Papers by Author: Kenji Toda

Abstract: We report synthesis of nanosized oxide materials using a novel water assisted solid state reaction (WASSR) method. This novel soft chemical synthesis method is very simple and can synthesize nanoparticle materials just by storing or mixing raw materials added a small amount (typically 10wt%) of water in a reactor at low temperature below 373 K. Combinations of raw materials have a significant influence on the reaction rate.

Abstract: Well-grown Ba₉Sc₂Si₆O₂₄:Ce³⁺ phosphors were synthesized by a novel melt quenching synthesis method. Sintered phosphor balls with excellent luminescent characteristics were obtained. This method is useful tool for rapid screening of phosphor materials.

Abstract: We report a novel soft chemical synthesis method, water assisted solid state reaction (WASSR) method. This method is very simple and can synthesize many ceramic materials just by storing or mixing raw materials added a small amount of water in a reactor at low temperature below 373 K. For example, well-crystalline SrMoO₄ was obtained using the WASSR method.

Abstract: Well-grown M₃MgSi₂O₈ (M = Ca, Sr and Ba):Eu²⁺ phosphors were synthesized by novel melt quenching synthesis method. The luminescence property of the Sr₃MgSi₂O₈:Eu²⁺ phosphor synthesized by the melt synthesis method is comparable to those of the sample synthesized by a conventional solid state reaction. Sintered phosphor balls with excellent luminescent characteristics were obtained.

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.