First-principles search for efficient activators for LaI3

Abstract

a b s t r a c tFirst-principles calculations were performed using density functional theory with Hubbard corrections or hybrid exchange-correlation functionals, as well as the GW approximation, to predict dopants that could serve as efficient activators for LaI 3 , a potentially very bright scintillator for which an appropriate activator has not been identified yet. The dopants considered in this work included a series of lanthanide ions (Ce, Pr, Nd, Eu, Gd, and Tb) and several ns 2 ions (Tl, Pb, Bi, and Sb). Based on both ground-state calculations and constrained DFT calculations to simulate excited states, the trivalent lanthanide dopants were shown not to constitute an improvement over Ce 3 þ , for which experimental data exist, as they showed occupied 4f states below the valence band maximum (VBM) and 5d states above the conduction band maximum (CBM). In contrast, the only divalent lanthanide considered, Eu 2 þ , displayed occupied 4f states within the band gap of the host, but its 5d states were calculated to be above the CBM. Eu 2 þ could nonetheless be exploited as an activator by increasing the band gap energy slightly through substitution of iodide ions by bromide ions. Similar results were obtained for Tl þ . Finally, Bi 3 þ and Sb 3 þ were predicted to be efficient activators in LaI 3 by virtue of having unoccupied p states below the CBM, which can serve as electron traps and can combine with holes at the VBM to form localized luminescence centers. Therefore, Bi-and Sb-doped LaI 3 should be grown and tested experimentally. Comparison with empirical relationships of the relative positions of the energy levels of rare-earth dopants and implications for efficient doping schemes and scintillation mechanisms in LaI 3 are also discussed.

Influence of Anion Charge on Li Ion Diffusion in a New Solid-State Electrolyte, Li3LaI6

“…22 The generalized gradient approximation (GGA) 23 in the form of Perdew−Burke−Ernzerhof exchange functional 22 was used. To consider the strong correlation effects of the transition metal in Li 3 ScI 6 , Li 3 YI 6 , and Li 3 LaI 6 halides, both structural optimizations and electronic structure calculations were carried out using the spin-dependent GGA plus Hubbard correction U (GGA + U) method, 24 and the effective U eff parameters were 5.00, 25 3.00, 26 and 10.32 eV 27 for the Sc 3d, Y 4d, and La 4f states, respectively. The plane-wave energy cutoff was set to 520 eV.…”

Needs, Trends, and Advances in Inorganic Scintillators

“…Definitely, much more reliable investigations were made for different first-principles calculations of specific crystals (see [209] as an example). Fairly good progress was achieved in first-principles calculation of activators, both rare earth ions (see [210] and [211]) and heavy ions [212], [213]. First-principle calculations make a step toward obtaining not only positions of energy levels, but some dynamical parameters, such as multiphonon capture and recombination rates [214]- [216], the parameters that are very important for reliable application of above-mentioned calculations using rate equations or kinetic Monte Carlo schemes.…”

Picosecond absorption spectroscopy of self-trapped excitons and transient Ce states in LaBr3 and LaBr3 :Ce

“…The first steps to synthesize an understanding of the recombination physics from these complementary experimental perspectives are discussed in the Conclusions section of this study. Rounding out the LaX 3 :Ce family, LaI 3 :Ce has been the subject of a few experimental and theoretical studies as well [19,20].…”