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.     

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.     

Use of CsCl to Enhance the Glass Stability Range of Tellurite Glasses for Er3+-Doped Optical Fiber Drawing

Tellurite glasses are important as a host of Er³⁺ ions because of their good solubility and because they present broadband optical gain compared with Er³⁺-doped silica, with the potential to increase the bandwidth of communication systems. However, the small glass stability range (GSR) of tellurite glasses compromises the quality of the optical fibers. We show that the addition of CsCl to tellurite glasses can increase their GSR, making it easier to draw good-quality optical fibers. CsCl acts like a network modifier in glass systems, weakening the network by forming Te–Cl bonds. We show that the thermal expansion coefficient mismatch is in the right direction for optical fiber fabrication purposes and that the Bi₂O₃ content can be used to control the refractive index of clad and core glasses. Single-mode and multi-mode Er³⁺-doped optical fibers were produced by the rod-in-tube method using highly homogeneous TeO₂–ZnO–Li₂O–Bi₂O₃–CsCl glasses.     

Effect of Neodymium:Yttrium Aluminum Garnet Laser Irradiation on Crystallization in Li2O–Al2O3–SiO2 Glass

A 355-nm neodymium:yttrium aluminum garnet laser, produced by a harmonic generator, was used for the nucleation process in photosensitive glass containing Ag⁺ and Ce³⁺ ions. The pulse width and frequency of the laser were 8 ns and 10 Hz, respectively. Heat treatment was conducted at 570°C for 1 h, following laser irradiation, to produce crystalline growth, after which a LiAlSi₃O₈ crystal phase appeared in the laser-irradiated Li₂O–Al₂O₃–SiO₂ glass. The present study compares the effect of laser-induced nucleation on glass crystallization with that of spontaneous nucleation by heat treatment.     

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.     

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.     

Pr3+/Er3+ Codoped Ge-As-Ga-S Glasses as Dual-Wavelength Fiber-optic Amplifiers for 1.31 and 1.55 μm Windows

Fluorescence emissions at both 1.31 and 1.55 μm communication windows were observed from Pr³⁺/Er³⁺ codoped Ge-As-Ga-S glasses with a single wavelength pumping at 986 nm. The lifetime of the Er³⁺:⁴ I _11/2 level decreased as the Pr³⁺ concentration increased, and that of the Pr³⁺:¹ G ₄ level increased as the Er³⁺ concentration increased. Energy transfer from the Er³⁺:⁴ I _11/2 level to the Pr³⁺:¹ G ₄ level was responsible for emission of the 1.31 μm fluorescence from the Pr³⁺:¹ G ₄ level. Ge-As-Ga-S glasses that have been doped with Pr³⁺ and Er³⁺ cations are promising amplifier materials for both 1.31 and 1.55 μm communication windows.     

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.     

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.     

Eu2+-Doped Glass Ceramics Containing BaF2 Nanocrystals as a Potential Blue Phosphor for UV-LED

The Eu²⁺-doped glass ceramics containing BaF₂ nanocrystals were prepared and their luminescence properties were investigated. The excitation spectra of Eu²⁺-doped glass ceramics showed an excellent overlap with the main emission region of an ultraviolet light-emitting diode (UV-LED) centered at 380 nm. The 450 nm emission of Eu²⁺ in glass ceramics under the 385 nm excitation was much stronger than that in glass. The Eu²⁺-doped glass ceramics containing BaF₂ nanocrystals may be used as a potential blue-emitting phosphor for UV-LED.     

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.     

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.     

Phase Relations in the System NaF-CaF2-NaAlSiO4-CaAl2Si2O8

The phase diagram of the pseudoternary reciprocal system NaF–CaF₂–NaAlSiO₄–CaAl₂Si₂O₈ is reported in this paper. The phase relations in the system have been investigated by differential thermal analysis, quenching melts, X-ray diffractometry, and optical and electron microscopies. The stable diagonal CaF₂–NaAlSiO₄ divides the system in two pseudoternary systems. The solidus temperatures in the two subsystems NaF–CaF₂–NaAlSiO₄ and CaF₂–NaAlSiO₄–CaAl₂Si₂O₈ are 805°± 2°C and 1095°± 4°C, respectively. An extensive region of liquid–liquid immiscibility is evident in the NaF–CaF₂–NaAlSiO₄ subsystem. The compositions of the two liquids fall outside the compositional surface NaF–CaF₂–NaAlSiO₄–CaAl₂Si₂O₈, but only a small deviation from the ternary behavior is observed.     

Synchrotron Radiation Ti-k XANES Study of TiO2─Y2O3-Stabilized Tetragonal Zirconia Polycrystals

Valence state and site symmetry of Ti ions in TiO₂–Y₂O₃–ZrO₂ powders with 2 mol% Y₂O₃ and 5, 10, 15, and 20 mol% TiO₂, respectively, are studied by X-ray absorption near-edge spectroscopy (XANES). Tetravalent Zr⁴⁺ ions are replaced predominantly by Ti⁴⁺ ions. Within the solubility region of Ti ions, a subsequent displacement of Ti ions from the center of symmetry is observed with increasing TiO₂ content in TiO₂–Y₂O₃-stabilized tetragonal ZrO₂ polycrystals (Ti-Y-TZP) under investigation. This behavior cannot be interpreted with a random substitution of Ti⁴⁺ ions on Zr⁴⁺ lattice sites. On the contrary, this correlation between the TiO₂ content in Ti-Y-TZP and the shift of Ti ions indicates an increasing interaction between the Ti ions with growing TiO₂ content, caused by a subsequent clustering of Ti ions.     

Effect of Yb3+-Codoping on the Upconversion Emission Intensity in Er3+-Doped ZBLAN Fluoride Glasses under 800-nm Excitation

The effect of Yb³⁺-codoping on the upconversion emission intensity in Er³⁺-doped ZBLAN fluoride glasses is investigated. The codoping of Yb enhanced the emission intensity for the samples excited by an 800-nm laser diode beam. The enhancement in a constant YbF₃ content (2 mol%) increased with increasing ErF₃ content was about 70% of the initial value at 550 nm for the glasses containing 8 mol% of ErF₃. The emission intensity at 550 nm in a constant ErF₃ content (5 mol%) increased remarkably with the addition of YbF₃ and was maximized around 7 mol% of YbF₃ content, giving an increased ratio of about 200% of the initial value. The reason for the enhancement is discussed and it is derived mainly from two-step excitation of Er³⁺ assisted by Yb³⁺ excited through the energy transfer from Er³⁺.     

Energy Transfer Enables 1.53 μm Photoluminescence from Erbium-Doped TiO2 Semiconductor Nanocrystals Synthesized by Ar/O2 Radio-Frequency Thermal Plasma

Highly crystalline, highly luminescent nanopowders of Er³⁺-doped TiO₂ have been successfully synthesized via one-step Ar/O₂ radio-frequency thermal plasma processing. Energy transfer from the TiO₂ host to Er³⁺ activators has been confirmed by combined means of UV-vis, excitation, and photoluminescence spectroscopies. As a consequence, bright photoluminescence at ∼1.53 μm was observed from the nanopowders either by directly exciting the Er³⁺ activator or by exciting the TiO₂ host lattice. A comparative study shows that the nanopowder of the same system made via coprecipitation lacks the energy transfer. The plasma-generated nanopowders may thus find applications in optoelectronic devices.     

Processing and Properties of Eu3+:LiTaO3 TransparentGlass–Ceramic Nanocomposites

We report here the processing and properties of transparent glass and glass–ceramic nanocomposites in the Li₂O–Ta₂O₅–SiO₂–Al₂O₃ system in the presence of Eu₂O₃ as luminescent probe. The formation of the LiTaO₃ crystal phase, the crystallite size, and the morphology with the progression of heat treatment have been examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), and Fourier transformed infrared reflectance spectroscopy measurements. The crystallite sizes obtained from XRD and TEM are found to increase with heat-treatment time and vary in the range of 2–20 nm. The measured photoluminescence spectra exhibit emission transitions of ⁵D_0,1→⁷F _j ( j =0, 1, 2, 3, and 4) of Eu³⁺ ions. From the nature of the emission transitions, the site symmetry in the vicinity of Eu³⁺ ions has been found to be near C_3v in the glass–ceramic nanocomposites. An inverse correlation has been observed between the asymmetric ratio ( I _ED/ I _MD) of Eu³⁺ ions and the dielectric constant (ɛ_r), with an increase in the heat-treatment time of glass, which is caused by the dipole–dipole interaction.     

Phase Equilibria and Structural Species in NdCl3–NaCl, NdCl3–CaCl2, PrCl3–NaCl, and PrCl3–CaCl2 Systems

Equilibrium phase diagrams for the systems NdCl₃–CaCl₂ and NdCl₃–NaCl were determined by differential thermal analysis. A simple eutectic was observed at 59 ± 1 mol% CaCl₂ and 600°± 2°C in the NdCl₃–CaCl₂ system. A compound NaCl.3NdCl₃ which melts incongruently at 545°± 5°C to NdCl₃ and a liquid containing approximately 47 mol% NaCl, and a eutectic at 68 mol% NaCl and 439°± 2°C were found in the NdCl₃–NaCl system. On the basis of agreements between the activities calculated by the Clausius–Clapeyron equation and Temkin's model using the present data for the NdCl₃–CaCl₂ system and the literature data for the PrCl₃–CaCl₂ system, the melts in the former system consist of Nd³⁺, Ca²⁺, and Cl⁻ ions and in the latter system of Pr³⁺, Ca²⁺, and Cl⁻ ions. The above approach indicates the presence of Na⁺, Cl⁻, and NdCl^2-₅ ions in the NaCl-rich melts and Nd³⁺, Cl⁻, and NdCl⁻₄ in the NdCl₃-rich melts in the NdCl₃–NaCl system. Analogous ions were indicated in the melts of the PrCl₃–NaCl system.     

Spectroscopic Properties of Er3+-Doped Na2O–La2O3–Al2O3–SiO2 Glasses

Er³⁺-doped sodium lanthanum aluminosilicate glasses with compositions of (90− x )(0.7SiO₂·0.3Al₂O₃)· x Na₂O·8.2La₂O₃· 0.6Er₂O₃·0.2Yb₂O₃·1Sb₂O₃ (in mol%) ( x = 12, 20, 24, 40, 60 mol%) were prepared and their spectroscopic properties were investigated. Judd–Ofelt analysis was used to calculate spectroscopic properties of all glasses. The Judd–Ofelt intensity parameter Ω _t ( t = 2, 4, 6) decreases with increasing Na₂O. Ω₂ decreases rapidly with increasing Na₂O while Ω₄ and Ω₆ decrease slowly. Both the fluorescent lifetime and the radiative transition rate increase with increasing Na₂O. Fluorescence spectra of the ⁴ I _13/2 to ⁴ I _15/2 transition have been measured and the change with Na₂O content is discussed. It is found that the full width at half-maximum decreases with increasing Na₂O.     

Proton Conductivity in Zr4+-Ion-Doped P2O5–SiO2 Porous Glasses

The effect of zirconium ions on glass structure and proton conductivity was investigated for sol-gel-derived P₂O₅–SiO₂ glasses. Porous glasses were prepared through hydrolysis of PO(OCH₃)₃, Zr(OC₄H₉)₄, and Si(OC₂H₅)₄. Chemical bonding of the P⁵⁺ ions was characterized using ³¹P-NMR spectra. The phosphorous ions, occurring as PO(OH)₃ in the ZrO₂-free glass, were polymerized with one or two bridging oxygen ions per PO₄ unit with increased ZrO₂ content. The chemical stability of these glasses was increased significantly on the addition of ZrO₂, but the conductivity gradually decreased from 26 to 12 mS/cm at room temperature for 10P₂O₅·7ZrO₂·83SiO₂ glass. A fuel cell was constructed using 10P₂O₅·5ZrO₂·85SiO₂ glass as the electrolyte; a power of ∼4.5 mW/cm² was attained.