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Near-Infrared to Visible Upconversion Emission in Er3+ and Yb3+ Codoped BaHfO3
Junhwi Lim,Donghee Kim,Y. S. Lee 한국물리학회 2018 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.73 No.7
We report on the upconversion (UC) emission property of Er3+ and Yb3+ codoped BaHfO3 polycrystals. We observed the green ( 540 nm) and the red ( 660 nm) UC emissions in Er3+ in the host material BaHfO3 with 980-nm near-infrared excitation. These emissions exhibited strong temperature evolutions. Interestingly, the UC emissions in Er3+ were found to be controlled with the Yb3+ doping. In Er3+ and Yb3+ codoped BaHfO3, the intensity of the red UC emission increased dramatically while that of the green UC emission showed a non-monotonic temperature dependence. These results suggested that the UC emission process in the Er3+ ion in BaHfO3 should be temperature-sensitive.
Junhwi Lim,Y. S. Lee,Sun A Yang,Sang Don Bu 한국물리학회 2016 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.68 No.11
We investigated the visible emission property of Pb(Zr,Ti)O3 (PZT) thin films irradiated with gammy-ray ( -ray) irradiated at various total doses up to 1000 kGy. The PZT thin films were prepared on Pt/Ti/SiO2/Si substrates by using a sol-gel method with a spin-coating process. The visible emission was found to emerge near 550 nm upon -ray irradiation, and the intensity of the emission increased with increasing dose. The spectrum of the -ray-induced emission was quite narrow, which was quite different from that due to normal defects such as oxygen vacancies. We suggest that the -ray irradiation generates inside the PZT films a specific type of defect state that can be detected by using low-temperature photoluminescence spectroscopy.
임준휘(Junhwi Lim),최규형(Kyuhyung Choi),장우진(Woojin Jang) 한국철도학회 2012 한국철도학회 학술발표대회논문집 Vol.2012 No.10
우리나라 전기철도는 편단 급전방식을 표준으로 하고 있다. 편단 급전방식은 변전소 사이에 구분소를 두어 절연구분장치를 설치해야 하고, 열차가 통과할 때 주 회로 차단기를 차단한 상태로 통과하여야 하는 문제가 있다. 병렬 급전방식은 이러한 문제점을 개선하고 전압강하를 경감, 최대전력수요 억제 등의 전력공급 측면에서 유리하다. 그러나 인접 변전소간의 상차각으로 인하여 루프전류가 발생하기 때문에 변전소간 위상 차가 3도 이내일 때로 제한되고 있어 실질적인 적용이 어려운 실정이다. 본 논문에서는 병렬급전 시 루프전류를 감소시키기 위하여 위상보상 장치를 적용하는 방안을 PSIM을 이용해 연구하였다. 이상과 같은 검토를 통하여 전기철도 병렬 급전을 위한 하나의 가능성을 제시하였다. Korean railway feeding system is alternating current Auto-Transformer system called AT which adopts the single power feeding method as the standard. The single power feeding method has some disadvantages such as the necessity of neutral section. and of breaking MCB with loads passing. The parallel power feeding method can resolve those those difficulties and also has advantages in terms of power efficiency by reducing maximum demand power and voltage drops. However, circulating current occurs between substations when voltage phase is different. That is why it is uneasy to apply parallel power feeding under voltage phase differences over3 degrees. This study suggests applying phase control device to reduce the circulating current simulated by PSIM. Through this, a possibility of the parallel power feeding is suggested.