A magnetically responsive photonic crystal of graphene oxide nanosheets.

Magnetically responsive photonic crystals of colloidal nanosheets hold great promise for various applications. Here, we systematically investigated the magnetically responsive behavior of a photonic crystal consisting of graphene oxide (GO) nanosheets and water. After applying a 12 T magnetic field perpendicular and parallel to the observation direction, the photonic crystal exhibited a more vivid structural color and no structural color, respectively, based on the magnetic orientation of GO nanosheets. The reflection wavelength can be modulated by varying the GO concentration, and the peak intensity can be basically enhanced by increasing both the time and strength of the magnetic application. To improve color quality, we developed a novel approach of alternately applying a magnetic field to two orthogonal directions, instead of using a rotating magnetic field. Finally, we achieved color switching by changing the direction of applied magnetic fields.