Kyu-Wang Lee

Coplanar ac discharges between cylindrical electrodes with a nanoporous alumina dielectric: Modular dielectric barrier plasma devices

Dielectric barrier discharges between coplanar Al rods having an /spl sim/2-/spl mu/m-thick layer of nanoporous alumina dielectric at the surface have been investigated. Rods 3 mm in diameter, 7 cm in length, and spaced by 5 mm produce stable and intense glow discharges in 50 torr of Ne when pairs of rods are driven by an alternating current (bipolar) waveform for which the peak voltage is /spl sim/460-510 V.

Microcavity device of PPV dimer based copolymer

Abstract PPV dimer based copolymers were synthesized to investigate their applicability to the microcavity device. The blue emitting copolymers consist of strictly alternating conjugated PPV dimer unit and non-conjugated alkyl group. Two microcavity devices based on distributed Bragg reflector (DBR) and the spin-coated copolymer thin film show promising lasing characteristics. The gain narrowed blue emissions at 374.5 and 428.5 nm with 3.0–4.2 nm linewidth were obtained and those are the lowest wavelength among the devices based on PPV derivatives. N 2 laser (337 nm) was used as a pulsed pump source and their lasing thresholds were around 0.3–1 microjoules. The lasing characteristics strongly depended on the microcavity structure and the copolymer film processing. Q factor of each devices were calculated to be 120 and 102, respectively. The stability of the copolymer under UV excitation was excellent that the devices have the operational lifetime of over 3×10 5 pulses at 10 μJ.

Ligand field properties of histidine on the sharp-line excitation spectrum of trans(imidazole)-bis(L-histidinato-O,N,N′)chromium(III) nitrate

Abstract Ligand field calculations have been performd based on the data from the absorption and low temperature sharp-line excitation spectra of trans(imidazole)-[Cr(L-his)2]NO3. The angular overlap parameters determined for imidazole nitrogen are 6233 cm−1 for eσNim and −549 cm−1 for eπNim. This indicates that the imidazole nitrogen is a weak σ-donor and its π-interaction can be interpreted by back-donation to the electron withdrawing empty molecular orbitals on the imidazole nitrogen.

Syntheses and optical characterization of poly[1,8–octanedioxy–1,4–phenylene–1,2–ethylene–1,4–phenylene] and its copolymer derivatives

Abstract We have investigated the optical properties of a series of poly( p -phenylene vinylene) (PPV) copolymers. Three-wide bandgap PPV copolymers were synthesized and characterized. The new PPV copolymers showed a large blue shift in both absorption and emission that their average bandgap is over 3.1 eV. A significant solvatochromic effect was observed in the photoluminescence (PL) spectra of copolymers. The dimethoxy-substituted copolymer showed the highest quantum efficiency and processability among three copolymers.

24.3: Improvement of Luminous Efficiency in AC PDP with Nano‐porous Al2O3 as Protecting Layer

Nano-porous Al2O3 thin film prepared by electrochemical anodization was formed on the dielectric layer as protecting layer in an AC PDP. The AC PDP adopting nano-porous Al2O3 as a protecting layer showed the reduced discharge current and the better luminance characteristics compared to the conventional AC PDP with MgO. The luminous efficiency of the AC PDP with nano-porous Al2O3 was 1.9 times as much as that of conventional PDP with MgO. The static sustain margin of the AC PDP with nano-porous Al2O3 was about 100 V at 600 torr and 70 V at 62.5 KHz.

Optical properties of luminescent PPV copolymers

Abstract Copolymers derived from poly(p-phenylenevinylene) PPV were synthesized and their optical properties are studied for lasing applications. Poly(octanedioxy-co-PPV) and methoxy group substituted derivatives consist of emitting conjugated polymer unit and non-conjugated alkyl chain. Methoxy substitutions to the phenyl ring increases the degree of alignments and orientation of the polymer chain, while its electronic effect is appeared to be small. The dMPPV copolymer is highly oriented and the molecular character of PPV unit is preserved and well isolated in copolymer. Microcavity device based on dMPPV copolymer exhibits excellent lasing characteristics and durability.

Blue lasing in poly(octanedioxy-co-DMPPV) copolymer microcavity

Abstract Poly[octanedioxy-co-DMPPV] copolymer was synthesized to fabricate the microcavity device. The blue emitting polymers consist of strictly alternating conjugated PPV and non-conjugated alkyl group. The microcavity based on distributed Bragg reflector (DBR) and the spin-coated copolymer thin film shows promising lasing characteristics. A strong blue emission at 437.9 nm with 6.5 nm line width was due to cavity enhancement and large gain from the copolymer layer. Third harmonic of Nd:YAG laser(355 nm) was used as a pulsed pump source and its energy threshold for lasing was around few microjoules per pulse. The lasing characteristics strongly depended on the microcavity structure and copolymer film processing. Q factor was calculated to be 67 and the operational lifetime of over 7×105 pulses was observed.

Site selective electronic spectroscopy and ligand field analysis of sodium cis-bis(iminodiacetato) chromate(III)

Abstract The five components of the 2 E g and 2 T 1g (O h ) states have been identified from the site selective low temperature excitation spectrum of Na[Cr(IDA) 2 ] · 1.5H 2 O. A ligand field analysis in the framework of the angular overlap model was performed to fit the unusually large (∼ 2000 cm −1 ) overall doublet splitting of this complex. Accounting for the effects of anisotropic π-bonding and the anisotropy in the interelectronic repulsion term as judged essential. The ligand field strength of the nitrogens is smaller than it is in amine complexes, because of inductive electron donation from the amino to the acetate group. The previously reported fluorescence emission did not occur in this complex, and only phosphorescence was observed in the solution luminescence spectrum. The photophysical properties, focused on the emission behavior, are discussed.

Nanoporous plasma electrodes for flat lamp

Summary form only given, as follows. The dielectrics having nanoporous structure have been well known for decades in the nanotechnologies, and recently, various applications are introduced using these dielectrics. We have developed the flat panel lamp using these nano-porous dielectrics as the DBD (dielectric barrier discharge) electrodes.