The combination of photoluminescence (PL) and cholesteric liquid crystal (CLC) provides interesting complementary features for an optimized display application. Distortion of the Bragg lattice of CLCs decreases selective reflection but increases fluorescence intensity; recovery of a uniform lattice in turn results in increased reflection and decreased fluorescence. This complementary relationship between the fluorescence and the Bragg reflection gives rise to self-compensations for color shifts due to either dynamic slow response of CLC helix or mismatch of oblique incidence of light with respect to the helical axis. These color shifts have long been intrinsic unsolved limitations of conventional CLC devices. Thus, the complementary coupling between the fluorescence and the CLC Bragg reflections plays an important role in improving the color performance and the quality of moving images.

We fabricated a photoluminescent cholesteric liquid crystal (PL-CLC) cell for a display application that can be used to display high-quality moving pictures under all ambient conditions including dark and sunlit conditions. The PL-CLC cell is switchable between the reflective mode under bright conditions and the emissive mode in the dark. The effective reflectance of the PL-CLC is higher than that of a conventional CLC device by more than 30%, and the contrast ratios were approximately 10 and 7 in the reflective and emissive modes, respectively. We directly compared the proposed PL-CLC cell with conventional LCD and CLC cells under sunlit, office, and dark environments and confirmed that the PL-CLC cell exhibited superior visibility under all ambient conditions.

We demonstrate that the polarization of emitted light from a photoluminescent cholesteric liquid crystals (PL-CLC) cell with well-designed electrodes can be electrically switchable among the linearly polarized, circularly polarized, and un-polarized states. Moreover, the degree of polarization can be continuously tunable from zero to the maximum degree of polarization of emitted light from the cell, that is, from 0 to 0.8 and 0 to 0.45 for circularly and linearly polarized light, respectively. The degrees of circular and linear polarizations are mainly governed by the perfectness of the CLC photonic bandgap, and the Sμ order parameter of the PL molecules, respectively. By continuously electrically manipulating the molecular ordering between the planar helicoidal state with a perfect photonic bandgap, the focal conic state with a macroscopic random ordering, and the unwound state with a highly uniaxial ordering, one can selectively produce those types of polarized emitted light with any degree of polarization. The wavelength dependency of the degree of polarization significantly varies depending on the types of polarization and LC alignment states.

Using a photo-luminescent cholesteric liquid crystal (PL-CLC) cell, tri-stable electrooptic switching behaviour was demonstrated. Stable planar, uniformly lying helix (ULH), and focal conic states were obtained at an electric field of zero after applying proper electric signals corresponding to each state. When a PL-CLC cell was placed on a ultraviolet (UV) back-light, the cell emitted fluorescent light with different types of polarization corresponding to the liquid crystal (LC) state: the planar, ULH, and focal conic states emitted circularly polarized light, linearly polarized light, and un-polarized light, respectively. Hence, the proposed PL-CLC cell worked as a tri-stable polarizationswitching light source. We also demonstrated that the PL-CLC cell can be used to fabricate a bistable fluorescent LC device.

A photoluminescent cholesteric liquid crystal (PL‐CLC) display was demonstrated to exhibit excellent still and moving images regardless of ambient illuminance. The coupling and decoupling effects between the fluorescent and photonic band gap of PL‐CLCs compensated for the low reflectance and color shift problems, which are the remaining issues related to CLC display.