Papers by Author: Dae Ho Yoon

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: 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: 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: About 2
-thick, amorphous SiON thin films were deposited by the PECVD method, and heated up to 1000oC in air to study the post-annealing effect on the composition and structure of the SiON film. SiON had a strong SiO2 binding energy with a weak N-binding, so that air-annealing resulted in nitrogen escape from the film. The inwardly transported oxygen from the atmosphere was simply supersaturated inside the annealed, amorphous SiON thin film.

Abstract: Bi and Eu co-doped Y2O3 was used as a red phosphor with a very high efficiency synthesized by the solid state reaction and co-precipitation The emission spectrum consisted of a weak band at 581, 587, 593 and 599 nm corresponding to the 5D0 → 7F1 transition, with sharp peaks of maximum intensity occurring at about 611 nm due to the 5D0 → 7F2 transition of Eu3+. In addition, the excitation spectrum exhibited a broad band between 250 and 550 nm with peaks occurring at about 310 – 400 nm and a sharp peak at 465.5 nm. The relative emission intensity was improved by co-precipitation synthesis as compared to solid state reaction synthesis. This implies that an appropriate co-precipitation synthesis could improve the luminescent efficiency, particularly for the samples prepared with the optimized firing temperature of 1100 °C.

Abstract: ZnO nanowalls and nanocolumns were synthesized on Si3N4 (50 nm)/Si (001) substrates at low growth temperature (350 and 400 oC) by metalorganic chemical vapor deposition (MOCVD) with no metal catalysts. ZnO nanowalls with extremely small wall thicknesses below 10 nm and nanocolumns with diameters over 100 nm were formed on the Si3N4/Si substrates relying on MOCVD-growth temperature. It was found that ZnO nanowalls have a strong c-axis preferred orientation with a hexagonal structure, while ZnO nanocolumns have a weak c-axis preferred orientation with broken stacking orders in synchrotron x-ray scattering experiments. In addition, strong free-exciton emission from the ZnO nanowalls was clearly observed in photoluminescence measurements. On the other hand, we could not observe any emission bands from the ZnO nanocolumn samples.