Achieving structured colour in inorganic systems: Learning from the natural world

Structural colour is observed in a number of naturally occurring minerals such as labradorite, bornite, hematite and ammolite, in addition to the well-known example of opal, the semi-precious gemstone. The origin of the structural colour is examined for these inorganic systems using electron microscopy to obtain structural information on the nanoscale. The structural colour that is observed in natural inorganic systems can be mimicked in synthetic inorganic systems, as exemplified by the synthetic opals reported herein. These systems exhibit stop bands, i.e. wavelength regions in which visible light cannot propagate, which show a shift in their wavelength location when the angle of the incident light is varied. When light-emitting phosphors and dyes are incorporated into the opal structures, their emission spectra are modified when the stop bands of the opals overlap the emission bands of the light-emitting materials.