SOL-GEL PROCESSING OF LAF3 THIN-FILMS

Lanthanum fluoride thin films were prepared on silica glass substrates by a sol-gel method using trifluoroacetic acid (TFA) as a fluorine so urce. A coating solution was produced from lanthanum acetate and trifl uoroacetic acid dissolved in 2-propanol. Trifluoroacetate gel films we re formed by spin coating the sol, which were converted to LaF3 thin f ilms by heat-treatment at 300-500 degrees C for 10 min. The formation of LaF3 is considered to result from the reaction between lanthanum io ns and the fluorine species generated by the decomposition of trifluor oacetate ions at elevated temperatures. The film fired at 300 degrees C had a smooth surface with a grain size of 30 nm, Cracks and voids we re only observed in the films fired at 400 and 500 degrees C. The film s fired at 800 and 400 degrees C exhibited transmittance of greater th an 90% in the visible region.