• Rapid Communication in Photoscience
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• 제4권2호
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• pp.45-47
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• 2015

We have successfully synthesized $AgInS_2$ core and $AgInS_2$/ZnS core/shell nanoparticles by the sonochemical method. The ultrasonic based $AgInS_2$ and $AgInS_2$/ZnS nanoparticle synthesis can be utilized as a simple and rapid method. The $AgInS_2$/ZnS nanoparticles show the higher fluorescence intensity and quantum yield than $AgInS_2$ nanoparticles. Fluorescence wavelength of $AgInS_2$/ZnS shows blue shift from 635 nm to 610 nm against $AgInS_2$ because of reducing the defect sites and increasing spatial confinements. For the fluorescence lifetime, $AgInS_2$/ZnS (124.8 ns) has longer lifetime than $AgInS_2$ (54.8 ns).

• 한국산학기술학회논문지
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• 제3권3호
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• pp.161-165
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• 2002

게르마늄첨가 다성분계 산화물 유리를 제조하여 자외선(UV) 조사에 따른 유리의 미세 구조변화를 PL(photo-luminescence)과 ESR(electron spin resonance)을 이용하여 관찰하였다. 게르마늄 첨가량이 증가함에 따라 PL방사량은 증가하였으며, UV 조사 후에는 처음과 반대되는 광혹화 현상으로 감소하는 현상을 나타냈다. UV조사로 변화된 특성은 열처리를 통하여 회복이 가능하였으며, ESR 측정에서도 PL결과와 같은 광혹화 현상(phodarkenine effect)과 열표백화 현상(thermal bleaching effect)이 확인되었다. 또한, XRD 분석을 통하여 이러한 현상이 비정질 상은 그대로 유지하는 미세구조 변화임을 알 수 있었다.

• 한국세라믹학회지
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• 제43권9호
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• pp.569-574
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• 2006

Transparent glass-ceramics containing fresnoite crystals have been prepared by controlled heat treatment in $K_2O-BaO-TiO_2-SiO_2$ and their nonlinear optical and luminescent properties were investigated using Maker fringe method and Spectrofluorometer. The second harmonic generation was observed in all samples and the values decreased with increasing $K_2O$ content. The luminescence of blue light at ${\sim}482nm$ could be observed and it was shown that the luminescent property was controlled by the $K_2O$ content.

• 대한의용생체공학회:의공학회지
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• 제32권2호
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• pp.85-92
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• 2011

Bioluminescence imaging (BLI) is the most sensitive animal imaging technique for molecular imaging research. Generally, highly sensitive CCD is used to detect an optical probe introduced in a living mouse. However, in many cases, the light signal emitted from a probe is too small to detect because it is scattered and attenuated by the tissue prior to being detected. The problem is that scattering and attenuation not only inhibit accurate measurement but also make image quality down. Thus we introduced a new method to reduce noise by using property of CCD and method to improve image quality of bioluminescence image by using two steps Gaussian blurring.

• 한국재료학회지
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• 제27권6호
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• pp.307-311
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• 2017

Organometal halide perovskite materials, due to the tunability of their electronic and optical properties by control of composition and structure, have taken a position of significant importance in optoelectronic applications such as photovoltaic and lighting devices. Despite numerous studies on the structure - property relationship, however, practical application of these materials in electronic and optical devices is still limited by their processability during fabrication. Achieving nano-sized perovskite particles embedded in a polymer matrix with high loading density and outstanding photoluminescence performance is challenging. Here, we demonstrate that the careful control of nanoparticle formation and growth in the presence of poly(methyl methacrylate) results in perovskite nanoparticle - polymer nanocomposites with very good dispersion and photoluminescence. Furthermore, this approach is found to prevent further growth of perovskite nanoparticles, and thus results in a more uniform film, which enables fabrication using the perovskite nanoparticles.

• 한국재료학회지
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• 제22권4호
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• pp.195-201
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• 2012

$Ce^{3+}$-doped yttrium aluminum gallium garnet (YAGG:$Ce^{3+}$), which is a green-emitting phosphor, was synthesized by solid state reaction using ${\alpha}$-phase or ${\gamma}$-phase of nano-sized $Al_2O_3$ as the Al source. The processing conditions and the chemical composition of phosphor for the maximum emission intensity were optimized on the basis of emission intensity under vacuum UV excitation. The optimum heating temperature for phosphor preparation was $1550^{\circ}C$. Photoluminescence properties of the synthesized phosphor were investigated in detail. From the excitation and emission spectra, it was confirmed that the YAGG:$Ce^{3+}$ phosphors effectively absorb the vacuum UV of 120-200 nm and emit green light positioned around 530 nm. The crystalline phase of the alumina nanoparticles affected the particle size and the luminescence property of the synthesized phosphors. Nano-sized ${\gamma}-Al_2O_3$ was more effective for the achievement of higher emission intensity than was nano-sized ${\alpha}-Al_2O_3$. This discrepancy is considered to be because the diffusion of $Al^{3+}$ into $Y_2O_3$ lattice is dependent on the crystalline phase of $Al_2O_3$, which affects the phase transformation of YAGG:$Ce^{3+}$ phosphors. The optimum chemical composition, having the maximum emission intensity, was $(Y_{2.98}Ce_{0.02})(Al_{2.8}Ga_{1.8})O_{11.4}$ prepared with ${\gamma}-Al_2O_3$. On the other hand, the decay time of the YAGG:$Ce^{3+}$ phosphors, irrespective of the crystalline phase of the nano-sized alumina source, was below 1 ms due to the allowed $5d{\rightarrow}4f$ transition of the $Ce^{3+}$ activator.

• 한국방사선학회논문지
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• 제9권1호
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• pp.39-45
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• 2015

본 연구는 고상법으로 형광체를 합성하였다. 모체 물질은 $La_2W_3O_{12}$에 활성제로 $Eu^{3+}$이온을 첨가하여 활성제 조성변화에 따른 XRD 분석과 여기 및 방출 스펙트럼 및 온도에 따른 형광 스펙트럼 분석과 수명시간을 측정하였다. $La_2W_3O_{12}:Eu^{3+}$의 1 mol%의 XRD 스펙트럼은 ICSD 카드 (78180)에 보고된 데이터 스펙트럼과 비교하였을 때 XRD 스펙트럼이 잘 일치함을 확인 하였다. $La_2W_3O_{12}$ 형광체에 활성제로 $Eu^{3+}$이온 1 mol%를 첨가한 여기 스펙트럼에서는 286 nm 근처에서 286 nm 넓은 전하전달밴드가 관찰된다. 이 전하전달밴드는 $WO_4$그룹과 $Eu^{3+}$이온의 전하 전달 밴드이며 $O^{2-}-W^{6+}$, $O^{2-}-Eu^{3+}$의 ligand-to-metal 전하 전달 흡수가 이루어진다. 350~500 nm 영역에서는 $Eu^{3+}$의 f-f 전이에 의한 피크가 나타났다. 여기 스펙트럼에서 $Eu^{3+}$의 $^7F_0{\rightarrow}{^5D_4},{^5D_4},{^5L_6},{^5G_4},{^5D_3},{^5D_2}$ 전이에 해당한다. 방출 스펙트럼은 280, 395 nm로 각각 여기한 결과 $Eu^{3+}$이온의 $^5D_0{\rightarrow}^7F_2$(618nm)에서 강한 피크가 보였다. 희토류 이온이 도핑 되지 않은 $La_2W_3O_{12}$ 형광체를 266 nm로 여기하여 온도에 변화 따른 방출 스펙트럼은 저온에서 상온으로 갈수록 형광의 세기가 약하게 나타났다. 온도에 따른 수명시간은 7 K($114{\mu}s$), 100 K($94{\mu}s$), 200 K($10{\mu}s$), 300 K($0.5{\mu}s$)로 나타났다.

• 한국재료학회지
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• 제10권3호
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• pp.241-245
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• 2000

고온에서 증발된 금속 갈륨 (Ga)을 암모니아 ($NH_3$) 기체와 직접 반응시켜 사파이어 (${\alpha}-Al_2O_3$) 기판 위에 GaN 후막을 성장하였다. 성장된 GaN는 주로 [0002] 방향으로 성장하였으나 낮은 성장온도에서는 [1011] 방향의 성장이 관찰되었으며 V-형태를 가진 매우 거친 표면을 보였다. 그러나 성장온도가 증가하면 [1010]와 [1011] 방향으로 성장이 관찰되었으며 피라미드면을 가진 육방정 결정이 성장되었다. 성장된 GaN의 두께는 온도가 증가할수록 증가하였으나, $1270^{\circ}C$의 고온에서는 열분해를 일으켜 두께가 감소하였다. 공급된 $NH_3$의 유량이 증가할수록 GaN의 결정성과 광특성은 향상되었다. X-선 회절기 (X-ray diffraction)와 광루미네센스(photoluminescence) 분석결과로 GaN 후막이 (1010) 면으로 성장되면 황색발광이 증가됨을 관찰할 수 있었다.

• 한국재료학회지
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• 제11권8호
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• pp.636-640
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• 2001

PDP용 녹색 형광체의 발광특성을 개선시키기 위해 고안된 액상의 화학적 합성법을 사용하여 조성식이 $Zn_{2-x}$ $SiO_4$:xMn(x=0.05, 0.08)인 형광체를 입자크기가 0.5~2$\mu\textrm{m}$로 조절하여 제조하였다. 제조된 형광체 입자는 구상이며 잘 분산된 형상을 봉주었고, 고상반응법에 비해 상대적으로 낮은 $1080^{\circ}C$에서 willemite구조의 단일상을 얻을 수 있었다. 또한 진공 자외선 영역의 147 nm의 여기원을 사용하여 광발광 특성을 조사하였다. 입자의 크기가 1$\mu\textrm{m}$이고 Mn의 도핑양이 8mole%일 때, 상용 형광체와 비교하여 발광세기는 약 40% 향상되었고 색좌표는 x=0.24, y=0.69로 거의 일치하는 결과를 얻을 수 있었다. 측정된 형광체의 잔광시간은 7.8ms이었다.

• 한국재료학회지
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• 제26권9호
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• pp.504-511
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• 2016

To prepare $Mn^{4+}$-activated $K_2TiF_6$ phosphor, a precipitation method without using hydrofluoric acid (HF) was designed. In the synthetic reaction, to prevent the decomposition of $K_2MnF_6$, which is used as a source of $Mn^{4+}$ activator, $NH_5F_2$ solution was adopted in place of the HF solution. Single phase $K_2TiF_6$:$Mn^{4+}$ phosphors were successfully synthesized through the designed reaction at room temperature. To acquire high luminance of the phosphor, the reaction conditions such as the type and concentration of the reactants were optimized. Also, the optimum content of $Mn^{4+}$ activator was evaluator based on the emission intensity. Photoluminescence properties such as excitation and emission spectrum, decay curve, and temperature dependence of PL intensity were investigated. In order to examine the applicability of this material to a white LED, the electroluminescence property of a pc-WLED fabricated by combining the $K_2TiF_6$:$Mn^{4+}$ phosphor with a 450 nm blue-LED chip was measured.