The origins of pre-existing and laser-induced ultraviolet (UV) and vacuum ultraviolet (VUV) optical absorption in state-of-the-art glassy silicon dioxide and the ways to improve it are reviewed. The main causes of pre-existing absorption in UV/VUV are oxygen vacancies, hydroxyl (silanol) groups, and strained bonds/localized states due to glassy disorder. The main absorption bands induced by UV/VUV excimer lasers are due to oxygen vacancies and due to silicon and oxygen dangling bonds (E'-centers and non-bridging oxygen hole centers, respectively). The optimized glasses are achieved via an intricate balance between a good stoichiometry, use of network modifiers (F or OH) to reduce the number of strained bonds, minimized number of Si-OH-related absorbers and using of interstitial hydrogen for annealing of photoinduced defects. The optimization is different for KrF, ArF or F₂ excimer laser energies. The most significant advance to increase VUV transparency and laser toughness is fluorine doping. F-doped ("modified") silica glasses show superior transparency and radiation resistance in VUV region and are suitable for photomask substrates in F₂-laser based microlithography or for deep-UV optical fibers.

The irradiation of LiF crystals with Au, Pb, Bi, and S ions in the range of 400 - 2200 MeV leads to a remarkable increase of the hardness. The effect appears for Bi and Pb ions at fluences above 10⁹ ions/cm² and for S ions above 10¹⁰ ions/cm². The increase of hardness follows the energy loss and is related to the formation of defects along the ion path. Defect complexes, clusters and aggregates with nanoscale dimensions serve as strong obstacles for dislocations and cause dispersion strengthening. Structural investigations reveal the generation of long-range stress in the adjacent non-irradiated part of the crystal. Close to the implantation zone, the stress exceeds the yield strength, causing microplastic deformation and work hardening. Compared to light S ions, heavy ions (Au, Pb, Bi) cause more severe structural damage, larger hardening effects, and higher internal and long-range stress.

A survey of the present situation with respect to knowledge of lattice defects, electronic excitations, such as excitons and localized excitons, as well as energy storage and transfer phenomena in LiBaF₃ crystals is given. Both phenomenological models and experimental interpretations of optical absorption bands, tentatively associated with F-type (electron) centers created by X-ray or electron irradiation, is reviewed. Interpretation of three radiative processes (super-fast core-valence transitions, slow trapped exciton luminescence and luminescence of structure defects) observed in undoped LiBaF₃ crystals is analyzed with respect to practical application. Attention is paid to the behavior of ultraviolet emission so far ascribed to self-trapped exciton luminescence and also observed as a result of electron recombination with localized hole at various temperatures (even at room temperature), depending on crystal purity and growth conditions. Finally, some aspects of ionic processes in thermal relaxation of defects are pointed to.

Two radiating processes in LiBaF₃ crystals, fast valence-core transitions (5.4 - 6.5 eV) and slow, so called self-trapped exciton luminescence (about 4.3 eV), are important for practical application. Here we present a study of 4.3 eV luminescence under X-ray excitation and photoexcitation as well as under photostimulation after X-irradiation of undoped and Ag-doped LiBaF₃ crystals at various temperatures. It is shown that 4.3 eV luminescence appears under X-ray excitation at least from 85 K to 400 K in both undoped and doped crystals. In all samples studied the excitation spectra of 4.3 eV luminescence contain both the main exciton like band at the edge of fundamental absorption at about 10 eV and weaker band in 7.8 - 8.6 eV region. Luminescence spectrum in the 3.8 - 4.8 eV region under 7.8 - 8.6 eV excitation differs slightly from that under 10 eV excitation. Several luminescence bands in 3.8 - 4.8 eV region arises in the temperature range 85 - 230 K under photostimulation in absorption band of F-type center at 2.9 eV created previously under X-irradiation. We propose the luminescence of LiBaF₃ crystals in the 3.8 - 4.8 eV region may be caused by localized excitons formed not only under excitation near the fundamental absorption but also in result of electron recombination with localized holes thermally destroyed above 230 K.

A wide emission band in the region of 425 nm is observed in all the examined crystals at photo and ionising irradiation. Maximum of the complex luminescence band is observed at 410 nm at 350 K and at 450 nm at 85 K. The shift of the peak of the band envelope towards shorter wavelengths as the temperature increases is related to thermal dependence of the intensity of elementary components of the luminescence band. The authors suggest that the complex luminescence band arises from electronic excitations at "antisite" defects, i.e., defects caused by stoichiometric deviations, when a portion of Li⁺ cations (cations of one type of the LiBaF₃ crystal lattice) occupy sites of Ba²⁺ cations (cations of another type) and vice versa.

A comparative study of optical properties of thermochemically reduced undoped LiBaF₃ crystals is reported. In LiBaF₃ crystals obtained or treated in a reducing atmosphere an absorption band at 240 nm and a corresponding luminescence band at 505 nm are observed at 85 K. The main constituent of the center may be an anion vacancy with a trapped electron (an F-type center in LiBaF₃ crystals).

Results of the glow rate technique application for analysis of the activation energy of thermostimulated annealing of X-ray created F-type color centers in pure and containing oxygen centers LiBaF₃ crystals are presented. It is shown that depending on the impurity composition two alternative mechanisms could be involved in the annealing of color centers. It is proposed that either the anion vacancy governed migration of F-centers resulting in recombination with complementary defects, or the thermal delocalization of radiation created fluorine (F_i) interstitials captured by anti-structure defects followed by recombination with all kinds of complementary F-type centers are responsible for the recombination of radiation defects above RT.

In order to characterize TiO₂ films in terms of the overall optical response, spectroscopic ellipsometry studies of the system TiO₂/Si were carried out. The films were grown by the atomic-layer chemical vapor deposition on Si(111) substrates. Optical measurements were performed by means of a photometric ellipsometer with rotating analyzer. Experimental results have been analyzed using multilayer and pseudodielectric function approximations.

At low temperatures, time-resolved polarized photoluminescence of anatase single crystals and nanocrystalline thin films was studied in a nanosecond time scale. In both kinds of samples, the emission spectra showed two relatively broad shifted bands peaking at about 2.35 eV and 2.75 eV and possessing decay times of above 1 μs and below 50 ns, respectively. The bands have been interpreted as those originating from the singlet and triplet states of the self-trapped exciton of anatase.

A study of the visible photoluminescence in single-crystal NiO and Ni_cMg_1-cO (c = 0.99, 0.98 and 0.95) solid solutions is presented for the first time. Two wide luminescence bands, peaked at approximately 12000 cm^-1 and approximately 18500 cm^-1, were observed. The dependence of their intensity and position on the excitation energy, temperature, and composition were investigated. We attribute the origin of two photoluminescence bands to the impurity- or defect perturbed Ni²⁺ excitons.

The Raman scattering by phonons and magnons was studied at room temperature in polycrystalline solid solutions Ni_cMg_1-cO and pure NiO. The experimental Raman spectrum of NiO consists of six well resolved bands, whose origin is due to the disorder-induced one-phonon scattering (bands at 400 and 500 cm^-1), two-phonon scattering (bands at 750, 900 and 1100 cm^-1) and two-magnon scattering (band at 1500 cm^-1). In Ni_cMg_1-cO solid solutions, a relative increase of one-phonon scattering is observed upon a dilution of nickel oxide by magnesium ions: at room temperature, the two-magnon band becomes invisible for c < 0.7, whereas the two-phonon contribution disappears at c < 0.5. Such behavior is explained by disorder-induced effect, caused by chemical substitution and off-center displacement of nickel ions.

Electronic and ionic thermostimulated (TS) relaxation (TSR) processes in nominally pure sapphire (α-Al₂O₃ grown with oxygen deficiency) have been investigated at 290 - 650 K by means of the TS current (TSC), ionic depolarization current (TSDC) and electron emission (TSEE) techniques. After thermal (ionic) polarization of the reduced sapphire wide (approximately 75 K) and asymmetric ionic dipolar TSDC peak at 590 K (disorientation of the anion vacancy-related dipoles) was detected. Above 450 - 500 K the anion vacancy hopping (migration) starts and their interaction with defects take place. This can lead to lattice dynamic disordering and anion vacancy diffusion-controlled processes in sapphire (especially -- in vacuum near the sample surface, grain boundaries, dislocations) in various TSR (TSC, TSDC, TSEE, TS heat release and bleaching) phenomena. The ionic TSDS peak at 590 K correlates with the wide TSEE peak at 615 K, with the rise stage of the radiation-induced electrical degradation (RIED) above 550 K (maximum at 745 K) and the chromium emission line broadening in ruby. The REID effect (observed above 550 K by E. R. Hodgson et al.), colloid formation and structure change of sapphire are caused by oxygen exchange at the grain boundaries, surfaces, dislocations and impurity-rich regions. Surface structure, impurity content, surrounding atmosphere (vacuum or air) and electric fields determine these phenomena.

Mixed Ta-Re oxide thin films were synthesized for the first time by dc magnetron co-sputtering. Local environment around tantalum and rhenium atoms was studied by the Ta and Re L₃-edges x-ray absorption spectroscopy in pure Ta₂O₅ and mixed Ta-Re oxide thin films (Ta:Re = 50:50, 38:62, 20:80 as determined from the ratio of the Ta-to-Re absorption edges). It was found that rhenium atoms are four-fold coordinated by oxygen atoms with R(Re-O) = 1.74 ± 0.01 Å and the mean square relative displacement (MSRD) σ² = 0.0012 ± 0.0005 Ų. In pure Ta₂O₅ thin film, tantalum ions are coordinated by six oxygen atoms at R(Ta-O) = 2.02 ± 0.01 Å with the MSRD σ² = 0.010 ± 0.001 Ų. The addition of rhenium ions shortens the Ta-O distance by about 0.02 - 0.03 Å and makes the Ta-0 distances distribution slightly broader with the MSRD σ² approximately equals 0.013 ± 0.001 Ų. The high frequency contribution in the Ta L₃-edge EXAFS signals, which is responsible in its Fourier transform for the peak beyond the first coordination shell, is due to the multiple-scattering effects within distorted [TaO₆] octahedron.

Structure of R₂O - R'₂O - SiO₂ - Nb₂O₅, R₂O - R'₂O - GeO₂ - Nb₂O₅, R₂O - R'₂O - P₂O₅ - Nb₂O₅ (R, R' = Li, Na, K) glasses were studied by means of Raman scattering and Rayleigh and Mandel's shtam-Brillouin scattering spectroscopy. The Kerr coefficient was measured as a function of glass composition. Microinhomogeneities responsible for Rayleigh scattering losses and electro-optical properties were found on the base of light scattering spectra processing. Comparison of alkali niobate glasses with various glass formers showed that optimum combination of high Kerr coefficient and low Rayleigh scattering losses may be achieved for alkali niobate phosphate glasses.

The influence of γ-irradiation on optical properties of the pseudobinary "stoichiometric" Sb₂S₃-GeS₂ and the non-stoichiometric Sb₂S₃-Ge₂S₃ chalcogenide glasses (ChG) prepared by a standard melt-quenching method is studied. It is established that in the case of the both investigated cut-sections the "γ-darkening" effect (i.e. the "red" shift of the fundamental optical absorption edge), consisting the dynamic (relaxing with time) and the static (remaining constant approximately two months after irradiation) components, takes place. The comparison of compositional trend of the "γ-darkening" effect for the pseudobinary and the non-stoichiometric investigated ChG is made. Phenomenological description of the observed effects is carried out taking the degree of chemical bond metallization, concentration of chemical bonds and free volume parameters into consideration.

Ab initio slab simulations have been performed for silver adhesion to the perfect and defective MgO(001) surfaces. For 1/4 Ag monolayer (ML) coverage of perfect substrate, we observe small silver adhesion energies over both O^2- and Mg²⁺ ions on a regular MgO(001) substrate (0.23 and 0.22 eV per Ag atom, respectively), with negligible interfacial charge transfer towards metal atoms. For larger Ag coverages (beginning with 1/2 ML), silver adsorption over regular O^2- ions is much more favorable. We demonstrate that point surface defects on a magnesia surface increase markedly the metal adhesion energy and cause a redistribution of the electron density across the interface. The results for electron (F_s° = O vacancy with two trapped electrons) and hole (V_s° = Mg vacancy with two holes trapped by nearest O^2- ions) centers in the Ag atom adhesion at different surface coverages are analyzed. For Ag atoms positioned over the point surface defects, the substrate binding energies increase by more than an order of magnitude (to 7.6 and 12.7 eV, repsectively) compared to a regular interface and are associated with marked charge transfer (approximately 1 e towards a Ag atom over a F_s center and approximately 1.5 e towards the nearest O^2- ions from a Ag atom over a V_s center). A comparison of these results with silver adhesion on α-Al₂O₃(0001) surfaces shows two similarities in the nature of the adhesion for Ag adsorption: (1) on the perfect MgO(001) and Al-terminated (stoichiometric) corundum (0001) substrates we observe physisorption with a weak atomic polarization, whereas (2) over a V_s center on the defective MgO and for O-terminated corundum, strong interfacial ionic bonding takes place.

The engineering of functionalized polymers for second order nonlinear optical applications is shortly described and discussed. The ways of chromophore orientation are also discussed with a special emphasis on static field poling. Practical application applications of these polymers are overviewed and an integrated optical amplifier is described in more details.

To examine the role of the protein for the proton transfer the comparative analysis of electro-acoustic effect and the photoelectric response of dried films of purple membranes (PM) of Halobacterium salinarum is carried out. The films of different degrees of orientation of the PM's as well as oriented films after the acid treatment for different periods of time are analyzed. It is shown that characteristic values of the electric signals in both experiments, namely the critical value of the bias voltage in electro-acoustic measurements and the maximum value of the photoelectric response, are sensitive to the orientation degree of the PM's in the film under consideration. The mean value of the internal electric field of the purple membrane is determined to be 2.4 10⁷ V/m and directed from the cytoplasmic side towards the endoplasmic side of the membrane. The changes in the photoelectric response signal at the presence of the external electric field are used to determine the photoconductivity of the stand-alone photoactive bacteriorhodopsin molecule. The model explaining the proton transfer mechanism in bacteriorhodopsin based on the experimental observations is postulated and developed.

A bioferroelectric approach to analysis of ferroelectric behavior of biological systems is presented. The optical properties of nerve fibers, biomembrane ion channels, and purple membrane films containing bacteriorhodopsin are analyzed. The features, influence of the proton subsystem and proton transfer on the hydrogen-bonded biomolecular structures are analyzed within the ferroelectric liquid-crystal model and possible biomedical applications discussed. The ferroelectric behavior of biological systems and the set of various bioferroelectric effects are considered within the limits of phenomenological theory of ferroelectrics. The nonlinear response to weak actions under conditions critical to human organism is one of specific features characterizing biological objects on molecular, cell and organism levels.

The changes in conformation and organization of poly(di-n-hexylsilane) (PDHS) chains initiated by heating the films above the phase transition temperature are investigated by optical spectroscopy, polarizing optical microscopy, and birefringence techniques. Appearance of two new absorption bands is observed after thermal treatment of the samples and explained by transition of PDHS into liquid-crystalline (LC) phase. Existence of the LC phase is confirmed by presence of birefringence in PDHS films at these temperatures and by stable orientation of nematic liquid crystal disposed on the thermally treated polymer. A pattern corresponding to classical columnar liquid-crystalline optical textures is observed under polarizing optical microscope above the phase transition temperature. An increased orientational order and defects created at cooling the polymer films down to room temperature are manifested by several new absorption and luminescence bands.

Energy gap is one of the fundamental energetic characteristics of a material. In this paper a new method for the determination of the energy gap values in molecular materials from ultraviolet-photoelectron spectroscopy (UPS) is proposed. In a first part it is shown how UPS spectra are affected by intermolecular and intramolecular vibrations and polarizations. In a second part, from experimental data concerning radical phthalocyanines, and by comparison with results concerning non-radical phthalocyanines, fullerenes and polyacenes, it is established that the photoemission spectra give us information on the insulating or semiconducting behavior of these materials. In the case of undoped materials the energetic difference between the upper electron and the Fermi level allows us to determine the energy gap value. The UPS data are compared to those issued from other well known techniques. A limitation appears when extrinsic electronic levels move the Fermi level out of the middle of the gap.

Charge separation dynamics in a Ladder-Type Methyl substituted Poly(Para-Phenylene) (m-LPPP) was investgiated by means of electric filed modulated femtosecond pump-probe absorption spectroscopy. The Stark shift of the absorption band modified by created excitons and electron-hole pairs provided information about the average intrapair charge separation distance. The electron and hole initially separated by ca. 7 Å moved away from each other to more than 30 Å during 600 ps and later the separation rate decreased. Neither the initial separation distance, nor that obtained at 600 ps were found to depend on the applied electric field, only the separation rate at stronger field was slightly faster.

We investigated carrier transport and capture in poly[2-methoxy-5-(2'-ethyl-hexyloxy)-1,4-phenylene vinylene] (MEH-PPV) Schottky diodes by thermally stimulated currents and current-voltage characteristics. Experimentally in the region from 80 K up to 450 K two distinct current peaks were found after the white light excitation. Their maxima were located in the temperature regions 214 - 244 K and 304 - 394 K respectively. The detailed numerical modeling revealed that the full TSC is a superposition of at least six traps and/or other thermally stimulated processes with different parameters. We observed effect of oxygen on these traps that was never reported before. The filling of three of these levels could be increased significantly by exposing the sample to the air. The two deepest traps with activation energies at about 0.76 - 0.8 eV and 0.76 - 0.9 eV are likely located nearby surface. Meanwhile the mid-deep trap with an activation energy 0.45 - 0.55 eV is most probably distributed over the sample depth. As far as these traps are related to the oxygen they could be identified as electron traps. In contrast none of the traps could be recharged by applied voltage. Instead the injected carriers created a long-living sample polarization. The non-exponential depolarization lasted for several thousands seconds and was not thermally activated even above the glass transition temperature. These facts make it necessary to include into analysis other possible physico-chemical mechanisms, e.g., reversible chemical reactions or chain structure reorganization induced by electric field.

In the last few years a range of techniques for opto-mechanical manipulations of organic films and small structures has been developed and significantly improved. Among these techniques a very promising candidate turned out to be the optically induced mass transport. Not only that the physical mechanisms underlying this phenomenon is not yet been fully understood, but in addition, the lateral dimensions of structures created in that way have been limited by the used light wavelength. In order to gain deeper insight into the physical fundamentals of this phenomenon and to open possibilities for applications (lithography, data storage, manipulation of molecules, ...) it is necessary to create and study reproducible, sharply defined single structures not only in a macroscopic but also in nanometer range. SNOM (Scaning Nearfield Optical Microscopy) seemed to us an intriguing method to approach this goal. We report here novel experimental results about the generation of ultra-small structures by optically driven mass transport. We have investigated different ways to generate localized mass transport in azobenzene-containing films by using focused light in far and nearfields. Thus, the dimensions of optically created structures range to 5 μm (lens focusing) and even down to 100 nm (SNOM nearfield). These experiments offer new expectations to manipulate ultra small objects on surfaces by optical means without mechanically touching them.

Organic materials have received considerable attention because of their large dipole moments and optical nonlinearities. Organic materials for photonic applications contain chromophore dipoles consisting of acceptor and donor groups bridged by a delocalized π-electron system. Both calculations and experimental data show a reversible highly dipolar photoinduced intramolecular charge transfer in betaine type molecules and trans/cis photoisomerization in azobenzene derivatives, accompanied by change of the sign and the value of the dipole moment. The switching is important for optoelectronic effects including second harmonic generation. Arrangement of polar molecules in films is studied by surface potential measurements.

Mentioned betaines comprise in molecule directly connected electron donor anion moiety and electron acceptor cation A novel class of active nonlinear optical (NL) materials -- strongly dipolar intramolecular salts (betaines) are offered. The betaines are principally different from the commonly used push-pull dipolar molecules. A donor moiety is directly bonded to heterocyclic N-onium cation moiety within the same molecule. The anion is five-member β-dicarbonyl compound, usually indan-1,3-dione. Calculations show that electric dipole moment is changed considerably at photo-induced intramolecular electron transfer from HOMO to LUMO, the difference between dipole moment values in the ground and excited states being unusual large. The HOMO is strongly localized on the anion moiety while the LUMO -- on the heterocyclic N-onium cation moiety. The hyperpolarizabilities are remarkable. Betaines are easy to synthesize and fine-tuning of their NLO properties is possible. Preparing of betaine solution in polymer matrices (host-guest systems) and formation of films is found to be the best method for examining the NLO properties. Obtained films are subjected to corona poling before measuring the change of surface potential. Due to strong photo oxidation it is necessary to exclude contact with air or avoid light while processing betaines films.

The work is focused on the refinement of the laser ablation method for a nanosized silver colloid preparation with regards to the nanoparticle size distribution, as well as to the reproducibility and stability of the ablated hydrosol. In the adopted procedure, additionally to the variation of the laser pulse energy, beam focusation and duration of laser ablation, we developed a technique based on further fragmentation of the ablated colloid solution by subsequent treatment with the 1064 and 532 nm nanosecond laser pulses. The method yields redistribution of nanoparticle diameters to a smaller mean size, as it was observed by transmission electron microscopy, quasielastic light scattering studies and surface plasmon (SP) optical extinction. It was shown that a similar fragmentation procedure is also effective in reduction of nanoparticle size and polydispersity of silver hydrosol prepared by routine chemical procedures and leads to a narrower SP extinction profile.

A difunctional NLO Azo-Dye chromophore has been synthesized and polymerization has been performed with a comonomer bearing a side-chain epoxy group. Deposition of the polymer on glass substrates was performed by spin-coating, resulting in uniform films up to 2 μm thickness. The orientation of the chromophore was performed under a "pin-to-plane" positive corona discharge followed by a heat- treatment in order to obtain reticulation of the films. Molecular orientation has been investigated using UV-Vis. and Raman spectroscopy. Poling of the films results in a decay of absorbance as well as in a blue shift of the spectrum. At the same time, the 1600 cm^-1 band disappears from the Raman spectra, indicating orientation of the chromophores. Cross-linking has been studied by FTIR and all-optical poling and showed an improved stability of the electro-optic thin films.

We have synthesized and investigated a novel electrondonor -- electronacceptor type photoactive amphiphilic azobenzene derivative containing the hydrophobic dicyclohexylamine moiety along with the hydrophylic carboxyl group at the opposite end of the molecule. Reversible trans/cis photoisomerization of this compound in solutions and in Langmuir-Blodgett multilayers has been observed on irradiation with alternating UV (360 nm) and visible (450 nm) light. The reversible changes of absorbance of main absorption band and surface potential of Langmuir-Blodgett multilayers on alternate irradiation is demonstrated.

A new insight into the nature of ferroelectricity is emerging from the study of ultra-thin ferroelectric films prepared of poly(vinylidene fluoride with trifluoroethylene) copolymer using Langmuir-Blodgett (LB) technique. Unique properties of these films indicate the existence of two-dimensional ferroelectricity. The retention of two polarized states in ferroelectric polymer LB films is studied using nonlinear dielectric spectroscopy. The technique is based on phase sensitive measurements of nonlinear dielectric spectroscopy. The amplitude of the current response at the 2nd harmonic of the applied voltage is proportional to the magnitude of the remnant polarization, while its phase gives the sign. We have found that 10 - 20 mm thick LB films can show fast switching time and long retention of the two polarized states. Nevertheless, LB films show a pronounced asymmetry in switching to the opposite states. Possible mechanisms of such behavior are discussed.

Fluorescence and reflectance spectra of dipolar N,N-dimethylaminobenzylidene 1,3-indandione (DMABI) molecular crystals of α and β crystallographic modifications have been studied over a wide temperature range. The luminescence spectral properties have been discussed by means of the self-trapped exciton model. The crystal phase transition in both α and β modifications resulting in the deeply-trapped excitonic state formation has been observed at low temperatures, below 60 K.

The excited state dynamics of N-(4-azaindan-1,3-dion-2-yl)pyridinium betaine (4N-IPB) in various solvents were studied using steady state absorption, fluorescence, and transient absorption measurements. The 4N-IPB molecules in solutions show weak fluorescence and possess a very large Stokes-shift of the fluorescence band even in non-polar solvents with low dielectric constants. The relaxation rate of 4N-IPB in alcohols faintly depends on the solvent viscosity. The excited state relaxation mechanism involving two excited states is similar to that of the IPB molecule, however the excited state relaxation of 4N-IPB is slightly faster.

The studies of two betaine molecules for optically induced intramolecular electron transfer important in photosynthesis and photoelectricity are presented. The investigated betaine molecules possess a large permanent dipole moment changing the sign and value at excitation within the intramolecular charge transfer band (380 - 410 nm). The molecules are mixed with poly(methylmetacrylate) polymer and solvent to cast thin films. The optical density of the intramolecular charge transition band and the change of surface potential of the prepared films are found to decrease at irradiation of the same wavelength. The decrease of optical density is avoided by protecting the polymer film from ambient oxygen. Photo-oxidation of betaine molecules is discussed.

Classical and quantum models explaining fast charge separation from the initially excited charge transfer (CT) states is presented in this paper. According to our suggestion a substantial dipole moment is localized in the CT complex after its optical excitation. Being a strong local perturbation this electronic dipole induces the changes in the equilibrium positions of atoms and molecules in the vicinity of its surrounding. Some under-damped vibrational modes of the extended phonons at the very initial times can create the driving force for the charge transfer via the feedback of the nonrelaxed environment. This model is demonstrated in the framework of the modified Marcus approach and by using a quantum model.

We review results of our recent large-scale computer simulations of point defects, excitons and polarons in ABO₃ perovskite crystals, focusing mostly on KNbO₃ and KTaO₃ as representative examples. We have calculated the atomic and electronic structure of defects, their optical absorption and defect-induced electron density redistribution. The majority of results are obtained using the quantum chemical method of the intermediate neglect of differential overlap (INDO) based on the Hartree-Frock formalism. The main findings are compared with results of ab initio Density Functional Theory (FP-LMTO) first-principles calculations. The results of the electronic structure calculations for different terminations of SrTiO₃ (100) thin films are discussed. These calculations are based on the ab initio Hartree-Fock (HF) method and Density Functional Theory (DFT). Results are compared with previous ab initio plane-wave LDA and classical Shell Model (SM) calculations. Calculated considerable increase of the Ti-O chemical bond nearby the surface is confirmed by experimental data.

Using the INDO quantum-chemical computational method we focus on oxygen-vacancy and F center defects on the non-polar (001) and polar (110) SrTiO₃ surfaces considering both cubic and tetragonal lattices of the material. The results obtained for the lattice relaxation around the defects on the polar (110) surface point to the significant role of the Coulomb interaction in this semi-ionic material. However, in the case of the oxygen vacancies the analysis of the electronic density redistribution leads to the conclusion that these defects make material more covalent due to the stronger hybridization between the O 2p and Ti 3d states. Wave functions of the F centers are found on the two defect-closest Sr atoms in an agreement with the available scanning microscopy and spectroscopy data and pointing to localization of two electrons within the O vacancy region. The analysis of the properties of O vacancies and F centers on the non-polar (001) surface points to somewhat different pattern. In particular, the wave functions of the F centers are found on the defect-nearest Ti atoms and are rather extended. One of the absorption energies obtained by the ΔSCF method matches the experimentally observed value of 2.1 eV found in fast-electron irradiation of strontium titanate.

The energy level positions in the optical gap and atomic geometry for the Fe⁴⁺ impurity substituting for a host Ti atom in SrTiO₃ are calculated using the Unrestricted Hartree-Fock (UHF) method and supercells containing up to 320 atoms. In agreement with experiment, the high spin (S = 2) state is much lower in energy than the zero-spin state. The energy level positions strongly depend on the asymmetric displacements of six nearest O ions which is a combination of the Jahn-Teller and breathing modes. A considerable covalent bonding between the Fe ion and four nearest O ions takes place. We predict a strong dependence of optical absorption energies on the crystal compression or internal tension, e.g. in perovskite solid solutions.

We investigate effects that an H impurity produces upon the geometry and the electronic structure in the BaTiO₃ and CaTiO₃ crystals considering several lattices of these materials. In order to study the H-doped barium and calcium titanates we use a quantum-chemical method based on the Hartree-Fock formalism and a periodic large unit cell (LUC) model. As a result, the interstitial H is found to bind to one of the O atoms forming the so-called OH group. In equilibrium, O-H distance is found to be 0.89 and 0.91 Å for BaTiO₃ cubic and tetragonal lattices, respectively. These results thus predict reduction of the O-H bond-length compared to a free radical, obviously due to rather compact crystalline lattice. In the case of the CaTiO₃ crystals, the O-H distance is found to be 0.89 and 1.04 Å for cubic and orthorhombic phases, respectively. We also study the impurity effect upon the lattice distortion and analyze the ferroelectric polarization in the tetragonal BaTiO₃. A qualitative study shows that the absolute values of the effective charges decrease while the Ti-O bond-lengths increase considerably in the defective region. Combining these two effects we obtain that the bulk ferroelectric polarization increases 1.27 times. Therefore, one can conclude that the ferroelectric degradation is not a bulk effect. This could also provide an explanation for the oxygen loss in the ferroelectric films near the surface under thermal annealing in hydrogen atmosphere. Diffusion of the hydrogen in the BaTiO₃ cubic lattice is also studied in the present work considering different types of trajectories. The diffusion path that gives the lowest potential energy barrier for the hydrogen motion is found to be of a parabolic form.

We study effects produced by an O vacancy and F center in cubic and tetragonal lead titanate (PbTiO₃) crystals as well as barium titanate (BaTiO₃) (001) surface. Displacements and charges of defect-surrounding atoms, lattice distortion and relaxation energies are carefully analyzed. It is found that the predominant cause of atomic movements in PbTiO₃ around an O vacancy in the Coulomb interaction while in the case of F center also changes in the chemical bonding within the atomic planes should be taken into consideration in order to explain atomic movements. We also observe a phenomenon known as bi-stability of the fundamental state, which occurs due to the rotation of some cationic planes. The obtained vibronic energy barriers for bi-stability are found to be around 1.0 eV. In the case of the BaTiO₃ crystal the computed average atomic movements around the O vacancies are around 0.12 Å and 0.15 Å for the cubic and tetragonal lattices, respectively. In the case of F center we observe somewhat smaller lattice distortion. In the latter case, however, we find a considerable redistribution of electronic charge leading to a polarization of the defect-surrounding lattice, especially if the F center is situated within the Ti-O₂ plane. In general, there is a reduction of the ferroelectric dipole moment for the tetragonal phase of the crystal due to the F center presence on BaTiO₃ (001) surface.

Using a quantum-chemical INDO method based on the Hartree-Fock formalism and the periodic large unit cell (LUC) model we present a theoretical interpretation of the structural and electronic properties of triplet excitons in the tetragonal BaTiO₃ and SrTiO₃ crystals. Our study demonstrates that the exciton structure has particularities in each material. In the BaTiO₃ the defect structure corresponds to the so-called Mott-Wannier-type exciton having a considerable separation, 7.0 Å, between the hole and the electron. Meanwhile, in SrTiO₃ the structural and electronic features of the triplet exciton are quite different. The hole-electron distance is about 2.14 Å and the defect is well localized in two contiguous atoms: the hole on one of the O atoms and the electron on the neighbor Ti atom. The calculated luminescence energy using the so-called ΔSCF method is found to be equal to 0.94 eV and 1.13 eV for BaTiO₃ and SrTiO₃, respectively. Since it falls within the infrared part of the spectrum, the experimentally detected green luminescence due to photo-excited states should be attributed to the singlet excitons.

Using the density functional theory (DFT) within the local density approximation (LDA) and a method based on the Hartree-Fock (HF) approximation, we study the structural, electronic and optical properties of F-centers (two electrons in an oxygen-vacancy) in the tetragonal lattice of the perovskite-type BaTiO₃ crystal. In this structure the F-center has two non-equivalent positions due to the two different O atoms; namely, the F-center situated in the Ti-O-Ti chains along the [001] polarization axes (V_a⁰) and the F-center situated in the Ti-O-Ti chains within the x-y plane (V_b⁰). Both cases are considered in our study. The obtained results point out that the crystal structure containing V_a⁰ center is energetically more stable than that of the V_b⁰) center. The two electrons of the F-center are found to be localized on the two adjacent Ti ions and their ground state is composed mainly of Ti 3d_z² atomic orbital. Besides, we have computed the allowed optical transitions for the F-center using the so-called ΔSCF method. As a result the obtained absorption energies are found to be equal to 1.47 eV for the V_a⁰ center as well as 3.07 and 4.27 eV for the V_b⁰ center.

The structural and electronic properties of Zr-doped PbTiO₃ crystals are investigated. A quantum-chemical INDO method based on the Hartree-Fock theory is employed, along with a periodic large unit cell (LUC) model, as implemented into the computational program SYM-SYM. The most stable defect configurations found to be those that allow the maximum displacements of oxygen atoms -- and the atomic relaxation around the Zr impurity are described for different impurity concentrations. Results are compared with those from various theoretical and experimental studies.

The calculation of the correlation radius distribution function is performed for the cases of undamped and overdamped soft mode dispersion laws. Taking into account the correlation radius dependence on the random field and this field distribution function we carried out the theoretical calculation of the correlation radius distribution function dependence on temperature, damping coefficient and random field distribution function parameters. It was shown that at temperature higher than Burns temperature T_d the most probable value of the correlation radius is equal to its maximal value independently on the system disorder, while in the dipole glass state it is close to the minimal value with broad tail of distribution function existing at broad temperature region.

Dielectric properties of epitaxial heterostructures of perovskite relaxor ferroelectric (RFE) PbMg_1/3Nb_2/3O₃, PbSc_0.5Nb_0.5O₃, PbMg_1/3Nb_2/3O₃-PbTiO₃, and PbSc_0.5Nb_0.5O₃-PbTiO₃ thin films were studied as a function of frequency (10² - 10⁶ Hz), temperature (77 - 725 K), and amplitude of applied ac-field (10³ - 10⁶ V/m). The contribution of the film-electrode interfaces to the properties of the heterostructures was evaluated, and the true properties of the films were reconstructed and analyzed. In the films, all typical features of RFE were found to be essentially similar to those in single crystals. Glass-like behavior in the RFE films was indicated by the Vogel-Fulcher relationship, deviation from the Curie-Weiss behavior, temperature evolution of the local order parameter, temperature evolution of the relaxation-time spectrum, and the maxima in the third-order nonlinear and scaled third-order nonlinear dielectric permittivities below the temperature of the dielectric maximum.

The nonlinear dielectric response of epitaxial heterostructures of relaxor ferroelectric PbMg_1/3Nb_2/3O₃ thin films was experimentally studied using digital Fourier analysis. The amplitudes and the phase angles of the dielectric harmonics were determined as a function of temperature and the amplitude of the sinusoidal ac field. The response of the films was reconstructed assuming a linear contribution of the film-electrode interface capacitance. In the films at low amplitudes of ac field, a glass-like behavior was identified by a maximum in the third-order nonlinear dielectric permittivity around the freezing temperature, accompanied by a square field dependence of the amplitudes of the odd harmonics and the absence of the even-order harmonics. With increasing amplitude of ac field, a glass-to-ferroelectric transition was indicated by a deviation from the square field dependence of the amplitudes of the odd harmonics, the appearance of the even-order harmonics, and the switching of the phase angle of the third harmonic to 90°. Such an unstable glassy behavior was suggested to originate due to the presence of interfaces, crystallographic strain, and nanometer-scale structural features.

Lead zirconate PbZrO₃ (PZ) and PbZr_0.53Ti_0.47O₃ (PZT) sol-gel films with a thickness of up to 1.5 μm were deposited on TiO₂/Pt/TiO₂/SiO₂/Si substrates by spin coating technique and heterostructures of the same composition as well as on Pb_0.92La_0.08 (Zr_0.65Ti_0.35)O₃ (PLZT-8) (with a thickness of 0.4 μm) were pulse laser deposited (PLD) on Pt/Ti/SiO₂/Si. Observation of a typical antiferroelectric (AFE) double hysteresis loop in obtained PZ heterostructures at room temperature was attributed to the superior dielectric strength in case of thin film materials. The thermal behavior of dielectric permittivity ε of PZ film reveals a maximum near 225°C on heating and 219°C on cooling. The higher resistance of antiferroelectric PZ thin films as compared to ferroelectric (e.g., PZT, PLZT-8) heterostructures to neutron irradiation (up to fluence 2x10²²m^-2)^* is recognized and discussed.

First time comprehensive study of high-current pulsed electron irradiation effects on the structural, optical and dielectric properties of relaxor (Pb_(1-x)La_x)(Zr_0.65Ti_0.35)_1-x/4O₃ ceramics with x = 4 and 9.75 at.% have been provided. The electron beam had the following parameters: energy E = 250 keV, current density I = 1000 A/cm², pulse duration τ = 300 ns, beam density - 10¹⁵ electrons/cm² per pulse. Infrared reflectivity spectra in the region of 100 ÷ 2000 cm^-1 were obtained in virgin, irradiated by 1500 pulses. The reconstruction of perovskite ABO₃ structure in irradiated samples has been studied by complex use of X-ray and neutron scattering and IR spectroscopy techniques revealing the changes in transverse and longitudinal phonon modes. Radiation effects on temperature behavior of dielectric permittivity ε in the region of phase transition were studied. The possible mechanisms of pulsed electron irradiation effect in relaxor PLZT ceramics are discussed.

The microscopic mechanism of spontaneous polarization and refractive indices in 180° ferroelectric domain walls of tetragonal barium titanate (BaTiO₃) is discussed by using a microscopic model. This model is based on the orbital approximation in correlation with the dipole-dipole interaction due to the local field acting on all constituent ions within the domain wall. It is found that the behavior of both the spontaneous polarization and refractive indices depends on the thickness of the domain wall which was varied between 5 and 20 Å. Moreover, the spontaneous polarization shows a hyperbolic tangent dependence for domain walls of a larger thickness and vanishes at the center of the domain wall. The refractive indices suggest the domain wall to act like a biaxial crystal resulting in refractive index profiles of a Gaussian shape for domain walls of approximately 20 Å. This dramatically affects optical transmission through the domain wall specifically for light being polarized parallel to the domain wall.

We report the deposition, characterization, and application of novel optically transparent electrodes, namely ultrathin chromium films and amorphous carbon layers (a-C:H), suitable for replacing ITO and other common materials used so far in electro-optics. The ultrathin layers provide sufficient optical transmission of up to 95% for layer thicknesses of 2 nm and 5 nm for Cr and a-C:H, respectively, showing a flat spectral dependence between 400 and 800 nm. These features are maintained when using these coatings as electrodes on tapered optical fibers as used for scanning near-field optical microscopy (SNOM). We show the successful application of such coated optical tips for ferroelectric domain switching on the nanometer scale.

Ferroelectric Pb_xZr_yTi_1-yO₃ (PZT) has been prepared by chemical solution deposition (CSD) and spin-coating technique, using acetate and alkoxide precursors. Rapid thermal annealing has been employed in order to obtain crystallization in the perovskite phase. Aiming to study the optical properties of the films, PZT was deposited on different glass substrates. Structural characterization of the films was done by X-ray diffraction, morphology was investigated by SEM micrography. Using standard photography analysis, the films were qualified in terms of crack density, their appearance strongly depending on the type of substrate. Using a visible to the near infrared spectrophotometer, the transmittance normal to the surface of the films was studied. Coupling of laser light into the films by the M-lines technique allowed the determination of the refractive index and the thickness of the ferroelectric layer. A waveguiding interferometer structure of Mach-Zehnder type was realized by photolithography and wet chemical etching.

Studing of the Raman spectra was established that an optical parameters of oxygen-polyhedral ferroelectric single crystals can be improved by increasing the degree of structural ordering of the cation sublattice along the polar axis by doping them. In this case the impurity ions with the ionic radii close to the radii of the main cations (Li⁺ and Nb⁵⁺) and charges intermediate between those of main cations (1<Z<5) in the area of rather low concentrations were shown to exert an ordering effect on the cation sublattice of a congruent lithium niobate single crystals. Moreover the crystal resistance to laser radiation is also observed to grow. It was determined that the effect of diminishing photorefraction while the crystal is doped correlate well with the discovered ordering of the sublattice along the polar axis and both of them are observed for the same, relatively narrow, range of concentrations and the type of doping impurities.

Investigations of transient photoluminescence induced by external electric fields parallel to the layers of GaAs/Al_0.35Ga_0.65As quantum wells are reviewed. The photoluminescence was detected by time-correlated single-photon counting technique at liquid nitrogen and liquid helium temperatures applying electric fields of nanosecond duration to the wells of different width. It is shown how experimentally one can resolve between excitonic and donor impact ionization processes in combining spectral and time domains. From the study of the spectral-temporal dynamics at initial moments we have determined the coefficient of exciton impact ionization as a function of electric field for various widths of the quantum wells.

Earlier we reported the investigation of the electrical properties of selectively doped and degenerate CdS/ZnSe quantum heterostructures grown by molecular beam epitaxy. The maximum Hall mobilities in these heterostructures were nevertheless still inferior to 400 cm²/Vs. The purpose of the present work was to optimize these quantum structures in order to increase the carrier mobility and to analyze in detail the scattering mechanisms. We demonstrate that the Hall mobility in the CdS quantum well (QW) can reach 2800 cm²/Vs for slightly doped structures at low temperatures and that it is mostly limited by interface alloying scattering.

Optically induced changes in excitonic transitions of type-I GaAs/AlAs single QW structures have been investigated by photoluminescence (PL) and wavelength-modulated reflectance (WMR) spectroscopies, under various excitation photon energies and at various temperatures. The remarkable difference was observed in PL and WMR spectra taken by the excitation only the QW and by the excitation both the QW and the AlAs barrier layers. The photoinduced broadening and red shift of excitonic features in the optical spectra dominates under photoexcitation within the QW by He-Ne laser, and could be associated with hole accumulation effects in the QW. Double-beam excitation WMR experiment showed that the damped excitonic transitions could be restored simultaneously exciting AlAs barriers by Ar⁺-ion laser. As it follows from the analysis of photomodulated PL, this behavior could be attributed to optical depletion of the QW from the excess holes via a competing recombination process related to the barrier electrons. It was found that a thermal quenching of the PL line is activated by an escape of less confined electrons from the QW while a thermal quenching of photoinduced changes in the WMR spectra is related to the depopulation of the QW hole states.

We propose a novel way for the formation of GHz-frequency current oscillations in nonuniformly photoexcited and dc-biased semiconductor that exhibit a negative differential resistivity. A nonuniform heating of the electron gas in presence of both light interference field and strong external dc-field induces a high-field domain structure, which then progress and moves in spatially modulated carrier plasma. As a result, the oscillations of current density appear in external circuit attached to the sample. Numerical simulations performed on a bulk GaAs crystal prove that periodicity and modulation depth of the oscillations depends on spacing and intensity of light interference pattern. An experimental possibility to induce and detect microwave pulses of GHz-frequency is demonstrated in high-resistivity GaAs sample, mounted in series with low-impedance micro-stripe line, under carrier generation by two interfering laser beams of 2-ns duration.

Hot carrier dynamics and related optical nonlinearities, which arise in dc-biased GaAs under spatially varying optical illumination, have been investigated using light diffraction on transient grating technique. Under dc-bias, time resolved four-wave mixing measurements had evidenced an oscillatory behavior and increased efficiency of light diffraction. The effect was found the largest at illumination intensity corresponding to the electron density between 10¹⁵ cm^-3 and 10¹⁶ cm^-3. Numerical modeling of nonlinear transport at various applied dc-voltages and photoexcitation levels revealed conditions for an efficient and fast refractive index modulation by a transient high-field domain grating. Experimental obervations have been explained in terms of nonuniform carrier heating and formation of transient Gunn-domain grating in the region of negative differential resistance. Our results open the possibility of measuring hot-carrier picosecond dynamics and predict a novel way of fast refractive index modulation in dc-biased compound semiconductors.

Intensive light emission (photoluminescence) from silicon nanocrystals has been interpreted in literature as recombinative emission. It has been supposed that the band structure is "pseidodirect." The literature analysis presented in our paper shows that the band structure is indirect and therefore intensive recombinative emission is not possible. According to new aspect, a part of electrons reaches the second conduction subband due to Auger recombination. Then the intensive visible radiation could be caused by transitions of these electrons from the second to the first conduction subband. We have constructed continuity equations for the electron concentration in the first and the second conduction subbands. This system of equations has been solved numerically with two adjustable parameters. At suitable values of these parameters our theoretical curve of the photoluminescence decay well coincides with experimental one.

Nano-hills formation on a surface of 6H-SiC by the N₂ laser focused beam was found. These nano-hills are situated along the circular line with diameter smaller than that of the focused laser beam. Results of the photoluminescence and studies of Friction Force Microscopy speak in favor of the increase of nitrogen concentration in the nano-hills. For explanation of this phenomenon the pressure of liquid matter in the subsurface area and the pressure of the laser beam on the surface of the sample are taken into account. The threshold character of the effect, accumulation effect and increase of N band on PL spectra testify to the main role of the Thermogradient Effect in this phenomenon.

Coatings of AlN, TiN and nanostructured multilayer AlN/TiN have been deposited by reactive sputtering on sapphire, tungsten carbide (WC) and stainless steel substrates. The microhardness, adhesion and formation of cracks under indentation tests, were investigated. It was found that the adhesion of coatings on steel was higher, than on WC for all investigated samples. Nanostructured multilayer AlN/TiN films have the best adhesion and fracture toughness both on the hard (WC) and on the soft (stainless steel) substrates if compared with that for AlN and TiN "single layer" coatings. The effect of γ-radiation on mechanical properties of transparent AlN films was investigated. After the exposure of γ-radiation (10⁶ Gy) the microhardness of AlN has increased by 33%. No debonding or destruction of AlN films under irradiation was observed.