Lead-halide perovskites have emerged as promising materials for photovoltaic and optoelectronic applications. Their significantly anharmonic lattice motion, in contrast to conventional harmonic semiconductors, presents a conceptual challenge in understanding the genesis of their exceptional optoelectronic properties. Here we report a strongly temperature dependent luminescence Stokes shift in the electronic spectra of both hybrid and inorganic lead-bromide perovskite single crystals. This behavior stands in stark contrast to that exhibited by more conventional crystalline semiconductors. We correlate the electronic spectra with the anti-Stokes and Stokes Raman vibrational spectra. Dielectric solvation theories, originally developed for excited molecules dissolved in polar liquids, reproduce our experimental observations. Our approach, which invokes a classical Debye-like relaxation process, captures the dielectric response originating from the incipient anharmonicity of the LO phonon at about 20 meV (160 cm⁻¹) in the lead-bromide framework. We reconcile this liquid-like model incorporating thermally-activated dielectric solvation with more standard solid-state theories of the emission Stokes shift in crystalline semiconductors.

卤化铅钙钛矿已成为光伏和光电子应用的有前途的材料。与传统的谐波半导体相比，它们具有显着的非简谐晶格运动，这对理解其特殊光电特性的起源提出了概念上的挑战。在这里，我们报告了杂化和无机溴化铅钙钛矿单晶的电子光谱中强烈依赖于温度的发光斯托克斯位移。这种行为与更传统的晶体半导体所表现出的行为形成鲜明对比。我们将电子光谱与反斯托克斯和斯托克斯拉曼振动光谱相关联。介电溶剂化理论最初是为溶解在极性液体中的受激分子而开发的，它再现了我们的实验观察结果。我们的方法调用了经典的德拜式弛豫过程，捕获了源自溴化铅框架中约 20 meV (160 cm ^-1 ) 的 LO 声子的初始非谐性的介电响应。我们将这种包含热激活介电溶剂化的类液体模型与晶体半导体中发射斯托克斯位移的更标准的固态理论相协调。