【作者】 夏星；

【导师】 刘祖黎；

【作者基本信息】 华中科技大学 ， 材料物理与化学， 2010， 博士

【摘要】 半导体纳米晶又常被称为量子点,这类材料通过随粒径变化的荧光颜色直观地展示了纳米材料的量子尺寸效应,并作为一种全新的无机发光材料,在生物、医学、光电器件、太阳能等领域的应用都被寄予极高的期望。本文首先对核壳结构半导体纳米晶进行了基于晶体结构差异的研究。以纤锌矿结构(WZ)的CdSe为核的核壳纳米晶在近十多年一直是材料研究领域的主要研究对象,并且在应用中也受到广泛的青睐；而近几年出现的闪锌矿结构(ZB)的CdSe却极少被用在核壳纳米晶的研究中。本文从核壳纳米晶的晶体结构、形貌、荧光性质等几个方面研究发现,基于ZB-CdSe的核壳纳米晶的发光性质要好于以传统的WZ-CdSe为核的样品,更加适合于在医学标记和检测上的应用,并且实验步骤相对简单,也更适合于规模化的量产。在核壳纳米晶上本文还进行了CdSe/ZnS的结构演化研究。由于优异的发光性能和稳定性,CdSe/ZnS长期以来一直是最受关注并且在应用研究中使用最广泛的核壳纳米晶,但对其结构变化的研究一直鲜有报道；另一方面,近年来许多异质结构纳米晶的形貌从最初量子点的“点”状逐渐演化出了多种形状,它们在多个领域的研究中被寄予厚望。本文以ZB-CdSe为核,在其表面包裹ZnS,通过对ZnS生长温度的实验发现CdSe/ZnS纳米晶具有随温度演化的形貌,其中在240℃时具有类似甲烷分子的四足体结构；但温度更高时CdSe和ZnS界面间的熔合会破坏四足体结构,并且伴随着明显的荧光蓝移现象。同时,本部分研究还发现CdSe/ZnS四足体中ZnS的生长具有不稳定性,当其生长至一定程度时便会由于晶体缺陷而产生明显分叉结构,使整体的发光效率降低。本文最后研究了CdZnSeS合金纳米晶,它克服了CdSe纳米晶的发光难以达到蓝色至绿色波长区域,并且合成步骤简单。本部分实验使用了十二硫醇参与纳米晶合成的反应,一方面它能在高温下分解,作为硫元素的前驱物在纳米晶表面形成-层薄薄的ZnS包覆层,另一方面它能很好的限制纳米晶成型时颗粒的长大,再结合实验中对Cd和Zn两种元素比例的控制,使材料的荧光能够轻易达到蓝色至绿色波长区域,并且可以由实验参数进行调控。该部分研究获得的短波长荧光纳米晶在光电器件和LED等方面具有应用的潜力。更多还原

【Abstract】 Semiconductor nanocrystals (NCs) are usually referred as quantum dots because of their distinct exhibition of the famous small scale effect in nanomaterials, that the color of their luminescence changes with the particles size. As a whole new type of inorganic emitter, semiconductor nanocrystals have been considered highly potential in applications of biology, photovoltaic device, and displays, etc.In this thesis, core/shell NCs were studied from the perspective of crystal structure. For more than a decade, core/shell NCs based on wurtzite CdSe have been the focus of quantum dots research and are widely used in biomedical applications; while studies on core/shell NCs based on the newly developed zinc-blende CdSe NCs are relatively rare. In this thesis, zinc-blende CdSe is found to be more suitable for preparation of core/shell NCs. NCs with a zinc-blende core have higher luminescence efficiency and are easier to prepare, which can be more advantageous in industrial production and in applications such as fluorescent marker.Also, as a representative core/shell NCs, CdSe/ZnS has been the most famous one due to its outrageous light-emitting properties and stabilities, but reports on its shape variation are still rare. Meanwhile, for many other types of hetero-structured nanocrystals, they have been manufactured into nearly all kinds of shapes, and these variants are thought to be highly promising in future applications. In this thesis, the conventional "dot" shaped CdSe/ZnS NCs are developed into different shapes. Typical tetrapod CdSe/ZnS NCs are obtained at 240℃, and yet it is found that higher temperature can be destructive to the tetrapod structure due to interface diffusion between CdSe and ZnS, which also leads to obvious blue shift in the luminescence. Also, the growth of ZnS in CdSe/ZnS tetrapod is found to be not straight forward; ZnS first elongates and then splits because of the accumulation of crystal defects. The luminescence efficiency also declines when the splitting starts.Finally, CdZnSeS NCs were studied. They showed rare blue to green luminescence which is hard for CdSe to reach, and besides, the preparation process was quite simple. In the experiment,12-dodecanethiol was adopted as a precursor of sulfur because it decomposes at high temperature. Meanwhile, research also found it was potent in controlling the particle size of final NCs. With this effect of 12-dodecanethiol and together with the adjustment of Cd to Zn ratio, the luminescence of obtained NCs can easily reach the wavelength range of blue to green, and moreover, the luminescence color can be tuned by the reaction design. These blue-green-emitting NCs can be useful in many applications such as displays and LEDs.更多还原