光子晶体调控弱光上转换材料制备与增强固态上转换发光研究

Upconversion (UC), that is, observation of photon emission, or more generally, population of excited state at higher energy (shorter wavelength) with excitation at lower energy (longer wavelength), has attracted much attention due to its potential applications. Triplet-triplet annihilation (TTA) is a promising upconversion approach due to its low excitation power density (solar light is sufficient), high upconversion quantum yield in solution state( > 30%), readily tunable excitation/emission wavelength. However, the developments of TTA-UC are facing some big challenges, for example the fabrication of devices suitable for practical applications appears far away, since it is quite difficult to obtain high-efficiency solid-state systems. The largest up-conversion efficiency reported up to now for a rigid polymeric matrix is less than 1%. Moreover，the up-conversion system should be completely shielded from the external environment, because oxygen is a quencher of all of the metastable triplets involved in the up-conversion process. In this project , we propose an original approach to incorporate bi-component organic systems for high-efficiency upconversion in the solid state. The photonic crystals (PCs) structure is firstly introduced in enhancing the efficiency of TTA-UC in the solid state. TTA-UC core-shell microspheres are going to be fabricated via one-step emulsion polymerization. Polymeric microspheres can be utilized as a decent scaffold to construct solid TTA-UC systems by incorporating triplet sensitizer and the annihilator into the microspheres. The upconversion molecules embed within the polymeric microspheres, provide the crucial benefit of shielding the up-conversion system from the external environment and especially from oxygen, which is a quencher of all of the metastable triplets involved in the upconversion process. Each polymeric microspheres can work as single upconverting unit, and then constitute large-area, crack-free PCs by conventional colloidal self-assembly. Taking advantage of the unique optical properties such as photonic stop band and ability of localizing photons, the PCs can efficiently controlling the energy transfer process in TTA-UC and help to explore the decisive factor in the TTA-UC emission. We try to discover the fundamental influence of the PCs structure in promote the triplet-triplet energy transfer (TTT) and triplet-triplet annihilation （TTA） process. In sum, our aim is to provide a new strategy towards real application of high efficient upconversion emission in solid state, through developing TTA-UC materials with PCs structure.

长波激发短波发射频率上转换在太阳能电池、光催化降解和生物成像等领域显现诱人应用前景。基于三线态-三线态湮灭机制上转换（TTA-UC）由于所需激发光能量接近太阳光强度、溶液态上转换效率较高，最具研究价值。然而空气中氧能完全猝灭上转换体系三线态；光敏剂和湮灭剂在固态中扩散和碰撞受限导致固态上转换效率极低。 本项目将光敏剂-湮灭剂以非共轭键连接以增强两者之间能量传递；用高分子包覆光敏剂与湮灭剂，制备单分散纳米微球，突破目前TTA上转换研究受限于绝氧和溶液条件。通用自组装构建光子晶体微腔结构；利用光子晶体独特的光子禁带、光子局域和带边慢光子效应，提高光敏剂的吸收效率、光敏剂与湮灭剂之间三线态能量转换效率和湮灭剂分子之间三线态湮灭效率；通过研究光子晶体微腔内上转换过程中的三线态能量转移通道，探讨影响弱光上转换发光效率的因素，实现高效固态上转换发光，为弱光上转换技术向固态器件应用探索一条新途径。

如何提高材料性能的研究是材料科学中的一个重点研究问题。对于TTA上转换材料，如何才能获得更高效量子产率的TTA上转换现象，是目前该领域的研究重点。三年来，围绕项目“光子晶体调控弱光上转换材料制备与增强固态上转换发光研究”的课题，开展上转换分子所处的不同微环境与弱光上转换发光性能关系的研究工作。主要探索了上转换介质效应，及固态上转换材料的研究开发，以期实现对TTA上转换效率的提升，并向固态器件化方向发展，取得主要相关创新性的研究工作成果如下：.1．.发现了通过“质子介质效应”提高上转换效率的新途径;.2．.发现了利用“外重原子效应”简单易行实现上转换效率增强的新思路;.3．.设计弱光频率上转换O/W型微乳液体系，克服了上转换绝氧条件的应用瓶颈;.4．.研究探索水凝胶固态上转换材料体系;.5．.研究光子晶体体系对上转换发光性能的调控关系，实现数量级的发光增强;.6．.研究弱光场下频率上转换发光材料在催化等领域的应用。.在项目支持下，共计发表论文共计10篇 (SCI一区IF>5论文2篇，二区IF>3论文4篇)；申请PCT专利1件，授权中国发明专利6件，授权中国实用新型专利2件，正在申请中国发明专利11件。.