• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.222.1-222.1
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• 2015

Recently, graphene quantum dots (GQDs) have attracted great attention due to various properties including cost-effectiveness of synthesis, low toxicity, and high photostability. Nevertheless, the origins of photoluminescence (PL) from GQDs are unclear because of extrinsic states of the impurities, disorder structures, and oxygen-functional groups. Therefore, to utilize GQDs in various applications, their optical properties generated from the extrinsic states should be understood. In this work, we have focused on the effect of oxygen-functional groups in PL of the GQDs. The GQDs with nanoscale and single layer are synthesized by employing graphite nanoparticles (GNPs) with 4 nm. The series of GQDs with different amount of oxygen-functional groups were prepared by the chain of chemical oxidation and reduction process. The fabrication of a series of graphene oxide QDs (GOQDs) with different amounts of oxygen-contents is first reported by a direct oxidation route of GNPs. In addition, for preparing a series of reduced GOQDs (rGOQDs), we employed the conventional chemical reduction to GOQDs solution and controlled the amount of reduction agents. The GOQDs and rGOQDs showed irreversible PL properties even though both routes have similar amount of oxyen-functional groups. In the case of a series of GOQDs, the PL spectrum was clearly redshifted into blue and green-yellowish color. On the other hand, the PL spectrum of rGOQDs did not change significantly. By various optical measurement such as the PL excitation, UV-vis absorbance, and time-resolved PL, we could verify that their PL mechanisms of GOQDs and rGOQDs are closely associated with different atomic structures formed by chemical oxidation and reduction. Our study provides an important insights for understanding the optical properties of GQDs affected by oxygen-functional groups. [1]

• 반도체디스플레이기술학회지
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• 제15권2호
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• pp.49-54
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• 2016

$SrAl_{12}O_{19}:Ce_x{^{3+}}$,$Eu_{0.01}{^{2+}}$ phosphors were synthesized through a combustion process and their optical properties were investigated using time-resolved photoluminescence. A PL spectrum showed two dominant peaks which appeared at 300 and 410 nm. It is seen that, as the $Ce^{3+}$ concentration increases, the intensity of 300 nm decreases and the intensity of 410 nm increases. This behavior has been explained by two independent energy transfer mechanism. The first energy transfer occurs from $Ce^{3+}$ ion to $Eu^{3+}$ ion. The second energy transfer takes place from $Ce^{3+}$ ion to $Ce^{3+}-O_{ME}$ complex created in the magnetoplumbite structural host materials. The blue emitting 410 nm peak has been explained by both energy transfer mechanisms.

• 한국진공학회지
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• 제20권6호
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• pp.449-455
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• 2011

$In_{0.4}Al_{0.6}As$ 버퍼층의 성장온도 변화에 따른 $In_{0.5}Ga_{0.5}As/In_{0.5}Al_{0.5}As$ 다중양자우물(multiple quantum wells, MQWs)의 광학적 특성을 포토루미네션스(photoluminescence, PL)와 시간분해 포토루미네션스(time-resolved PL, TRPL) 측정을 이용하여 분석하였다. $In_{0.4}Al_{0.6}As$ 버퍼층은 기판의 온도를 $320^{\circ}C$에서 $580^{\circ}C$까지 다양하게 변화시키며 $1{\mu}m$ 성장하였으며, 그 위에 $In_{0.5}Al_{0.5}As$ 층을 $480^{\circ}C$에서 $1{\mu}m$ 성장한 후 InGaAs/InAlAs MQWs을 성장하였다. MQWs는 6-nm, 4-nm, 그리고 2.5-nm 두께의 $In_{0.5}Ga_{0.5}As$ 양자우물과 10-nm 두께의 $In_{0.5}Al_{0.5}As$ 장벽으로 이루어졌다. 4-nm QW과 6-nm QW로부터 PL 피크가 나타났으나, $In_{0.4}Al_{0.6}As$ 성장온도 변화가 가장 큰($320^{\circ}C$에서 $580^{\circ}C$까지 변화) 시료는 6-nm QW에서의 PL 피크만 나타났다. 낮은 온도($320^{\circ}C$에서 $480^{\circ}C$까지 변화)에서 성장한 $In_{0.4}Al_{0.6}As$ 버퍼층 위에 성장한 MQWs의 PL 특성이 우수하게 나타났다. 발광파장에 따른 TRPL 결과로 4-nm QW과 6-nm QW에서의 캐리어 소멸시간을 얻었다.

• 한국전기전자재료학회논문지
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• 제14권9호
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• pp.762-767
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• 2001

We report the white light emission from the multilayer organic electroluminescent(EL) device using exciplex emission. The exciplex at 500nm originated between poly(N-vinylcarvazole)(PVK) and 2,5-bis(5'-tert-butyl-2-benzoxazoly)thiophene(BBOT) and exciplex of 50nm originated from N,N'-diphenyl-N,N'-(3-methyphenyl)-1,1'-biphenyl-4,4'-diamine(TPD) and BBOT were observed. Also, the energy transfer from PVK to BBOT and poly(3-hexylthiophene)(P3HT) in mixed emitting materials was occurred. The electroluminescence(EL) spectra of organic EL device which have a device structure of ITO/CuPc(5nm)/emitting layer(100nm)/BBOT(30nm)/LiF(1.4nm)/Al(200nm) were slightly changed as a function of the applied voltage. The luminance fo 12.3 ${\mu}$W/$\textrm{cm}^2$ was achieved at 20V and EL spectrum measured at 20V corresponds to Commission Internationale de L\`Eclairage(CIE) coordinates of x=0.29 and y=0.353.

• 반도체디스플레이기술학회지
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• 제18권1호
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• pp.48-52
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• 2019

The blue emitting fluorescence of $SrAl_{12}O_{19}:Ce_{0.09}{^{3+}}$, $Eu_{0.01}{^{2+}}$ phosphor includes two kinds of independent energy transfer mechanism through electric multipole interactions between donor and acceptor ions. The first energy transfer takes place between the $Ce^{3+}$ ion and the $Eu^{2+}$ion which strongly depends on the concentration $Eu^{2+}$ions. The second energy transfer occurs between the $Ce^{3+}$ ion and the $O_{Me}-Ce^{3+}$ complexes. Both energy transfer mechanisms of blue emitting peak at 410 nm were investigated by fitting of Gaussian functions. The result shows that the peak at 410 nm is two overlapping emissions originated by $Eu^{2+}$ions and $O_{Me}-Ce^{3+}$ complexes and as time elapses $Eu^{2+}$peak remains whereas $O_{Me}-Ce^{3+}$ related peak disappears.