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The crystal structure of deuterated methane hydrate (structure I, space group: Pm3n) was investigated by neutron powder diffraction at temperatures of 7.7–185 K. The scattering amplitude density distribution was examined by a combination of Rietveld method and maximum entropy method (MEM). The distribution of the D atoms in both D2O and CD4 molecules was clarified from three-dimensional graphic images of the scattering amplitude density. The MEM results showed that there were low-density sites for the D atom of D2O in a particular location within the D2O cage at low temperatures. The MEM provided more reasonable results because of the decrease in the R factor that is attainable by this method. Accordingly, the low-density sites for the D atom of D2O probably exist within the D2O cage. This suggests that a spatial disorder of the D atom of D2O occurs at these sites and that hydrogen bonds between D2O molecules become partially weakened. With regard to the CD4 molecules, there were high-density sites for the D atom of CD4, and the density distribution of the C and D atoms was observed separately in the scattering amplitude density image. Consequently, the C-D bonds of CD4 were not observed clearly because the CD4 molecules had an orientational disorder. The D atoms of CD4 were displaced from the line between the C and O atoms, and were located near the face center of the polygon in the cage. Accordingly, the D atoms of CD4 were not bonded to specific O atoms. This result is consistent with the hydrophobicity of the CD4 molecule. We also report the difference between the small and the large cages in the density distribution map and the temperature dependence of the scattering amplitude density. [ABSTRACT FROM AUTHOR]

Optical spectroscopic properties of Er3+ and Tm3+ ions in a tellurite glass, TeO2-BaO-SrO-Nb2O5 (TBSN), were investigated for C- and S-band optical amplifications. On the basis of consideration for cross relaxation among Tm3+ ions and multiphonon relaxation, it was shown that the presence of Nb2O5, which was a source of the highest energy phonon, contributed to the relaxation processes in TBSN glasses. [ABSTRACT FROM AUTHOR]

The spectroscopic properties of Tm3+ ions in (57-x)PbO–xPbF2–25Bi2O3–18Ga2O3 (mol %) glasses were investigated through measurements of absorption, emission, and lifetime measurements. The PbF2 substitution in this glass system raised the lifetime of the 1.48 μm emission. The lifetime for the 3H4 level was changed from 272 to 416 μs when the PbF2 content increased from x=0 to 15. In a 47PbO–15PbF2–25Bi2O3–18Ga2O3 glass, the phonon-assisted energy transfer involving two phonons with the energy of 550 cm-1 dominated the cross relaxation of the Tm3+: 3H4, 3H6→3F4, 3F4 route in spite of the presence of the overlap between the 3H4→3F4 emission and 3H6→3F4 absorption spectra. As a result, PbO–PbF2–Bi2O3–Ga2O3 glasses were thought to be useful for the S-band optical fiber amplifiers. [ABSTRACT FROM AUTHOR]