表面包裹和浓度对水溶性II-IV族荧光量子点生长机制和尺寸调控的影响

II-VI semiconductor nanocrystals are of great interest for its tunable photoluminescence (PL) properties. To achieve bright and spectrally narrow PL prosperities, fundamentally, it requires the preparation of high quality quantum dots with passivatied surface, focusing size distribution and less lattice defects. It should be noted that, normally these intrinsic characteristics of nanocrystals are closely related to the crystal growth mechanisms of nanocrystals and its kinetic process. Previously (J. Am. Chem. Soc. 2010), the growth of water-soluble mercaptoacetic acid-coated CdS quantum dots (QDs) with two concentrations was selected by candidates and co-authors. It demonstrates that the growths of CdS QDs are controlled by the classic Ostwald ripening mechanism and oriented attachment (OA) growth mechanism, respectively. Obviously different evolution rule of the emission spectra of CdS nanocrystals can further be found between the observed OR and OA based growth. However, since the OR and OA mechanism usually occur simultaneously in crystal growths, the evolution of PL properties could be more complicated in traditional synthesis process. In this work, we aim at introducing different types of surface adsorptions to tune the crystal growth of CdS. The kinetic rules of size, morphology, and lattice structure of CdS nanocrystals in mixed/complexed OR+OA mechanism will be investigated. After that, efforts will be made to shed light on the relationship between the PL evolution rule of nanocrystal and the mixed OR+OA mechanism of CdS. On the basis of studies on CdS, we also attempt to find out the general relationship between the growth kinetics of nanocrystals and its PL properties, in other kinds of II-VI semiconductor materials. We anticipate this work could provide the fundamental understanding for introducing the surface adsorption to tune the crystals growth of II-VI semiconductor nanocrystals, thus to tailor and achieve the desired types of QDs with bright and spectrally narrow PL properties.

获得窄光谱、高亮度量子点荧光发射的关键在于受激纳米材料需要有较单一的尺寸分布、高的结晶度和钝化的表面状态，而这些特性的获得在本质上是取决于纳米材料的生长机制和动力学过程。申请人及其合作者在前期工作中通过生长动力学和荧光性质的同步跟踪研究，首次揭示在两种极端的表面包裹下CdS 量子点呈现出不同的生长机制，从而调制材料相应的微结构，使材料最终的发光特性出现不同特征(J. Am. Chem. Soc.)。本项目拟在前期基础上，通过调节不同强度的表面包裹来控制纳米晶的生长，研究纳米材料在两种生长机制并存下的混合衍化规律及其对量子点的微结构调制，阐明生长机制、生长动力学与发光机制之间更为普适性的关联。在此基础上，利用表面包裹调制纳米材料生长机制的原理，对几类II-VI族半导体量子点开展合成科学研究，找到获得窄尺寸分布、高荧光量子产率的材料调控方法。本工作可望为类似量子点的合成和发光性质的研究提供依据

本研究针对量子点荧光性质调控领域存在的最优发光性质难以可重复获得这一问题，通过调节不同的表面包裹状态来控制纳米晶的生长，研究纳米材料表面修饰与取向接合、聚集生长等非典型生长机制的关系，以及相应生长动力学存在的情况对量子点的微结构调制，进而阐明生长动力学因素、生长机制与发光性质之间更为普适性的关联。通过对几类典型II-VI族半导体量子点(如CdS、CdTe)、Ag2S量子点等开展合成科学研究，实现对这些量子点的不同强度和种类的表面修饰。利用紫外、荧光、动态光散射等手段系统地原位监测纳米材料的生长过程和荧光性质的变化，结合对生长过程纳米晶的HRTEM分析，建立生长动力学模型，拟合生长过程，并研究了pH、温度、表面包裹强度等对生长机制的影响。通过以上研究结果，揭示了不同生长机制下，量子点的尺寸分布、微结构和荧光性质（颜色纯度、亮度和寿命）的内在联系。通过对纳米晶表面状态的红外分析，获得对表面包裹状态与生长机制的机理性认识，找到获得窄尺寸分布、高荧光量子产率的材料发光性质调控方法。本工作可望为类似量子点的合成和发光性质的研究提供依据。