Antireflective glass articles with a porosity-graded layer and methods of making the same

A glass article, comprising:

• a glass substrate comprising a thickness and a first primary surface;
• and
• a porosity-graded layer that extends from the first primary surface of the substrate to a first depth within the substrate,
• wherein the first depth is from about 250 nm to about 3000 nm,
• wherein the porosity-graded layer comprises a plurality of pores having an average pore size from about 5 nm to 100 nm,
• wherein the porosity-graded layer comprises a surface porosity at the first primary surface and a bulk porosity at the first depth, the surface porosity greater than the bulk porosity, and
• further wherein the porosity-graded layer comprises a refractive index as a function of depth within the substrate, nPGL(Z), from the first primary surface to the first depth, given by
• n2PGL(z)=n2substrate(1−fpore)+n2air*fpore,
• where nsubstrate is the refractive index of the glass substrate, nair is the refractive index of air, and fpore is the volume fraction of the plurality of pores at the depth, z.

A method of making a glass article, comprising:

• providing a silica-saturated solution;
• filtering the silica-saturated solution to remove insoluble silica particles from the silica-saturated solution and form a filtrated solution;
• and
• immersing a glass substrate comprising a thickness and a first primary surface with the filtrated solution, the immersing conducted to form a porosity-graded layer that extends from the first primary surface of the substrate to a first depth within the substrate,
• wherein the silica-saturated solution comprises SiO2 gel, H2SiF6, H3BO3 or CaCl2, de-ionized H2O, and an optional amount of HCl,
• wherein the first depth in the substrate is from about 250 nm to about 3000 nm,
• wherein the porosity-graded layer comprises a plurality of pores having an average pore size from about 5 nm to 100 nm, and
• further wherein the porosity-graded layer comprises a surface porosity at the first primary surface and a bulk porosity at the first depth, the surface porosity greater than the bulk porosity.