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[en] The main spectroscopic properties (absorption, emission, decay times) of Pr3+-doped Ca4GdO(BO3)3 (GdCOB) have been determined for the three X, Y, Z polarizations. The Judd - Ofelt analysis, extended to anisotropic crystals, normalized and modified to take into account the influence of the 4f5d lowest energy level, has been performed and gives reasonable agreement with experimental data. The band energy approach is used for estimations of probabilities of relative cross relaxations and multiphonon relaxation. [copyright] 2001 American Institute of Physics
[en] In this paper, we present the photoluminescence properties of Pr3+-, Dy3+- and Tm3+-doped potassium-niobium-germanate glasses and glass ceramics. From the x-ray diffraction measurement, the glass structure was established. These glasses have shown strong absorption bands in the near-infrared region. Compared with Pr3+-, Dy3+- and Tm3+-doped glasses, their respective glass ceramics have shown stronger emissions due to the presence of the K3.8Nb5Ge3O20.4 crystalline phase. For Pr3+ -doped glass, two weak emission bands centred at 616 nm(3P0 → 3H6) and 648 nm(3P0 → 3F2) and for glass ceramic strong emission bands centred at 533 nm(3P0 → 3H5), 616 nm(3P0 → 3H6) and 648 nm(3P0 → 3F2) along with weak emissions at 688 nm(3P1 → 3F3), 709 nm(3P0 → 3F3) and 732 nm(3P0 → 3F4) have been observed with 450 nm(3H4 → 3P2) excitation wavelength. Among them, 648 nm(3P0 → 3F2) has shown bright red emission. For the Pr3+ -doped glass and glass ceramic, upconversion emission spectra have also been measured. Bright blue upconversion luminescence was observed under 1D2 level excitation. With regard to Dy3+ : glass, a weak emission band centred at 576 nm(4F9/2 → 6H13/2) and for glass ceramic a blue emission band centred at 485 nm(4F9/2 → 6H15/2) and a bright fluorescent yellow emission at 576 nm(4F9/2 → 6H13/2) have been observed, apart from 4F9/2 → 6H11/2(664 nm) emission transition with an excitation at 389 nm(6H15/2 → 4I13/2, 4F7/2) wavelength. Emission bands of 1G4 → 3F4(650 nm), 3F3 → 3H6(707 nm) and 1G4 → 3H5(774 nm) transitions have been observed for the Tm3+ : glass and glass ceramic, with an excitation at 3H6 → 1G4(473 nm). Among them, the 1G4 → 3F4 transition (650 nm) shows bright red emission. The stimulated emission cross-sections of all the emission bands of Pr3+, Dy3+ and Tm3+ : glasses and glass ceramics have been computed based on their measured full width at half maximum (Δλ) and lifetimes (τm)
[en] Complex current-voltage and electroluminescence (EL) investigations were performed for the single layered light emitting diodes on the base of the methoxy-modified pyrazoloquinoline (PQ) incorporated into polysilane matrices. The quantum chemical simulations performed for the isolated PQ chromophore molecule as well as for the complexes consisting of molecules and surrounding polymers show a principal role of dipole-dipole interactions for the appearance of the trapping levels substantially modifying carrier kinetics and the observed current-voltage and electroluminescent-current features. In particular, a significant change of the power index in the EL-current dependences versus the state dipole moments of the PQ chromophore determining chromophore-polymer chain interactions was established. The performed current-voltage investigations have shown that different power dependences at different voltages may indicate the inclusion of different carriers, which originate not only from the Shottky barrier jumps but also substantially due to trapping by the polaron and localized exciton states. The latter may also change the exciton kinetics and the diffusion lengths determining the power index of electroluminescent-current kinetics
[en] Experimental and theoretical simulations of linear and nonlinear optical susceptibilities of the novel Na3La9O3(BO3)8, a ternary oxyborate nonlinear single crystal, are reported here. The calculations were based on one of the most accurate methods for the computation of the linear and nonlinear optical susceptibilities of solids within density functional theory. Our calculations show that the edges of optical absorption for ε2perpendicular ω) and ε2parallel (ω) are located at 5.2 eV, in good agreement with our measurements. The anisotropy is in good agreement with the theoretical data. The same is true for the birefringence. We found that our calculated and measured refractive indices are in good agreement with those obtained by previous measurements. The imaginary and real parts of the second order second harmonic generation (SHG) susceptibility χ222(2)(ω) and χ112(2)(ω) were evaluated. Our calculation shows that χ112(2)(ω) is the dominant component, which shows the largest total Reχijk(2)(0) value (2.3 pm V-1) compared to χ222(2)(ω). This value shows very good agreement with experimental data (2.0 pm V-1) obtained by previous measurements and our measurements. One specific feature of the investigated crystals consists in substantial anisotropy of their properties, which plays a crucial role in the observed experimental dependences. These crystals possess very highly nonlinear optical properties. The coefficient of the SHG is about three to five times larger than that of KH2PO4 (KDP)
[en] In this paper, we present the photoluminescence properties of Eu3+-, Tb3+-, Dy3+- and Tm3+-doped potassium-titanium-germanate glasses and glass ceramics. Following the x-ray diffraction measurement, the glass structure was established. Compared to Eu3+-, Tb3+-, Dy3+- and Tm3+-doped glasses, their respective glass ceramics show stronger emissions due to the presence of the K2TiGe3O9 crystalline phase. For Eu3+-doped glass and glass ceramics, five emission bands centered at 578 nm (5D0 → 7F0), 592 nm (5D0 → 7F1), 614 nm (5D0 → 7F2), 653 nm (5D0 → 7F3) and 702 nm (5D0 → 7F4) have been observed with 394 nm (5D0 → 7L6) excitation wavelength. Of them, 614 nm (5D0 → 7F2) has shown a bright reddish-orange emission. For Tb3+-doped glass and glass ceramic, four emission bands centered at 490 nm (5D4 → 7F6), 549 nm (5D4 → 7F5), 586 nm (5D4 → 7F4) and 621 nm (5D4 → 7F3) have been observed with an excitation at 378 nm (3F6 → 5G6) wavelength. Of them, 549 nm (5D4 → 7F5) has shown a bright green emission. With regard to Dy3+:glass and glass ceramic, a blue emission band centered at 485 nm (4F9/2 → 6H15/2) and a bright fluorescent yellow emission at 576 nm (4F9/2 → 6H13/2) have been observed, apart from (4F9/2 → 6H11/2) (665 nm) emission transition with an excitation at 387 nm (6H15/2 → 4I13/2), 4F7/2) wavelength. Emission bands of 1G4 → 3F4 (650 nm) and 3F3 → 3H6 (700 nm) transitions for the Tm3+:glass and glass ceramic, with excitation at 3H6 → 1G4 (468 nm), have been observed. The stimulated emission cross sections of all the emission bands of Eu3+, Tb3+, Dy3+ and Tm3+:glasses and glass ceramics have been computed based on their measured Δλ (FWHM) and lifetimes (τm)
[en] We report calculations of the linear and nonlinear optical susceptibilities (second harmonic generation) for calcium samarium oxyborate Ca4SmO(BO3)3 using the full-potential linear augmented plane wave method. Our calculations show that this compound is metallic-like with density of states at the Fermi energy EF, N(EF) = 421.6 states/Ry-cell or a bare electronic specific heat coefficient of 73.14 mJ mole-1 K-2. We find that the metallic behaviour is due to the strong overlap of the Sm and O states around EF. We have performed calculations for the two contributions to ε(ω), namely, intra-band and inter-band transitions. The effect of the intra-band term is significant for energies less than 1 eV. We have calculated the various components of the second-order susceptibility tensor and find that χ111(2)(ω) is the dominant component. We find opposite signs for the contributions of 2ω and 1ω inter-/intra-band to the real and imaginary parts of the dominant component throughout the wide optical frequency range.
[en] The structural, optical, morphological and nonlinear optical properties of Cu:ZnO spray-coated films are studied. The surface morphology of Cu:ZnO thin films turned out to be homogenous, crack free and well covered with pea-shaped grains. The peak shift observed in the x-ray photoelectron spectroscopy spectra of the Cu:ZnO thin films infers the defect states present in the films. The satellite peak observed at 939.9 eV for Cu2P core-level spectra confirms the +2 oxidation state of Cu in the films. The formation of additional defect levels in the nanostructures upon Cu doping was investigated using photoluminescence (PL) and Raman spectroscopy studies. The luminescent centers in the violet, blue and green spectral region were observed. The most prominent emission was centered at the blue color center for 5% Cu:ZnO thin films. The enhancement in the PL emission intensity confirms the increase in the defect state density upon Cu doping. The shifting of the UV emission peak to the visible region validates the increase in the non-radiative recombination process in the films upon doping. The phonon modes observed in Raman analysis around 439, 333 and 558 cm−1 confirm the improvement in the crystallinity and formation of defect states in the films. X-ray diffraction reveals that the deposited films are of single-phase wurtzite ZnO structure with preferential growth orientation parallel (0 0 2) to the C-axis. The third-order optical susceptibility χ(3) has been increased from 3.5 × 10−4 to 2.77 × 10−3 esu due to the enhancement of electronic transition to different defect levels formed in the films and through local heating effects arising due to continuous wave laser illumination. The enhanced third harmonic generation signal investigated using a Nd:YAG laser at 1064 nm and 8 ns pulse width shows the credibility of Cu:ZnO films in frequency tripling applications. (paper)
[en] Two principally novel chromophores A, B based on fluorene electron donor were synthesized and explored by 1H NMR, 13C NMR, and MS spectra. The delocalized energy levels have been estimated by UV–Vis absorption spectra. The principal innovation consists in modification by addition of amino group. The titled materials have demonstrated a high solubility in common organic solvents, good compatibility with polymers. The maximally achieved electro-optic efficiency of the poled film possessing 25 wt% of A doped in PMMA (25 wt% A/PMMA) achieved a value of 18 pm/V at wavelength 1310 nm, and 25 wt% B/PMMA possessed an electrooptical coefficient equal to 43 pm/V. This one open a perspective of their direct application in optoelectronic telecommunication devices for laser light modulation.
[en] We report theoretical calculations of the band structure of AgCd2GaS4 using the full-potential linear augmented plane wave method and experimental measurements of the valence band x-ray photoelectron spectroscopy. We find that the valence band maximum and the conduction band minimum are located at the Γ point of the Brillouin zone resulting in a direct energy gap of 1.0 eV compared to our measured experimental value of 2.15 eV. Our analysis of the partial density of states shows that there is a weak covalent interaction between Ag and Ga atoms and between Ag and Cd atoms, and a substantial covalent interaction between Ag and S atoms. Thus the Ga-Ag and Cd-Ag bonds are basically of ionic character, and Ag-S bonds are of covalent character. The theoretical results of the density of states are in agreement with the valence band x-ray photoelectron spectroscopy measurements with respect to spectral peak positions. We have analyzed the calculated density of states and find a strong/weak hybridization between the Ag, Cd, Ga and S states in the valence and conduction bands
[en] The DC conductivity of p-sexiphenyl films 0.2-2.5 μm thick deposited on glass substrates was investigated at temperatures between 4.2 and 300 K to evaluate role of the grain boundary interfaces in the transport properties. Molecular dynamics simulations and quantum chemical modelling of the experimentally observed conductivity have shown that there exist at least three different phases of the films effectively contributing to the observed features of the DC conductivity: conductivity caused by proper crystalline states, conductivity originating from amorphous-like intergrain region and conductivity caused by grain boundaries. A comparison of experimental data with those calculated theoretically shows that the main contribution to the observed DC conductivity is supplied by the boundary region between the crystalline grains and the amorphous-like background, even though this region occupies a relatively low proportion of the total volume