Ma Xiaoman, Gao Huaxiong, Meng Chaoying, Pan Fang, Ye Honggang
School of Physical Science and Technology, Xinjiang University, Urumqi 830046, People's Republic of China.
Department of Applied Physics, and MOE Key Laboratory for Nonequilibrium Synthesis and Modulation of Condensed Matter, Xi'an Jiaotong University, Xi'an 710049, People's Republic of China.
J Phys Chem Lett. 2023 Aug 3;14(30):6860-6866. doi: 10.1021/acs.jpclett.3c01641. Epub 2023 Jul 25.
The Stokes shift is negligible in bulk perovskites but large in two-dimensional (2D) CsPbBr perovskites. The issue has attracted a lot of discussion, but it remains controversial. Here, we report the temperature-dependent absorption and photoluminescence (PL) spectra of CsPbBr perovskite nanoplatelets (NPLs). We observe a temperature-dependent Stokes shift changing from 26 to 41 meV. This phenomenon was attributed to the exciton fine structure according to the great difference in peak width. The triple bright exciton levels all participate in the absorption process and result in a wide absorption peak, while only the lowest exciton level contributes to photon emission and exhibits a relatively narrow PL peak. The PL decay curves also present the characterization of bright and dark exciton couplings at low temperatures. The splitting of triple bright excitons is induced by the morphology anisotropy of the 2D structure, so the large Stokes shift is proposed to be an intrinsic property of 2D perovskites.
在体相钙钛矿中，斯托克斯位移可忽略不计，但在二维（2D）CsPbBr钙钛矿中却很大。这个问题已经引发了大量讨论，但仍然存在争议。在此，我们报告了CsPbBr钙钛矿纳米片（NPLs）的温度依赖吸收光谱和光致发光（PL）光谱。我们观察到温度依赖的斯托克斯位移从26 meV变化到41 meV。根据峰宽的巨大差异，这一现象归因于激子精细结构。三重明亮激子能级都参与吸收过程并导致宽吸收峰，而只有最低激子能级对光子发射有贡献并呈现相对窄的PL峰。PL衰减曲线在低温下也呈现出明亮和暗激子耦合的特征。三重明亮激子的分裂是由二维结构的形态各向异性引起的，因此大斯托克斯位移被认为是二维钙钛矿的固有特性。
