Electrically Tunable Soft Photonic Gel Formed by Blue Phase Liquid Crystal for Switchable Color-Reflecting Mirror.

We report a robust soft photonic crystal system, fabricated using blue phase (BP) liquid crystal, which can efficiently filter the visible light. The BP gel system is obtained without surface treatment or polymerization, and thus is facile and cost effective to fabricate. Perfect monodomain with vivid color is achieved with a low electric field, which can be further tuned to reflect a second color. Most importantly, apart from the field-induced color switching, a dark/transparent state is also achieved due to complete unwinding of the BP helical structure. A potential application as a tunable color-reflecting mirror, which can be switched between "reflecting" and "transparent" states, is proposed.