Influence of aging time of the starting solution on the physical properties of fluorine doped zinc oxide films deposited by a simplified spray pyrolysis technique

Fluorine doped zinc oxide (FZO) films were fabricated from fresh and aged (4, 8, 12 and 16 days) starting solutions using a simplified and low cost spray pyrolysis technique. The X-ray diffraction study showed that the preferential orientation is along the (0 0 2) plane for all the films irrespective of the age of the solution. The crystallite size calculated using the Scherrer’s formula is comparatively smaller only for the film prepared from the starting solution having aging time 4 days which may be due to the efficient incorporation of fluorine atoms into the ZnO lattice. This phenomenon is confirmed by the minimum resistivity value (3.14 × 10⁻² Ω cm) obtained in this particular case. The visible transmittance and the optical band gap values are found to be in the range of 63–83% and 3.20–3.31 eV, respectively. The optical transmittance is found to decrease gradually as the aging time of the solution increases and the optical band gap is found to be slightly higher in the case of the film prepared from the fourth day solution. The scanning electron microscopy results depicted that the microstructure of ZnO:F films are largely influenced by the aging of the starting solution.     

Crystal field parameters and energy level structure of the MnO4 tetroxo anion in Li3PO4, Ca2PO4Cl and Sr5(PO4)3Cl crystals

A comparative study concerning the electronic structure of the Mn⁵⁺ ion in the Li₃PO₄, Ca₂PO₄Cl, Sr₅(PO₄)₃Cl host lattices has been carried out in the framework of the exchange charge model. The crystal field parameters have been evaluated using the structural data as the only input information. The 10 K absorption spectra of the investigated compounds have been measured in order to verify the correspondence between experimental and calculated energy levels. A systematic trend of the crystal field splitting of the most intense transitions has been evidenced and discussed by considering the symmetry properties of the coordination polyhedra around Mn⁵⁺.     

Characterization of new-layered Cr(III)-doped chlorocadmiumphosphate, Cd(HPO4)Cl·[H3N(CH2)6NH3]0.5 crystal by EPR and optical studies

Cr(III)-doped Cd(HPO₄)Cl·[H₃N(CH₂)₆NH₃]_0.5, a new-layered cadmium phosphate, is synthesized in acidic condition at room temperature. EPR and optical studies are carried out at room temperature. Polycrystalline EPR spectrum reveals the presence of two sites of Cr(III) ions in this layered phosphate lattice with zero-field splitting values of 24.24 and 7.65 mT, indicating that Cr(III) ions are in distorted octahedral sites. The optical absorption spectrum of the sample indicates near octahedral symmetry for the dopant ions. Crystal field, inter-electronic and bonding parameters are evaluated by collaborating EPR and optical data. The evaluated parameters suggest the mode of entry of Cr(III) ion into the layered phosphate as interstitial site, and bonding between the metal and ligand is partially covalent.     

Securing multiplexed information by in-plane rotation of random phase diffusers constituting a sandwich diffuser placed in the Fourier plane of a double random phase encoding system

We propose the encryption and multiplexing of two-dimensional input images by rotating the constituent diffusers of a sandwich random phase diffuser kept in the Fourier plane of a double random phase encoding system. Successive recording of encrypted images is done by taking the input images one by one. The results of multiplexing in encryption and decryption due to different sets of rotation of one or both of the random constituent phase masks have been presented. The use of an aperture system in addition to the rotation of one or both of the random phase masks enhances the multiplexing capability and security of the system avoiding the generation of cross-talk images at the time of decryption. Simulation results are presented in support of the proposed techniques. The decrypted images obtained from a multiplexed encrypted image have been recorded successfully. Mean square-error (MSE) and signal-to-noise ratio (SNR) values as a function of the number of multiplexed images have been calculated.     

Total reaction and fusion cross sections at sub- and near-barrier energies for the system 7Li + 28Si

Fusion cross sections are extracted for the ⁷Li$ + $²⁸Si system, via reaction cross section and transfer measurements at sub- and near-barrier energies ( E _lab = 5.7 to 14MeV). The energy evolution of transfer to reaction cross section ratios is determined with the aid of CDCC calculations, which subsequently allows the deduction of fusion cross sections at sub- and near-barrier energies. It is shown that fusion can be well represented in a BPM context. Fusion cross sections are compared for the systems ⁷Li$ + $²⁸Si and ⁶Li$ + $²⁸Si, the latter studied previously, and are found to exhibit different strengths. Last, the direct channels determined at 13MeV, are found to be dominated by a 2n -transfer mechanism.     

Effect of phase shift in shape changing collision of solitons in coupled nonlinear Schrödinger equations

Soliton interactions in systems modelled by coupled nonlinear Schr?dinger (CNLS) equations and encountered in phenomena such as wave propagation in optical fibers and photorefractive media possess unusual features: shape changing intensity redistributions, amplitude dependent phase shifts and relative separation distances. We demonstrate these properties in the case of integrable 2-CNLS equations. As a simple example, we consider the stationary two-soliton solution which is equivalent to the so-called partially coherent soliton (PCS) solution discussed much in the recent literature. Received 1st October 2001 / Received in final form 4 February 2002 Published online 2 October 2002 RID="a" ID="a"e-mail: lakshman@bdu.ernet.in     

Theoretical expression for change of extraordinary refractive index in annealed proton exchanged LiNbO3 optical waveguides

A general expression for the change in extraordinary refractive index of the annealed proton exchanged LiNbO₃ waveguide has been deduced. The expression deduced explains the experimental results of decrease in change of extraordinary refractive index with annealing. The effect of annealing time has also been incorporated following Cao's model (Cao, Ramaswamy, Srivastava, J. Lightwave Technol. 10 (1992) 1302–1313). The concentration profile of protons in the annealed waveguide has been deduced theoretically, which is consistent with the previous results. The spontaneous polarization has been considered as the central mechanism for change in extraordinary refractive index due to proton exchange with annealing.     

IR-poled second-harmonic generation in glass

Infrared (IR)-induced second-harmonic generation in the chalcogenide glasses is observed. A phenomenological approach of IR picosecond non-linear optical (NLO) response in glass is developed for the middle IR spectral range (5–15 μm). The observed effect is explained within the framework of fifth-order NLO susceptibilities. A model that reproduces the basic characteristics of the experimental data, in which the optical non-linearities caused by photoinduced electron–phonon anharmonic interactions, is proposed. The role of the IR-induced phase matching conditions in the observed phenomenon is discussed.     

Microwave-assisted synthesis of flower-like and leaf-like CuO nanostructures via room-temperature ionic liquids

Flower-like and leaf-like cupric oxide (CuO) single-crystal nanostructures have been successfully synthesized using ionic liquid 1-octyl-3-methylimidazolium trifluoroacetate ([Omim]TA) under the microwave-assisted approach. By controlling the concentration of [Omim]TA and reaction temperature, shape transformation of CuO nanostructures could be achieved in a short period of time. The results indicate that ionic liquid [Omim]TA plays an important role in the formation of different morphologies of CuO crystals. The crystal structure and morphology of products were characterized by X-ray powder diffraction (XRD), infrared spectrum (IR), scanning electron microscope (SEM), transmission electron microscopy (TEM), and selected-area electron diffraction (SAED). A possible mechanism for CuO nanostructure was proposed. In addition, UV-vis spectroscopy was employed to estimate the band gap energies of CuO crystals.     

Electro-optic polymer assisted optical switch based on silicon slot structure

One kind of electro-optic polymer assisted Mach-Zehnder optical switch based on silicon slot structure is presented in this paper. The interference arms of the switch are slot structures instead of regular single-mode waveguides. By filling electro-optic material in the void slot of the arms, direct electro-optic modulation can be introduced. Theoretical model and detailed analysis are given in this paper. The length-independent product V_πL is about 74 mV cm when slot width is 100 nm, and 37 mV cm when slot width is 50 nm, when the polymer with a electro-optical coefficient of γ₃₃ = 130 pm/V is assisted. An ultralow energy consumption of only 37 fJ/bit is achievable, and the turn-on time of the switch is less than 1.5 ps.