An optical film structure that includes: an optical film comprising a physical thickness from about 50 nm to about 3000 nm, and a silicon-containing nitride or a silicon-containing oxynitride. The optical film exhibits a maximum hardness of greater than 18 GPa, as measured by a Berkovich Indenter Hardness Test over an indentation depth range from about 100 nm to about 500 nm on a hardness stack comprising a test optical film with a physical thickness of about 2 microns disposed on an inorganic oxide test substrate, the test optical film having the same composition as the optical film. Further, the optical film exhibits an optical extinction coefficient (k) of less than 1×10−2 at a wavelength of 400 nm and a refractive index (n) of greater than 1.8 at a wavelength of 550 nm.