Electrically tunable photonic band gap structure in monodomain blue-phase liquid crystals

• Published in: NPG Asia materials Vol. 12; no. 1
• Main Authors: Manda, Ramesh, Pagidi, Srinivas, Heo, Yunjin, Lim, Young Jin, Kim, MinSu, Lee, Seung Hee
• Format: Journal Article
• Language: English
• Published: London Nature Publishing Group UK 29.05.2020; Nature Publishing Group
• Subjects: 639/301/923/919; 639/624/399/1022; 639/624/399/919; Bandpass filters; Biomaterials; Chemistry and Materials Science; Cholesteric liquid crystals; Color; Controllability; Crystal structure; Electric fields; Electric filters; Electromagnetic wave filters; Energy Systems; Industrial applications; Light; Materials Science; Optical and Electronic Materials; Optical filters; Optical materials; Optics; Periodic variations; Photonic band gaps; Photonic crystals; Response time; Selectivity; Sound filters; Stability; Structural Materials; Surface and Interface Science; Thin Films; Visible spectrum; Wave reflection
• ISSN: 1884-4049; 1884-4057
• DOI: 10.1038/s41427-020-0225-8

Photonic band gap materials have the ability to modulate light. When they can be dynamically controlled beyond static modulation, their versatility improves and they become very useful in scientific and industrial applications. The quality of photonic band gap materials depends on the tunable wavelength range, dynamic controllability, and wavelength selectivity in response to external cues. In this paper, we demonstrate an electrically tunable photonic band gap material that covers a wide range (241 nm) in the visible spectrum and is based on a monodomain blue-phase liquid crystal stabilized by nonmesogenic and chiral mesogenic monomers. With this approach, we can accurately tune a reflection wavelength that possesses a narrow bandwidth (27 nm) even under a high electric field. The switching is fully reversible owing to a relatively small hysteresis with a fast response time, and it also shows a wider viewing angle than that of cholesteric liquid crystals. We believe that the proposed material has the potential to tune color filters and bandpass filters. Optical materials: Filtering out light of a specific color A material that reflects light of a specific and electrically controllable color has been created by researchers in South Korea and the USA. A structure made up of a repeating pattern can significantly influence the way a wave, such as sound or light, passes through it when the wavelength is similar to the pattern’s periodicity. This principle is the basis of photonic band gap materials, which can block transmission of light of a specific color. A team led by Min Su Kim from Johns Hopkins University, Baltimore, and Seung Hee Lee from Jeonbuk National University, Jeonju, produced a liquid-crystal-based photonic band gap material that reflects spectrally pure visible light. An applied electrical field could tune the specific color across a wide range of wavelengths. The material could be used for tunable color optical filters. An electrically tunable photonic band gap structure of monodomain blue phases shows the wide tunable band gap range of ~241 nm. A novel chiral monomer enables us to stabilize the blue phases and to induce electrostriction upon biased electric fields. This device also exhibits a color gamut 85% of NTSC with high color purity owing to narrow bandwidth of 31 nm.