报告题目：A Brief Perspective on Halides as Optoelectronic Materials

报 告 人：Koushik Biswas教授  Arkansas State University, USA

主 持 人：张立军 教授

报告时间：2018年6月27日 14:30

报告地点：南区唐敖庆楼D区429报告厅

主办单位：材料科学与工程学院

摘  要：

The remarkable success of organic-inorganic lead (Pb) halide perovskites (e.g., CH3NH3PbI3) as solar absorbers has generated lot of interest accompanied by a surge in research activity into this general family of ionic compounds. They are broadly grouped under perovskite-type crystals, built from metal-halogen octahedral framework, [MX6] (M = metal, X = halogen). Different arrangements of these [MX6] octahedra may lead to low-dimensional structures, which can dramatically influence the optoelectronic properties of such crystals. A case in point, is the semiconducting CsPbBr3 (band gap ~2.3 eV) built from corner sharing 3-dimensional (3D) network of [PbBr6], whose bulk crystals are not known as efficient light emitters. Its single crystals possess good carrier mobility and lifetime, appropriate for radiation detectors. However, highly luminescent CsPbBr3 nanocrystals and Cs4PbBr6/CsPbBr3 composite crystals have been reported recently, observing bright green emission with very fast (sub nanosecond) radiative lifetime. Cs4PbBr6 structure is comprised of almost disjointed [PbBr6] octahedra held together by Cs-Br bridges, which stands in contrast to the 3D network found in CsPbBr3. Using density functional calculations, we will discuss the electronic consequences caused by differences in dimensionality in the two crystal structures. The emergence of strongly bound excitonic features in Cs4PbBr6 and Type-I band alignment with CsPbBr3 support the notion of carrier confinement causing fast, green luminescence in samples containing CsPbBr3 nano-islands embedded within Cs4PbBr6. Similar considerations on structural differences can be extended to compare the scintillation properties CsCaI3 and KCaI3. Although, both are built from [CaI6] motifs, one has a 3D network (CsCaI3) while another has edge-sharing layered structure (KCaI3). It is reflected in properties of charge carriers, and in the light yield comparisons between the two materials.

个人介绍：

Koushik Biswas is an Associate Prof. of Physics at Arkansas State University, USA. He received his PhD from Texas Tech University in 2007. As a postdoctoral researcher, he worked at the National Renewable Energy Lab and Oak Ridge National Lab before joining Arkansas State in 2012. Koushik’s research interests include ab-initio computational study of luminescent materials for radiation detection. This project is supported by the US Department of Homeland Security.