Takahiro Murata

Compositional dependence of the valency state of Cr ions in oxide glasses

Absorption spectra of Cr ions in multi-component oxide glasses melted in Ar were measured. The integrated extinction coefficient is used as a parameter to analyze the redox reaction of Cr3+ and Cr6+ in glass samples. The relative content of Cr6+ increased and that of Cr3+ decreased with increasing basicity in silicate and borate glasses; this result is consistent with previous studies. On the contrary, only Cr3+ exist in phosphate glasses. Cr4+ ions were found only in aluminate, gallate and alumino-silicate glasses with modifier contents ≥ 60 mol%. The relationship between point defects and Cr4+ formation is examined on the basis of electron spin resonance measurements. We concluded that the superoxide ion radical (O2−) and the peroxy bonding (-O-O-) oxidize Cr3+ to Cr4+ in aluminate, gallate, and alumino-silicate glasses.

Red phosphorescence properties of Mn ions in MgO–GeO2 compounds

Abstract Red phosphorescence properties on Mn ions doped MgO–GeO2 compounds, Mg4GeO6,Mg2GeO4, and MgGeO3, were investigated. The red phosphorescence was observed in MgGeO3:Mn2+. The red phosphorescence intensity of MgGeO3:Mn2+ increased withadding the MgF2 and Yb2O3. The red phosphorescence duration time of sample with a batch composition of 44 mol%-MgO, 6 mol%-MgF2, 50 mol%-GeO2, 0.1 mol%-MnO, and 0.05 mol%-Yb2O3 is approximately 30 min. The mechanism of red phosphorescence in MgGeO3:Mn2+ is discussed in terms of the relationship between valency state of manganese ions and point defects in matrix compound.

Relationship between the local structure and spontaneous emission probability of Er3+ in silicate, borate, and phosphate glasses

Abstract Extended X-ray absorption fine structure (EXAFS) measurements have been performed on Er31 in silicate, borate, and phosphate glasses in order to investigate the local structure surrounding the Er31.Er31 ions coordinate to non-bridging oxygen ion sites, where alkali or alkaline earth ions terminate the network structure of silicate glasses. In borate glasses, the local structure surrounding Er31 ions is altered by the structural change ofthe borate anion. Er31 ions coordinate to non-bridging oxygen ion sites and BO4 structural units in the cases with and without the formation of non-bridging oxygen, respectively. The former is similar to the case in silicate glasses. Er31 ions selectively coordinate to the PyO site regardless of the glass composition variation. A correlation was observed between the spontaneous emission probability for 4I13/2 → 4I15/2 transition of Er3+ and the average Er–O distance calculated by EXAFS analysis. It shows the maximum value near 2.32 Å, and we conclude that the overlapping radial integral of the 4f and 5d orbitals of Er3+ would be the largest at the optimum Er31– O22 distance 2.3 Å.

Rayleigh scattering in silica glass with heat treatment

Abstract We investigated Rayleigh scattering in silica glass with heat treatment under various conditions, including quenching and slow cooling, and its relation to fictive temperature. The Rayleigh scattering intensity varied according to the conditions of the heat treatment. The scattering intensity in slowly cooled samples is less than that in quenched samples after heating at the same temperature. We evaluated fictive temperatures based on measurements of infrared absorption and Raman scattering. The Rayleigh scattering intensity was related to the fictive temperature regardless of the heat treatment conditions, and a linear relation between them was obtained. In addition, we suggest that the decrease in scattering intensity in slowly cooled samples results from structural relaxation due to viscous flow during the cooling process.

Effect of antimony oxide on the deposition and dispersion of metallic copper nanoparticles in phosphate glasses for optical nonlinear materials

Phosphate glasses containing metallic copper nanoparticles were prepared by melt-quenching and post heat treatment method. The average size, size-distribution, concentration, and dispersion of metallic copper nanoparticles in phosphate glasses were investigated by using both spectrophotometer and transmission electron microscope. The time-temperature-deposition diagram for the glass dispersed with metallic copper nanoparticles was constructed based on the particle size and dispersion of metallic copper nanoparticles in phosphate glasses.

Matrix effect on local structure surrounding Yb3+ and spontaneous emission probability in oxide glasses

Abstract Extended X-ray absorption fine structure measurements have been performed on Yb3+ in silicate, borate, phosphate, and gallate glasses in order to investigate the local structures surrounding Yb3+. The local structures of Yb3+ ions in silicate, borate, and phosphate glasses were similar to those of Er3+ ions. Yb3+ ions do not occupy the network structural sites, but sit around the terminal region of the network or the region between the networks in these glasses. On the other hand, Yb3+ ions substitute the Ga3+ sites in complex anion structural units of the K2O-Ga2O3-Nb2O5 glasses. We classified the local structures surrounding Yb3+ ions in oxide glasses into two types: the former and the latter are interstitial and substitutive types, respectively. The relationship between the spontaneous emission probability for 2F5/2 – 2F7/2 transition of Yb3+ and the local structure of Yb3+ in oxide glasses are discussed in terms of these two types.