Material Refractive Index TiO2 - anatase 2.55 TiO2 - rutile 2.90 Fe2O3 - hematite 3.01 ZrO2 2.20 ZnO 2.03 ZnS 2.38 BiOCl 2.15 The low refractive index material may be silicon dioxide, magnesium fluoride, aluminum oxide, a polymer such as polymethyl methacrylate, polystyrene, ethylene vinyl acetate, polyurea, polyurethane, polydivinyl benzene and the like.