We have performed micro-photoluminescence measurements on a single CsPbBr3 nanocrystal (NC) with a size comparable to the Bohr diameter (7 nm). When the NC has an orthorhombic crystal symmetry, we observe an exciton fine structure composed of three peaks linearly polarized. We took advantage of the polarization properties of micro-photoluminescence to monitor in situ both the energy and linewidth of individual peaks when increasing temperature. We reveal that two regimes exist, at low and high temperature, which are dominated by acoustic or longitudinal optical phonon (Frohlich term) couplings, respectively. The acoustic contribution does not change when the energy of the excitonic transition varies in the range of 2.46–2.62 eV, i.e., with NC sizes corresponding to this range. We find that line broadening is mainly ruled by the Frohlich term, which is consistent with the polar nature of CsPbBr3.

中文翻译：

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CsPbBr3 单纳米晶中的激子-声子耦合

我们对尺寸与玻尔直径 (7 nm) 相当的单个 CsPbBr3 纳米晶体 (NC) 进行了微光致发光测量。当 NC 具有正交晶体对称性时，我们观察到由三个线性极化峰组成的激子精细结构。我们利用微光致发光的偏振特性在温度升高时原位监测单个峰的能量和线宽。我们揭示了在低温和高温下存在两种状态，分别由声学或纵向光学声子（Frohlich 项）耦合主导。当激子跃迁的能量在 2.46-2.62 eV 范围内变化时，声学贡献不会改变，即 NC 尺寸对应于这个范围。我们发现线展宽主要受 Frohlich 项支配，