II-VI族半导体量子点荧光闪烁及其抑制机理的理论研究

Single quantum dots are ideal materials for bioimage and quantum communication,but their development and application are hindered by their fluorescence blinking.Knowledge on the generation and elimination of fluorescence blinking are urgent for the science and product development of semiconductor quantum dots. Starting from available physical models that were constructed on experiments, we proposed to study the blinking generation and suppression mechanism for II-VI semiconductor quantum dots, ME where M = Zn and Cd,and E = S, Se and Te, by means of quantum chemistry calculations. Our study includes: (1) The formation and distribution of electron traps in the body,surface and surroundings of quantum dots, as well as the electronic characteristics of quantum dots with various types of electron traps. (2) The correlation of electron traps with nonradiative Auger recombination of charge carriers, as well as the relationship between quantum dot blinking and the physical and chemical features of electron traps. (3) The effect of chemical component, structure,size, inner and surface vacancies of quantum dots, doped atoms, solvent, shell and external fields on electron traps, as well as the molecular mechanism of chemical modification and physical modulation for blinking elimination. Our study will provide not only theoretical and computational basis for the establishment of a better physical model for the fluorescence blinking of quantum dots, but also principles for the molecular design of non-blinking semiconductor quantum dots.

单量子点是理想的生物成像和量子通信材料，但荧光闪烁现象阻碍了其发展和应用。抑制或消除荧光闪烁是量子点研究中亟待解决的问题。本项目从实验研究建立的物理模型出发，运用量子化学计算方法研究II-VI族半导体量子点（ME，M = Zn和Cd，E = S、Se和Te）荧光闪烁的产生及调控机制，包括：（1）研究量子点内部、表面及介质中电子陷阱的形成和分布规律，分析具有不同类型电子陷阱的量子点的电子结构特征；（2）研究电子陷阱与载流子非辐射俄歇复合之间关联规律，建立量子点荧光闪烁与电子陷阱物理化学特征之间的联系；（3）研究量子点化学组成结构及尺寸、量子点内部及表面缺陷、供电子及吸电子配体、溶剂效应、核壳效应、外加电场等对电子陷阱和量子产率的影响，分析利用结构设计、化学修饰及物理调控方法消除荧光闪烁的分子机制。研究成果将为完善量子点荧光闪烁物理机制提供理论支持，为制备无闪烁半导体量子点提供分子设计原理。

II-VI族半导体量子点在生物传感器、发光二极管等领域展现出良好的应用前景。荧光闪烁现象作为单量子点本身固有的性质，严重制约了量子点在以单颗粒作为光源的领域的应用。抑制和消除这种闪烁现象具有重要意义。本项目运用量子化学计算方法，研究了CdSe量子点表面缺陷的形成与分布规律、量子点尺寸形貌对电子转移和电子-空穴复合过程的影响、控制量子点荧光闪烁现象的关键因素等内容，取得下述主要成果：（1）研究了Cl配体钝化前后CdSe量子点表面缺陷的载流子捕获能力变化规律，发现Cl配体能够有效消除表面缺陷、抑制载流子陷阱的生成。此项研究对无表面缺陷CdSe量子点的制备具有一定指导意义。（2）研究了Mn掺杂以及量子点尺寸、结构对电子转移过程和电子-空穴复合过程的影响。研究发现：与未掺Mn的量子点相比，Mn掺杂量子点的电子注入速率提高了80%。随着量子点尺寸增大，电子-空穴复合速率减小；尺寸相同的量子点，空心笼结构的电子-空穴复合速率小于核壳结构的电子-空穴复合速率。（3）激子（电子和空穴）辐射跃迁和非辐射跃迁过程与量子点的荧光闪烁密切相关。我们分析了量子点几何构型、化学组成和电子结构与激子跃迁过程的关系，揭示了亮态和暗态的形成原因。研究结果表明表面缺陷明显抑制激子辐射跃迁，导致量子点呈现暗态。重组能通常被用来解释量子点的荧光性质，重组能越大量子点的荧光量子产率越低。本研究工作对设计和制备无闪烁的单量子点具有一定的指导意义。