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

Abstract

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 ¹⁹F 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 °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.