Patent ID: 8221902

Claim:
A material comprising an oxyfluoride film on a substrate, wherein: a) the oxyfluoride has a porous semicrystalline structure, wherein the pore volume is greater than or equal to 50%, the pore diameter is less than or equal to 100 nm; and the wall of the pores is composed of an assembly of elementary semicrystalline oxyfluoride particles and its thickness is less than or equal to 50 nm; a refractive index of 1.08 to 1.25, measured in the visible range for a relative humidity level below 80%, and a chemical composition corresponding to the formula (Mg (1−x) Ca x ) (1−y) M y F (2+(n−2)y−2z−t) O z (OH) t M′ w in which: n is the valency of M, n being 1 to 4; M represents at least one element selected from Al, Si, Ge and Ga; M′ represents at least one element selected from the group consisting of the group consisting of Co, Cr, Ni, Fe, Cu, Sb, Ag, Pd, Cd, Au, Sn, Pb, Ce, Nd, Pr, Eu, Yb, Tb, Dy, Er and Gd; 0.1≦w≦0.1; 0.1≦x≦1; 0≦y≦0.5; z<1; t<2; z+t>0; and b) the film is composed of a single layer and it has a thickness between 100 nm and 2 μm.