Structure and Nonlinear Optical Properties of Lanthanide Borate Glasses

The third–order nonlinear optical susceptibility, χ⁽³⁾, of lanthanide (lanthanum, praseodymium, neodymium, and samarium) borate glasses has been measured by the third harmonic generation method. The structure of the present glass system has been studied by infrared and Raman spectroscopic methods. The network structures of the present Ln₂O₃–B₂O₃ glasses have been confirmed to be basically similar to each other. Praseodymium, neodymium, and samarium borate glasses exhibit χ⁽³⁾ values that are larger than lanthanum borate glasses, because of the optical resonance effect, in accordance with the f – f transition. Especially, the χ⁽³⁾ value for 30Pr₂O₃·70B₂O₃ glass is 1.8 × 10⁻¹² esu, which is a factor of ∼60 larger than that of SiO₂ glass. This striking enhancement of χ⁽³⁾ is mainly attributed to the large transition moment to the first excitation state.     

Effect of the Atomic Ratio of Ba to Ti on Optical Properties of Gold-Dispersed BaTiO3 Thin Films

Gold-dispersed BaTiO, thin films were prepared by the rf magnetron sputtering method. The atomic ratio of Ba to Ti in the films was varied and the effects on the linear and nonlinear optical properties were investigated. As the atomic ratio increased, the value of χ⁽³⁾/α₅₃₂ for the gold-dispersed BaTiO₃ thin films slightly increased. It was found that the increase in the value of χ⁽³⁾/α₅₃₂ is due mainly to a change in the crystalline state of the BaTiO₃ matrix. However, it was also found that the atomic ratio had a smaller effect on the value of χ⁽³⁾/α₅₃₂ than did the refractive index of the matrix.     

Third-Harmonic Generation from Some Chalcogenide Glasses

Third-order optical nonlinear susceptibilities (χ⁽³⁾) of some high-refractive-index chalcogenide glasses were evaluated from third-harmonic generation. Compared with oxide glasses whose χ⁽³⁾ has been known, χ⁽³⁾ of the present glasses was higher by an order of magnitude. The addition of selenium drastically increased χ⁽³⁾. The highest χ⁽³⁾ was 1.4 × 10^–11 esu, being comparable with those of high-χ⁽³⁾-organic compounds. Further, χ⁽³⁾ generally increased with increasing density in the present glasses.     

Nonlinear Optical Properties of B2O3-Based Glasses: M2O-B2O3(M = Li, Na, K, Rb, Cs, and Ag) Binary Borate Glasses

The third-order nonlinear optical susceptibilities χ⁽³⁾ of M₂O-B₂O₃ (M = Li, Na, K, Rb, Cs, and Ag) binary borate glasses have been measured by the third harmonic generation (THG) method. It is found that the enhancement of χ⁽³⁾by the structural change of BO₃ units to BO₄ units is small, while the enhancement of χ⁽³⁾ due to the formation of non- bridging oxygen is rather significant. The effects of alkali cations on the χ⁽³⁾ of alkali borate glasses are discussed in terms of the M-O bond character, focusing on the covalency of Li₂O-B₂O₃ glasses. Comparison of the χ⁽³⁾ values for Cs₂O-B₂O₃ and Ag₂O-B₂O₃ glasses which contain cations of comparable polarizability reveals that the χ⁽³⁾ value is much greater for Ag₂O-B₂O₃ glasses than for Cs₂O-B₂O₃glasses, which is possibly due to the great contribution of Ag(4 d_z2 + 5 s + 5 p_z ) hybrid orbitals to the nonlinear optical response.     

Tellurite Glasses for Broadband Amplifiers and Integrated Optics

The present investigation discusses the advantage of using RE-ion-doped (Nd³⁺, Tm³⁺, and Er³⁺) TeO₂ glasses for developing fiber and planar broadband amplifiers and lasers. The spectroscopy of RE-ion-doped fibers and glasses is discussed along with the thermal properties of glass hosts. The results of emission from the ³H₄ level in single-mode Tm³⁺-doped tellurite fiber show that the emission band overlaps with Er³⁺ emission from the ⁴I_13/2 level and Nd³⁺ emission from the ⁴F_3/2 level in silicate and tellurite glasses, thereby enabling the development of amplifiers and lasers between 1350 and 1650 nm. Recent results using Z-scan measurements of nonlinear refractive index and absorption demonstrate that the third-order nonlinearity in undoped TeO₂ glasses is of the order of 2 × 10⁻¹⁵ to 3 × 10⁻¹⁵ cm²·W⁻¹ between 1300 and 1550 nm. These results are briefly discussed in view of an amplifier operation combined with ultrafast all-optical switching.     

Optical Study of Lithium–Bismuth–Borate Glasses

Glasses with compositions x Bi₂O₃(75− x )B₂O₃25Li₂O₃ for 0≤ x ≤40 mol% have been prepared using the normal melt-quenching technique. The optical absorption and reflection spectra were recorded at room temperature in the wavelength range 190–1100 nm. From the absorption edge studies, the values of the optical band gap ( E _opt) and Urbach energy (Δ E ) have been evaluated. Optical parameters such as refractive index and complex dielectric constant have been determined. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple–DiDomenico model. Color parameters and color difference data L ^*, U ^*, V ^*, C ^*, h _ue, W , Y _e, Δ L ^*, Δ U ^*, Δ V ^*, Δ C ^*, and Δ E have been calculated.     

Nonlinear Optical Properties of TeO2-Based Glasses: La2O3-TeO2 Binary Glasses

The third-order nonlinear optical susceptibilities, X⁽³⁾, of the xLaO_1.5·(100 – x)TeO₂ binary glasses have been measured by the third harmonic generation (THG) method. In order to investigate the origin of high-intensity third harmonic generation, the various optical properties, such as nonlinear refractive index ( n ₂), Abbe number ( v _d), dispersion energy ( E _d), average excitation energy ( E ₀), (energy gap ( E _g), and polarizability (α_m), have been estimated from the refractive index and UV-visible absorption spectrum measurements. The linear refractive index, polarizability, and E _d/ E ₀² increased, and Abbe number and energy gap decreased, with increasing LaO_1.5 content. The nonlinear optical susceptibility X⁽³⁾ is discussed in relation to these optical parameters.     

Thermal Expansion of the Low-Temperature Form of BaB2O4

Thermal expansion of the low-temperature form of BaB₂O₄ (β-BaB₂O₄) crystal has been measured along the principal crystallographic directions over a temperature range of 9° to 874°C by means of high-temperature X-ray powder diffraction. This crystal belongs to the trigonal system and exhibits strongly anisotropic thermal expansions. The expansion along the c axis is from 12.720 to 13.214 Å (1.2720 to 1.3214 nm), whereas it is from 12.531 to 12.578 Å (1.2531 to 1.2578 nm) along the a axis. The expansions are nonlinear. The coefficients A, B , and C in the expansion formula L _t = L ₀(1 + At + Bt ²+ Ct ³) are given as follows: a axis, A = 1.535 × 10⁻⁷, B = 6.047 × 10⁻⁹, C = -1.261 × 10⁻¹²; c axis, A = 3.256 × 10⁻⁵, B = 1.341 × 10⁻⁸, C = -1.954 × 10⁻¹²; and cell volume V, A = 3.107 × 10⁻⁵, B = 3.406 × 10⁻⁸, C = -1.197 × 10⁻¹¹. Based on α _t = (d L _t /d t )/ L ₀, the thermal expansion coefficients are also given as a function of temperature for the crystallographic axes a , c , and cell volume V.     

Partially Reduced Cuprous Oxide Nanoparticles Formed in Porous Glass Reaction Fields

This paper describes the formation of cuprous oxide (Cu₂O) particles ∼10 nm in diameter and their reduction by hydrogen gas in porous glasses. Nanoparticles of Cu₂O coated with metallic copper are expected to show high third-order optical nonlinear susceptibilities (χ⁽³⁾). The porous glass is a medium in which nanoparticles can be partially reduced without forming agglomerations. Images obtained using transmission electron microscopy showed that particles with the desired core-shell structure were actually formed, even though some particles were not reduced uniformly from the surface. The χ⁽³⁾/α (α: absorbance) values in relevant conditions (10⁻¹³ esu·cm) were similar to that of copper because of the formation of a byproduct of copper nanoparticles on reduction.     

Crystallization and Properties of Fe2O3—CaO—SiO2 Glasses

Nucleation and crystal growth rates and properties were studied in a two-stage heat treatment process for Fe₂O₃-CaO-SiO₂ glasses. Glass transition (T_g) and crystallization temperatures (T _c ) for the glasses lay between about 612.0° and 710.0°C, and 858.5° and 905.0°C, respectively, and magnetite was the main crystal phase. For a glass of 40Fe₂O₃. 20CaO·40SiO₂ (in wt%) the maximum nucleation rate was (68.6 ± 7) × 10⁶/mm³·s at 700°C, and the maximum crystal growth rate was 9.0 nm/min^1/2 at 1000°C. The mean crystal size of the magnetite increased from 30 to 140 nm with variation of nucleation and crystal growth conditions. The glass showed the maxima in saturation magnetization and coercive force, 212.1 × Wb/m² and 30.8 × 10³ A/m, when heat-treated for 4 h at 1000°C and 1050°C, respectively. The variation of the saturation magnetization could be quantitatively interpreted well in terms of the volume fraction of the magnetite, whereas that of the coercive forces could be explained only qualitatively in terms of the particle size of the magnetite. Hysteresis losses showed the maximum value of 1493 W/m³ when heat-treated at 1000°C for 4 h prenucleated at 700°C for 60 min, and increased linearly with increasing heat treatment time under a magnetic field up to 800 × 10³ A/m.     

Deviation from Stoichiometry in Cr2O3 at High Oxygen Partial Pressures

The deviation from stoichiometry, δ, in Cr₂−δO₃ was measured by a tensivolumetric method in the high pO₂ range of ≊10⁴ to 10⁴ Pa at 1100°C. The value of δ, or chromium vacancy concentration, was≊9×10⁻⁵ mol/mol Cr₂O₃ in air for Cr₂O₃ with 99.999% purity. The chemical diffusion coefficient, DT, determined from equilibration data was ≊4.6× cm²·s⁻¹ at 1100°C for pO₂= 2.2 ×10¹ Pa. The self-diffusion coefficient of Cr ions was calculated from and δ and found to be≊1.6×10-17 cm²-s⁻¹, in good agreement with recently measured values.     

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.     

Transition from Ionic to Electronic Conduction in Pure ThO2 Under Reducing Conditions

Open-circuit emf and ac conductivity studies were conducted on two batches of dense polycrystalline ThO₂. The open-circuit emf data were used to delineate the low- p o₂ ionic domain boundary for "pure" ThO₂, which is presented as a log P_θ line on a log Po₂-1/ T diagram. In addition the ionic conductivity, σ_ion, and the high-Po₂ log P_θ boundary were also determined, mainly from ac conductivity measurements, which also confirmed the Po₂^I/4 dependence of σ_p, the p-type electronic conductivity, shown by other investigators. The main results are, for the first batch, log Pθ= 12.7−220.2 × 10³/4.575T, log σ_ion= 1.9−44.3×10³/4.575T, and log P_θ=−1.0−31.4 × 10³/4.575T; for the second batch, log Pθ=11.2−219.7 × 10³/4.575T, log σ_ion= 1.7−41.6 × 10³/4.575T, and log Pθ=0.6−40.4 × 10³/4.575T. The oxygen permeability of ThO₂ tubes and the oxidation rate constant of Th were predicted from the conductivity and emf data and compared with direct measurements previously reported. The calculated and previously measured permeabilities agreed very well; however, the correlation between the predicted and previously measured oxidation kinetics was somewhat less satisfactory.     

Comparison of the Luminescence Properties of Dy3+ in α-Sialon and Oxynitride Glass

Dy-α-sialon and β-Si₃N₄ materials containing Dy-oxynitride glass were hot pressed at 1800°C for 1 h. The luminescence spectra of Dy³⁺ in these samples were compared when excited at 350 nm. The results showed that two strong emission bands in the region 470–500 nm and 570-600 nm, associated with the ⁴F_9/2→⁶H_15/2 and ⁴F_9/2→⁶H_13/2 transitions of Dy³⁺ ions, were observed in Dy-α-sialon. However, no emission peak was detected from the β-Si₃N₄ sample, despite it containing the same amount of Dy³⁺ cations. This proved that only the Dy³⁺ cations in the α-sialon structure, not those in the oxynitride glass, produce the luminescence spectrum.     

Mechanism of the Blue Up-Conversion in Tm3+/Nd3+-doped Calcium Aluminate Glasses

Blue up-conversion fluorescence from the Tm³⁺:¹ G ₄→³ H ₆ (480 nm) transition has been observed from calcium aluminate glass codoped with Tm³⁺/Nd³⁺. The mechanism for the up-conversion process consists of a two-photon process. An excitation beam with a wavelength of 791 nm first excites Tm³⁺ to the ³ H ₄ level, where Tm³⁺ again absorbs the 1060 nm emission from Nd³⁺:⁴ F _3/2→⁴ I _11/2 to attain the Tm³⁺:¹G₄ level. Lifetime and intensity variations with compositions suggest the presence of an efficient energy transfer from Nd³⁺ to Tm³⁺. The highest 480 nm emission intensity has been obtained from the glass with 0.1 mol% of Nd₂O₃ and 0.2 mol% of Tm₂O₃.     

Optical Properties of Dysprosium-Doped Low-Phonon-Energy Glasses for a Potential 1.3 μm Optical Amplifier

Dysprosium-doped glasses were prepared in the system of gallium-based sulfide, tellurite, zirconium-baed and indium-based fluorides and their optical properties were studied. From the absorption cross sections of five f-f bands, three Judd-Ofelt parameters, ω _t ( t = 2, 4, 6), of Dy³⁺ ion were determined. The compositional variaton of the ω₂value showed the order sulfide > tellurite > fluorozirconate > fluoroindate, whereas the ω₆ value showed the opposite tendency. Compositional variaton of the fluorescence intensity ratio of the (⁴F_9/2⁶H_13/2)/(⁴F_9/2)→⁶H_15/2) is explained by the ratio of ω₂/ω₆ of doped Dy³⁺. The emission probabilities A and the branching ratio β from ⁶H_9/2 and ⁶F_11/2 levels, which are the doublet initial level of the 1.3 μm luminescence, were calculated for the glasses, and it was found that both values showed a tendency similar to that of ω₂ against the glass composition. In the sulfide glass, A was 2.6 × 10³S^-1 and β was 93%, both the highest in all of the glasses investigated. By 1.06 μm pumping of a Nd: YAG laser, the sulfide glass showed strong 1.3 μm emission and the lifetime was 25 μs, resulting in a quantum efficiency of 7%. This value is higher than that of the Pr³⁺:¹G₄ level in ZBLAN glass with β= 60%.     

Binary Titania-Silica Glasses Containing 10 to 20 Wt% TiO2

A series of glasses in the TiO₂-SiO₂ system was prepared by the flame hydrolysis boule process. Clear glasses containing as much as 16.5 wt% TiO₂ were obtained. More TiO₂ caused opacity due to phase separation and anatase/rutile crystallization during glass boule formation. Glasses in the 12 to ∼17 wt% TiO₂ range were metastable and showed structural rearrangements on heat treatment at temperatures as low as 750CEC (∼200° below the annealing point). These changes were accompanied by large changes in thermal expansion. Thermal treatment can be designed to produce almost any desired expansion between α_-200+700=−5 × 10^-7/°C and +10 × 10^-7/°C. Zero expansion between 0 and 550°C was obtained. Evidence that these changes are due to phase separation and anatase formation is presented. Viscosity data in the glass transition range, refractive index, and density are also presented.     

Phosphorus-Implanted Glass for Radiotherapy: Effect of Implantation Energy

A chemically durable glass that contains a large amount of phosphorus is useful for in situ irradiation of cancers. It can be activated to be a β-emitter with a half-life of 14·3 d by using neutron bombardment. Microspheres of the activated glass that are injected to tumors can irradiate the tumors directly with β-rays without irradiating neighboring normal tissues. In the present study, P⁺ ions in various doses have been implanted into a pure silica glass in a plate form at 200 keV. Almost all the implanted phosphorus is present in the inner region of the glass rather than in the surface region, taking the form of phosphorus colloids for all the doses in the range of 5 × 10¹⁶-1 × 10¹⁸ cm^-2. A large number of amorphous phosphorus colloid particles with diameters of 10-150 nm are formed in the silica glass that has been implanted with a dose of 1 × 10¹⁸ cm^-2; these colloid particles are distributed widely in a layer that is centered at a depth of 200-250 nm. All the investigated glasses hardly release any phosphorus and silicon into water at a temperature of 95°C, even after 7 d. A silica glass that has been implanted with P⁺ ions at 200 keV with a dose of 1 × 10¹⁸ cm^-2 is believed to be useful as a radiotherapy glass with sufficient phosphorus content and high chemical durability.     

Structure, Thermal Behavior, Chemical Durability, and Optical Properties of the Na2O–Al2O3–TiO2–Nb2O5–P2O5 Glass System

The FTIR, Raman, UV-Vis, ³¹P MAS-NMR, DTA, and refractive index measurements have been combined to investigate a series of glasses with the general formula 20Na₂O–5Al₂O₃− x TiO₂–(45− x )Nb₂O₅–30P₂O₅, 15≤ x ≤45. The glass structure, as well as thermal, optical, and chemical durability properties, were then described as functions of the f _Nb/ f _Ti ratio. An increase of the f _Nb/ f _Ti ratio correlates with a decrease in length of the average phosphate chains linked through Nb–O–P and Ti–O–P bonds, with an increase in the glass stability and with increase in the linear refractive indices at 632.8 nm from 1.79 to 1.89. Furthermore, niobium is more effective than titanium in improving chemical durability.     

The Influence of ZnF2 Doping on the Electrical Properties and Microstructure in Bi2O3–ZnO-Based Varistors

ZnO varistors with different amounts of ZnF₂ from 0.00 to 0.80 mol% were prepared using a solid-state reaction technique, to explore the potential application of ZnO. The F-doping effects on the microstructure and electrical properties of ZnO-based varistors were investigated. The average grain size of ZnO increased from 4.93 to 6.48 μm as the ZnF₂ content increased. Experimental results showed that as the ZnF₂ content increased, the breakdown voltage decreased from 617 to 367 V/mm, and the nonlinear coefficient did not change much. However, a slight increase was observed in the leakage current. Besides, when the ZnF₂ content increased, the donor concentration increased from 0.669 × 10¹⁸ to 8.720 × 10¹⁸ cm⁻³. The study indicated that ZnF₂ played a similar role as sintering aids to promote grain growth and the substitutional F atoms in the bulk served as a donor to increase the donor concentration.