Yu. S. Zavorotnyi

Synthesis of silver nanocomposites by SCF impregnation of matrices of synthetic opal and Vycor glass by the Ag(hfac)COD precursor

Silver-containing nanocomposites were prepared by impregnating Vycor glass (a pore diameter of 4 nm) and synthesized opal matrices (an interstitial void size of 40 nm) with cyclooctadiene complex of silver hexafluoroacetylacetonate (Ag(hfac)COD), a silver precursor, dissolved in supercritical carbon dioxide and were examined by optical absorption spectroscopy, atomic force microscopy, and electron spin-resonance spectroscopy. It was demonstrated that the absorption spectra of Vycor glass and opal matrices impregnated with Ag(hfac)COD molecules and subjected to thermal treatment in air at temperatures above 50°C exhibit plasmon resonances characteristic of Ag nanoparticles at 420–430 nm. The peculiarities of the plasmon resonance band for both types of samples were attributed to the morphology of the pore space in which silver particles are formed. Paramagnetic Cu(hfac)2 molecules (copper hexafluoroacetylacetonate) were used as a spectroscopic probe for estimating the distribution of the precursor in the pores of Vycor glass and opal matrices during supercritical fluid impregnation.

Synthesis, structure, and thermal behavior of polymeric zinc(II) pivalate*

The reaction of zinc(ii) acetate hydrate with pivalic acid (HOOCBut− = HPiv) in air at 100 °C afforded the new 1D coordination polymer {Zn(Piv)2}n (1), in which the metal atoms are in a tetrahedral ligand environment. The thermal behavior of the resulting compound and the sublimation and vaporization processes in the temperature range of 430–550 K were studied by differential scanning calorimetry and thermogravimetric analysis. The structure of compound 1 was determined by X-ray powder diffraction.

Broadband photoluminescence of hybrid Si/SiO x nanoparticles synthesized from silicon monoxide

Hybrid nanoparticles npSi/SiOx, having bright broadband photoluminescence (PL), have been synthesized using thermal disproportionation of silicon monoxide method and were used to derive sols and polymeric composites in the form of microdispersed PTFE particles and PBMA films. The peculiarities of behavior of both shape and intensity of inhomogeneously broadened PL band’s under laser excitation were determined for npSi/SiOx in sols and composites. Theese peculiarities are caused by relatively wide distribution of Si nuclei, quantum-confinement shifts in absorption (monocrystalline Si nucleus) and photoluminescence (oxygen deficient centers (npODC) in the amorphous SiOx shell) along with the effect of saturation of PL. Continuous laser exposure (at wavelength of 405 nm) of npSi/SiOx sols and composites causes the bleaching of PL. Kinetics of PL bleaching is individual for each sample type, however it always has a substantially nonexponential behavior and the bleaching rate falls two orders after ∼103 s of photoirradiation. The effect of postradiation restoration of the PL after the end of laser photoirradiation is revealed. Kinetics of restoration is essentially nonexponential, but individual for each sample type. Full restoration of PL band’s both intensity and shape for all samples requires no less than 15 h after the end of laser photoirradiation. Restoration completeness reveals the complete reversibility of PL bleaching in all npSi/SiOx based systems studied. A model is considered in which PL bleaching is caused by electron transfer from photoexcited npODC to a suitable trap and further posttreatment restoration of the PL caused by the tunneling recombination of electrons and ionized npODC+. The possibility of controlling the npSi/SiOx photosensitivity is discussed based on creating a specific shell around npSi/SiOx stimulating or, conversely, overwhelming the photoinduced charge separation.

Binuclear terbium(iii) pivalates with 4,7-diphenyl-1,10-phenanthroline: synthesis, structure, thermal decomposition, and magnetic and luminescence properties

New binuclear pivalate complexes (bath)2Tb2(piv)6 and (bath)2Tb2(piv)6·H2O (piv = = ButCCO2−, bath is 4,7-diphenyl-1,10-phenanthroline) were synthesized. The thermal behavior of these complexes was studied by differential scanning calorimetry and thermogravimetric analysis. The composition of the complexes in the gas phase was determined, and their magnetic and photoluminescence properties were studied. The structures of the compounds (bath)2Tb2(piv)6 and (bath)2Tb2(piv)6·H2O were determined by X-ray diffraction.

Optical spectroscopy of the Eu(FOD)3 complex impregnated into the free volume of nanoporous glass and polymethylmethacrylate using supercritical carbon dioxide

The absorption and photoluminescence spectra of Eu(FOD)3 molecules (FOD = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedionate) impregnated into samples of nanoporous Vycor glass and polymethylmethacrylate using supercritical carbon dioxide were measured. The influence of the matrix on the shape and intensity of the absorption bands of Eu(FOD)3 molecules and the photoluminescence bands of Eu3+ ions was analyzed.

Preparation of fluorescent nanocomposites with CdSe/CdS quantum dots by dispersion polymerization in supercritical carbon dioxide

A new method for preparing fluorescent polymer nanocomposites based on dispersion copolymerization of methyl methacrylate and styrene in the presence of CdSe/CdS quantum dots in supercritical carbon dioxide medium is proposed. A one-step scheme of the formation of fine poly(methyl methacrylate)/polystyrene/CdSe/CdS nanocomposites is realized, and the factors influencing their photoluminescent characteristics and photochemical stability under prolonged exposure to natural conditions (sunlight) and intense UV irradiation in air are examined.

Fabrication of fine powder fluorescent polymer nanocomposites based on CdSe quantum dots using supercritical carbon dioxide

A method of diffusion introduction of CdSe quantum dots (QDs) into polymer microparticles in supercritical carbon dioxide was proposed, implemented, and studied. Photoluminescence (PL) spectra of fine nanocomposite powders based on polymethyl methacrylate/polystyrene and CdSe QDs were measured and analyzed. Produced samples are characterized by a pronounced PL band with a general maximum at 620 nm. It was found that QD introduction into polymer microparticles by impregnation in a supercritical carbon dioxide medium efficiently stabilizes them in space and significantly increases photochemical stability of their luminescence characteristics.

Luminescence of nanocomposites obtained via SCF impregnation of polymer powders with CdSe quantum dots

The luminescence features have been studied in ultradisperse CdSe quantum dot-based composites embedded in low-density polyethylene (LDPE) and polytetrafluoroethylene (PTFE) powders using supercritical carbon dioxide. The thermal treatment of the LDPE sample in air is shown to cause the CdSe photoluminescence band shift toward the shorter wavelengths, whereas for PTFE it shifts to the longer wavelengths with a decrease in its integrated intensity. In both cases, the photoluminescence band behavior under near-UV radiation is determined by the photooxidation processes on the CdSe nuclei.

Luminescence of Ti{sup 3+} ions in silica glass

The d - d luminescence of Ti{sup 3+} ions was first observed in the double Ti/SiO{sub 2} system at room temperature. Silica glass doped with titanium was synthesised in a steady- state laser plume. The luminescent state was obtained by producing oxygen-deficient centres in the chemical reaction between Ti and SiO{sub 2}. Comparison of the luminescence and absorption spectra of the titanium-doped silica glass with the spectra of a Ti{sup 3+}:Al{sub 2}O{sub 3} crystal suggests that the 690-nm luminescence band belongs to Ti{sup 3+} ions. (laser applications and other topics in quantum electronics)