EFFICIENT ELECTROPHOSPHORESCENCE IN ORGANIC-INORGANIC NANOHYBRID AND ITS APPLICATION TO LIGHT-EMITTING DEVICE

本课题旨在阐明有机-无机纳米杂化材料的电致磷光发光机理及其在发光二极管中的应用。本项目取得的成果总结如下：1.有机半导体、4，4‘-N，N’-二氨基联苯(CBP)和稀土卤化物(CBP)纳米杂化薄膜的制备及纳米杂化薄膜的电致发光研究得到的薄膜透明、均匀。透射电子显微镜观察表明，稀土卤化物纳米粒子呈球形分散在CBP介质中。纳米粒子的直径在大约10~15 nm的范围内变化。2)通过光激发，所有的纳米杂化薄膜都显示出来自CBP的荧光。CBP的磷光和稀土卤化物的发射不是o…更多的烤肉。3)利用纳米杂化薄膜，制备了有机半导体、ITO/空穴传输层/纳米杂化薄膜/电子传输层/Al-Li复合电致发光器件。结果：1.所有器件均表现出来自CBP的磷光(凝胶磷光)。利用空穴传输型有机半导体和电子传输型有机半导体制备了6种嵌入CeF_3纳米粒子的纳米杂化薄膜。1)在所有纳米杂化薄膜中只观察到有机半导体的荧光。2)当空穴传输有机半导体作为电致发光器件的发光层时，观察到有机半导体的电致磷光。另一方面，在具有电子传输有机半导体和CeF3纳米杂化材料的EL器件中观察到了CeF3的发射。根据上述结果，提出了以下的电致发光机理：首先，在f轨道上只有一个电子的Ce^(3+)很容易电离Ce^&lt；4+&gt；形成闭合壳层。然后，Ce^&lt；4+&gt；捕获电子，形成C^(3+*)。在低电离势的空穴传输有机半导体中，C^(3+*)发生Dexter型能量转移，形成有机半导体的激发三重态。结果，观察到了电致磷光现象。相反，在具有高电离势的电子传输型有机半导体中，没有发生能量转移。因此，观察到了CeF_3的发射。较少

This project was conducted toward clarifying mechanism of electrophosphorescence in the organic-inorganic nano-hybrids and application of the nano-hybrids to light emitting diode. The results of this project are summarized as follows.1. Preparation of organic-inorganic nano-hybrids and electrophosphorescence in the nano-hybrid1) Nano-hybrid films embedded with rare earth halides (CeI_3, CeBr_3, CeF_3, TbI_3) nano-particles were prepared by simultaneous vacuum-deposition of an organic semiconductor, 4,4'-N,N'-dicarbazole-biphenyl (CBP), and rare earth halides at a base pressure of 10^<-4> Pa. The obtained films were transparent and uniform. TEM observation demonstrated that spherical nano-particles of rare earth halides were dispersed in CBP medium. The diameter of the nano-particles varied within the range of approximately 10 to 15 nm.2) By photo-excitation, the all nano-hybrid films exhibited fluorescence from CBP. Phosphorescence from CBP and emission of rare earth halides were not o … More bserved. 3) Using the nano-hybrid films, one fabricated electroluminescent (EL) devices combined with organic semiconductors, ITO/hole transport layer/nano-hybrid film/electron-transport layer/Al-Li. All devices exhibited phosphorescence (electrophosphorescence) from CBP.2. Mechanism of electrophosphorescence in nano-hybridsUsing hole-transporting organic semiconductors and electron-transporting organic semiconductors, 6 kinds of nano-hybrid films embedded with CeF_3 nano-particles.1) Only fluorescence from the organic semiconductors was observed in the all nano-hybrid films.2) When hole-transporting organic semiconductors employed as emissive layer in EL devices, electrophosphorescence from the organic semiconductors was observed. On the other hand, emission from CeF_3 was observed in EL devices having the nanohybrids with electron-transporting organic semiconductor and CeF_3.From above-mentioned results, the following mechanism of electrophosphorescence was suggested. Firstly, Ce^(3+), which has one electron in the f-orbital, easily ionizes Ce^<4+> to form closed shell. Then, the Ce^<4+> captures electron, and forms C^(3+*). In the hole-transporting organic semiconductors with low ionization potential, Dexter-type energy transfer from C^(3+*) is carried out, and forms excited triplet state of the organic semiconductors. As a result, electrophosphorescence is observed. In the electron-transporting organic semiconductor with high ionization potential, on the contrary, the energy transfer does not occur. Accordingly, emission form CeF_3 is observed. Less