Intrinsic defects, nonstoichiometry, and aliovalent doping of ABO perovskite scintillators

Abstract

authoren We have employed a range of atomistic simulation methods to explore aspects of defect chemistry in ABO3 (where A2+= Ba2+ or Sr2+, and B4+= Zr4+ or Hf4+) perovskites, placing emphasis on processes relevant for application of these materials as high performance scintillators. Specifically, we examined intrinsic defect reactions, A and B excess nonstoichiometry and the solution of Me3+ rare earth cations. As has been predicted in previous studies, we find that Schottky disorder is the lowest energy intrinsic process. For nonstoichiometry, we predict that AO‐excess is compensated by oxygen vacancies and BO2‐excess is charge compensated by A vacancies (see abstract figure). Finally, for Me3+ solution, we considered several reactions for Me3+ cations ranging in size from Lu3+ to La3+, and the preferred reaction depends on the specific Me3+ cation and whether or not phase separation occurs. Nonstoichiometry mechanisms in ABO3 perovskites. Red spheres correspond to O2−, blue to A2+, and green to B4+.

Long term in vivo imaging with Cr3+ doped spinel nanoparticles exhibiting persistent luminescence

“…(iii) Intrinsic defects have been well identified in lots of materials see for instance refs. [7,65]. In garnet for instance, lots of possible defects are reported such as vacancies, interstitials, antisites or other native defects [65,66] and such defects may play a fundamental role.…”

“…Notice that in some cases, the emitting centers can also play the role of trap centers. The latter can be due to lattice defects, impurities [7,8], or various codopants which are introduced to enhance traps within the material in the energy bandgap, mainly just below the conduction band in the case of electron traps or just above the valence band in the case of hole traps [9][10][11]. Under light, excited states are generated and the excitation, instead of being radiatively relaxed, can be non-radiatively captured by the traps.…”

Chemically engineered persistent luminescence nanoprobes for bioimaging

“…In persistent phosphors, two kinds of active centers are involved: the trap centers and the emitter centers (see Figure 1). Traps can be due to lattice defects, impurities 19, 20, or various co-dopants introduced during the synthesis within the material energy bandgap, mainly just below the conduction band in the case of electron traps or just above the valence band in the case of hole traps 21,22. Under light, excited levels are generated and instead of being radiatively relaxed they can be non-radiatively captured into traps.…”

Role of Multiple Charge States of Ce in the Scintillation of ABO3 Perovskites

“…While most of the past efforts related to transparent ceramic scintillators have explored binary halides [9][10][11], garnets [12], and ortho-and pyro-silicates [13,14], more recent studies have focused on perovskites [15,16]. In particu-lar, A 2+ B 4+ O 3 perovskite oxides with A ∈{Ca, Sr, Ba} and B ∈{Zr, Hf} and A' 3+ B' 3+ O 3 with A' ∈{Y, Gd, Lu} and B' ∈{Al} doped with Ce as an activator impurity have been investigated owing to their excellent gamma ray attenuation resulting from their high density and high effective atomic number [17][18][19][20][21]. Despite the significant efforts, however, only a limited amount of success has been achieved in making Ce-doped perovskites scintillating.…”

“…First-principles calculations within the framework of density functional theory (DFT) and 'beyond' approaches can be particularly useful in studying systematic trends and gaining insights into chemical and electronic properties of materials, and thereby aid the search for better materials or improved modifications of existing materials. In fact, over the past decade, DFT has been extensively employed to study and search for novel and improved rare-earth-doped inorganic scintillator materials and has already significantly contributed to our present understanding of these materials [17,[26][27][28][29][30][31][32][33][34]. The main aim of the present study is to understand trends in thermodynamic stability of Ce dopants within the per-ovskite crystal structure across a range of chemistries as a function of Ce charge state, doping site and synthesis conditions.…”