导电高聚物中的载流子裂变和随机激光机理的研究

【作者】 李盛；

【导师】 孙鑫；

【作者基本信息】 复旦大学 ， 理论物理， 2005， 博士

【摘要】 本文由两个专题构成,包括聚合物分子中的载流子分裂和随机激光机制。 传统上,聚合物是体现化学工业的关键领域。然而,在最近几年,聚合物却成了在物理学的基础和应用研究的重点研究对象。一方面是电致发光和光电效应为今后的光电的应用提供了新的可能。另一方面,由于聚合物的链状结构,也为基于一维结构的模型和理论提供了出色的试验材料。早期的聚合物研究集中在基态和输运性质。最近,基于激发态和动力学过程的奇异的现象开始被探测,尤其是在飞秒激光光谱的进展,使得揭示高聚物中多种光诱导的动力学过程的细节成为了可能。在这篇论文里,我们研究了高聚物中由于光诱导的载流子的结构的变化,我们的动力学模拟显示了一个特别的光诱导过程:在光激发下,高聚物分子中的载流子被分裂成两个新的载流子。一个正的双极化子裂变成两个正的单极化子,以及一个正单极化子可以裂变成一个正的双极化子和一个负的单极化子。光诱导的载流子裂变不需要一个外电场的帮助,是一个典型的对称性破缺。在凝聚态物理里,基于描述载流子性质自旋和电荷,载流子可以分为自旋载流子和电荷载流子。在无机材料中,他们的载流子有电子和空穴,都带有自旋和电荷。不同于无机材料,有机材料中的载流子是复合了晶格结构的载流子。因此,除了具有和无机材料的电子和空穴类似的具有电荷和自旋的极化子以外,在有机材料中还存在电荷而没有自旋的双极化子。结合上面发现的载流子的裂变,我们发展了ESR(电子自旋共振,电荷载流子的自旋反转)的对偶性质,自旋载流子的电荷反转。 对于随机激光,在六十年代,Letokhov的前瞻性的工作预言了在随机的介质能实现激射现象。在上世纪80年代,Markushev在Nd掺杂的晶体粉末上观察到了激射现象,他们发现当单个晶体颗粒尺寸比光波的波长长的时候,可以将颗粒看作一个谐振腔,从此,粉末微腔激光的大量研究工作便基于此展开来。1994年Lawandy等人通过抽运随机分布的TiO微粒和Rodanmine构成的胶体溶液,在溶液的表面附近观察到了激光辐射,也就是随机激光,这也激发出了一个新的研究领域。从而,随机激光这个新名词也开始出现。为了在随机固体材料中实现共更多还原

【Abstract】 This paper consists with two topics, involving carrier fission in polymeric molecule and the mechanism of random laser.Traditionally, polymers represent a key field of the chemical industry. However, in recent years, polymers have also become significant for physics in regard to both fundamental studies and applications. On the one hand, the discoveries of electroluminescence and photovoltaics have provided new possibilities for optoelectronic applications. On the other hand, due to its chain structure, the polymer is an excellent material for testing theories and models based on a onedimensional system. Earlier research on polymers has concentrated on ground-state and transport properties. Recently, many novel phenomena and applications based on excited states and dynamical process have been explored. Thanks especially to substantial progress in femtosecond laser spectroscopy, it is possible to reveal the details of various photoinduced dynamical processes in polymers. In this thesis, we study the structural change of the carrier induced by photoexcitation in polymers. Our dynamical simulation shows some special photoinduced processes whereby the carriers insimulation shows some special photoinduced processes whereby the carriers in polymeric molecule is split into two carriers. One positive bipolaron can be slipt into two positive polaron, and one positive polaron can be split into one a negative polaron and the other a positive bipolaron—where this photoinduced carrier fission does not need the aid of an external electric field, which is a typical symmetry breaking. In condensed matter physics, according to two degrees of freedom describing the properties of carriers, carriers can be divided into two categories: charge carriers and spin carriers. In inorganic materials, their carriers are electron and hole that both possess their spin and charge. Yet, the carrier in organic material is a composite particle that, different from inorganic material, are characterized with the surrounding lattice configuration. Thereby, besides the charged spin polaron that is similar to the electron or hole in organic material, there also exist spinless charged carrier, such as bipolaron. Because polaron is a spin carrier, combining with the polaron fission, we also developed a new dual principle of ESR (electron spin resonance), charge flipping of spin carrier.In 1968, the pioneer work of Lethokov predicted that laser action could be realized in randomly distributed scattering media. In the 1980s, Markushev et al. observed lasing in Nd-doped laser crystal powder. They found a single particle, with size much larger than the optical wavelength, served as a laser resonator. Since then, there has been much work on powder lasers. In 1994, Lawandy [4] applied 530nm laser pulse to pump the colloidal solution consisting of TiO2 particles suspended in Rodanmine methanol solution. Once the gain approached and surpassed the threshold value, laser action could be observed over the surface of the liquid, which triggered many experimental and theoretical studies on this field. The term "random laser" appeared. In order to realize laser with resonant feedback in random solid media,: Cao et al. [6] switched to a solid luminescence semiconductor. When the pump beam (the fourth harmonic X =266nm Nd: YAG laser) is focused on the ZnO polycrystalline thin film surface and its intensity exceeds a threshold value, narrow discrete sharp peaks emerges in the emission spectrum, and simultaneously, a couple of bright更多还原