Ab initio prediction of fast non-equilibrium transport of nascent polarons in SrI2: a key to high-performance scintillation  

作　　者：Fei Zhou Babak Sadigh Paul Erhart Daniel Åberg 

机构地区：[1]Physical and Life Sciences Directorate,Lawrence Livermore National Laboratory,Livermore,CA,USA [2]Department of Physics,Chalmers University of Technology,Gothenburg,Sweden

出　　处：《npj Computational Materials》2016年第1期77-83,共7页计算材料学（英文）

基　　金：the auspices of the US Department of Energy by Lawrence Livermore National Laboratory under contract No.DE-AC52-07NA27344;support from the National Nuclear Security Administration Office of Nonproliferation Research and Development(NA-22).

摘　　要：The excellent light yield proportionality of europium-doped strontium iodide(SrI2:Eu)has resulted in state-of-the-artγ-ray detectors with remarkably high-energy resolution,far exceeding that of most halide compounds.In this class of materials,the formation of self-trapped hole polarons is very common.However,polaron formation is usually expected to limit carrier mobilities and has been associated with poor scintillator light-yield proportionality and resolution.Here using a recently developed first-principles method,we perform an unprecedented study of polaron transport in SrI2,both for equilibrium polarons,as well as nascent polarons immediately following a self-trapping event.We propose a rationale for the unexpected high-energy resolution of SrI2.We identify nine stable hole polaron configurations,which consist of dimerised iodine pairs with polaron-binding energies of up to 0.5 eV.They are connected by a complex potential energy landscape that comprises 66 unique nearest-neighbour migration paths.Ab initio molecular dynamics simulations reveal that a large fraction of polarons is born into configurations that migrate practically barrier free at room temperature.Consequently,carriers created duringγ-irradiation can quickly diffuse away reducing the chance for nonlinear recombination,the primary culprit for non-proportionality and resolution reduction.We conclude that the flat,albeit complex,landscape for polaron migration in SrI2 is a key for understanding its outstanding performance.This insight provides important guidance not only for the future development of high-performance scintillators but also of other materials,for which large polaron mobilities are crucial such as batteries and solid-state ionic conductors.

关 键 词：POLARON EQUILIBRIUM IODINE 

分 类 号：O46[理学—电子物理学]