Electrically Tunable Liquid Photonic Crystals with Large Dielectric Contrast and Highly Saturated Structural Colors

Monodisperse CeO₂ and CeO₂@SiO₂ particles with controllable size and surface charge are synthesized on large scale by polyol and sol–gel reactions. These particles and the traditional SiO₂ particles are dispersed in propylene carbonate to form three kinds of electrically tunable liquid photonic crystals (PCs). Due to the intrinsic relationship between the applied field strength and lattice constant, these liquid PCs show various structural colors across the visible spectrum under different electric fields. It is found that the large dielectric contrast between CeO₂ or CeO₂@SiO₂ particles and propylene carbonate will render the liquid PC a wide photonic bandgap and highly saturated colors with little fading of reflection intensities in electric field, which address the problem of color fading for previous PCs with small dielectric contrast. Among them, only the CeO₂@SiO₂ based liquid PC simultaneously possesses broad tuning range and highly saturated colors in electric and angular tuning. Meanwhile, the highly dielectric particles also bring this liquid PC faster electrical response, more reproducible signals in on–off switching, and better stability for long-time working. Based on this liquid PC, an electric cell array is fabricated to show dynamic pixel patterns under programmed electric field, which reveals its potentials for reflective-mode display unit.