Transmission of TE-polarized light through metallic nanoslit arrays assisted by a quasi surface wave

Optically thick metallic nanoslit arrays are opaque to TE-polarized light, in contrast to enhanced transmission of TM-polarized light. Here, we numerically show that, by introducing an ultrathin high-index dielectric coating on the metal surfaces, a quasi surface wave can be excited at the metasurfaces to enhance the transmission of TE-polarized light. The quasi surface wave is shown to behave like surface plasmon waves, and enhance the transmission in similar mechanisms as surface plasmon waves do for TM-polarized light. In this work, we suggest a way of manipulating TE-polarized light in metallic subwavelength structures. ? 2014 The Japan Society of Applied Physics

Opposite size dependences of the red/green upconversion intensity ratio in sub-20 nm Yb

Upconversion nanophosphors (UCNPs) of lanthanide-doped efficient ternary fluoride (β-NaGdF4:Yb3+,Er3+) with sizes below 20 nm are synthesized in a facile solvothermal route. Upconversion luminescence (UCL) of the UCNPs is found to increase with increase of the nanoparticle size prepared at a higher solvothermal-treatment temperature, due to reduction of the surface defects. Interestingly, opposite size dependences of the red/green UCL intensity ratio are observed for the same series of UCNPs in different surface conditions, i.e., with increase of the nanoparticle size, the ratio decreases for as-prepared dry powders, but increases for moisturized counterparts after being exposed in air for some days, and interesting the ratio decreases again after annealing of the moisturized samples. The phenomenon is explained due to the effect of surface defects and adsorbed water molecules, respectively, dominating in nonradiative relaxations, which usually facilitate red UCL. The disclosed phenomenon clarifies some contradictory observations on UCL in the literature

Artificial TE-mode surface waves at metal surfaces mimicking surface plasmons

National Natural Science Foundation of China [61275063]; Natural Science Foundation of Fujian Province of China [2011J06002]; National Key Scientific Program [2012CB933503]; Fundamental Research Funds for the Central Universities [2012121009]Manipulation of light in subwavelength scale can be realized with metallic nanostructures for TM-polarization components due to excitation of surface plasmons. TE-polarization components of light are usually excluded in subwavelength metal structures for mesoscopic optical interactions. Here we show that, by introducing very thin high index dielectric layers on structured metal surfaces, pseudo surface polarization currents can be induced near metal surfaces, which bring to excitation of artificial TE-mode surface waves at the composite meta-surfaces. This provides us a way to manipulate TE-polarized light in subwavelength scale. Typical properties of the artificial surface waves are further demonstrate for their excitation, propagation, optical transmission, and enhancement and resonances of the localized fields, mimicking those of surface plasmon waves. (C) 2014 Optical Society of Americ

Opposite size dependences of the red/green upconversion intensity ratio in sub-20 nm Yb3+, Er3+-doped beta-NaGdF4 nanophosphors

National Natural Science Foundation of China [61275063, 61205051]; National Key Scientific Program [2012CB933503]; Fundamental Research Funds for the Central Universities [2012121009]Upconversion nanophosphors (UCNPs) of lanthanide-doped efficient ternary fluoride (beta-NaGdF4: Yb3+, Er3+) with sizes below 20 nm are synthesized in a facile solvothermal route. Upconversion luminescence (UCL) of the UCNPs is found to increase with increase of the nanoparticle size prepared at a higher solvothermal-treatment temperature, due to reduction of the surface defects. Interestingly, opposite size dependences of the red/green UCL intensity ratio are observed for the same series of UCNPs in different surface conditions, i.e., with increase of the nanoparticle size, the ratio decreases for as-prepared dry powders, but increases for moisturized counterparts after being exposed in air for some days, and interesting the ratio decreases again after annealing of the moisturized samples. The phenomenon is explained due to the effect of surface defects and adsorbed water molecules, respectively, dominating in nonradiative relaxations, which usually facilitate red UCL. The disclosed phenomenon clarifies some contradictory observations on UCL in the literature. Copyright (C) EPLA, 201