• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2009년도 9th International Meeting on Information Display
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• pp.52-55
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• 2009

A red phosphor, $(Sr,Ca)_2P_2O_7:Eu^{2+},Mn^{2+}$, for UV-LED was synthesized under a reducing atmosphere, and its luminescent properties were investigated. The phosphor absorbs ultraviolet light at around 400 nm and efficiently emits red light at approximately 610 nm through an energy transfer from $Eu^{2+}$ to $Mn^{2+}$. Using the varied input current test for the phosphor-loaded LED lamps, it was found that the luminescent efficiency of the phosphor decreased with increasing light flux. This might be due to an increased probability of excited-state absorption and the consequent non-radiative relaxation in $Mn^{2+}$ ions in the condition of high photon influx.

• Bulletin of the Korean Chemical Society
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• 제10권3호
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• pp.298-302
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• 1989

The strengths of two-photon transitions from the ground state to excited vibronic states in benzene are calculated by using the CNDO/2-U wave functions. The role of vibronic coupling in two-photon absorption process is discussed. The $A_{1{\bar{g}}}-A_{2g}^+$ two-photon transitions, which are forbidden by the identity-forbidden selection rule in single frequency two-photon absorption, are too weak to be experimentally observed even when two photons of different energies are used. It is because the transitions are forbidden also by the pseudo-parity selection rule which are applicable for alternant hydrocarbons such as benzene. It is also shown that the vibronic coupling is not very effective in altering the pseudo-parity property of the electronic state. The strength of the vibronically induced two-photon absorption is strongly affected by the presence of an electronic state from which two-photon absorption can borrow the intensity. It is pointed out that the pseudo-parity selection rule may be violated in such cases.

• Bulletin of the Korean Chemical Society
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• 제31권10호
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• pp.2806-2808
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• 2010

The structure of 3-aminophenol $(CO_2)_1$ cluster was computationally studied both in the ground and the lowest singlet excited electronic states. The ground state structure and binding energy of the cluster was investigated using the second-order M$\ddoot{o}$ller-Plesset perturbation theory (MP2) at the complete basis set (CBS) limit. The excited state geometry of the cluster was obtained at the second-order approximate coupled cluster (CC2) level with cc-pVDZ basis set, and the $S_0-S_1$ absorption spectrum was simulated by calculating Franck-Condon overlap integral. The ground state geometry of the global minimum with a very high binding energy of 4.3 kcal/mol was found for the cluster, due to the interaction between amino group and $CO_2$ in addition to the strong $\pi-\pi$ interaction between the aromatic ring and $CO_2$. The excited state geometry shows a very big shift in the position of $CO_2$ compared to the ground state geometry, which results in low intensity and broad envelope in the Franck-Condon simulation.

• Rapid Communication in Photoscience
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• 제2권3호
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• pp.72-75
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• 2013

Bulk nanobubble is one of the nanoscopic gaseous state found in the solution. We measured transient absorption spectra of eosin Y in the excited triplet state ($^3EY^{2-*}$) to elucidate differences in the dissipation process of the bulk nanobubble of oxygen molecule at air pressure. The time dependence of the oxygen dissipation process was classified three time domains (P1, P2 and P3). The comparison of ordinary bubbling method gave different results at P3 in contrast to similar results at P1 and P2, indicating the existence of characteristic dissolving state in the case of nanobubble.

• Journal of Photoscience
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• 제9권2호
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• pp.317-319
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• 2002

All-optical switching has been demonstrated in bacteriorhodopsin (bR) based on nonlinear intensity induced excited state absorption. The transmission of a cw probe laser beam at 410 nm corresponding to the peak absorption of M state through a bR film is switched by a pulsed pump laser beam at 570 nm that corresponds to the maximum initial 8 state absorption. The switching characteristics have been analyzed using the rate equation approach considering all the six intermediate states (B, K, L, M, N and 0) in the bR photocycle. The switching characteristics are shown to be sensitive to life time of the M state, absorption cross-section of the 8 state at probe wavelength ($\sigma$ $\_$Bp/) and peak pump intensity. It has been shown that the probe laser beam can be completely switched off (100 % modulation) by the pump laser beam at relatively low pump powers, for $\sigma$$\_$Bp/ = O. The switching characteristics have been used to design all-optical NOT, OR, AND and the universal NOR and NAND logic gates for optical computing with two pulsed pump laser beams.

• Bulletin of the Korean Chemical Society
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• 제28권8호
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• pp.1256-1260
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• 2007

Two β-diketone derivatives bearing triphenylene (1-naphthalene-2-yl-3-triphenylen-2-yl-propane-1,3-dione (NTPD)) and naphthalene (1,3-di-naphthalene-2-yl-propane-1,3-dione (DNPD)) and their Ln(III) complexes (Ln = Er or Gd) were synthesized and their photophysical properties were investigated. The sensitized emission of Er3+ ion in Er3+-[NTPD]3(terpy) and Er3+-[DNPD]3(terpy) was observed upon excitation at absorption maximum of ligands. Their photophysical studies indicate the sensitization of Er3+ luminescence by energy transfer through the excited triplet state of β-diketone ligand. The energy transfer rate through the excited triplet state of β-diketone ligand to Er3+ ion occurs faster than that of the oxygen quenching rate.

• Bulletin of the Korean Chemical Society
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• 제10권3호
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• pp.227-230
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• 1989

The lowest excited state of styrylquinoxaline (StQx) has been studied by the SCF-MO-CI P-P-P and MM2 method. Results suggest that the lowest excited state is of a ${\pi},{\pi}^{\ast}(S_1$) nature with the n,${\pi}^{\ast}(S_2)$ state lying slightly above it. On the basis of these calculations the observed electronic spectra are discussed. The calculated absorption spectra are qualitatively similar to experimental ones with their characteristic visible bands. MM2 force field calculation suggested that the postulated conformers are different from each other in energy and planarity and are seperated by a barrier of about 4 Kcal/mole.

• 대한화학회지
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• 제23권5호
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• pp.314-319
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• 1979

바닥 말무리 dinoflagellate의 광합성 에너지 수용 색소인 peridinin의 전자 흡수스펙트럼을 PPP SCF MO 계산결과와 형광 편광 실험결과에 견주어 분석하였다. 청색광 부위의 흡수띠 (470 nm)는 $B{\leftarrow}A$ 천이에 대응하여 분자의 장축과 거의 평행 방향으로 편광되어 있음이 예측된다. 소위 "cis peak" 영역의 근자외선 흡수띠는 두개의 비교적 약한 ${\pi}{\rightarrow}{\pi}^*$천이 $(C{\leftarrow}A$와 $D{\leftarrow}A)$에 기인하며 그 편광축은 $^1B{\leftarrow}A$편광축 방향과 근접되어 있음이 MO 계산과 편광 측정에 의해 추정되었다. 그리고 락톤 카르보닐 원자단의 전자구조는 $^1B$ 상태에서도$^1A$ 상태 (ground state)에 비해서 과히 변화함이 없으나, allene기는 charge transfer적 성격을 농후하게 띠고 있어서 들뜬상태에서는 allene기가 전자결핍상태가 되는 것이 예측된다.

• Bulletin of the Korean Chemical Society
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• 제28권4호
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• pp.647-651
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• 2007

In order to investigate the excited-state intramolecular proton transfer (ESIPT) process of dihydroxyanthraquinones (DHAQ; 1,5-DHAQ and 1,8-DHAQ) in organic-inorganic hybrid matrices, transparent SiO2, SiO2- Al2O3, and Al2O3 matrices chemically bonded with DHAQ were prepared using a sol-gel technique. The absorption maxima of 1,5- and 1,8-DHAQ in SiO2 matrices are observed at around 420 nm, whereas those of DHAQ in both SiO2-Al2O3 and Al2O3 matrices are markedly shifted to longer wavelength compared with those in SiO2 matrix. This indicates that DAHQ forms a chemical bond with an Al atom of Al2O3. The DHAQ in SiO2 matrix shows a markedly Stokes-shifted emission which is originated from the ESIPT in DHAQ. Based on the emission lifetimes of DHAQ, the ESIPT of DHAQ was found to be strongly affected by the chemical interaction with Al atom in the Al2O3-related matrices.

• Bulletin of the Korean Chemical Society
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• 제22권2호
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• pp.219-227
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• 2001

The silver colloidal effects on the excited-state structure and intramolecular charge transfer (ICT) of p-N,N-dimethylaminobenzoic acid (DMABA) in aqueous cyclodextrin (CD) solutions have been investigated by UV-VIS absorption, steady-state and time-resolved fluorescence, and transient Raman spectroscopy. As the concentration of silver colloids increases, the ratio of the ICT emission to the normal emission (Ia /Ib) of DMABA in the aqueous $\alpha-CD$ solutions are greatly decreased while the Ia /Ib values in the aqueous B-CD solutions are significantly enhanced. It is also noteworthy that the ICT emission maxima are red-shifted by 15-40 nm upon addition of silver colloids, implying that DMABA encapsulated in $\alpha-CD$ or B-CD cavity is exposed to more polar environment. The transient resonance Raman spectra of DMABA in silver colloidal solutions demonstrate that DMABA in the excited-state is desorbed from silver colloidal surfaces as demonstrated by the disappearance of νs (CO2-)(1380 cm-1 ) with appearance of ν(C-OH)(1280 cm -1) band, respectively. Thus, in the aqueous B-CD solutions the carboxylic acid group of DMABA in the excited-state can be readily hydrogen-bonded with the secondary hydroxyl group of B-CD while in aqueous and $\alpha-CD$ solutions the carboxylic acid group of DMABA has the hydrogen-bonding interaction with water. Consequently, in the aqueous B-CD solutions the enhancement of the Ia /Ia value arises from the intermolecular hydrogen-bonding interaction between DMABA and the secondary hydroxyl group of B-CD as well as the lower polarity of the rim of the B-CD cavity compared to bulk water. This is also supported by the increase of the association constant for DMABA/ B-CD complex in the presence of silver colloids.