Specific Features of the Local Structure and Transport Properties of ZrO2–Sc2O3–Y2O3 and ZrO2–Sc2O3–Yb2O3 Crystals

Optics and Spectroscopy - The specific features of the local structure of ZrO2–Sc2O3–Y2O3 and ZrO2–Sc2O3–Yb2O3 crystals are revealed by optical spectroscopy using the Eu3+...     

Electrical transport characteristics of ZnO–Bi2O3–B2O3 glasses

Optically clear glasses in the ZnO–Bi₂O₃–B₂O₃ (ZBBO) system were fabricated via the conventional melt-quenching technique. Dielectric constant and loss measurements carried out on ZBBO glasses unraveled nearly frequency (1 kHz–10 MHz)-independent dielectric characteristics associated with significantly low loss (D?=?0.004). However, weak temperature response was found with temperature coefficient of dielectric constant 18?±?4 ppm °C^?1 in the 35–250 °C temperature range. The conduction and relaxation phenomena were rationalized using universal AC conductivity power law and modulus formalism respectively. The activation energy for relaxation determined using imaginary parts of modulus peaks was 2.54 eV which was close to that of the DC conduction implying the involvement of similar energy barriers in both the processes. Stretched and power exponents were temperature dependent. The relaxation and conduction in these glasses were attributed to the hoping and migration of Bi³⁺ cations in their own and different local environment.     

Crystallization and conductivity of 2CaO–La2O3–5P2O5 glass–ceramic with Al2O3 addition

Al₂O₃ was added to a 2CaO–La₂O₃–5P₂O₅ metaphosphate, to replace 10% of the Ca²⁺ ions by Al³⁺, forming a phosphate with the nominal composition 1.8CaO–0.1Al₂O₃–La₂O₃–5P₂O₅. The effect of Al₂O₃ addition and heat treatment on the microstructure and conductivity of the resulting glass–ceramics was investigated by XRD, SEM, TEM, and AC impedance spectroscopy. Upon transformation from glass to glass–ceramic, conductivities increased significantly. The glasses were isochronally transformed at 700 and at 800 °C for 1 h or 5 h, in air, following heating at 3 or 10 °C/min. With Al₂O₃ addition, after a heat treatment at 700 °C, 100–300 nm nano-domains of LaP₃O₉ crystallized from the glass matrix. Annealing at 800 °C produced a further order of magnitude conductivity increase for the Al-free glass, but less so for the Al-containing glass.     

Ultrasonic and FT-IR studies on Bi2O3–Er2O3–PbO glasses

Glasses in the 90Bi₂O₃–(10?x)Er₂O₃?xPbO (x = 3, 5, 7, 9 and 10 mol%) system have been prepared by the melt-quenching technique. Elastic properties and FT-IR spectroscopic studies have been employed to study the role of PbO in the structure of the investigated system. Elastic properties and Debye temperature were recorded using sound wave velocity measurements at 4 MHz at room temperature. The results showed that density increased and molar volume decreased, while both sound velocities increased with an increase in x. Infrared spectra of the glasses revealed that the bismuthate network is affected by an increase in PbO content. The results are interpreted in terms of the conversion of [BiO₆] into [BiO₃] structural units, indicating that Pb ions have been substituted for erbium ions as tetrahedral network formers. The elastic moduli increased with increasing PbO content due to the increased average bond strength and degree of connectivity, as a direct effect of the increase in [BiO₃] structural units.     

Spectral dispersion of linear optical properties for Sm2O3 doped B2O3–PbO–Al2O3 glasses

Glasses having composition (B₂O₃)₂₅ (PbO)₇₀ (Al₂O₃)₅ (Sm₂O₃)_x ,where x=0, 0.5, 1, 2, 3 and 5 g were prepared using the normal melt quench technique. Spectral reflectance and transmittance at normal incidence of the glass samples are recorded with a spectrophotometer in the spectral range 220–2200 nm. These measured values are introduced into analytical expressions to calculate the real and imaginary parts of the refractive indices. Wemple–DiDomenico single oscillator model and one-term Sellmeier dispersion relations are used to model the real refractive indices. Dispersion parameters such as: single oscillator energy, dispersion energy, lattice oscillating strength, average oscillator wavelength, average oscillator strength and Abbe's number are deduced and compared. Absorption dispersion parameters such as: Fermi energy, optical energy gap for direct and indirect transitions, Urbach energy and steepness parameter are calculated. Effects of doping Sm₂O₃ on these linear optical parameters are investigated and interpreted.     

Broadband 1.5-μm emission of high erbium-doped Bi2O3–B2O3–Ga2O3 glasses

High Erbium-doped glass showing the wider 1.5-μm emission band is reported in the Bi₂O₃–B₂O₃–Ga₂O₃ system and its thermal stability and optical properties such as absorption, emission spectra, absorption and stimulated emission cross-sections and fluorescence lifetime are investigated. Compared with other glass hosts, the gain bandwidth properties of high Er³⁺ content in BBG glass are better than those of tellurite, germanate, silicate and phosphate glasses. The broad and flat ⁴I_13/2→⁴I_15/2 emission and the larger stimulated emission cross-section of Er³⁺ ions around 1.5 μm enable it to be used as a host material for potential broadband optical amplifiers at C and L bands in the microchip configuration.     

YAG laser-induced β-BaB2O4 crystalline dot formation in Sm2O3–BaO–B2O3 glasses

A continuous-wave (CW) YAG laser (power: 0.75–0.9 J/s, irradiation time: 15 s–15 min) with a wavelength of 1064 nm is irradiated to 11.1Sm₂O₃·44.4BaO·44.4B₂O₃ glass, and the formation of β-BaB₂O₄ (β-BBO) crystalline dots with a diameter of 30–150 μm is confirmed from micro-Raman spectra. β-BBO crystals with around 200 μm length grow towards the interior of the glass. The incorporation of Sm³⁺ into β-BBO crystalline dots is suggested from micro-Raman and fluorescence spectra. The second harmonic generation is detected from the array (10×10=100 dots) of β-BBO crystalline dots, indicating that each crystalline dot formed by YAG laser irradiation is a nonlinear optical crystal. CW YAG laser irradiation to glass with Sm³⁺ ions is a nice technique for a spatially controlled crystal growth.     

Influence of different Fe2O3 content on crystallization of MgO–Al2O3–SiO2–TiO2 system glass-ceramics

The crystallization behaviors of MgO–Al₂O₃–SiO₂–TiO₂ system glasses doping with different content Fe₂O₃ were investigated by means of differential thermal analysis and X-ray diffraction. The kinetic parameter of activation energy for crystallization (E) was obtained by the Owaza Johnson–Mehl–Avrami method. The results show that during the heat treatment, the intermediate phase of µ-cordierite initially precipitated from the glass matrix, and with the increasing temperature, it transformed to α-cordierite. The more the Fe₂O₃ content, the lower the crystallization peak temperature (T _p).But the lowering of T _p value did not mean that the value of E decreases correspondingly. The experimental results suggest that only with appropriate content (about 4.2 wt%), Fe₂O₃ can promote the crystallization of this glass effectively.     

Structure,dielectric and bioactivity of P2O5–CaO–Na2O–B2O3 bioactive glass

Bioactive phosphate glasses have been widely investigated for bone repair. Phosphate glass system of 47P₂O₅–30.5CaO–(22.5?x)Na₂O–xB₂O₃ has been prepared by melt quenching technique. From the Raman analysis, it is confirmed that phosphate network form metaphosphate structure. Bioactivity of the glass is studied by immersing the prepared glass in simulated body fluid (SBF). All the glasses exhibited bioactivity after soaking in SBF. Addition of B₂O₃ to the glass by replacing the Na₂O produces considerable effect on the dielectric and bioactivity of the glass. Ion dynamics are also analyzed through imaginary modulus and imaginary dielectric permittivity.     

The broadband NIR emission properties of Bi doped La2O3–Al2O3–SiO2 glass

Bi₂O₃ doped 65SiO₂–20Al₂O₃–15La₂O₃ (in mole%) glasses were prepared by the traditional melting–quenching method. The spectroscopic properties and mechanism of NIR broadband emission in these glasses were investigated in this work. Three excitation wavelengths of 500, 700 and 800 nm were used to test emission spectra. The emission band under 500 nm excitation can be regarded as combination of emission bands under 700 and 800 nm excitation. 2.0 mole% is found to be the optimal Bi₂O₃ doping level in this glass. Under 500 nm excitation its emission peak, FWHM and lifetime of emission band are 1160 nm, 300 nm and 569 μs, respectively. The longest fluorescent lifetime reaches 620 μs under 700 nm excitation. The valence state of Bi in these glasses is suggested to be lower than +3 by X-ray photoelectron spectroscopy. With the help of energy matching, we infer that both Bi⁰ and Bi⁺ centers are responsible for the NIR fluorescence of Bi₂O₃ doped 65SiO₂–20Al₂O₃–15La₂O₃ glass.     

Manifestation of up-conversion in Yb3+/Tm3+ doped Li2O–Y2O3–SiO2 glass system

In this study, we have investigated the principal role of Y₂O₃ on the emission features of Tm³⁺ ion and up-conversion phenomenon in Tm³⁺ and Yb³⁺ co-doped Li₂O–Y₂O₃–SiO₂ glass system. The concentration of Y₂O₃ is varied from 0 to 5 mol% while that of Yb³⁺ and Tm³⁺ is fixed. When the glasses are doped with Tm³⁺ ions, the intense blue and red emissions were observed, whereas Yb³⁺ doped glasses exhibited NIR emission at about 980 nm. When the glasses are co-doped with Tm³⁺ and Yb³⁺ ions and excited at 900 nm, the blue and red emission lines were observed to be reinforced and strengthened with increase in the concentration of Y₂O₃. The IR emission band detected at about 1.8 μm due to ³F₄ → ³H₆ transition of Tm³⁺ ions is also observed to be strengthened due to co-doping. The reasons for enhancement in the intensity of various emission bands due to co-doping have been identified and discussed with the help of rate equations for various emission transitions.     

Induced crystallization and the physical properties of PbO–Sb2O3–As2O3: MoO3 glass system

PbO–Sb₂O₃–As₂O₃ glasses mixed with different concentrations of MoO₃ (ranging from 0 to 1.0 mol%) were crystallized. The samples were characterized by X-ray diffraction, scanning electron microscopy and differential thermal analysis techniques. The X-ray diffraction and the scanning electron microscopic studies have revealed the presence of Pb₅Sb₂O₈, PbSb₂O₆, SbAsO₄, Sb₂MoO₆, Sb₄Mo₁₀O₃₁, As₄Mo₃O₁₅, Pb₅Sb₄O₁₁ crystalline phases in these samples. The differential thermal analysis indicated that the surface crystallization prevails over the bulk crystallization as the concentration of the crystallizing agent is increased. The infrared (IR) spectral studies exhibit bands due to MoO₄ structural units in addition to the conventional bands due to various antimonate and arsenate structural groups. The studies on PbO–Sb₂O₃–As₂O₃: MoO₃ glass-ceramics with respect to various physical properties viz., dielectric properties over a range of frequency and temperature, optical absorption, electron spin resonance (ESR) and magnetic susceptibility at room temperature have also been reported. The optical absorption, ESR and magnetic susceptibility studies indicated that the molybdenum ions exist in Mo⁵⁺ state in addition to Mo⁶⁺ state in these samples. The redox ratio found to increase as the concentration of the MoO₃ is increased. The variations observed in all these properties with the concentration of the crystallizing agent have been analyzed in the light of different oxidation states and environment of molybdenum ions in the glass ceramic network.     

Optical properties of glasses in the Li2O–MoO3–P2O5 system

Glasses xLi₂O–(50-x)(MoO₃)₂–50P₂O₅ with x = 10, 20, 30, and 40 mol% were prepared and their optical and electrical properties were investigated. Analysis of the IR spectra revealed that the Li⁺ ions act as a glass modifier that enter the glass network by breaking up other linkages and creating non-bridging oxygens in the network. The optical absorption edge of the glasses was measured for specimens in the form of thin blown films and the optical absorption spectra of those were recorded in the range 200–800 nm. From the optical absorption edges studies, the optical band gap (E _opt) and the Urbach energy (E _e) values have been evaluated by following the available semi-empirical theories. The linear variation of (αhν)^1/2 with hν, is taken as evidence of indirect interband transitions. The E _opt values were found to decrease with increasing Li₂O content by causing increase in the number of non-bridging oxygens in network. The Urbach tail analysis gives the width of localized states between 0.48 and 0.74 eV.     

Transport numbers in the molten system NaF–KF–AlF3–Al2O3

Transport numbers in the molten system NaF–KF–AlF₃ (Al₂O₃, CaF₂) were investigated by the Hittorf method. It was confirmed that in molten cryolite, Na₃AlF₆, 1,010 °C, the current is transported almost exclusively by the Na⁺ cations (t(Na⁺)?=?0.99). When AlF₃ was added to a Na₃AlF₆ melt, the transport number of sodium cations decreased to 0.74 at the composition corresponding to NaAlF₄. In molten K₃AlF₆, the transport number of K⁺ cations equals 0.836 at 1,005 °C. In melts containing both Na⁺ and K⁺, the cations contribute to the charge transport approximately in the ratio of the squares of their ionic radii. When 5 mass % of CaF₂ was added to the molten NaF–KF–AlF₃ system, it remarkably influenced the transport numbers of potassium and fluoride anions.     

Influence of iron ions on dielectric properties of the PbO–Bi2O3–B2O3 glass system

PbO–Bi₂O₃–B₂O₃ glasses containing small concentrations of Fe₂O₃ (0–1 mol%) were subject to dielectric studies (dielectric constant ε′; loss tan δ; and ac conductivity σ _ac) over a wide range of frequency and temperature. From spectroscopic (infrared, optical absorption and ESR spectra) and magnetic susceptibility studies, variations in these properties with dopant ion concentration were analyzed in terms of different oxidation states and iron ion environment in the glass network.     

Upconversion Properties of Er3+/Yb3+ Co-doped TeO2–TiO2–K2O Glasses

The Er³⁺/Yb³⁺ co-doped TeO₂–TiO₂–K₂O glasses were prepared by conventional melting procedures, and their upconversion spectra were performed. The dependence of luminescence intensity on the ratio of Yb³⁺/Er³⁺ was studied, and the relationship between green upconversion luminescence intensity and Er³⁺ concentration is discussed in detail. The 546 nm green upconversion luminescence intensity is optimised in the studied glasses either when the Yb³⁺/Er³⁺ ratio is 25/1 and Er³⁺ concentration is 0.1 mol%, or when the Yb³⁺/Er³⁺ ratio is 10/1 and Er³⁺ concentration is 0.15 mol%. These glasses could be one of the potential candidates for LD pumping microchip solid-state lasers.