Influence of solution composition on the formation of SiO₂/LaF₃ composites in the sol-gel process

Influence of starting solution composition on the formation of SiO₂/LaF₃ composites was examined in the sol-gel process of tetramethylorthosilicate, methanol, water and N,N-dimethylformamide. Trifluoroacetic acid (TFA) and lanthanum acetate were used as chemical sources for LaF₃. Microcrystals of LaF₃ with a size of 10 nm were formed in silica matrix by heating dried gels above 300°C. Colorization, crack formation and fragmentation during drying and heating gels were greatly dependent on the amount of TFA. It was possible to suppress fragmentation of the heated gels by using lanthanum trifluoroacetate gels as precursor in preparing the starting solutions.