Narrow Results

Carrier transport and trapping was investigated in poly[2-methoxy-5-(3′,7′-dimethyloctyloxy)-1,4-phenylenevinylene] (MDMO-PPV) layers by thermally stimulated currents (TSC) depending on the exciting light spectral range. The upper edge of the light spectra was varied from 1.77 eV up to 3.1 eV to assure selective excitation of the defect states. We had shown that material conductivity is affected by several thermally activated processes, i.e., carrier generation from trapping states and thermally stimulated mobility growth. If the below band gap excitation was used, the effective photoconductivity activation energy values of 0.13–0.15 eV were obtained. After the above band gap excitation, the effective photoconductivity activation energy values decreased to 0.05 eV. The energy distribution of the trapping state density was shown to follow the Gaussian distribution function. The deeper states with activation energies of 0.28–0.3 eV and 0.8–0.85 eV were identified too. The results are direct indication by photo-thermo-electrical methods of distributed in energy trapping and transport states with the standard deviation of the density of states of about 0.015 eV.

ZnO nanopillars with the strong violet photoluminescence were fabricated via the vapor-phase transport method. The annealing effect on photoluminescence property was probed to indicate the defect-origins of visible emissions and their thermodynamic stabilities. Moreover, the electron structures of ZnO with zinc interstitial, oxygen vacancy and oxygen interstitial were calculated based on the density functional theory. Three important points were demonstrated: zinc interstitial as an instable donor determines the violet emission and the concentration of free carriers; oxygen vacancy as a steady donor is responsible for the green emission; and oxygen interstitial may induce the yellow-green emission and lead to the red-shift and asymmetry of photoluminescence spectra. These results are beneficial to understand the defect-origins of the visible emissions and their stabilities in ZnO nanostructures, and extending optical and electronic applications.

BaAl₂O₄:Eu²⁺, Dy³⁺ phosphors with a good long lasting property can be easily obtained via a solid state reaction assisted with Li₂CO₃. The influence of Li₂CO₃ quantity on the lattice structure of BaAl₂O₄:Eu²⁺, Dy³⁺ phosphors, their photoluminescence (PL) property, and decaying process was studied by XRD, PL, and afterglow decay measurement, respectively. The results show that incorporating Li₂CO₃ in preparing process would obviously affect their lattice structure, accompanied by the variation of their luminescent property. With the increase of Li₂CO₃, their fluorescence property would gradually increase, at $m=0.04$ (${Ba}_{0.96}{Al}_2{O}_4:{\mathrm{\text{Eu}}}_{0.01}^{2+},{\mathrm{\text{Dy}}}_{0.03}^{3+}\cdot m{\mathrm{\text{Li}}}_2{\mathrm{\text{CO}}}_3)$ reach their maximum emission intensity, and then decrease; but their phosphorescence property would continue to strengthen whether in brightness and decaying time up to $m=0.07$, and then decrease.

A molecular structural mechanics method has been implemented to investigate the vibrational characteristics of single-layer graphene (SLG) with defects. By adopting the lumped mass unit to replace carbon atoms, and the beam element with circular cross-section to mimic C–C covalent bonds, SLG is modeled as a space framework. The simulation results show that the chirality almost has no effect on the natural frequency and the vibration mode of SLG, while boundary conditions have great influences. The influences of defects with different number and location on the natural frequencies are also studied. It is concluded that vibration mode is insensitive to the vacancy defect, small hole and short flaw, but large holes and long flaws can affect the vibration characteristics. So the graphene sheet even with small defect effects might be selected as the nanosensor material as well as pristine graphene. The conclusions in this paper may provide some references for the design of nanosensor.