Shin-ichi Todoroki

Relation between the Ω6 intensity parameter of Er3+ ions and the 151Eu isomer shift in oxide glasses

The Ωt intensity parameters (t=2,4,6) of Er3+ ions in several oxide glasses and the isomer shift (IS) of 151Eu Mossbauer spectra in glasses of the same composition were determined. Among these Ωt’s, the Ω6 parameter was found to have a good relation with IS; Ω6 decreases with an increase of IS which reflects the 6s electron density of rare‐earth ions. From the theoretical expression of Ωt, Ω6 is considered to be more affected by the overlap integrals of the 4f and 5d orbitals than Ω2 and Ω4, and to increase with an increase of these overlap integrals. These overlap integrals are supposed to decrease when the 6s electron density is larger, since the 6s electron density shields the 5d electron orbital.

Formation and Microstructures of Anodic Alumina Films from Aluminum Sputtered on Glass Substrate

A transparent porous alumina nanostructure was formed on a glass covered tin-doped indium oxide ~ITO! substrate by anodization of a highly pure sputtered aluminum layer. Details of the fabrication and microstructures of porous anodic alumina films are described and a possible mechanism of anodization is outlined. The variation of anodic current density reflects three processes, i.e., ~i! anodization of the sputtered aluminum layer, ~ii! transition of electrolysis from aluminum to the underlying ITO film, and~iii! electrochemical reactions on the ITO film beneath the anodic alumina film. As all the aluminum is completely anodized, the resultant oxide films on the ITO/glass substrate possess a parallel porous structure ~f80-100 nm, cell size in ;350 nm! with a thin arched barrier layer ~;80 nm! and exhibit a high transmittance in the ultraviolet-visible light range ~75-100% transmittance 300-900 nm!.

Room-temperature persistent hole burning of Sm 2+ in oxide glasses

Persistent spectral hole burning in Sm2+-doped borate glasses is observed at room temperature. The possible number of holes is approximately five times larger than in halide glass systems because of the larger inhomogeneous linewidth and smaller hole width of borate glass. In this system the photoionization of trapping electrons other than Sm ions at a site is likely to be dominant because of the absence of an antihole adjacent to the hole.

Oxyfluoride tellurite glasses doped by erbium: thermal analysis, structural organization and spectral properties

Abstract The effects of fluorine substitution in zinc tellurite glass system doped with rare earths on the spectral properties of the Er 3+ ions are investigated. Differential thermal analysis, vibrational spectroscopies studies and in situ high-temperature X-ray diffraction measurements have been considered in term of fluorine influence. As a function of composition, we have principally measured optical absorption, spontaneous emission, and lifetime measurements. Judd–Ofelt intensity parameters of Er 3+ in these host glasses were determined and used to calculate radiative transition rates and lifetimes. The bulk composition variation and addition of fluoride compounds in tellurite glasses result among others, in broad emission spectra, improved emission lifetime and difference in relative band intensities compared to pure oxide glass.

Phonon sideband of Eu3+ in sodium borate glasses

Abstract The phonon sideband (PSB) of Eu3+ associated with the 7F0-5D2 transition was investigated for the B2O3Na2O glasses doped with 1 mol% Eu2O3. It was found that the coupling of the phonon mode with Eu3+ ions in the glasses was through B-O− or B-O stretching vibration of BO3 units and vibrations of BO4− units in tetra- and diborate groups. The results showed that B-O− bonds present around Eu3+ ions, which have the highest phonon energy, contributed to the nonradiative decay by multiphonon relaxation of Eu3+ ions even in low-alkali borate glasses. Moreover, the electron-phonon coupling strength of each borate group was found to be influenced by the fraction present and by the site selectivity of Eu3+ ions for the group.

Origin of periodic void formation during fiber fuse.

An optical discharge running through a single-mode silica glass fiber during fiber fuse was observed and the front part of the generated damage was examined. Their pump power dependences were investigated using a 1.48 mum laser light at powers ranging from 1.1 to 9.0 W. Periodic voids were left by an optical discharge that was in a cavity with a tail. The tail appears because the optical discharge is strongly enclosed in core region. Another mode of periodic void formation was found at near the threshold pump power for fiber fuse propagation. The optical discharge in this case also forms a transient tail during the void formation cycle.

Refractive index and material dispersions of multi-component oxide glasses

Abstract Refractive index dispersion curves in the wavelength region of 0.40 to 5.03 μm are presented for multi-component oxide glass systems: borate, silicate, aluminate, germanate, tellurite, antimonate and heavy metal gallate. The material dispersion was determined using the refractive index data. Reflection spectra in the ultraviolet and infrared regions were measured to investigate the effects of electronic transitions and lattice vibrations on the material dispersion. Thallium tellurite, thallium antimonate and lead gallate glasses exhibit zero material dispersion wavelengths (ZMDWs) over 2.4 μm. The factors affecting the ZMDW are discussed.

Origin of inhomogeneous linewidth of Eu3+ fluorescence in several oxide glasses

The local structure around Eu3+ ions in several oxide glasses (silicate, borate, germanate, and aluminosilicate) was investigated using both Mossbauer spectroscopy and fluorescence measurement including the fluorescence line narrowing technique. The origin of inhomogeneous broadening of fluorescence spectra is discussed. Except for silicate glasses, the isomer shift of 151Eu varied with the population of oxygen species with different microscopic optical basicity. For silicate glasses, it was found that the isomer shift and Stark splitting of 7F1 level showed no compositional dependence. It was assumed that regardless of alkali content, Eu3+ ions in silicate glasses attract a certain number of nonbridging oxygens (NBOs), which is the only species with a negative charge, when incorporated stably into a glass matrix. Further, it was generally found that larger amounts of alkali ions or smaller amounts of macroanions, such as BO4■, AlO4■, and GeO62■, bring about smaller values of inhomogeneous linewidth, ΔνIH...

Phonon sideband spectra and local structure around Eu3+ ions in sodium silicate glasses

The local structure around Eu3+ ions in sodium silicate glasses was investigated by the phonon sideband associated with 5D2 ← 7F0 transition of Eu3+. Since the shapes of the electronic transition were asymmetric due to the Stark splitting of 5D2 level, the spectra were analyzed by assuming the superposition of the Gaussian distributions of phonon energy and coordination of non-bridging oxygen of the Qn (n = 3, 2, 1) unit in silicate glass. The phonon energy almost corresponded to those of the stretching vibrations of Qn units by Raman spectra. The type and fraction of the Qn units coordinating Eu3+ varied with alkaline content. The compositional variations of Qn units were similar to those determined by NMR for undoped alkaline silicate glasses. It is shown that the local structure around Eu3+ is affected by the composition of matrix glass and the phonon sideband analysis can become a powerful technique to estimate the local distribution of Qn in silicate glasses.

Fabrication and characteristics of nanostructures on glass by Al anodization and electrodeposition

An ovel fabrication process of metal and semiconductor nanostructure arrays directly onto glass substrates is described below. An aluminum film was sputter-deposited on a glass substrate coated with a tin-doped indium oxide (ITO) film. The film was then anodically oxidized to obtain a porous alumina template with pore diameters ranging from 5 to 120 nm. Through appropriate chemical dissolution, the barrier layer of the anodic alumina film was removed and the underlying ITO film was exposed to the electrolytes, thus making it possible to deposit metals or semiconductors in the pores of anodic alumina films by a direct current (dc) electrodeposition. In Ni electrodeposition, the porous alumina films not only define the dimensions of the Ni nanowires but also influence their crystalline orientation, showing a textured {220} orientation for f 18 nm nanowires. In addition, through a cathodic electrosynthesis, a peroxocompound of titanium and ruthenium was deposited in the pores of anodic alumina film on ITO/glass substrate. After heating at 873 K for 2 h, a translucent TiO2/RuO2/Al2O3 composite nanostructure on the ITO/glass substrate was finally fabricated. # 2003 Elsevier Ltd. All rights reserved.