The invention relates to a nanostructured porous oxyfluoride film deposited onto a substrate, to a method for its production, and also to various applications.The oxyfluoride has a porous semicrystalline structure and a refractive index of 1.08 to 1.25, measured in the visible range for a relative humidity level below 80%. Its chemical composition corresponds to the formula (Mg(1−x)Cax)(1−y)MyF(2+(n−2)y−2z−t)Oz(OH)tM′w in which n is the valency of M, n being 1 to 4, M represents at least one element chosen from Al, Si, Ge and Ga, M′ represents at least one element chosen from the group composed of Co, Cr, Ni, Fe, Cu, Sb, Ag, Pd, Cd, Au, Sn, Pb, Ce, Nd, Pr, Eu, Yb, Tb, Dy, Er and Gd, and 0≦w 0 and t