Browsing by Author "Luo, LY"

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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
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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.
Evidence for the assembly of carboxyphenylethynyl zinc porphyrins on nanocrystalline TiO2 surfaces
(2006)
Lo, CF
;
Luo, LY
;
Diau, EWG
;
Chang, IJ
;
Lin, CY
UV-visible absorption and AFM studies suggest that carboxyphenylethynyl zinc porphyrins aggregate on nanocrystalline TiO2 surfaces in an H-type fashion.
Femtosecond fluorescence dynamics of porphyrin in solution and solid films: The effects of aggregation and interfacial electron transfer between porphyrin and TiO(2)
(2006-01-12)
Luo, LY
;
Lo, CF
;
Lin, CY
;
Chang, IJ
;
Diau, EWG
The excited-state relaxation dynamics of a synthetic porphyrin, ZnCAPEBPP, in solution, coated on a glass substrate as solid films, mixed with PMMA and coated on a glass substrate as solid films, and sensitized on nanocrystalline TiO(2) films were investigated by using femtosecond fluorescence up-conversion spectroscopy with excitation in the Soret band, S(2). We found that the S(2) -> S(1) electronic relaxation of ZnCAPEBPP in solution and on PMMA films occurs in 910 and 690 fs, respectively, but it becomes extremely rapid, < 100 fs, in solid films and TiO(2) films due to formation of porphyrin aggregates. When probed in the S(1) state of porphyrin, the fluorescence transients of the solid films show a biphasic kinetic feature with the rapid and slow components decaying in 1.9 - 2.4 and 19 - 26 ps, respectively. The transients in ZnCAPEBPP/TiO(2) films also feature two relaxation processes but they occur on different time scales, 100 - 300 fs and 0.8 - 4.1 ps, and contain a small offset. According to the variation of relaxation period as a function of molecular density on a TiO(2) surface, we assigned the femtosecond component of the TiO(2) films as due to indirect interfacial electron transfer through a phenylethynyl bridge attached to one of four meso positions of the porphyrin ring, and the picosecond component arising from intermolecular energy transfer among porphyrins. The observed variation of aggregate-induced relaxation periods between solid and TiO(2) films is due mainly to aggregation of two types: J-type aggregation is dominant in the former case whereas H-type aggregation prevails in the latter case.
Luminescence and energy transfer of Eu- and Mn-coactivated CaAl2Si2O8 as a potential phosphor for white-light UVLED
(2005-07-26)
Yang, WJ
;
Luo, LY
;
Chen, TM
;
Wang, NS
;
應用化學系
A series of Eu2+- and Mn2+-coactivated CaAl2Si2O8 phosphors have been synthesized at 1400 degrees C under a reduced atmosphere and their luminescence properties have been investigated as a function of activator and coactivator concentrations. We have discovered that energy transfers from Eu2+ to Mn2+ by directly observing significant overlap of the excitation spectrum of Mn2+ and the emission spectrum of Eu2+ as well as the systematic relative decline and growth of emission bands of Eu2+ and Mn2+, respectively. The critical distance and average separation of Eu2+ and Mn2+ have also been calculated. By utilizing the principle of energy transfer, we have also demonstrated that with appropriate tuning of activator content CaAl2Si2O8:Eu2+ Mn2+ phosphors exhibit great potential to act as a phosphor for white-light ultraviolet light-emitting diodes (UVLEDs).
Tuning the emission and morphology of cyclometalated iridium complexes and their applications to organic light-emitting diodes
(2005)
Wu, FI
;
Su, HJ
;
Shu, CF
;
Luo, LY
;
Diau, WG
We have synthesized two highly efficient phosphorescent iridium metal complexes, Ir( DPQ)(2)( acac) and Ir(FPQ)(2)(acac), which are based on cyclometalated quinoline ligands, and discuss details of their electrochemical behavior and photophysical properties (viz. absorption and photoluminescence). Single-crystal X-ray diffraction studies of Ir(DPQ)(2)(acac) reveal a distorted octahedral geometry, in which the quinoline N atoms and the C atoms of the orthometalated phenyl groups are located at mutual trans and cis positions, respectively. In contrast, Ir(FPQ)(2)( acac) is an amorphous solid and undergoes a glass transition at 92 degreesC, which we attribute to the presence of the long di-n-octyl chains in the fluorenyl groups. The phosphorescence of these Ir complexes originates from the dominant 3 MLCT excited state shifts to red that occur upon introducing a phenyl substituent and/or a large conjugating aromatic ring into the ligand. A polymer light-emitting diode (PLED) device that uses Ir(FPQ)(2)(acac) as a phosphorescent dopant and a PVK/PBD blend as the host material produces very high efficiency (an external quantum efficiency of 8.16% at 100 mA cm(-2)) and a pure-red emission with 1931 CIE ( Commission Internationale de L'Eclairage) chromaticity coordinates of (x = 0.68, y = 0.32).