• Advances in nano research
• /
• 제1권3호
• /
• pp.125-131
• /
• 2013

This study is aimed to calculate the radiative lifetime of Wannier-Mott excitons in nanoclusters of a narrow-bandgap semiconductor embedded in a wide-bandgap one. The nanocluster linear dimensions are assumed to be much larger than the radius of the exciton so that the latter is not destructed by the confinement potential as it takes place in small quantum dots. The calculations were carried out for an example of InAs nanoclusters put into the GaAs matrix. It is shown that the radiative lifetime of Wannier-Mott excitons in such clusters increases with the decrease of the cluster dimensions, this tendency being more pronounced at low temperatures. So, the creation of excitons in nanoclusters of a narrow-bandgap material embedded in a wide-bandgap one can be used to significantly prolong their radiative lifetime in comparison with that of excitons in a bulk semiconductor.

• 천문학회지
• /
• 제48권1호
• /
• pp.67-73
• /
• 2015

We present a novel method to implement time-delayed propagation of radiation fields in cosmological radiative transfer simulations. Time-delayed propagation of radiation fields requires construction of retarded-time fields by tracking the location and lifetime of radiation sources along the corresponding light-cones. Cosmological radiative transfer simulations have, until now, ignored this "light-cone effect" or implemented ray-tracing methods that are computationally demanding. We show that radiative transfer calculation of the time-delayed fields can be easily achieved in numerical simulations when periodic boundary conditions are used, by calculating the time-discretized retarded-time Green's function using the Fast Fourier Transform (FFT) method and convolving it with the source distribution. We also present a direct application of this method to the long-range radiation field of Lyman-Werner band photons, which is important in the high-redshift astrophysics with first stars.

• Bulletin of the Korean Chemical Society
• /
• 제35권5호
• /
• pp.1397-1402
• /
• 2014

The complete active space self-consist field method followed by the internally contracted multireference configuration interaction method has been used to compute the potential energy curves of $X^2\prod_g$, $a^4\prod_u$, $A^2\prod_u$, $b^4\sum_{g}^{-}$, and $B^2\sum_{g}^{-}$ states of $S{_2}^+$ cation with large correlation-consistent basis sets. Utilizing the potential energy curves computed with different basis sets, the spectroscopic parameters of these states were evaluated. Finally, the transition dipole moment and the Franck-Condon factors of the transition from $A^2\prod_u$ to $X^2\prod_g$ were evaluated. The radiative lifetime of $A^2\prod_u$ is calculated to be 887 ns, which is in good agreement with experimental value of $805{\pm}10$ ns.

• 한국세라믹학회지
• /
• 제31권8호
• /
• pp.861-868
• /
• 1994

CaO-Al2O3 glass is a good candidate as optical fiber amplifier and laser. In this study, optical properties for 4I13/2longrightarrow4I15/2 transition of Er3+ ions doped in CaO-Al2O3 glasses were investigated. Optical absorptions, radiative transition probabilities and lifetimes for 4I13/2 level were evaluated by using Judd-Ofelt theory. Also, induced- emmision cross-sections of 4I13/2longrightarrow4I15/2 transition were calculated. Radiative transition probability and lifetime of 4I13/2 level were 144.6s-1, 690$mutextrm{s}$ respectively for 60CaO.40Al2O3 glass(FS0) and 152.6s-1, 660 $mutextrm{s}$ for 54 CaO.36Al2O3.10SiO2 glass (FS10). Each induced-emission cross sections for FS0 and FS10 was 0.749$\times$10-20 $\textrm{cm}^2$, 0.892$\times$10-20 $\textrm{cm}^2$. Obtained values were comparable with those of ZBLA glass studied as optical fiber amplifier and laser material.

• 한국전기전자재료학회:학술대회논문집
• /
• 한국전기전자재료학회 2003년도 제5회 영호남 학술대회 논문집
• /
• pp.121-125
• /
• 2003

Time-resolved photoluminescence from InGaN/GaN multi-quantum well structures was investigated for two different shapes of square- and trapezoidal wells grown by metal-organic chemical vapor deposition. To compare to the conventional square well structure with a radiative recombination lifetime of 0.170 nsec, the large value of lifetime of 0.540 nsec from trapezoidal well were found at room temperature. This value is similar to the value for GaN host material indicating no confinement effect of quantum well. Furthermore, the high resolution transmission electron microscopy image provides the In clustering effect in the trapezoidal well structure.

• Transactions on Electrical and Electronic Materials
• /
• 제4권5호
• /
• pp.19-23
• /
• 2003

Time-resolved photoluminescence from InGaN/GaN multi-quantum well structures was investigated for two different shapes of square-and trapezoidal wells grown by metal-organic chemical vapor deposition. To compare to the conventional square well structure with a radiative recombination lifetime of 0.170 nsec, the large value of lifetime of 0.540 nsec from trapezoidal well were found at room temperature. This value is similar to the value for GaN host material indicating no confinement effect of quantum well. Furthermore, the high resolution transmission electron microscopy image provides the In clustering effect in the trapezoidal well structure.

• 한국광학회지
• /
• 제1권1호
• /
• pp.52-57
• /
• 1990

피코초 레이저와 고속 전자장치를 사용하여 subnanosecond에서 microsecond 넓은 범위에 걸쳐서 발광 소멸 시간을 측정할 수 있는 time-correlated single photon counting(TCSPC) 장치를 개발하였다. 이 TCPSC를 사용하여 색소레이저에 있어서 saturable absorber로 많이 쓰이는 DODCI의 소멸시간 및 회전 완화시간을 측정함으로써 여기상태에서의 동력학과 회전운동에 관해 연구하였다.

• 한국광학회지
• /
• 제9권4호
• /
• pp.221-226
• /
• 1998

$Er_2O_3$를 첨가한 $PbO-Bi_2O_3-Ga_2O_3$ 삼성분계 중금속 산화물 유리로부터 발생하는 $1.5\mu\textrm{m}$와 2.7$\mu\textrm{m}$ 등의 형광에 대하여 복사 천이율, 형광 수명, 흡수 및 유도 방출 단면적 등을 조사하였다. 중금속 산화물 유리의 낮은 포논 에너지($~500cm^{-1}$)로 인하여 기존 산화물 유리로부터 관찰할 수 없었던 형광들의 양자 효율이 크게 높아졌으며 방출 단면적도 증가하였다. 한편, 798 nm 여기광의 상향 전이를 통한 녹색과 적색의 형광이 방출됨을 확인하였고, 각 에너지 준위의 형광 수명을 이용하여 다중포논 완화(multiphonon relaxation)를 정량적으로 규명하였다. $Er^{3+}:^4S_{3/2}{\rightarrow}^4I_{15/2}$ 천이에 의한 녹색 형광은 기지 유리(host glass)의 밴드 갭(band gap)흡수에 의한 비복사 천이의 영향을 받으므로 이 형광의 양자 효율을 높이기 위해서는 유리를 불활성 기체 분위기에서 용융하거나 자외선쪽 투과단이 짧은 유리 망목 형성제(glass-vetwork former)가 첨가된 기지 조성을 선택하는 것이 바람직하다.

• 천문학회보
• /
• 제36권2호
• /
• pp.72.2-72.2
• /
• 2011

We have performed the first self-consistent, large-scale simulation of cosmic reionization by stellar sources, including the Population III stars that emerged and were hosted by minihalos at very high redshifts (z~40). Based on this result, we calculate the redshifted radiation background from these stars and the relic H II regions which can be observed at near-infrared and infrared regime. Formation of the first stars inside minihalos are quenched by radiative feedback at z~15, while the relic H II regions have much longer lifetime due to the slow recombination rate. Therefore, the radiation output from the relic H II regions, dominated by Lyman alpha photons, will be observed both in the near-infrared and infrared regime. The estimated background from the first stars inside minihalos are still sub-dominant compared to that from stars inside larger halos, however, and thus complementary observations are necessary, such as redshifted 21-cm line observation.

• Journal of Photoscience
• /
• 제11권3호
• /
• pp.95-99
• /
• 2004

Optical absorption and emission studies have been carried out to understand the effect of deuterium on the solvent dependent photophysical properties of curcumin in deuterated solvents such as $CDCl_3,\;(CD_3)_2SO,\;(CD_3)_2CO,\;CD_3OD\;and\;CD_3CN$. Optical absorption spectral studies showed that there is no significant shift in absorption maxima compared to the non-deuterated solvent. The fluorescence maxima shows significant shift with polarity of solvent but not much affected by the deuteration. The fluorescence quantum yield of curcumin increased marginally in almost all the deuterated solvents, indicating reduction in the non-radiative pathways. The fluorescence decay was biexponential in all the solvents and the average fluorescence lifetime was not much affected with deuteration, but showed decrease with increasing solvent polarity. Based on these studies, it is concluded that intermolecular hydrogen transfer is only partially responsible for the excited state deactivation of curcumin.