Methane production from carbon dioxide and hydrogen is known as the Sabatier reaction. However, methanation process by the Sabatier reaction requires high temperatures and high pressures. Therefore, we tried to generate methane by mechanochemical method, using ball-milling as a new methanation process. As a result of ball milling for 3 hours at room temperature, generation of methane was observed. On the other hand, carbon dioxide was consumed more than expected. As for further verification, ball-milling was carried out for 6 hours under carbon dioxide atmosphere. EDX elemental analysis of the milled powder revealed significantly increased carbon content, suggesting the reaction of LaNi5 surface with CO2 followed by the formation of carbides or carbonates of La or Ni. A unique XRD profile was observed in the milled sample, yielding broad amorphous-like peak, possibly from La, and broad peak of Ni. It was shown that ball milling may cause phase separation into La and Ni not only in hydrogen atmosphere but also in carbon dioxide atmosphere.
Up-conversion phosphors emit light with shorter wavelength than that of excitation light. This phenomenon is caused by multi-photon excitation and energy transfer in f orbital of rare earth elements. In this study, La2ZnTiO6 and La2MgTiO6 doped with different amounts of Er and Yb was synthesized by the complex gelation method and the up-conversion (UPC) emission was investigated. In addition, we investigated the difference in optimum amount of Er and Yb for UPC emission due to host crystals. Main crystal phases of the synthesized samples were identified as La2ZnTiO6 and La2MgTiO6 respectively by X-ray diffraction. Up-conversion emissions were measured using a spectrometer with a multi-channel photo detector and a diode laser emitting excitation light at 980nm. The optimum amount of Er and Yb in (La, Er, Yb)2ZnTiO6 for the up-conversion emission were 1mol% and 5mol%, respectively. On the other hand, the optimum amount of Er and Yb in (La, Er, Yb)2MgTiO6 were 2mol% and 2mol%, respectively. The optimized sample showed strong green and red emissions. As the result, it was shown that the double perovskite type oxide doped with Er and Yb showed UPC luminescence, and the optimum doping amount of Er and Yb depended on the host crystal.