Analysis on Band Gaps of MCM-41 Type of Materials

The concept and analysis method of photonic crystals and band gaps are introduced into one-dimenslonal (1D) ordered mesoporous materials. MCM-41 type of materials are treated theoretically as photonie crystals. The formation of band gaps is exhibited and confirmed by a calculation of transfer matrix technique. PBG was found around 9-42 nm in soft X-ray region. The photonie band-gap was predicted to be dependent on incident direction, pore size and lattice constant. The mesoporous materials with different pore sizes and different lattice constants have different band-gap widths.     

Temperature‐Responsive Luminescent Solar Concentrators: Tuning Energy Transfer in a Liquid Crystalline Matrix

Temperature‐responsive luminescent solar concentrators (LSCs) have been fabricated in which the Förster resonance energy transfer (FRET) between a donor–acceptor pair in a liquid crystalline solvent can be tuned. At room temperatures, the perylene bisimide (PBI) acceptor is aggregated and FRET is inactive; while after heating to a temperature above the isotropic phase of the liquid crystal solvent, the acceptor PBI completely dissolves and FRET is activated. This unusual temperature control over FRET was used to design a color‐tunable LSC. The device has been shown to be highly stable towards consecutive heating and cooling cycles, making it an appealing device for harvesting otherwise unused solar energy.     

Efficient and Stable Thin-Film Luminescent Solar Concentrators Enabled by Near-Infrared Emission Perovskite Nanocrystals

A novel triphenylphosphine (TPP) treatment strategy was developed to prepare the near-infrared emission CsPbI₃ nanocrystal (NC)-polymer composite thin-film luminescent solar concentrators (LSCs) featuring high absolute photoluminescence quantum yield (PLQY), low reabsorption, and high stability. The PL emission of the LSCs is centered at about 700 nm with 99.4±0.4 % PLQY and narrow full width at half maximum (FWHM) of 75 meV (30 nm). Compared with LSCs prepared with classic CsPbI₃ NCs, the stability of the LSCs after TPP treatments has been greatly improved, even after long-term (30 days) immersion in water and strong mercury-lamp irradiation (50 mW cm⁻²). Owing to the presence of lone-pair electrons on the phosphorus atom, TPP is also used as a photoinitiator, with higher efficiency than other common photoinitiators. Large-area (ca. 75 cm²) infrared LSCs were achieved with a high optical conversion efficiency of 3.1 % at a geometric factor of 10.     

Electrically tunable polarisation-independent blue-phase liquid crystal binary phase grating via phase-separated composite films

A simple method for fabricating polarisation-independent blue-phase liquid crystal phase grating is demonstrated by implementing photopolymerisation-induced phase separation through a binary photomask. The dynamic focusing property of the proposed liquid crystal grating is independent of the polarisation state of incident light. The efficiency of various diffraction orders for the phase grating was measured as a function of the applied voltage. Experimental results show that the maximum diffraction efficiency reaches 36% for the ±1 order, which approaches the theoretical limit ~41%. The measured rise time is 1.4 ms and fall time is 2.2 ms. Such a tunable grating has great potential for photonic applications.     

Analysis for the Isomers of Naphthylamine by Reversed-Phase HPLC with Temperature Controlled

Generally, the analysis of isomers by high performance liquid chromatography (HPLC) requires the liquid-solid adsorption chromatography (LSC) since few satisfactory separations of isomers can be achieved by regular reversed-phase chromatography. Because the moisture absorption from air by the mobile phase will change markedly the separable property of isomers on LSC system, the analysis of isomers by LSC is still a troublesome problem.     

Highly polarized absorption and emission from polymer-stabilized smectic guest-host systems

ABSTRACT

The optical properties of luminescent molecules dissolved in liquid crystals have led to their proposed use in luminescent thin-film polarizers. These molecules are typically required to fulfil a range of criteria related to their absorption and emission properties, degree of alignment and stability; however, concurrently satisfying these requirements has proven a barrier in their practical use. We obtained highly polarized absorption and emission luminescent thin-film polarizer using reactive liquid crystalline monomers and highly dichroic luminescent dyes, both of which have polymerizable end groups. In situ photopolymerization of the liquid crystalline mixtures in the highly ordered SmB phase resulted in the formation of cross-linked polymeric networks in which the anisotropic absorption and emission of the film were fixed. The as-obtained product exhibited a high dichroic ratio (DR = 30) with a large fluorescence quantum yield (?_F = 0.77). The device is both cheap and easy to fabricate and has the potential to be used in practical electro-optic applications.     

Polymorphic transitions mediated by surfactants in liquid crystal nanodroplet

Recently, various techniques have been developed using photonic crystals. Liquid crystals (LC) confined in a nanodroplet mimicked photonic crystals, such as those of opal. Therefore, investigating the phase behaviour of LC molecules in nanodroplets is very important in the next-generation optical field. In this study, the chemical interaction between surfactants and LCs in nanodroplets is reproduced using a dissipative particle dynamics method. We identify the phase behaviour of LCs and investigate how the chemical interaction affect on the orientation of LCs. In particular, by adding surfactant molecules, various morphological behaviours were observed in the LC nanodroplet. The phase transition temperature varied depending on R_ND (amount of surfactant molecules). Furthermore, difference of the self-assembly structure also appeared inside the droplet depending on R_ND. Our simulation offers a theoretical guide to control morphologies of self-assembled LCs inside a nanodroplet, a novel system that may find applications in nanofluidic devices or in photonic crystal technology.     

Soft luminescent solar concentrator film with organic dye and rubbery matrix

We propose a soft luminescent solar concentrator (LSC) with superior light propagation. The rubbery poly(ethylene-co-vinyl acetate) (EVA) was adopted to replace the conventional brittle poly(methyl methacrylate) (PMMA). We analyzed the transmittance, photoluminescence efficiency, crystallinity, and surface properties of LSC to understand the optical and structural properties of the LSC. In addition, we modified the optical slab model to provide insights into the optical phenomenon in plate-type LSC devices; we evaluated the solar absorption efficiency of the glass and emitting layers. We also evaluated the solar concentration performances of the LSC devices by measuring the photocurrent density generated using a monocrystalline silicon solar cell. We compared the transporting ability of emitted light into an edge by calculating the collection efficiency based on the concentration factor and optical efficiencies (absorption and photoluminescence). The concentration factor, optical efficiency, and collection efficiency of the EVA-LSC with 4000 ppm of Lumogen F Red 305 were 0.31, 3.1, and 40%, respectively. The overall optical properties of the EVA-LSC were comparable to those of the PMMA-LSC. Moreover, the light decay property of EVA-LSC was superior by 1.2 times than PMMA-LSC. Therefore, we suggest EVA can replace PMMA and be used for flexible and large-area LSC applications.     

Anomalous light scattering in photonic cholesteric liquid crystals

ABSTRACT

We have carried out polarisation and angle-resolved measurements of the light scattered from photonic cholesteric liquid crystals. Both in samples doped with laser dyes and in inactive (non-doped) samples we have observed pronounced directional dependences of the scattered light, finding angular ranges where the scattering is greatly enhanced and regions where the effect is almost suppressed. Moreover, the total amount of scattered light has also been found to depend strongly on the polarisation and direction of the incident beam. All the results have been interpreted successfully in terms of a simple expression proposed for the scattering cross section, in which the density of states of the ingoing and outgoing beams plays a major role. The expression would be applicable not only to cholesteric liquid crystals but to any one-dimensional photonic material.     

A three-layer egg-configurated Bragg microcavity of polyglycerol coated cholesteric-liquid-crystal encapsulated by hollow-glass-microsphere

ABSTRACT

This letter reports the optical pumped lasing behaviours of a three-layer Bragg resonance cavity consisting of dye-doped cholesteric liquid crystal (DDCLC) microdroplet, polyglycerol-2 and hollow glass microsphere. The function of PG2 is to control the parallel anchoring of the liquid crystal (LC) molecules on the surface of the LC microdroplet. The whispering-gallery mode (WGM), radial Bragg (photonic bandgap, PBG) mode and Bragg WGM (BWGM) are observed in DDCLC microspheres with different helical pitches and LC refractive indices. The formation mechanisms of six types of lasing emission conditions are analysed in detail. The study results present the prospect of controlling the output mode of the laser. Furthermore, such solid shell-based DDCLC microspheres have outstanding potential applications in miniaturised 3D Bragg lasers, sensors, and integrated and tunable optical devices.     

In vivo imaging of the morphology and changes in pH along the gastrointestinal tract of Japanese medaka by photonic band-gap hydrogel microspheres

Colloidal crystalline microspheres with photonic band-gap properties responsive to media pH have been developed for in vivo imaging purposes. These colloidal crystalline microspheres were constructed from monodispersed core–shell nano-size particles with poly(styrene-co-acrylic acid) (PS-co-PAA) cores and poly(acrylic acid-co-N-isopropylacrylamide) (PAA-co-PNIPAM) hydrogel shells cross-linked by N,N′-methylenebisacrylamide. A significant shift in the photonic band-gap properties of these colloidal crystalline microspheres was observed in the pH range of 4–5. This was caused by the discontinuous volume phase transition of the hydrogel coating, due to the protonation/deprotonation of its acrylic acid moieties, on the core–shell nano-sized particles within the microspheres. The in vivo imaging capability of these pH-responsive photonic microspheres was demonstrated on a test organism – Japanese medaka, Oryzia latipes – in which the morphology and change in pH along their gastrointestinal (GI) tracts were revealed under an ordinary optical microscope. This work illustrates the potential of stimuli-responsive photonic band-gap materials in tissue-/organ-level in vivo bio-imaging.     

Global phase diagram for the honeycomb potential

We calculate the global phase diagram using classical statistical mechanics for an isotropic pair potential that has been previously [Rechtsman et al., Phys. Rev. Lett. 95, 228301 (2005)] shown to produce the low-coordinated two-dimensional honeycomb crystal as the ground-state structure. Low-coordinated crystals are of practical interest because they have desirable photonic band-gap properties. The phase diagram is obtained from Helmholtz free energies calculated using thermodynamic integration and Monte Carlo simulations. Our results show that the honeycomb crystal remains stable in the global phase diagram even after temperature effects are taken fully into account. Other stable phases in the phase diagram are high and low density triangular phases and a fluid phase. We find no evidence of gas-liquid or liquid-liquid phase coexistence.     

Nematic liquid crystal gyroids as photonic crystals

ABSTRACT

We demonstrate nematic and cholesteric liquid crystal (LC) gyroids and show their photonic properties as photonic crystals by using numerical modelling. The LC gyroids are designed as composite optical materials, where we take one labyrinth of passages to be a solid dielectric, whereas the other (complementing) labyrinth of passages is taken to be filled by chiral or achiral nematic LC, with the intermediate gyroid surface imposing homeotropic (perpendicular) surface anchoring. The nematic inside the gyroid matrix is shown to exhibit a variety of possible orientational profiles which are characterised by complex networks of topological defects – from ordered, semi-ordered, to completely disordered. The diversity of possible nematic states is shown to lead to a rich structure of photonic bands, which can be tuned by the LC volume fraction and the cholesteric pitch, including control over full – direct and indirect – band gaps.     

Chromatographic Behavior of Aromatic Diamines in Hydro-Organic, Micellar and Submicellar Reversed Phase Liquid Chromatographic Modes

The chromatographic behavior (retention, elution strength, efficiency, peak asymmetry and selectivity) of some aromatic diamines in the presence of methanol with or without anionic surfactant SDS in the four different reversed phased liquid chromatographic (RPLC) modes, i.e., hydro-organic, micellar (MLC), low submicellar (LSC) and high submicellar (HSC), was investigated. In the three surfactant-mediated modes, the surfactant monomers coat the stationary phase even up to 70 % methanol; this results in the suppression of peak tailing (by masking the silanol groups on the stationary phase). In MLC and HSC, the solute retention decreases by increasing the surfactant concentration, while this situation was reversed in LSC. In the region between MLC and HSC modes (25–50 % methanol), retention of late eluting solutes was increased by increasing methanol content which is seemingly due to disaggregation of SDS micelles. Changes in selectivity were observed after changing the concentrations of SDS and methanol, in a greater extent when concentration of SDS was changed. Among the four studied RPLC modes, HSC showed the best efficiency with nearly symmetrical peaks. Prediction of retention of solutes in HSC based on a mechanistic retention model combined with Pareto-optimality method allowed the full resolution of target diamines in practical analysis times.     

Determination of the molecular orientation of very thin films on solid substrates: surface liquid crystal layers and rubbed polyimide films

The molecular orientation of very thin films on solid substrates can be determined quantitatively by measuring the polarized infrared (IR) absorption spectra of samples as a function of angle of incidence. The quantitative molecular orientation is derived by fitting the incident angle dependence and the dichroic ratio with theoretical calculations. We applied this method to a technologically important system: liquid crystal (LC)/rubbed polyimide film. To understand the alignment mechanism of LC molecules in contact with rubbed polyimide films, we have quantitatively determined the molecular orientation of rubbed polyimide films and a surface LC layer in contact with a rubbed polyimide film. In this paper two relations are discussed: (1) correlation between the inclination angle of polyimide backbone structures in rubbed films and the pretilt angle of bulk LC in contact with them, and (2) relation among the molecular orientation of a rubbed polyimide film and those of surface and bulk LC layers in contact with it.     

Holographic recording in chiral and linear isomers of single-component phototropic liquid crystals: an experiment and theoretical approach

Phototropic liquid crystals (PtLC) comprising one component are a new class of liquid crystals (LC) which due to the phenomenon of photochemical phase transition are of special interest, especially in view of their potential applications in photonic devices. So far, however, only a little attention has been paid to these materials. In this paper, we discuss holographic recording in chiral and linear single-component PtLCs from the family of 4-alkyl-4?-alkoxyazobenzene and we develop the one-dimensional mathematical model describing the formation of the diffraction grating. The grating formation process and its dynamics, resulting from the photoinduced isotropic-to-nematic phase transition, have been described by the mechanism that assumes the formation and growth of the liquid-crystalline domains of different sizes induced by the sinusoidally modulated Gaussian light intensity distribution. We show that the model is based on one parameter, that is the incubation time which can be easily obtained experimentally and which can be used for the fitting of the experimental data. Reporting new PtLCs materials and the model that describes the processes of holographic recording in these types of materials can be useful in the design of new phototropic LC materials and for optimisation of the experimental conditions.     

Effects of monomer structures on the evolution of liquid–crystal texture and crystallization during thin-film polymerization

We investigated in situ the effects of monomer structures on the formation and evolution of liquid–crystal texture and crystallization during thin-film polymerization of a series of liquid–crystalline and crystalline polymers. The monomers used in this study consisted of 2,6-acetoxynaphthoic acid (ANA), p-acetoxybenzoic acid (ABA), acetoxy acetanilide (AAA), and isophthalic acid (IA). The polycondensation reactions were conducted on the heating stage of a polarizing microscope. The formation of liquid crystallinity was found to be strongly dependent on the straight-monomer structures of ANA and ABA and their percentages as well as the reaction temperature. For the ANA/AAA/IA and ABA/AAA/IA reaction systems, the critical straight-monomer content (ANA or ABA) existed to form the liquid–crystalline (LC) state. Interestingly, the critical content to form liquid crystallinity decreased with an increase in the reaction temperature. Above the critical content, the appearance of a defective LC phase and the annihilation of disclinations were observed during the polycondensation reactions. The number of defects decreased with increasing reaction time through annihilation. The annihilation rate increased whereas the defect density decreased with increasing straight-monomer content. For the same molar ratio, the reaction system containing ANA had a faster annihilation rate than that containing ABA. Below the critical content, crystalline polymers were formed. Nucleation and crystal growth were observed during the reactions, and the rate of crystal growth decreased with increasing ANA or ABA content. For the systems having the same molar ratio of ANA or ABA, the ANA/AAA/IA system had a higher tendency to yield the LC phase than the ABA/AAA/IA system because ANA has a longer mesogenic unit. © 1999 John Wiley & Sons, Inc. J Polym Sci B: Polym Phys 37: 3084–3096, 1999     

The effect of atmospheric plasma treatments on plastic scintillator for beta-ray measurement

A plastic scintillator (PS) can be used for beta-ray measurements using a liquid scintillation counter (LSC) without the necessity for a liquid scintillator when liquid samples of beta-emitters are placed on the PS. However, the measurement efficiency with the PS in this study was not high, especially in the case of tritium. With a sample of tritiated water, a long measurement time was necessary with a conventional LSC. However, the measurement efficiency was improved drastically by modifying the PS surface with atmospheric-pressure glow-plasma processing (the plasma method). A 2 Bq, 20 μL sample of tritiated water placed between two PS sheets was successfully measured within 2 min by an LSC. The measurement efficiency was same as that of using liquid scintillator: 48 ± 2 % for tritiated water. The measurement efficiency was initially increasing over time, and after almost 6 h, it plateaued and remained at a constant value for several weeks. Additionally, the measurement efficiency of the plasma-modified PS was identical when it was used soon after the treatment and after being properly stored for 1 week The results show that plasma-modified PS can be used stably after storage in a freezer or a deep freezer. The plasma method is advantageous because it produces little radioactive waste fluid. This paper presents these results and the results of an investigation of the surface of the plasma-modified PS under observation with an atomic force microscope, and the mechanism behind the high measurement efficiency is discussed.     

Double telecom band thermo-optic switch based on dual-line filled photonic liquid crystal fibres

We demonstrate a thermo-optic switch based on photonic liquid crystal fibres (PLCFs) in which two lines of air hole are selective filled with liquid crystal (LC), with a high extinction ratio of more than 20 dB around 1310 nm and 1550 nm. Only in the range of 2.0°C it can perform a turn off and on operation of transmitted light in the second telecom band around 1550 nm while the first telecom bands around 1310 nm is still on. Due to the splitting of the bandgap, the switching function is achieved in this kind of PLCFs. Before the cleaning point (CP) of LC, a broad bandgap from about 1120 nm to 1320 nm splits into two ones, which are continuing inducing huge bandgap extension to shorter wavelength and longer wavelength after the CP of LC, respectively. Moreover, the temperature responses around the CP of LC is also investigated. Its sensitivity is about ?92.32 nm/°C around the CP of LC. Therefore, such kind of selective-filled PLCFs could find potential applications as thermo-optic switch and temperature sensor in the telecom band.     

Highly Fluorescent Pyridinium Betaines for Light Harvesting

We report the findings of our experimental and theoretical investigations into the properties of pyridinium enolates and their potential utility in light‐harvesting applications, such as in luminescent solar concentrators (LSCs). We present the synthesis, structures, photophysical characterization, and wavefunction‐based quantum‐chemical studies of five cyclobetaines. The performance of an LSC device incorporating one of these cyclobetaines is shown to be comparable to state‐of‐the‐art devices.