• Bulletin of the Korean Chemical Society
• /
• v.7 no.3
• /
• pp.196-200
• /
• 1986

The solvent change and salt do not affect the fluorescence quantum yield of 1,3-dimethylnaphtho[1,2-e]uracil indicating the considerable energy gap between the lowest singlet $({\pi},\;{\pi}^{\ast})\;and\;(n,\;{\pi}^{\ast})$ states in the compound. The results are consistent with the strong quenching of fluorescence by ethyl iodide. Fluorescence quantum yield is nearly independent of temperature, probably due to the relatively inefficient internal conversion. Unusual spectral difference is observed in isopentane and ethanol at 77K. The temperature dependence of emission in isopentane and in ethanol suggests that the increase of charge transfer character by the conformational change in isopentane leads to the structureless and red-shifted fluorescence, while in ethanol the decrease of the charge transfer character by the hydrogen bonding interaction results in the structured and blue-shifted fluorescence along with phosphorescence at the low temperature. Temperature dependence of emission in poly(methylmethacrylate) matrix indicates that $T_1{\to}S_0$ radiationless decay is an important process responsible for the strong temperature dependence of phosphorescence.

• Bulletin of the Korean Chemical Society
• /
• v.28 no.8
• /
• pp.1249-1255
• /
• 2007

We have investigated the photophysical properties of dansyl-N-methylaminobenzoic acid (DABAH) as a ligand and its lanthanide (Ln3+)-cored complexes (Ln3+-(DABA)3(terpy)) in order to determine the main energy transfer pathway for sensitized near infrared emission of Ln3+ ions (Ln3+ = Nd3+ and Er3+) in Ln3+- (DABA)3(terpy). The fluorescence spectrum of DABAH shows a large Stokes shift with increasing solvent polarity. This large Stokes shift might be due to the formation of a twisted intramolecular charge transfer (TICT) state, as demonstrated by the large dipole moment in the excited state. It is in good agreement with the result that the phosphorescence even in the Gd3+-cored complex based on the DABAH ligand was not observed, maybe due to the highly forbidden character of the S1 → T1 transition in the DABAH ligand. A short decay component (ca. 1 ns) was observed in Er3+-(DABA)3(terpy) whereas the fluorescence lifetimes of DABAH and its Gd3+-(DABA)3(terpy) are observed about ~10 ns. The short component could be originated from the energy transfer process between the ligand and the Ln3+ ion. Based on the fluorescence of DABAH its Ln3+- (DABA)3(terpy), the sensitization of Ln3+ luminescence in the Ln3+-(DABA)3(terpy) takes place by the energy transfer via the TICT state of DABAH in the excited singlet state rather than via the excited triplet state.

• Journal of Electrochemical Science and Technology
• /
• v.14 no.4
• /
• pp.361-368
• /
• 2023

In lithium-sulfur (Li-S) batteries, encapsulation of sulfur in activated carbon (AC) materials is a promising strategy for preventing the dissolution of lithium polysulfide into electrolytes and enhancing cycle life, because instead of solid-liquid-solid reactions, quasi-solid-state (QSS) reactions occur in the AC micropores. While a high weight fraction of sulfur in S/AC composites is essential for achieving a high energy density of Li-S cells, the deterioration mechanisms under such conditions are still unclear. In this study, we report the deterioration mechanisms during charge-discharge cycling when the discharge products overflow from the AC. Analysis using scanning electron microscopy and energy-dispersive X-ray spectrometry confirms that the sulfur in the S/AC composites migrates outside the AC as cycling progresses, and it is barely present in the AC after 20 cycles, which corresponds to the capacity decay of the cell. Impedance analysis clearly shows that the electrical resistance of the S/AC composite and the charge-transfer resistance of QSS reactions significantly increase as a result of sulfur migration. On the other hand, the charge-discharge cycling performance under limited-capacity conditions, where the discharge products are encapsulated inside the AC, is extremely stable. These results reveal the degradation mechanism of a Li-S cell with micro-porous carbon and provide crucial insights into the design of a S/AC composite cathode and its operating conditions needed to achieve stable cycling performance.

• Journal of the Korean Society of Safety
• /
• v.13 no.4
• /
• pp.172-179
• /
• 1998

The effects of $^{60}Co\;{\gamma}-Ray$ irradiation on TSC characteristics of TFE type polytetrafluoroethylene(PTFE) were investigated. The $\alpha$ peak on TSC curve of PTFE was decreased, while the $\beta$ peak was reversely increased by the increasing of $\gamma$-irradiation doses up to 80 krad(0.8 kGy). Moreover, $\alpha$ and $\beta$ peaks on TSC curve of the irradiated PTFE are changed with the increasing of the forming temperature and forming electric field. In annealing the irradiated PTFE specimens at room temperature in air, it was shown a continuous recovery of TSC characteristics with time, which is assumed the traped charge carriers are liberated from the shallow traps and undergoes a recombination process during room temperature decay.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2001.07a
• /
• pp.597-600
• /
• 2001

In this paper, we evaluated the effect of accumulated charges on hydrophobicity of room temperature vulcanized(RTV) silicone rubber, which could improve the contamination performance of porcelain insulators, with uv radiation time. Outdoor insulating material could be charged by the corona discharge on field intensified area of insulator and discharge between the water drops. In addition, we performed the accelerated uv radiation on samples and investigated the change of charging decay with time. In this results, it is found that silica-like structure on the surface of RTV silicone rubber was formed by uv treatments and this layer have the characteristic of retaining the charges on surface for a long time. These charges have effects on its hydrophobicity and so adversely effects on contamination performance. Based on our results, we discussed the other degradation mechanism with well known ones.

• Proceedings of the Polymer Society of Korea Conference
• /
• 2006.10a
• /
• pp.21-22
• /
• 2006

Significant progress has been realized in the design and synthesis of light emitting polymers with emission over the whole range of the visible spectrum. However up to seventy-five percent of charge recombination events can lead to triplet states that decay non-radiatively. Following the pioneering work in the field of small molecule organic light emitting devices it has been found that solution processible iridium polymer complexes can be used to harness the wasted triplet energy. In this paper new results concerning electrophosphorescence of solution processible tethered iridium polymer derivatives will be presented. Furthermore our approaches to the design of new high triplet energy conjugated polymer hosts will be reported.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 1989.06a
• /
• pp.114-117
• /
• 1989

An infrasonic wide band transducer fabricated by polytetrafluoroethylene(PTFE)is studied experimentally. The sensitivity of the transducer depends largely on the surface charge of the Electret and is typically between-50 and -62[dBV] for a sound-pressure level of 1[ubar]. The sensitivity of the transducer does not decay over periods of the order of years at room temperature. The frequency response is within 1.5[dB] from 1 to 6,000[Hz] and within 12[dB] from 0.05[Hz] to 1[Hz] respectively. The resonance frequency of the element is 510 [Hz]. We conjectures that the element is applicable to accustics, communication system, seismological observation and other similar filed.

• Proceedings of the KIEE Conference
• /
• 1998.07d
• /
• pp.1255-1257
• /
• 1998

In this study,$ 5{\times}5$ dot-matrix display was implemented with powder electroluminescent device (PELD). Generally PELD which have a luminance from powder phosphor with electric field, inserted phosphor and dielectric layer between electrodes is basic structure. To make high brightness PELD compared to conventional device, new type of PELD was proposed as follows. New PELD had only one layer, which was mixed phosphor (ZnS:Cu) and dielectric (BaTiO3) material appropriately between electrodes. To compare and estimate the conventional and new type of PELD, the EL spectrum, transferred charge density, brightness and decay time was measured. As above result, we fabricated a hish brightness $ 5{\times}5$ dot-matrix display with new type of PELD. Its brightness was 6400 $cd/m^2$ at 200 V, 400Hz.

• Macromolecular Research
• /
• v.15 no.2
• /
• pp.129-133
• /
• 2007

Significant progress has been realized in the design and synthesis of light emitting polymers that emit over the entire visible spectrum. However, up to seventy-five percent of charge recombination events can lead to triplet states that decay non-radiatively. Following the pioneering work in the field of small molecule organic light emitting devices, it has been found that solution processible iridium polymer complexes can be used to harness the wasted triplet energy. In this paper, new results with respect to the electrophosphorescence of solution processible tethered iridium polymer derivatives are presented. Furthermore, our approaches to the design of new high triplet energy conjugated polymer hosts are also reported.

• Bulletin of the Korean Chemical Society
• /
• v.20 no.11
• /
• pp.1263-1268
• /
• 1999

The fluorescence properties and photoisomerization behavior of 1-(9-anthryl)-2-(2-quinolinyl)ethene (2-AQE) have been investigated in various solvents. Instead of phenyl ring in 1-(9-anthryl)-2-phenylethene, the intro-duction of quinoline ring reduces not only the fluorescence yield but also the photoisomerization yield, due to competition of efficient radiationless deactivation and an increase in the torsional barrier for twisting in the singlet manifold. The S1 decay parameters were found to be solvent-dependent due to the charge-transfer character of lowest S1 state. Polar solvents reduce the activation barrier to twisting, thus slight enhancing the isomerization of t-2-AQE in the singlet manifold. As solvent polarity is increased, Φf of c-2-AQE is greatly reduced, but Φc →ｔ is practically independent of solvent polarity. Dual fluorescence in t-2-AQE was observed and two fluorescing species could be assigned t-2-AQE and c-2-AQE, where the ratio between two species was dependent on the solvent polarity. Interestingly, in the concentration above 1×10 -4 M, the shapes of the fluorescence excitation spectra of t- and c-2-AQE are significantly altered without spectral changes of their fluorescence and absorption, probably due to the formation of excimer.