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Phase pure nanoparticles of NaCe(WO4)2green phosphor were synthesized via a template-free solvothermal method using water (NaCeW-a) and ethylene glycol (NaCeW-b) as reaction solvents. Rietveld refinements using powder neutron diffraction (NPD) data confirms that both NaCeW-a and NaCeW-b crystallize in the Scheelite-like tetragonal I41/aspace group. However, local structure analysis using total scattering atomic pair distribution function (PDF) refinements in a shorter ‘r’ range (1.5 to 10 Å) established the noncentrosymmetric I4̅ space group where Na/CeO8polyhedra are slightly distorted, distributed in 2b and 2d sites. The interesting observation of noncentrosymmetry locally in both NaCeW-a and NaCeW-b is supported by optical nonlinear second harmonic generation (SHG) measurements. Closer inspection of the scanning electron micrograms showed a distinct difference in the particle morphology as a function of reaction solvent. Observation of the +3 valence state of the cerium ion in NaCe(WO4)2via X-ray photoelectron spectroscopy measurements was further corroborated by magnetic (VSM) measurements. In addition, both the samples emitted bright narrow green emission upon UV excitation with no considerable change in emission intensity with respect to solvent. Hence, the sharp green light emission and SHG properties make the NaCe(WO4)2a potential candidate for solid state display and nonlinear optical applications.

A new type of modified bismuth silicate glass has been manufactured with vanadium and copper cations in a traditional rapid cooling method. FTIR spectra have been used to identify the different structural units of this glass. The spectral analysis showed the presence of BiO3and BiO6as basic structural units in all studied samples and the presence of bismuth as a former the glass network with silica. The radiation shielding properties were explored using a narrow beam transmission method in 0.662, 1.173 and 1.33 MeV. The effective atomic numbers for the sample containing the highest CuO ratio showed higher energy values than the other studied samples studied. The mean free path of the prepared glasses has been compared to other commercial radiation shielding. The comparison indicates that the glasses produced are more efficient in relation to radiotherapy compared to conventional commercial radiation protection glass. Microhardness measurements were made of the glass recorded at load at 300 g. The replacement of CuO by V2O5has been found to increase the cross-link density in addition to the observed difference in the atomic mass of Cu and V, thus increasing the hardness.

The topography of indium tin oxide (ITO) films with incorporated silver nanoparticles and irradiated by single pulses of 18 ns Nd:YAG laser has been investigated. The study was carried out with two Ag/ITO films having resistances of 50 Ω and 4 Ω/square sheet resistances. The periodic structures in both samples were created after the laser treatment. The photo-induced periodic structures have a different character while the sheet resistance plays a major role in the growth process of these structures. The results of optical and non-linear optical investigations lead us to the conclusion that the temporary polarization of samples and high temperature of illuminated spot during laser treatment is responsible for the shape of periodic structures. This conclusion has been also confirmed by local permittivity measurements using evanescent microwave microscope and theoretical calculations concerning the temperature distributions during laser illumination.

The electrical conductivity measurements of the p-quinquephenyl films possessing microcrystallite structure are done at temperature between 10 K–300 K. The investigated film thickness varies within 0.2–2.5 µm. The measurements were performed with Al(Au) electrodes for the films deposited by spin coating in argon atmosphere on glass substrates. The molecular dynamics simulations as well as quantum chemical calculations have shown that three different mechanisms contribute to the observed electrical feature, which are: the conductivity originated from proper crystalline states; this of the amorphous-like inter-grain region and the one created in the grain boarder interfaces. Comparing the experimental data and theoretically calculated dependencies, we have shown that the main contribution to the observed DC conductivity of this material results from the interfaces located at the borders of polycrystalline grains, although they possess a relatively low part of the total film volume. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Acoustically induced optical second harmonic generation (AIOSHG) in InAs single crystals was investigated. With increasing acoustical power, the AIOSHG for fundamental CO laser light (λ = 7.1 μm) increases and achieves its maximum value at acoustical power density about 1.70 W/cm2. The value of the AIOSHG for InAs was substantially higher than for key inorganic photo-refractive and ferroelectrics materials. With decreasing temperature, the AIOSHG signal strongly increases below 42 K. The AIOSHG maxima were observed at acoustical frequencies ranged at 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 phase transformations. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

A series of new donor−π-acceptor ruthenium acetylide systems built around thiophene-based π-conjugating spacers of different lengths have been developed. Comparison of the linear and third-order nonlinear optical properties of these donor−π-acceptor chromophores shows that the elongation of the oligothiophene-based spacer or further introduction of a double bond leading to a dithienylethylene spacer produces a considerable bathochromic shift of the absorption maximum together with a dramatic enhancement of the molecular cubic hyperpolarizability. Furthermore acoustically induced second-harmonic generation (AISHG) has been observed for film composites of these complexes incorporated in PMMA matrixes and reaches values among the highest reported so far.

Infrared (IR)-induced two-photon absorption (TPA) in synthesized PbO–Ga2O3–Bi2O3–CdO (PGBC) glasses doped by Eu³⁺ and Tm³⁺ rare earth (RE³⁺) ions was investigated. Temperature-dependent measurements of TPA were carried out in the mid-IR spectral range. A CO pulsed laser (λ = 5.5 μm, energy power density up to 3.8 GW/cm² per pulse with picosecond pulse duration) was applied as the source of photoinducing IR radiation. An optical parametrical generator cut from a proustite crystal was used as the source of the fundamental TPA beam within the 3–7.5 μm spectral range. Absolute values of the TPA coefficients were more than 13% higher than corresponding values obtained for other similar glasses (As2Te3–CaCl2–PbCl2 [1] or Sb2Se3–BaCl2–PbCl2 [2]). The PGBC system investigated possessed a shorter time response (about 12 ps) compared with other IR nonlinear optical glasses. It was also established that all nonlinear optical susceptibilities were dependent on the type of RE³⁺ ion. A maximum value of the TPA was achieved for the glasses doped by Tm³⁺. The TPA values increased significantly below 45 K. Ab initio molecular dynamics and quantum chemical simulations were performed in order to evaluate the possible role of electron–phonon anharmonic interactions in the observed phenomena. The influence of the external CO photoinduced pump beam through the photoinduced electrostricted anharmonic electron–phonon interactions was simulated. A decrease of picosecond delaying time response compared with other glasses was achieved. To obtain independent confirmation of the observed dependencies, measurements were carried out of χxxxx(E) during the external IR pumping. The measured and theoretically calculated dependencies of the third-order susceptibilities were also compared. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Conductivity of N-phenyl (N = 3,4) thin films (with thickness 2-15 µm) was investigated experimentally and theoretically using molecular dynamics simulations of microcrystallite (MC) occurrence and quantum chemical band structure calculations. At the first time, process of carrier kinetics is considered within a framework of self-consistent band structure approach. The external electric field was varied up to 10⁶ V cm^-1 using Al-Au electrodes with different voltage polarities. Depending on the film thickness and N, we have discovered the appearance of minima of effective activation energy. The observed effects are explained as a competition between the diffusion recombination of carriers from the trapping MC levels and the potential gradients on the MC surfaces. A good agreement between the performed theoretical simulations and experimental data is achieved.

Appearance of ferroelectricity has been predicted in the SxSe1-x (x=0.08-0.18) single crystalline films (thickness below 5 nm) using quantum chemical and molecular dynamics simulations. Direct measurements of the spontaneous polarization show appearance of the ferroelectricity for the film thickness below 5 nm with sulfur content × = 0.10-0.30. Inelastic neutron scattering and Raman measurements confirms substantial role of electron-phonon anharmonicity in the observed ferroelectric phase transition

Besides the traditional borate materials, g -BaB 2 O 4 [1] and LiB 3 O 5 (LBO) [2] such crystals as Li 2 B 4 O 7 (LTBO) [3], CsLiB 6 O 10 (CLBO) [4], YAl 3 (BO 3 ) 4 (YAB) [5], Ca 4 GdO(BO 3 ) 3 (GdCBO) [6] and Ca 4 YO(BO 3 ) 3 (YCOB) [7] are currently being intensively investigated for non-linear optical applications. These materials typically have high viscosity and very often melt non-congruently. These properties create technological problems that can be resolved by applying very precise devices for operating the growth conditions. Another important problem that appears in the borates is an existence of vacancy-induced phase transitions [8]. The occusence of phase transitions in the vacancy-induced YAB crystals is because they possess cationic subsystems formed by ions of different weights. In order to stimulate the vacancy-bearing process, we have doped the crystals with the Nd ions. The defectiveness of the crystals was determined using light scattering similarly to the method described in Ref. [9]. The dimensionless parameter D was introduced as a ratio of the integral light scattering intensity in defective crystals to the same intensity in perfect crystals.

The influence of intrinsic defects on optical properties of lithium niobate studied using an electronic-structure simulation technique. The simulation technique is based on molecular dynamics cluster geometry optimization, nonlocal pseudopotential calculation, and Green function electron−phonon interaction. Two models of defects are considered. The first one (electrostatically highly imbalanced) corresponds to mixture of oxygen vacancies and NbLi antisites. The second one corresponds to the Nb antisites charge compensated by appropriate vacancies, e.g., lithium vacancies, and corresponds to more realistic defect configuration. We present a band energy approach with a molecular dynamics cluster optimization that accounts for the various structural modifications related to the nonstoichiometry of LiNbO3 crystals. The variation of the optical properties with the deviation from the stoichiometric composition can be understood within this approach. Especially, the role of the electron−phonon contributions to the electrooptics coefficient is shown. Comparison of the first and second models shows that the virtual model corresponding to mixture of oxygen vacancies and NbLi antisites is more suitable for describing of the optical properties. In particular, model calculations yield a large dependence of the electrooptics coefficient r22 on the crystal composition, in agreement with the experimental data. The observed minimum of the r22 coefficient versus the nonstoichiometry in the plot is interpreted as being by a diminishing in the noncentrosymmetry of the electrostatic potential around Nb−O6 clusters.

A sharplike modulation of the linear electrooptic (LEO) coefficient with pressure (p) and temperature (T) has been observed for the first time. The modulation depth of the LEO (r222) tensor component in the C60−TTF (for the He−Ne laser, λ = 633 nm) was equal to about 2.6%. By varying the applied hydrostatic pressure to up to 15 GPa and the temperature from 4.2 to 25 K, we have unambiguously demonstrated that the observed effect is caused by the incorporation of the TTF moiety. This effect is absent from the unsubstituted fullerenes when the applied hydrostatic pressure is increased to 19 GPa and the temperature varied from 4.2 to 150 K. Norm-conserving self-consistent pseudopotential and molecular dynamics simulations independently reproduce these modulations and attribute them to the electron−vibration interactions associated with the LEO coefficients. The contribution of the interconformational tunneling under the applied pressure and temperature is demonstrated. The data obtained give a possibility for using the discovered effect for contactless measurements of low temperatures and high pressures.

Interest in SiC nanopowders has been growing due to the possibilities for using their nonlinear optical properties. The objective of the present work was to investigate these properties through PISHG (photoinduced second harmonic generation) and phototransparency measurements. The relation between structural parameters, such as hexagonality, and external forcing signals, such as pressure, PISHG, and phototransparency, was established. The high sensitivity of SHG to pressure suggests that the material investigated may be suitable for application in contactless pressure measurements.

Band energy structure of GaxAl1‐xN solid alloy (x=0.15; 0.65) is calculated. All one‐electron methods of band energy calculations (self‐consistent norm‐conserving pseudo‐potential (NCPP), linear muffin tin orbital method (LMTO) and linear combination atomic orbital (LCAO)) methods give considerable disagreement with the experimental data. We demonstrate that better agreement with experiment is achieved when the NCPP wavefunctions are orthogonalised to the core‐like states. Simultaneously additional geometry optimization improve the agreement with the optical data. We have carried out theoretical and experimental investigation of the band density of states for two representatives of the investigated wurtzite GaxAl1‐xN solid alloys (with x=0.15 and 0.65).

Photoinduced nonlinear optical phenomena in Sb_2Te_3–CaCl_2–PbCl_2 glasses have been studied by experimental and theoretical quantum chemistry and molecular dynamics methods. Additionally, photoinduced two-photon absorption (TPA) and second-harmonic generation (SHG) were measured in the IR region from 5.8 to 18 μm. A CO laser (λ=5.5 μm) and parametrically generated wavelengths (5.7–13.4 μm) were used as a source of pump light. With an increase of the photoinducing power, the SHG signal increased for a probe CO_2 laser (with double frequency λ=5.7 μm) and achieved its maximum value at a photoinducing power of 1.65 GW/cm^2 per pulse. Absolute values of the SHG intensities were more than 1 order of magnitude less than those of χ_222 nonlinear optical tensor components for Ag_3AsSe_3 single crystals. The SHG signal increases strongly for a temperature decrease from 39 to 26 K. Femtosecond probe–pump measurements indicate a SHG maximum at a pump–probe delay time of ∼18 ps. The spectral positions of the TPA maxima depend strongly on the pump power. Differently from the SHG behavior, the TPA results show at least two time-delayed maxima, namely, at 14–17 and 45 ps. These dependencies are explained within the framework of the quantum-chemistry approach, which takes into account photoinduced anharmonic electron–vibration interactions. The Sb–Te tetrahedral plays a key role in the observed photoinduced nonlinear optics effects. The results clearly show that these effects can be used as powerful tools for investigation of picosecond IR nonlinear optics. In addition, these glasses are promising materials for IR femtosecond quantum electronics.

Photoinduced nonlinear optics phenomena in 1, 4-cis-polybutadiene have been investigated. Both an external electrostatic field as well as UV laser photoinducing light lead to enhancement of the local non-centrosymmetry determining optical second harmonic generation (SHG). Using ab initioquantum chemical calculations and experimental nonlinear optics data we have shown that there exist values of the external fields corresponding to the maximal SHG values. Low-temperature ordering (below 10 K) (due to decrease of thermoreorientation) and hydrostatic pressure-induced strength also favour photoinduced SHG. Time-resolved SHG measurements indicate an existence of at least two short-time components (about picosecond range), that may be caused by different mechanisms of the observed phenomenon. It has been shown both experimentally and theoretically that the degree of non-centrosymmetry for the corresponding butadiene bonds is closely connected with the UV-photoinducing power, temperature, hydrostatic pressure and delaying time between the photoinducing and probing beams.