Microstructural, dielectric and spectroscopic properties of Li2O-Nb2O5-ZrO2-SiO2 glass system crystallized with V2O5

Li₂O-Nb₂O₅-ZrO₂-SiO₂ glasses mixed with different concentrations of V₂O₅ were crystallized. The samples were characterized by XRD, SEM and DTA techniques. The SEM pictures indicated that the samples contain well defined and randomly distributed crystal grains. The X-ray diffraction studies have revealed the presence of several crystalline phases in these samples. Optical absorption, ESR and photoluminescence spectral studies on these samples have indicated that a considerable proportion of vanadium ions do exist in V⁴⁺ state in addition to V⁵⁺ state and the redox ratio seems to be increasing with increase in the concentration of crystallizing agent V₂O₅. The infrared spectral studies have pointed out the existence of conventional SiO₄, ZrO₄, NbO₆, VO structural units in the glass ceramic network. The study of dielectric properties suggested a decrease in the insulating character of the glass ceramics with increase in the crystallizing agent. A.C. conductivity in the high temperature region seems to be connected mainly with the polarons involved in the process of transfer from V⁴⁺↔V⁵⁺ ions.     

Spectroscopic and magnetic studies of manganese ions in ZnO-Sb2O3-B2O3 glass system

ZnO-Sb₂O₃-B₂O₃ glasses containing different concentrations of MnO ranging from 0 to 1.0 mol% were prepared. A number of studies, viz. optical absorption, infrared and ESR spectra and magnetic susceptibility, were carried out as a function of manganese ion concentration. The analysis of the results indicate that manganese ions mostly exist in Mn²⁺ state in these glasses when the concentration of MnO≤0.6 mol% and above this concentration, these ions seem to exist in Mn³⁺ state in the glass network.     

Emission features of Ho ion in Nb2O5, Ta2O5 and La2O3 mixed Li2O-ZrO2-SiO2 glasses

Li₂O-ZrO₂-SiO₂: Ho³⁺ glasses mixed with three interesting d-block elemental oxides, viz., Nb₂O₅, Ta₂O₅ and La₂O₃, were prepared. Optical absorption and photoluminescence spectra of these glasses have been recorded at room temperature. The luminescence spectra of Nb₂O₅ and Ta₂O₅ mixed Li₂O-ZrO₂-SiO₂ glasses (free of Ho³⁺ ions) have also exhibited broad emission band in the blue region. This band is attributed to radiative recombination of self-trapped excitons (STEs) localized on substitutionally positioned octahedral Ta⁵⁺ and Nb⁵⁺ ions in the glass network. The Judd-Ofelt theory was successfully applied to characterize Ho³⁺ spectra of all the three glasses. From this theory various radiative properties, like transition probability A, branching ratio β_r and the radiative lifetime τ_r, for ⁵S₂ emission levels in the spectra of these glasses have been evaluated. The radiative lifetime for ⁵S₂ level of Ho³⁺ ions has also been measured and quantum efficiencies were estimated. Among the three glasses studied the La₂O₃ mixed glass exhibited the highest quantum efficiency. The reasons for such higher value have been discussed based on the relationship between the structural modifications taking place around the Ho³⁺ ions.     

Effect of Bi2O3 on EPR, optical transmission and DC conductivity of vanadyl doped alkali bismuth borate glasses

Glasses with composition xBi₂O₃·(30−x)M₂O·70B₂O₃ (M=Li, Na) containing 2 mol% V₂O₅ have been prepared over the range 0≤x≤15 (x is in mol%). The electron paramagnetic resonance spectra of VO²⁺ of these glasses have been recorded in the X-band (≈9.3 GHz) at room temperature (RT≈300 K). Spin Hamiltonian parameters, g_∥, g_⊥, A_∥, A_⊥, dipolar hyperfine coupling parameter, P, and Fermi contact interaction parameter, K, have been calculated. The molecular orbital coefficients, α² and γ², have been calculated by recording the optical transmission spectra. In xBi₂O₃·(30−x)Li₂O·70B₂O₃ glasses there is decrease in the tetragonality of the V⁴⁺O₆ complex for x up to 6 mol% whereas for x≥6 mol%, tetragonality increases. In xBi₂O₃·(30−x)Na₂O·70B₂O₃ glasses there is increase in the tetragonality of the V⁴⁺O₆ complex with increasing x. The 3d_xy orbit expands with increase in Bi₂O₃:M₂O ratio. Values of the theoretical optical basicity, Λ_th, have also been reported. The DC conductivity increases with increase in temperature. The order of conductivity is 10⁻⁵ ohm⁻¹ m⁻¹ at low temperature and 10⁻³ ohm⁻¹ m⁻¹ at high temperature. The DC conductivity decreases and the activation energy increases with increase in Bi₂O₃:M₂O ratio.     

Study of molybdenum coordination state and crystallization behavior in MoO3-La2O3-B2O3 glasses by Raman spectroscopy

The ternary MoO₃-La₂O₃-B₂O₃ glasses containing a large amount of MoO₃ (10-50 mol%) are prepared, and their structure and crystallization behavior are examined from the Raman scattering spectrum measurements and X-ray diffraction analyses. It is found that the glass transition and crystallization temperatures and the thermal stability against crystallization decrease with increasing MoO₃ content. It is suggested that the main coordination state of Mo⁶⁺ ions in the glasses is isolated (MoO₄)²⁻ tetrahedral units giving strong Raman bands at 830-860 and 930 cm⁻¹. It is found that the crystalline phases in the crystallized glasses are mainly LaMoBO₆ and LaB₃O₆, and the main crystallization mechanism in MoO₃-La₂O₃-B₂O₃ glasses is surface crystallization. LaMoBO₆ crystals are found to give strong Raman bands at 810-830 and ∼910 cm⁻¹.     

Dielectric relaxation and a.c. conduction phenomena of PbO-PbF2-B2O3 glasses doped with FeO

PbO-PbF₂-B₂O₃ glasses containing different concentrations of FeO have been prepared. The glasses are characterized by X-ray diffraction and differential thermal analysis. The dielectric properties viz., dielectric constant, loss, conductivity, over a moderately wide range of frequency and temperature and dielectric breakdown strength have been investigated. The results of these studies have been analyzed in the light of different oxidation states of iron with the aid of the data on IR, ESR, optical absorption and magnetic susceptibility measurements. The analysis shows that iron ions exist mainly in Fe³⁺ state, occupy tetrahedral positions and increase the insulating strength of the glass if FeO is present in smaller concentrations. However, if FeO is present in higher concentrations in the glass matrix, (i) the dielectric relaxation intensity has been observed to increase, (ii) the intensity and the half width of the ESR signal has been observed to decrease and (iii) the value of magnetic moment (evaluated from magnetic susceptibility) has been observed to drop to a value of 4.6 μ_B from 5.7 μ_B. From these results it has been concluded that in this concentration range, iron ions exist mainly in divalent state.     

Luminescence studies on ZnO-P2O5 glasses doped with Gd2O3:Eu nanoparticles and Eu2O3

Zinc phosphate glasses doped with Gd₂O₃:Eu nanoparticles and Eu₂O₃ were prepared by conventional melt-quench method and characterized for their luminescence properties. Binary ZnO-P₂O₅ glass is characterized by an intrinsic defect centre emission around 324 nm. Strong energy transfer from these defect centres to Eu³⁺ ions has been observed when Eu₂O₃ is incorporated in ZnO-P₂O₅ glasses. Lack of energy transfer from these defect centres to Eu³⁺ in Gd₂O₃:Eu nanoparticles doped ZnO-P₂O₅ glass has been attributed to effective shielding of Eu³⁺ ions from the luminescence centre by Gd-O-P type of linkages, leading to an increased distance between the luminescent centre and Eu³⁺ ions. Both doped and undoped glasses have the same glass transition temperature, suggesting that the phosphate network is not significantly affected by the Gd₂O₃:Eu nanoparticles or Eu₂O₃ incorporation.     

Prediction of defect structure in lithiated tin- and titanium-doped α-Fe2O3 using atomistic simulation

The defect structure of lithiated tin- and titanium-doped α-Fe₂O₃ has been assessed using interatomic potential calculations. Of the models considered for lithiation, a model in which Li⁺ occupies an interstitial site balanced by the reduction of Fe³⁺ to Fe²⁺ on an Fe³⁺ site was found to be more favourable than the substitution of Li⁺ on an Fe³⁺ octahedral site balanced by an O²⁻ vacancy. Insertion of lithium into the interstitial site between two adjacent M⁴⁺ ions was particularly favourable. The calculated lattice parameters decrease on lithiation as has been observed experimentally.     

Emission analysis of Dy and Pr:Bi2O3-ZnF2-B2O3-Li2O-Na2O glasses

In this paper, we present the spectral results of Dy³⁺ and Pr³⁺ (1.0 mol%) ions doped Bi₂O₃-ZnF₂-B₂O₃-Li₂O-Na₂O glasses. Measurements of X-ray diffraction (XRD), differential scanning calorimetry (DSC) profiles of these rare-earth ions doped glasses have been carried out. From the DSC thermograms, glass transition (T_g), crystallization (T_c) and melting (T_m) temperatures have been evaluated. The direct and indirect optical band gaps have been calculated based on the glasses UV absorption spectra. The emission spectrum of Dy³⁺:glass has shown two emission transitions ⁴F_7/2→⁶H_15/2 (482 nm) and ⁴F_7/2→⁶H_13/2 (576 nm) with an excitation at 390 nm wavelength and Pr³⁺:glass has shown a strong emission transition ¹D₂→³H₄ (610 nm) with an excitation at 445 nm. Upon exposure to UV radiation, Dy³⁺ and Pr³⁺ glasses have shown bright yellow and reddish colors, respectively, from their surfaces.     

Nickel ion—A structural probe in BaO-Al2O3-P2O5 glass system by means of dielectric, spectroscopic and magnetic studies

BaO-Al₂O₃-P₂O₅ glasses containing different concentrations of NiO (ranging from 0 to 1.0 mol%) were prepared. A number of studies viz., chemical durability, differential thermal analysis, spectroscopic (infrared, optical absorption spectra), magnetic susceptibility and dielectric properties (constant ε′, loss tan δ, AC conductivity σ_AC over a range of frequency and temperature) of these glasses have been carried out. The studies on chemical durability indicate that there is a significant increase in the corrosion resistance of the glasses; where as the results of differential thermal analysis suggests that there is a substantial improvement in the glass forming ability, with increase in the concentration of NiO up to 0.6 mol% in the glass matrix. The optical absorption, magnetic susceptibility and IR spectral studies point out nickel ions occupy both tetrahedral and octahedral positions in the glass network; the later positions seems to be dominant when the concentration of NiO is beyond 0.6 mol% in the glass matrix. The studies of dielectric properties reveal that the presence of nickel oxide in the glass network causes a considerable improvement in the insulating strength of the se glasses when the concentration of NiO?0.6 mol%.     

α-Fe2O3-In2O3 mixed oxide nanoparticles synthesized under hydrothermal supercritical conditions

α-Fe₂O₃-In₂O₃ mixed oxide nanoparticles system has been synthesized by hydrothermal supercritical and postannealing route, starting with (1−x)Fe(NO₃)₃·9H₂O·xIn(NO₃)₃·5H₂O aqueous solution (x=0-1). X-ray diffraction and Mössbauer spectroscopy have been used to study the phase structure and substitutions in the nanosized samples. The concentration regions for the existence of the solid solutions in the α-Fe₂O₃-In₂O₃ nanoparticle system together with the solubility limits of In³⁺ ions in the hematite lattice and of Fe³⁺ ions in the cubic In₂O₃ structure have been evidenced. In general, the substitution level is considerably lower than the nominal concentration x. A justification of the processes leading to the formation of iron and indium phases in the investigated supercritical hydrothermal system has been given.     

EPR and magnetic susceptibility studies of iron ions in ZnO-Fe2O3-SiO2-CaO-P2O5-Na2O glasses

Room temperature electron paramagnetic resonance (EPR) spectra and temperature dependent magnetic susceptibility data have been obtained on bulk x(ZnO,Fe₂O₃)(65−x)SiO₂20(CaO, P₂O₅)15Na₂O (6≤x≤21 mole%) glasses prepared by melt quenching method. EPR spectra of the glasses revealed absorptions centered at g≈2.1 and 4.3. The variations of the intensity and line width of these absorption lines with composition have been interpreted in terms of the variation in the concentration of the Fe²⁺ and Fe³⁺ ions in the glass and the interaction between the iron ions. EPR and magnetic susceptibility data of the glasses reveal that both Fe²⁺ and Fe³⁺ ions are present in the glasses, with their relative concentration being dependent on the glass composition. The studies reveal superexchange type interactions in these glasses, which are strongly dependent on their iron content.     

Spectroscopic features of Pr, Nd, Sm and Er ions in Li2O-MO (Nb2O5, MoO3 and WO3)-B2O3 glass systems

Li₂O-MO (Nb₂O₅, MoO₃ and WO₃)-B₂O₃ glasses doped with four rare earth ions, viz., Pr³⁺, Nd³⁺, Sm³⁺ and Er³⁺ (of 1.0 mol% each) were prepared. The glasses were characterized by X-ray diffraction, differential scanning calorimetry, ESR, optical absorption and photoluminescence spectra. From the measured intensities of various absorption bands of these glasses, the Judd-Ofelt parameters Ω₂, Ω₄ and Ω₆ have been evaluated. The Judd-Ofelt theory could successfully be applied to characterize the absorption and luminescence spectra of these glasses. From this theory, various radiative properties like transition probability A, branching ratio β_r, the radiative life time τ_r and the emission cross-section σ^E for various emission levels of these glasses have been determined and reported. An attempt has also been made to throw some light on the relationship between the structural modifications and luminescence efficiencies of all the three glasses. The analysis of the data indicated high non-radiative losses in Nb₂O₅ mixed glasses.     

Li2O-(LiCl)2-B2O3-Al2O3系统玻璃的Raman光谱研究

我们用Raman光谱研究了Li₂O(LiCl)₂B₂O₃-Al₂O₃系玻璃的结构,着重研究了Al₂O₃的影响。对于Li₂O-B₂O₃系玻璃,Li₂O含量增加使玻璃中存在的BO₃三角体转变为BO₄四面体, 关键词：     

Structural investigation of xAg2O·(100−x)·[2B2O3·As2O3] glasses doped with manganese ions

Structural analysis of x[(100−y)Ag₂O·yMnO]·(100−x)[2B₂O₃·As₂O₃] glasses, with x=10 mol% and 0≤y≤10 mol%, was performed by means of FT-IR and FT-Raman spectroscopies. The purpose of this work is to investigate the structural changes that appear in the xAg₂O·(100−x)·[2B₂O₃·As₂O₃] glasses with the addition and increase in manganese ions content. FT-IR measurements revealed the presence of pyro-, ortho-, di-, tri-, tetra- and penta-borate groups and structural units characteristic to As₂O₃ in the structure of the studied glasses. FT-IR spectroscopy measurements also show that BO₃ units are the main structural units of the glass system. The presence of structural units characteristic to Ag₂O were not directly evidenced by FT-IR spectroscopy. In addtition, the FT-Raman analysis evidenced the presence of boroxol rings in the structure of the studied glasses.     

The photoluminescent properties of Eu in MgO-Ga2O3-SiO2 nanocrystalline glass-ceramic

The MgO-Ga₂O₃-SiO₂ glass-ceramic (GC) containing MgGa₂O₄ nanocrystals and glasses doped with Eu³⁺ ions were prepared by the sol-gel method. The down-conversion and up-conversion luminescence (UCL) properties were studied. The results indicated that the relative intensity of f-f transitions of Eu³⁺ decreased in contrast with that of charge transfer (CT) absorption with the increase in heating temperature. Using a Xe lamp and 800 nm femtosecond (fs) laser excitation, strong red luminescence of Eu³⁺ in MgO-Ga₂O₃-SiO₂ glasses and GC was observed.     

Effect of hydroxyl groups on Er doped Bi2O3-B2O3-SiO2 glasses

A series of Er³⁺-doped Bi₂O₃-B₂O₃-SiO₂-Na₂O glasses with different hydroxyl groups were prepared and the interaction between the Er³⁺ ions and OH groups was investigated. Infrared spectra were measured in order to calculate the exact content of OH groups in samples. The observed increase of the fluorescence lifetime with the oxygen bubbling time has been related to the reduction in the OH content concentration evidenced by infrared (IR) absorption spectra, which confirmed that the OH groups were dominant quenching centers of excited Er³⁺ and a cause of concentration quenching of 1.5 μm band emission. Various nonradiative decay rates from ⁴I_13/2 of Er³⁺ with the change of OH content were determined from the fluorescence lifetimes and radiative decay rates, which were calculated on the basis of Judd-Ofelt theory.     

Synthesis and laser patterning of Bi-doped Y3Fe5O12 crystals in germanosilicate glasses

New germanosilicate glasses giving the crystallization of yttrium iron garnet Y₃Fe₅O₁₂ (YIG) and Bi-doped YIG, 23Na₂O-xBi₂O₃-(12−x)Y₂O₃-25Fe₂O₃-20SiO₂-20GeO₂ (mol%), are developed, and the laser-induced crystallization technique is applied to the glasses to pattern YIG and Bi-doped YIG crystals on the glass surface. It is clarified from the Mössbauer effect measurements that iron ions in the glasses are present mainly as Fe³⁺. It is suggested from the X-ray diffraction analyses and magnetization measurements that Si⁴⁺ ions are incorporated into YIG crystals formed in the crystallization of glasses. The irradiations (laser power: 32-60 mW and laser scanning speed: 7 μm/s) of continuous wave Yb:YVO₄ fiber laser (wavelength: 1080 nm) are found to induce YIG and Bi-doped YIG crystals, indicating that Fe³⁺ ions in the glasses act as suitable transition metal ions for the laser-induced crystallization. It is suggested that YIG and Bi-doped YIG crystals in the laser irradiated part might orient. The present study will be a first step for the patterning of magnetic crystals containing iron ions in glasses.     

Dielectric and piezoelectric properties of Fe2O3-doped (Na0.5K0.5)0.96Li0.04Nb0.86Ta0.1Sb0.04O3 lead-free ceramics

The effect of a small amount Fe₂O₃ (0.1-2 mol%) doping on the electrical properties of (Na_0.5K_0.5)_0.96Li_0.04Nb_0.86Ta_0.1Sb_0.04O₃ (NKLNTS) ceramics was investigated. It was found that the B-site substitution of Fe³⁺ does not change the crystal structure within the studied doping level and all modified ceramics have a pure tetragonal perovskite structure at room temperature. The addition of Fe₂O₃ can promote the sintering of NKLNTS ceramics, and simultaneously cause the grain growth so that Fe³⁺-doped NKLNTS compositions show degraded densification at higher doping level. Furthermore, the dielectric properties of the NKLNTS ceramics do not show a significant change by Fe₂O₃ doping. However, the addition of Fe₂O₃ was found to have a significant influence on the electric fatigue resistance and the durability against water. The presence of oxygen vacancies caused by the replacement of Fe³⁺ for B-site ions makes the NKLNTS ceramics harder.     

Blue light emission from Eu ions in sol-gel-derived Al2O3-SiO2 glasses

Blue light-emitting glasses were successfully prepared by doping Eu²⁺ ions in the system Al₂O₃-SiO₂. The Al₂O₃-SiO₂ glasses doped with Eu³⁺ ions were synthesized using a sol-gel method, followed by heating in hydrogen gas atmosphere to reduce into the Eu²⁺ ions. The obtained glasses exhibited emission spectra with peak at ∼450 nm due to 4f⁶5d→4f⁷ (⁸S_7/2) transition, the intensities of which strongly changed depending on their glass composition and heating conditions. The emission quantum efficiency of 48% was achieved by heating the glass with the ratio of Al³⁺ to Eu³⁺ at about 6 at 1000 °C in hydrogen gas atmosphere. It was found that the Al₂O₃-SiO₂ glasses were appropriate not only for homogeneously doping the Eu³⁺ ions in glass structure but also reducing to Eu²⁺ ions, resulting in enhanced blue light-emission properties.