V. I. Gerasimova

Modification of the optical properties of fluoropolymers by supercritical fluid impregnation with europium β-diketonates

Optical properties of a number of fluoroacrylate-based fluoropolymers doped with europium β-diketonates by means of supercritical fluid impregnation were studied. The influence of the type of polymer matrix on the process of impregnation of europium β-diketonate molecules into it and the evolution of the optical properties of the doped polymers during a long-term storage were revealed. A comparative analysis of the quantum yield (λexc = 300 and 380 nm) and thermosensitivity of the photoluminescence of Eu3+ ions for different europium β-diketonates and polymer structures was performed. It was demonstrated that the supercritical fluid extraction of unreacted photoinitiator residues from polymer samples makes it possible to substantially enhance their transparency at wavelengths shorter than 300 nm.

Laser-induced formation of structures of silver nanoparticles in fluoracrylate films impregnated with Ag(hfac)COD molecules

Methods of absorption spectroscopy and transmission electron microscopy (TEM) are used to study the processes of the laser-induced formation of silver nanoparticles (Ag NPs) in films of fluoracrylate polymers (FAPs) impregnated with Ag(hfac)COD molecules in a medium of supercritical CO2. An observation of the behavior of plasmon resonance (PR) bands in the impregnated FAP samples reveals the presence of a few features in the formation of Ag NPs under exposure to a continuous laser emission in the visible light range. Firstly, the formation of Ag NPs depends on the properties of the matrix (degree of polymerization) and on the power and dose of the laser exposure; its mechanism differs from the thermochemical one. Secondly, only in this case (using TEM) did we find the effect of the formation of periodic layered structures of nanoparticle layers situated inside a film perpendicular to the direction of emission. In addition, while recording the absorption spectra for a long time (a few days) after laser exposure, we revealed the effect of the postradiation growth of PR bands in the samples kept under darkroom conditions at room temperature. The models and formation mechanisms of Ag NPs are discussed for each case under consideration.

Color Centers in Sulfur-Doped Silica Glasses: Spectroscopic Manifestations of an SO2 Interstitial Molecule

The absorption spectra of sulfur-doped silica glass are investigated under different external actions (laser irradiation, saturation of samples in a hydrogen atmosphere, and thermal annealing). It is found that the absorption band at 400 nm has a vibrational structure. A correlation between changes in the intensities of the absorption bands at 237 and 400 nm under different actions is revealed. Reasoning from analysis of the results obtained, a model is proposed according to which these bands are assigned to an S+2 interstitial molecular ion. It is demonstrated that none of the optical centers considered in this work is responsible for the observed ESR signal.

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.

Photo–induced processes in Ag and Eu β-diketonates incorporated into aerogel matrix of silicon dioxide by supercritical fluid impregnation

Samples of silicon dioxide aerogel with embedded Ag and Eu β-diketonate molecules are obtained by impregnation in supercritical carbon dioxide (SC-CO2). The sample impregnated by Eu(tta)3 molecules possesses photoluminescence properties. Moreover, adsorption of Eu(tta)3 on the walls of the pores results in a strong broadening of the Stark components of its photoluminescence spectra. It is found that aerogel impregnation by AgFOD molecules followed by laser irradiation causes the formation of Ag nanoparticles in the sample volume as a result of AgFOD photolysis and subsequent diffusion self-assembly. The Ag nanoparticles assemble into filament structures due to self-organization as they focus laser radiation.

Specific features of the formation of color centers in nanoporous glasses doped with copper β-diketonate through different solvents

The EPR and optical spectra of Cu2+ ions impregnated in the nanoporous Vycor glass in the form of copper β-diketonate (Cu(hfac)2) dissolved in supercritical CO2, ethanol, and benzene are investigated. It is revealed that the spectra recorded immediately after the impregnation of the samples represent a superposition of two EPR spectra with hyperfine structures. This indicates that there are two structural forms of Cu(hfac)2 molecules located in fixed positions in pores. After long-term storage of the samples in air, the EPR spectra irrespective of the solvent type represent a superposition of three spectra. Each spectrum contains four hyperfine-structure components with a large splitting. The form of the third spectrum depends on the duration of storage of the sample and can be associated with water absorbed from the atmosphere and adsorbed on the pore walls. The bonds between the impregnated Cu(hfac)2 molecules and the pore walls are weak, which is confirmed by the experiments with immersion of the impregnated samples in a pure solvent. The EPR spectra of Cu2+ ions introduced into oxide glasses through a batch with subsequent melting differ substantially from the spectra of the silica glasses impregnated with Cu(hfac)2 solutions, even though the former spectra also correspond to Cu2+ complexes with symmetry D4h.

Electron phototransfer in the course of χ(2) grating formation in aluminosilicate optical fibers doped with rare-earth ions

The paper presents the first results of the systematic investigation into the dependence of the efficiency of the second-harmonic generation (SHG) on the concentration of photovoltaic centers. It is assumed that theE’-centers on aluminum and the Sm2+ and Er2+ ions serve as photovoltaic centers. The model describing the microscopic changes that occur in the course of the χ(2) grating formation (seeding) in pure and terbium-, samarium-, and erbium-doped aluminosilicate optical fibers has been advanced.