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.     

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.     

Tm3+-Doped Gallium–Germanium–Bismuth–Lead Glasses as 1.47 μm Fiber Amplifier Materials

We report the spectroscopic properties of Tm³⁺-doped and Tm³⁺/Ho³⁺-codoped [Ga₂O₃–GeO₂–Bi₂O₃–PbO (PbF₂)] glasses for S-band optical amplifications. The Judd–Ofelt intensity parameters have been determined based on the measured absorption spectra. It is found that PbF₂-modified glasses exhibit a lower Ω₂ value, and the addition of PbF₂ caused the chemical bond associated with Tm³⁺ ions to be more ionic. The PbF₂-free glasses have large peak emission cross-sections in the range of 2.15–2.18 × 10⁻²¹ cm². Meanwhile, the studied glasses exhibit broad 1.47 μm emission with the full width at half-maximum of 119–126 nm. The results indicate that these glasses are useful host material for broadband S-band fiber amplifiers.     

Quantitative Identification of Phonon Modes Controlling the Multiphonon Relaxation in Heavy-Metal Oxide Glasses

The phonon mode(s) controlling the multiphonon relaxation (MPR) in PbO–Bi₂O₃–Ga₂O₃ glass was analyzed, and the effect of GeO₂ addition on the MPR process was investigated. MPR rates were obtained from the lifetimes of the Tm³⁺:³ H ₄ level in glasses over the temperature range 20–280 K. In PbO–Bi₂O₃–Ga₂O₃ glass, phonons from the bending vibration between GaO₄ tetrahedra (∼550 cm⁻¹) controlled the MPR process. On the addition of GeO₂, the phonon mode at ∼770 cm⁻¹ due to the stretching vibration of GeO₄ tetrahedra started to affect the MPR process. Phonon modes controlling the MPR process in PbO–Bi₂O₃–Ga₂O₃–GeO₂ glass were both 550 cm⁻¹ and 770 cm⁻¹.     

Phase Formation and Dielectric Characterization of the Bi2O3–TeO2 System Prepared in an Oxygen Atmosphere

Solid-state synthesis of compositions from the Bi₂O₃–TeO₂ system show that, under an oxygen atmosphere, Te⁴⁺ oxidizes to Te⁶⁺ and yields four room-temperature stable compounds: Bi₂Te₂O₈, Bi₂TeO₆, Bi₆Te₂O₁₅, and new a compound with the nominal composition 7Bi₂O₃·2TeO₂. Dense ceramics can be prepared from all these compounds by sintering between 650° and 800°C under an oxygen atmosphere. The permittivity of these compounds varies from ∼30 to ∼54, the Q × f value from 1.100 to 41.000 GHz (∼5 GHz), and the temperature coefficient of resonant frequency from −43 to −144 ppm/K. Bi₆Te₂O₁₅ and 7Bi₂O₃·2TeO₂ do not react with silver, and, therefore, they have the potential to be used for applications in low-temperature cofired ceramic (LTCC) technology.     

Crystalline Phases and YAG Laser-Induced Crystallization in Sm2O3–Bi2O3–B2O3 Glasses

The glass formation region, crystalline phases, second harmonic (SH) generation, and Nd:yttrium aluminum garnet (YAG) laser-induced crystallization in the Sm₂O₃–Bi₂O₃–B₂O₃ system were clarified. The crystalline phases of Bi₄B₂O₉, Bi₃B₅O₁₂, BiBO₃, Sm _x Bi_{1− x} BO₃, and SmB₃O₆ were formed through the usual crystallization in an electric furnace. The crystallized glasses consisting of BiBO₃ and Sm _x Bi_{1− x} BO₃ showed SH generations. The formation of the nonlinear optical BiB₃O₆ phase was not confirmed. The formation (writing) region of crystal lines consisting of Sm _x Bi_{1− x} BO₃ by YAG laser irradiation was determined, in which Sm₂O₃ contents were∼10 mol%. The present study demonstrates that Sm₂O₃–Bi₂O₃–B₂O₃ glasses are promising materials for optical functional applications.     

Formation and Properties of GeSe2–Ga2Se3–PbI2 Novel Chalcohalide Glasses

The glass-forming region of the GeSe₂–Ga₂Se₃–PbI₂ system was determined and homogeneous glasses were prepared. The maximum dissolvable PbI₂ can be up to 50 mol%. The structures of glasses were characterized by Raman spectroscopy. The thermal, optical, and some basic physical properties of the glasses were investigated. The results show that GeSe₂–Ga₂Se₃–PbI₂ glasses have a wide region of transmission window (0.7–16 μm) and high refractive index (∼2.5) with the addition of PbI₂. The glasses have good glass-forming ability and high glass transition temperatures. Consequently, these novel glasses may be promising candidate materials for infrared optics and nonlinear optical field.     

Glass-Forming Systems Involving GeO2 with Bi2O3, Ti2O, and PbO

The previously studied system GeO₂-Bi₂O₃-TI₂O was extended with the addition of PbO using air- and water-quenched melted samples. Large areas of glass formation were found in the systems GeO₂–Bi₂O₃–PbO and GeO₂–PbO–Tl₂O at all but the lowest GeO₂ contents. Glasses were examined by powder X-ray diffraction, differential thermal analysis, thermomechanical analysis, and Archimedes'technique to obtain glass transition and crystallization exotherm temperatures, thermal expansion coefficients, and densities, which are presented in diagrams for the GeO₂-PbO binary and for the two ternary systems. Based on calculated values of λ₀, the wavelength for zero material dispersion, compositions in this system may be useful for construction of ultralow-loss optical waveguides in the μm region.     

Effect of Molybdenum on the Structure and on the Crystallization of SiO2–Na2O–CaO–B2O3 Glasses

Crystallization of the poorly durable Na₂MoO₄ phase able to incorporate radioactive cesium must be avoided in SiO₂–Al₂O₃–B₂O₃–Na₂O–CaO glasses developed for the immobilization of Mo-rich nuclear wastes. Increasing amounts of B₂O₃ and MoO₃ were added to a SiO₂–Na₂O–CaO glass, and crystallization tendency was studied. Na₂MoO₄ crystallization tendency decreased with the increase of B₂O₃ concentration whereas the tendency of CaMoO₄ to crystallize increased due to preferential charge compensation of BO₄⁻ entities by Na⁺ ions. ²⁹Si MAS NMR showed that molybdenum acts as a reticulating agent in glass structure. Trivalent actinides surrogate (Nd³⁺) were shown to enter into CaMoO₄ crystals formed in glasses.     

Pyrochlore Phase Formation in the System Bi2O3–ZnO–Ta2O5

The subsolidus phase diagram of the system Bi₂O₃–ZnO–Ta₂O₅ in the region of the cubic pyrochlore phase has been determined at 1050°C. This phase forms a solid solution area that includes the ideal composition P, Bi₃Zn₂Ta₃O₁₄; possible solid solution mechanisms are proposed, supported by density measurements of Zn-deficient solid solutions. The general formula of the solid solutions is Bi_{3+ y} Zn_{2− x} Ta_{3− y} O_{14− x − y} , based on the creation of Zn²⁺, O²⁻ vacancies in Zn-deficient compositions and a variable Bi/Ta ratio.     

The Bi2O3–Nb2O5–NiO Phase Diagram

The Bi₂O₃–Nb₂O₅–NiO phase diagram at 1100°C was determined by means of solid-state synthesis, X-ray diffraction, and scanning electron microscopy. A ternary eutectic with a melting point below 1100°C was found to exist in the field between NiO, Bi₂O₃, and the end-member of the δBi₂O₃–Nb₂O₅ solid solution. The existence of the previously reported Bi₃Ni₂NbO₉ phase was disproved. A pyrochlore homogeneity range around Bi_1.5Ni_0.67Nb_1.33O_6.25 was determined together with all the phase relations in this phase diagram.     

Subsolidus Phase Relations in the Ga2O3-In2O3-SnO2 System

Subsolidus phase relationships in the Ga₂O₃–In₂O₃–SnO₂ system were studied by X-ray diffraction over the temperature range 1250–1400°C. At 1250°C, several phases are stable in the ternary system, including Ga₂O₃( ss ), In₂O₃( ss ), SnO₂, Ga_{3− x} In_{5+ x} Sn₂O₁₆, and several intergrowth phases that can be expressed as Ga_{4−4 x} In_{4 x} Sn _{n −4}O_{2 n −2} where n is an integer. An In₂O₃–SnO₂ phase and Ga₄SnO₈ form at 1375°C but are not stable at 1250°C. GaInO₃ did not form over the temperature range 1000–1400°C.     

Properties of BaO–R2O3– Ga2O3–GeO2 (R = Y, Al, La, and Gd) Glasses

Barium gallogermanate glasses were prepared with substitutions of Al₂O₃, Y₂O₃, La₂O₃, and Gd₂O₃ for Ga₂O₃. The effects of these substitutions on the glass transformation temperature, viscosity, thermal expansion, and molar volume have been determined. The changes in properties associated with each substitutional ion are consistent with structural roles reported for these ions in other glasses. Aluminum acts as an intermediate with [AlO₄^–] tetrahedra substituting directly for [GaO₄^–] tetrahedra. Yttrium and gadolinium act as "atypical" modifier ions because of their large field strengths. Finally, the properties of the La₂O₃-substituted glasses indicate a possible dual structural role for La³⁺ ions in these glasses.     

Upconversion Luminescence in Er3+ Doped and Yb3+/Er3+ Codoped Yttria Nanocrystalline Powders

Y_1.9Er_0.1O₃ and Y_1.7Yb_0.2Er_0.1O₃ nanocrystalline powders were prepared via a reverse-strike coprecipitation method using nitrates and ammonia as raw materials. The obtained powders were of cubic-phase structure of Y₂O₃ and the particle size was in the range of ∼60–80 nm. Strong red (⁴F_9/2–⁴I_15/2) and green (²H_11/2/⁴S_3/2–⁴I_15/2) upconversion luminescence were observed in all the samples when excited with a 980-nm continuous wave diode laser. The possible upconversion mechanisms in Y_1.9Er_0.1O₃ and Y_1.7Yb_0.2Er_0.1O₃ were discussed. Power studies indicated that two-photon processes are responsible for the green and red upconversion luminescence in these systems. The codoping of Yb³⁺ greatly enhanced the red (⁴F_9/2–⁴I_15/2) upconversion emission.     

125Te, 27Al, and 71Ga NMR Study of M2O3–TeO2 (M = Al and Ga) Glasses

The structures of M₂O₃–TeO₂ (M = Al and Ga) glasses have been investigated by means of ¹²⁵Te, ²⁷Al, and ⁷¹Ga NMR spectroscopies. The structural units of respective cations in M₂O₃–TeO₂ glasses were quantitatively analyzed. The fractions of TeO₄ trigonal bipyramid, AlO₆ and GaO₆ octahedra decreased and those of TeO₃ trigonal pyramid, AlO₄, AlO₅, and GaO₄ polyhedra increased with increasing M₂O₃ content. Based on the local structures around Te, Al, and Ga atoms, the structure models of M₂O₃–TeO₂ glasses were proposed.     

Effect of Sb2O3 on Thermal Properties of Glasses in Bi2O3–B2O3–SiO2 System

Glasses with compositions 50Bi₂O₃– x Sb₂O₃–10B₂O₃–(40– x ) SiO₂ ( x =0, 1, 3, 5, 8, 10) have been prepared by conventional melt quench technique. Substitution of Sb₂O₃ for SiO₂ exerted an obvious effect on properties of glasses, especially, increased glass transition temperature ( T _g) and crystalline temperature ( T _c) greatly. Results of infrared transmission spectra attributed the effect to the formation of new bridging bonds of Sb–O–B and Sb–O–Si in glass network.     

Subsolidus Phase Relationships in the Ga2O3–Al2O3–TiO2 System

Subsolidus phase relationships in the Ga₂O₃–Al₂O₃–TiO₂ system at 1400°C were studied using X-ray diffraction. Phases present in the pseudoternary system include TiO₂ (rutile), Ga_{2−2 x} Al_{2 x} O₃ ( x ≤0.78 β-gallia structure), Al_{2−2 y} Ga_{2 y} O₃ ( y ≤0.12 corundum structure), Ga_{2−2 x} Al_{2 x} TiO₅ (0≤ x ≤1 pseudobrookite structure), and several β-gallia rutile intergrowths that can be expressed as Ga_{4−4 x} Al_{4 x} Ti _{n −4}O_{2 n −2} ( x ≤0.3, 15≤ n ≤33). This study showed no evidence to confirm that aluminum substitution of gallium stabilizes the n =7 β-gallia–rutile intergrowth as has been mentioned in previous work.     

Phase Relations and Lattice Constants in the MgO-Al2O3-Ga2O3 System at 1550°C

Phase relations and lattice constants in the MgO–Al₂O₃–Ga₂O₃ system at 1550°C have been determined experimentally. In a large part of this system, only a nonstoichiometric spinel is stable. Compositions as extreme as 12.5 mol% MgO–20.5 mol% Ga₂O₃–67 mol% Al₂O₃ for a homogeneous spinel are possible. In the bordering phase diagrams of MgO–Al₂O₃ and MgO–Ga₂O₃, the composition of the spinel is as high as 63 mol% Al₂O₃ or Ga₂O₃, respectively. The contributions of all simple ionic exchange reactions on the lattice constant of the spinel have been deduced from X-ray diffractometry data.     

Preparation and Upconversion Properties of Yb3+, Ho3+: Lu2O3 Nanocrystalline Powders

Yb³⁺, Ho³⁺: Lu₂O₃ nanocrystalline powders were synthesized by a reverse-strike co-precipitation method using NH₄HCO₃ and NH₃·H₂O as precipitators. X-ray diffraction analysis and field emission scanning electron microscopy observation showed that the phase composition of the powders was cubic and the particle size was 30–50 nm. Under the excitation of a 980 nm continuous wave diode laser, green and red emissions centered around 548 and 667 nm, respectively, were observed and the green emission dominated the upconversion spectrum. Power studies revealed that a two-photon process was involved in the upconversion emissions and the possible upconversion mechanisms were discussed.