COMPOSITE OPTICAL MATERIALS EXHIBITING STRUCTURAL COLOUR

摘要

A composite optical material such as a polymer opal is provided having a three dimensional arrangement of core particles distributed in a matrix. The refractive index of the material of the core particles is different to the refractive index of the material of the matrix and the three dimensional arrangement has a periodicity such that, when a surface of the material is illuminated with white light, the composite material exhibits structural colour. The three dimensional periodic arrangement is a reduced symmetry arrangement based on a crystallographic close-packed arrangement but strained therefrom to have reduced symmetry compared to the crystallographic close-packed arrangement. Bragg reflections from planes that would be forbidden in the crystallographic close-packed arrangement are allowed and visible in the reduced symmetry arrangement. This provides a variation in intensity and/or wavelength of structural colour with rotation of the material about an axis perpendicular to the surface when viewed obliquely while the viewing angle remains substantially constant. Also disclosed are methods for the manufacture of such material.