LaF3 films were fabricated on CaF2 (1 1 1) and SiO2 glass substrates at a relatively low temperature of 250 degreesC by vacuum evaporation. X-ray diffraction revealed that [0 0 1] of the LaF2 film deposited on CaF2 (1 1 1) was parallel with [1 1 1] of CaF2 and the film was also orderly arranged in-plane direction. It has been found out experimentally that LaF, grows epitaxially on CaF2 (1 1 1). The LaF3 film on CaF2 (1 1 1) had a bulk-like dense structure. On the other hand, SiO2 glass was selected as a typical substrate that did not have any orientation at all. The LaF3 film on SiO2 glass was random poly-crystallites and the film structure was columnar with narrow openings where the air could easily enter and absorb. The insides of LaF, films on CaF2 (1 1 1) and SiO2 glass had accurately stoichiometric compositions. However, in the films, total areas exposed to the air were hydroxidized and oxidized because of chemical reactions with water and molecular oxygen adsorbed on the exposed areas. Thus, the exposed areas were lack of fluorine. The total area exposed to the air in the columnar LaF3 film on SiO2 glass was much larger than that in the epitaxial LaF3 film on CaF2 (1 1 1). Therefore, the film on SiO2 glass had much more O and OH concentrations than the film on CaF2 (1 1 1). Vacuum ultraviolet (VUV) light was much more absorbed at F-poor areas exposed to the air in LaF3 films than the stoichiometric film insides. It is significant for LaF, film deposition to make dense film structures and reduce the total exposed areas. Polycrystalline columnar LaF3 films on the materials useless for the epitaxial growth as well as SiO2 glass have much larger optical losses than the epitaxial LaF3 films. The optical transparency of LaF3 films in VUV regions has been improved using hetero-epitaxial growth technique.