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새로운 이차원 구조의 사성분 화합물 KAgBi<sub>2</sub>S<sub>4</sub>의 합성 및 구조 특성 연구
최덕수 ( Duc-su Choi ),박윤봉 ( Younbong Park ) 충남대학교 기초과학연구원 2022 충남과학연구지 Vol.39 No.1
In an effort to search for novel quaternary bismuth sulfide compounds, we have explored K/Ag/Bi/S system and encountered novel quaternary bismuth sulfide compound, KAgBi<sub>2</sub>S<sub>4</sub> using K<sub>2</sub>S<sub>x</sub> molten salt at intermediate temperature. The black hexagonal crystals of KAgBi<sub>2</sub>S<sub>4</sub> are obtained at 350℃ and crystallized in the space group P6<sub>3</sub>/mmc (no.194) with a=4.0216(3)Å, c=30.066(3)Å, γ=120°, Final R<sub>1</sub>/wR<sub>2</sub>=4.37/13.15%. The structure of KAgBi<sub>2</sub>S<sub>4</sub> is composed of negatively charged [M<sub>3</sub>S<sub>4</sub>]<sub>n</sub> <sup>n-</sup> layers separated by charge balancing K<sup>+</sup> ions which are loosely packed in the interlayer spaces.
최강식 ( Kang Sik Choi ),박윤봉 ( Younbong Park ) 충남대학교 기초과학연구원 2019 충남과학연구지 Vol.36 No.1
In order to improve the thermal quenching effect and emission efficiency in the conventional SrSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2+</sup> phosphor, Sr<sup>2+</sup> ions were partially substituted with Mg<sup>2+</sup> ions. The resulting (SrMg)Si<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2+</sup> phosphor was synthesized by a solid-state reaction and was characterized using X-ray powder diffraction and emission spectroscopy. Compared to the pure SrSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2+</sup>, the emission intensity of new (SrMg)Si<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2+</sup> phosphor was increased by 27 %, and the ratio of thermal quenching effect was increased up to 80.5 %. These improvements were mainly due to the size effect of Mg<sup>2+</sup>, which lead to the relaxation of local strain around the Eu<sup>2+</sup> ions in the (SrMg)Si<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2+</sup> structure. As a result, Sr<sub>0.55</sub>Mg<sub>0.4</sub>Si<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu<sup>2+</sup><sub>0.05</sub> proves a better phosphor with high thermal stability suitable for its white light LED application.
BaF<sub>2</sub> 용융염을 활용한 Lu<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>:Ce<sup>3+</sup> 형광체의 광 특성 개선
최강식 ( Kang Sik Choi ),박윤봉 ( Younbong Park ) 충남대학교 기초과학연구원 2020 충남과학연구지 Vol.37 No.1
Greenish yellow Lu<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>:Ce<sup>3+</sup> (LuAG:Ce) as a conversion phosphor for high-quality light emitting diode (LED) device was prepared through solid state reaction using BaF<sub>2</sub> as a flux. It showed an excellent thermal stability, a high quantum efficiency and a broader photoluminescence excitation spectrum compared with pure LuAG:Ce without BaF<sub>2</sub>. Its improved thermal stability results from the fewer intrinsic defects at high temperature, confirmed by uniformity of surface and size. To evaluate its feasibility for white LED, the LuAG:Ce and commercial Y<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>:Ce<sup>3+</sup> (YAG:Ce) were applied to a blue LED with a silicone resin, and their characteristics were compared and analyzed. As a result, the LuAG:Ce phosphor revealed extremely efficient light emission without an efficiency loss under blue LED in comparison with the YAG:Ce phosphor.
2015 개정 교육과정의 중학교 과학 교과서와 고등학교 화학 교과서의 연계 단원에 사용된 비유의 분석
김민하 ( Minha Kim ),박윤봉 ( Younbong Park ) 충남대학교 기초과학연구원 2021 충남과학연구지 Vol.38 No.1
In this study, we analyzed the analogies used in the interrelated chapters between Middle School Science and High School Chemistry textbooks published under the 2015 revised national curriculum. High School textbooks utilize more analogies than the Middle School textbooks, since the level of the contents gets more difficult moving into upper levels of chemistry textbooks. A frequency analysis of the analogy use shows that the section of “structure of matter” has the highest frequency, while “properties of matter” has the lowest. Most of the analogies are represented in a proper manner, but limitations and clear boundaries of analogies use have not been sufficiently mentioned. Based on these results, educational implications are discussed.
박윤봉 충남대학교 기초과학연구소 1995 忠南科學硏究誌 Vol.22 No.1
The reaction of Cu metal with telluride in the sodium polytelluride flux at 400 ℃ produced the simple two-dimensional [CuTe]^- anionic layer compound with sodium ion as a charge balancing cation. The anionic structure resembles ideal anti-PbO structure. Its synthesis and characterization are discussed in detail.
Milling을 이용한 ZnS:Cu,Cl 형광체의 결정 상 변화 및 EL 특성 연구
이유희,한상도,박윤봉 충남대학교 기초과학연구소 2005 忠南科學硏究誌 Vol.32 No.1
A Green phosphor(ZnS:Cu,Cl) was manufactured by solid-liquid reaction for ELD (Electroluminescence Display). The effect of artificial crystal defect on phosphor surface for the ZnS phase conversion and luminescence efficiency have been studied. It was found that ZnS:Cu,Cl could convert to cubic phase more easily due to the formation of artificial crystal defect on 1st fired phosphor by milling process, resulting in improvement of luminescence of phosphor under the driven EL condition. We found out an optimized milling condition through considering effect of each milling conditions such as milling time and rate on defect. Also we determined relationship between EL emission luminescence and driving conditions. A efficient improvement above 50% was observed in electroluminescence by the artificial defect on ZnS:Cu,Cl phosphors compared to crude phosphor.