• Title/Summary/Keyword: Decay time

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Synthesis and Photoluminescence Studies on Sr1-xBaxAl2O4 : Eu2+, Dy3+

  • Ryu, Ho-Jin;Singh, Binod Kumar;Bartwal, Kunwar Singh
    • Journal of the Korean Ceramic Society
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    • v.45 no.3
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    • pp.146-149
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    • 2008
  • Strontium-substituted $Sr_{1-x}Ba_xAl_2O_4:Eu^{2+},\;Dy^{3+}$ compositions were prepared by the solid state synthesis method. These compositions were characterized for their phase, crystallinity and morphology using powder x-ray diffraction (XRD) and scanning electron microscopy (SEM) techniques. Photoluminescence properties were investigated by measuring excitation spectra, emission spectra and decay time for varying Ba/Sr concentrations. Photoluminescence results show higher luminescence and long decay time for $Sr_{1-x}Ba_xAl_2O_4:Eu^{2+},\;Dy^{3+}$(x=0). This is probably due to the influence of the 5d electron states of $Eu^{2+}$ in the crystal field. Long persistence was observed for these compositions due to $Dy^{3+}$ co-doping.

Optical Properties of ZnO Films Grown by Pulsed Laser Deposition (펄스 레이저 증착법으로 성장된 ZnO 막의 광학 특성)

  • Cho, Shin-Ho
    • Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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    • 2005.11a
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    • pp.113-114
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    • 2005
  • We present the effect of substrate temperature on the structural and optical properties of ZnO films grown on sapphire substrate by pulsed laser deposition. Growing at higher substrate temperature results in an increase in the surface roughness. The optimum c-axis orientation of the ZnO films occurs at the substrate temperature of 700$^{\circ}C$ The decay time shows a rapid increase in the substrate temperature from 400$^{\circ}C$ to 500$^{\circ}C$ and falls down gradually as the substrate temperature is approached to 700$^{\circ}C$.

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A Simplified Fast Running System Code Development to Simulate the Loop Transients (회로의 과도 현상을 모사하기 위한 간단한 Fast-Running System Code의 개발)

  • Won Pil Baek;Soon Heung Chang
    • Nuclear Engineering and Technology
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    • v.15 no.3
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    • pp.188-196
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    • 1983
  • A simplified fast-running system code is developed to simulate loop transients such as pump coastdown, loop failures and natural circulation. Special emphasis is put on the numerical investigation of the natural circulation system with multiloop. For this purpose, 5 governing equations are derived, and they are discretized by the space-time integration technique. The developed computer program is applied to three sample problems; transition from 2-loop to 1-loop operation, transition from 1-loop to 2-loop operation, and the transient behavior with decay power in the case of 2-loop operation.

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Energy Transfer between Calixarene and Naphthalene

  • Kook, Seong-Keun
    • Bulletin of the Korean Chemical Society
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    • v.23 no.8
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    • pp.1111-1115
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    • 2002
  • The photoluminescence of calixarene crystals has been studied as functions of temperature, time, and concentration. The vibronic bands shift to longer wavelength and become significantly sharper as temperature decreases. The experimental results r eveal that the structural transformation occur during the annealing process. Time-resolved spectra of calixarene at 12 K are monitored. Spectral features, which demonstrate characteristic of energy transfer processes, are not observed. The depopulation of excited state density is mainly controlled by unimolecular decay process dominating other decay processes. The lifetime was found to be 2.6 $\pm$ 0.1 ns. For the case of calixarene mixed with naphthalene, the fluorescence spectrum shows that the band centered at 340 nm lies 2840 $cm^{-1}$ below the relatively broad 310 nm band found for calixarene crystals. The spectra also exhibit that the emission intensity increases with increasing calixarene concentration. The results are evident that the calixarene emission is quenched by the naphthalene. Phosphorescence of calixarene mixed with naphthalene crystals is observed to determine whether the emission is due to naphthalene. The phosphorescence peaks were compared with the ground-state vibrational frequencies of naphthalene and found to be in good agreement. The results indicate that inter-molecular energy transfer occurs between calixarene and naphthalene.

Error analysis for continuous wave cavity ring-down spectrometer (연속발진 레이저를 이용한 광자감쇠 분광기의 오차요인 분석)

  • 김재완;한재원;유용심;이해웅
    • Korean Journal of Optics and Photonics
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    • v.10 no.3
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    • pp.214-220
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    • 1999
  • We calculated the deviation of decay time owing to intensity noise of ring-down signal and the sensitivity owing to shot noise, dark current, and bit resolution error of the data acquisition device. We verified the sources of systematic errors caused by the drift of cavity loss depending on bias voltage and the oscillation of decay time caused by interfering effect of mirrors.

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Synthesis and Characterization of High Luminance ${Zn_2}{SiO_4}$:Mn Phosphors (고발광 ${Zn_2}{SiO_4}$:Mn 형광체의 제조 및 특성)

  • 성부용;정하균;박희동;김대수
    • Journal of the Korean Ceramic Society
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    • v.37 no.8
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    • pp.774-780
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    • 2000
  • In order to improve luminescence prperty of phosphors, we have synthesized Zn2SiO4:Mn phosphors by a new chemical synthetic route, i.e., the homogeneous precipitation method. This method has featured that the formation of phosphoris completed at relatively low temperature of 105$0^{\circ}C$ and the particle morphology exhibits spherical shape to be well-dispersed and uniform size. At all the Mn concentration explored, phosphors prepared by this method have exhibited the improved emission intensities. In particular, the emission intensities of phosphors with Mn doping contents between 1 at% and 3.5 at% were higher about 40% than that of commercial phosphor. On the other hand, the decay time has been decreased from 23 ms to 11 ms with increasing Mn concentration. In addition, the phosphor composition containing 3 at% Mn has displayed the most saturated color.

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Surface Charcterization of plasma-treated silicone insulating materials (플라즈마 처리된 실리콘 절연재의 표면 특성화)

  • Song, J.Y.;Huh, C.S.;Youn, B.H.;Lee, T.H.;Yoo, H.C.;Seo, Y.J.;Lee, K.T.;Kim, N.R.;Lee, U.H.
    • Proceedings of the KIEE Conference
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    • 2002.11a
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    • pp.176-178
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    • 2002
  • Surface states of silicone polymer treated by plasma were investigated by the analysis by x-ray photoelectron spectroscopy(XPS) and surface voltage decay after corona charging. Plasma treatment causes the silica -like oxidative layer, which was confirmed with XPS, and lowers surface resistivity with increasing the plasma treatment time. Using the decay time constant of surface voltage, the calculated surface resistivity was compared with the value directly measured by voltage-current method using three electrodes system. A good agreement between two methods was obtained. In addition, we estimated the thermal activation energy for surface conduction, Based on our results, we could understand the relationship between surface chemical states and surface electrical properties.

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Combining Four Elements of Precipitation Loss in a Watershed (유역내 네가지 강수손실 성분들의 합성)

  • Yoo, Ju-Hwan
    • Proceedings of the Korea Water Resources Association Conference
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    • 2012.05a
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    • pp.200-204
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    • 2012
  • In engineering hydrology, an estimation of precipitation loss is one of the most important issues for successful modeling to forecast flooding or evaluate water resources for both surface and subsurface flows in a watershed. An accurate estimation of precipitation loss is required for successful implementation of rainfall-runoff models. Precipitation loss or hydrological abstraction may be defined as the portion of the precipitation that does not contribute to the direct runoff. It may consist of several loss elements or abstractions of precipitation such as infiltration, depression storage, evaporation or evapotranspiration, and interception. A composite loss rate model that combines four loss rates over time is derived as a lumped form of a continuous time function for a storm event. The composite loss rate model developed is an exponential model similar to Horton's infiltration model, but its parameters have different meanings. In this model, the initial loss rate is related to antecedent precipitation amounts prior to a storm event, and the decay factor of the loss rate is a composite decay of four losses.

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A study on charging and electrical stability characteristics with no-insulation and metal insulation in form of racetrack type coils

  • Quach, Huu Luong;Kim, Ho Min
    • Progress in Superconductivity and Cryogenics
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    • v.22 no.3
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    • pp.13-19
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    • 2020
  • This study presents the experiment and simulation results on the magnetic field response and electrical stability behaviors of no-insulation (NI) and metal insulation with stainless steel tape (MI-SS) which wound in form of racetrack type coils. First of all, the structural design of the racetrack type bobbin was shown along with its parameters. Then, the current-voltage tests were carried out to measure the critical current of both test coils. Also, the sudden discharging and charging tests were performed in the steady state to estimate the decay field time and magnetic field response, respectively. Finally, the overcurrent tests were conducted in the transient state to investigate the electrical stability of these test coils. Based on the experimental results, the contact surface resistances were calculated and applied to the field coils (FCs) of 10-MW-class second generation high temperature superconducting generator (2G HTSG) used in wind offshore environment. The charging delay time and electrical stability for NI and MI-SS HTS FCs of 10-MW-class 2G HTSG are analyzed by the equivalent circuit model and the key parameters which were obtained from the electromagnetic finite element analysis results.