calculated emission probability for the ⁴I_13/2 level. The highest emission cross section (6.9 × 10⁻²¹ cm²) corresponds to the TeO₂–TiO₂–Nb₂O₅–BaF₂ glass with a figure of merit for the bandwidth of 524.4 cm² nm. Upconversion emissions at 530, 548 nm, and 660 nm have been obtained under infrared excitation at 800 nm in the ⁴I_9/2 level and compared with those obtained under one photon excitation. The green emission corresponding to the ⁴S_3/2 → ⁴I_15/2 transition is dominant in all glasses. The excitation wavelength dependence of the upconverted luminescence together with its time evolution after infrared pulsed excitation suggest that energy transfer upconversion processes are responsible for the green upconversion luminescence.     

Crystal growth and spectral properties of Pr:La2(WO4)3

Pr³⁺-doped La₂(WO₄)₃ single crystal with dimensions up to Ø 20 mm × 35 mm has been grown by the Czochralski method. The structure of the Pr³⁺:La₂(WO₄)₃ crystal was determined by the X-ray powder diffraction and the Pr³⁺ concentration in this crystal was determined. The absorption and fluorescence spectra of Pr³⁺:La₂(WO₄)₃ crystal were measured at room temperature, and the fluorescence lifetime of main emission multiplets were estimated from the recorded decay curves. The spectral properties related to laser performance of the crystal were evaluated.     

High temperature phase relation in the system La2O3WO3

The system La₂O₃WO₃, especially the La₂O₃-rich portion was studied by a thermal analysis, high temperature X-ray diffraction, annealing of fused samples, solid state reaction and DTA methods up to the liquidus. Eight intermediate phases, La₂O₃:WO₃ = 3:1, 5:2, 3:2, 1:1, 7:8, 1:2, 1:3 and 2:9, were found and characterized. In addition, two unquenchable solid solution phases based upon La₂O₃X and H, have been found. A phase diagram is presented.     

Structural properties of Al2O3-La2O3 binary oxides prepared by sol-gel

The structural properties of La₂O₃ and Al₂O₃-La₂O₃ binary oxides prepared by sol-gel were studied by XRD, HRTEM and UV-vis. The binary oxides with high lanthana contents show an amorphous structure after calcination at 650 °C. At calcination temperatures higher than 1000 °C there is a phase transformation from the amorphous state to the crystalline LaAlO₃ with a perovskite structure. The structure of La₂O₃ is consistent with the hexagonal system; however, some crystalline microdomains with a monoclinic structure were detected by HRTEM. Islands of La₂O₃ and LaAl₁₁O₁₈ phases were detected at high lanthana concentration in the binary oxide. The modification in the coordination shell of the Al³⁺ cations due to the interaction with La³⁺ cations confirms the formation of phases with a perovskite structure and the presence of islands of the LaAl₁₁O₁₈ phase.     

CO2 absorption and desorption of Bi2O3-La2O3 powders prepared by mechanical synthesis

In order to obtain CO₂-absorbents to eliminate CO₂ concentration locally, Bi₂O₃-La₂O₃ mixed powders were prepared by mechanical alloying (MA) method using a planetary ball-milling machine. CO₂-absorption and desorption properties were checked by TG-DTA for the obtained powder samples. As a result, the sample shown by (Bi₂O₃)_1−x(La₂O₃)_x [x≤0.50] was found to form α-Bi₂O₃-solid solution with repeated CO₂-adsorption and desorption around 400- 500 °C. Absorbed and desorbed CO₂ contents varied with MA time: the 72 h MA’ed sample had a larger CO₂ content than the 24 h MA’ed sample. The performance depended on the sample composition, and (Bi₂O₃)_0.70(La₂O₃)_0.30 was found to have the highest performance in the present system.     

Dielectric, magnetic and spectroscopic properties of Li2O–WO3–P2O5 glass system with Ag2O as additive

Li₂O–WO₃–P₂O₅ glasses containing small concentrations of Ag₂O from 0 to 1 mol% were prepared. A number of studies viz., chemical durability, dielectric studies (constant ′, loss tan δ, a.c. conductivity σ_ac over a range of frequency and temperature), spectroscopic (infrared, optical absorption ESR spectra) and magnetic susceptibility studies of these glasses, have been carried out. The interesting variations observed in all these properties with the concentration of Ag⁺ ions have been analyzed in the light of different oxidation states and environment of tungsten ions in the glass network.