基于掺杂量子点的量子点单颗粒荧光闪烁机理研究

Fluorescence blinking is a common phenomenon in various fluorescent substances and limits their applications in many fields, such as single molecular tracking and single photon sources. Only a few types of nonblinking quantum dots have been reported and the physical mechanism behind fluorescence blinking is still in debate so far. Here we propose to study the fluorescence blinking behavior of single doped quantum dots and reveal the physical mechanism behind. Nonblinking quantum dots would be rationally designed and synthesized according to the theoretical model. The fluorescence properties of manganese-doped quantum dots are independent to temperature and surface ligands. Therefore, they are an ideal model for the study of nonradiative recombination process in fluorescence blinking. The manganese-doped quantum dots are fabricated using a nucleation-doping method and coating with an outer layer to enhance their stability. Fluorescence microscope imaging systems would be built up to observe the fluorescence blinking for single quantum dots. Accompanied with a pulse laser and a single-photon counting system, the fluorescence decay for each single quantum dot could be measured. A detailed study for the blinking behavior of single quantum dots affected by doping concentration and position, surface ligands, particel size and temperature would be carried out. According to all the results above, a theoretical model for the physical mechanism of fluorescence blinking phenomenon would be proposed. Directing by this theoretical model, we would find out a general strategy to suppress the fluorescence blinking for quantum dots. Finally, we would design and synthesize nonblinking doped quantum dots and even other types of nonblinking quantum dots.

荧光闪烁现象普遍存在于各种荧光物质中，并限制了它们在单分子示踪和单光子光源等方面的应用。目前仅有少数几种非闪烁量子点被报道，而荧光闪烁的物理机理仍在争论中。本项目拟通过研究掺杂量子点单颗粒的荧光闪烁行为，揭示荧光闪烁现象背后的物理机理，建立理论模型，指导设计与合成非闪烁量子点。锰掺杂量子点的荧光性质具有良好的温度稳定性，且对表面配体不敏感，是研究荧光闪烁中非辐射复合过程的理想模型。锰掺杂量子点使用成核掺杂方法合成，并在表面包覆上壳层以增加其稳定性。利用荧光显微成像系统，结合脉冲激光与单光子计数技术，观测量子点单颗粒的荧光闪烁现象和测量单颗粒荧光寿命。通过统计和分析掺杂浓度、掺杂空间位置、表面配体、尺寸以及温度等参数对其荧光闪烁和寿命的影响，建立荧光闪烁的机理模型。在该理论模型的指导下，总结出抑制量子点荧光闪烁的普适策略，最终设计和合成非闪烁掺杂量子点，并推广到其它类型量子点体系中。

胶体量子点是一种新型的纳米荧光材料。它具有稳定性高、吸收带宽、发射光谱窄且可调、斯托克斯位移大等优异的光谱学性质。因此，量子点在生物医学成像、光电器件等众多领域具有巨大的应用潜力。然而量子点单颗粒的荧光闪烁问题困扰了人们二十年。它不仅限制了量子点在单分子示踪和单光子源等方向的应用，同时也影响了基于量子点的光电器件的效率。本项目致力于研究量子点荧光闪烁的机理，并发展非闪烁量子点体系。.本项目首先通过理性设计锰掺杂量子点的结构，结合时间分辨荧光光谱监测等手段，获得具有高荧光效率、高稳定性、准单通道荧光衰减、荧光寿命大范围连续可调的锰掺杂量子点。首次报道了完全基于量子点的荧光寿命复用加密解密应用和生物荧光多通道标记应用。我们提出把量子点荧光闪烁作为光化学动力学过程处理的创新策略，直接计算量子点电离和去电离的新分析方法。通过系统调控激发光的光功率密度、脉冲重频、波长等参数，获得电离与去电离过程的反应速率的变化规律。实验上揭示了量子点荧光闪烁的电离过程为热电子电离过程，去电离过程为热电子过程和自发去电离过程的共同作用。排除了在领域内长期争议的多激子俄歇电离机理和带边激子电离机理。利用上述荧光闪烁机理，我们设计并合成了一系列非闪烁CdSe/CdS核壳量子点，突破了所谓的量子点“非闪烁体积阈值”。在此基础上，进一步设计并合成出一系列具有非闪烁和抗光漂白特性的均匀合金CdSe/CdZnS及CdSeS/CdZnS核壳量子点。这些量子点几乎覆盖可见光谱范围。.本项目研究的成果大部分已整理成文，发表高水平SCI论文4篇，其中包括Journal of the American Chemical Society 2篇，Journal of Physical Chemistry Letters 1篇，ACS Central Science 1篇。另有一篇Advanced Materials邀请文章在审稿中。本项目成果还申请了一项名为“一种荧光寿命测量方法及装置”的发明专利。.