Hyong Sik Won

Luminescent Properties of Ca-α-SiAlON : Eu2 + Phosphors Synthesized by Gas-Pressured Sintering

Rare-earth-doped oxynitride or nitride compounds have been reported to be photoluminescent and may then serve as new phosphors with good thermal and chemical stabilities. In this work, Ca-α-SiAlON:Eu 2+ based yellow and orange oxynitride phosphors with compositions of Ca 0.485 Eu 0.015 Si 9.2 Al 2.8 O 1.8 N 14.2 and Ca 0.94 Eu 0.06 Si 9 Al 3 ON 15 were prepared using the gas-pressured sintering method. The crystallinity and particle morphology of the prepared phosphors were characterized. The temperature dependence of photoluminescence properties was investigated from 25 to 150°C. The Stokes shift and zero-phonon line was calculated mathematically and estimated from the spectral data. The prepared Ca-α-SiAlON:Eu 2+ phosphors showed superior thermal quenching properties compared to commercially used YAG:Ce 3+ phosphors. In addition, the activation energies (ΔE) for thermal quenching of the prepared Ca-α-SiAlON:Eu 2+ phosphors were determined by Arrhenius fitting.

Metallic nanocluster gratings generated by near-field coupling of localized surface plasmons

Metallic nanocluster gratings composed of a 3-dimensionally periodic distribution of silver nanoparticles are successfully formed in a dielectric. A periodic arrangement of silver nanoclusters are created by holographic interference of two continuous-wave laser beams in a glass medium with embedded ~10 nm silver nanoparticles. The diffraction efficiency is much higher for the nanocluster gratings formed by TE-polarized (parallel to grating fringes) beams than those formed by TM-polarized beams. This strong polarization dependence in the formation of nanocluster gratings reveals that strong near-field coupling between localized surface plasmons excited at the metallic nanoparticles is one of the dominant mechanisms governing the rearrangement of the silver nanoparticles. The nonlinear response of metallic nanoparticles is greatly enhanced when the incident light is polarized along the lines of the silver nanoparticles.

Polymeric variable optical attenuator based on surface plasmon polariton

We propose a polymeric variable optical attenuator based on long range surface plasmon polaritons (LRSPPs) along a thin metal stripe embedded in polymers. The device is operated by controlling radiation loss of the LRSPP mode resulting from the temperature gradient of the polymer cladding caused by a heater. For guiding LRSPPs and efficient coupling of single mode fibers, gold stripes with 20-nm thickness, 4-μm width and 1-cm length are utilized. To obtain long physical lifetime, the heater is formed on the top of the polymer cladding with a 200-nm Au film which is about ten times thicker than the thin metal waveguide. The fabricated device is characterized at a wavelength of 1.55 μm, exhibiting high attenuation of less than 30 dB with the operating power of 100 mW. The fiber-to-fiber total insertion loss of 6.1 dB is achieved when using single mode fibers.