DeCrescent Ryan A, Du Xinhong, Kennard Rhiannon M, Venkatesan Naveen R, Dahlman Clayton J, Chabinyc Michael L, Schuller Jon A
Department of Physics, University of California Santa Barbara, Santa Barbara, California 93106, United States.
Department of Electrical and Computer Engineering, University of California Santa Barbara, Santa Barbara, California 93106, United States.
ACS Nano. 2020 Jul 28;14(7):8958-8968. doi: 10.1021/acsnano.0c03783. Epub 2020 Jul 15.
Recently, unconventional bright magnetic dipole (MD) radiation was observed from two-dimensional (2D) hybrid organic-inorganic perovskites (HOIPs). According to commonly accepted HOIP band structure calculations, such MD light emission from the ground-state exciton should be strictly symmetry forbidden. These results suggest that MD emission arises in conjunction with an as-yet unidentified symmetry-breaking mechanism. In this paper, we show that MD light emission originates from a self-trapped p-like exciton stabilized at energies below the primary electric dipole (ED)-emitting 1s exciton. Using suitable combinations of sample and collection geometries, we isolate the distinct temperature-dependent properties of the ED and MD photoluminescence (PL). We show that the ED emission wavelength is nearly constant with temperature, whereas the MD emission wavelength exhibits substantial red shifts with heating. To explain these results, we derive a microscopic model comprising two distinct parity exciton states coupled to lattice distortions. The model explains many experimental observations, including the thermal red shift, the difference in emission wavelengths, and the relative intensities of the ED and MD emission. Thermodynamic analysis of temperature-dependent PL reveals that the MD emission originates from a locally distorted structure. Finally, we demonstrate unusual hysteresis effects of the MD-emitting state near structural phase transitions. We hypothesize that this is another manifestation of the local distortions, indicating that they are insensitive to phase changes in the equilibrium lattice structure.
最近，在二维有机-无机杂化钙钛矿（HOIPs）中观察到了非常规的明亮磁偶极（MD）辐射。根据普遍接受的HOIP能带结构计算，基态激子的这种MD发光应该严格地被对称性禁止。这些结果表明，MD发射是与一种尚未确定的对称性破缺机制一起出现的。在本文中，我们表明MD发光源自一种自陷的p类激子，它稳定在低于主要电偶极（ED）发射的1s激子的能量处。通过样品和收集几何结构的适当组合，我们分离出了ED和MD光致发光（PL）不同的温度依赖性特性。我们表明，ED发射波长随温度几乎不变，而MD发射波长随着加热呈现出显著的红移。为了解释这些结果，我们推导了一个微观模型，该模型包含两个与晶格畸变耦合的不同宇称激子态。该模型解释了许多实验观察结果，包括热红移、发射波长的差异以及ED和MD发射的相对强度。对温度依赖性PL的热力学分析表明，MD发射源自局部畸变的结构。最后，我们展示了MD发射态在结构相变附近的异常滞后效应。我们推测这是局部畸变的另一种表现，表明它们对平衡晶格结构中的相变不敏感。
