Nonlinear optical characteristics of self-assembled films of ZnO

In the present work, we have investigated the nonlinear optical properties of self-assembled films formed from ZnO colloidal spheres by z-scan technique. The sign of the nonlinear component of refractive index of the material remains the same; however, a switching from reverse saturable absorption to saturable absorption has been observed as the material changes from colloid to self-assembled film. These different nonlinear characteristics can be mainly attributed to ZnO defect states and electronic effects when the colloidal solution is transformed into self-assembled monolayers. We investigated the intensity, wavelength and size dependence of saturable and reverse saturable absorption of ZnO self-assembled films and colloids. Values of the imaginary part of third-order susceptibility are calculated for particles of size in the range 20–300 nm at different intensity levels ranging from 40 to 325 MW/cm² within the wavelength range of 450–650 nm. PACS 81.16.Dn; 42.65.-k; 42.65.An; 42.70.-a; 42.70.Nq; 78.20.Ci     

Luminescence tuning and enhanced nonlinear optical properties of nanocomposites of ZnO-TiO2

In this article we present the spectral and nonlinear optical properties of ZnO-TiO(2) nanocomposites prepared by colloidal chemical synthesis. Emission peaks of ZnO-TiO(2) nanocomposites change from 340 nm to 385 nm almost in proportion to changes in E(g). The nanocomposites show self-defocusing nonlinearity and good nonlinear absorption behaviour. The nonlinear refractive index and the nonlinear absorption increase with increasing TiO(2) volume fraction at 532 nm and can be attributed to the enhancement of exciton oscillator strength. ZnO-TiO(2) is a potential nanocomposite material for the tunable light emission and for the development of nonlinear optical devices with a relatively small limiting threshold.     

Isolation and characterization of a novel multibridged tetradentate dianionic form of pyridoxic acid. Crystal structure of tetranuclear [Cu4(PAA)2(Bipyam)4(H2O)2Cl2](NO3)2·CH3OH·10H2O

The X-ray analysis of the tetranuclear copper(II) complex formed from pyridoxic acid and 2,2′-dipyridylamine reveals a novel metal binding mode of pyridoxic acid as a multibridged tetradentate dianion. Here the pyridoxic acid moiety uses all possible sites except the pyridine nitrogen for metal coordination.     

Optical characterization of the deep Cr level in GaAs

Comparison between the excitation spectra of luminescence (ESL) of the 0.57 eV band (typical of p or SI materials) and of the 0.62 eV band (typical of n samples) with the photoionization cross-sections σ⁰_n(hv) and σ⁰_p(hv) of the chronium level leads us to attribute unambiguously these luminescence transitions to the (Cr³⁺?Cr²⁺) center in chromium doped GaAs.     

New lithium-ion conducting perovskite oxides related to (Li, La)TiO3

We describe the synthesis and lithium-ion conductivity of new perovskite-related oxides of the formulas, LiCa_1.65□_0.35Ti_1.3B_1.7O₉ (B =Nb,Ta)(I,II), LiSr₂Ti_2.5W_0.5O₉ (III) and LiSr_1.65□_0.35Ti_2.15W_0.85O₉(IV). OxidesI andII crystallize in orthorhombic (GdFeO₃-type) structure, while oxidesIII andIV possess cubic symmetry. All of them exhibit significant lithium-ion conduction at high temperatures, the highest conductivity of ∼ 10⁻²S/cm at 800°C among the oxides is exhibited by the composition IV. The results are discussed in the light of previous work on lithium-ion conducting perovskite oxides containingd ₀ cations.     

Li2MTiO4 (M=Mn, Fe, Co, Ni): New cation-disordered rocksalt oxides exhibiting oxidative deintercalation of lithium. Synthesis of an ordered Li2NiTiO4

We describe the synthesis and characterization of a new series of oxides, Li₂MTiO₄ (M=Mn, Fe, Co, Ni) that crystallize in the rocksalt structure. For M=Ni, we have also obtained a low-temperature modification that adopts a Li₂SnO₃-type structure. All the phases, excepting M=Ni, undergo oxidative deinsertion of lithium in air/O₂ at elevated temperatures (>150°C), yielding LiMTiO₄ (M=Mn, Fe) spinels and a spinel-like Li_1+xCoTiO₄ as final products.     

Backscattering of laser light from colloidal silica

Light-scattering experiments gained prominence as potential applications of quantum optics, non-linear optics, and photon localization. The possibility of the realization of lasing action in random media has created much interest in the study of the coherent structure of the backscattered light from disordered media. Backscattering (BS) studies are carried out to analyze the possibilities of photon localization in colloidal silica. The scattering enhancement is best associated with the density of the scatterers. The width of the BS cone and, hence, the mean-free path is related to the concentration of the medium. The dependence of the photon wavelength on the possible characteristics of the scattering is presented.     

Effect of self assembly on the nonlinear optical characteristics of ZnO thin films

In the present work, we report the third order nonlinear optical properties of ZnO thin films deposited using self assembly, sol gel process as well as pulsed laser ablation by z scan technique. ZnO thin films clearly exhibit a negative nonlinear index of refraction at 532 nm and the observed nonlinear refraction is attributed to two photon absorption followed by free carrier absorption. Although the absolute nonlinear values for these films are comparable, there is a change in the sign of the absorptive nonlinearity of the films. The films developed by dip coating and pulsed laser ablation exhibit reverse saturable absorption whereas the self assembled film exhibits saturable absorption. These different nonlinear characteristics in the self assembled films can be mainly attributed to the saturation of linear absorption of the ZnO defect states.