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Comprehensive studies on piezo-optical (elasto optical) effects stimulated by bicolor coherent treatment using Er:glass laser, at λ = 1540 nm and its second harmonic generation (λ = 770 nm) insitu with mechanical stress, ultrasonic velocities and elastic coefficients of PbO−ZrO 2 −SiO 2 : TiO 2 glass ceramics were carried out as a function of concentration of crystallizing agent TiO 2 . The contribution to the piezo-optical effects is attributed to Pb 2 Ti 2 O 6 pyrochlore crystal phases appeared in the glasses during crystallization. The observed piezo-optical effects are attributed to simultaneous interference of the contributions due to the induced gratings (because of the bicolor treatment) and the piezo-optically originated birefringence. The variation of piezo optical coefficients, ultrasonic velocities and various elastic coefficients viz., Young's modulus, shear modulus, micro hardness etc., with the concentration of TiO 2 exhibited the maximal effect at 0.6 mol% content of TiO 2 . From the quantitative analysis these results together with the results of other studies ( viz., XRD, SEM, EPR, IR, optical absorption spectral studies), it is predicted that the PbO−ZrO 2 −SiO 2 glass crystallized with 0.6 mol% of TiO 2 is embedded with higher concentration of Pb 2 Ti 2 O 6 pyrochlore crystal phases (a crystal phase consisting of Ti 4+ ions) and such crystal phases are found to be responsible for observed maximal effects of all the mentioned properties for this sample.

Phase relation in the Tl 4 SnSe 4 –TlSbSe 2 –Tl 2 SnSe 3 quasiternary system were studied by the DTA and X-ray diffraction in combination with mathematical modeling. The phase diagrams of the Tl 4 SnSe 4 –TlSbSe 2 and Tl 2 SnSe 3 –TlSbSe 2 systems, the perspective views of the phase interaction in the ternary system, the liquidus surface projection, the isothermal section at 423 K were built for the first time. The Tl 4 SnSe 4 –TlSbSe 2 –Tl 2 SnSe 3 system is of the invariant eutectic type and is characterized by the formation of limited solid solutions following initial ternary compounds. New complex compounds are not formed.

The studies of changes in the energy gap of the CuInS2 photovoltaic׳s films were carried out. It was observed substantial absorption edge spectral red shift by varying laser wavelengths, power density, and beam profile. The maximum energy gap shift (up to 0.24 eV) was achieved during illumination by the Er:glass (λ=1540 nm) 35 ns pulsed lasers generating at wavelength 1.54 μm. The performed quantum chemical simulations have given an explanation of the observed photoinduced effects. The structural and quantum chemical analysis indicates on a principal role of the partial cationic atom׳s reorientations. The performed studies should open a new approach for desirable changes of photovoltaic efficiency in the studied films.

We have synthesized single crystals of TlHgCl3, which posses an orthorhombic symmetry, space group Pnma, with lattice constants a = 9.1601(4) A, b = 4.3548(2) A and c = 14.0396(5) A. The measurements of the optical absorption of TlHgCl3 are performed on parallel-plate samples with polished optical quality surfaces of d = 0.03 mm. The band gap is estimated to be 2.74 eV from the position of fundamental absorption edge at α = 200 cm−1. We have used our measured crystallographic data of TlHgCl3 as input data for calculating the electronic band structure, density of states, electronic charge density and the optical properties. The all-electron full potential linearized augmented plane wave plus local orbital (FP-L(APW + lo)) method is used. Calculations are performed with three types of exchange correlations; local density approximation (LDA), general gradient approximation (PBE-GGA) and the recently modified Becke-Johnson potential (mBJ). The PBE-GGA is used to optimize the atomic positions by minimization of the forces (1 mRy/au) acting on the atoms. The obtained values of the band gap from various exchange correlations are 2.39 eV (LDA), 2.55 eV (PBE-GGA) and 2.69 eV (mBJ). It is clear that mBJ succeeded by a large amount in bringing the calculated energy gap closer to the experimental one. The calculated electronic band structure exhibits that the conduction band minimum and the valence band maximum are located at Z point of the BZ, resulting in a direct band gap. The calculated density of states provides information about the hybridization between the states and the bonding nature. The electronic charge density show that Hg and Cl atoms form partial ionic/covalent bonding between Cl–Hg–Cl. Furthermore, for a deep insight into the electronic structure we have investigated the optical properties.

We have found an enhancement of the photovoltaic efficiency from the Cu2ZnSnSexS4−x films by illumination by the two coherent beams of 1320 nm 15 ns pulsed Nd:YAG laser. The observed changes did not exceed 10 % and were reversible. Following the performed quantum chemical simulations it was established that the origin of the effect is caused by photopolarization of the intrinsic defect trapping levels within the energy gap and photoinduced phonons. The contribution of the harmonic and anharmonic phonons was evaluated. The optimization of the photovoltaic efficiency was achieved due to the varying of Se/S ration. Additionally the pumping of the trapping intrinsic defect levels was done.

A possibility of changes the non-linear optical response was shown for the first time in the BiFeO3 doped by the Eu and Nd materials synthesized by the sol–gel method. Grain size here plays a substantial role. At the same time the latter is responsible for the non-linear optical response. The photoinduced optics was performed by the Nd:YAG lasers of different powers for samples of different nanosizes.

The energy band structure, electronic charge density and optical features of Tl4PbSe3 and Tl4PbTe3 single crystals were studied within a framework of the recently modified Becke–Johnson potential (mBJ). The earlier experimentally defined atomic positions were additionally optimized by minimizing the forces acting on the atoms using a generalized gradient approximation (PBE–GGA) approach. The performed band structure calculations have shown that the conduction band minimum (CBM) and the valence band maximum (VBM) are located at the Γ point of the first Brillouin zone, resulting in a direct energy band gap equal to about 0.21 eV (PBE–GGA) and 0.32 eV (mBJ) for Tl4PbSe3 in comparison to the experimental value (0.34 eV), while for Tl4PbTe3, the band gap is equal to 0.10 eV (PBE–GGA) and 0.18 eV (mBJ) compared with the experimental value (0.19 eV). We have established that the mBJ approach succeeds by a large amount in bringing the calculated energy gaps into close agreement with the measured one. The angular momentum projected density of states explores the existence of weak hybridization between the states, defining the degree of covalent bonding. The calculated valence band electronic charge density space distribution confirms the prevailing covalent origin of the chemical bond. The calculated optical dispersion for the principal optical constants shows that these materials exhibit negative uniaxial anisotropy. We have measured the dispersion of the imaginary part of the dielectric susceptibility e2 (ω) and evaluated the experimental optical band gaps. The measured e2 (ω) dispersion confirms our theoretical evaluations that the substitution of Se by Te causes a band gap reduction.

We report the first observation of the laser stimulated piezoelectricity in Er 3+ doped GeO 2 –Bi 2 O 3 glasses containing silicon nanocrystals, prepared using the simple well known melt quenching technique. Two split beams originated from the same nanosecond lasers were used for the performance of the bicolor laser treatment. The fundamental ( λ = 1064 nm) and the doubled frequency ( λ = 532 nm) signal of a pulsed nanosecond Nd:YAG laser, as the fundamental ( λ = 1540 nm) and the doubled frequency ( λ = 770 nm) signal of an Er:glass laser were used. The ratio of power densities between the fundamental and the doubled frequency beams has been varied from 4:1 to 8:1. This value was chosen to achieve the maximum output photoinduced piezoelectric response. The present photoinduced piezoelectricity effect opens a new road for obtaining optically operated piezoelectric devices in germanate composites doped with rare-earth ions.

In this work, we report on the synthesis and non-linear optical studies of PMMA polymer films deposited on Si〈111〉 wafers by using the spin-coating method. The transport features were measured using a four-probe method. The excitation was provided by 10 ns pulses of λ =1.32 μm YAG: Nd laser. The photoinduced laser light was polarized by a rotating Fresnel polarizer, and the output light powers were detected using a fast response photomultiplier. At low voltages, the photoinduced dependence of optical constants does not show an essential change with respect to the photoinduced power. The effect exists only on the nano-interfaces occurring on the borders. Drastic changes are observed only at higher voltages (about 6 V), which correlates with a drastic increase of the current. A novel mechanism describing low dc-elecric field for the trapping current by tunneling is proposed.

A new type of nanomaterial for optoelectronic is proposed. As such a material cleaved nanolayers of layered CdBr2 single crystals is chosen. A principal possibility to prepare thin hexagonal single crystalline layers of CdBr2 nanocrystals (possessing 6H polytype) with thickness up to several nanometers was shown. The studies of the optical absorption clearly show an occurrence of the blue spectral shift for the absorption edge up to 30 nm. During illumination by the 5 ns nitrogen laser at the wavelength at about 337 nm below the energy band gap it was established a substantial increase of the photoinduced absorption coefficient up to 25 cm−1 at pump power density equal to about 1 GW cm−2. The maximal photoinduced effect was observed for the thinnest film possessing thickness about 4 nm. The linear electrooptical effect was maximal at ambient temperature.

We have discovered substantial influence of the 3 μs CO2 laser treatment on the output third harmonic generation (THG) for Tl4SnS3 and Tl4PbTe3 single crystals. The treatment was performed in the regime of the pump-probing delay. The optimal pump-probe delaying time was 230 ps for the Tl4SnS3 crystals and 250 ps for the Tl4PbTe3 single crystals. It is crucial that for the Tl4PbTe3 the effect is substantially smaller. The effect may be explained within a framework of conception of excitation of the effective phonon subsystem effectively contributing to the THG.

In this work, we demonstrate possibility to use spectra of the parametrically tuned laser beam for operation by magnetoelectric properties of the (1 − x )BiFeO 3− x CuFe 2 O 4 (BFCI). The role of the photoexcited wavelength is crucial due to photoexcited phonons. It may indicate on a spectral sensitivity of the studied nanocomposites. We have studied spectral dependences of magneto-electric constant versus the magnetic field frequency for different sizes of the nanoparticles with and without the nanosecond laser pulses illumination and we have shown an occurrence of principal spectral shifts in the corresponding magneto-electric maxima. Additionally we have explored relative changes of dielectric permittivity and coercivity versus different photoinducing wavelengths. The performed experiments unambiguously show that the external laser treatment will lead to substantial shift of corresponding dielectric and magnetic parameters in the studied nanocomposites. It is principally the finding of clear spectral dependences for the mentioned dielectric and magnetic parameters. One can see their sensitivity to the photoinduced wavelength which reflects the photoexcitations of different part of wavelengths. One can see the spectral shift up to 100 nm for the two principal spectral maxima with respect to the dielectric and magnetic changes which may indicate on the two principally different contributions to the effects observed.

In this work, we report on the synthesis and nonlinear optical features of novel temperature operated materials based on Tl4HgI6 single crystals. Nonlinear optical, differential scanning calorimetry (DSC) and mechanical properties of the titled crystals are studied within the temperature range 300–500 K. We have established that Tl4HgI6 single crystal show both positive and negative value of linear expansion temperature coefficient. The temperature region of rapid reduction coefficient for linear expansion is very small (only 2°–5°), which corresponds to occurrence of structural transformation for the Tl4HgI6 single crystal. Comparison between the temperature dependence of the photo-induced optical second harmonic generation for the fundamental 5.5 μm wavelength is performed. We present an explanation for structural phase transition of the crystal Tl4HgI6 considering temperature changes of crystal lattice parameters and describing the transition from centrosymmetric phase P4/mnc, at ambient temperature to non-centrosymmetric P4nc at T > 458 K. The photo induced changes indicate a possibility of occurrence of intermediate non-centrosymmetry phase. Particular analysis is devoted to correlate with the temperature dependence of the DSC within the same temperature range. Physical mechanisms responsible for the observation of the dependences are given and they are based on the condensation of the soft phonon modes which are closely related with the anharmonic electron–phonon interactions responsible for the effects.

Results of a study on the application of a copolymer of fluorine as acceptor and 1H-pyrazolo[3,4-b]quinoxaline as a donor in bulk heterojunction solar cells are given. To the best of our knowledge, 1H-pyrazolo[3,4-b]quinoxaline co-polymers were not applied in organic photovoltaic devices yet. Organic photovoltaic devices as well as devices of active layers with TiO2 nanocrystals of different crystallite size were investigated. The methods of polymer and TiO2 nanocrystllites synthesis are presented and their physical properties are given. The fabricated photovoltaic structures possess high values of U oc voltage as as well as relatively high parameters of I sc currents. The maximally achieved parameters corresponded to open circuit voltage U oc = 1.13[V], and short current density Isc = 33.49[μA] under illumination 1,3 [μW cm−2], which correspond to energy conversion efficiency equal to about 0.80 %. The TiO2 nanocrystallites play a crucial role in the photovoltaics parameters.

I.V. Kityk, R. Viennois and K. Plucinski Electrical Engineering Dept., Czestochowa University of Technology, Armii Krajowej 17, Czestochowa, Poland Institut Charles Gerhardt, University Montpellier 2 and CNRS, Pl. E. Bataillon, Montpellier, France Condensed Matter Physics Department, University of Geneva, 21 Quai E. Ansermet, Geneva, Switzerland Electronic Department, Military University of Technology, Kaliskiego 2, 00-908, Warsaw, Poland

We have shown the possibility of operation by the piezooptical response of PbO–GeO2 glasses doped with rare earth ions and silver nanoparticles by illumination of double frequency CO2 nanosecond laser. Substantial influence of thermoannealing on the output photoinduced elastooptical susceptibilities was established. The effect is very sensitive to temperature and to the corresponding tensor components. The effect of thermoannealing leads to enhanced long-range ordering with the occurrence of corresponding trapping levels within the forbidden gaps. The discovered effects may be used for creation of low-temperature IR laser triggers.

We have studied the photoinduced effects in the nanocrystallized Y3Fe5O12 films deposited on the Gd3Ga5O12 substrates. We have found for the first time substantial changes of the birefringence, two-photon absorption and circularly polarized absorption in different regimes of treatment of the nanocrystallized films. The explanations of the observed phenomena are suggested. The absorption spectra were modeled by the DFT based calculations of the electronic structure and density of states, which have revealed the well-pronounced differences between the densities of states of the tetra- and octahedrally coordinated iron ions. In addition, the crystal field calculations of the Fe3+ energy levels at the octahedral and tetrahedral positions have been performed.

The study of photoluminescence and nonlinear optical properties of red (emitted at 650 nm), yellow (emitted at 570 nm) and green (emitted at 530 nm) CdTe quantum dots (QD) spin coated on quartz substrate that had been prepared by changing the ratio between octadecylphosphonic acid and octadecence within 0.1:1–1:1 was carried out. Spectral width of the emission spectra indicates an enhancement with the increasing of QDs sizes, namely ca. 25, 28 and 50 nm for the QD size of 2.5, 3.5 and 5 nm, correspondingly. The entire QDs samples feature a spherical morphology with a relatively narrow size distribution. The optical second harmonic generation (SHG) stimulated by coherent bicolor treatment at 1,540 nm and its second harmonic generation was studied versus the laser light power density and incident angle.

The possibility of coherent laser induced enhanced charge density acentricity in the layered single crystals of CdBr 2 is demonstrated experimentally. The possible manipulation through non-centrosymmetry was achieved by introduction of the I ion dopants which perform some kind of intercalation. The effects show strong dependence on hydrostatic pressure and are detected by second order nonlinear optical effects as well as by piezoelectricity. The proposed method opens a new opportunity for formation charge density acentricity on the nano level. More important is that the corresponding technology is relatively cheap.

Absorption, photo- and electroluminescence spectra of some trityl substituted 1 H -pyrazolo[3,4- b ]quinolines derivatives (methyl- and phenyl substituted) and fabrication of the single layered organic light emitting diodes are reported. The bulky trityl substituent was introduced to prevent aggregation and crystallization of the dopant in polymer matrix. Role of ground state dipole moments in the observed red Stokes shift, electroluminescent features and photocarrier transport is explored. The maximally achieved brightness about 50 Cd/m 2 is observed in the spectral range extending from 443 nm up to 462 nm. The voltage threshold was varied from 7.8 V up to 10 V. The brightness-current dependences show an existence of at least two types of carrier injections.

The absorption spectra of (NH 2 (C 2 H 5 ) 2 ) 2 CuCl 4 (DEACC) single crystals and nanocrystals (NC) incorporated into the polymethyl methacrylate (PMMA) polymer matrices were investigated both experimentally and theoretically. It was established that the crystal field spectra of Cu 2+ ion detect clearly the quantum size effects. The observed spectra were analyzed using first principle crystal field quantum chemical calculations. It was shown that incorporation of NCs into the polymer matrix allows to identify the charge-transfer (CT) bands in the spectra of DEACC crystals.

Azo-carbazoles dyes were synthesized. These materials are promising for diffraction gratings recording and for the quantum electronic devices. In this work second-order nonlinear optical optical features of such dyes were studied both theoretically and experimentally. Quantum chemical calculations have been performed using the molecular dynamics, applying geometrical optimization through (MM+) force field method (all-atom force-field model), semi-empirical Allinger method (AM1) and finally PM3 method.

An all electron full potential linearized augmented plane wave method has been applied for a theoretical study of the band structure, density of states, and electron charge density of a noncentrosymmetric chalcopyrite compound HgGa(2)S(4) using three different approximations for the exchange correlation potential. Our calculations show that the valence band maximum (VBM) and conduction band minimum (CBM) are located at Gamma resulting in a direct energy gap of about 2.0, 2.2, and 2.8 eV for local density approximation (LDA), generalized gradient approximation (GGA), and Engel-Vosko (EVGGA) compared to the experimental value of 2.84 eV. We notice that EVGGA shows excellent agreement with the experimental data. This agreement is attributed to the fact that the Engel-Vosko GGA formalism optimizes the corresponding potential for band structure calculations. We make a detailed comparison of the density of states deduced from the X-ray photoelectron spectra with our calculations. We find that there is a strong covalent bond between the Hg and S atoms and Ga and S atoms. The Hg-Hg, Ga-Ga, and S-S bonds are found to be weaker than the Hg-S and Ga-S bonds showing that a covalent bond exists between Hg and S atoms and Ga and S atoms.

A correlation between the resistivity-voltage dependences of the hydrogenated SiN/Si(111) films and the photo-induced third-harmonic generation (PITHG) at λ = 1064 nm in the reflected light regime was found. The contribution to the PITHG is both due to linear photo-induced surface changes as well as due to the hydrogen dopants. When the fundamental power density increases to higher than 1.2 GW/cm2, there occurs a drastic decrease of the PITHG. Maximal PITHG changes are observed at a pump-probe delay time about 18 ps and the value of the PITHG slightly increases with the enhanced applied dc-electric field during illumination by a third-harmonic laser beam as a photo-inducing one. The deviation from the tripled frequency wavelength to higher wavelengths substantially suppresses the output PITHG signal. The crucial role of the interface trapping levels and silicon-hydrogen charge transfer is shown.

We present the temperature dependence of piezooptical coefficients for three samples of TeO 2 –GeO 2 –PbO glasses doped with 0.5% of Eu 2 O 3 , 0.5% and 1% of Au 2 O 3 , after different thermoannealing times. We have established that there exist two temperatures singularities – minima in the range 655–695 K and maxima – at 850 K. It is crucial that for the glasses annealed during 61 h, at temperatures about 850 K, the anomaly of piezooptical coefficient disappears. Simultaneously the minima within the range 655–695 K changed depending on the duration of the thermoannealing which leads to low temperature shift of the minima. Towards lower temperature the piezooptical maxima occurs around 850 K and disappears after the increase of the annealing time. It is also crucial that the values of the piezooptical coefficients decrease with the enhancement of the thermoannealing. The observed temperature dependence with the piezooptical coefficients has a good correlation with the temperature dependences of the DSC. We have found that the pure glasses and glasses doped only by Au 2 O 3 and Eu 2 O 3 possess the piezooptical coefficients one order less with respect to the samples possessing simultaneously Au 2 O 3 and Eu 2 O 3 .

We performed the temperature measurements of transport and non-linear optical properties, particularly optical third harmonic generation of PbTe and Gd-doped PbTe to elucidate the effect of the rare earth ion doping on behavior of the thermal conductivity and the third-order non-linear optical susceptibility. The feature of Gd-doped PbTe shows the existence of small values of the low temperature resistivities, (\({10^{-6}\Omega\,\hbox{cm}}\)) and a very significant value of mobility \({\mu=1.5^{\ast}10^{6}\hbox{cm}^{2}\hbox{V}^{-1} \hbox{s}^{-1}}\). The thermal conductivity κ decreases with incorporation of the rare earth ion (Gd) in PbTe matrice. The optical third harmonic generation (THG) shows that the great contribution of the phonons observed for PbGdTe compared to the PbTe, enhances the lattice thermal conductivity of network \({(\hbox{k}_{\rm ph})}\).

Nonlinear optical measurements were performed to elucidate the influence of magnetic ions on the behavior of charge carriers in magnetic semiconductors—Pb 1− x Yb x X (X = S, Se, Te at x = 1–3%). It was shown that nonlinear optical methods could be used as sensitive tools for investigations of electron–phonon anharmonicity near low-temperature semiconductor–insulator phase transitions. There exists a difference between surface and bulk-like contributions to the nonlinear optical effects. It was shown that only low-temperature Two Photon Absorption (TPA) oscillator may be related to the number of the electron–phonon anharmonic modes responsible for the observed phase transformation. The explanation of the anomalous temperature dependences is given in accordance with dipole momentum's behaviors determined by low-temperature spin–spin interactions and by electron–phonon anharmonic interactions. We have discovered that low-temperature dependence of specific heat of Pb 1− x R x Te (R = Yb, Pr with x = 3% and 1.6%, respectively) exhibits a non-magnetic order caused by large electron–phonon contributions and structural disorder effects.

A large effective second-order optical susceptibility equal to about 52 pm/V for ZnO films with thickness about several μm deposited on MgO substrate by molecular epitaxial method was achieved using a bicolour coherent treatment by a pulsed 1.32 μm Nd–YAG laser and its second harmonic at λ = 0.66 μm. The written grating was stable during 24 days and its optical susceptibility decreased not more than 26% with respect to the initially written one after interruption of optical treatment. The same measurements performed for the ZnO films deposited by metaloorganic chemical vapor deposition, pulsed laser ablation and spray pyrolysis have shown that the output optical susceptibility is at least half order less. The temperature dependences of the second order susceptibilities have shown that it achieves a maximum near a temperature of 261 K. Other methods do not show substantial temperature dependences. We have found that maximal second harmonic generation signal was achieved for the films with thickness of about 2.75 μm.

We have evidenced the high sensitivity of infra red-induced second harmonic generation (IR-ISHG) to the structural changes that occurred in amorphous hydrogenated silicon films (a-Si:H) prepared by Rf-glow discharge technique at different substrate temperatures and doping types. In every case, a maximal signal of the IR-induced SHG is achieved at a temperature of about 110 K and pump–probe delaying time about 22–38 ps. This one indicates a marked effect of doped subsystems in the observed non-linear optical effects. A tremendous effect of doping is established from a drastic change of the IR-induced SHG behavior presenting an anomaly at about 400 MW/cm2 for a pumping power with wavelength 3.7 μm. A minimum of the SHG is observed in that case for standard non-doped films. Note here that the doping type does not markedly affect the behavior of the second-order non-linear optical susceptibility. The thermo-annealing leads to a slight decrease of the effective second-order susceptibilities. More drastic changes are observed with doped samples for the pump-probe delaying time from about 39 till 24 ps.

It was shown that the Pd nanoparticles (NP) deposited on ITO substrate by seed-deposited technology show substantial acoustically induced non-linear optical effects. The effects appear at low temperatures. It was established that the Pd films and ITO substrates do not give the sufficiently high effect. Coating of the Pd NP on the Pt ones gives additional enhancement of the effect. The NP obtained using different technological regimes shows high sensitivity to the acoustically induced SHG. So this method may be recommended like a high sensitive method for detection of the Pd NP.

We have evidenced the high sensitivity of infrared-induced second harmonic generation (IR-ISHG) to the structural changes occurred in amorphous hydrogenated silicon films (a-Si: H) prepared by RF-glow discharge technique at different substrate temperatures and doping types. In every case, a maximal signal of the IR-induced SHG is achieved at temperature of about 110 K and pump-probe delaying time about 22–39 ps. It indicates a marked effect of doped subsystems in the observed nonlinear optical effects. A substantial effect of doping is established from a drastic change of the IR-induced SHG behavior presenting an anomaly at about 400 MW/cm2for a pumping power with wavelength 1.54μm. A minimum of the SHG is observed in that case for standard nondoped films. Note here that the doping type does not affect the behavior of the second-order nonlinear optical susceptibility. The thermo annealing leads to a slight decrease of the effective second-order susceptibilities. Larger changes are observed with doped samples for the pump-probe delaying time from about 39 till 24 ps.

The second-order optical properties of silver (Ag) nanoparticles (NP) on the ITO substrates of different resistance are investigated. The photoinduced effect at 1.32 μm demonstrates a marked dependence of the photoinduced optical SHG versus the Ag NP sizes. Particularly, it was shown that there exist a maximum of the SHG for the interparticle distance about 124 nm corresponding to about 35 nm.Comparison with the photoinduced effects in the Ag NP on the glass and with the ITO substrate indicates on a crucial role of the Ag NP/ITO interfaces in the observed dependences. The effect may be a consequence of the interface localized trapping levels creating a great number of effective centers, which stimulate an occurrence of the SHG signal. The maximally achieved second-order optical susceptibility at 1.32 μm wavelength corresponds to the value of about 6.37 pm/V.

Measurements of transport and non-linear optical (NLO) properties of the new, synthesized semiconductor Pb0.9835Pr0.0165Te in the vicinity of low-temperature metal–semiconductor phase transformations were performed. A correlation between the temperature behaviour of transport properties near the phase transition and NLO susceptibilities of second- and third-order was observed. FTIR spectra show the substantial role played by the Pr3+ localized levels in the observed anomalies.Among the transport properties, the resistivity, Seebeck coefficient and specific heat were measured. The presence of the minimum at about in the temperature dependence of the resistivity ρ(T) is due to the metal–semiconductor transition in Pb1−xPrxTe and the low-temperature upturn observed in the resistivity is well fitted by the Mott law. Substitution of PbTe by other rare earths shows the crucial role played by Pr in the observed dependences.Experimental temperature measurements using photo-induced NLO (pumped by a UV-laser as well as by second harmonics of the YAG–Nd lasers) and a probing YAG–Nd (at λ = 1.06 µm) laser, show the existence of two maxima in the photo-induced second harmonic generation (PISHG) at temperatures 17 and 30 K, the behaviours of which substantially depend on the wavelength of the pump beam. At the same time the third-order two-photon absorption possesses maxima near 50 K, i.e. at about . Such discrepancies in the positions of the temperature maxima are caused by the difference in contributions of the photo-induced anharmonic phonons near the surfaces PISHG and the bulk. Varying the penetration depth of the photo-inducing light one can operate with the output NLO properties.

In this paper, we report on the experimental studies of optical birefringence of A 2 BX 4 (K 2 ZnCl 4 , Rb 2 ZnCl 4 , and K 2 SeO 4 ) type of crystals in a wide temperature range which show para-electric, ferroelectric properties with incommensurate phases for the 633 nm wavelength. We found that with the decrease of the nanocrystallite sizes, temperature range of the incommensurate phase is enhanced. At the same time the ferroelectricity disappeared at crystallite sizes below 8 nm due to nano-confinement effects which change the electron–phonon anharmonic interactions which are responsible for such kinds of phase transitions. Additional superposition of the external electric field leads to drastic changes in the relative amount of the ferroelectrics and incommensurate phases. The effect is explained within the Landau–Ginzburg phenomenological approach with Lifshitz invariant. Additional confirmation of the observed effects was obtained by optical second harmonic generation. During the decrease of the nanocrystallite sizes below 12 nm there occurs some harmonic soliton waves which are propagated in several directions parallel to the crystallographic axes. Despite the absence of the long-range disorder there occurs some non-centrosymmetry.

Photoinduced optical and second-order non-linear optical effects in the interfaces separating In2O3–SiON (O/N ratio equals 1) films doped with A1, Sn and glass substrates were investigated using the photoinduced optical second harmonic generation. The photoinduced effective second-order optical susceptibility deff (at λ=1.76 μm ) shows a good correlation with the linear optical susceptibility, particularly with the shift of the absorption edge. The maximal response of the photoinduced optical response signal was observed for the pump–probe delaying time of 34 ps . The performed experimental measurements indicate that the observed effects are mainly caused by the interface potential gradients on the border glass–In2O3–SiON film and by additional polarization due to insertion of the Al and Sn atoms. The observed phenomenon may be proposed as a sensitive tool for investigation of thin semiconducting interfacial layers and simultaneously such films may be used as materials for non-linear optical devices.

Acoustically induced optical second harmonic generation (AIOSHG) was investigated in single and polycrystalline InAs. With increasing acoustic power, the AIOSHG for fundamental CO laser light (λ = 7.1 µm) increases and achieves its maximum value at acoustic power density of about 1.72 W cm–2. The values of the AIOSHG were substantially higher for the polycrystalline InAs than for inorganic photo-refractive and ferroelectrics materials. With decreasing temperature, the AIOSHG signal strongly increases below 50 K, which correlates with the occurrence of condensation of low-frequency anharmonic 'soft' phonon modes. The AIOSHG maxima were observed at acoustical frequencies ranged between 7–11 kHz. Comparing the obtained results with the acoustically induced IR spectra at low temperature, one can conclude that the observed effect is associated with acoustically-induced electron–phonon anharmonicity.

The giant increase of the absorption of the radiation with the doubled frequency in a region of high values of the optically-induced electric fields (about 105–106 V/cm) has been observed during the investigation of the optical poling process in germanium-silicate glass. The absorption suppresses the writing of the second-order susceptibility grating and leads to the restriction of the maximum efficiency of the photoinduced second harmonic generation in glass. We demonstrate that the observed effect is not anisotropic and may be considered as a consequence of a competition between the charge separation by the local trapping levels due to electrostricted photoinduced phonons and recombination diffusion of carriers.

Luminescence and absorption at wavelengths 600–1000 nm from Yb3+ ions embedded in PbO–Bi2O3–Ga2O3–BaO glass hosts is reported at room and helium liquid temperatures. We have found that excited pulsed XeII laser light (λ=714 nm) gives substantial luminescence at 980 nm with efficiency up to 63.2%. Kinetics of luminescence gives a decay time about 1050 μs. Explanation of the obtained results is presented within the framework of the Judd–Ofelt method and inclusion of electron–phonon anharmonicity.

Giant anisotropy in the charge density distribution for different crystal sequences of the new synthesized pentaborate Ba[B5O8(OH)3] crystals was predicted on the basis of self-consistent band structure calculations. Self-consistent calculations using a norm-conserving nonlocal pseudopotential showed that the anisotropy observed results from the specific geometry of clusters under consideration, as well as from the anisotropy of covalent 2pO2pB bonds within the layers and weaker 2pO2pO bonds between the layers. A comparison of the calculated imaginary part of dielectric susceptibility with ellipsometric measurements was made in order to verify our calculations. The role played by Ba cations in the formation of the observed anisotropy was proved. A correlation between the band structure dispersion and electron charge density distribution is shown.

SiNxCy films were synthesized using a technique of chemical evaporation at low pressure. We have carried out quantum chemical and molecular dynamics simulations of the film structure versus the nitrogen/carbon ratio. The film thickness varied between 8–24 nm. The stoichiometry of these films was measured after their deposition on Si[111] substrates using an extended x-ray absorption fine structure (EXAFS) method. A comparison was made of the experimentally obtained and molecular dynamics optimized structure. At the same time, pressure derivatives of the total energy within the calculated local density approach agree well with the experimental data. Sufficient agreement between the experimental EXAFS data and the simulated structural data indicates the crucial role of anharmonic electron–phonon interactions.

Photoinduced second harmonic generation (SHG) in Bi2Se3–CaBr2–PbCl2 optical fibers have been studied using experimental and theoretical quantum chemical and molecular-dynamics methods. Infra-red (IR) induced SHG was measured in the IR region within the 5.5–21 μm . CO laser ( λ=5.5 μm ) was used as a source of the photoinducing IR light. The glasses had diameters varied within the 5–35 μm . The lengths of the fibers varied from 0.5 cm up to the 1.4 m. We have found that with increasing photoinducing power, the SHG for the doubled frequency 5.3 μm of the CO2-laser increases and achieves its maximum value at photoinducing power 1.35 GW / cm 2 per pulse. The maximal by achieved values of the second-order nonlinear optical susceptibilities d222 was equal about 1.5 pm/V. With decreasing temperature, the SHG signal strongly increases within the 75–220 K temperature range. Picosecond probe–pump measurements indicate on the occurrence of the SHG maximum at pump–probe time delay about 25 ps. These dependencies we explain within a framework of the quantum chemical approach taken into acount photoinduced anharmonic electron–phonon interactions. We have found that Bi–Se tetrahedral bonds play a key role in the observed IR photoinduced nonlinear optical (NLO) effects. The obtained results show that the mentioned glasses may be applied as materials for IR picosecond–second quantum electronics.

Photostimulated nonlinear optical effects in new synthesized PbO-Ga 2 O 3 -Bi 2 O 3 -CdO (PGBC) glasses doped by Yb 3+ , Er 3+ and Dy 3+ rare earth (RE) ions were discovered. Temperature-dependent measurements of optical photoinduced second harmonic generation (PISHG) and two-photon absorption (TPA) have been performed in the IR range. CO pulse laser ( u; =5.5 v; µm, energy power density up to 3.8 v GW/cm 2 per pulse) was applied as a source of photoinducing and probing light. Absolute values of the photoinduced SHG turned out to be more than 22% larger than corresponding values obtained for other glasses: As 2 Te 3 -CaCl 2 -PbCl 2 [1] or Sb 2 Se 3 -BaCl 2 -PbCl 2 [2] type. The investigated PGBC system possesses essentially shorter time response (of about 18 v; ps) comparing with other glasses. We have also established that all nonlinear optical susceptibilities are dependent on the RE type. A maximal value of the PISHG is achieved for essentially lower photoinducing CO-laser beam power (of about 0.40 v G...

We have found that the optical treatment by bicolor two laser beams at 1064 and 532 nm, at energy densities 80–120 mJ/cm2 originating from the same 10 ns Nd3+ garnett lasers causes the occurrence of the piezooptical effect in 50–80 nm γ-glicyne polymer nanocomposites at nanoparticle content about 6.5% in weighting unit. We propose to use this effect for optical triggers.

We have observed substantial influence of the illumination by 3.5 μs CO 2 laser on the piezooptical coefficients of 59 PbO – 41 GeO 2 (in wt.%) glasses prepared with Tm 2 O 3 , Er 2 O 3 , Yb 2 O 3 using the following concentrations (in wt.%): B–Tm 2 O 3 (0.5)/Yb 2 O 3 (1.0)/Er 2 O 3 (0.5); C–Tm 2 O 3 (0.5)/Yb 2 O 3 (1.0)/Er 2 O 3 O(1.0); D–Tm 2 O 3 (0.5)/Yb 2 O 3 (1.0)/Er 2 O 3 (2.0). We have found that the maximal changes were observed for B samples that contain the lowest concentration of Er 2 O 3 . The maximal changes are observed around 360 nm near the fundamental absorption edge. There exists some correlation between the maximal intensities of the photoluminescence and the maximal piezooptical changes. The CO 2 lasers cause preliminary photothermal changes. The existence of the maxima may be caused by a competition between the phonon and anharmonic phonon subsystems, which are very sensitive to the temperature.

Despite considerable progress achieved over the past few years in understanding ultrathin oxynitrides, several fundamental questions, in particular, the oxynitridation mechanism and the mechanisms behind the beneficial role of nitrogen are still not well understood. To improve understanding of the explanations which have been proposed for the phenomena specific to silicon oxynitride and for the nature of the defects, a study of the electron structure of a MOS system using silicon oxynitrides as the gate oxide and based on a molecular dynamics geometry optimization method, was carried out. Investigations of the band energy parameters versus the SiON film thickness and oxygen to nitrogen ratio were done theoretically as well as experimentally. Theoretical calculations were done by norm-conserving non-local pseudopotentials together with molecular dynamics geometry optimization. Experimental investigations included spectroscopic investigations of the film absorption. Both theoretical and experimental data indicate that the effective band energy gap possess modulated-like dependence versus the film thickness and oxygen/nitrogen ratio. The origin of the observed phenomenon is caused by specific electron-phonon anharmonic interactions between the film and the Si substrate.

The photoinduced optical second harmonic generation (PISHG) in 1,4- cis -polybutadiene has been investigated as a function of temperature in the vicinity of the glassing and crystallisation temperatures. Both the addition of centrosymmetric tetraphene molecules as well as the trans -isomers lead to an enhancement of the local non-centrosymmetric charge density distribution determining optical second harmonic generation. Using ab initio quantum chemical calculations with the inclusion of electron–vibration anharmonic interactions and combined with experimental PISHG data we show that increasing molecular localisation favours increasing non-centrosymmetry detected by PISHG. Two maxima of the PISHG signals have been observed at temperatures of ≅52 and 153 K for the specimens doped with p -terphenyl molecules and those doped with isomer trans -polybutadiene phase. Good correlation of the experimental data is obtained with theoretical calculations. The main mechanism of the observed temperature anomalies is connected with the enhancement of electron–vibration anharmonicity during glassing and crystallisation structural rearrangements.