| Project/Area Number |
07650016
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Applied materials science/Crystal engineering
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| Research Institution | TOTTORI UNIVERSITY |
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Principal Investigator |
TANAKA Shosaku Tottori University, Faculty of Engineering, Professor, 工学部, 教授 (90032284)
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| Co-Investigator(Kenkyū-buntansha) |
OHMI Koutoku Tottori University, Faculty of Engineering, Research Assistant, 工学部, 助手 (90243378)
ISHII Akira Tottori University, Faculty of Engineering, Associate Professor, 工学部, 助教授 (70183001)
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| Project Period (FY) |
1995 – 1996
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| Project Status |
Completed (Fiscal Year 1996)
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| Budget Amount *help |
¥2,200,000 (Direct Cost: ¥2,200,000)
Fiscal Year 1996: ¥700,000 (Direct Cost: ¥700,000)
Fiscal Year 1995: ¥1,500,000 (Direct Cost: ¥1,500,000)
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| Keywords | Semiconductors / Rare-earth luminesncet centers / Energy transfer process / 5d excited state / Charge transfer excited state / Electroluminescence / IIa-VIb compound semiconductors / IIa-IIIb_2-VIb_4 compound semiconductors / IIa-IIIb2-VIb4族化合物半導体 / 局在形発光中心 |
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| Research Abstract |
Luminescence of rare-earth ions doped in semiconductors arises from electronic transition in an open 4f^n shell. Because 4f^n electrons is screened by outer electrons in (5s) ^2 (5p) ^6 closed shells, the energy states of the 4f^n of rare-earth ions in the various host materials are hardly influenced by the crystal field. Therefore, rare-earth ions give specific luminescence with sharp line spectra and emission wavelength is hardly dependent on the lattice temperatures. Exciation of rare-earth ions may result from the following processes. Creation of electon hole pairs due to band to band excitation occurs first. Subsequent capture and recombination of electron-hole pairs at rare-earth ion site resulting in the exciation of 4f^n electrons follows. Finally rare-earth ions give rise to luminescence due to the transition in the 4f^n electron configutations. To clarify excitation and luminescence process of rare-earth ions in semiconductors, it is essential to understand the energy transfe
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r process from electron hole pairs to 4f^n electrons. For Ce^<3+> ions, it is known that Ce^<3+> centers are ionized through 5d excited state resulting in Ce^<4+> ions. In this study, role of ionization of Ce^<3+> ions and capture of electrons in the excitation process is investigated. The results are described in the following.
1. SrS : Ce, which has been receiving a great deal of attention as electroluminescent materials, has been studied. It is known that strong interaction between electron in 5d excited state of Ce^<3+> ions and electrons in conduction band exists, and ionization of Ce^<3+> is essential in the excitation process. To clarify this process, temperature dependence of luminescence intensity was investigated, and it is found that capture of electron of electron to Ce^<3+> ions is strongly affected by carriar migration in the lattice. To further investigate the excitation process, the photo-induced current and luminescence were measured using excimer laser excited dye laser pulses. It is found that Ce^<3+> centers are ionized when Ce^<3+> centers are excited to 5d state due to light irradiation. This result implies that excitation process through 5d state exists in SrS : Ce.
2. Similar experiments on SrGa_2S_4 : Ce thin films were carried out. Ce^<3+> substitutes the Sr^<2+> site. Although ionic nature of Sr site in SrGa_2S_4 is stronger than that for SrS,it is found that the interactionin between electron-hole pairs and 5d electron of Ce^<3+> exists. It is also found that the excitation through host lattice takes place efficiently, and Ce^<3+> gives rise strong blue luminencence. Less
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