Browsing by Author "Chen, IC"

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Effect of host compositions on the afterglow properties of phosphorescent strontium aluminate phosphors derived from the sol-gel method
(2001-05-01)
Chen, IC
;
Chen, TM
;
應用化學系
;
Department of Applied Chemistry
The effect of compositions of host precursors on the afterglow and phosphorescent decay properties of Eu2+- and Dy3+-coactivated strontium aluminates (SAED) synthesized by a sol-gel process has been investigated. A variety of strontium aluminates such as Sr3Al2O6, SrAl2O4, and SrAl12O19 have been identified in the samples prepared from starting precursors with Al/Sr ratios ranging from 1 to 12, respectively. The initial afterglow intensity (I-0) for SAED phases was found to vary with Al/Sr ratio of the sol-gel precursor, with a maximal I-0 appearing in the sample with Al/Sr of 2 in which SrAl2O4 dominated. The afterglow decay rate was found to be fastest for sample with Al/Sr ratio of 1:1 in which Sr3Al2O6 phase dominated. Moreover, the afterglow decay rates for those with Al/Sr ratio of 2:1 to 12:1, in which SrAl2O4 and SrAl12O19 dominated, were found to be slow and similar.
Improved performance and stability of organic light-emitting devices with Al-Cu alloy cathode
(2005-02-28)
Chen, IC
;
Hwang, SW
;
Chen, CH
;
應用化學系
;
友訊交大聯合研發中心
We have developed a stable green organic electroluminescent (EL) device by using an Al-Cu alloy as a cathode, which has better performance and reliability than the device with an Al cathode. The device with an Al-Cu alloy cathode achieved an EL efficiency of 3.78 cd/A(2.18 lm/W) at 20 mA/cm(2) and the operating voltage was 5.46 V, while device with Al cathode had an EL efficiency of 3.1 cd/A(1.34 lm/W) and 7.3 V at the same drive condition. The Al-Cu device achieved a 20% decay lifetime (t(80)) of 1234 h at an initial brightness of 756 cd/m(2), which is twice the lifetime of conventional device with the state-of-the-art LiF/Al cathode. (C) 2005 American Institute of Physics.
Photochemistry and photodissociation of benzosultine and naphthosultine: electronic relaxation of sultines and kinetics and theoretical studies of fragment o-quinodimethanes
(2005-02-28)
Tang, KC
;
Lee, SJ
;
Chi, SH
;
Lu, KL
;
Chen, WC
Fluorescence decays of benzosultine and naphthosultine excited at 263 nm are detected with time-correlated single-photon counting (TCSPC). Both molecules display biexponential decay with a rapid component (time constants 90 and 350 ps for benzosultine and naphthosultine, respectively) assigned to an electronically excited state S-n at high energy and the slow one (constants 7.5 and 9.0 ns for benzosultine and naphthosultine, respectively) to the S-1 state. Dissociation of both molecules was investigated with nanosecond laser flash photolysis combined with transient absorption to detect the intermediates and products. With excitation at 266 nm, benzosultine yields a transient with absorption maximum at lambda(max) = 370 nm; this transient has a short-lived component with lifetime around 1 mus and a long-lived component. Both components are insensitive to molecular oxygen. The short-lived component is tentatively assigned to the dissociation intermediate and the long-lived to be singlet o-benzoquinodimethane (o-BQDM). Photolysis of naphthosultine yields two transient species with absorption at; lambda(max) = 420 and 520 nm; we assign the former band to triplet-triplet absorption of naphthosultine and the latter to absorption by the product singlet o-naphthoquinodimethane. Optimal geometries, energetics, and vertical transitions of benzosultine, naphthosultine, o-benzoquinodimethane, and o-naphthoquinodimethane are calculated using methods based on density-functional theory (B3LYP/6-311++G**) and time-dependent density-functional theory (TD-DFT). The results of these calculations imply that the ground electronic state of these two o-quinodimethanes (o-QDM) is singlet with a structure of diene form. Their triplet states display a biradical structure. The energy separation between singlet and triplet states of o-benzoquinodimethane is calculated to be ca. 93.6 kJ/mol, but for o-naphthoquinodimethane, it is only ca. 27.8 kJ/mol. (C) 2004 Elsevier B.V. All rights reserved.
RPC-news: a real-time, personalized, Chinese news system
(1997)
Chang, DW
;
Chen, IC
;
Ke, HR
;
Chang, RC
;
交大名義發表
With the speedy growth of information quantity, people need a mechanism to discover automatically the information that interests them. Such a mechanism is called selective dissemination of information (SDI). Describes the design and implementation of an SDI system with the ability of delivering real-time, personalized news articles. In addition to delivering English news, it delivers Chinese articles also. Focuses on the problems that other researches seldom address. First, discusses how to store and delete news articles efficiently, then describes the user model to let users specify their interests. Finally, presents an efficient method to embed the ability to deliver Chinese as well as English news articles in the system.
Sol-gel synthesis and the effect of boron addition on the phosphorescent properties of SrAl2O4 : Eu2+,Dy3+ phosphors
(2001-03-01)
Chen, IC
;
Chen, TM
;
應用化學系
;
Department of Applied Chemistry
The effects of boron addition on the microstructure and afterglow properties of the long-phosphorescent SrAl2O4:Eu2+,Dy3+ (SAED), synthesized via a novel sol-gel route, were systematically investigated. Significant improvement on luminescence intensity and the lengthening of afterglow persistent time in boron-added SAED (BSAED) phases were observed, as compared to those without boron addition and commercial phosphors. Typical bluish-green emissions attributed to the doublet phosphorescence with wavelengths peaking at 412 and 501 nm for BSAED phase and 398 and 486 nm for the pristine SAED phase were observed. Afterglow with wavelengths peaking at 403 and 485 nm was observed for BSAED phase, whereas that with wavelengths peaking at 486.5 nm was found for the pristine SAED phase, as indicated by time-dependent afterglow decay profiles. Results from scanning electron microscopic morphological studies were used to investigate the modification of microstructure of the BSAED phases.
Synthesis of optically active tetraoxa-cage compounds by chemical resolution
(2000-02-01)
Chen, IC
;
Wu, HJ
;
應用化學系
;
Department of Applied Chemistry
The first synthesis of optically active tetraoxa-cage compounds has been accomplished by using (-)-camphanic chloride as a resolving reagent in a short sequence. The synthesis of the tetraoxa-cages with different functional groups on the side chain was also demonstrated.
Two-step oxygen injection process for growing ZnO nanorods
(2003-12-01)
Tseng, YK
;
Hsu, HC
;
Hsieh, WF
;
Liu, KS
;
Chen, IC
Uniform hexagonal prismatic zinc oxide rods were grown over the entire alumina substrate at 550 degreesC using a two-step oxygen injection process, whether the substrates were coated with a catalyst or not. X-ray diffraction showed that all of the depositions exhibited a preferred orientation in the (002) plane. The influence of oxygen concentration was investigated by changing the oxygen flow rate. Oxygen concentration affected the size of ZnO nanorods, especially the diameter. The ZnO nanorods were further checked using high-resolution transmission electron microscopy, photoluminescence, Raman spectroscopy, and room-temperature ultraviolet lasing. The results showed that the rods were single crystals and had excellent optical properties. By observing the growth process, we found that the diameter increased slowly, but the longitudinal growth rate was very high. The growth of ZnO nanorods revealed that the uniform hexagonal prismatic ZnO nanorods were synthesized through vapor deposition growth and a self-catalyzed vapor-liquid-solid (VLS) process.