Sapphire thin film coated substrate

An anti-reflective coating on a substrate comprising a multilayered structure of more than three layers comprising:

• a topmost anti-reflective material layer comprising of sapphire or Al2O3 on top of one or more anti-reflective material layers with a matching refractive index that is higher than the topmost anti-reflective material layer;
• two or more middle anti-reflective material layers, wherein the middle anti-reflective material layer immediately below the topmost anti-reflective material layer is a second anti-reflective material layer and has a matching refractive index that is higher than that of the topmost anti-reflective material layer;
• and
• a bottommost anti-reflective material layer below the two or more middle anti- reflective material layers, wherein the bottommost anti-reflective material layer is deposited on top of the substrate;
• wherein the topmost anti-reflective material layer, the two or more middle anti-reflective material layers, and the bottommost anti-reflective material layer have alternatively higher and lower refractive indices in respect with each other,
• wherein the second anti-reflective material layer has a refractive index higher than 1.75 in visible light region, and wherein the second anti-reflective material layer comprises one or more of yttrium aluminium garnet (YAG), AlAs, ZnSiAs2, AgBr, TlBr, C, B4C, SiC, AgCl, TlCl, bismuth germanium oxide (BGO), lead germanium oxide (PGO), CsI, KI, LiI, NaI, RbI, CaMoCL, PbMoCL, SrMoCL, AlN, GaN, LiNbO3, Sc2O3, ZnO, GaP, KTaO3, and BaTiO3.