Effect of Yb3+-Codoping on the Upconversion Emission Intensity in Er3+-Doped ZBLAN Fluoride Glasses under 800-nm Excitation

The effect of Yb³⁺-codoping on the upconversion emission intensity in Er³⁺-doped ZBLAN fluoride glasses is investigated. The codoping of Yb enhanced the emission intensity for the samples excited by an 800-nm laser diode beam. The enhancement in a constant YbF₃ content (2 mol%) increased with increasing ErF₃ content was about 70% of the initial value at 550 nm for the glasses containing 8 mol% of ErF₃. The emission intensity at 550 nm in a constant ErF₃ content (5 mol%) increased remarkably with the addition of YbF₃ and was maximized around 7 mol% of YbF₃ content, giving an increased ratio of about 200% of the initial value. The reason for the enhancement is discussed and it is derived mainly from two-step excitation of Er³⁺ assisted by Yb³⁺ excited through the energy transfer from Er³⁺.     

Surface Roughness of Yttria-Containing Aluminosilicate Glass-Ceramics as Indicative of Their Machinability

Several series of Y₂O₃-containing aluminosilicate glasses were prepared by an ordinary melting method, and their physical properties, such as density and Vickers hardness, were measured. Heat treatment of these glasses at 1200°C precipitated tubular and hexagonal Ca₄Y₆O(SiO₄)₆ oxyapatite crystals which were characterized by scanning electron microscopy and X-ray diffraction analysis. The homogeneously crystallized glass-ceramics were lathed, and the machinabilities of these samples were estimated by measuring the lathed surface roughness. Then, the relationship between surface roughness and other properties was analyzed to optimize the glass composition. Substitution of BaO for CaO was conducted and the physical properties were examined.     

Determination of Diffusion Coefficients of Dopants in Wet Gels During Leaching

Diffusion of germanium and titanium ions during the leaching of GeO₂-SiO₂ wet gel in water and TiO₂-SiO₂ wet gel in HCl was studied. The gels were densified by heating, and the composition profiles of the densified glasses were observed with a transmission interference microscope. In order to calculate the apparent diffusion coefficients, the observed results were fitted to a solution of the diffusion equation. The diffusion coefficients for germanium and titanium ions in the gels are about 3.0×10⁻⁶ and 1.1×10⁻⁶ cm²/s, respectively.     

Preparation of Amorphous Silicas Doped with Organic Molecules by the Sol-Gel Process

Molecular dispersions of amorphous siliceous materials doped with organic molecules were prepared by a sol-gel process in which Si(OC₂H₅)₄ was hydrolyzed in neutral or acidic solution. An amorphous silica which was doped with quinizarin on the order of 5×10⁻⁵ mol/mol SiO₂ showed photochemical hole burning at ∼4 K.     

Development of gas electron multiplier foils with a laser etching technique

Fine-pitch gas electron multiplier (GEM) foils have been produced for cosmic X-ray polarimeters using a carbon dioxide laser etching technique. The finest hole pitch of the foil which can be produced repeatedly is and the smallest hole diameter is . The electron amplification factor was measured as a function of applied voltage. The behavior of the factor is almost the same as the -pitch standard foil fabricated by CERN. Our GEMs had no rate-dependent gain instability, which is expected of the GEMs having holes of good cylindrical geometry. The amplification factor of the foil in a mixture of 70% argon and 30% carbon dioxide reaches about 5000 without any micro-discharge at a voltage of 570 V between foil electrodes.     

Electronic structures of quinizarin complexed with TiO2 clusters

Electronic structure calculations using the semiempirical method PM3 were performed on quinizarin complexed with TiO₂ clusters. At first, electronic structure calculations of quinizarin complexed with small TiO₂ clusters were performed to check a reliability of the parameters. The calculated transition energies were correlated to the observed absorption spectra. Then, TiO₂ cluster was expanded into rutile type cluster which contained 11 Ti⁴⁺ ions. The LUMO of quinizarin complexed with the cluster was greater than the CB of the matrix. The replacements of Ti⁴⁺ ions by Si⁴⁺ ions changed the densitiy of states of the matrix. The increase of Si⁴⁺ sites shifted the CB to larger energy, and a change of relative energy level of the CB to the LUMO of the dye was observed. This result was consistent with a consideration from the TiO₂ content dependence of the fluorescence lifetimes of quinizarin.     

Formation and Crystallization in the Yttrium Aluminosilicate Glasses Containing Zinc Oxide

Formation of yttrium aluminosilicate glasses containing zinc oxide from batches melted at 1550°C was investigated. Densities, thermal expansion coefficients, and Vickers hardnesses were measured for some glasses. In a specific compositional region, crystals with a convex and pyramidal habit were observed on the glass surface. The crystal was identified as ZnAl₂O₄ (gahnite) which has a Moh's hardness number of ∼8.