Fluorescent light source with continuously tunable polarization via modification of molecular orientation

Abstract

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.

Orientation Control of Smectic Liquid Crystals via a Combination Method of Topographic Patterning and In-Plane Electric Field Application for a Linearly Polarized Illuminator

“…On the basis of the fluorescent spectra, we obtained the degree of linear polarization (ρ) using the following equation: where I ∥ and I ⊥ are the fluorescent intensities when α is 0° and 90°, respectively. In our case, ρ was 0.64, which was slightly higher than that of the nematic LC phase, which means that the smectic-based illuminator can be applied to a linearly polarized light illumination system.…”

Highly Polarized Fluorescent Illumination Using Liquid Crystal Phase

“…The resultant ρ indicates the light is highly polarized, with a value of 0.80, which is comparable to polymeric 22 or inorganic linear polarized illumination. 25 Specifically, our case showed considerably higher ρ than other illumination systems based on rod-shaped LC molecules such as electroluminescent system 34 and fluorescent dye-doped system 35 because our illuminating film is composed of fluorescent smectic LC molecules of which orientation can be controlled by the electric field. Basically, the molecular orientational order that highly affects to the degree of linear polarization increases under high electric field and with a decrease of impurities such as dyes, ions, and particles.…”

“…Additionally, the order parameter (S) of LC directors can be determined by the following equation. 34,35…”

“…This quantitative measurement of the fluorescence intensity shows that fluorescent bent-core molecules can be used for polarized illumination, once the complex B7 phase, which is hard to control using conventional methods, is properly aligned using our technique. Additionally, the order parameter ( S ) of LC directors can be determined by the following equation. , and the value of S is 0.73, which is comparable with commonly aligned nematic phase.…”