Two-Dimensional Mapping of Er3+ Photoluminescence in CaF2 Crystal Lines Patterned by Lasers in Oxyfluoride Glass

The laser-induced crystallization method is applied to an oxyfluoride glass with the composition of 41.5SiO₂–21.3Al₂O₃–4.8CaO–12.6NaF–16.4CaF₂–2.9NiO–0.5ErF₃ (mol%), and the lines consisting of CaF₂ nanocrystals (diameter: ∼20 nm) are patterned on the glass surface. It is found from micro-photoluminescence (PL) spectra of Er³⁺ ions that Er³⁺ ions are incorporated into CaF₂ nanocrystals formed by laser (continuous-wave Yb:YVO₄ fiber laser with a wavelength of 1080 nm) irradiations. Two-dimensional mappings of the PL intensity for the ⁴S_3/2→⁴I_15/2 transition of Er³⁺ ions are measured for the surface and cross section of the patterned lines. It is found that two phases giving different PL intensities are formed in the laser-irradiated region, suggesting that the center part of the laser-irradiated region consists of Er³⁺-doped CaF₂ nanocrystals and the surrounding of the center part gives the fluoride ion rich coordination state for Er³⁺ ions. The formation mechanism of Er³⁺-doped CaF₂ nanocrystals is related to the temperature distribution of the laser-irradiated region.     

Effects of Doping Trivalent Ions in Bismuth Borate Glasses

Bismuth borate glasses from the system: 40Bi₂O₃–59B₂O₃–1Tv₂O₃ (where Tv=Al, Y, Nd, Sm, and Eu) and three glasses of composition: 40Bi₂O₃–60B₂O₃, 37.5Bi₂O₃–62.5B₂O₃ and 38Bi₂O₃–60B₂O₃–2Al₂O₃ were prepared by melt quenching and characterized by density, UV-visible absorption spectroscopy and differential thermal analysis (DTA) studies. Bismuth borate glasses exhibit a very strong optical absorption band just below their absorption edge. Glasses were devitrified by heat treatment at temperatures above their glass transition temperatures and the crystalline phases produced in them were characterized by Fourier transform infrared (FTIR) absorption spectroscopy and X-ray diffraction (XRD). Bi₃B₅O₁₂ was found to be the most abundant phase in all devitrified samples. DTA studies on glasses and FTIR and XRD analysis on crystallized samples revealed that very small amounts of trivalent ion doping causes significant changes in the devitrification properties of bismuth borate glasses; rare-earth ions promote the formation of metastable BiBO₃–I and BiBO₃–II phases during glass crystallization.     

Photoluminescence Characteristics of Sol–Gel Materials Prepared from Bimetallic Erbium Alkoxides Coordinated by Al or Ti

Er³⁺-doped Al₂O₃–SiO₂ and TiO₂–SiO₂ powders were prepared by the sol–gel process using bimetallic erbium isopropoxides coordinated with Al or Ti. The local environment surrounding Er³⁺ ions was controlled orderly at the precursor stage. The phase development of two different systems as a function of temperature was characterized by XRD, and the amount of OH groups remaining within the samples was investigated by a Fourier-transformed infrared spectrometer with increasing annealing temperatures. The photoluminescence spectra and lifetimes of two systems annealed at different temperatures were measured and discussed. The strong emission and long lifetime were observed in Er³⁺-doped Al₂O₃–SiO₂ system, ascribed to the homogeneous distribution of Er³⁺ ion.     

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.     

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.     

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.     

Ultrafast Optical Switches and Wavelength Division Multiplexing (WDM) Amplifiers Based on Bismuth Oxide Glasses

Glasses with a high refractive index exhibit interesting properties. All optical switching and broadband amplification performances have been demonstrated using glasses based on bismuth oxide (Bi₂O₃). Optical Kerr shutter (OKS) switching and degenerated four-wave mixing experiments for nonresonant-type Bi₂O₃–B₂O₃–SiO₂ glasses have been performed using femtosecond lasers. This glass exhibits an ultrafast response (<150 fs) in OKS operation. Moreover, terahertz-range (THz-range) optical switching has been successfully performed with this glass, using a 1.5-THz pulse train. Erbium-doped bismuth-based oxide glasses also have been prepared for wavelength division multiplexing (WDM) amplifiers. These glasses exhibit broadband emission and negligible concentration quenching, which indicates that the bismuth-based glass is suitable for broadband amplifiers and highly doped short-length fiber applications for metro use.     

Compositional Dependence of Infrared-to-Visible Upconversion in Yb3+- and Er3+-Codoped Germanate, Gallate, and Tellurite Glasses

Upconversion fluorescences of the green ⁴S_3/2→⁴I_15/2 and red ⁴F_9/2→⁴I_15/2 transitions of the Er³⁺ ion are studied for Yb³⁺- and Er³⁺-codoped sodium germanate, potassium tantalum gallate, and barium tellurite glasses by InGaAs laser-diode pumping. The phonon energies of the host glasses are determined by infrared-reflection measurements. Compositional effects on the Judd—;Ofelt parameters for the Er³⁺ ion, the spontaneous emission probability (SPE) of the ²F_5/2→²F_7/2 transition for the Yb³⁺ ion, and the phonon energy of the glass network are discussed in terms of glass structure. The factors that affect the upconversion fluorescence intensities of the Er³⁺ ion are discussed, using the phonon energy of the host glass and the SPE for the Yb³⁺ ion in the germanate, gallate, and tellurite glasses.     

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.     

Compositional Dependence of Phase Separation and Photoluminescence in Er-Doped Alkaline Borosilicate Glasses

Er³⁺-doped materials have attracted great attention. In this study, the effects of the kind of alkali (Li, Na, and K), Er₂O₃ concentration (up to 3 mol%), and P₂O₅ addition (0 and 2 mol%) on the phase separation, optical absorption, and photoluminescence (PL) of the alkali borosilicate glasses were investigated. The relationship between microstructure and optical properties of the glasses is discussed. It was found that the development of the droplet phase enhances both the light-scattering effect (enhancing the PL intensity) and the concentration-quenching effect (reducing the PL intensity). As a result, the variation of the PL intensity of the Er^{3+ 4}I_13/2→⁴I_15/2 transition with Er₂O₃ content is mainly caused by the conflict between the light-scattering effect and the concentration-quenching effect. The 1 mol% Er₂O₃-doped, P₂O₅-containing, sodium borosilicate glass has the optimum microstructure and thus the highest PL intensity.     

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.     

Spectroscopic Properties and Thermal Stability of Er3+-Doped Germanotellurite Glasses for Broadband Fiber Amplifiers

The thermal stability and spectroscopic properties of Er₂O₃-doped TeO₂–GeO₂–ZnO–Na₂O–Y₂O₃ glasses for 1.5 μm fiber amplifiers were investigated. The thermal stability of the 75TeO₂·20ZnO· 5Na₂O glass was improved by introducing GeO₂ and Y₂O₃. The radiative transition and the nonradiative transition have a dominant influence on the ⁴I_13/2 level lifetime of Er³⁺ in high- and low-GeO₂ regions, respectively. Adding Y₂O₃ increases the ⁴I_13/2 level lifetime of Er³⁺ significantly. The Judd–Ofelt (J-O) parameter Ω₆ shows a strong correlation with the 1.5 μm emission bandwidth; and the larger the Ω₆, the wider the bandwidth.     

Interaction between Barium Titanate and Binary Glasses

Interactions between BaTiO₃, and three binary glasses were studied through the reaction of BaTiO₃, powder with glass powder. For PbO–B₂O₃ and PbO–SiO₂ glasses, the reaction led to stable compound formation, the substitution of Pb in the BaTiO₃ structure, and noticeable grain growth of BaTiO₃. The interaction phenomena for these two glass systems were very similar. The substitution of Pb into BaTiO₃ is assisted by chemical reactions in which BaB₂O₄ or Ba₂SiO₄ is formed. The substitution into BaTiO3 also seems to be closely related to the grain growth of BaTiO₃. On the other hand, only compound formation was observed during the processing of BaTiO₃ with Bi₂O₃–B₂O₃ glass. Neither BaTiO₃ grain growth nor Bi substitution took place with the Bi₂O₃–B₂O₃ glass system. Based on the observed reactions and the glass viscosity, several sintering aids for BaTiO₃ ceramic products are suggested in this paper.     

Populations and Emission Properties of the 5I6 and 5I7 Levels in Ho3+ Doped into PbO–Bi2O3–Ga2O3 Glasses

Emission properties of PbO–Bi₂O₃–Ga₂O₃ glasses doped with Ho³⁺ were investigated for fiber-optic amplification at the 1.18 μm wavelength region. When the glasses were doped with Ho³⁺ ions only, there was a weak emission at 1.18 μm with a lifetime of ∼200 μs. However, when Yb³⁺ ions were codoped, the lifetime of the 1.18 μm emission increased to 630 μs together with a significant increase in intensity. A similar enhancement in the intensity and lifetimes was realized for the 2.05 μm emission. These effects are due to energy transfer from the Yb³⁺:²F_5/2 to the Ho³⁺:⁵I₆ level. Devitrification of the ternary PbO–Bi₂O₃–Ga₂O₃ glasses was efficiently suppressed by adding 10 mol% GeO₂. Optimum Ho³⁺ concentration was ∼0.4 mol%, whereas Yb³⁺ ions can be added up to the solubility limit.     

Fabrication and Efficient Infrared-to-Visible Upconversion in Transparent Glass Ceramics of Er–Yb Co-Doped CaF2 Nano-Crystals

Transparent glass ceramics containing CaF₂ nano-crystals co-doped with Er–Yb were developed by heat treatment of glasses in the system SiO₂–Al₂O₃–CaF₂–LnF₃ (Ln=Er, Yb). The crystal size of CaF₂ increased with increasing heat-treatment temperature. Upconversion emission intensities at 660 and 540 nm increased dramatically with increasing heat-treatment temperature. The cathode luminescence mapping indicates that the visible Er-luminescence arises mainly from the precipitated CaF₂ nano-crystals with a phonon energy lower than that of a silicate matrix. It is concluded that both Er and Yb were concentrated in the CaF₂ nano-crystals, and the quantum efficiency of Er³⁺-luminescence and the energy transfer efficiency from Yb³⁺ were considerably improved after ceramization.     

Scintillation from Eu2+ in Nanocrystallized Glass

A Eu²⁺-doped SiO₂–Al₂O₃–CaO–CaF₂ glass was prepared and converted into a transparent glass ceramic by heat treatment. The crystalline phase and its size were determined by X-ray diffraction and a transmission electron microscopy. The scintillation of Eu²⁺ ions in both glass and ceramic under X-ray excitation was investigated and compared with that in a single-crystal scintillator.     

Al2O3–ZrO2–SiO2 Ternary Glasses for Molybdenum Oxidation Barriers

The wettability of binary and ternary glasses belonging to SiO₂–Al₂O₃–ZrO₂ diagram has been studied using the sessile drop technique at 1750° and 1800°C. The ternary SiO₂–Al₂O₃–ZrO₂ (90–5–5 wt%) glass has proved to be well appropriated as a molybdenum oxidation barrier coating. The addition of 5 wt% of MoO₂ slightly improves its wettablity at higher temperatures without affecting its oxidation barrier properties. The Mo comes into the glass network as a mixture of Mo⁵⁺, Mo⁴⁺, and Mo⁶⁺. After oxidation at 1000°C in oxygen atmosphere, the molybdenum remains in the glass network as Mo⁶⁺.     

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.     

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.     

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.