Band-Edge Engineering To Eliminate Radiation-Induced Defect States in Perovskite Scintillators
2020
Liu, X. Y. (Xiang Yang) | Pilania, Ghanshyam | Talapatra, Anjana Anu | Stanek, Christopher R. | Uberuaga, Blas Pedro
Under radiative environments such as extended hard X- or γ-rays, degradation of scintillation performance is often due to irradiation-induced defects. To overcome the effect of deleterious defects, novel design mitigation strategies are needed to identify and design more resilient materials. The potential for band-edge engineering to eliminate the effect of radiation-induced defect states in rare-earth-doped perovskite scintillators is explored, taking Ce³⁺-doped LuAlO₃ as a model material system, using density functional theory (DFT)-based DFT + U and hybrid Heyd–Scuseria–Ernzerhof (HSE) calculations. From spin-polarized hybrid HSE calculations, the Ce³⁺ activator ground-state 4f position is determined to be 2.81 eV above the valence band maximum in LuAlO₃. Except for the oxygen vacancies which have a deep level inside the band gap, all other radiation-induced defects in LuAlO₃ have shallow defect states or are outside the band gap, that is, relatively far away from either the 5d¹ or the 4f Ce³⁺ levels. Finally, we examine the role of Ga doping at the Al site and found that LuGaO₃ has a band gap that is more than 2 eV smaller than that of LuAlO₃. Specifically, the lowered conduction band edge envelopes the defect gap states, eliminating their potential impact on scintillation performance and providing direct theoretical evidence for how band-edge engineering could be applied to rare-earth-doped perovskite scintillators.
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