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고상반응법으로 합성한 Sm3+ 을 첨가한 calcium pyrophosphate 분말 특성 연구
홍경수,양임정 한국물리학회 2022 새물리 Vol.72 No.2
Samarium-doped calcium pyrophosphate (Ca2P2O7:Sm3+) powder is synthesized using the solid-state reaction method. X-ray diffraction patterns and Fourier transform infrared spectra reveal that Ca2P2O7:Sm3+ forms in different phases depending on sintering temperature. This study examines the radiative energy relaxation of Sm3+ ions in Ca2P2O7 by taking absorption and emission spectra at room temperature. An emission wavelength of almost 600 nm with near ultraviolet excitation is observed as a result of the transition of 4G5/2 ! 6H7/2. Phase transition is induced, as the sintering temperature varies from 900 oC to 1200 oC. Emission intensity is measured as the doping concentration of Sm3+ increases up to 0.100 mol at each sintering temperature. The emission intensity of -Ca2P2O7 prepared at 1200 oC increases as Sm3+ concentration increases but is quenched above a certain concentration. Therefore, an optimized concentration of Sm3+ requires highly efficient -Ca2P2O7. This work reports that Ca2P2O7:Sm3+ powder is a good candidate for a red-orange emitting phosphor.
홍경수,양호순 한국물리학회 2019 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.74 No.3
Rare-earth-doped phosphors for near ultraviolet excitation are under an extensive research for applications to white-light-emitting diodes. In this study, we prepare red-orange emitting samarium- doped rhombohedral tricalcium phosphate particles by using the solid-state reaction method. The synthesis procedures are reported, the formation of prepared particles is conrmed using X-ray diraction patterns, and the morphology and the elemental composition are measured using a scan- ning electron microscope. We also investigate the photophysical properties of trivalent samarium- doped tricalcium phosphate phosphors by taking absorption, excitation, and emission spectra at room temperature. We show that the trivalent samarium-doped tricalcium phosphate phosphors are red-emitting phosphors and have higher eciency with near ultraviolet excitation. The emission intensity increases very sharply up to a samarium concentration of 2.5 mol% and then decreases as the concentration increases. Therefore, the samarium doping concentration in the tricalcium phosphate phosphor needs to be optimized.
홍경수,Eun Sick Pak,배종성,정의덕,진종성,하명규,김종필 한국물리학회 2012 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.60 No.9
We have prepared ZnO nanofibers by using the electrospinning method and have analyzed the variations in their structure, optical properties, and chemical bonding states with the annealing temperature and the annealing conditions. After annealing at 500 ℃, the average diameter and the average grain size are determined to be approximately 170 nm and 50 nm, respectively. The ZnO nanofibers have a clearly visible dislocation-free crystal structure. The 2<i>p</i> level of Zn caused Zn-O bonds and the O 1<i>s</i> core level caused physisorbed O<sub>2</sub>. When the nanofibers are annealed at 700 ℃, both ions exhibit shifts of the binding energies compared with those annealed at 500 ℃. The observed band in the visible region shows a strong temperature dependence and a red-shift with the oxygen flow in annealing process, which is related to oxygen vacancies.
홍경수,연병길,Hong, Kyung Sue,Yeon, Byeong Kil 대한생물정신의학회 1997 생물정신의학 Vol.4 No.1
Disturbances in memory are the most common problem in patients with an organic mental syndrome. Other patients with significant psychiatric disorders also often have difficulty with memory. So it is very important in the clinical practice of psychiatry to understand the biological and neurocognitive mechanisms of memory proessing, and to develop the assessment tools with which memory function can be evaluated reliably and validly. Moreover, memory researches provide an important viewpoint from which we can understand the pathophysiological mechanisms of major neuropsychiatric illnesses. This article focuses on our understanding of memory functions in clinical and neurobiological aspects. The relevant material will be presented in four parts : 1) terminologies needed in defining major stages of various types of memory processing : 2) neurochemical and neuroanatomical basis of memory processing : 3) brief bed-side screening tests and more comprehensive neuropsychological tests for the evaluation of memory function : 4) the characteristics of memory dysfunction in several major psychiatric illnesses.