Scientific highlights

ENHANCED LUMINESCENCE OF CYANINE DYE NK88 ADSORBED ON LAYERED SILICATE SAPONITE

Hybrid materials involving photoactive organic dyes is the newest research topic of the department of hydrosilicates. Using templates of layered silicates, one is able to sensitively control the structure of dye supramolecular assemblies and the photophysical and optical properties of the resulting hybrid material. In recent years incorporation of more complex materials has been investigated, as well as incorporation of third components, such as surface active compounds and modifiers. Highly photoactive materials were successfully developed using a silicate template modification and by optimization of the materials’ structure. The hybrid materials involved layer-by-layer assemblies, ternary colloids and gels and thin optical films of controllable structure. The most interesting properties, i.e. photophysical and photochemical phenomena of these materials included high luminescence, optical anisotropy, photosensitization, and resonance transfer of light energy.

Publication:

  • BOHÁČ, PeterCZÍMEROVÁ, AdrianaBUJDÁK, Juraj. Enhanced luminescence of 3,3′-diethyl-2,2′-thiacyanine cations adsorbed on saponite particles. In Applied Clay Science, 2016, vol. 127-128, p. 64-69.

 

ACCELERATION OF RELATIVISTIC ELECTRON DYNAMICS BY MEANS OF X2C TRANSFORMATION: APPLICATION TO THE CALCULATION OF NONLINEAR OPTICAL PROPERTIES

The use of the Dirac equation is crucial for describing systems containing heavy atoms. It bridges quantum mechanics and the theory of relativity. The solution of its time-dependent form allows new insight into spectroscopic experiments and provides new routes to theoretical predictions of molecular properties. For the first time it was explained how an approximate transformation (X2C) known from the time-independent Dirac equation can be used in the time-dependent case. The developed method was used to calculate linear and non-linear optical (NLO) properties of molecules. Pilot applications have shown that the new method offers more than 7-times speed-up practically without the loss of accuracy. Therefore it applicable for larger systems, for example heavy metal complexes, which are of interest for modern optoelectronic applications due to potentially high values of NLO properties. Our program is currently one of the two in the world capable of obtaining molecular properties from the time-dependent Dirac equation.

 

Publication:

  • KONEČNÝ, Lukáš – KÁDEK, Marius – KOMOROVSKÝ, Stanislav – MALKINA, Oľga – RUUD, Kenneth – REPISKÝ, Michal. Acceleration of relativistic electron dynamics by means of X2C transformation: Application to the calculation of nonlinear optical properties. In Journal of Chemical Theory and Computation, 2016, vol. 12, no., p. 5823-5833. (5.301 – IF2015).

 

APPLICATION OF MODERN SPECTROSCOPIC METHODS FOR INVESTIGATION OF FLUORIDE SYSTEMS

Using NMR spectroscopy at high temperatures (HT) in the liquid as well as in the solid state (MAS), a question discussed in literature for more than 70 years on the formation of so called oxo-fluoro-aluminates was resolved. HT NMR and MAS NMR were applied to the systems of Na3AlF6-(Al2O3, Fe2O3 or FeO). It was found that specific oxo-fluoro-aluminates formed in the liquid phase can vaporise, and after condensation they decompose to cryolite (Na3AlF6) and Al2O3. This result was achieved in cooperation with the CNRS team (CEMHTI-CNRS, Orléans, France) equipped with the most modern experimental setups. This observation is important for aluminium smelters all around the world, because any new knowledge about the processes that take place in production pots can be used in modelling of new generation pots, thus saving energy and reducing environmental impact. This technique has been applied in investigation of aluminium phosphate dissolutions in cryolite melt.

Publications:

  • ŠIMKO František – RAKHMATTULIN A. – BESSADA C. – and BOČA Miroslav. MAS NMR study of the solidified cryolite systems with FeO addition. Journal of Fluorine Chemistry 165 (2014) 116−122.
  • RAKHMATTULIN A. – KEPPERT M. – ŠIMKO František – BESSADA C. Aluminium phosphate behaviour in Na3AlF6-Al2O3 melts: a new insight from in situ high temperature NMR measurements. New Journal of Chemistry, 40 (2016) 1737-1741.

 

LUMINESCENT MATERIALS FOR POTENTIAL APPLICATIONS IN PHOSPHOR CONVERTED WHITE LIGHT EMITTING DIODEDS (pc-WLED)

The glasses in the systems Y2O3-Al2O3 aY2O3-Al2O3-SiO2 were prepared from precursor powders by flame spraying method in the form of glass microspheres. The precursor powders were synthetised by sol-gel Pechini method to achieve better homogeneity of the system. The prepared glasses were doped with rare-earth and transition metal ions with photoluminescence properties suitable for LED diodes emitting white light applications, e.g. Ce3+, Mn2+, at low concentration. The glass-ceramics materials prepared by controlled crystallization of Ce3+ doped glasses at low concentration exhibits strong green-yellow emission under blue light excitation comparable with commercial phosphors. Moreover, glass heat treatment at suitable time-temperature regimes leads to the white light emission under NUV excitation. Co-dopind of Ce3+ system with Mn2+ ions enable to prepare the phosphors with improved emission in the orange-red spectral region.

Publications:

  • HALADEJOVÁ, Katarína – PRNOVÁ, Anna – KLEMENT, Róbert – TUAN, Wei-Hsing – SHIH, S. J. – GALUSEK, Dušan Aluminate glass based phosphors for LED applications. In Journal of the European Ceramic Society, 2016, vol. 36, no. 12, p. 2969-2973.

Project:

  • VEGA 1/0631/14 New rare-earth aluminates based inorganic phosphors for application in LEDs emitting white light.

 

HOLLOW AMPRPHOUS AND POLYCRYSTALLINE YAG MICROSPHERES PREPARED BY FLAME SYNTHESIS

Hollow glass microspheres (HGMs) are a low cost but high performance material with a number of various applications such as fillers for polymer-based composites, paints, as hydrogen storage, as thermal insulation material, or agents for cancer treatment. From powders precursors we prepared successfully Y3Al5O12 glassy and polycrystalline hollow microspheres with diameter of 5‑35 mm by flame spheroidization process in oxygen-methane (O2/CH4) flame. By controlled heating at 1200°C the hollow polycrystalline microspheres (HPMs) have been prepared with the average size of the YAG grains 540 ± 40 nm. Hollow YAG microspheres with low overall density and high Y2O3 content are appropriate for radiotherapy treatment of liver cancer.

SEM images of YAG HGMs (a), cross section of YAG HGMs (b) and of the cavity inside a heat-treated microsphere of YAG HPMs (c).

  • More information: Dušan Galusek, dusan.galusek@tnuni.sk
  • KRAXNER, Jozef – CHOVANEC, Jozef – HALADEJOVÁ, Katarína – PETRÍKOVÁ, I. – GALUSEK, Dušan. Hollow polycrystalline YAG microspheres by flame synthesis, submitted to Materials Letters

 

A NOVEL STRUCTURALLY UNIQUE SURFACTANT FOR POLYMER-CLAY NANOCOMPOSITES

The intercalation of clay minerals, mainly montmorillonites (MT), with a broad range of organic cationic surfactants has attracted widespread attention among researchers due to their possible application as additives for polymers. Polymer-clay nanocomposites frequently exhibit improved mechanical, barrier or thermal properties arising from the synergy of their components. Aliphatic quaternary ammonium ions have been most often utilized for organic modification of clays, but the use of relativelynpolar organocations is rare. The structurally unique 9, 10-dihydroxy-octadecyltrimethylammonium (OH-ODTMA) cationic surfactant, synthesized from commercially available oleylamine, was successfully intercalated into montmorillonite as well as oleyl trimethyl ammonium cation, the precursor of the aforementioned novel surfactant, and the commercially available and widely used ODTMA cation. The effect of alkyl chain functionalization on surfactant, properties and arrangement in montmorillonite interlayers was studied. IR and NMR spectroscopy indicated the coexistence of ordered (all-trans) and disordered (gauche) chain conformations. The 13C MAS NMR spectra showed that the ordering of surfactant molecules within the gallery of montmorillonite strongly depended on the presence of functional groups. Compared to ODTMA-MT, the amount of gauche conformers was significantly higher in MT intercalated with OH-ODTMA and oleyltrimethylammonium cations. The novel alkylamonnium surfactant functionalized with two OH groups in the middle of the backbone not only represents a prospective ingredient for organoclay–polyurethane nanocomposites, but can also act as a gateway to the synthesis of other functionalized clay modifiers with specifically tailored properties for particular applications.

Publication:

  • JANKOVIČ Ľuboš – KRONEK, J. – MADEJOVÁ Jana – HRONSKÝ, V. (9,10-Dihydroxyoctadecyl)ammonium: A structurally unique class of clay intercalable surfactants. In European Journal of Inorganic Chemistry, 2015, p. 2841-2850. (2.942 – IF2014).

Projects:

  • Vega 2/0132/13 – Preparation and properties of novel organoclays for polymer and environmental applications
  • APVV 0362-10 – Organoclays and their composites with polymers

 

A NEW METHOD FOR ACCELERATED CORROSION TESTING ON CONSTRUCTION MATERIALS

A new method for accelerated corrosion testing on construction materials like superalloys in molten fluorides was developed. Various metal fluorides that can be considered as corrosion products of specific materials were added to the basic corrosion media for the system FLINAK(eut)-MFx (MFx = CrF3, FeF2, FeF3 and NiF2) plus Incoloy 800H/HT. This method represents a new approach to long term corrosion tests, which might shorten corrosion investigations from thousands to dozens of hours.

 

Publication:

  • PAVLÍK Viliam. – KONTRÍK MartinBOČA Miroslav Corrosion behaviour of Incoloy 800H/HT in fluoride molten salt FLINAK(eut)-MFx (MFx = CrF3, FeF2, FeF3 and NiF2), New Journal of Chemistry 39 (2015) 9841- 9847.