Papers by Author: Tadashi Ishigaki

Abstract: Red-emitting RbLa₂Ti₂TaO₁₀:Eu³⁺ phosphors were synthesized by a conventional solid-state reaction method, and crystal structure and photoluminescence properties were investigated in the detail. RbLa₂Ti₂TaO₁₀ has tetragonal structure with a space group of P4/mmm, in which the B-site cations (Ta and Ti) are arranged into non-ordering sequence. The RbLa₂Ti₂TaO₁₀:Eu³⁺ phosphors exhibited strong red emission, which is due to the 4f-4f transitions of Eu³⁺, at excitation wavelength of 396 nm. The concentration quenching phenomena for RbLa₂Ti₂TaO₁₀:Eu³⁺ phosphors was investigated using percolation model with two-dimensional interactions among the Eu³⁺ sites in the host lattice. Both the critical concentration values with the calculation and experiment are estimated to be x = 0.3-0.4, which indicates that the concentration quenching for RbLa₂Ti₂TaO₁₀:Eu³⁺ phosphors was due to the energy transfer between the nearest Eu³⁺ ions in these compounds

Abstract: We report novel soft chemical synthesis method, solid hydratethermal reaction (SHR) method as a new soft chemistry. This method is very simple and can synthesize the ceramic materials just by storing the mixture of raw materials added a small amount of water in a reactor at low temperature below 373 K. For example, nanosize YVO₄ (under 100 nm in diameter) was obtained using the SHR method.

Abstract: Efficient and well-grown SrAl₂O₄:Eu,Dy phosphors were synthesized by an innovative melt synthesis method. The luminescent intensity and after-grow intensity of the SrAl₂O₄:Eu,Dy phosphors synthesized by the melt synthesis method are comparable to those of the sample synthesized by a conventional solid state reaction. Sintered phosphor balls with excellent luminescent characteristics were obtained.

Abstract: A yellow-emitting NaAlSiO₄:Eu²⁺ phosphor was synthesized using SiO powder as a reducing agent and a silica source material. The emission intensity of the NaAlSiO₄:Eu²⁺ phosphor synthesized using SiO powder is higher than that of a sample produced using a conventional silicate phosphor synthesis reaction using SiO₂ powder. The ratio of non-reduced Eu³⁺ ions in the NaAlSiO₄:Eu²⁺ phosphor synthesized using SiO powder was decreased by the reduction effect of SiO powder.

Abstract: We succeeded in the single crystal growth of Ba₂SiO₄:Eu²⁺ by novel synthesis method which was gas (SiO) and solid (Ba - Sc - Al - Eu - O) phase hybridized. The Ba₂SiO₄:Eu²⁺ single crystal was synthesized by interfacial crystal growth after the reaction of the SiO gas with the surface of Ba - Sc - Al - Eu - O substrate in the reductive atmosphere. The single crystals were plate-like crystals with about 500 μm sizes and emitted green light around 500 nm under 300 - 450 nm excitation.

Abstract: Anatase TiO₂ having high temperature stability and specific surface area was synthesized using a gel precursor in very mild conditions. The precursor gel was obtained by dialysis treatment of Na₁₆Ti₁₀O₂₈–HNO₃ solution. The samples were characterized by X-ray diffraction analysis, transmission electron microscopy, Brunner–Emmett–Teller method for specific surface area measurements, and thermogravimetric analysis.