Taeha Joo

Proton transfer reaction is one of the most fundamental processes in chemistry and life science. Excited state intramolecular proton transfer (ESIPT) has been studied as a model system of the proton transfer, since it can be conveniently initiated by light. We report ESIPT reaction dynamic of 1-hydroxy-anthraquione (1-HAQ) in solution by highly time-resolved fluorescence. ESIPT time of 1-HAQ is determined to be 45 ± 10 fs directly from decay of the reactant fluorescence and rise of the product f

Photophysical properties of a newly-synthesized porphyrin derivative, trans-bis(ferrocene carboxylato)(5,10,15,20-tetraphenylporphyrinato)tin(IV) [Sn(TPP)(FcCOO)2] were investigated by means of steady-state and fs-time resolved laser spectroscopic techniques, and compared with those of a standard molecule, trans-dichloro(5,10,15,20-tetraphenyl-porphrinato)tin(IV) [Sn(TPP)Cl2]. The fluorescence spectrum of Sn(TPP)(FcCOO)2 was observed to exhibit dual emission bands originating from the S2-state a

Photophysics of 10-hydroxybenzo[h]quinoline (HBQ) has been in controversy, in particular, on the nature of the electronic states before and after the excited state intramolecular proton transfer (ESIPT), even though the dynamics and mechanism of the ESIPT have been well established. We report highly time resolved fluorescence spectra over the full emission frequency regions of the enol and keto isomers and the anisotropy in time domain to determine the accurate rates of the population decay, spe

Photochromic ring closure reaction dynamics of 1,2-bis(2-methylbenzo[b]thiophene-3-yl)hexafluoro cyclopentene is investigated by means of time-resolved fluorescence spectra. Compared with a single wavelength probe, direct measurement of the emission spectra during the reaction provides unambiguous and straightforward picture for the ring closure reaction pathway. We observe two different emission bands in the fluorescence of the open ring isomer. From the global analysis for the spectra, we obta

The short, intense, and low emittance electron beams are crucial to make high quality X-ray beam for X-ray free electron laser (XFEL). A RF photo-cathode (RF PC) gun of 1.6 cell cavity is installed at Gun Test Stand (GTS) in Pohang Accelerator Laboratory (PAL). For the successful construction of PAL-XFEL, the bunch length of the beam should be measured accurately at the exit of the gun where the beam energy is 4.5 MeV. Electro-Optic Sampling (EOS) is a very promising method to measure the bunch

The excitonic carrier dynamics taking place in In$_x$Ga$_{1-x}$N/GaN multi-quantum-well systems have been studied by using low temperature picosecond-time-resolved photoluminescence (LT-TRPL), high resolution transmission electron microscopy (HR-TEM), X-ray photoelectron spectroscopy (XPS), Dynamic time of flight secondary ion mass spectrometry (TOF-SIMS), and quantum mechanical simulation methods. Both time-integrated and time-resolved photoluminescence spectra of In$_x$Ga$_{1-x}$N/GaN multi-qu

라디오 주파수 마그네트론 스퍼터링 방법을 이용하여 제작한 자가 형성된 보머-웨버 (Volmer-Weber)형 산화아연 나노 결정체의 광학적 특성을 연구하였다. 먼저, 방사광 엑스선 회절 실험 (포항가속기 연구소 5C2 빔라인)을 이용하여 산화아연 나노 결정체의 구조를 분석하였고, 헬륨-카드뮴 레이저 (325 nm)를 이용하여 6 K~ 300 K 범위에서 온도 의존성 광발광 (temperature dependent photoluminescence) 특성과 펨토초 레이저를 이용한 저온 시분해 발광 (low-temperature time-resolved photoluminescence) 특성을 연구하였다. 엑스선 회절 실험에서는 보머-웨버형 산화아연 나노 결정체들이 c축 우선 방향성을 보였다. 온도 의존 광발광 실험에서는 보머-웨버형 산화아연 나노 결정체가 낮은 온도 영역 (6 K~20 K)에서 3.368 eV와 3.312 eV의 두 개의 강한 자외선 발광 특성을 보이나 온도가 증가하면서