We present a method to fabricate a thin film color filter based on a mixture of photo-polymerizable liquid crystal and chiral dopant. A chiral nematic liquid crystal layer reflects light for a certain wavelength interval Δλ (= Δn.P) with the period and Δn the birefringence of the liquid crystal. The reflection band is determined by the chiral dopant concentration. The bandwidth is limited to 80nm and the reflectance is at most 50% for unpolarized incident light. The thin color filter is interesting for innovative applications like polarizer-free reflective displays, polarization-independent devices, stealth technologies, or smart switchable reflective windows to control solar light and heat. The reflected light has strong color saturation without absorption because of the sharp band edges. A thin film polarizer is developed by using a mixture of photo-polymerizable liquid crystal and color-neutral dye. The fabricated thin film absorbs light that is polarized parallel to the c axis of the LC. The obtained polarization ratio is 80% for a film of only 12 μm. The thin film polarizer and the color filter feature excellent film characteristics without domains and can be detached from the substrate which is useful for e.g. flexible substrates.
Chiral nematic liquid crystals have attracted substantial interest. They spontaneously self-organize to form a helical structure with no complex fabrication procedure required and exhibit a reflection band for a certain wavelength interval. Since the photonic band gap can be tuned by applying external factors (heat, voltage, light, elasticity) chiral nematic liquid crystals are potentially interesting for large area optical filters and shutters, reflective displays and tunable lasers. In this work, a device which consists of a mixture of photo-polymerizable liquid crystal, non-reactive nematic liquid crystal and a chiral dopant is fabricated. By selecting the appropriate chiral dopant concentration, it is possible to make devices for different operation wavelengths. The influence of UV illumination on a partially polymerized chiral liquid crystal is investigated. A blue-wavelength shift of the photonic band gap is obtained as a function of power, duration time of UV illumination and the thickness of the cells. Interestingly the width and depth of the photonic band gap is unaffected by the change in UV curing conditions, which indicates that there is no degradation by the UV light.
The ability to control the position and orientation of nanorods in a device is interesting both from a scientific and a
technological point of view. Because semiconductor nanorods exhibit anisotropic absorption, and spontaneous and
stimulated emission, aligning individual NRs to a preferred axis is attractive for many applications in photonics such as
solar cells, light-emitting devices, optical sensors, switches, etc. Electric-field-driven deposition from colloidal
suspensions has proven to be an efficient method for the controlled positioning and alignment of anisotropic particles. In
this work, we present a novel technique for the homogeneous deposition and alignment of CdSe/CdS NRs on a glass
substrate patterned with transparent indium tin oxide interdigitated electrodes, with a spacing of a few micrometers. This
method is based on applying a strong AC electric field over the electrodes during a dip-coating procedure and subsequent
evaporation of the solvent. The reproducible and homogeneous deposition on large substrates is required for large size
applications such as solar cells or OLEDs. The accumulation, alignment, and polarized fluorescence of the nanorods as a
function of the electrical field during deposition are investigated. A preferential alignment with an order parameter of
0.92 has been achieved.