Preferential Eu Site Occupation and Its Consequences in the Ternary Luminescent HalidesAB2I5∶Eu2+

Abstract

Several rare-earth doped, heavy metal halides have been recently identified as potential next-generation luminescent materials with high efficiency at low cost. AB 2 I 5 :Eu 2+ (A=Li-Cs; B=Sr, Ba) is one such family of halides. Its members, such as CsBa 2 I 5 :Eu 2+ and KSr 2 I 5 :Eu 2+ , are currently being investigated as high performance scintillators with improved sensitivity, light yield, and energy resolution less than 3% at 662 keV. Within the AB 2 I 5 family, our firstprinciples based calculations reveal two remarkably different trends in Eu site occupation. The substitutional Eu ions occupy both eight-coordinated B1 (VIII) and the seven-coordinated B2 (VII) sites in the Sr-containing compounds. However, in the Ba-containing crystals, Eu strongly prefer the B2 (VII) sites. This random versus preferential distribution of Eu affects their electronic properties. The calculations also suggest that in the Ba-containing compounds one can expect formation of Eu-rich domains. These results provide atomistic insight into recent experimental observations about the concentration and temperature effects in Eu-doped CsBa 2 I 5. We discuss the implications of our results with respect to luminescent properties and applications. We also hypothesize Sr, Ba-mixed quaternary iodides ABa VIII Sr VII I 5 :Eu, as scintillators having enhanced homogeneity and electronic properties.

Growth and luminescent properties of new Eu2+doped RbBa2I5 scintillator

“…In the luminescence spectra of the RbBa 2 I 5 crystals, only one type of Eu 2+ emission centers is observed. This result correlates with theoretical calculations in which Eu 2+ preferentially occupies sevenfold coordinated Ba 2+ sites in ABa 2 I 5 ternary halides [18].…”

Crystal structure, electronic structure, temperature-dependent optical and scintillation properties of CsCe2Br7

“…thermal ionization of the excited state of Ce 3+ 40,41 and non-radiative relaxation from its 5d state to the 4f state. In the case of KSr 2 I 5 :Eu 2+ , although the Eu ions occupy both eightfoldcoordinated site and the sevenfold-coordinated site, 43 only one symmetric Gaussian-shaped Eu 2+ 5d-4f emission peak can be identified in RL spectrum. However, in our case, based on the PDOS of CsCe 2 Br 7 (Fig.…”

“…Similar phenomenon is also found in KSr 2 I 5 :Eu 2+ single-crystal scintillator. In the case of KSr 2 I 5 :Eu 2+ , although the Eu ions occupy both eightfoldcoordinated site and the sevenfold-coordinated site, 43 only one symmetric Gaussian-shaped Eu 2+ 5d-4f emission peak can be identified in RL spectrum. 44 However, the causes are still not understood yet.…”

Direct observation of Eu atoms in AlN lattice and the first‐principles simulations

“…The electronic wave functions were sampled on dense grids, for example, a 4 × 6×1 grid with 6‐12 irreducible k ‐points depending on the symmetry, for the super cells of AlN(110) surface systems with Eu or Eu–O doping in the Brillouin zone (BZ) of the crystals using the Monkhorst and Pack method . The localized Eu 4f states were described using the Hubbard U ( U = 2.5 eV) approach . Tests of k ‐mesh density and cut‐off energies showed a good convergence (~1 meV/atom).…”

“…Pentaleri and co‐workers studied substitutional impurities in zinc‐blende aluminum nitride . Recently ab initio density functional theory was applied successfully in study of the doping of Eu in scintillation and luminescent materials . In the current paper, we prepared the high‐pure AlN: Eu phosphors by gas‐reduction‐nitridation (GRN) method and investigated the preferred sites of Eu ions in the AlN samples by a combination of multiple experimental techniques (SEM, EXAFS/XANES, STEM) and first‐principles calculations.…”