Chemical processing for inorganic fluoride and oxyfluoride materials having optical functions

Chemical processing such as a sol–gel method can offer interesting and useful routes for designing and synthesizing inorganic metal fluoride and oxyfluoride materials for applications in optics and photonics. In our series of studies during the last decade, a variety of fluoride materials including alkaline earth fluorides (MgF2, CaF2, SrF2 and BaF2), rare-earth fluorides (LaF3, NdF3, GdF3, etc.), rare-earth oxyfluorides (LaOF, EuOF, GdOF, Sm4O3F6, Er4O3F6, etc.) and complex fluorides (SrAlF5, BaMgF4, BaLiF3, LiGdF4, etc.) have been prepared, using trifluoroacetic acid as a fluorine source, in the form of nanoparticles, thin films and oxide/fluoride nanocomposites. They can be utilized as anti-reflective coatings, luminescent materials, VUV materials, IR materials, and so forth. This article summarizes fundamentals and possible applications of optically useful inorganic fluoride and oxyfluoride materials, with emphasis on porous single-layer anti-reflective coatings and visible photoluminescence of doped Eu3+ or Eu2+ ions. Furthermore, our recent results on LaF3:Ce3+ and LaOF:Ce3+ are originally reported here.