Mild condition synthesis without high temperature process of Eu2+-doped barium orthosilicate nanophosphor via Water-Assisted Solid-State Reaction (WASSR) method

A green-emissive Ba2SiO4:Eu2+ nanophosphor has been succeeded to practically synthesize at the lowest temperature of 220 °C by a Water-Assisted Solid-State Reaction (WASSR) method, which has been developed by our group. The Ba2SiO4 was prepared with employing various barium and silicon sources, and the reaction proceeded only in the combination of Ba(OH)2·8H2O and amorphous SiO2. In addition, the results of X-ray powder diffraction gave evidence that the Ba2SiO4 phase was formed through a Ba2[SiO2(OH)2]2 phase as an intermediate in this synthetic method. The obtained primary particle size was found to be 15–20 nm because of employing mild condition without high temperature process. Additionally, the nanophosphors exhibited a green emission attributed to 4f65d1→4f7 transition of Eu2+ under the near UV excitation of 360 nm. The result indicates that Eu3+ is partly reduced to Eu2+ without using reduction gas. •A green-emissive Ba2SiO4:Eu2+ phosphor was prepared at lowest temperature of 220 °C.•The Ba2SiO4 phase was formed through a Ba2[SiO2(OH)2]2 phase as an intermediate.•The primary obtained particle size was found to be 15–20 nm.•Eu3+ is partly reduced to Eu2+ without using reduction gas.