Teiichi Hanada

Fluorescence properties of Er3+ ions in glass ceramics containing LaF3 nanocrystals

Abstract Transparent oxyfluoride glass ceramics containing LaF3 and ErF3 were prepared and the fluorescent characteristics of Er3+, such as emission spectra and lifetime of excited states were investigated. By heat-treatment of the as-prepared glass above the glass transition temperature, the formation of LaF3 nanocrystals was confirmed by X-ray diffraction (XRD). With increasing annealing temperature and time, the fluorescence intensity at 540 nm and around 1000 nm increased and the lifetime of the 4 S 3/2 level became longer. Also the 540 nm upconversion intensity by 970 nm pumping increased drastically. These results could be attributed to the change of ligand field of Er3+ ions and the decrease of effective phonon energy because of the precipitation of LaF3 nanocrystals and the incorporation of some of Er3+ ions into fluoride.

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.

Hydroxyl groups in erbium-doped germanotellurite glasses

Abstract Germanotellurite glasses in the compositions of TeO 2 –GeO 2 –ZnO–Y 2 O 3 –Na 2 O–Er 2 O 3 were prepared by various conditions. The effect of the composition and various drying procedures on the content and the vibration frequency of OH groups was investigated. Among various drying techniques for removing the OH groups, it has been found that bubbling a mixture of dry oxygen gas and carbon tetrachloride shows significant effect on removing OH groups. Also the quenching effect of OH upon the lifetimes of the 4 I 11/2 and 4 I 13/2 levels of Er 3+ in germanotellurite glasses was slight with low Er 3+ and OH content.

Monolithic Electrode for Electric Double-Layer Capacitors Based on Macro/Meso/Microporous S-Containing Activated Carbon with High Surface Area

Macro/meso/microporous carbon monoliths doped with sulfur have been prepared from sulfonated poly(divinylbenzene) networks followed by the activation with CO2 resulted in the activated carbon monoliths with high surface area of 2400 m2 g−1. The monolithic electrode of the activated carbon shows remarkably high specific capacitance (175 F g−1 at 5 mV s−1 and 206 F g−1 at 0.5 A g−1).

Mechanisms and concentration dependence of Tm3+ blue and Er3+ green up-conversion in codoped glasses by red-laser pumping

Abstract Tm3+-Er3+ codoped tellurite glasses were pumped at 650 nm and the up-conversion characteristics of Tm3+ and Er3+ luminescences were investigated. By Er3+ codoping, the Tm3+-460 nm up-conversion luminescence due to the 1D2→3F4 transition was quenched and the Tm3+-480 nm up-conversion luminescence due to the 1G4→3H6 transition was selectively sensitized, due to which the intensity became more than 20 times larger than in the absence of Er3+. Both Tm3+-480 nm and Er3+-550 nm up-conversion luminescence intensities have a maximum in the range where the ratio of Er3+- to Tm3+-content is about two. The result was discussed in the context of the energy transfer efficiency calculated from the lifetime of the Er3+:4I 13 2 level, the competition between the excited state absorption efficiency of Tm3+:1G4←3F4 and the ground state absorption of Er3+:4F 9 2 ←4I 15 2 estimated from the Judd-Ofelt analyses, and the concentration quenching of the Er3+:4S 3 2 level, mainly due to the cross relaxation. It is concluded that the small optimum ratio of the donor- to acceptor-content (≅2) should be ascribed to the specific mechanisms in the present sensitized up-conversion.

1.4 mu m band emission properties of Tm3+ ions in transparent glass ceramics containing PbF2 nanocrystals for S-band amplifier

Tm3+ ion doped transparent oxyfluoride glass ceramics containing PbF2 nanocrystals were prepared and infrared fluorescence properties of Tm3+ ions were investigated. From luminescence decay measurement, it is revealed that part of the Tm3+ ions were incorporated into fluoride crystals by annealing as-made glass above glass transition temperature. Temperature dependence of the 1.4 μm band emission properties of Tm3+ ions in transparent glass ceramics was investigated. With lowering temperature, the intensity ratio of the 1.4 μm emission band to the 1.8 μm band increased. At the same time, the center of gravity of the 3H4–3F4 emission shifted to a longer wavelength and it reached about 1485 nm at 25 K. Under 50 K, the peak of the 1.4 μm band split and then the shape of the spectra became flatter. These properties can be utilized for the 1.5 μm (S-band) optical amplifier.

Local structure and 1.5 μm quantum efficiency of erbium doped glasses for optical amplifiers

Abstract The Judd-Ofelt intensity parameters, local structure and 1.5 μm luminescence characteristics of Er 3+ ions were investigated in silicate glasses with the composition of (75 − x)SiO 2 · xAlO l3/2· 25NaO 1/2 · 0.5 ErO l3/2 with various aluminum contents. Radiative decay rate from the 4 I 13/2 level was determined by Judd-Ofelt analyses, and non-radiative decay rate was obtained combined with the lifetime measurement. With increasing Al 2 O 3 content, the multiphonon decay rate decreased, which almost corresponded to the energy shift observed in the phonon sideband spectra, whereas the emission probability of 4 I 13/2 → 4 I 15/2 increased. Accordingly, the quantum efficiencies of the 1.5 μm emission were enhanced from 50% to almost 90%. The results are discussed in terms of the change in the local structure and orbital electron density of Er 3+ ions with the structural evolution of the glass.

Structural characterization of hierarchically porous alumina aerogel and xerogel monoliths

Detailed nanostructures have been investigated for hierarchically porous alumina aerogels and xerogels prepared from ionic precursors via sol-gel reaction. Starting from AlCl3.-6H2O and poly(ethylene oxide) (PEO) dissolved in a H2O/EtOH mixed solvent, monolithic wet gels were synthesized using propylene oxide (PO) as a gelation initiator. Hierarchically porous alumina xerogels and aerogels were obtained after evaporative drying and supercritical drying, respectively. Macroporous structures are formed as a result of phase separation, while interstices between the secondary particles in the micrometer-sized gel skeletons work as mesoporous structures. Alumina xerogels exhibit considerable shrinkage during the evaporative drying process, resulting in relatively small mesopores (from 5.4 to 6.2 nm) regardless of the starting composition. For shrinkage-free alumina aerogels, on the other hand, the median mesopore size changes from 13.9 to 33.1 nm depending on the starting composition; the increases in PEO content and H2O/EtOH volume ratio both contribute to producing smaller mesopores. Small-angle X-ray scattering (SAXS) analysis reveals that variation of median mesopore size can be ascribed to the change in agglomeration state of primary particles. As PEO content and H2O/EtOH ratio increase, secondary particles become small, which results in relatively small mesopores. The results indicate that the agglomeration state of alumina primary particles is influenced by the presence of weakly interacting phase separation inducers such as PEO.

Rigid Crosslinked Polyacrylamide Monoliths with Well‐Defined Macropores Synthesized by Living Polymerization

Rigid crosslinked polyacrylamide monoliths with well-defined macropores have been successfully fabricated by organotellurium-mediated living radical polymerization (TERP) accompanied by spinodal decomposition. The TERP forms homogeneous networks derived from N,N-methylenebis(acrylamide) (BIS), in which spinodal decomposition is induced to form macropores. Macropore diameter can be controlled from submicrons to a few microns, and also the obtained networks contain mesopores in the macroporous skeletons, which are collapsed by evaporative drying. They are promising materials with hydrophilic polyacrylamide surfaces and have enough strength to preserve the macropores from the surface tension arising in the repetitive swelling and drying that may occur in many applications.

Electrical Conduction Properties of Sr-Doped LaPO4 and CePO4 under Oxidizing and Reducing Conditions

Electrical conduction properties of Sr-doped LaPO 4 and Sr-doped CePO 4 under H 2 O/O 2 and H 2 O/H 2 conditions were investigated with conductivity measurements. Conductivities of I mol % Sr-doped LaPO 4 were 10 - 5 . 2 -10 - 3 . 5 S cm - 1 at 500-925°C under wet reducing conditions and were close to those under wet oxidizing conditions. It was found from the H/D isotope effect on conductivity that the material showed dominant protonic conduction under wet reducing conditions. As for 1 mol % Sr-doped CePO 4 , conductivities were 10 - 2 . 8 -10 - 2 . 0 S cm - 1 at 500-925°C under wet oxidizing conditions and much higher than those of 1 mol % Sr-doped LaPO 4 under the same conditions. Such high conductivities of Sr-doped CePO 4 seemed attributable to electronic conduction due to partial oxidation of Ce 3 + to Ce 4 + caused by substituting Sr2 + for Ce 3 + . Under wet reducing conditions, however, conductivities of the material decreased to 10 - 5 . 2 -10 - 3 . 4 S cm - 1 at 500-925°C, which was almost comparable with those of 1 mol % Sr-doped LaPO 4 . It was concluded that Sr-doped CePO 4 showed mixed protonic and p-type electronic conductions under wet reducing conditions. Based on the results of conductivity measurements, defect structures in Sr-doped LaPO 4 and CePO 4 under wet oxidizing and reducing conditions are discussed.