在深蓝色发射系统中，最大限度地再生单线态激子仍然是一个相当大的挑战，以获得低成本、高效率的荧光材料。然而，长寿命三重态激子的形成通常主导辐射过程，由于单重态激子的抑制，使得获得高色纯度的深蓝色发射极为困难。
该文中，通过压力驱动的反向系统间交叉（RISC）成功地实现了双钙钛矿Cs2Na0.4Ag0.6InCl6合金中非常明亮的深蓝色发射，其是一种从激发三重态向单重态能量转移的异常光物理过程。其中，CNAICB固有的宽发射与激发三重态的自陷激子（STE）有关，而激发单重态中填充的STE的辐射复合是观察到的深蓝色发射的原因。
此外，在5.01 GPa，深蓝色发射对应于国际航空委员会（CIE）坐标（0.16,0.06），符合Rec.2020显示标准的要求。同样，压力作为一种有效的工具被引入，以排除自由激子复合的可能性，并澄清关于Cs2AgInCl6低波长发射起源的长期传统争议。
该研究不仅证明了压力是提高深蓝色发射的有效手段，而且还对无铅CNAICB双钙钛矿的结构-性能关系提供了深刻的见解。
附：英文原文
Title: Pressure-Driven Reverse Intersystem Crossing: New Path toward Bright Deep-Blue Emission of Lead-Free Halide Double Perovskites
Author: Zhiwei Ma, Qian Li, Jiajun Luo, Shunran Li, Laizhi Sui, Dianlong Zhao, Kaijun Yuan, Guanjun Xiao, Jiang Tang, Zewei Quan, Bo Zou
Issue&Volume: September 10, 2021
Abstract: Maximizing the regeneration of singlet excitons remains a considerable challenge in deep-blue emission systems to obtain low-cost, high-efficiency fluorescent materials. However, the formation of the long-lifetime triplet excitons generally dominates the radiative process, making it greatly difficult to harvest deep-blue emission with high color purity because of the depression of singlet excitons. Here, a very bright deep-blue emission in double perovskite Cs2Na0.4Ag0.6InCl6 alloyed with Bi doping (CNAICB) was successfully achieved by pressure-driven reverse intersystem crossing (RISC), an abnormal photophysical process of energy transfer from the excited triplet state back to the singlet. Therein, the inherently broad emission of CNAICB was associated with the self-trapped excitons (STEs) at excited triplet states, whereas the radiative recombination of STEs populated in excited singlet states was responsible for the observed deep-blue emission. Moreover, the deep-blue emission corresponds to Commission Internationale de L’Eclairage (CIE) coordinates (0.16, 0.06) at 5.01 GPa, which meets the requirement of Rec. 2020 display standards. Likewise, pressure was introduced as an efficient tool to rule out the possibility of the recombination of free excitons and clarify the long-standing conventional dispute over the origin of the low-wavelength emission of Cs2AgInCl6. Our study not only demonstrates that pressure can be a robust means to boost the deep-blue emission but also provides deep insights into the structure–property relationship of lead-free CNAICB double perovskites.
DOI: 10.1021/jacs.1c06207
Source: https://pubs.acs.org/doi/10.1021/jacs.1c06207
