Browsing by Author "Stoilova A."
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Item Effect of InP/ZnS quantum dots aggregation on the kinetics of birefringence recorded in thin azopolymer composite films(2024-09-01) Stoilova A.; Dimov D.; Trifonova Y.; Mateev G.; Lilova V.; Nazarova D.; Nedelchev L.The article describes the preparation of new thin film composite materials based on the azopolymer (poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt]) doped with three different concentration of InP/ZnS quantum dots with size of 7.5 nm. Clusters of aggregated InP/ZnS were microscopically observed in the fabricated composite samples. Birefringence (Δn) was induced in the films at two different wavelengths of the pump laser (355 nm and 444 nm) and the obtained higher values of Δnmax for the samples doped with quantum dots up to 2 wt% in comparison to the non-doped film and the sample with the highest nanocrystals concentration are discussed, based on the measured fluorescence spectra, in terms of possible local energy transfer between the azobenzene chromophores and the InP/ZnS quantum dots.Item Evaluating the Cytotoxicity of the Azo Polymer PAZO on ATCC TIB-208 Cell Lines(2023-01-01) Stoilova A.; Manoylov I.; Ganova P.; Trifonova Y.The commercially available azo polymer (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]), abbreviated usually as PAZO, is a visible light-responsive material, predominately investigated in recent years as media for optical record of information [1, 2]. Another attractive field of application, for which this polymer has been developed, represents the fabrication of photo-triggered biomolecules delivery systems [3, 4]. Since the quality of a material of being toxic to cells is an essential factor for its usage in such systems, we evaluated the cytotoxicity of the PAZO polymer on ATCC TIB-208 cells. To our knowledge, no results on evaluating the cytotoxicity of this azo polymer have been reported to date. MTT assay was performed to quantify the cell viability and the Dunnett's Multiple Comparison Test was used for the statistical analysis. The experimental procedure included the following steps: ATCC TIB-208 cells were cultured for 24 hours (5×105cells/ml). On the next day, the PAZO polymer was added to the cell suspension at concentrations: 1000 μg/ml, 400μg/ml, 160μg/ml, 64μg/ml, 25.6μg/ml, 10.24μg/ml, and the cells were incubated for another 24 hours. Than the MTT viability test was performed. The absorbance was measured at 590 nm with background subtraction at 620nm. The obtained results show low negative impact (<20%) of the PAZO polymer on the cell viability at concentration 25.6μg/ml and 10.24μg/ml. At concentration 64μg/ml and 160μg/ml of the polymer in the cell suspension the A20 cells viability is 70%/ 50%, respectively.Item Optical constants of azopolymer PAZO thin films in the spectral range 320 - 800 nm(2018-04-05) Berberova N.; Sharlandjiev P.; Stoilova A.; Nedelchev L.; Nazarova D.; Blagoeva B.Azobenzene containing polymers (azopolymers) have been investigated for a number of applications - holographic data storage, polarization optical elements, diffractive gratings, etc. Herein we report on the optical characteristics of films obtained from the commercially available water soluble azopolymer PAZO (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt). Thin films were deposited by spin coating and their thickness was determined by a Talystep precision profilometer. The FTIR spectra of PAZO were measured between 3000 cm-1 and 500 cm-1. For the first time, to the best of our knowledge, we evaluated the PAZO complex refractive index continuously in a broad spectral range (320 - 800 nm) based on transmission and reflection spectrophotometric data. The wavelength dependence of the complex refractive index of organic dyes layers cannot be readily described with dispersion models used for crystals, metals or semiconductors. This is why we used a derivative approach on a wavelength-by-wavelength basis to solve a set of two nonlinear equations with two unknowns - the real and imaginary parts of the refractive index. The determination of the optical constants of PAZO films is effective and robust.Item OPTICAL PROPERTIES OF ELECTROSPRAY DEPOSITED PAZO POLYMER FILMS DOPED WITH GeTe4-Cu CHALCOGENIDE PARTICLES(2022-01-01) Stoilova A.; Lilova V.; Ivanova V.; Trifonova Y.; Dimov D.Composite films based on the azopolymer poly[1-[4-(3-carboxy-4-hydroxyphenylazo)benzenesulfonamido]-1,2-ethanediyl, sodium salt] doped with GeTe4-Cu chalcogenide particles have been prepared through electrospray deposition. Polarization microscopy was applied to study the films morphology. The transmittance coefficient (T), the reflectance coefficient (R), the refractive index (n), the extinction coefficient (k), the optical absorption coefficient (α) and the optical band gap (Formula presented) of the composite films and of the pure azo polymer film were determined. A significant change in the optical properties of the composite films in comparison to the non-doped azo polymer film has been observed.Item Optical properties of novel azo multi-functional dye thin films(2019-01-01) Stoilova A.; Trifonova Y.; Lilova V.By evaluation the practical applicability of new synthesized compounds, starting point represents the thin film optical properties analysis, which provides rich information about chemical bonding, layer thickness, electronic structure, etc. Here, we present optical properties determination of thin nanocomposite films of three novel N-phthalimide azoazomethine dyes containing OH-group at ortho-position in respect to the -CH=N- chromophore group and designed with different electron donating and electron withdrawing substituents. The structure of these previously synthesized by us dyes is shown below. With the aim to explore potential practical application of these novel azo multi-functional dyes, we prepared thin nanocomposite films via vacuum thermal evaporation and low temperature spray technique, and determined the transmittance coefficient (T), the reflectance coefficient (R), the refractive index (n), the extinction coefficient (k), the optical absorption coefficient (a) and the optical band gap (Eg) of the fabricated thin films in the spectral range between 340 and 800 nm. The thin films prepared through vacuum thermal evaporation show higher transmittance, higher reflectance, higher refractive index (n=1.5÷2.1) and higher values of the optical band gap (Eg=2.93÷3.53, eV). The effect of the substitutions and of the fabrication method on the optical performance of the nanocomposite thin films has been discussed.Item OPTICAL PROPERTIES OF PAZO POLYMER COMPOSITE FILMS DOPED WITH PARTICLES OF A NOVEL COPPER HYDANTOIN COMPLEX(2021-01-01) Lilova V.; Trifonova Y.; Stoilova A.; Georgieva S.; Todorov P.In this work the transmittance coefficient (T), the reflectance coefficient (R), the refractive index (n), the extinction coefficient (k), the optical absorption coefficient (a) and the optical band gap (Eof thin (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]), shortly PAZO, azopolymer films with embedded particles of Cu(II) 3-amino-5,5‘-dimethylhydantoin at three different concentrations have been determined. The influence of the dopants concentration on the optical performance of the composite films has been discussed.Item Photoinduced birefringence in pazo polymer nanocomposite films with embedded particles of biologically active metal complexes(2019-01-01) Mateev G.; Stoilova A.; Nazarova D.; Nedelchev L.; Todorov P.; Georgieva S.; Trifonova Y.; Lilova V.The composite materials based on azo polymers doped with metal particles attract considerable attention due to their advantageous electrical and optical properties. The present communication reports results from measuring the photoinduced birefringence in composite films of the azopolymer (poly[1-[4-(3-carboxy-4-hydroxyphenylazo) benzenesulfonamido]-1,2-ethanediyl, sodium salt]), shortly PAZO, doped with metal complexes of Cu(II) 3-amino-5,5'-dimethylhydantoin (CLP) and Ni(II) 3-amino-5,5'-dimethylhydantoin (NLP) of different concentrations. The thin film materials are prepared via spin coating. The thickness of the samples is in the range between 500 nm and 800 nm. The photoinduced birefringence is measured by a classical polarimetric setup, where a vertically polarized He-Cd laser emitting at ? = 442 nm is used as a pump laser, while a DPSS laser emitting at = 635 nm is used as a probe laser. The influence of the dopants concentration on the maximal induced birefringence and the time of response are discussed.Item Se-BASED CHALCOGENIDE GLASSES AS HOLOGRAPHIC MEDIA(2020-01-01) Trifonova Y.; Stoilova A.; Ivanova V.; Lilova V.; Petkov P.The present paper reports on the effect of the addition of IIIA metal (Ga or In) to Se-based chalcogenide thin films on the diffraction efficiency. The holographic scalar recording is accomplished using standard interferometric configuration with argon laser with a wavelength of 448 nm, spatial frequency of 2,2.10s m−1 and diameter of the spot 2 mm. The diffraction efficiency relation to the glassy system composition and the time of illumination at constant intensity of a laser beam is investigated. The results are interpreted in terms of the electronic structure in disordered systems.Item Structure of GeSe4-In and GeSe5-In glasses(2010-10-13) Kaban I.; Jóvári P.; Petkova T.; Petkov P.; Stoilova A.; Hoyer W.; Beuneu B.(Ge0.2Se0.8)100-xInx and (Ge0.17Se0.83)100-xInx (x = 0, 5, 10, 15 at.%) chalcogenide glasses have been studied with high-energy x-ray diffraction, neutron diffraction and extended x-ray absorption spectroscopy at Ge, Se and In K-edges. The experimental data were modelled simultaneously with the reverse Monte Carlo simulation method. GeSe4/2 tetrahedra are shown to be the main structural units in the binary and ternary glasses investigated. Indium bonds to the excess Se atoms in the ternary Ge-Se-In glasses. While the majority of In atoms have three Se neighbours, some In atoms may be tetrahedrally coordinated by Se. © 2010 IOP Publishing Ltd.Item Tautomeric influence on the photoinduced birefringence of 4-substituted phthalimide 2-hydroxy Schiff bases in PMMA matrix(2021-05-01) Blagoeva B.; Stoilova A.; Dimov D.; Yordanov D.; Nazarova D.; Georgiev A.; Antonov L.The photoinduced birefringence of two 4-substituted phthalimide 2-hydroxy Schiff bases, containing salicylic (4) and 2-hydroxy-1-naphthyl (5) moieties has been investigated in PMMA matrix. Their optical behaviour as nanocomposite films was revealed by combined use of DFT quantum chemical calculations (in ground and excited state) and experimental optical spectroscopy (UV–Vis and fluorescence). The results have shown that solid-state reversible switching takes place by enol/keto tautomerization and Z/E isomerization. Birefringence study was performed in the PMMA nanocomposite films using pump lasers at λrec = 355 nm and λrec = 442 nm. Fast response time and high stability of anisotropy up to 58% for (4) and 95% for (5) after turning off the excitation laser, was observed, which makes these materials appropriate candidates for cutting-edge optical information technology materials. The possibility for multiple cycles of recording, reading and optical erasure of the photoinduced birefringence at λrec = 442 nm in 5 has been demonstrated. The obtained results have shown that the maximum value of the measured birefringence is close to the anisotropic characteristics of the most frequently used azo materials.Item Technological research on converting iron ore tailings into a marketable product(2021-05-01) Mitov I.; Stoilova A.; Yordanov B.; Krastev D.We present three technological scenarios for the recovery of valuable components from gangue, stored in the tailings dam at Kremikovtzi metallurgical plant in Bulgaria, into marketable iron-containing pellets. In the first approach the iron concentrate was recovered through a two-stage flotation process, desliming, and magnetic separation. In the second proposed process, the iron concentrate was subjected to four sequential stages of magnetic separation coupled with selective magnetic flocculation. The third route entails the not very common practice of magnetizing roasting, followed by selective magnetic flocculation, desliming, and magnetic separation. The iron concentrate was pelletized in a laboratory-scale pelletizer. Each technology has been assessed with regard to the mass yield of iron concentrate, the iron recovery. and the iron, lead, and zinc content in order to identify the most effective route.Item Visualization of pathologic changes in liver tissue via polarized light(2022-01-01) Stoilova A.; Blagoeva B.; Nazarova D.; Stoykova E.; Berberova-Buhova N.; Nedelchev L.; Machikhin A.In this work, we applied two polarized light based approaches to visualize histological patterns of liver pathologies. The first one involves acquisition of two images through a polarizing microscope, one image (Ppar) acquired with the analyzer oriented parallel to the polarization of illumination and the other (Pper) acquired with the analyzer oriented perpendicular to the illumination. The final image is based on the polarization ratio, Preconstructed = (Ppar - Pper)/(Ppar + Pper). Using the second technique, the histological specimens were illuminated with a polarized laser beam with wavelength of 635 nm. Polarimetric parameters as azimuth, angle of ellipticity, degree of polarization and reflected power have been measured to quantify the change in the polarization state of the incident light after interaction with the sample of the healthy tissue and of the tissue with abnormal morphological changes.