Sulfur incorporation into nanoporous AAO films varies from 6.3 up to 11.9%.
Refractive index is calculated by means of an iterative method based on the Snell's law.
The incorporated sulfate anions vary the refractive index of the nanoporous AAO film.
The variation of the refractive index Δneff = 0.08 is constant within 400–1200 nm range.
Refractive index values increase as decrease the amount of sulfates into AAO films.