Optically transparent articles and structures that include or are otherwise disposed on a substantially transparent substrate. These articles and structures also include a stack of N (N>2) bi-layers on the substrate, the stack having a thickness of at least 5 nm. Each bi-layer is defined by (a) a first layer; and (b) a second layer disposed on the first layer, the layers having at least one of different compositions and different microstructures. The stack has a stack refractive index between about 1.2 and about 2.2 or between about 100% and about 150% of a refractive index of the substrate, and a stack hardness of 15 GPa or greater when measured with a Berkovich Indenter Hardness Test along an indentation depth in the range from about 10% to about 50% of the thickness of the stack disposed on a glass test substrate having a hardness between 6.5 and 8 GPa.