The second layer 813 may be a crosslinked resin layer and may have a refractive index in the range of 1.2 to 1.6, or in the range of 1.4 to 1.55, for example. The refractive index refers to the refractive index measured at 632 nm, unless specified differently or unless the context clearly indicates differently. In some embodiments, the first layer 811 has a refractive index of at least 1.4, or at least 1.5, or at least 1.6, or at least 1.7, or at least 1.75. In some embodiments, the first layer 811 has a refractive index of no more than 2.2, or no more than 2.1, or no more than 2.0. In some embodiments, the first layer 811 has a refractive index larger than that of the second layer 813. The first and second layers 811 and 813 provide a refractive index contrast (absolute value of the difference in the refractive index of the second layer 813 and the refractive index of the first layer 811) across a nanostructured interface 812. In some embodiments, the refractive index contrast is constant along a nanostructured interface 812. In some embodiments, the refractive index contrast is in a range of 0.1, or 0.2, or 0.3 to 1.0. In some embodiments, the second layer 813 is an ultralow refractive index material, such as those described in U.S. Pat. App. Pub. No. 2012/0038990 (Hao et al.), and has a refractive index in a range of 1.2 to 1.35 and the first layer 811 is a high index layer having a refractive index greater than 1.6 or greater than 1.7.