Using light to exchange information offers large bandwidths and high speeds, but the miniaturization of optical components is limited by diffraction. Converting light into electron waves in metals allows one to overcome this problem. However, metals are lossy at optical frequencies and large-area fabrication of nanometer-sized structures by conventional top-down methods can be cost-prohibitive. We show electromagnetic energy transport with gold nanoparticles that were assembled into close-packed linear chains. The small interparticle distances enabled strong electromagnetic coupling causing the formation of low-loss subradiant plasmons, which facilitated energy propagation over many micrometers. Electrodynamic calculations confirmed the dark nature of the propagating mode and showed that disorder in the nanoparticle arrangement enhances energy transport, demonstrating the viability of using bottom-up nanoparticle assemblies for ultracompact opto-electronic devices.
We demonstrated the synthesis of LaPO 4 :Er:Yb-doped nanoparticles/nanorods and LaPO 4 :Er@Yb core-shell nanoparticles/nanorods by a solution-based technique. The mechanism related to morphology control of LaPO 4 : Er:Yb nanorods/nanoparticles is proposed and discussed. Bright-green (550 nm) and red (670 nm) emission were observed due to the transitions 2 H 11/2 + 4 S 3/2 f 4 I 15/2 and 4 F 9/2 f 4 I 15/2 , respectively. The experimental data for 550-and 670-nm emission bands of doped nanoparticle/nanorod and core-shell nanoparticles/nanorods have been fit with a straight line with a slope of ∼2, which confirms the two-photon absorption process. The enhancement of upconversion emission of LaPO 4 :Er:Yb-doped nanoparticles and LaPO 4 :Er@Yb core-shell nanoparticles/nanorods are mainly due to modifications of surface-related effects. It is found that the tensile strain increases from +1.0% to +1.9% with changing the shape from nanoparticle to nanorod and reversal of the lattice strain (compressive) is obtained for coated nanoparticle/ nanorod. It is worth mentioning that the lattice strain varies with changing the shape and surface coating on nanocrystals and the upconversion emission intensity increases with decreasing the tensile lattice strain and it increases with increasing compressive strain. Analysis suggests that the lattice strain plays an important role in modification of the upconversion properties of the rare-earth-doped nanocrystals.
Bleach Imaged Plasmon Propagation (BliPP) in Single Gold Nanowires by David SolisHere, we present a novel approach to visualize propagating surface plasmon polaritons through plasmon-exciton interactions between single gold nanowires and a thin film of a fluorescent polymer. A plasmon polariton was launched by exciting one end of a single gold nanowire with a 532 nm laser. The local near-field of the propagating plasmon modes caused bleaching of the polymer emission. The degree of photobleaching along the nanowire could be correlated with the propagation distance of the surface plasmon polaritons. Using this method of bleach-imaged plasmon propagation (BliPP), we determined a plasmon propagation distance of 1.8 ± 0.4 !lm at 532 nm for chemically grown gold nanowires. Our results are supported by finite difference time domain electromagnetic simulations.ACKNOWLEDGEMENT
A comprehensive understanding of the type of modes and their propagation length for surface plasmon polaritons (SPPs) in gold nanowires is essential for potential applications of these materials as nanoscale optical waveguides. We have studied chemically synthesized single gold nanowires by a novel technique called bleach-imaged plasmon propagation (BlIPP), which relies on the plasmonic near-field induced photobleaching of a dye to report the SPP propagation in nanowires. We observed a much longer propagation length of 7.5 ± 2.0 μm at 785 nm compared to earlier reports, which found propagation lengths of ~2.5 μm. Finite difference time domain simulations revealed that the bleach-imaged SPP is a higher order m = 1 mode and that the lowest order m = 0 mode is strongly quenched due to the loss to the dye layer and cannot be resolved by BlIPP. A comparative assessment of BlIPP with direct fluorescence imaging furthermore showed that the significant difference in propagation lengths obtained by these two techniques can be attributed to the difference in their experimental conditions, especially to the difference in thickness of the dye layer coating on the nanowire. In addition to identifying a higher order SPP mode with long propagation length, our study infers that caution must be taken in selecting indirect measurement techniques for probing SPP propagation in nanoscale metallic waveguides.
Strong green and red visible emissions were obtained from ZrO2:Yb3+–Er3+ nanocrystals synthesized by sol-gel method and annealed at 1000 °C for 5 h. The average crystallite size was ∼70 nm with tetragonal phase for total concentration lower than 3 mol % and cubic phase for concentration higher than 5 mol %. The color coordinate of the upconverted signal was tailored by controlling the dopant composition that change the red/green ratio dominated by the cross relaxation and energy back transfer process as was demonstrated theoretically and confirmed experimentally. Both coefficients were calculated, C51∼1.02×10−16 and C5b∼6.04×10−17, from the theoretical model based on the rate equations. The highest energy transfer efficiency was η∼64% for 2 mol % of Yb and 2 mol % of Er3+. However, for the highest upconverted signal was only η∼29% obtained for 2 mol % Yb and 1 mol % Er with effective decay time τeff∼438 μs for red and τeff∼290 μs for green band.
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