Applications In Electro-optical Devices Research Articles

Significantly enhanced transmittance and EO property in PMN-PT via optimized two-step pressure-free sintering

It is a great challenge to prepare Pb(Mg1/3Nb2/3)O3–PbTiO3 (PMN-PT) ceramics of very high transparency with only oxygen atmosphere pressureless sintering process. To address this issue, this work proposed an optimal low-cost two-step oxygen atmosphere sintering process with a first step at high temperature (T1) for minutes, followed by a second step at lower temperature (T2) for hours without applied pressure. High transmittance of 70 % in the near-infrared wavelength was achieved by our novel two-step process, which far exceeds the performance of PMN–PT ceramics prepared by only oxygen atmosphere sintering process reported in the past and demonstrates comparable performance compared to the costly hot-pressing sintering process. Meanwhile, it shows a high quadratic electro-optic (EO) coefficient of 42.1 × 10−16 m2 V−2, which is meaningful for applications in EO devices. Furthermore, the effect of the temperature difference between the first and second sintering step on the microstructure, transmittance, domain structure, ferroelectric and dielectric property, and polarization switching were discussed. The enhanced transparency is mainly attributed to the higher relative density, and weaker photoluminescence effect with lesser light absorption loss at optimal T1-T2. The improved EO property is due to greater polarization response originating from the interaction of defect dipoles and nanodomains. Such a process should facilitate the cost-effective preparation of other transparent electro-optic materials for practical applications.

A novel double-layer liquid crystal electro-optic switch and its infrared shielding properties investigation

ABSTRACT In this study, a novel light switch was developed by integrating polymer dispersion liquid crystals (PDLC) and polymer-stabilised cholesteric liquid crystals (PSCLC), leveraging the infrared shielding properties of these two liquid crystal films. The optimal formulation for each layer of the liquid crystal structure was investigated. Subsequently, the effects of light intensity, high temperature, and humidity on the performance of the light switch were examined. This new light switch can be selectively driven layer by layer at room temperature, achieving three states: the off state, PDLC layer-driven state, and full-driven (on state). This functionality serves the purpose of electrogenerated temperature control. Samples under optimal conditions exhibited a 31% enhancement in infrared shielding compared to a single-layer PDLC film. Moreover, the IR shielding rate could be adjusted according to the voltage applied, realising an intelligent temperature-control effect. The results of this study suggest that such bilayer liquid crystal structures hold significant potential for application in electro-optical devices and smart curtain systems.

Superior energy storage density and bright upconversion emission in Er-modified KNN-based multifunctional ferroelectric ceramics

Developing highly tunable multifunctional performances in one ferroelectric system is in line with the integration trend of electronic equipment. Herein, rare earth erbium (Er) modulated 0.95K0.5Na0.5NbO3–0.05Bi(Li0.5Nb0.5)O3–x%Er photoluminescent–ferroelectric energy storage multifunctional ceramics are prepared. All the compositions exhibit a similar grain size and compact microstructure. In addition, the optimized Er dopant enhances the enhanced relaxor characteristic and reduces oxygen vacancies. The introduction of Er3+ into perovskite lattice contributes to the observed photoluminescence behavior. Therefore, high effective energy storage density (Wrec) of 7.17 J/cm3, energy storage efficiency (η) of 65.4%, and strong green/red upconversion photoluminescence are obtained in x = 0.2 sample. This work opens up a paradigm to develop multifunctional ferroelectric ceramics for application in electro-optical devices.

Ambient Degradation Anisotropy and Mechanism of van der Waals Ferroelectric NbOI2.

The spontaneous centrosymmetry-breaking and robust room-temperature ferroelectricity in niobium oxide dihalides spurs a flurry of explorations into its promising second-order nonlinear optical properties, and promises potential applications in nonvolatile electro-optical and optoelectronic devices. However, the ambient stability of the niobium oxide dihalides remains questionable, which overshadows their future development. In this work, the chemical degradation of NbOI2 is comprehensively investigated using combined chemical and optical microscopies in conjunction with spectroscopies. We unveil the highly anisotropic degradation kinetics of NbOI2 driven by the hydrolysis process of the unstable dangling iodine bonds dominantly on the (010) facet and progressing along the c axis. Knowing its degradation mechanism, the NbOI2 flake can then be stabilized by the hexagonal boron nitride encapsulation, which isolates the air moisture. These findings provide direct insights into the ambient instability of NbOI2, and they deliver possible solutions to circumvent this issue, which are essential for its practical integration in photonic and electronic devices.

Spontaneous formation of liquid-crystalline nuclei in blue-phase liquid crystals based on different chirality

The self-assembly of three-dimensional nanostructures of blue-phase liquid crystals is becoming the spotlight of soft matter research and has potential applications in photonic crystals, sensors, electro-optic devices, and others.

The Role of Rubrene Concentration on Dielectric Parameters of Nematic Liquid Crystal

In this study, the dielectric parameters of E7 coded nematic liquid crystal (NLC) composites containing the different amounts of rubrene fluorescent dye were investigated. E7, E7+0.5 wt.% Rubrene, and E7+1.0 wt.% Rubrene samples were prepared. Frequency dependent dielectric constants (ɛ′ and ɛ′′), dielectric anisotropy (Δε′), and ac conductivity (σac) graphs of rubrene doped E7 NLC composites were obtained by dielectric spectroscopy method and compared with pure E7 NLC. By using these graphs, relaxation frequency (fR), relaxation time (τR), dielectric strength (δɛ′), and crossover frequency (fc) parameters of the E7 NLC and its rubrene doped composites were determined. An increase in fR from 3.045 MHz to 3.697 MHz for 0 V and from 627 kHz to 686 kHz for 40 V was observed with increasing rubrene concentration. On the other hand, a decrease in τR from 0.052 μs to 0.043 μs for 0 V and from 0.254 μs to 0.232 μs for 40 V was seen with increasing rubrene concentration. Furthermore, an increase in fc from 1.145 MHz to 1.298 MHz was obtained with increasing rubrene concentration. The results show that the dielectric parameters change with the concentration of rubrene and it is thought that this study will provide a basis for investigating the dielectric properties of rubrene doped NLC composites. Moreover, it is concluded that the produced composites are a suitable base material for electro-optical device applications such as smart displays, photonics and electrical circuit elements.

La-doped PMN–PT transparent ceramics with ultra-high electro-optic effect and its application in optical devices

Transparent electro-optic (EO) ceramics of La-doped 0.75Pb(Mg_1/3Nb_2/3)O₃–0.25PbTiO₃ (0.75PMN–0.25PT) were prepared successfully. High transparency of 69% in the near-infrared (IR) wavelength (1550 nm) was achieved at 2 mol% La doping, meanwhile it shows an extremely high quadratic EO coefficient of 45.4×10⁻¹⁶ m²·V⁻², which is indispensable for applications in EO devices. The distribution of a polar nanodomain structure of the samples experiences disorder–order–disorder evolution in a La doping range. It is found that a parallelly-stacked polar nanodomain structure with an easier and faster polarization switching in the 2 mol% La-doped sample suggests that an ordering distribution of polar nanoregions would be critical to inducing large EO effect, transparency, and piezoelectric response. A triple-cavity tunable optical filter (TOF) with a single transmission peak and a tuning voltage below 30 V in a tuning range of 190–197 THz was designed based on our ceramics. The work is believed to bridge the relationship among doping-engineering, EO properties, and polarization behavior, which would guide the further optimization of transparent EO ceramics.

A novel phthalocyanine based discotic liquid crystal for efficient corrosion inhibition of mild steel

ABSTRACT Discotic liquid crystals have been extensively investigated for their applications in electro-optical devices. Very recently their potential as corrosion inhibitor has been realised. Effective methods for the prevention of corrosion of mild steel (MS) are still challenging research for industrial chemists. In the present work, MS samples in 1.0 M HCl medium were used to test the corrosion inhibition capacity of a metal-free phthalocyanine (Pc)-based discotic liquid crystal (DLC) using potentiodynamic and electrochemical impedance parameters. The phthalocyanine discotic liquid crystal (PcDLC) exhibited an excellent corrosion inhibition with a maximum inhibition efficiency of 89.61%. This superior ability was attributed to the strong adsorption of PcDLC on to the surface of mild steel as confirmed from the potentiodynamic polarisation data that fit into the cathodic inhibitor category. The protective layer of inhibitors generated on the MS surface was examined using scanning electron microscopy (SEM) and FTIR. The density function theory (DFT) approach was used to investigate the relationship between molecular structures and inhibitory efficacy, which indicated a strong interaction between the inhibitor and the surface iron atoms.

A bistable cholesteric liquid crystal film stabilized by a liquid-crystalline epoxy/thiol compound-based polymer.

Bistable cholesteric liquid crystals have promising application prospects in various fields, such as smart windows and displays. However, the long-term stability of two individual states is not easy to achieve, hindering their practical use. In this research, the bistable feature was enhanced by constructing a microsphere-type polymer with a liquid-crystalline epoxy/thiol monomer in negative dielectric anisotropic cholesteric liquid crystals. Spectroscopic and optical examinations revealed that either the transparent planar state or the opaque focal conic state can be maintained without the aid of an external field. Moreover, they can be switched to each other by applying a high- or low-frequency electric field. Further, factors such as the chemical structure of thiol compounds, curing temperature and curing time were investigated to explore their influences on the micro morphology of the polymer and thereby the electro-optical properties. In addition, the frequency-dependent driving scheme was analysed. Finally, bistable switching was demonstrated using an optimized sample. This energy-efficient bistable film shines light on future applications in smart windows, photonic paper and other electro-optical devices.

Deterministic topological defects and quantum dot assembly in a nematic liquid crystalline medium

Liquid crystal (LC) materials exhibit interesting electro-optic switching and molecular ordering properties. Furthermore, the addition of chemically compatible active emitters such as core-shell quantum dots (QD) in a LC medium allows optical as well as dielectric tuning in an anisotropic, reconfigurable ordered medium. Order in a nematic LC phase is characterized by an orientational order parameter. In this work, we demonstrate the use of patterned substrates to generate arrays of integer topological defects in a nematic LC medium doped with cadmium selenide (core) cadmium sulfide (shell) core–shell QDs. We demonstrate the formation of metastable air-pillar-induced integer topological defects (TDs) in relatively thinner 9 μm LC sandwich cells, and the formation of field-induced TDs in thicker (25 μm) cells. Simultaneously, the self-assembly of core-shell QDs into square arrays on the patterned substrates is discussed, highlighting potential electro-optic device applications. The surfactant hexadecyltrimethylammonium bromide (CTAB) is found to play a significant role in LC TD formation as well as QD spatial organization at the optimized concentration. Self-assembly and ordering of single- and multi-component LCs within structured devices is a highly relevant problem for modern optoelectronic devices. This work opens new possibilities for classical as well as quantum light sources which require spatially ordered optical emitters in a reconfigurable dielectric medium at a micron-scale.

Metallomesogen Mixtures as Potential Materials for Application in Liquid Crystal Devices

In this work, we present a new approach for development of metallomesogen (MOM) mixtures for potential applications in electrooptical devices. Through combination of molecular engineering and physical mixing technique, we propose to overcome the major drawbacks of MOMs, including their inaccessible transition temperature and low solubility in liquid crystal hosts. In the present study, we report on the miscibility of bi-ligand Cu, Ni and Pd complex salicylal-diaminates metallomesogens as model structures. Accordingly, we studied the phase diagrams of two binary MOM mixtures with different metals and ligands. The preliminary results indicate the complete mesogenic miscibility, distinct eutectic points and wide mesogenic range, which provide as model materials in electro-optical devices.

Nonlinear terahertz Kerr effect in quasi-2D MnPS3

The quadratic electro-optic effect (Kerr effect) is shown to be efficiently induced by a terahertz (THz) electric field in the quasi-two-dimensional (2D) material MnPS3. The waveform of the THz-induced response practically follows the intensity of the employed nearly single-cycle THz pulse. While neither THz-induced absorption nor the linear electro-optical effect are observed, we demonstrate that the THz electric field induces the refraction coefficient anisotropy experienced by light at the wavelength of 800 nm. In our experiment, the anisotropy results in polarization rotation of the light and corresponds to a nonlinear refractive index of the sample of approximately 13.1 × 10−14 W−1 cm2. This promotes the quasi-2D MnPS3 as a promising candidate for practical application in future ultrafast electro-optical devices.

Ferroelectric Smectic Liquid Crystals as Electrocaloric Materials

The 1980s saw the development of ferroelectric chiral smectic C (SmC*) liquid crystals (FLCs) with a clear focus on their application in fast electro-optic devices. However, as the only known fluid ferroelectric materials, they also have potential in other applications, one of which is in heat-exchange devices based on the electrocaloric effect. In particular, ferroelectric liquid crystals can be both the electrocaloric material and the heat exchanging fluid in an electrocaloric device, significantly simplifying some of the design constraints associated with solid dielectrics. In this paper, we consider the electrocaloric potential of three SmC* ferroelectric liquid crystal systems, two of which are pure materials that exhibit ferroelectric, antiferroelectric, and intermediate phases and one that was developed as a room-temperature SmC* material for electro-optic applications. We report the field-induced temperature changes of these selected materials, measured indirectly using the Maxwell method. The maximum induced temperature change determined, 0.37 K, is currently record-breaking for an FLC and is sufficiently large to make these materials interesting candidates for the development for electrocaloric applications. Using the electrocaloric temperature change normalised as a function of electric field strength, as a function of merit, the performances of FLCs are compared with ferroelectric ceramics and polymers.

Effective switching of an all-solid-state mode-locked laser by a graphene modulator.

Although sophisticated novel saturable absorber materials are available for the development of ultrafast lasers, innovative approaches and devices play an increasingly important role in continuously adjusting mode-locked lasers with electrical gating. In this study, electrically switched operational regimes of an Nd:YVO4 all-solid-state mode-locked laser with a high modulation ratio (from 900 ns to 15 ps) are demonstrated for the first time. The laser can automatically switch multiple operation regimes with the assistance of electrical signals using techniques such as Q-switching, Q-switched mode-locking (QML), and continuous-wave mode-locking (CWML). The device is operated at an ultralow electrical modulation power (0.1 nW) to generate sub 15 ps pulses with a high average output power (as much as 800 mW) from a mode-locked laser operating at 1064 nm. The results verify the reversible switching of the operational regimes from QML to CWML and provide a basis for exploring their applications in electro-optical devices.

Investigation on Optical and Thermal Transport Properties of L-Tartaric Acid Single Crystal for Electro-Optical Device Applications

Investigation on Optical and Thermal Transport Properties of L-Tartaric Acid Single Crystal for Electro-Optical Device Applications

A DFT study of the second-order nonlinear optical properties of Ru(II) polypyridine complexes.

It is important to search for efficient nonlinear optical (NLO) materials due to their potential applications in electro-optic devices. Theoretical investigations into the second-order NLO responses of ten novel Ru(II) polypyridyl complexes based on [Ru(phen)2(bipy)]2+ and [Ru(bphen)2(bipy)]2+ have been performed using density functional theory. The effects on the second-order NLO response of introducing a substituent to the bipy group and of varying the ligand from phen to bphen are studied. The introduction of an electron-withdrawing/donating group improves the static first hyperpolarizability (βtot) for [Ru(phen)2(bipy)]2+ derivatives, where the introduction of a strong electron-donating group, vinyl dimethylamine, increases the βtot value from 10 a.u. for an unsubstituted complex to 16 425 a.u. However, substituting the phen ligand for a bphen group has only a slight effect on the βtot values. Research into the electronic structures, UV-vis absorption spectra, and charge transfer properties was also carried out to further understand the second-order NLO properties of the ten complexes. The frontier orbital energy gap, electron density distribution, and charge-transfer direction and quantity are crucial elements impacting the second-order NLO responses of the complexes. Varying the electronic properties is considered to be an effective method for tuning the second-order NLO responses of materials. We hope our work will provide some helpful information for designing and synthesizing cost-effective and high-performance NLO materials.

Discotic anthraquinones as novel corrosion inhibitor for mild steel surface

Liquid crystals are primarily known for their application in electro-optical devices and their application potential in preventing corrosion has rarely been explored. This report elucidates the application of a room temperature anthraquinone based discotic liquid crystal 1,5-dihydroxy-2,3,6,7-tetrakis(3,7-dimethyloctyloxy)-9,10-anthraquinone 3 (RTAQ) as a corrosion inhibitor on mild steel surfaces. It also attempts to bring out the importance of mesogenic organization towards inhibiting corrosion for metals. The aforementioned RTAQ exhibits, cathodic type of inhibition. The inhibition efficiency obtained for RTAQ was found to be 83.96% at a higher concentration of the inhibitor. The results obtained from quantum studies are in good agreement with the experimental studies.

Nematic Structures under Conical Anchoring at Various Director Tilt Angles Specified by Polymethacrylate Compositions.

Dependence of the director tilt angle of nematic liquid crystal (LC) under conical anchoring from the two-component polymer mixture composition has been studied. We varied the ratio of poly(isobutyl methacrylate) (PiBMA), which specifies a conical anchoring for the nematic liquid crystal LN-396, and poly(methylmethacrylate) (PMMA) assigning a tangential alignment for the same nematic. An oblique incidence light technique to determine a tilt angle has been used. It has been shown that the tilt angle increases from to when PiBMA:PMMA ratio changes in the range 30:70 to 100:0. The specific optical textures viewed under the polarizing microscope and proper orientational structures have been considered for various compositions of the polymer films. An electric field action on the formed orientational structures has been investigated. The obtained results are promising for the application in various electro-optical LC devices with a conical anchoring in which the director tilt angle is a crucial parameter: a controlled diffraction gratings, an electrically operated achromatic rotators of linear light polarization, etc.

Flexibility of Room-Temperature-Synthesized Amorphous CdO-In2O3 Alloy Films and Their Application as Transparent Conductors in Solar Cells.

Due to their low-temperature deposition, high mobility (>10 cm2/V·s), and electrical conductivity, amorphous ionic oxide semiconductors (AIOSs) have received much attention for their applications in flexible and/or organic electro-optical devices. Here, we report on a study of the flexibility of CdO-In2O3 alloy thin films, deposited on a polyethylene terephthalate (PET) substrate by radio frequency magnetron sputtering at room temperature. Cd1-xInxO1+δ alloys with the composition of x > 0.6 are amorphous, exhibiting a high electron mobility of 40-50 cm2/V·s, a low resistivity of ∼3 × 10-4 Ω·cm, and high transmittance over a wide spectral window of 350 to >1600 nm. The flexibility of both crystalline and amorphous Cd1-xInxO1+δ films on the PET substrate was investigated by measuring their electrical resistivity after both compressive and tensile bending with a range of bending radii and repeated bending cycles. Under both compressive and tensile bending with Rb = 16.5 mm, no significant degradation was observed for both the crystalline and amorphous films up to 300 bending cycles. For a smaller bending radius, the amorphous film shows much less electrical degradation than the crystalline films under compressive bending due to less film delamination at the bending sites. On the other hand, for a small bending radius (<16 mm), both crystalline and amorphous films degrade after repeated tensile bending, most likely due to the development of microcracks in the films. To demonstrate the application of amorphous Cd1-xInxO1+δ alloy in photovoltaics, we fabricated perovskite and bulk-heterojunction organic solar cells (OSCs) on glass and flexible PET utilizing amorphous Cd1-xInxO1+δ layers as transparent electrodes. The organic-inorganic hybrid perovskite solar cells (PSCs) exhibit a power conversion efficiency (PCE) of ∼11 to 12% under both front and back illumination, demonstrating good bifacial performance with bifaciality factor >90%. The OSCs fabricated on an amorphous Cd1-xInxO1+δ-coated flexible PET substrate achieve a promising PCE of 12.06%. Our results strongly suggest the technological potentials of amorphous Cd1-xInxO1+δ as a reliable and effective transparent conducting material for flexible and organic optoelectronic devices.

Electrically switchable and optically tunable liquid crystal/ silicone oil based non-aqueous emulsions for electro-optical device applications

Liquid crystal/silicone oil based emulsions have been prepared and characterized for interfacial interactions, optical and electro-optical behaviour. Emulsions are stabilized without any surface-active agent via non-covalent interactions, surface alignment and anchoring conditions. Emulsions are characterized by polarizing optical microscopy. Distinct mesomorphic phases, droplet geometries (radial, hedgehog, bipolar) and transitions viz. radial to bipolar and bipolar to broken bipolar are observed as a function of varying silicone oil concentration in liquid crystal. These emulsions are quite stable and show reversible characteristics as a function of time and temperature. The stability of these emulsions has been explained considering hydrophobic interactions, decrease in internal surface tension and anchoring energy etc. Further, the liquid crystal/silicone oil devices have been fabricated and tested for switching and electro-optical behaviour. The emulsion contains 25% silicone oil in liquid crystal matrix shows the best switching characteristics at low deriving voltage 5 V, about 87% enhancement in optical transmission, 8.3 dB contrast and lower Frederiks threshold ~65%. Such switchable and optically tuneable surfactant-free emulsions with controlled morphological dynamics can provide a new door to design novel functional soft material platform for better optical, electro-optical, photonics, sensing and liquid crystals elastomer applications. • Surfactant-free, electrically switchable and optical tuneable liquid crystals/silicone oil emulsions. • 87% enhancement in transmission, 8.3 dB contrast and lower Fredrick's threshold ~65% has been achieved in emulsion systems. • Tuning of optical and electro-optical parameters depends on the boundary conditions, topological deformations.