Controlled synthesis of luminescent Mn-doped Zn2SiO4 microspheres by thermal hydrolysis of urea

We report a novel method to synthesize Mn-doped zinc silicate (SiO2@Zn2SiO4:Mn2+, SiO2@ZSM) microspheres with a core-shell structure. Monodisperse SiO2 microspheres with mesoporous silica shells were used as templates, and urea as a dissolution and precipitation agent. Highly crystalline ZSM phases are exclusively grown within the mesoporous silica shells through the thermal hydrolysis of urea, followed by sintering at high temperature. We can control access of Zn and Mn species to the pores in the shell, which allows to produce core-shell microspheres with tunable shell thickness. Annealing the as-synthesized microspheres at 1223 K and 1023 K yielded a green-emitting α-phase (SiO2@α-ZSM) and a yellow-emitting β-phase (SiO2@β-ZSM), respectively. Various spectroscopic data confirm the formation of the core-shell structure and showed superior luminescent properties. This novel synthetic method opens an effective strategy for the production of highly crystalline α- and β-ZSM phases in a controlled manner.