Sol-Gel Synthesis of Silica-Based Oxyfluoride Glass-Ceramic Thin Films: Incorporation of Eu³⁺ Activators into Crystallites

Transparent oxyfluoride glass-ceramic thin films were prepared using a sol-gel method starting from rare-earth trifluoroacetate/silicon alkoxide solutions. SiO₂-LaF₃ and SiO₂-LaOF glass-ceramics were formed by heating at temperatures of 300°-500°C and 600°-900°C, respectively. Eu³⁺ activators were successfully incorporated into oxyfluoride crystals, as evidenced by their luminescent properties, such as capability of a charge-transfer (O^2--Eu³⁺) excitation, suppression of a multiphonon relaxation, and occurrence of a cross-relaxation at low Eu³⁺ concentrations. As a result, the films exhibited strong red emission by ultraviolet excitation. The incorporation supposedly originated from decomposition of the (La,Eu)-trifluoroacetates in the silica-gel matrix.