Spectroscopic studies on Li2O–MgO–Bi2O3–B2O3 glasses

MgO-Li₂O-Bi₂O₃-B₂O₃ glasses were prepared by melt quench technique and analyzed with the help of refractive index, optical, IR, and Raman spectroscopy studies. The present glasses exhibited the mixed modifier effect (MME) through refractive index change non-linearly. The variation in the indirect optical band gap and band tailing in MgO content have been discussed with the glass structure. Based on the obtained values of α_o2-, optical basicity, and interaction parameters, the present glasses were termed as very semi covalent acidic oxide glasses. Raman and Infrared spectra reveal that these glasses are built up of BO₃, BO₄ units of B₂O₃ and octahedral [BiO₆], pyramidal [BiO₃] units of Bi₂O₃ were observed.     

Spectroscopic and dielectric studies on PbO–MoO3–B2O3 glasses incorporating small concentrations of TiO2

This paper deals with the investigation of a variety of physical properties including dielectric constant (over a wide range of frequency and temperature), optical absorption, luminescence, electron spin resonance (ESR) and infrared spectra of a TiO₂-doped lead molybdenum borate glass system. The composition chosen for the study is 30PbO–4MoO₃–(66–x)B₂O₃:xTiO₂ (with x ranging from 0.2 to 2.0). Quantitative analysis of the results of this study shows that, when the content of TiO₂ is around 0.8 mol%, the titanium ions exist predominantly in the tetravalent state and occupy substitutional positions in the glass network. A substantial increase in the insulating strength of these glasses on TiO₂ doping has also been observed. When the concentration of TiO₂ is increased beyond 0.8 mol%, it is observed that titanium ions exist primarily in the Ti³⁺ state and molybdenum ions in the Mo⁵⁺ state; analysis of the results further suggests that both of these ions participate in the depolymerization of the glass network.     

Spectroscopic investigations on PbO–As2O3 glasses crystallized with TiO2

PbO–As₂O₃ glasses mixed with different concentrations of TiO₂ (ranging from 0 to 1.0 mol%) were crystallized. The samples were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy (EDS) techniques. Studies were extended to optical absorption, IR, ESR, luminescence and magnetic susceptibility on these samples. The X-ray diffraction studies reveal the presence of Pb₃O₄, Ti(As₂O₇), Pb(As₂O₆), Pb₃(AsO₄)₂ PbTi₃O₇ and Ti₂O₃ crystal phases. The optical absorption studies together with ESR and magnetic susceptibility measurements indicated that the titanium ions exist in both Ti³⁺ and Ti⁴⁺ states in all the samples and there is an increase in titanium ions in the trivalent state with increasing concentration of nucleating agent TiO₂. The quantitative analysis of these results indicated that there is a growing degree of disorder in the glass network with increasing concentration of the crystallizing agent. The luminescence studies indicated that the samples crystallized with low concentrations of TiO₂ show high luminescence efficiency in the visible region.     

Picosecond nonlinearity of GeO2–Bi2O3–PbO–TiO2 glasses at 532 and 1,064 nm

The third-order optical properties of GeO₂–Bi₂O₃–PbO–TiO₂ glasses at 532 nm and 1,064 nm were studied to evaluate their potential for optical limiting and all-optical switching. The Z-scan technique was used to determine the nonlinear (NL) refractive index, n ₂, and the NL absorption coefficient, α ₂, of samples with different amounts of the constituent oxides. Values of n ₂ ≈ + 0.7 × 10^?14 cm²/W at 1,064 nm and ≈+1.5 × 10^?14 cm²/W at 532 nm were measured. The NL absorption coefficient, α ₂, was smaller than the minimum that our apparatus can measure (α ₂ < 0.01 cm/GW) in the near-infrared (1,064 nm); in the visible region (532 nm), we obtained α ₂ ≈ 4.4 cm/GW. The set of NL parameters measured indicates the potential usefulness of the GeO₂–Bi₂O₃–PbO–TiO₂ glasses for all-optical switching at 1,064 nm and for optical limiting at 532 nm.     

Synthesis and properties of MoO3–V2O5–PbO glasses

Lead vanadate glasses of the system xMoO₃–50V₂O₅–(50-x)PbO (0 ≤ x ≤ 25 mol. %) were synthesized and studied by FTIR and ultrasonic spectroscopy and differential scanning calorimetry to investigate the role of MoO₃ content on their atomic structure. The elastic properties and Debye temperatures of the glasses were investigated using sound velocity measurements at 4 MHz. The activation energy for the glass transition was derived from the dependence of the glass-transition temperature (T_g ) on the heating rate. Similarly, the activation energy of the crystallization process was also determined. According to the IR analysis, the vibrations of the vanadate structural units are shifted towards higher wavenumbers on the formation of bridging oxygens. The change of density and molar volume with MoO₃ content reveals that the molybdinate units are less dense than the lead oxide units. The observed compositional dependence of the elastic moduli is interpreted in terms of the effect of MoO₃ on the coordination number of the vanadate units. A good correlation was observed between the experimentally determined elastic moduli and those computed according to the Makishima–Mackenzie model. It is assumed that MoO₃ plays the role of a glass former by increasing the activation energy for the glass transition and the activation energy for crystallization and by increasing both the thermal stability and the glass formation range of the vanadate glasses.     

Spectroscopic Properties of Er3+/Yb3+-codoped PbO–Bi2O3–Ga2O3–GeO2 Glasses

We investigate the spectroscopic properties of the 1.5-μm emission from the ⁴I_13/2 → ⁴I_15/2 transition of Er³⁺ ions in PbO–Bi₂O₃–Ga₂O₃–GeO₂ glasses for applications in broadband fiber amplifiers. The measured emission peak locates at 1,532 nm with a full width at half-maximum of ∼45 nm. The glasses exhibit a large stimulated emission cross-section of 0.89 × 10⁻²⁰ cm² and a large product of 40.0. Infrared-to-green upconversion occurs simultaneously upon excitation of the 1.5-μm emission with a commercially available 980 nm laser diode. The green-upconversion intensity has a quadratic dependence on incident pump laser power, indicating a two-photon process. Energy transfer processes and nonradiative phonon-assisted decays could account for the population of the ²H_11/2 of Er³⁺. The results indicate the possibility towards the development of lead–bismuth–gallate–germanate based glasses as photonics devices.     

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.     

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.     

Broadband infrared luminescence in Yb-doped Bi2O3–GeO2 glasses

The Yb-doped Bi₂O₃–GeO₂ glasses were prepared by the conventional melt quenching technique. Near-infrared (NIR) broadband emission was found at about 1024 nm, and 1330 nm (under 785 nm excitation), and the measured fluorescent lifetime was about several hundred microseconds. The emission intensity of Yb-doped Bi₂O₃–GeO₂ glasses increased with increasing of Yb dopant in our experiments. The NIR emission should be related to Yb³⁺ and lower valence Bi ions.     

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.     

Ultrasonic and X-ray studies on BaPb1−xBixO3

By means of ultrasonic measurements for BaPb_1−xBi_xO₃ (x = 0.15 ∼ 0.75), it is shown that softened transverse optical phonon modes (ω_TO(O)′s ∼ 150 K in the temperature scale) appear in only the samples in the metallic region (x ≲ 0.30). X-ray measurements show that all the present samples do not exhibit any macroscopic crystal transformation between 25 K and 300 K, so that the appearance of the soft phonon modes must be closely related to the presence of the conduction electrons.     

Ultrasonic,FTIR and thermal investigations of SiO2–Na2O–CaO–P2O5 glasses doped with CeO2

The longitudinal and shear ultrasonic wave velocities for different compositions of SiO₂–Na₂O–CaO–P₂O₅ glasses were measured at room temperature (305 K) using a pulse-echo method at a frequency of 4 MHz. The elastic moduli, Poisson's ratio, microhardness, Debye temperature and other ultrasonic parameters were obtained from experimental data and analyzed using bond compression theory. By calculating the number of network bonds per unit volume, the average stretching constant, and the average ring size, information about the structure of the glass can be deduced. Structural changes after doping with CeO₂ were investigated by FTIR spectroscopy, and by measurements of the thermal expansion coefficient, glass transition and softening temperature to throw more light on the characterization of these glasses.     

Structural and optical properties of WO3–PbO–B2O3 glass-ceramic

The WO₃–PbO–B₂O₃ glasses and glass ceramics are prepared and investigated with the help of XRD, density, molar volume, UV–visible and FTIR spectroscopy. XRD pattern reveals the glassy behavior up to 4% concentration of WO₃ and ceramic behavior of the prepared samples with concentration of WO₃ >4%. Band gap of glass samples decreases with increase in the WO₃ concentration from 0–5%. The samples with WO₃ concentration >5% do not respond to UV–visible absorption. The density and molar volume measurements show the compaction of structure of the samples, which is due to the formation of BO₄ groups. FTIR spectroscopy shows the formation of BO₄ group and W–O–W bending vibration at high concentration of WO₃.     

Near-infrared broadband luminescence and energy transfer in Bi–Tm–Er co-doped lanthanum aluminosilicate glasses

The Bi–Tm–Er co-doped SiO₂–Al₂O₃–La₂O₃ (SAL) glasses, which exhibited a broadband near-infrared (NIR) emission, were investigated by the optical absorption and photoluminescence spectra. A super broadband NIR emission extending from 0.95 to 1.6 μm with a full-width at half-maximum (FWHM) of 430 nm which covered the whole O, E, S, C and L bands, was observed in Bi–Tm–Er co-doped samples under 808 nm excitation, as a result of the overlap of the Bi-related emission band (centered at 1270 nm) and the emission from Tm^{3+ 3}H₄→³F₄ transition (1450 nm) as well as Er^{3+ 4}I_13/2→⁴I_15/2 transition (1545 nm). In addition, a super broadband emission with amplitude relatively flat from 0.95 to 2.1 μm has been observed. The possible energy transfer between Bi-related centers, Tm³⁺ ions and Er³⁺ ions was proposed.     

Effect of B2O3 on the structure and properties of tungsten–tellurite glasses

The elastic properties and Debye temperatures of xB₂O₃–70TeO₂–(30–x)WO₃, (0 ≤ x ≤ 30 mol%) glasses have been investigated using sound velocity measurements at 4 MHz. Ultrasonic and thermal parameters, combined with the results of IR spectroscopic analyses, were employed to explore the effect of B₂O₃ on the structure of tungsten–tellurite glasses. According to IR analysis, there is competition between WO₆ and TeO₄ units to form BO₄ units, and the vibrations of the tellurite structural units are shifted towards lower wavenumbers on the formation of non-bridging oxygens. It is assumed that B₂O₃ acts as a modifier by decreasing the glass-transition temperature T _g and increasing both the thermal stability and glass formation range of the tellurite glasses. The change in density and molar volume with B₂O₃ content reveals that the borate units are less dense than the tellurite structural units. The observed compositional dependence of elastic moduli is interpreted in terms of the effect of B₂O₃ on the coordination number of the tellurite units. A good correlation was observed between experimentally determined elastic moduli and those computed with the Makishima–Mackenzie model.     

Luminescence and energy transfer in La2O3–Nb2O5–B2O3:M3+ (M=Bi,Eu, Dy) glasses

The luminescence and energy transfer processes in La₂O₃–Nb₂O₅–B₂O₃:M³⁺ (M=Bi, Eu, Dy) glasses were investigated using luminescence spectroscopy (excitation and emission, down to 4.2 K) and decay time measurements at room temperature. The observation of niobate luminescence implies a considerable degree of short- and intermediate-range order in these glasses. Energy transfer from the niobate groups to the lanthanide ions was observed for Eu³⁺, but not for Dy³⁺, suggesting that the energy transfer process occurs to the charge-transfer state of the Eu³⁺ ion, rather than to its f-levels. Inter-Eu³⁺ energy transfer was negligible in the concentration range investigated (up to 3 mol%). In contrast, cross-relaxation processes between Dy³⁺ ions were active at concentrations as low as 0.5 mol%. In the Bi³⁺ doped glasses the energy transfer was observed from the Bi³⁺ excited levels to the oxygen deficient niobate groups.     

Thermal properties of 3BaO–3TiO2–B2O3 glasses

Transparent glasses in the system 3BaO–3TiO₂–B₂O₃ (BTBO) were fabricated via the conventional melt-quenching technique. The as-quenched samples were confirmed to be non-crystalline by differential thermal analysis (DTA). Thermal parameters were evaluated using non-isothermal DTA experiments. The Kauzmann temperature was found to be 759 K based on heating-rate-dependent glass transition and crystallization temperatures. A theoretical relation for the temperature-dependent viscosity is proposed for these glasses and glass-ceramics.     

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.