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Title: Ab initio prediction of fast non-equilibrium transport of nascent polarons in SrI 2: a key to high-performance scintillation [First-principles study of hole polaron formation and migration in strontium iodide]

Abstract

The excellent light yield proportionality of europium-doped strontium iodide (SrI 2:Eu) has resulted in state-of-the-art γ-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 SrI 2, 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 SrI 2. 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 during γ-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 formore » polaron migration in SrI 2 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.« less

Authors:
 [1];  [1];  [1];  [2]
  1. Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Physical and Life Science Directorate
  2. Chalmers Univ. of Technology, Gothenburg (Sweden). Dept. of Applied Physics
Publication Date:
Research Org.:
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1305858
Report Number(s):
LLNL-JRNL-678128
Journal ID: ISSN 2057-3960
Grant/Contract Number:
AC52-07NA27344
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
npj Computational Materials
Additional Journal Information:
Journal Volume: 2; Journal ID: ISSN 2057-3960
Publisher:
Nature Publishing Group
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY

Citation Formats

Zhou, Fei, Sadigh, Babak, Aberg, Daniel, and Erhart, Paul. Ab initio prediction of fast non-equilibrium transport of nascent polarons in SrI2: a key to high-performance scintillation [First-principles study of hole polaron formation and migration in strontium iodide]. United States: N. p., 2016. Web. doi:10.1038/npjcompumats.2016.22.
Zhou, Fei, Sadigh, Babak, Aberg, Daniel, & Erhart, Paul. Ab initio prediction of fast non-equilibrium transport of nascent polarons in SrI2: a key to high-performance scintillation [First-principles study of hole polaron formation and migration in strontium iodide]. United States. doi:10.1038/npjcompumats.2016.22.
Zhou, Fei, Sadigh, Babak, Aberg, Daniel, and Erhart, Paul. Fri . "Ab initio prediction of fast non-equilibrium transport of nascent polarons in SrI2: a key to high-performance scintillation [First-principles study of hole polaron formation and migration in strontium iodide]". United States. doi:10.1038/npjcompumats.2016.22. https://www.osti.gov/servlets/purl/1305858.
@article{osti_1305858,
title = {Ab initio prediction of fast non-equilibrium transport of nascent polarons in SrI2: a key to high-performance scintillation [First-principles study of hole polaron formation and migration in strontium iodide]},
author = {Zhou, Fei and Sadigh, Babak and Aberg, Daniel and Erhart, Paul},
abstractNote = {The excellent light yield proportionality of europium-doped strontium iodide (SrI2:Eu) has resulted in state-of-the-art γ-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 during γ-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.},
doi = {10.1038/npjcompumats.2016.22},
journal = {npj Computational Materials},
number = ,
volume = 2,
place = {United States},
year = {Fri Aug 12 00:00:00 EDT 2016},
month = {Fri Aug 12 00:00:00 EDT 2016}
}

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