Tomoko Akai

Colorless transparent fluorescence material: Sintered porous glass containing rare-earth and transition-metal ions

Transparent fluorescence oxide glass with high emission yields has been prepared. Porous glass was impregnated with rare-earth and transition-metal ions and consequently sintered at 1100°C into a compact nonporous glass. Reduction sintering is indispensable for obtaining fluorescence glass with high emission yield. Sintering of glass impregnated with Eu ions in a reducing atmosphere enhances the emission intensity by about 15 times than that sintered in air. The Eu2+ and Ce3+ ions and Sn2+ and Cu+ ions incorporated in SiO2 glass obtained by reduction sintering exhibit intense fluorescence in the near-ultraviolet and visible ranges, their emission yields are 97%, 70%, 100%, and 90%, respectively.

Green and red high-silica luminous glass suitable for near- ultraviolet excitation

We report on the preparation of transparent and colorless green-and red-emitting luminous glasses by sintering high-silica porous glass impregnated with rare-earth ions. These kinds of glasses can be efficiently excited by near-UV sources. The fluorescence of the glasses under near-UV excitation is dependent on energy transfer processes. In order to obtain strong visible emission, it is necessary to co-dope some optically inert rare-earth ions into the glasses. The roles of the optically inert rare-earth ions are discussed.

Reversible control of silver nanoparticle generation and dissolution in soda-lime silicate glass through x-ray irradiation and heat treatment

Reversible generation and dissolution of 3 nm silver particles in a glass containing only silver ions are repeatedly achieved through a combination of x-ray radiation and heat treatment. X-ray irradiation and 400 °C heat treatment induce a yellow color, whereas heating at 500 °C can change the glass to colorless again. X-ray irradiation produces large amounts of silver atoms and defects, mainly nonbridging oxygen hole centers (NBOs), in glass. Heating at 400 °C accelerates the aggregation of silver atoms into forming silver particles. The NBOs can continuously oxidize the silver atoms of particles into silver ions at higher temperature, leading to dissolution of the silver particles.

Characterization of Li1 − δMn2 − 2δO4 defect spinel materials by their phase transition, magnetic and electrochemical properties

The effects of both the initial Li:Mn ratio and the Mn valency on the electrochemical and the magnetic properties and on the structural changes were investigated using stoichiometric and nonstoichiometric LiMn 2 O 4 samples prepared by a solid-state reaction between 673 and 1173 K. A small but known additional plateau near 3.0-3.2 V was observed on discharging the Li/LiMn 2 O 4 cell using samples with an Mn valency < 3.60 +. However, no plateau at ∼3.2 V was observed for the cell using samples with an Mn valency of 3.61 +. Below 280 K the structure of the former samples changed from a cubic spinel structure into two phases with a cubic and a tetragonal structure, whereas the structure of the latter, i.e. an Mn 4+ -rich sample, remained cubic down to 20 K. Therefore, the additional plateau could be correlated with the instability of the cubic spinel structure of the sample.

Leaching behavior of CRT funnel glass.

The leaching behavior of cathode ray tube (CRT) funnel glass containing 23 mass percent of Pb in 0.001 N HCl, distilled water, and 0.001 N NaOH at 90°C was investigated using a static method. The weight loss and leached amount of each component was measured and surface changes observed by SEM. The leaching mechanism is discussed. In acid solution, the leached amount of Pb showed t(1/2) dependence, that is, diffusion-controlled dependence, which is common in lead silicate glasses. In water and basic solutions, the leached amount showed saturation after higher initial dissolution than in acid and the deposition of many particles on the surface was observed. The amount leached was less for Pb than other components. The deposited particles formed a protective layer, which suppressed the dissolution of the glass. This dense layer must be formed as a result of a high initial dissolution rate.

Blue emission from Eu2+-doped high silica glass by near-infrared femtosecond laser irradiation

Eu2+-doped high silica glass (HSG) is fabricated by sintering porous glass which is impregnated with europium ions. Eu2+-doped HSG is revealed to yield intense blue emission excited by ultraviolet (UV) light and near-infrared femtosecond laser. The emission profile obtained by UV excitation can be well traced by near-infrared femtosecond laser. The upconversion emission excited by 800 nm femtosecond laser is considered to be related to a two-photon absorption process from the relationship between the integrated intensity and the pump power. A tentative scheme of upconverted blue emission from Eu2+-doped HSG was also proposed. The HSG materials presented herein are expected to find applications in high density optical storage and three-dimensional color displays.

Spectroscopic properties of Nd3+-doped high silica glass prepared by sintering porous glass

A new kind of Nd3+, -doped high silica glass (SiO2 > 96% (mass fraction)) was obtained by sintering porous glass impregnated with Nd3+, ions. The absorption and luminescence properties of high silica glass doped with different Nd3+, concentrations were studied. The intensity parameters Omega(t) (t = 2, 4, 6), spontaneous emission probability, fluorescence lifetime, radiative quantum efficiency, fluorescence branching ratio, and stimulated emission cross section were calculated using the Judd-Ofelt theory. The optimal Nd3+ concentration in high silica glass was 0.27% (mole fraction) because of its high quantum efficiency and emission intensity. By comparing the spectroscopic parameters with other Nd3+ doped oxide glasses and commercial silicate glasses, the Nd3+-doped high silica glasses are likely to be a promising material used for high power and high repetition rate lasers.

Tailoring of clusters of active ions in sintered nanoporous silica glass for white light luminescence

To tailor clusters of active ions in glasses is laborious but critical for obtaining high efficient luminescence. Here, we present a facile method to tailor clusters of active ions by using one kind of porous host, the nanoporous silica glass. The white light-emitting glasses were prepared by sintering of nanoporous silica glasses impregnated with Ce3+, Tb3+, Mn2+ and Al3+ ions. The combination of blue, green and red emissions of Ce3+, Tb3+ and Mn2+ ions in the glasses under ultraviolet light excitation create white light emissions. The fluorescence of the glasses under long-wavelength ultraviolet excitation are dependent on energy transfer processes between the active ions; and the Al3+ plays a key role in adjusting of the energy transfer processes.

Chemical behavior of platinum-group metals in oxide glasses

Solubilities of platinum group metals (Pd, Rh, Pt) in several glasses were investigated by the use of optical absorption measurements. The concentrations of these ions in the glasses were determined by chemical analysis. The absorption cross-sections of the ions were determined by relating the absorption coefficient and the analyzed concentration. Using these cross-sections, the solubilities of these ions in multicomponent glasses were investigated. It was found that solubilities of these metals are < 100 ppm in soda-lime-boro-silicate and soda-lime-alumino-boro silicate glasses. Also found was their volatility during melting. Light scattering measurements were also carried out to obtain information on the existence of metal particles. It was found that a considerable fraction of Pt exists as metal particles in soda-lime-alumino-boro-silicate glasses.

Structural Study of Al(acac)3 Catalyzed CH3SiO3/2 Gel

A transparent CH3SiO3/2 gel and an opaque one have been prepared from methyltriethoxysilane. Al(acac)3 is added to obtain the transparency. The two gels are studied by XRD, NMR and infrared spectroscopy. Some amount of silanols remains in the form of T2(CH3SiO(OH)) in the transparent gel, but few in the opaque gel. There is a diffraction peak reflecting intermolecular correlation in the XRD curves, which appears broader at a lower angle in the transparent gel than in the opaque gel. These results are discussed by assuming a larger hindrance in polymerization of silanols in the transparent gel.