Study of Excitation and Luminescence Process of Rare-Earth Ions Doped in Semiconductors

稀土离子在半导体中的发光是由开放的4f^n壳层中的电子跃迁引起的。由于4f^n电子在（5s） ^2 (5p) ^6闭合壳层中被外层电子屏蔽，所以稀土离子在各种基体材料中的4f^n能级几乎不受晶体场的影响。因此，稀土离子具有特定的发光，具有清晰的谱线，并且发射波长几乎不依赖于晶格温度。稀土离子的激发可以由以下过程引起。由于带间激发，首先产生电子空穴对。随后在稀土离子位置的电子-空穴对的捕获和重组导致4f^n电子的激发。最后，稀土离子由于4f^n电子构型的跃迁而发光。为了阐明稀土离子在半导体中的激发和发光过程，有必要了解从电子空穴对到4f^n电子的能量转移过程。对于Ce^<3+>离子，已知Ce^<3+>中心通过5d激发态电离生成Ce^<4+>离子。本研究探讨了Ce^<3+>离子电离和电子俘获在激发过程中的作用。结果如下：1。SrS: Ce作为电致发光材料受到了广泛的关注。已知Ce^<3+>离子5d激发态电子与导带电子之间存在强相互作用，激发过程中Ce^<3+>的电离是必不可少的。为了阐明这一过程，研究了发光强度的温度依赖性，发现Ce^<3+>离子的电子捕获受到晶格中载流子迁移的强烈影响。为了进一步研究激发过程，用准分子激光激发染料激光脉冲测量了光致电流和发光。发现当Ce <3+>中心被光激发到5d态时，Ce <3+>中心被电离。这说明SrS中存在5d态激发过程。在SrGa_2S_4: Ce薄膜上进行了类似的实验。Ce^<3+>取代Sr^<2+>位点。虽然SrGa_2S_4中Sr位的离子性质比Sr位强，但发现存在电子空穴对与Ce^<3+>的5d电子之间的相互作用。通过主晶格的激发是有效的，Ce^<3+>产生了较强的蓝色亮度。少

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 … More 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