| 研究実績の概要 |
In this year, I successfully synthesized sub-2 nm lead halide perovskite nanocrystals with precise size control. I studied the size-dependence of the clusters' properties and demonstrated how the smallest clusters showed increased vibrations and increased disorder, which in turn lead to decreased optical properties. Specifically, the fluorescence quantum yield and fluorescence lifetimes sharply decreased when reducing the size from 2.4 nm to 1.2 nm. In line with quantum confinement effects, the wavelength was also shown to decrease sharply. By using transmission electron microscopy imaging with atomic resolution and a 3 ms temporal resolution, I showed that the increased disorder in smaller clusters was consistent with quick quasi-melting transitions accessible at room temperature. I demonstrated how the internal structure of the clusters, with crystallographic defects such as twinning stabilized the clusters and increased their melting point. Similarly, caesium-based structures also showed an increased melting point and increased structural rigidity, compared to methylammonium-based clusters, in line with their heightened stability. Future plans involve expanding this study to larger (10 nm) perovskite nanocrystals and investigate the temperature dependence of the quasi-melting equilibrium.
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