Yu. S. Zavorotny

Laser fabrication of periodic microstructures from silver nanoparticles in polymer films

The fabrication of photoand thermostable periodic structures from silver nanoparticles in polymer plates (cross-linked oligourethanemethacrylate impregnated with silver precursors Ag(hfac) and Ag(fod) dissolved in the supercritical carbon dioxide) is studied. The process is based on the local (depending on the irradiated spot size) photochemical decomposition of the silver precursors in the polymer matrix that initiates the atomic aggregation and creation of silver nanoparticles with the plasmon resonance in absorption in the spectral range 420–430 nm. The third-harmonic radiation of a Nd:YAG laser (355 nm) and the Kr+-laser (521 nm) radiation are employed for the recording of periodic structures with submillimeter and micron resolutions. The photosensitivity of the polymer matrices impregnated with the silver precursors to the UV and visible radiation is discussed.

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.

Polyvalent States of Chromium Ions in Silica Glasses Prepared by Plasma-Chemical Deposition

The spectral–luminescent properties of chromium-doped silica glass prepared by gas-phase plasma-chemical deposition are investigated. The absorption, photoluminescence, and EPR spectra are measured for bulk glass samples in the form of a core of optical fiber preforms. The influence of gamma irradiation and additional reducing thermochemical treatment on the spectral characteristics of the synthesized glasses is analyzed.

One photon and two photon process in photo-decomposition of germanium oxygen deficient centres

UV photon-induced transformation of germanium oxygen deficient centres (GODC) in germanium-doped silica glass have been studied using photocurrent measurements, absorption and fluorescence bleaching. It has been identified that the photocurrent are generated via a two photon effect. Evidence have been found suggesting that the UV photon-induced destruction of GODCs is achieved via two reaction pathways, a single photon pathway and a two photon pathway. The process is discussed.

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.

Effect of electric field on one-quantum photodecay of oxygen-deficient centers in germanosilicate fibers

The effect of a strong electric field (up to 106 V/cm) on one-quantum UV photoexcitation and photodecomposition of germanium oxygen deficient centers (GODC) in twin-hole germanosilicate fibers with internal wire electrodes is reported. The fiber has been irradiated with the UV light of a deuterium lamp and triplet photoluminescence of GODC has been used to monitor the kinetics of its photodecay. Applying such an electric field did not affect the spectral characteristics of GODC but increased the rate of their one-quantum photodecomposition, while direct photoionization and charge separation did not take place. We have also shown that this effect is caused by the suppression of secondary photoinduced recombination processes of intermediates, rather than by acceleration of primary photodecomposition of GODC.

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.

ONE- AND TWO-QUANTUM UV PHOTO-REACTIONS IN PURE AND DOPED SILICA GLASSES. 2. GERMANIUM OXYGEN DEFICIENT CENTERS (GODC).

Germanium oxygen deficient centers (GODC) are the most widespread defects in the molecular network of germanosilicate glasses. UV laser induced photodecomposition of GODC plays a key role for the effect of photosensitiviy of germanosilicate glasses [1,2]. This effect involves absorption of light by GODC, photochemical modification of defects and even density of glass, and, as a result, the change of refractive index as high as 10-3-10-2 [3,4]. The UV absorption band of GODC at 242 nm corresponds to the S0—S2 transition (Fig. 1). Concentration of GODC is controlled by glass and fiber fabrication conditions [4], and may amount to as much as NGODC = 1020 cm-3.