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The authors studied white polymer light-emitting diodes (PLEDs) based on blue exciton emission by poly(9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFD) and orange-to-red emission from exciplexes formed at the interface between the PFD and poly(4-methyl-triphenylamine-co-acetoaldehyde) (TPA-AA). It is thought that the orange-to-red light-emitting exciplexes formed at the TPA-AA/PFD interface have intermolecular charge-transfer (CT) characteristics, namely, TPA-AA+·PFD–, in which TPA-AA and PFD act as a donor (D) and an acceptor (A), respectively, and long intermolecular distances. TPA-AA is a nonconjugated polymer with good solubility in chloroform and acts as a hole transport layer (HTL). A bilayer PLED, ITO (indium tin oxide)/TPA-AA/PFD/Al, was fabricated by spin-coating, and white electroluminescence (EL), corresponding to Commission Internationale d’Eclairage (CIE) chromaticity coordinates of (0.36, 0.28) and a brightness of 39.6 cd/m2, was achieved at 16 V. In order to decrease the turn-on voltage and enhanc...

Application of the concept of three-color (red (R), green (G), and blue (B)) light-mixing to obtain white light is the most suitable way to realize white-light-emitting devices with very high color-rendering indices (CRI). White-light-emitting devices based on the three-color-mixing method could be used to create lighting and display technologies. Here, white-light-emitting electrochemical cells (LECs) with very high CRIs are reported, which were fabricated by using blend films composed of a fluorescent π-conjugated polymer (FCP), poly(9,9-dioctylfluorene-co-benzothiadiazole) (PFBT), and a phosphorescent iridium complex, [Ir(ppy)2 (biq)]+ (PF6 )- (where (ppy)- =2-phenylpyridinate and biq=2,2'-biquinoline). The LECs fabricated with PFBT, the benzothiadiazole content of which is 0.01 mol %, showed blue electroluminescence (EL) emission originating from the fluorene segments and green EL emission from the benzothiadiazole units simultaneously. White LECs were then realized by adding red-emitting Ir complexes as guest molecules to the blue-green-emitting PFBT. By optimizing the proportions of the PFBT and Ir complexes in the active layers (PFBT/[Ir(ppy)2 (biq)]+ (PF6 )- =1:0.2 (mass ratio)), white-light emission with Commission Internationale de l'Eclairage (CIE) coordinates of (0.29, 0.34) and a very high CRI value of 91.5 was achieved through RGB color-mixing. It was noted that the emission mechanism was based on Forster resonance energy transfer and Dexter energy transfer from excited PFBT to [Ir(ppy)2 (biq)]+ (PF6 )- . The utilization of LECs based on blue-green FCPs and red Ir complexes looks very promising for the prospect of realizing white-light-emitting devices with very high CRIs.

The authors fabricated OLED devices with enhanced out-coupling efficiency, made using corrugated substrates which have nanostructures imprinted from a self-assembled block-copolymer pattern. We optimized the substrate for transparent OLED lighting by shortening the pattern pitch to develop a new substrate that is transparent with 0.1 % haze and an out-coupling efficiency 1.79 times that of a device made with a flat glass substrate.

Light-emitting electrochemical cells (LECs) are seen as a promising technology that could usher in a new generation of lighting devices that are both energy- and cost-efficient. This has created an urgent need for highly efficient white-emitting LECs. Technologies have to be developed for realizing efficient white emission, suited to the simple structure of LEC devices. Utilizing exciplex emission is one means of obtaining white emission. In this chapter, the authors present an approach to obtaining white emission based on emission from exciplexes formed between a fluorescent conducting polymer (FCP) and aromatic amines. The exciplexes, which are complexes that can form between molecules in the excited state, emit light as electrons are transferred from the lowest unoccupied molecular orbital (LUMO) of the FCP to the highest occupied molecular orbital (HOMO) of the amine. The exciplex emission includes longer wavelengths and is broader in spectrum than the excitonic emission of FCP, such that white light can be obtained by combining the two types of emissions. By using the right amine in the proper concentration, we were able to produce white emission with x/y CIE color coordinates of 0.33/0.31 and a color rendering index (CRI) of 80 with a device having only a single active layer.

A novel corrugated substrate has been developed for OLED lighting applications. The substrate enhances the light extraction efficiency without changing the spectra or luminous intensity distributions due to its self-assembled quasi-periodic structure. By combining the corrugated substrate with a specially designed lens array, a 102% improvement in power efficiency was achieved in a large area light-emitting device.

Organic light-emitting diodes featuring layers with a spontaneously formed buckled geometry are demonstrated to offer at least a twofold improvement in light extraction efficiency across the entire visible spectrum.

We have developed a liquid crystalline retardation film technology by using a rod-like liquid crystalline polymer (LCP) for various LCD modes. In particular, considerable improvements in viewing angle performance have been achieved for the Twisted Nematic (TN) and the transmissive/transflective Electrically Controlled Birefringence (ECB) modes by using hybrid aligned nematic film ‘NH Film’.

To improve quality of images of LCDs such as their viewing angle performance and coloration, liquid crystalline retardation film technology has been developed by using rod-like liquid crystalline polymer. The resulting liquid crystalline retardation film has several advantages over conventional uni- or biaxial stretched retardation film. By using liquid crystalline polymer, the direction of the principal axis can be determined freely for roll-to-roll lamination. Optical well-controlled structures such as twisted nematic, hybrid nematic and homeotropic structures can be stabilized for ideal compensation of various LCD modes including STN, TN, ECB, VA and IPS LCDs.

A liquid crystal (LC) photonic device with an anisotropic optical heterojunction structure has been fabricated. The device has a phase-retarding nematic LC (NLC) layer sandwiched between two polymer cholesteric LC films with right-handed helices of different pitches. Electrotunable non-reciprocal light transmittance and unidirectional circularly polarized (CP) lasing emission have been successfully demonstrated for this device structure. Two left CP (LCP) lasing emission peaks are observed at the edges of the overlapping region between the two photonic bands in the structure and are shifted upon the application of a voltage. In contrast, a non-reciprocal right CP (RCP) lasing emission peak emerges at one of the band edges and diminishes upon the application of a voltage. These phenomena are interpreted based on the selective reflection of RCP light and the reorientation of the NLC molecules by the application of a voltage.

In the application of cholesteric liquid crystal (CLC) polymer film to mono-color polarizers, diffusive reflection is preferred rather than mirror reflection at the point of visibility. This led us to develop a diffusion-type CLC (D-CLC) film. The newly developed D-CLC film exhibits high circular dichroism with bright color reflection that can be observed from almost all directions. The layer structure of the D-CLC film was directly confirmed by analysis with transmission electron microscopy (TEM). It was found that the diffusive property and polarization of the reflected light are mainly affected by the layer structure of the D-CLC.

Two-dimensional (2D) titania arrays with periods of 0.8–2.0 μm were fabricated by polymerization of a photosensitive titanium-containing monomer film using interference photolithography. The 2D precursor arrays were prepared by exposing a mixture of methacrylic acid, ethyleneglycol dimethacrylate, and titanium ethoxide doped with photoinitiator to 355 nm, 15 ns pulses from a Nd-Yttrium–aluminum–garnet laser and then rinsing with methanol. Pure titania arrays were obtained from the precursor arrays by subsequent calcination at 575 °C. The structure of the arrays fabricated by this method was confirmed with optical microscopy and scanning electron microscopy.

The authors present white polymer light-emitting electrochemical cells (PLECs) fabricated with polymer blend films of poly(9,9-di-n-dodecylfluorenyl-2,7-diyl) (PFD) and π-conjugated triphenylamine molecules. The PLECs have bulk heterojunction structures composed of van der Waals interfaces between the PFD segments and the amine molecules. White-light electroluminescence (EL) can be achieved via light-mixing of the blue exciton emission from PFD and long-wavelength exciplex emission from excited complexes consisting of PFD segments (acceptors (As)) and the amine molecules (donors (Ds)). Precise control of the distances between the PFD and the amine molecules, affected through proper choice of the concentrations of PFD, amine molecules, and polymeric solid electrolytes, is critical to realizing white emission. White PLECs can be fabricated with PFD and amine molecules whose highest occupied molecular orbital (HOMO) levels range from −5.3 eV to −5.0 eV. Meanwhile, PLECs fabricated with amine molecules whose ...

Photoinduced circular anisotropy has been demonstrated in thin films of a main-chain polymeric liquid crystal (PLC) system doped with photochromic $\mathsf{W}$-shaped molecules containing two azobenzene groups by irradiating with circularly polarized light (CPL). Reversible photoinduced circular dichroism (CD) was observed with sign relevant to the handedness of the CPL. The experimentally observed CD spectra were analyzed using the DeVoe polarizability model associated with the coupled oscillator method. We also propose a mechanism for the photoinduced circular anisotropy in our system; nucleating the $\mathsf{W}$-shaped molecules with preferential twisted conformation by CPL irradiation, and triggering the local formation of a chiral structure in the $\mathsf{W}$-shaped-molecule-doped main-chain PLC medium.

We have studied the lasing characteristics from a dye-doped nematic layer sandwiched by two polymeric cholesteric liquid crystal (PCLC) films as photonic band gap materials. The nematic layer possessing birefringence brings about the following remarkable optical characteristics; (1) reflectance in the photonic band gap (PBG) region exceeds 50% due to the retardation effect, being unpredictable from a single CLC film, (2) efficient lasing occurs either at the notch of PBG or at the photonic band edge, (3) the lasing emisions contain both right- and left-circular polarizations, and (4) tunable lasing can be achieved by the reorientation of nematic liquid crystal molecule under the application of an electric field.

We report optical and photoresponsive behavior of nonlinear liquid crystals in two-dimensional (2D) periodicstructure. 2D structure made of photoresist and titania is constructed by interference photolithography using gratingmask. Then azobenzene-doped nematic liquid crystal is infiltrated into these arrays, and photoresponsive behavior ofthe azobenzene-doped liquid crystal in the periodic structure is investigated. In particular, we show that the diffractionfrom these liquid crystal infiltrated grating structures can be optically modulated by an Ar + laser at 488 nm.Keywords: Nonlinear liquid crystals, confined structure, periodic arrays, diffraction 1. INTRODUCTION Nematic liquid crystals (NLC) possess very broadband [from 400 nm to 20 microns] birefringence andtransparency, and extraordinarily large optical nonlinearity [1,2]. By far the largest nonlinear refractive index changingmechanism is the optically induced reorientation of the nematic axis of aligned nematic films. Conventional methods ofaligning NLCs employ either surfactant- or rubbed-polymer coated cell windows, for homeotropic or planar alignment,respectively. In a previous publication [3], we have demonstrated that planar aligning action may also be engendered bya 1-D sub-wavelength grating inscribed on the glass windows. Furthermore, we showed that the surface gratings, incombination with the intensity dependent refractive index of the liquid crystal, could function as a nonlinear diffraction.In this paper, we report a novel method of fabricating 2-D grating structures, and observation of nonlinear diffractionfrom these structures impregnated with supra-nonlinear nematic liquid crystals [4].

Summary form only given. Nematic liquid crystals (NLC) possess very broadband birefringence and transparency [from 400 nm to 20 /spl mu/m], and extraordinarily large optical nonlinearity. Conventional methods of aligning NLCs employ surfactant and rubbed polymer coating on the cell windows. In this presentation, we demonstrate that similar aligning action may also be engendered by surface relief [1D and 2D] gratings inscribed on the glass windows. Furthermore, these cells exhibit all-optical diffraction capability.

We fabricated novel hybrid structures composed of a dye-doped low-molecular-weight cholesteric liquid crystal sandwiched by multi-layered polymer cholesteric liquid crystal films and evaluated their lasing characteristics. Lasing was observed with an extremely reduced threshold (12 nJ/pulse) by a factor of 10 compared with that in a simple dye-doped low-molecular-weight cholesteric liquid crystal cell. Lasing characteristics experimentally obtained were discussed by comparing them with the simulated photonic density of states spectra.

— A liquid-crystal line retardation-film technology by using a rod-like liquid-crystalline polymer (LCP) for various LCD modes have been developed. In particular, considerable improvements in viewing-angle performance have been achieved for the twisted-nematic (TN) and the transmissive/transflective electrically controlled birefringence (ECB) modes by using hybrid aligned nematic film (NH Film).

We have succeeded in fabricating monodomain polymer cholesteric liquid crystal (PCLC) films by spin coating a polymer solution onto glass substrates with polyimide coated and rubbed unidirectionally. The thickness and helical pitch were well characterized by controlling the rotational speed of the spin coater and the chiral unit content of the polymer solution, respectively. Lasing from dye-doped PCLC films utilizing the photonic structure was confirmed.