Gertruda V. Klimusheva

Electrical conductivity of lyotropic and thermotropic ionic liquid crystals consisting of metal alkanoates

The electrical properties of ionic smectic liquid crystal (ISLCs), specifically, (i) oriented and non‐oriented samples of lyotropic ISLC potassium caproate and (ii) oriented samples of thermotropic ISLC cobalt decanoate, are investigated in detail. The electrical conductivity of lyotropic smectic potassium caproate is higher than that of isotropic electrolytes. A giant anisotropy in the electrical conductivity of oriented samples of thermotropic ISLC cobalt decanoate is observed. The mobility of charge carriers in lyotropic ISLC is measured for the first time. The unusual electrical properties of ISLCs, which are governed by their layered structure, show that they have application potential in optoelectronic devices.

Strong thermal optical nonlinearity caused by CdSe nanoparticles synthesised in smectic ionic liquid crystal

Spectral and nonlinear optical properties of cadmium octanoate composites containing CdSe nanoparticles (NPs) have been studied by using optical absorption spectroscopy and laser scanning technique (Z-scan). CdSe NPs are chemically synthesised in thermotropic ionic liquid crystal (ILC) phase of cadmium octanoate which is used as nanoreactor. Anisotropic glassy nanocomposites are obtained by the rapid cooling of the ILC phase of nanocomposites to room temperature. The sizes of the CdSe NPs are determined from the absorption spectra. The thermo-optical nonlinearity of the new nanocomposites is characterised by extremely large value of the nonlinear refractive index, n2, under relatively low-powered CW laser irradiation. This nonlinearity is caused by (1) the efficient light-induced heating due to the CdSe NPs strong exciton absorption, and (2) consequent thermal dissipation, which in turn, produces the photoelastic tensions in the glassy smectic matrix.

Tunable optical and nonlinear optical response of smectic glasses based on cobalt alkanoates

The nonlinear optical response of anisotropic smectic glasses based on cobalt alkanoates has been studied using dynamic holography. Laser-dynamic gratings induced by the action of nanosecond laser pulses were observed and analysed for such materials. It was found that the cubic optical nonlinearity of all the anisotropic glasses studied had an electronic origin in the nanosecond range, caused by nonlinear polarisation of the cobalt alkanoate complexes. Fundamental optical (refractive index and absorption coefficient) and nonlinear optical (nonlinear susceptibility and polarisability) parameters of mesomorphic glasses based on cobalt alkanoates could be tuned by varying the length of the alkanoate anion chain, thereby determining the interlayer smectic distance.

Monodispersity and ordering of semiconductor quantum dots synthesised in ionic liquid crystalline phase of cadmium alkanoates

Structural and optical properties of cadmium alkanoates nanocomposites with cadmium sulfide (CdS) quantum dots (QDs) have been studied by using various techniques: small angle X-ray scattering, transmission electron microscopy, optical absorption spectroscopy and photoluminescence. QDs are chemically synthesised in thermotropic ionic liquid crystalline (ILC) phase of cadmium alkanoates that have smectic-type ordering and are used as nanoreactors. Anisotropic glassy nanocomposites are obtained by rapid cooling the thermotropic ILC nanocomposites to the room temperature. For synthesis of CdS QDs are used cadmium capronate matrix or cadmium octanoate matrix and their binary mixture. Our results show that in the new cadmium alkanoates matrices, the CdS QDs have a small dispersion of their sizes, their shape is nearly spherical, they are stable over time and they are ordered in a layered smectic A matrix. QDs in cadmium octanoate and in cadmium capronate matrices have the dominant characteristic sizes of 2.7 and 2.8 nm, respectively. In the binary mixture, the QDs have two dominant characteristic sizes of 2.7 and 3.6 nm. The glassy nanocomposites show spectra both of absorption and of photoluminescence in near-ultraviolet and blue visible spectral range.

Nonlinear optical properties of composites based on conductive metal-alkanoate liquid crystals

The dynamic holography in new composite materials based on a novel class of metal-alkanoate ionic liquid crystals (ILCs) is studied experimentally and theoretically. The composites are formed as a dielectric dye film covered by lyotropic metal-alkanoate ILC and ionic smectic glasses with doped dye molecules. The dynamic gratings are created by nanosecond pulses of double frequency Nd:YAP laser, the recording demonstrates fast erasure time of residual thermal gratings. The nonlinear optical properties are determined by the resonance nonlinearity in photosensitive centres of ILC. Note, that permanent relief gratings will be formed on a dielectric dye film only as well as in composite cells either with nematic LC or with polymers under action of pulsed laser radiation. Lyotropic ILC layer applied over the dye film provides the dynamic regime of grating recording in composite cells. We found a secondary thermal grating is much smaller, the conductive ILC matrix provides effective heat dissipation and erasure of this thermal grating. A theory of Raman-Nath self-diffraction holography on thin films followed from the wave equation and the nonlinear mechanism of absorption saturation is developed to explain experimental results.

Enhanced optical nonlinearity of the “nonlinear host–nonlinear guest” glassy nanocomposites made of the mesomorphic cobalt octanoate and noble metal nanoparticles

In this paper, we performed optical and nonlinear optical characterization of the newly designed anisotropic glassy materials composed of the mesomorphic cobalt octanoate and noble metal nanoparticles. Both the host (the cobalt octanoate) and the dopant (noble metal nanoparticles) absorb light in the near-UV–visible region of the optical spectrum. This feature allowed us to explore an impact of such overlapped light absorption on the optical nonlinearity of the devised “guest–host” system at the off-resonance frequency by means of the femtosecond laser scanning technique (Z-scan). Minor fractions of noble metal nanoparticles in the cobalt octanoate led to the twofold increase in the optical nonlinearity of the nanocomposites. Optical and nonlinear optical properties of the glassy nanocomposites were analyzed by applying the formalism of the Maxwell Garnett theory.

Structural characteristics of different types of nanoparticles synthesised in mesomorphic metal alkanoates

ABSTRACT The class of thermotropic ionic liquid crystals (LCs) of the metal alkanoates possesses a number of unique properties, such as intrinsic ionic conductivity, high dissolving ability and ability to form time-stable mesomorphic glasses. These ionic LCs can be used as nanoreactors for the synthesis and stabilisation of different types of nanoparticles (NPs). Thus, some semiconductors, metals and core/shell NPs were chemically synthesised in the thermotropic ionic liquid crystalline phase (smectic A) of the cadmium octanoate (CdC8) and of the cobalt octanoate (CoC8). By applying the scanning electron microscopy, the cadmium and cobalt octanoate composites containing CdS, Au, Ag and core/shell Au/CdS NPs have been studied. NPs’ sizes and dispersion distribution of the NPs’ size in the nanocomposites have been obtained. GRAPHICAL ABSTRACT

Dynamic holography grating recording in ionic liquid crystals

The study of photorefractive materials attracts a big interest due to large variety of their optical as well as electro-optical effects. As was shown by our investigations dye-doped ionic liquid crystal (DILC) appeared to be a promising medium for the said processes. Doping of ILC with electro-chromic additives leads to significant changes in both electrical and optical properties of ILC with electro- chromic additives leads to significant changes in both electrical and optical properties of ILC with respect to pure substances. Doped ILC was used as a medium for dynamic holography grating recording. Electric current passing through the DILC film induces the appearance of an absorption band in different spectral regions.Existence of self-diffraction during a single pulse as soon as its rather high efficiency pointed out that the mechanism of grating creation might include optical and electro-optical nonlinearity.

Optical activity of chiral liquid crystals under different light intensities

Rotation of the light polarization plane in both pure and dye-doped chiral liquid crystals (CLC) was investigated close to the CLC selective reflection region. Spectral dependences of the angle of the polarization plane rotation and circular dichroism were obtained for a number of CLC-compounds. Selection of an appropriate dye-stuff and liquid crystal compound allows to design electrically controlled two-color filter with good color alliance and contrast. Gyrotropy of dye-doped CLC was studied using Nd-laser radiation with varying light intensity. Under the light intensities above 250 kW/sq. cm a polarization nonlinearity was observed as a variation of polarization plane rotation of the light passes through the cell.

Mesomorphic glass nanocomposites made of metal alkanoates and nanoparticles as emerging nonlinear-optical materials

Mesomorphic metal alkanoates is very promising yet overlooked class of nonlinear-optical materials. Metal alkanoates can exhibit a broad variety of condensed states of matter including solid crystals, plastic crystals, lyotropic and thermotropic ionic liquid crystals, liquids, mesomorphic glasses, and Langmuir–Blodgett films. Glass-forming properties of metal alkanoates combined with their use as nano-reactors and anisotropic host open up simple and efficient way to design various photonic nanomaterials. Despite very interesting physics, the experimental data on optical and nonlinearoptical properties of such materials are scarce. The goal of the present paper is to fill the gap by discussing recent advances in the field of photonic materials made of metal alkanoates, organic dyes, and nanoparticles. Optical and nonlinear-optical properties of the following materials are reviewed: (i) mesomorphic glass doped with organic dyes; (ii) smectic glass composed of cobalt alkanoates; (iii) semiconductor nanoparticles embedded in a glassy host; (iv) metal nanoparticles - glass (the cobalt octanoate) nanocomposites.