Synthesis and photoluminescence properties of the Eu(III)-containing silica nanoparticles via a mechanochemical solid-state reaction between SiO₂ and EuCl₃·6H₂O

In this study, Eu³⁺-containing amorphous silica nanoparticles and Eu compounds were successfully synthesized via a mechanochemical solid-state reaction between silica nanoparticles and EuCl₃·6H₂O. This reaction was induced by a grinding process, and the states of Eu³⁺ in the silica/europium composites were investigated. The silica/europium composites exhibited orange–red color luminescence owing to the ⁵D₀–⁷F₀, ⁵D₀–⁷F₁, and ⁵D₀–⁷F₂ transitions, which indicated the presence of Eu³⁺ in the silica framework and the newly formed Eu compounds such as EuOCl and Eu(OH)₂Cl. The mechanochemical reaction because of the grinding process effectively induced an interaction between the silica surface and europium chloride; subsequently, Eu(OH)₂Cl was formed in the silica/europium composites. Additionally, the Eu(OH)₂Cl in the silica/europium composite exhibited a higher thermal stability than that of simple Eu(OH)₂Cl, indicating that the mechanochemical reaction mediated the formation of Eu(OH)₂Cl and new chemical bonding between the newly formed Eu(OH)₂Cl and the silica surface, providing improved thermal stability to Eu(OH)₂Cl. Thus, we successfully prepared silica nanoparticles containing not only Eu(III) in the silica framework but also Eu compounds that exhibit unique chemical bonding during a mechanochemical reaction.