• 한국재료학회지
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• 제22권9호
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• pp.489-493
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• 2012

Green phosphors $K_2BaW_2O_8:Tb^{3+}$(1.0 mol%) were synthesized by solid state reaction method. Differential thermal analysis was applied to trace the reaction processes. Three endothermic values of 95, 706, and $1055^{\circ}C$ correspond to the loss of absorbed water, the release of carbon dioxide, and the beginning of the melting point, respectively. The phase purity of the powders was examined using powder X-ray diffraction(XRD). Two strong excitation bands in the wavelength region of 200-310 nm were found to be due to the ${WO_4}^{2-}$ exciton transition and the 4f-5d transition of $Tb^{3+}$ in $K_2BaW_2O_8$. The excitation spectrum presents several lines in the range of 310-380 nm; these are assigned to the 4f-4f transitions of the $Tb^{3+}$ ion. The strong emission line at around 550 nm, due to the $^5D_4{\rightarrow}^7F_5$ transition, is observed together with weak lines of the $^5D_4{\rightarrow}^7F_J$(J = 3, 4, and 6) transitions. A broad emission band peaking at 530 nm is observed at 10 K, while it disappears at room temperature. The decay times of $Tb^{3+}$ $^5D_4{\rightarrow}^7F_5$ emission are estimated to be 4.8 and 1.4 ms, respectively, at 10 and 295 K; those of the ${WO_4}^{2-}$ exciton emissions are 22 and 0.92 ${\mu}s$ at 10 and 200 K, respectively.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2003년도 International Meeting on Information Display
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• pp.885-886
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• 2003

A bilayer is used as an anode electrode for organic electroluminescent devices. The bilayer consist of an ultrathjn ZnO layer adjacent to an hole-transporting layer and an Indium tin oxide(ITO) outerlayer. We tried to bring low the barrier between the devices as deposited ZnO films on ITO substrates. We fabricated the organic EL structure consisted of Al as cathode, $Al_{2}O_{3}$ as electro transport layer, Alq3 as luminously layer, triphenyl diamine(TPD) as hole transport layer and ZnO(l nm )/ITO(l50 nm) as anode. The result of this experiment was not good compared with the case of using ITO, Nevertheless, at this structure we obtained the lowest turn-on voltage as the value of 19 V and the good brightness (6200 $cd/m^{2}$) of the emission light from the devices. Then the quantum efficiency was to be 1.0%.

• 센서학회지
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• 제9권5호
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• pp.341-349
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• 2000

CsI에 활성제로 $Br^-$ 이온을 1, 3, 5 혹은 10 mole % 첨가하여 Czochralski방법으로 CsI(Br) 단결정을 육성하였다. 육성한 CsI(Br) 단결정의 결정구조는 체심입방체였으며, 격자상수 ${\alpha}_0$는 $4.568\;{\AA}$이었다. CsI(Br) 단결정들의 흡수단 파장은 243 nm이었다. 그리고 흡수단 파장으로 여기 시킨 발광스펙트럼의 파장범위는 $Br^-$ 이온 농도에 관계없이 $300{\sim}600\;nm$이었고, 중심파장은 모두 약 440 nm이었으며, 발광강도는 $Br^-$ 이온을 3 mole % 첨가하였을 때 가장 컸다. $Br^-$ 이온을 3 mole % 첨가한 CsI(Br) 섬광체의 에너지 분해능은 $^{137}Cs$(662 keV)에 대해서는 15.0%, $^{54}Mn$(835 keV)에 대해서는 13.1%이었고, $^{22}Na$의 511 keV와 1275 keV에 대한 에너지 분해능은 각각 18.0% 와 6.3%이었다. 형광감쇠곡선은 빠른 감쇠 성분과 느린 감쇠 성분으로 구성되어 있으며, 빠른 감쇠성분은 $Br^-$ 이온의 농도에 관계없이 약 41 ns로 거의 일정하였다. 그리고 CsI(Br) 섬광체들의 시간 분해능은 $Br^-$ 이온 농도가 증가할수록 저하하는 경향을 나타내었다.

• Macromolecular Research
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• 제17권9호
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• pp.672-681
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• 2009

A series of inert and photo-stable Er(III)-encapsulated complexes based on ${\pi}$-extended dendritic anthracene ligands bearing G3-aryl-ether dendron ([G3-AnX]-$CO_2H$), which retain different ${\pi}$-bridging systems, such as single (X= S), double (X= D) and triple (X= T) bonds was designed and synthesized to establish the structure-property relationship. The near infrared emission intensities of Er(III)-encapsulated complexes were enhanced dramatically by increasing the ${\pi}$-conjugated extension of anthracene ligands. The time-resolved luminescence spectra show monoexponential decays with a lifetime of $2.0{\sim}2.4ms$ for $Er^{3+}$ ions in thin films, and calculated intrinsic quantum yields of $Er^{3+}$ ions are in the range of $0.025{\sim}0.03%$. As a result, all Er(III)-encapsulated dendrimer complexes exhibit the near IR emission with the following order: $Er^{3+}-[G3-AnD]_3$(terpy) > $Er^{3+}-[G3-AnS]_3$(terpy) ${\approx}$ $Er^{3+}-[G3-AnT]_3$(terpy), because $Er^{3+}-[G3-AnD]_3$(terpy) has a higher relatively spectral overlap J value and energy transfer efficiency. In addition, the lack of detectable phosphorescence and no significant spectral dependence of the ${\pi}$-extended anthracene moieties on the solvent polarity support energy transfer from their singlet state to the central $Er^{3+}$ ion taking place in $Er^{3+}-[G3-AnX]_3$(terpy).

• Bulletin of the Korean Chemical Society
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• 제34권1호
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• pp.95-98
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• 2013

The photoluminescence (PT) properties of Al-doped ZnO thin films grown by the sol-gel dip-coating method have been investigated. At 12 K, nine distinct PL peaks were observed at 2.037, 2.592, 2.832, 3.027, 3.177, 3.216, 3.260, 3.303, and 3.354 eV. The deep-level emissions (2.037, 2.592, 2.832, and 3.027 eV) were attributed to native defects. The near-band-edge (NBE) emission peaks at 3.354, 3.303, 3.260, 3.216, and 3.177 eV were attributed to the emission of the neutral-donor-bound excitons ($D^0X$), two-electron satellite (TES), free-to-neutral-acceptors (e,$A^0$), donor-acceptor pairs (DAP), and second-order longitudinal optical (2LO) phonon replicas of the TES (TES-2LO), respectively. According to Haynes' empirical rule, we calculated the energy of a free exciton (FX) to be 3.374 eV. The thermal activation energy for $D^0X$ in the nanocrystalline ZnO thin film was found to be ~25 meV, corresponding to the thermal dissociation energy required for $D^0X$ transitions.

• 센서학회지
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• 제6권1호
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• pp.16-23
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• 1997

섬광검출기로 널리 사용되고 있는 BGO 결정을 Czochralski 방법으로 육성하였다. 그리고 들뜸빛띠, 방출빛띠 및 형광수명시간을 측정하여 엑시톤과 $Eu^{+3}$ 이온의 전하전달상태 사이에 에너지가 전달되고, 그 전달효율이 결정의 온도가 높아질수록 증가함을 확인하였다. 이것은 BGO 섬광체에 Eu를 첨가함으로써 방사선 저항을 증가시키는 과정에 대한 하나의 메카니즘이 된다. 한편 Eu를 많이 첨가할수록 방사선 저항은 증가되지만 섬광으로 부적당한 $Eu^{3+}$ 이온의 $^{5}D_{0}$, 준위에서 방출되는 형광이 커졌다. BGO 결정에 Eu를 0.1몰% 첨가하면 방사선유도 색중심밀도가 약 20배 줄고, 섬광에 이용되는 $Bi^{3+}$ 이온과 엑시톤이 방출하는 형광량에 비해서 형광수명시간이 $^{5}D_{0}$ 형광방출량은 1% 미만이었다.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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• pp.171.2-171.2
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• 2015

Nowadays, trivalent rare-earth ($RE^{3+}$) ions activated metal oxides have been proved to be excellent host materials due to their various applications. Facile wet-chemical technique have been considered as the best synthetic route due its intensive interest in the preparation of nanostructures. Europium ion doped lanthanum hydroxide ($La(OH)_3:Eu^{3+}$) phosphors were synthesized by the facile wet chemical method using the hexamethylenetetramine (HMTA) as a mediated surfactant. The thermal behavior for the $La(OH)_3:Eu^{3+}$ phosphors was investigated by thermogravimetric and differential thermal analysis method. The morphological studies were measured by scanning electron microscope and transmission electron microscope measurements, indicating three-dimensional (3D) flower-like $La(OH)_3:Eu^{3+}$ nanorod bundles. After subsequent annealing process, the lanthanum oxide ($La_2O_3:Eu^{3+}$) phosphor exhibited similar kind of morphology. The synthesized $La(OH)_3:Eu^{3+}$ and $La_2O_3:Eu^{3+}$ samples were characterized by X-ray powder diffraction and Fourier transform infrared spectroscopy. Furthermore, photoluminescence and cathodoluminescence properties were studied in details.

• Journal of Radiation Protection and Research
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• 제40권3호
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• pp.147-154
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• 2015

The scatter photons and photoneutrons from high energy photon beams (more than 10 MV) will increase the undesired dose to the patient and the staff working in linear accelerator room. This undesired dose which is found at out-of-field area can increase the probability of secondary malignancy. The purpose of this study is to determine the equivalent dose of scatter photons and neutrons generated by 3 different treatment techniques: 3D-conformal, intensity modulated radiation therapy (IMRT) and volumetric modulated arc therapy (VMAT). The measurement was performed using two types of the optically stimulation luminescence detectors (OSL and OSLN) in the Alderson Rando phantom that was irradiated by 3 different treatment techniques following the actual prostate cancer treatment plans. The scatter photon and neutron equivalent dose were compared among the 3 treatments techniques at the surface in the out-of-field area and the critical organs. Maximum equivalent dose of scatter photons and neutrons was found when using the IMRT technique. The scatter neutrons showed average equivalent doses of 0.26, 0.63 and $0.31mSv{\cdot}Gy^{-1}$ at abdominal surface region which was 20 cm from isocenter for 3D, IMRT and VMAT, respectively. The scattered photons equivalent doses were 6.94, 10.17 and $6.56mSv{\cdot}Gy^{-1}$ for 3D, IMRT and VMAT, respectively. For the 5 organ dose measurements, the scattered neutron and photon equivalent doses in out of field from the IMRT plan were highest. The result revealed that the scatter equivalent doses for neutron and photon were higher for IMRT. So the suitable treatment techniques should be selected to benefit the patient and the treatment room staff.

• 한국재료학회지
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• 제31권10호
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• pp.582-585
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• 2021

Y₂O₃:Eu_x (x = 0.005, 0.01, 0.02, 0.03, 0.05, 0.1 mol) phosphors are synthesized with different concentrations of Eu³⁺ ions by solvothermal method. The crystal structure, surface and optical properties of the Eu doped Y₂O₃ phosphors are investigated using X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), and photoluminescence (PL) and photoluminescence excitation (PLE) analyses. From X-ray diffraction (XRD) results, the crystal structure of the Eu doped Y₂O₃ phosphor is found to be cubic. The maximum emission spectra of the Eu doped Y₂O₃ phosphors are observed at 0.05 mol Eu³⁺ concentration. The photoluminescence of 615 nm in the Eu doped Y₂O₃ phosphors is associated with ⁵D₀ → ⁷F₂ transition of Eu³⁺ ions. The decrease in emission intensity of 0.1 mol Eu doped Y₂O₃ is interpreted by concentration quenching. The International Commission on Illumination (CIE) coordinates of 0.05 mol Eu doped Y₂O₃ phosphor are X = 0.6547, Y = 0.3374.

• 전기화학회지
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• 제16권3호
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• pp.184-189
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• 2013

졸-겔법 및 졸-겔법과 연소법을 함께 사용한 하이브리드법으로 각각 얻어진 건식 젤을 열처리하여 $Ba_2SiO_4:Eu^{2+}$ ($B_2S:Eu^{2+}$) 분말을 합성하였으며, 이들 공정에 따른 구조 및 발광 특성 변화를 조사 하였다. Si 공급원으로서는 tetraethyl orthosilicate (TEOS)를 사용하였다. 졸-겔법에 의한 건식 젤로 하소 과정 없이 합성한 경우 TEOS 양의 변화에 따라서 상전이가 관찰되었으며, 1.2M TEOS에서 $B_2S:Eu^{2+}$ 단일상을 얻었을 수 있었다. 반면에 하소 과정을 거친 1.2M TEOS로 합성된 분말에서는 졸-겔법과 하이브리드법 모두 $B_2S:Eu^{2+}$와 미량의 $BaSiO_3:Eu^{2+}$ ($BS:Eu^{2+}$) 상이 혼재하는 분말을 얻을 수 있었으나, 이들 분말은 하소 과정 없이 합성된 것보다 발광특성이 약 두배 정도 우수하였다. 하이브리드법에 의한 $B_2S:Eu^{2+}$는 졸-겔법에 의한 것에 비하여 발광강도가 약간 떨어지나 공정 시간을 획기적으로 단축 시킬 수 있는 장점을 보이고 있었다. 1.1M TEOS로 하소 과정을 거쳐 하이브리드법으로 얻어진 분말은 $B_2S:Eu^{2+}$ 단일상으로 구성되어 있었으며, $Eu^{2+}$이온의 $4f^65d^1{\rightarrow}4f^7$ 전이에 의한 가장 강한 강도를 갖는 녹색 발광 (505 nm) 스펙트럼을 보이고 있었다.