Haque Anamul, Chonamada Trupthi Devaiah, Dey Arka Bikash, Santra Pralay K
Centre for Nano and Soft Matter Sciences, Jalahalli, Bengaluru, India-560013.
Surface Physics & Materials Science Division, Saha Institute of Nuclear Physics, 1/AF Bidhannagar, Kolkata, India-700064.
Nanoscale. 2020 Oct 22;12(40):20840-20848. doi: 10.1039/d0nr05771a.
Anion exchange of CsPbX3 nanocrystals (NCs) is an easy pathway to tune the bandgap over the entire visible region. Even the mixing of pre-synthesized CsPbBr3 and CsPbI3 NCs at room temperature leads to the formation of mixed halide CsPbBr3-xIx NCs. Understanding the reaction mechanism and the kinetics of interparticle mixing is essential for fundamental aspects and device applications. Here, we probed the kinetics of ion migration through time-dependent steady-state photoluminescence (PL) spectroscopy. We found three primary PL peaks after the mixing of NCs-bromide side peak, iodide side peak, and a new peak that emerges during the reaction. The reaction follows first-order kinetics and the activation energy is 0.75 ± 0.05 eV. We propose that the free oleylammonium halides which are in dynamic equilibrium with the NCs, eventually promote interparticle mixing that follows the anion migration from the surface to the core of the nanocrystal, which is the rate-limiting step. Overall, the inherent reaction rate between the halide anions and the nanocrystals governs the reaction kinetics.
CsPbX3纳米晶体（NCs）的阴离子交换是在整个可见光区域调节带隙的简便途径。即使在室温下将预先合成的CsPbBr3和CsPbI3 NCs混合，也会导致形成混合卤化物CsPbBr3-xIx NCs。了解反应机理和粒子间混合的动力学对于基础研究和器件应用至关重要。在此，我们通过时间相关稳态光致发光（PL）光谱探究了离子迁移的动力学。我们发现NCs混合后出现三个主要的PL峰——溴化物侧峰、碘化物侧峰以及反应过程中出现的一个新峰。该反应遵循一级动力学，活化能为0.75±0.05 eV。我们提出，与NCs处于动态平衡的游离油胺卤化物最终促进了粒子间混合，这种混合遵循阴离子从纳米晶体表面向核心的迁移，而这是速率限制步骤。总体而言，卤化物阴离子与纳米晶体之间的固有反应速率决定了反应动力学。
