Sol-gel processing and luminescent properties of rare-earth oxyfluoride materials

Luminescent rare-earth oxyfluoride materials were prepared by a sol-gel method using trifluoroacetic acid as a fluorine source. Crystalline (La, Eu)OF powders and thin films were obtained by heating gels at typically 600-800°C. Transparent SiO₂-LaOF glass-ceramic thin films were also prepared by mixing the trifluoroacetate sols and silica sols, spin-coating on silica glass substrates and heating at temperatures 600-900°C. Eu³⁺ ions doped in the oxyfluoride materials exhibited a strong red ⁵D₀ → ⁷F₂ emission (611 nm) by a charge-transfer (O^2--Eu³⁺) excitation with ultra-violet radiation (265 nm). It was strongly suggested that the Eu³⁺ activators were preferentially incorporated into the crystalline LaOF phase in the SiO₂-LaOF glass-ceramics.