High refractive index organic–inorganic hybrid coatings with TiO2 nanocrystals

High refractive index hybrid coatings were prepared by directly incorporating anatase titania (TiO2) nanocrystals (NCs) into (3-glycidyloxypropyl) trimethoxysilane organic silica sol followed by a sol–gel process. The anatase TiO2 NCs were prepared by controlling hydrolysis of titanium alkoxide in acid solution, and they show a narrow size distribution centered at about 4 nm and very good dispersibility in the silica sol. After doped with TiO2, the coatings possessed excellent surface smoothness and high optical transparency in the visible range. The refractive index at 632.8 nm increased from 1.502 to 1.663 as the TiO2 weight content goes from 10% to 50%. Besides, the hybrid coatings also had good thermal stability and high hardness of 3H, which have promising application in antireflection coatings.