• Journal of the Korean Vacuum Society
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• v.15 no.1
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• pp.64-72
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• 2006

We demonstrated organic light-emitting devices (OLEDs) based on the organic thin-film materials such as tris-(8-hydroxyquinoline) aluminum $(Alq_3)$. The structure of OLEDs was vacuum deposited upon transparent and thin glass substrates pre-coated with a transparent, conducting indium tin oxide thin film. The luminance characteristics, current, capacitance, and dispersion factor for degraded OLEDs, which were made by various bias currents $(0.5mA\;{\leq}\;I_{Bias}\;{\leq}9mA)$, are studied. The current dependences of lifetime were divided at approximately 2mA, and they represented nearly linear behaviors but had different slopes in a logarithmic plot of lifetime versus bias current. With lighting OLEDs, the anomaly of capacitance, as shown in the CV curve, occurred because of two factors, polarization in the bulk of organic materials and the interface between the metal and organic layers. In decayed OLEDs that had lower bias currents of less than 2mA, it was found that the degradation of luminance was related to both the decrease of polarization and to the lowering of the injection barrier.

• Korean Journal of Materials Research
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• v.26 no.3
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• pp.117-122
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• 2016

White organic light-emitting diodes with a structure of indium-tin-oxide [ITO]/N,N-diphenyl-N,N-bis-[4-(phenylm-tolvlamino)-phenyl]-biphenyl-4,4-diamine [DNTPD]/[2,3-f:2, 2-h]quinoxaline-2,3,6,7,10,11-hexacarbonitrile [HATCN]/1,1-bis(di-4-poly-aminophenyl) cyclo -hexane [TAPC]/emission layers doped with three color dopants/4,7-diphenyl-1,10-phenanthroline [Bphen]/$Cs_2CO_3$/Al were fabricated and evaluated. In the emission layer [EML], N,N-dicarbazolyl-3,5-benzene [mCP] was used as a single host and bis(2-phenyl quinolinato)-acetylacetonate iridium(III) [Ir(pq)2acac]/fac-tris(2-phenylpyridinato) iridium(III) $[Ir(ppy)_3]$/iridium(III) bis[(4,6-di-fluoropheny)-pyridinato-N,C2] picolinate [FIrpic] were used as red/green/blue dopants, respectively. The fabricated devices were divided into five types (D1, D2, D3, D4, D5) according to the structure of the emission layer. The electroluminescence spectra showed three peak emissions at the wavelengths of blue (472~473 nm), green (495~500 nm), and red (589~595 nm). Among the fabricated devices, the device of D1 doped in a mixed fashion with a single emission layer showed the highest values of luminance and quantum efficiency at the given voltage. However, the emission color of D1 was not pure white but orange, with Commission Internationale de L'Eclairage [CIE] coordinates of (x = 0.41~0.45, y = 0.41) depending on the applied voltages. On the other hand, device D5, with a double emission layer of $mCP:[Ir(pq)_2acac(3%)+Ir(ppy)_3(0.5%)]$/mCP:[FIrpic(10%)], showed a nearly pure white color with CIE coordinates of (x = 0.34~0.35, y = 0.35~0.37) under applied voltage in the range of 6~10 V. The luminance and quantum efficiency of D5 were $17,160cd/m^2$ and 3.8% at 10 V, respectively.

• Nuclear Medicine and Molecular Imaging
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• v.42 no.6
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• pp.469-477
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• 2008

Purpose: The goal of this paper is to present the design and performance of a position encoding circuit for $16{\times}16$ array of position sensitive multi-anode photomultiplier tube for small animal PET scanners. This circuit which reduces the number of readout channels from 256 to 4 channels is based on a charge division method utilizing a resistor array. Materials and Methods: The position encoding circuit was simulated with PSpice before fabrication. The position encoding circuit reads out the signals from H9500 flat panel PMTs (Hamamatsu Photonics K.K., Japan) on which $1.5{\times}1.5{\times}7.0\;mm^3$ $L_{0.9}GSO$ ($Lu_{1.8}Gd_{0.2}SiO_{5}:Ce$) crystals were mounted. For coincidence detection, two different PET modules were used. One PET module consisted of a $29{\times}29\;L_{0.9}GSO$ crystal layer, and the other PET module two $28{\times}28$ and $29{\times}29\;L_{0.9}GSO$ crystal layers which have relative offsets by half a crystal pitch in x- and y-directions. The crystal mapping algorithm was also developed to identify crystals. Results: Each crystal was clearly visible in flood images. The crystal identification capability was enhanced further by changing the values of resistors near the edge of the resistor array. Energy resolutions of individual crystal were about 11.6%(SD 1.6). The flood images were segmented well with the proposed crystal mapping algorithm. Conclusion: The position encoding circuit resulted in a clear separation of crystals and sufficient energy resolutions with H9500 flat-panel PMT and $L_{0.9}GSO$ crystals. This circuit is good enough for use in small animal PET scanners.