Murakami Yoichi, Enomoto Riku
Laboratory for Zero-Carbon Energy, Institute of Innovative Research, Tokyo Institute of Technology, Meguro, Tokyo, Japan.
Front Chem. 2023 Jul 13;11:1217260. doi: 10.3389/fchem.2023.1217260. eCollection 2023.
Photon upconversion (UC) is a technology that converts lower-energy photons (longer wavelength light) into higher-energy photons (shorter wavelength light), the opposite of fluorescence. Thus, UC is expected to open a vast domain of photonic applications that are not otherwise possible. Recently, UC by triplettriplet annihilation (TTA) between organic molecules has been studied because of its applicability to low-intensity light, although the majority of such studies have focused on liquid samples in the form of organic solvent solutions. To broaden the range of applications, solid-state UC materials have been an active area of research. We recently developed air-stable, high-performance molecular UC crystals that utilize a stable solid-solution phase of bicomponent organic crystals. This article begins with a brief overview of previous challenges in developing and improving solid-state TTA-UC materials. Then, we briefly review and explain the concept as well as advantages of our molecular solid-solution UC crystals. We applied these organic crystals for the first time to a water environment. We observed blue UC emission upon photoexcitation at 542 nm (green-yellow light) and then measured the excitation intensity dependence as well as the temporal stability of the UC emission in air-saturated water. In nondegassed water, these organic crystals were stable, functioned with a low excitation threshold intensity of a few milliwatts per square centimeter, and exhibited high photo-irradiation durability at least over 40 h; indicating that the developed organic crystals are also viable for aqueous conditions. Therefore, the organic crystals presented in this report are expected to extend the domain of UC-based photonic applications in practical water systems including diagnostic, clinical, and therapeutic applications.
光子上转换（UC）是一种将低能量光子（较长波长的光）转换为高能量光子（较短波长的光）的技术，与荧光相反。因此，预计UC将开启一个广阔的光子应用领域，而这些应用用其他方法是无法实现的。最近，由于有机分子之间的三重态-三重态湮灭（TTA）上转换适用于低强度光，因此受到了研究，尽管大多数此类研究都集中在有机溶剂溶液形式的液体样品上。为了拓宽应用范围，固态UC材料一直是一个活跃的研究领域。我们最近开发了空气稳定的高性能分子UC晶体，该晶体利用双组分有机晶体的稳定固溶体相。本文首先简要概述了开发和改进固态TTA-UC材料之前所面临的挑战。然后，我们简要回顾并解释了我们的分子固溶体UC晶体的概念及其优势。我们首次将这些有机晶体应用于水环境中。在542 nm（绿黄色光）光激发下，我们观察到了蓝色UC发射，然后测量了空气饱和水中UC发射的激发强度依赖性以及时间稳定性。在未脱气的水中，这些有机晶体是稳定的，在每平方厘米几毫瓦的低激发阈值强度下发挥作用，并且至少在40小时内表现出高光辐照耐久性；这表明所开发的有机晶体在水性条件下也是可行的。因此，本报告中介绍的有机晶体有望扩展基于UC的光子应用领域，应用于包括诊断、临床和治疗应用在内的实际水系统中。
