Browsing by Author "Cheng, JA"

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Enhanced phosphorescence and electroluminescence in triplet emitters by doping gold into cadmium selenide/zinc sulfide nanoparticles
(2005-10-01)
Liu, HW
;
Laskar, IR
;
Huang, CP
;
Cheng, JA
;
Cheng, SS
Gold-cadmium selenide/zinc sulfide (Au-CdSe/ZnS) nanocomposites (NCs) were synthesized and characterized by transmission electron microscopy (TEM), energy dispersive X-ray (EDX) analysis, ultraviolet-visible (UV-visible) absorption and photoluminescence (PL) emission spectroscopy. The PL intensity in the Au-CdSe/ZnS NCs system was found to be much greater than that of CdSe/ZnS nanoparticles (NPs) alone, because of the surface-enhanced Raman scattering of An NPs. Adding Au-CdSe/ZnS NCs to the cyclometalated iridium(Ill) complex (Ir-complex) greatly enhanced the PL intensity of a triplet emitter. Three double-layered electroluminescence (EL) devices were fabricated where the emitting zone contains the definite mixture of Ir-complex and the NCs [molar concentration of Ir-complex/NCs = 1:0 (Blank, D-1), 1: 1 (D-2) and 1:3 (D-3)] and the device D-2 exhibited optimal EL performances. (c) 2005 Elsevier B.V. All rights reserved.
Observing enhanced phosphorescence and electroluminescence from triplet emitter by quantum dot doping
(2005)
Laskar, IR
;
Liu, HW
;
Huang, CP
;
Cheng, JA
;
Chen, TM
Luminescent CdSe/ZnS core-shell-type quantum dots (QDs) were synthesized by chemical colloidal methods. The photoluminescence (PL) intensity of a triplet emitter [bis(4-trifluoromethyl)-2-phenylbenzothiazolatoacetylacetonate-iridium(III) (Ir complex 1) and bis(4-methyl)-2-phenylbenzothiazolatoacetylacetonate-iridium(III) (Ir-complex 2)] was dramatically enhanced when bluish-green emitting CdSe/ZnS QDs were incorporated into these compounds. Experimental results indicate that the emissive region of QDs substantially overlaps with the low-energy absorption bands of Ir-complexes, indicating that the photons were absorbed by both the QDs and the Ir-complexes and that the energy absorbed by the QDs was transferred efficiently to the Ir-complex triplet emitter, resulting in the observed enhancement of PL intensity. A slow quenching of QDs emission was observed in a prepared set of solutions with gradual increasing of Ir complex concentration at a fixed QDs concentration in thin film PMMA matrix, which supports the energy transfer from Ir complex to QDs. In the fabricated double-layer electroluminescent (EL) devices, the emitting layer contained either only Ir-complex or a mixture of Ir-complex and CdSe/ZnS QDs with a specific molar ratio [Ir-complex/QDs = 1/0 (D-I); 1/0.5 (D-II),..., 1/10 (D-V)]. The EL intensity and the luminance efficiency for D-II were higher (luminescence yield = 19.3cd A(-1)) than those of the other devices. The PL and EL enhancement of the triplet emitter were also strongly supported by using ZnSe QDs rather than CdSe/ZnS QDs.
Observing enhanced phosphorescence and electroluminescence from triplet emitter by quantum dot doping
(2005-01-01)
Laskar, IR
;
Liu, HW
;
Huang, CP
;
Cheng, JA
;
Chen, TM
Luminescent CdSe/ZnS core-shell-type quantum dots (QDs) were synthesized by chemical colloidal methods. The photoluminescence (PL) intensity of a triplet emitter [bis(4-trifluoromethyl)-2-phenylbenzothiazolatoacetylacetonate-iridium(III) (Ir complex 1) and bis(4-methyl)-2-phenylbenzothiazolatoacetylacetonate-iridium(III) (Ir-complex 2)] was dramatically enhanced when bluish-green emitting CdSe/ZnS QDs were incorporated into these compounds. Experimental results indicate that the emissive region of QDs substantially overlaps with the low-energy absorption bands of Ir-complexes, indicating that the photons were absorbed by both the QDs and the Ir-complexes and that the energy absorbed by the QDs was transferred efficiently to the Ir-complex triplet emitter, resulting in the observed enhancement of PL intensity. A slow quenching of QDs emission was observed in a prepared set of solutions with gradual increasing of Ir complex concentration at a fixed QDs concentration in thin film PMMA matrix, which supports the energy transfer from Ir complex to QDs. In the fabricated double-layer electroluminescent (EL) devices, the emitting layer contained either only Ir-complex or a mixture of Ir-complex and CdSe/ZnS QDs with a specific molar ratio [Ir-complex/QDs = 1/0 (D-I); 1/0.5 (D-II),..., 1/10 (D-V)]. The EL intensity and the luminance efficiency for D-II were higher (luminescence yield = 19.3cd A(-1)) than those of the other devices. The PL and EL enhancement of the triplet emitter were also strongly supported by using ZnSe QDs rather than CdSe/ZnS QDs.
Solution-processible small molecular organic light-emitting diode material and devices based on the substituted aluminum quinolate
(2004-07-27)
Cheng, JA
;
Chen, CH
;
Liao, CH
;
友訊交大聯合研發中心
;
D Link NCTU Joint Res Ctr
We have discovered a new type of small molecular host material based on aluminum(III) 8-hydroxyquinolates, Al(Saq)(3), which was synthesized with three 5-(N-ethylanilinesulfonamide)-8-quinolinoline as bidentate ligands. By X-ray diffraction crystallographic analysis, the crystals of meridional Al(Saq)(3) are monoclinic, space group P2(1)/c, a = 17.952(3) Angstrom, b = 17.7160 Angstrom, c = 17.080(3) Angstrom, beta = 99.895(4)degrees. Its peak photoluminescence in solid phase appears at 488 nm. Its LUMO/HOMO (-3.13/-6.04 eV) and optical band gap (E-g 2.91 eV) were determined by cyclic voltammetry. In solid thin film morphological investigation, it shows good thermal properties and high quantum efficiency. When doped with 0.7 wt % of the high fluorescent green dopant 10-(2-benzothiazolyl)-1,1,7,7-tetramethyl-2,3,6,7-tetrahydro-1H,5H,11H-benzo-[l]pyrano[6,7,8-ij]quinolizin-11-one (C-545T), energy transfer from Al-(Saq)(3) to dopant will occur and high green light emission can be achieved. For fabrication of OLEDs using spin-coating techniques, its electroluminescence is at 1931 CIEx,y (0.21, 0.41).
The fluorescent quantum efficiency of copolymers containing coumarin-6 at the side-chain
(2005-02-01)
Cheng, JA
;
Chang, CP
;
Chen, CH
;
Lin, MS
;
應用化學系
Coumarin-6 containing acrylates (CA) with different spacers were synthesized. Copolymers of CA with methyl methacrylate (MMA) in CA/MMA in the weight ratios of 1/20, 1/40 and 1/60 were prepared by using AIBN as initiator. The copolymer compositions were determined from uv-visible spectroscopic analyses, according to Beer's law. UV absorption and photoluminescence (PL) spectra indicated a concentration quenching, which increased with increasing coumarin-6 concentration in the copolymer compositions and also increasing the spacer length from the copolymer to coumarin-6 moiety, leading to a decreased fluorescence efficiency (phi(s)/phi(o)) as well as a red shift of lambda(max). Furthermore, as the spacer, n in -(CH2)(n)-, increases from n = 2, 3 to 6, excimers formed due to overlap of chromophores, resulting in the splitting of the PL emission band and lowering the PL intensity. Experimental results revealed that when the ratio of CA/MMA = 1/60 and the spacer n = 2, the copolymer film showed an optimized fluorescent quantum efficiency.
The study of the sublimable six-coordinated aluminum quinolate with sulfonamide substitutents
(2004-10-21)
Cheng, JA
;
Chen, CH
;
Yang, HL
;
應用化學系
;
友訊交大聯合研發中心
A sublimationable blue-green host materials based on tris(8-hydroxyquinolato)aluminum, meridional tris(5-N-ethylanilinesulfonamide-8-quinolato) aluminum, mer-Al(Saq)(3), was investigated and characterized by thermogravimetric analysis (TGA) and H-1 nuclear magnetic resonance (NMR). Via molecular engineering, the sublimation enthalpy of mer-Al(Saq)(3) can be adjusted by introducing the N-ethylanilinesulfonamide substitutent. Its electroluminescence (EL) was also characterized by the device architecture of glass/ITO (200 nm)/CuPc (15 nm)/NPB (60 nm)/mer-Al(Saq)(3) (55 nm)/LiF (1 nm)/Al (200 nm). It shows a blue-green spectrum with blue-green of 1931 CIEx,y(0.25, 0.39). Our experiments revealed that the Al-N bond order might not be the major issue in sublimation process. (C) 2004 Elsevier B.V. All rights reserved.
White organic electroluminescence from an exciplex based on the novel substituted aluminium quinolate complex
(2005)
Cheng, JA
;
Chen, CH
;
應用化學系
;
友訊交大聯合研發中心
;
Department of Applied Chemistry
A saturated white organic light-emitting device was obtained from an exciplex mechanism by using a novel blue-green fluorescent tris(5-mesitylsulfone-8-hydroxyquinolato)aluminium(III), Al(MSq)(3). Its absorption and photoluminescence appear at 3.25 eV and 2.56 eV. In photoluminescence, an exciplex, generated from an Al(MSq)(3)/TPD blend, was found at 2.10 eV. The lifetime of the Al(MSq)(3)/TPD blend is 22.3 ns, which is longer than that of either Al(MSq)(3) or TPD. Due to the exciplex formation, the orange light generated can be combined with the blue-green light generated from Al(MSq)(3) to achieve a white light emission. In an optimized electroluminescence device structure of [glass/ITO (200 nm)/PEDOT:PSS (75 nm)/blend (72 nm)/BCP (8 nm)/LiF (1 nm)/Al (200 nm)], the saturated white light emission was observed at Commision Internationale De L'Eclairage (CIE) coordinates of (0.35, 0.34). The EL spectrum of the device is also independent of the applied voltage. Its maximum brightness and efficiency are 26 cd m(-2) at 15.2 V/67 mA cm(-2), and 597 muW A(-1) at 12.5 V/28 mA cm(-2), respectively.