MgF2 antireflective coatings by sol-gel processing: film preparation and thermal densification

Magnesium fluoride sols for the wet chemical processing of porous MgF2 antireflective coatings were prepared by the reaction of MgCl2 with HF. The formation and crystallisation of MgF2 nanoparticles were followed by F-19 NMR spectroscopy, X-ray diffraction (XRD) and dynamic light scattering (DLS) in the liquid phase. The crystallization of the resulting films was monitored by XRD experiments. At temperatures exceeding 550 degrees C the film material and glass substrates undergo a chemical reaction, MgO is formed and SiF4 evaporates as a volatile product. Microstructure and optical properties were characterized as a function of the annealing temperature. The mechanical stability of MgF2 films was evaluated by the Crockmeter test using both felt and steel wool. It is shown that porous MgF2 films prepared by this synthesis have a vast potential for the large-area processing of antireflective coatings.