Ⅱ-Ⅵ族半导体纳米线的溶液法合成、发光及激发态调控

发布时间：2018-04-24 04:28

本文选题：半导体纳米线 + 溶液法　；参考：《北京理工大学》2015年博士论文

【摘要】：自二十世纪八十年代以来,纳米科学逐渐发展成为一门跨领域、多学科交叉的前沿学科。作为一类经典的纳米材料体系,半导体纳米线因其一维结构所带来的独特偏振光学特性、低激光激发阈值、增强的压电特性等性质,一直倍受关注。半导体纳米线的制备方法可简单的分为气相法和液相法,与气相制备法相比,溶液法制备的半导体纳米线具有尺寸小(可表现量子限域效应)、反应温度低、有机配体包覆、可连续制备等特点,是这一领域的重要研究方向。然而,溶液法制备的纳米线存在荧光量子产率低下、光谱调控范围窄、性能单一、发光理论研究滞后等问题,阻碍了相关研究的进一步发展。针对上述问题,本论文开展了II-VI族半导体纳米线的研究,发展了溶液-液滴-固体法(Solution-Liquid-Solid,SLS)合成技术,通过掺杂、合金化等策略实现了胶体纳米线发光性质的调控,开发了多种多功能半导体纳米线,利用低温稳态荧光光谱和时间分辨光谱,初步阐明了所制备的半导体纳米线的发光机制。所取得的主要进展如下:(1)合金化是调控半导体材料发光光谱的有效策略,合金半导体材料的制备必须克服反应前驱体活性差别的难题,与零维纳米晶相比,半导体纳米线的合金化过程不仅需要在横截面方向实现,还需在长轴方向完成均匀合金,生长条件要求更加苛刻。本论文发展了SLS的制备技术,通过前驱体、催化剂、反应温度的调控,以原位生成的Bi纳米液滴为微反应容器,制备了波长范围可调(508 nm-628 nm)的CdSe_xS_(1-x)合金纳米线,其荧光量子产率高达8.8%,比单纯的CdSe或CdS纳米线的荧光量子产率(1%)提高了一个数量级。另外,未经排列的纳米线已经显示出明显的偏振发光特性,偏振度(polarization ratio)可达0.6。为了理解激子在合金半导体中的运动过程以及合金化提高纳米线荧光量子效率的机理,利用低温稳态荧光光谱和时间分辨光谱对CdSe_xS_(1-x)合金纳米线的激发态复合过程进行了深入的研究和分析,通过了解低温下合金纳米线荧光光谱的变化,并进一步结合时间分辨光谱和荧光寿命的结果,提出了合金半导体纳米线中激子的迁移和限域竞争复合发光机制:即半导体纳米线的荧光量子产率是由辐射复合速率和界面缺陷的捕获速率共同决定的,在合金纳米线中,由于成分导致的势能谷的存在,光生激子一旦产生会被势能谷局域束缚,大大降低了其向表面的迁移,这就使激子有效辐射复合的几率大大增加,荧光量子产率也相应增高。(2)掺杂是现在半导体技术中控制材料性质的主要策略之一,尤其是同时具备多种功能的半导体材料是现代半导体技术和应用的重要方向。但是,由于纳米晶体本身的“自清洁”效应(Self-Purification),如何实现半导体纳米材料的掺杂一直是纳米材料制备的挑战之一,特别是对纳米线来说,如何保证掺杂离子在纳米线长轴方向的均匀性是不可忽视的一大挑战。我们以Bi纳米液滴为微反应容器,以Cd(S_2CNEt_2)_2为单前驱体,发展了一种简单的SLS单源前驱体掺杂法,制备了Mn~(2+)和Eu~(3+)掺杂的CdS一维半导体纳米线,并提出了SLS单源前躯体掺杂法制备胶体稀磁半导体纳米线的成核及生长机理。另外,通过改变掺杂所用的Mn~(2+)含量(0.18%-0.81%),可以调控Mn~(2+)掺杂的CdS稀磁半导体纳米线的双色发光峰中蓝光和橙光的比例,实现白光发射。该掺杂策略具有两大突出特点:简单通用、掺杂均匀。
[Abstract]:Since 1980s, nanoscience has gradually developed into a cross field and interdisciplinary frontier. As a class of classic nanomaterials, semiconductor nanowires have been attracting more and more attention because of their unique polarization optical properties, low laser excitation threshold, and enhanced piezoelectric properties. The preparation method of conductor nanowires can be easily divided into gas phase method and liquid phase method. Compared with the gas phase preparation method, the semiconductor nanowires prepared by solution method have the characteristics of small size (which can show quantum confinement effect), low reaction temperature, organic ligand encapsulation, continuous preparation, etc., which is an important research direction in this field. However, solution method has been used to prepare the nanowires. The nanowires have low fluorescence quantum yield, narrow spectrum control range, single performance and delayed luminescence theory, which hinders the further development of the related research. In this paper, the research of II-VI semiconductor nanowires is carried out in this paper, and the solution liquid drop solid method (Solution-Liquid-Solid, SLS) synthesis technology is developed. A variety of multifunctional semiconductor nanowires have been developed by over doping and alloying, and a variety of multi-functional semiconductor nanowires have been developed. The luminescence mechanism of the semiconductor nanowires has been preliminarily clarified by the low temperature steady-state fluorescence spectrum and time resolved spectrum. The main progress is as follows: (1) alloying is the regulation of semiconductor materials. The effective strategy of the luminescence spectrum is that the preparation of the alloy semiconductor material must overcome the problem of the difference in the activity of the precursor. Compared with the zero dimension nanocrystalline, the alloying process of the semiconductor nanowires needs not only to be realized in the direction of cross section, but also to complete the uniform alloy in the direction of the long axis, and the requirement for the growth condition is more demanding. This paper develops the SLS By controlling the precursors, catalysts and reaction temperature, the Bi nanowires with tunable wavelength range (508 nm-628 nm) are prepared by the precursor, catalyst, and reaction temperature. The fluorescence quantum yield of the nanowires is up to 8.8%, which is more than the fluorescence quantum yield (1%) of the pure CdSe or CdS nanowires. In addition, the unarranged nanowires have shown obvious polarization luminescence properties. The degree of polarization (polarization ratio) is up to 0.6. in order to understand the movement of the exciton in the alloy semiconductor and the mechanism of improving the fluorescence quantum efficiency of the nanowire by alloying. The low temperature stable fluorescence spectrum and the time resolved spectrum are used for the combination of CdSe_xS_ (1-x). The excited state complex process of the nanowires is deeply studied and analyzed. By understanding the changes in the fluorescence spectra of the alloy nanowires at low temperature and further combining the time resolved spectra and the fluorescence lifetime, the mechanism of the migration of excitons and the limited domain competitive composite luminescence mechanism in the alloy semiconductor nanowires, that is, semiconductor nanowires, is proposed. The fluorescence quantum yield is determined by the radiation recombination rate and the capture rate of the interfacial defects. In the alloy nanowires, the potential energy valley, due to the presence of the composition, will be bound by the potential energy valley locally, greatly reducing the migration of the exciton to the surface, which greatly increases the probability of the effective radiation recombination of the exciton. The yield of light quantum is also higher. (2) doping is one of the main strategies to control the properties of semiconductors, especially the semiconductor materials with multiple functions at the same time are the important direction of modern semiconductor technology and applications. However, the "self cleaning" effect (Self-Purification) of the nanocrystalline itself can be realized half. The doping of conducting nanomaterials has been one of the challenges for nanomaterials. Especially for nanowires, how to ensure the uniformity of the doped ions in the long axis of nanowires is an unnegligible challenge. We developed a simple SLS single source with Bi nano droplets as microreactor and Cd (S_2CNEt_2) _2 as a single precursor. Mn~ (2+) and Eu~ (3+) doped CdS one-dimensional semiconductor nanowires were prepared by precursor doping, and the nucleation and growth mechanism of colloidal diluted magnetic semiconductor nanowires prepared by SLS single source precursor doping method were proposed. In addition, the Mn~ (2+) doped CdS dilute semiconductor nanowires could be regulated by changing the content of Mn~ (2+) (0.18% -0.81%) used in doping. The white light emission is achieved by the ratio of blue light and orange light in the two-color emission peak. The doping strategy has two outstanding characteristics: simple and universal, and uniform doping.

【学位授予单位】：北京理工大学
【学位级别】：博士
【学位授予年份】：2015
【分类号】：TB383.1

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