Optical Absorption Characteristics of Ni2+ in Mixed-Alkali Borate Glasses

Nickel-containing mixed-alkali borate glasses were prepared and their spectral absorption in the visible and near-ir were measured and used to determine the ligand field strength, Racah parameter, and state of coordination of Ni²⁺ ions. The change in these parameters with alkali content is discussed in terms of mixed-alkali effect. Nickel ions were found to occupy octahedral sites in the 20 mol% (Li₂O+Na₂O) glasses, whereas in the 30 mol% (Na₂O+K₂O) glasses Ni^Z+ ions are believed to occupy both octahedral and tetrahedral sites. In most cases slight deviations were observed which increased with increasing alkali content. The results obtained suggest that the substitution of one alkali for another in alkali borate glasses did not produce gross alterations of the glass network sufficient to induce deviations from linearity in property-composition relations.     

Compositional Dependence of Absorption Spectra of Ti3+ in Silicate, Borate, and Phosphate Glasses

Absorption spectra of Ti³⁺ were measured for silicate, borate, and phosphate glasses doped with 0.5 mol% Ti₂O₃.The absorption coefficient at the peak wavelength of the ₂T₂→₂E transition of Ti³⁺ is used as a parameter showing the relative content of Ti³⁺ions in glass samples. The effect of glass composition on Ti³⁺/Ti⁴⁺ redox was studied. For multicomponent glasses, a basicity parameter calculated from glass composition is proposed in terms of coulomb force between the cation and the oxygen ion. The value of the absorption coefficient depends on basicity in silicate and borate glasses; however, it is independent of composition in phosphate glasses.     

Effect of Nd3+ on the Spectroscopic Properties of Bismuth Borate Glasses

In this paper, the spectroscopic properties of bismuth borate glasses doped with different Nd³⁺ concentrations have been investigated. The intensity parameters Ω _t ( t =2, 4, 6), spontaneous emission probability, fluorescence lifetime, radiative quantum efficiency, fluorescence branching ratio, and stimulated emission cross section were determined. The highest radiative quantum efficiency of the glasses is 54%. The optimal Nd³⁺ concentration in the glasses is proposed for high quantum efficiency. The good spectroscopic properties show the possible utilization of the Nd³⁺ doped bismuth borate glasses as laser materials.     

Determination of the Fe2+/Fe3+ Ratio in Nuclear Waste Glasses

The Fe²⁺/Fe³⁺ ratios of 47 simulated nuclear waste glass samples with ratios varying from 0.01 (oxidized) to 1.6 (reduced) were determined by wet-chemical and Mössbauer spectral analyses. The wet-chemical method involved the spectrophotometric determination of Fe²⁺ and total iron using remote spectroscopy with fiber optic chemical sensing. Interferences from other species present in these glasses were examined and alternative analytical techniques were investigated. Results of wet-chemical and Mössbauer spectral analysis were comparable; however, the wet-chemical method is probably preferable for the analysis of highly radioactive glasses until such glasses have been shown to have satisfactory Mössbauer spectra.     

Reduction of Eu3+ to Eu2+ in Aluminoborosilicate Glasses Prepared in Air

Eu₂O₃-doped aluminoborosilicate glasses were prepared in air at high temperature. Luminescence measurements were used to investigate a valence change from Eu³⁺ to Eu²⁺ ions in the aluminoborosilicate glasses. The results showed that the doped Eu³⁺ ions were partially reduced to Eu²⁺ in the Eu₂O₃:RO–Al₂O₃–B₂O₃–SiO₂ (RO=CaO, SrO, BaO, Li₂O) glasses, but not in the Eu₂O₃:RO–Al₂O₃–B₂O₃–SiO₂ (RO=Na₂O, K₂O) glasses. The changes of Eu reduction with different RO components were discussed with the variation of optical basicity of RO and with different valency of R cations. The effects of co-doping BaO and ZnO in aluminoborosilicate glasses on Eu reduction were also investigated and discussed.     

Absorption Spectra and Concentration-Dependent Luminescence of Mn2+ in Silicate Glasses

Glasses activated with Mn²⁺ exhibit green to red luminescence. A widely accepted model proposes that these colors denote 4- and 6-coordination, respectively, for Mn²⁺. The luminescence and absorption of Mn²⁺-activated silicate glasses were studied; the luminescence changed from green to red with increasing Mn²⁺ concentration. The difference in the intensities of emission bands with peaks near 520 and 620 nm accounts for the luminescent color. No experimental evidence for a change in coordination from 4 to 6 was found. Exchange-coupled groupings are proposed to explain red emission in these glasses and possibly in borate and phosphate glasses studied by other workers. Improved resolution of bands and theoretical calculations demonstrate that a covalent-octahedral Mn²⁺ species can account for the spectral data for the silicate glasses.     

Compositional Dependence of Absorption and Fluorescence of b3+ in Oxide Glasses

The integrated absorption cross section, the spontaneous emission probability, and the stimulated emission cross section of Yb³⁺ were determined in silicate, phosphate, borate, germanate, aluminate, gallate, and ZBLAN host glasses. The compositional dependence of the stimulated emission cross section of the ²F_5/2→²F_7/2 transition is determined mainly by the integrated absorption cross section in the glasses. A peak stimulated emission cross section above 1 pm², which is the highest value in glasses, was obtained in a gallate glass with a composition of 40K₂O·20Ta₂O₅. 40Ga₂O₃. The factors affecting the integrated absorption cross section are discussed using the Judd-Ofelt parameters of Er³⁺ calculated in previous studies.     

Electron Spin Resonance of High-Spin Co2+ in Alkali Borate and Alkali Germanate Glasses

Electron spin resonance spectra of high-spin Co²⁺ doped in alkali borate and alkali germanate glasses have been measured at 4.2 K. For comparison, the corresponding spectrum in a 33K₂O·67SiO₂ glass has also been measured. On the basis of the spectral line shape, the observed spectra, together with those in the literature, seem to be classified into four spectral types that represent Co²⁺ ions in octahedral coordination, a mixture of some types of coordination, tetrahedral coordination with nearly axial symmetry, and distorted tetrahedral coordination.     

Molecular Dynamic Simulation of Eu3+ -Doped Sodium Borate Glasses and Their Fluorescence Spectra

A molecular dynamic simulation was performed for sodium borate glasses containing a small amount of Eu₂O₃ to investigate the local structures of cations in glass. A new potential V_B-B in the form -A exp[-C(r - 0.239)²] was added to the regular modified Born-Mayer-Huggins-type potentials, Φ_B-B, Φ^B-O, and ΦO-O, to account for the directional tendency of the borate network structure. With this potential added, both the radial distribution of sodium borate glasses observed by small-angle X-ray diffraction and the change in coordination number of boron with sodium content obtained by NMR agreed well with the simulation. The average coordination number of Ed³⁺ ions in the simulated glasses varied from 7.5 to 8.6, depending on the composition of the host sodium borate glasses. The inhomogeneous line width of the ⁵D₀-⁷F_z emission peak also changed, depending on the sodium content, with a maximum at 18 mol% Na_zO content; this result agrees well with experimental data obtained from laser-induced fluorescence spectra.     

Correlation between Radiative Transition Probabilities of Nd3+ and Composition in Silicate, Borate, and Phosphate Glasses

Compositional dependence of spontaneous emission probabilities between initial ⁴ F _3/2 and terminal ⁴ I _J J = 9/2, 11/2, 13/2, 15/2) levels of Nd³⁺ were studied for about 90 samples of silicate, borate, and phosphate glasses using the Judd–Ofelt theory. The effect of the covalency of the Nd–O bond on the magnitude of intensity parameters was estimated from the variation of spectral profiles of the ⁴ I _9/2→⁴ G _5/2, ² G _7/2 and ⁴ F _7/2, ⁴ S _3/2 transitions. Intensity parameters Ω₄ and Ω₆ and the spontaneous emission probabilities were strongly affected by the ionic packing ratio of the glass host. The results were discussed in terms of the site selectivity of Nd³⁺ ions in glasses.     

Polymorphism of BaTiO3 Acceptor Doped with Mn3+, Fe3+, and Ti3+

The effect of Mn doping on the cubic to hexagonal phase transition temperature in BaTiO₃ has been determined by quenching samples with different Mn contents from a range of temperatures. Under conditions of equilibrating samples in air over the range 1000°–1400°C, cubic solid solutions BaTi_{1− x} Mn _x O_3−δ form over the range 0≤ x ≤0.015(5), whereas hexagonal solid solutions form for x ≥0.02, depending on the temperature. The results are compared with those on doping BaTiO₃ with Fe³⁺ and observations made concerning acceptor doping with Ti³⁺.     

CO2 Retention in High-Alkali Borate Glasses

A study of the high-alkali region of glass formation in the system Na₂O +B₂O₃ reveals that retention of CO₂ from carbonate starting materials can become a serious preparative problem at the high-alkali extreme. Results presented for glasses prepared using both Na₂O and Na₂CO₃ show that residual CO₂ can lead to major differences in physical properties which in this work are represented by the viscosity-related glass transition temperature .     

Energy Transfer and Population Inversion in Heavy Metal Oxide Glasses Doped with Tm3+ and Tb3+

Emission properties and energy transfer of PbO–Bi₂O₃–Ga₂O₃–GeO₂ glasses codoped with Tm³⁺ and Tb³⁺ ions were investigated. The 1.48-μm emission due to the Tm³⁺:³H₄→³F₄ transition can be used to amplify the S-band (1460–1530-nm) signal light. With Tb³⁺ addition, the lifetime and emission intensity of the Tm³⁺:³F₄ level decreased sharply via the Tm³⁺:³F₄→Tb³⁺:⁷F_0,1,2 energy transfer. Population densities of the ³F₄ and ³H₄ levels in Tm³⁺ calculated from rate equations clearly verified that population inversion in Tm³⁺ ions became possible with as little as 0.1 mol% of Tb³⁺ addition.     

Influence of Fe3+/Fe2+ Ratio on the Crystallization of Iron-Rich Glasses Made with Industrial Wastes

The influence of the Fe³⁺/Fe²⁺ ratio on the crystallization of iron-rich glasses was investigated in this study. The glass batches were made from two hazardous industrial wastes: mud (goethite and jarosite) originating from the zinc hydrometallurgical process and electric arc furnace dust (EAFD). Glass compositions were prepared by adding different percentages of carbon powder. The crystallization process was investigated by a combined thermogravimetry/differential thermal analysis technique, in air or nitrogen atmospheres, using powder and bulk glass samples. The crystalline phases formed, i.e., pyroxene and spinels, and their relative ratio were determined by X-ray diffractometry. The experimental results indicated that melting temperature and crystallization behavior were influenced by the initial Fe³⁺/Fe²⁺ ratio and by the amount of carbon added to the glass batch. For goethite and jarosite glass compositions, decreasing the Fe³⁺/Fe²⁺ ratio increased the crystallization rate by favoring magnetite formation. For EAFD glass compositions, the addition of carbon to the batch inhibited chromite–magnetite spinel formation and favored the attainment of an amorphous glassy phase.     

Energy Transfer Process for the Blue Up-Conversion in Calcium Aluminate Glasses Doped with Tm3+ and Nd3+

Excitation of Tm³⁺ to ³ H ₄ using the 791 nm pump source showed the frequency up-converted blue emission (∼480 nm) due to the Tm³⁺:¹ G ₄→³ H ₆ transition in Tm³⁺/Nd³⁺ codoped CaO·Al₂O₃ glasses. Intensity and lifetime changes with rare-earth concentrations suggested the efficient energy transfer of Tm³⁺:³ H ₄→ Nd³⁺:⁴ F _5/2 and Nd³⁺:⁴ F _3/2→ Tm³⁺:¹ G ₄. The latter transfer enabled Tm³⁺ to reach its ¹ G ₄ level, and the blue emission became possible through the ¹ G ₄→³ H ₆ transition. Quantitative analysis with rate equations proved that these two transitions were the most efficient among all the possible energy transfer routes between Tm³⁺ and Nd³⁺. Calculated up-conversion efficiency of the Tm³⁺/Nd³⁺ combination in CaO·Al₂O₃ glass was 6.6 × 10⁻³, and it was ∼4 orders of magnitude larger than those reported for other oxide glasses.     

2.0 μm Emission Properties and Energy Transfer between Ho3+ and Tm3+ in PbO—Bi2O3—Ga2O3 Glasses

Emission properties of 2.0 μm fluorescence and the energy transfer between Ho³⁺ and Tm³⁺ in 57PbO·25Bi₂O₃·18Ga₂O₃ (mol%) glass codoped with Ho³⁺ and Tm³⁺ were investigated. Cross-relaxation rates in Tm³⁺ increased approximately 5 times when the Tm₂O₃ concentration was increased from 1.0 to 1.5 wt%. Coefficients of the forward Tm³⁺→ Ho³⁺ energy transfer were about 15 times larger than those of the Tm³⁺← Ho³⁺ backward transfer. Analysis of the energy transfer and gain spectra indicated that the highest gain at the 2.0 μm wavelength region could be achieved from the glass with 1.5 wt% of Tm₂O₃ and 0.3 wt% of Ho₂O₃.     

Occurrence of Ti3+ and Fe2+ in Mullite

Electron paramagnetic studies showed that Ti³⁺ and Fe²⁺ occur in mullites taken from a refractory material which was fused-cast under a reducing atmosphere. Exposure of the mullite samples to temperatures >1600°C caused oxidation of Ti³⁺ and Fe²⁺ to Ti⁴⁺ and Fe³⁺, respectively.