Magneto-Optical Functionality and Energy Transfer in Metal-Halide Perovskite Nanocrystals Doped with Transition Metals

该项目的总体目标是研究掺杂过渡金属（TM，主要是Mn）的钙钛矿纳米晶体的磁光功能和能量转移。卤化铅钙钛矿（APbX 3，A = Cs，MA，FA; X = Cl，Br，I）的特定晶体结构预期允许在六重配位晶格位点上掺入TM 2+阳离子（替代Pb 2+）-与II-VI族硫属化物的TM掺杂的更“传统”情况相反，其中掺杂剂通常掺入四重配位位点上。这些材料的独特性还依赖于不同的能带结构（导带由p态形成，价带由s态形成）和与II-VI纳米晶体相比更多的离子键。此外，当降低温度时，发生从立方相到四方相和最后正交相的晶体相变。 尽管文献中有几篇关于Mn ~（2+）掺杂的APbX_3纳米晶体的报道，但到目前为止还没有任何证据证明由sp-d交换相互作用引起的任何巨磁光功能。我们打算使用磁圆二色性测量和磁光致发光实验在很宽的温度范围内，以调查是否巨大的sp-d交换效应存在于这种新型材料类，其中的轨道的杂化可能显着不同的II-VI纳米晶体由于不同的配位位点的掺杂剂和更多的离子键。此外，当降低温度时，卤化铅钙钛矿经历特定的晶体相变，导致发射能量的不连续变化。计划研究这种晶体相变如何影响从带态到发光掺杂剂（和返回）的能量转移，以及这种效应是否可以用于实现具有两个不同临界温度的双发射器，通过仔细调节带隙，例如通过Br/I比或Br尺寸，相对于Mn 2+掺杂剂的内部4 T1 - 6A 1跃迁。

The overall goal of this project is to investigate the magneto-optical functionality and the energy transfer of perovskite nanocrystals doped with transition metals (TM, mainly Mn). The specific crystal structure of lead halide perovskites (APbX3, A = Cs, MA, FA; X = Cl, Br, I) is expected to allow for incorporation of TM2+ cations on six-fold coordinated lattice sites (replacing Pb2+) – in contrast to the more 'traditional' case of TM doping of II-VI chalocogenides, where the dopants are usually incorporated on four-fold coordinated sites. The uniqueness of these materials relies in addition on the different bandstructure (conduction band formed by p-states, valence band by s-states) and the more ionic bonds as compared to II-VI nanocrystals. Moreover, crystal phase transitions from the cubic to the tetragonal and finally the orthorhombic phase occur when lowering the temperature. In spite of several reports on Mn2+ doped APbX3 nanocrystals in literature there is no proof of any giant magneto-optical functionality caused by sp-d exchange interaction up to now. We intend to use magnetic circular dichroism measurements and magneto-photoluminescence experiments over a wide range of temperatures to investigate whether giant sp-d exchange effects are present in this novel material class, where the hybridization of the orbitals might significantly differ from II-VI nanocrystals due to the differently coordinated sites of the dopants and the more ionic bonds. In addition lead halide perovskites undergo a specific crystal phase transition when reducing the temperature leading to a discontinuous change of the emission energy. It is planned to investigate how this crystal phase transition affects the energy transfer from band states to luminescent dopants (and back), and whether this effect can be used for realizing dual emitters with two distinct critical temperatures by carefully adjusting the bandgap, e.g. by the Br/I ratio or the nanocrystal size, with respect to the internal 4T1 – 6A1 transition of the Mn2+ dopant.