Browsing by Author "Kim, JH"

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Bright red-emitting electrophosphorescent device using osmium complex as a triplet emitter
(2003-07-28)
Kim, JH
;
Liu, MS
;
Jen, AKY
;
Carlson, B
;
Dalton, LR
A series of efficient and bright double-layer light-emitting devices have been fabricated using the osmium (Os) complex as the triplet emissive dopant in both a blue-emitting polyfluorene derivative (PF-TPA-OXD) containing hole-transporting triphenylamine (TPA) and electron-transporting oxadiazole (OXD) as side chains and a blend of 2-(4-t-butylphenyl)-5(4-biphenylyl)-1,3,4-oxadizole (PBD) in poly(N-vinylcarbazole) (PVK). Due to a balanced charge injection and transport in PF-TPA-OXD and very efficient energy transfer from this polymer to the Os complex, the resulting device (indium tin oxide/HTL/OsCF3:PF-TPA-OXD/Ca/Ag) reaches a maximum external quantum efficiency of 2.1% with a peak brightness of 2920 cd/m(2). These results are significantly higher than those obtained from the commonly used host, PVK:PBD (0.49% and 1270 cd/m(2)). (C) 2003 American Institute of Physics.
Bright white light electroluminescent devices based on a dye-dispersed polyfluorene derivative
(2004-08-16)
Kim, JH
;
Herguth, P
;
Kang, MS
;
Jen, AKY
;
Tseng, YH
A series of efficient and bright white light-emitting diodes were fabricated using the blends of two fluorene-derived fluorescent dyes, (4,7-bis-(9,9,9('),9(')-tetrahexyl-9H,9(')H-[2,2(')]bifluoren-7-yl)-benzo[1,2,5]thiadiazole) (FFBFF-emits green) and (4,7-bis-[5-(9,9-dihexyl-9H-fluoren-2-yl)-thiophen-2-yl]-benzo[1,2,5]thiadiazole) (FTBTF-emits red) in an efficient blue-emitting polyfluorene-derived copolymer (poly[(9,9-bis(4-di(4-n-butylphenyl)aminophenyl))]-stat-(9,9-bis(4-(5-(4-tert-butylphenyl)-2-oxadiazolyl)-phenyl))-stat-(9,9-di-n-octyl)fluorene) (PF-TPA-OXD). The resulting white light-emitting device reaches a maximum external quantum efficiency of 0.82% and a maximum brightness of 12 900 cd/m(2) at 12 V. The Commission Internationale d'Enclairage chromaticity coordinates of the device remain very close to that of pure white emission at a relatively broad bias range from 6 V (x=0.36, y=0.37) to 12 V (x=0.34, y=0.34). (C) 2004 American Institute of Physics.
Highly efficient electrophosphorescent devices with saturated red emission from a neutral osmium complex
(2005-06-28)
Niu, YH
;
Tung, YL
;
Chi, Y
;
Shu, CF
;
Kim, JH
Highly efficient electrophosphorescent polymer light-emitting diodes (LEDs) with saturated red emission (Commission Internationale de L'Eclairage chromaticity coordinates exactly at x = 0.67, y = 0.33) are achieved by blending a novel neutral Osmium complex into a single-component bipolar polymer host that possesses balanced hole- and electron-transporting ability. By using a tetraphenylenebiphenyldiamine (TPD)-based cross-linkable hole-transport layer as well as a layer of 1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBI) as an electron-tran sport layer, a device structure with both effective hole/electron injection and efficient carriers/excitons blocking or confinement at both electrode sides is constituted. In this way, external quantum efficiency 12.8% is reached the first time with an organometallic complex with heavy metal core other than iridium.
On multirate rearrangeable Clos networks
(1998-08-04)
Du, DZ
;
Gao, B
;
Hwang, FK
;
Kim, JH
;
應用數學系
In the multirate switching environment each (connection) request is associated with a bandwidth weight. We consider a three-stage Clos network and assume that each link has a capacity of one (after normalization). The network is rearrangeable if for all possible sets of requests such that each input and output link generates a total weight not exceeding one, there always exists a set of paths, one for each request, such that the sum of weights of all paths going through a link does not exceed the link capacity. The question is to determine the minimum number of center switches which guarantees rearrangeability. We obtain a lower bound of 11n/9 and an upper bound of 41n/16. We then extend the result for the three-stage Clos network to the multistage Clos network. Finally, we propose the weighted version of the edge-coloring problem, which somehow has escaped the literature, associated with our switching network problem.