No abstract

The optical properties of zinc (hydr)oxide and its porous composites with 2% and 5% graphite oxide (GO), thus forming ZnGO-2 and ZnGO-5, are investigated using reflectance spectroscopy and two-photon fluorescence (TPF) imaging. The bandgap energies for the Zn(OH)(2), ZnGO-2, and ZnGO-5 samples are determined to be in the range between 2.88 and 3.60 eV. The size of light-emitting regions (~from 4.5 to 45 μm) and pore size (~from 20 to 255 μm) are measured using the TPF imaging technique.

The band gap energies of micro/meso-porous zinc (hydr)oxide and its composites with 2 wt. % and 5 wt. % graphite oxides are reported using three optical characterization techniques. The obtained energy gaps (from 2.84 eV to 2.95 eV) of the composites are smaller than that for zinc oxide (∼3.2 eV) and zinc (hydr)oxide (∼3.06 eV). The band gap narrowing of the composite materials is due to the presence of defects, larger particle size, and weaker confinement. The bonds between zinc (hydr)oxide lattice and the carbon of graphene phase also contribute to this phenomenon. The structural properties of these materials are presented using Transmission Electron Microscopy, Scanning Tunneling Electron Microscopy, X-Ray analysis, and Two-Photon Fluorescence imaging Microscopy.

A Hamiltonian model for a molecular segment or molecular chain with phonon or vibrational coupling is introduced which admits analytic solutions. A time correlation function Q(t) for the average position of an electron inserted at the end of a chain with a thermal average of the phonons is defined. A prominent feature of the dynamics is that the phonons drive the electron density to decay to a steady-state distribution along the chain. We demonstrate that two imaging methods based on the time derivatives of Q(t) at zero time are capable of producing the average velocity of the electron along the chain using a reasonable number of the time derivatives. We further show that this average velocity increases as the coupling to the phonons is increased and as the temperature is increased; that is, the decay to a steady state is enhanced in both cases.

Time-resolved photoluminescence is used to determine carrier recombination through radiative and nonradiative processes in zinc hydroxide Zn(OH)(2) and its porous composites with graphite oxide (GO). The decay times, measured by a streak camera, are found to be larger for zinc hydroxide (~1215±156 ps) than its composites (~976±81 ps for ZnGO-2 and 742±59 ps for ZnGO-5), but no significant changes in rise times (from 4.0 to 5.0 ps) are recorded. The dominant mechanism for the radiative process is attributed to free carrier recombination, while microporous networks present in these materials are found to be pathways for the nonradiative recombination process via multiphonon emission.