Band-Edge Engineering To Eliminate Radiation-Induced Defect States in Perovskite Scintillators

Abstract

Under radiative environments such as extended hard Xor 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-earthdoped perovskite scintillators is explored, taking Ce 3+ -doped LuAlO 3 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 Ce 3+ activator ground-state 4f position is determined to be 2.81 eV above the valence band maximum in LuAlO 3 . Except for the oxygen vacancies which have a deep level inside the band gap, all other radiation-induced defects in LuAlO 3 have shallow defect states or are outside the band gap, that is, relatively far away from either the 5d 1 or the 4f Ce 3+ levels. Finally, we examine the role of Ga doping at the Al site and found that LuGaO 3 has a band gap that is more than 2 eV smaller than that of LuAlO 3 . 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.

Gd-admixed (Lu,Gd)AlO3 single crystals: breakthrough in heavy perovskite scintillators

“…According to the theoretical DFT computations in ref. 32 , the conduction band edge of GdAP should be lowered by ~2.5 eV compared to that of LuAP. Therefore, the decreasing edge of the conduction band should effectively cover all the mentioned shallow electron traps, provided that the positions of the traps remain unchanged.…”

“…Notably, a recent theoretical study, which used density functional theory, focused on the possibility of eliminating the effects of radiation-induced damage by bandgap engineering the LuAP:Ce scintillator 32 . The above study examined the role of the Ga admixture at the Al site and found that LuGaO 3 should have a bandgap that was more than 2 eV smaller than that of LuAlO 3 .…”

“…Therefore, ref. 32 provides a direct theoretical concept for how band-edge engineering could be applied to rare-earth-doped LuAP scintillators, and such a study calls for experimental verification.…”

Accurately predicting optical properties of rare-earth, aluminate scintillators: influence of electron–hole correlation

“…Where the HSE06 hybrid functional is used for final electronic structure calculations, we use 33% exact exchange instead of the usual 25%. 78 The screening parameter is 0.2 Å À1 . In all cases, we maintain a minimum momentum space resolution of 0.7 Å À1 .…”

Barriers to carriers: faults and recombination in non-stoichiometric perovskite scintillators

“…For example, to mitigate the effects of traps, either defect engineering [32], with the goal of eliminating the defects responsible for the traps, or band-edge engineering [7] to eliminate the effects of the traps, can improve transport processes. These kinds of efforts have improved the light output in garnets almost 5-fold [29,31] and seem promising for perovskites as well [25]. However, even if all traps, or their effects, are eliminated, there is a chance that the carriers escape the local region and are thus unable to recombine and scintillate.…”