Colloidal photonic crystals with tunable reflection wavelengths or intensities derived from their reconfigurable structures

Colloidal photonic crystals (CPCs), which are the ordered assemblies of colloidal particles, can reflect specific wavelengths of light. In particular, CPCs with controllable optical properties are promising materials for advanced photonic applications. Principally, the optical properties of CPCs, i.e., reflection wavelengths and reflection intensities, are controllable. These two characteristics are closely related to the assembled structures of CPCs, especially interplanar spacing and regularity of the assembled structures. The reflection wavelength is proportional to the interplanar spacing of the structure; thus, uniform expanding/contracting of particle-to-particle distance causes red/blue shift of reflection peaks. On the other hand, the regularity affects the reflection intensity; reversible order-disorder transitions enable tuning of the reflection peak intensities. To control the structures of CPCs, various stimuli-responsive polymers and electromagnetic interactions of colloids have been employed. This review explains the above methods and clarifies the future perspectives.