Development of complex magnesium fluoro aluminates via the fluorolytic sol–gel synthesis

Abstract

The diverse industry for optical applications demands materials with many exceptional properties, which often can only be ensured by the development of novel compounds. Specifically, the stability towards abrasion or moisture should go hand in hand with optical characteristics like a low refractive index or high transmittance. Hence, we present fluorolytic sol–gel syntheses of complex magnesium fluoro aluminates and examine resulting layer applicability. Using ¹⁹F static as well as ¹⁹F MAS NMR, XRD, and TG/DTA analysis, miscellaneous synthetic methods concerning different molar ratios between Mg and Al were discussed. We determine that two phases are predominantly in xerogels employing the sol–gel synthesis: MgAlF₅·2H₂O as well as MgAl₂F₈·2H₂O. In addition, the formation of strongly disordered structures can be observed within the sol. Furthermore, thermal treatment induces a decomposition of the complex to the particular compounds, MgF₂ and AlF₃. Layers, which were applied by dip coating, show antireflective behavior and vastly increased stability towards moisture.