The dielectric contrast effect is usually evoked to explain anisotropy of optical properties of elongated nanoobjects, for example, semiconductor nanowires. We applied two-dimensional polarization imaging microscopy to measure the polarization of photoluminescence (PL) excitation and PL intensity of nanoaggregates of in-situ formed MAPbBr₃ perovskite nanoparticles in a stretched polymeric matrix. Scanning electron microscopy images of these objects were also acquired to characterize their sizes and shapes. We find that individual perovskite aggregates with sizes of 100–300 nm often possess a PL excitation polarization degree as high as 0.5–0.9, which is up to three times higher than the polarization degree of absorption predicted by the dielectric contrast effect. Small aggregates of nanoparticles possess an emission polarization degree substantially higher than that of excitation. Computer simulations of many possible scenarios show that the dielectric contrast alone cannot quantitatively explain the polarization properties of the studied objects. We propose energy transfer to localized emitting sites and the dependence of PL yield on excitation power density as possible factors strongly influencing the polarization properties of PL emission and PL excitation, respectively.

中文翻译：

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MAPbBr3 钙钛矿纳米结构的光致发光偏振。介电对比效应可以解释吗？

通常会引起介电对比效应来解释细长纳米物体（例如半导体纳米线）的光学特性的各向异性。我们应用二维偏振成像显微镜测量原位形成的 MAPbBr _{3纳米聚集体的光致发光 (PL) 激发偏振和 PL 强度}拉伸聚合物基质中的钙钛矿纳米粒子。还获取了这些物体的扫描电子显微镜图像，以表征它们的大小和形状。我们发现尺寸为 100-300 nm 的单个钙钛矿聚集体通常具有高达 0.5-0.9 的 PL 激发偏振度，比介电对比效应预测的吸收偏振度高出三倍。纳米粒子的小聚集体具有远高于激发的发射偏振度。许多可能场景的计算机模拟表明，单靠介电对比无法定量解释所研究物体的偏振特性。