Photochemical upconversion is a process whereby two lower-energy photons are converted into a higher-energy photon by sensitized triplet–triplet annihilation. While recent interest in this process has been motivated by improving the efficiencies of solar cells, many applications are being explored. In this review, we address the underlying physicochemical phenomena that are responsible for photochemical upconversion. We review their kinetics, and the requirements for annihilators and sensitizers to design efficient upconversion systems. We discuss the spin physics of the bi-excitonic interactions and how the spin character of the triplet pairs can fundamentally limit the upconversion efficiency and give rise to the magnetic field effect on delayed photoluminescence. Finally, we address light-matter coupling phenomena that could be employed to enhance photochemical upconversion.

中文翻译：

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光化学上转换

光化学上转换是通过敏化三重态-三重态湮灭将两个低能光子转化为高能光子的过程。虽然最近人们对这一过程的兴趣是由提高太阳能电池的效率引起的，但许多应用仍在探索中。在这篇综述中，我们讨论了导致光化学上转换的潜在物理化学现象。我们回顾了它们的动力学，以及设计高效上转换系统对湮没剂和敏化剂的要求。我们讨论了双激子相互作用的自旋物理以及三重态对的自旋特性如何从根本上限制上转换效率并引起延迟光致发光的磁场效应。最后，我们解决了可用于增强光化学上转换的光-物质耦合现象。