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공침법을 이용한 Lu<sub>3</sub>Al<sub>5</sub>O<sub>12</sub>:Ce<sup>3+</sup> 나노 형광체 합성과 광학적 특성 분석
강태욱,강현우,김종수,김광철,Kang, Taewook,Kang, Hyeonwoo,Kim, Jongsu,Kim, Gwangchul 한국반도체디스플레이기술학회 2019 반도체디스플레이기술학회지 Vol.18 No.4
LuAG:Ce(Lu3Al5O12:Ce3+) nano phosphor were synthesized by applying the coprecipitation method. It is used to increase the color rendering of phosphor ceramic plate for high power LEDs and laser lighting. Internal quantum efficiency and absorption of LuAG:Ce nano phosphor are 51.5 % and 64.4 %, respectively, which is higher than the previously studied nano phosphors. The maximum absorption wavelength of this phosphor is 450 nm blue light, and the emission wavelength is 510 nm. The emission wavelength shifted to longer wavelength when the concentration of Ce increased in the heat treatment of the reducing atmosphere. Thermal quenching of LuAG nano phosphor was 70 % at 200 ℃, it was explained by their significant quenching of all raman scattering modes, implying the restriction of electron-phonon couplings caused by their defects.
고연색 백색 광원용 BaSi<sub>2</sub>O<sub>2</sub>N<sub>2</sub>:Eu 형광체의 광학·구조 특성 분석
이성훈,강태욱,강현우,정용석,김종수,허훈,Lee, Sunghoon,Kang, Taewook,Kang, Hyeonwoo,Jeong, Yongseok,Kim, Jongsu,Heo, Hoon 한국재료학회 2019 한국재료학회지 Vol.29 No.7
Green $BaSi_2O_2N_2:0.02Eu^{2+}$ phosphor is synthesized through a two-step solid state reaction method. The first firing is for crystallization, and the second firing is for reduction of $Eu^{3+}$ into $Eu^{2+}$ and growth of crystal grains. By thermal analysis, the three-time endothermic reaction is confirmed: pyrolysis reaction of $BaCO_3$ at $900^{\circ}C$ and phase transitions at $1,300^{\circ}C$ and $1,400^{\circ}C$. By structural analysis, it is confirmed that single phase [$BaSi_2O_2N_2$] is obtained with Cmcm space group of orthorhombic structure. After the first firing the morphology is rod-like type and, after the second firing, the morphology becomes round. Our phosphor shows a green emission with a peak position of 495 nm and a peak width of 32 nm due to the $4f^65d^1{\rightarrow}4f^7$ transition of $Eu^{2+}$ ion. An LED package (chip size $5.6{\times}3.0mm$) is fabricated with a mixture of our green $BaSi_2O_2N_2$, and yellow $Y_3Al_5O_{12}$ and red $Sr_2Si_5N_8$ phosphors. The color rendering index (90) is higher than that of the mixture without our green phosphor (82), which indicates that this is an excellent green candidate for white LEDs with a deluxe color rendering index.
AgNWs/Ga-doped ZnO 복합전극 적용 CdSe양자점 기반 투명발광소자
박재홍,김효준,강현우,김종수,정용석,Park, Jehong,Kim, Hyojun,Kang, Hyeonwoo,Kim, Jongsu,Jeong, Yongseok 한국반도체디스플레이기술학회 2020 반도체디스플레이기술학회지 Vol.19 No.4
The silver nanowires (AgNWs) were synthesized by the conventional polyol process, which revealed 25 ㎛ and 30 nm of average length and diameter, respectively. The synthesized AgNWs were applied to the CdSe/CdZnS quantum dot (QD) based transparent light-emitting device (LED). The device using a randomly networked AgNWs electrode had some problems such as the high threshold voltage (for operating the device) due to the random pores from the networked AgNWs. As a method of improvement, a composite electrode was formed by overlaying the ZnO:Ga on the AgNWs network. The device used the composite electrode revealed a low threshold voltage (4.4 Vth) and high current density compared to the AgNWs only electrode device. The brightness and current density of the device using composite electrode were 55.57 cd/㎡ and 41.54 mA/㎠ at the operating voltage of 12.8 V, respectively, while the brightness and current density of the device using (single) AgNWs only were 1.71 cd/㎡ and 2.05 mA/㎠ at the same operating voltage. The transmittance of the device revealed 65 % in a range of visible light. Besides the reliability of the devices was confirmed that the device using the composite electrode revealed 2 times longer lifetime than that of the AgNWs only electrode device.