Recent advances in polymer colloidal crystal lasers.

Colloids with a size in the nanometres to micrometres range are frequently used in both fundamental research and industrial applications. In this context, colloidal crystals (CCs)-3D ordered arrays of monodispersed colloidal microparticles with a diameter of several hundred nanometres-have garnered a great deal of attention in the intriguing research realm of photonic crystals (PCs) due to the feasible and high-throughput 3D-PC fabrication with CCs. For optoelectronic applications, it is of prime importance to construct 3D-PCs with photonic band-gaps (PBGs) in the visible wavelength range. With regard to photonic device applications, many reports have been made on a wide variety of optical reflection sensors and displays using CCs that shift the visible PBG wavelength in response to external stimuli. This Minireview describes the research progress in the investigation of CCs and their laser applications. We highlight not only the research background of CCs as 3D-PCs, but also new potential applications of CCs as flexible and widely tunable lasers by low-threshold optical excitation.