发光聚合物中激子极化激元及其凝聚和激射行为的研究

Light-emitting polymers are one of the ideal candidates of ultra-low threshold laser. Newly emerged exciton-polaritons mechanism has great potential, however, its research is mostly limited in inorganic semiconductors. There have been very few reports on the polymer based cavity exciton-polaritons, thus the mechanism remains in mist. We plan to study the interaction between light and polymers in a high-quality planar microcavity, as well as their condensation and lasing action, in order to solve one of key scientific problems which is the mechanism of generation and dynamics of exciton-polaritons. The emission spectra of light-emitting polymer-based microcavities will be measured under various conditions, along which suitable theoretical models will be adopted for the understanding of the dispersion relationship between energy and momentum of exciton-polaritons. Based on the various composite of light-emitting polymer in the microcavity, we plan to study the coherence of emitting photons when the condensation and lasing action of excition-polaritons occur. The coupling relationship between the exciton and the light, as well as the density of state and its evolution, will thus be illustrated. In order to improve the operation performance, we will mix the light-emitting polymer in a transparent polymer matrix. Through the measurement of fluorescent lifetime and polarization state around the threshold of condensation and lasing action, the dynamics of exciton-polaritons in a polymer composite in a microcavity will be studied in detail. The results will help for better understanding the phase transition of light-polymer interaction in a microcavity, as well as their dynamics evolution, and hence provide key information for the application of novel ultra-low threshold polymer lasers.

发光聚合物是超低阈值激光器的理想材料之一。超低阈值激光器研究发现了激子极化激元激射的新机理，是很有潜力的研究方向，然而其在发光聚合物体系中的研究才刚起步，机理尚未阐明。本项目以微腔中发光聚合物与光相互作用的体系为研究对象，拟开展微腔内发光聚合物中激子极化激元及其凝聚和激射行为的研究，解决激子极化激元的产生及其动力学演化这一关键科学问题。项目采用光学泵浦探测微腔内发光聚合物的发射谱，得出激子极化激元能量与动量的色散关系。通过改变微腔内发光聚合物的组分，研究激子极化激元凝聚和激射时光子的相干特性，得到激子与光子的耦合关系、激子极化激元的态密度及其演化规律。采用透明聚合物基体提高发光聚合物的工作寿命，并对激子极化激元凝聚和激射阈值附近的荧光寿命和偏振状态进行探测，揭示微腔内聚合物中光与物质相互作用的相变过程，阐明强耦合时激子极化激元凝聚的动力学演化机理，指导新型超低阈值聚合物激光器的研究。

激光器从诞生以来，已为人类科技进步做出重要贡献。当前激光器研究的重要问题之一是降低激射阈值。因此，探索激射新机理成为一个备受关注的研究方向。近年来，人们发现利用在光学微腔中形成的激子极化激元所产生的激射行为，在原理上可以实现无阈值激射（即出现激子极化激元的凝聚效应）。因此，针对激子极化激元的产生及其动力学演化机理这一关键科学问题，本项目开展了高质量光学微腔的研制、以及微腔与发光聚合物结合产生激子极化激元，并通过光谱探测的技术手段对其激射行为（包括凝聚的动力学机制）进行研究，从而进一步理解光学微腔中发光聚合物与光相互作用的强耦合状态。..在项目开展的研究中，我们分别尝试了MDMO-PPV、BDMO-PPV和BEHP-PPV三种发光聚合物材料，测量其在脉冲泵浦下的光谱以及增益、损耗系数等光学特性，这些是研究发光聚合物中激子极化激元相关的基本属性。综合比较后，本项目采用BEHP-PPV发光聚合物开展后续的研究。为了提升发光聚合物的稳定性，本项目采用两种方案：1）将BEHP-PPV与透明聚合物CHDV单体掺杂后再紫外固化；2）将氮化硅薄膜通过我们研究组发展起来的低温ICP-CVD沉积工艺生长到BEHP-PPV薄膜上。本项目研究发现，后者具有良好的光学特性，并且易于同传统微纳加工技术结合，实现集成光子结构的制备。在该混合材料平台上，我们进一步利用微纳加工技术制作了包括微盘在内的嵌入发光聚合物的光学微腔结构并进行了测试，研究了微腔中光与物质相互作用所出现增益和损耗等，并利用角度分辨荧光测试技术对微腔中的形成激子极化激元进行探测，为研制超低阈值激光器积累重要信息。..本项目取得研究结果合计发表SCI收录论文5篇，EI收录国际会议论文3篇，申请发明专利1项。