Browsing by Author "Trifonova Y."
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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 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 Physico-chemical characterization of new tellurium based chalcogenide materials(2018-01-01) Trifonova Y.; Ivanova V.; Lilova V.; Vasileva D.; Boteva T.Bulk samples of Ge-Te-Cu system are synthesized by melt-quenched technique into a water/ice mixture. The synthesis is carried out at a constant heating rate of 5.10-2 K s-1 reaching the final temperature of 1373 K. Some physico-chemical properties of the synthesized bulk samples are defined. The density of the latter undergoes various changes with Cu content increase most likely due to the gradual substitution of tellurium atoms with copper leading to structural changes in the samples. The dependencies of the bulk samples compactness, molar volume and free volume on their composition follow that of the density. A change in the structure of GeTe4-Cu leading to extreme physico-chemical properties is observed in accordance with the theory of Thorphe for transitions in the structure of covalent chalcogenide glasses at an average coordination number 2,4. It proceeds at Zglass = 2,46 corresponding to a content of 10 mol % of Cu.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 Structural investigation of tellurium based thin films(2018-01-01) Ivanova V.; Trifonova Y.; Lilova V.; Mikli V.; Stoyanova-Ivanova A.Tellurium based materials possess a low temperature phase change transition. Sometimes they cannot be obtained in an amorphous state under normal conditions. Thus they can be used as an active element in phase change memory devices. Our study is dedicated to the synthesis of tellurium based materials using the systems (GeTe3)100-xInx, x = 5 mol %, 10 mol %, 15 mol % and 20 mol % and (GeTe4)100-xInx, x = 5 mol %, 10 mol %, 15 mol % and 20 mol %, the deposition of thin films on their ground and the investigation of their morphology, topology and structure aiming to obtain new knowledge for evaluation of the possibility for application of these materials in phase change memory devices.