Dianyuan Wang

Tunable Plasmonic Dispersion and Strong Coupling in Graphene Ribbon and Double Layer Sheets Structure

Based on the interplay between propagating surface plasmon polaritons (PSPs) in graphene ribbon and double layer sheets structure, we theoretically demonstrate a tunable strong coupling mechanism significantly different from reported conventional noble metal nanostructures. The strong electromagnetic coupling between the low order antisymmetric and high order symmetric PSPs modes occurs due to the intersections of dispersion curves, which leads to a modification of plasmonic dispersion and multiple significant anti-crossing regions. Of particular, this strong coupling is controllable through external gate voltage of graphene sheets or ribbon. The results offer an effective regime to dynamically tune the interaction of graphene PSPs, which may find applications in the field of nanophotonic devices in the mid-infrared range.

Energy transfer upconversion in Er 3+ -doped and Er 3+ , Ho 3+ -codoped Cs 2 NaGdC1 6 crystals

Powder samples Cs2NaGdCl6:10%Er3+ and Cs2NaGdCl6:10%Er3+,20%Ho3+ investigated were prepared. Upconversion and down-conversion spectra from both Er3+ and Ho3+ ions was measured and investigated at room temperature under excitation into the 2H11/2 levels of Er3+ ions by using a 514.5 nm Ar+ laser. The observed emissions were all clearly assigned and analyzed according to the energy level diagrams of Ho3+ and Er3+ ions. It was concluded that many emissions with peaks at 423 nm (5G5 -> 5I8), 492 nm (5F3 -> 5I8), 587 nm (5G4 -> 5I6), 657 nm (5F5 -> 5I8) and 760 nm (5I4 -> 5I8) were all from Ho3+ ions, although Ho3+ ions cannot be excited by a ground-state-absorption (GSA). Therefore, all the emissions from Ho3+ ions were caused by multistep energy transfer from Er3+ to Ho3+ ions. And the 388 nm and 410 nm upconversion emissions were assigned to be 4G11/2->4I15/2 and 2H9/2->4I15/2 transitions of Er3+ ions, respectively. The possible upconversion mechanism for them was deduced to be excitation state absorption (ESA) and energy transfer (ET). In addition, the result that the slopes of 388nm and 410nm upconversion emissions of Er3+ ions were smaller in Er3+-doped than Er3+, Ho3+-codoped Cs2NaGdCl6 crystals was explained successfully.

Solution Growth of Two-Dimensional Bi2Se3 Nanosheets for Two-Color All-Optical Switching

Two-dimensional Bi2Se3 nanosheets with hexagonal shape are synthesized by a solution synthetic route. The Bi2Se3 nanosheets are 120 nm in edge width and 7 nm in thickness. The size of the Bi2Se3 nanosheets can be controlled by choosing different kinds of reducing agents including hydroxylamine and ethylenediamine. Subsequently, we demonstrate a configuration of two-color all-optical switching based on plasma channels effect using the as-synthesized Bi2Se3 nanosheets as an optical media. The signal light can be modulated as two states including dot and ring shape by changing the intensity of control light. The modulated signal light exhibits excellent spatial propagation properties. As a type of interesting optical material, ultrathin two-dimensional Bi2Se3 nanosheets might provide an effective option for photoelectric applications.

Microstructure and NIR to VIS upconversion luminescence of Y2O3:Er translucent ceramics

Y2O3:5%Er nanocrystalline powder was prepared by low temperature combustion method. The crystal structure and morphology were analyzed by means of XRD and HRTEM. The resultant powders were sintered into translucent ceramics at 1570°C in vacuum for 6 hours. The micrograph of unpolished surface and fracture surfaces showed that the sintered Y2O3:Er ceramics with average grain size at about 10μm had homogeneous micro-structure and low pore volume. Under the excitation of 980 nm, 808 nm and 785 nm diode lasers, respectively, very strong green and red upconversion emissions from Er3+ ions were observed, the power dependence of upconversion emission intensity was measured to deduce the upconversion mechanism. A trend of upconversion intensity increase first and then decrease with the excitation time was also found for the first time.

Upconversion fluorescence in LiKGdF5 single crystal co-doped with Er3+, Tb3+

The upconversion fluorescence was recorded at room temperature and investigated in LiKGdF5: 2%Er3+, 0.4%Tb3+ single crystal grown by the hydrothermal synthesis technique under 514.5 nm and 785 nm laser excitation, respectively. Under 514.5 nm laser excitation, four strong upconverted emission bands with peaks at 410 nm (violet), 470 nm, 486 nm and 492 nm (blue) were obtained. The former two emission bands were assigned to be corresponding to 2H9/2 -> 4I15/2 and 2P3/2 -> 4I11/2 transitions of Er3+ ions, and the latter two are possibly corresponding to 5D4 -> 7F6 of Tb3+ and 4F7/2 -> 4I15/2 of Er3+. The power dependence for 410 nm and 470 nm indicates that they arose from two-photon upconversion processes. While for 486 nm and 492 nm emission, the logarithmic slope is 0.98, which was explained by mutiphonon assisted upconversion process and energy transfer from 4F7/2 (Er3+) to 5D4 (Tb3+). Under 785 nm laser excitation, besides four weak upconverted emissions mentioned above, three strong emissions with peaks at 523 nm (2H11/2 -> 4I15/2), 550 nm ( 4S3/2 -> 4I15/2) and 660 nm (4F9/2 -> 4I15/2) were also observed. The possible upconversion mechanism for these seven emissions was all given with the help of the power dependence of upconversion emission intensity and the energy level diagram of Er3+ ions.