• 센서학회지
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• 제18권1호
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• pp.48-53
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• 2009

$Eu^{2+}$-doped ${SrAl_2}{O_4}$ and $Eu^{2+}$, $Dy^{3+}$ co-doped ${SrAl_2}{O_4}$ phosphors have been synthesized by conventional solid state method. Photocurrent properties of $Eu^{2+}$ doped ${SrAl_2}{O_4}$ and $Eu^{2+}$, $Dy^{3+}$ co-doped ${SrAl_2}{O_4}$ phosphors, in order to elucidate $Dy^{3+}$ co-doping effect, during and after ceasing ultraviolet-ray (UV) irradiation have been investigated. The photocurrent of $Eu^{2+}$, $Dy^{3+}$ co-doped ${SrAl_2}{O_4}$ phosphors during UV irradiation was 4-times lower than that of $Eu^{2+}$-doped ${SrAl_2}{O_4}$ during UV irradiation, and 7-times higher than that of $Eu^{2+}$-doped ${SrAl_2}{O_4}$ after ceasing UV irradiation. The photocurrent results indicated that holes of charge carriers captured in hole trapping center during the UV irradiation and liberated after-glow process, and made clear that $Dy^{3+}$ of co-dopant acted as a hole trap. The photocurrent of ${SrAl_2}{O_4}$ showed a good proportional relationship to UV intensity in the range of $1{\sim}5mW/cm^2$, and $Eu^{2+}$-doped ${SrAl_2}{O_4}$ was confirmed to be a possible UV sensor.

• 한국분말재료학회지
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• 제23권5호
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• pp.348-352
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• 2016

Quantum dots (QDs) are capable of controlling the typical emission and absorption wavelengths because of the bandgap widening effect of nanometer-sized particles. These phosphor particles have been used in optical devices, photovoltaic devices, advanced display devices, and several biomedical complexes. In this study, we synthesize ZnSe QDs with controlled surface defects by a heating-up method. The optical properties of the synthesized particles are analyzed using UV-visible and photoluminescence (PL) measurements. Calculations indicate nearly monodisperse particles with a size of about 5.1 nm at $260^{\circ}C$ (full width at half maximum = 27.7 nm). Furthermore, the study results confirm that successful doping is achieved by adding $Eu^{3+}$ preparing the growth phase of the ZnSe:Eu QDs when heating-up method. Further, we investigate the correlation between the surface defects and the luminescent properties of the QDs.

• Imaging Science in Dentistry
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• 제46권3호
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• pp.179-184
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• 2016

Purpose: In the present study, we coined the term 'alveolar dome' and aimed to demonstrate the prevalence of alveolar domes through digital periapical radiographs. Materials and Methods: This study examined 800 digital periapical radiographs in regard to the presence of alveolar domes. The periapical radiographs were acquired by a digital system using a photostimulable phosphor (PSP) plate. The ${\chi}^2$ test, with a significance level of 5%, was used to compare the prevalence of alveolar domes in the maxillary posterior teeth and, considering the same teeth, to verify the difference in the prevalence of dome-shaped phenomena between the roots. Results: The prevalence of alveolar domes present in the first pre-molars was statistically lower as compared to the other maxillary posterior teeth (p<0.05). No statistically significant difference was observed in the prevalence of alveolar domes between the maxillary first and second molars. Considering the maxillary first and second molars, it was observed that the palatal root presented a lower prevalence of alveolar domes when compared to the distobuccal and mesiobuccal roots (p<0.05). Conclusion: The present study coined the term 'alveolar dome', referring to the anatomical projection of the root into the floor of the maxillary sinus. The maxillary first and second molars presented a greater prevalence of alveolar domes, especially in the buccal roots, followed by the third molars and second pre-molars. Although the periapical radiograph is a two-dimensional method, it can provide dentists with the auxiliary information necessary to identify alveolar domes, thus improving diagnosis, planning, and treatment.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2008년도 International Meeting on Information Display
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• pp.1547-1550
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• 2008

We are suggesting a new index to represent the performance of PDP, such as Specific Performance Index (SPI) that includes luminous efficacy and panel reflectance. High Xe gas mixture and low panel capacitance are well known as key factors to improve luminous efficacy of PDP [1]. However, higher driving voltage and longer discharge time lag is an obstacle when applying these technologies. Modified cell design, new materials and driving waveform enable us to overcome these obstacles. High efficient phosphor is also a key material to improve luminous efficacy. Phosphors coated with pigment are used to reduce panel reflectance. High performance 50-inch HD PDP with luminous efficacy of 2.3 lm/W has been developed.

• 대한전자공학회논문지SD
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• 제39권8호
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• pp.17-23
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• 2002

전자빔 증착 장비를 이용하여 SrS:CuCl TFEL 소자를 제작한 후, 발광특성을 조사하였다. 형광체 모체는 SrS 분말을 사용하였고, 발광중심체로는 CuCl 분말을 0.05 ~ 0.6 at% 범위에서 첨가하였다. 증착 온도 500℃, 전자빔 전류 20 ~ 40 mA 및 증착율 5 ~ 10 /sec의 조건에서 형광층 두께를 6000 으로 증착시켰다. CuCl 농도가 낮을 때에는 monomer, dimer, trimer 및 tetramer 발광센터에 의한 청색 발광을 확인할 수 있었으나 휘도가 낮았다. CuCl 농도가 높을 때에는 dimer와 trimer 발광센터에 의한 밝은 녹청색 빛을 방출하였다. 최적의 발광특성은 CuCl 농도를 0.2 at% 첨가한 SrS:CuCl TFEL 소자에서 관찰되었으며, 문턱전압, 휘도(L/sub 40/), 효율(η/sub 20/) 및 CIE 색좌표는 각각 55 V, 728 cd/㎡, 0.49 lm/W 및 (0.21, 0.33)을 나타내었다.

• 마이크로전자및패키징학회지
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• 제26권4호
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• pp.83-88
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• 2019

화학양론적 조성과 비화학양론적 조성을 갖는 LiBaPO₄:Eu²⁺ 계 형광체를 고상반응으로 제조한 후 환원 분위기에서 열처리한 다음 분말의 결정구조와 광 특성을 X선 회절 분석과 발광 분석을 통하여 조사하였다. XRD 분석 결과, 900℃에서 중간상으로서 Ba₃(PO₄)₂ 상이 주 결정상 LiBaPO₄와 함께 나타났다. 1,100℃에서 낮은 농도의 유로피움이 도핑된 조성의 결정구조는 삼방정(trigonal) 구조에 속하는 반면, 4 mol% Eu²⁺ 이상의 조성에서는 단사정(monoclinic) 계를 나타내었다. 4 mol% 이상의 Eu²⁺이 첨가된 비화학양론적 조성에서는 단일상의 LiBaPO₄가 형성되었다. 단일상의 LiBaPO₄:Eu²⁺ 계 형광체는 480nm에서의 청록색 발광스펙트럼을 나타내었다.

• 한국세라믹학회지
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• 제51권6호
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• pp.605-611
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• 2014

$SrGd_{2-x}(MoO_4)_4:Er^{3+}/Yb^3$ phosphors with doping concentrations of $Er^{3+}$+ and $Yb^{3+}$ ($x=Er^{3+}+Yb^{3+}$, $Er^{3+}=0.05$, 0.1, 0.2, and $Yb^{3+}=0.2$, 0.45) were successfully synthesized by the cyclic microwave-modified sol-gel method, and their upconversion mechanism and spectroscopic properties have been investigated in detail. Well-crystallized particles showed a fine and homogeneous morphology with grain sizes of $2-5{\mu}m$. Under excitation at 980 nm, $SrGd_{1.7}(MoO_4)_4:Er_{0.1}Yb_{0.2}$ and $SrGd_{1.5}(MoO_4)_4:Er_{0.05}Yb_{0.45}$ particles exhibited a strong 525-nm emission band, a weak 550-nm emission band in the green region, and a very weak 655-nm emission band in the red region. The Raman spectra of the doped particles indicated the domination of strong peaks at higher frequencies of 1023, 1092, and $1325cm^{-1}$ and at lower frequencies of 223, 2932, 365, 428, 538, and $594cm^{-1}$ induced by the incorporation of the $Er^{3+}$+ and $Yb^{3+}$+ elements into the $Gd^{3+}$ site in the crystal lattice, which resulted in the unit cell shrinkage accompanying a new phase formation of the $[MoO_4]^{2-}$ groups.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2005년도 하계학술대회 논문집 Vol.6
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• pp.441-443
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• 2005

According as CCFL(Cold Cathode Fluorescent lamp) of light source in Backlight unit for Note PC (Personal computer) is presently needed to low power consumption and long life time, the development focus of CCFL is going on the discharge gas, phosphor and electrode material. First of all, discharge voltage characteristic of CCFL is closely connected with electrode material For low discharge voltage, the characteristic of electrode material is needed to low work function, low sputtering ratio and superior manufacturing property. We developed new CCFL with Nb/Ni Clad electrode superior to conventional CCFL. Because Nb/Ni Clad electrode with Ni material and Nb material, the electrical characteristic is superior to other electrode materials. The electrode of Nb/Ni Clad is composed that Ni of outside material has superior manufacturing property and Nb of inside material has low work function. Nb/Ni Clad of new electrode material is made by process of Rolling mill at high pressure and heat treatment. We compared electrical characteristic of Nb/Ni clad electrode with conventional Mo electrode by measurement. Mo electrode and Nb/Ni Clad electrode of cup type with diameter 1.1 mm and length 3.0mm are used to this experiment. Material content of Mo electrode is Mo 100%. But, Nb/Ni Clad electrode is composed by content of Nb 40% and Ni 60%. The result of comparison measurement between new CCFL with Nb/Ni Clad electrode and conventional CCFL was appeared that CCFL with Nb/Ni Clad electrode had superior characteristic than conventional CCFL. As a result of experiment, we completed Note PC with low power consumption and long life time by application of new CCFL with Nb/Ni Clad electrode.

• Imaging Science in Dentistry
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• 제49권2호
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• pp.97-102
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• 2019

Purpose: This study was conducted to evaluate the effect of different spatial resolutions of a photostimulable phosphor plate (PSP) radiography system on the detection of proximal caries lesions. Materials and Methods: Forty-five extracted human permanent teeth were radiographed using a PSP system (VistaScan Perio Plus) and scanned at the 4 resolutions (10 lp/mm, 20 lp/mm, 25 lp/mm, and 40 lp/mm) available in the system. Three independent examiners scored the images for the presence and absence of proximal caries lesions using a 5-point scale. The presence or absence of caries was confirmed by histological sections of the examined teeth (defined as the gold standard). Intra- and inter-observer reproducibility was calculated by the weighted kappa test. One-way analysis of variance with the post hoc Tukey test was used to compare the area under the receiver operating characteristic curve for the classifications made with each resolution. Results: For the detection of enamel lesions, the spatial resolution of 10 lp/mm was significantly superior to the other resolutions. However, the spatial resolution did not affect the detection of caries lesions in dentin (P>0.05). Conclusion: Spatial resolution may influence the accuracy of the detection of incipient caries lesions in radiographs with PSP plates. Images with low spatial resolution seem to be more appropriate for this purpose.

• 한국표면공학회지
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• 제54권3호
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• pp.112-118
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• 2021

Dy³⁺- and Eu³⁺-codoped BaWO₄ phosphors for white light-emitting diode were synthesized with different activator ions via a solid-state reaction process. The structural, morphological, and optical properties of the BaWO₄:Dy³⁺,Eu³⁺ phosphors were investigated as a function of Eu³⁺ concentration at a fixed concentration of Dy³⁺ ions. XRD patterns exhibited that all the synthesized phosphors had a tetragonal system, irrespective of the concentrations of Dy³⁺ and Eu³⁺ ions. The excitation spectra of the synthesized phosphors were composed of three intense bands centered at 251, 355, and 393 nm and several weak peaks. For the BaWO₄:Dy³⁺,Eu³⁺ phosphors synthesized with 1 mol% of Eu³⁺, the emission spectra under ultraviolet excitation at 393 nm showed two strong blue and yellow bands at 485 and 577 nm corresponding to the ⁴F_9/2⁶H_15/2 and ⁴F_9/2⁶H_13/2 transitions of Dy³⁺ ions, respectively and several weak bands in the range of 600-700 nm resulting from the 4f transitions of Eu³⁺ ions. As the concentration of Eu³⁺ ions increased, intensities of the blue and yellow emission bands gradually decreased while those of the red emissions increased rapidly and the energy transfer efficiency from Dy³⁺ to Eu³⁺ ions was 95.3% at 20 mol% of Eu³⁺. The optimum white light emission with x=0.363, y=0.357 CIE 1931 chromaticity coordinates was obtained for the sample doped with 5 mol% Dy³⁺ and 1 mol% of Eu³⁺.