A composition includes a first population of strongly plasmonic nanorods and a second population of strongly plasmonic nanorods. The two populations each have a size range of the nanorods, creating a size range gap between the two populations. This size range gap creates a transparency window that can be seen in an extinction spectrum of the composition, which is characterized by the sizes of the nanorods in both populations. The composition may be included in a filter providing a transparency to a defined wavelength characterized by the size range gap of the nanorods.