Origin of resolution enhancement by co-doping of scintillators: Insight from electronic structure calculations

Åberg, Daniel; Sadigh, Babak; Schleife, André; Erhart, Paul

doi:10.1063/1.4880576

Cited by 36 publications

(32 citation statements)

References 40 publications

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“…Later, it was argued by the present authors that Sr-doping causes the creation of shallow electron trap complexes, which leads to reduced Auger quenching. 14 The present paper describes the argumentation in detail and presents a careful analysis of the thermodynamic properties and electronic structures of the most important intrinsic and extrinsic defects -including their complexes -in Ce and Sr-doped LaBr 3 including selftrapped polaronic configurations. To demonstrate that the present model is consistent with experimental observations, a comprehensive set of calculated absorption and emission energies for the relevant Ce complexes is carried out.…”

Section: -9mentioning

confidence: 99%

First-principles study of codoping in lanthanum bromide

et al. 2015

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Co-doping of Ce-doped LaBr3 with Ba, Ca, or Sr improves the energy resolution that can be achieved by radiation detectors based on these materials. Here, we present a mechanism that rationalizes of this enhancement that on the basis of first principles electronic structure calculations and point defect thermodynamics. It is shown that incorporation of Sr creates neutral VBr − SrLa complexes that can temporarily trap electrons. As a result, Auger quenching of free carriers is reduced, allowing for a more linear, albeit slower, scintillation light yield response. Experimental Stokes shifts can be related to different CeLa − SrLa − VBr triple complex configurations. Co-doping with other alkaline as well as alkaline earth metals is considered as well. Alkaline elements are found to have extremely small solubilities on the order of 0.1 ppm and below at 1000 K. Among the alkaline earth metals the lighter dopant atoms prefer interstitial-like positions and create strong scattering centers, which has a detrimental impact on carrier mobilities. Only the heavier alkaline earth elements (Ca, Sr, Ba) combine matching ionic radii with sufficiently high solubilities. This provides a rationale for the experimental finding that improved scintillator performance is exclusively achieved using Sr, Ca, or Ba. The present mechanism demonstrates that co-doping of wide gap materials can provide an efficient means for managing charge carrier populations under out-of-equilibrium conditions. In the present case dopants are introduced that manipulate not only the concentrations but the electronic properties of intrinsic defects without introducing additional gap levels. This leads to the availability of shallow electron traps that can temporarily localize charge carriers, effectively deactivating carrier-carrier recombination channels. The principles of this mechanism are therefore not specific to the material considered here but can be adapted for controlling charge carrier populations and recombination in other wide gap materials.

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Section: -9mentioning

confidence: 99%

First-principles study of codoping in lanthanum bromide

et al. 2015

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“…Consequently, the positions of the energy levels of the dopants calculated from first-principles methods can provide valuable guidance in the search for bright scintillators. Similar approaches can also be employed to investigate co-doping schemes that may lead to improved resolution [14][15][16]. In this work, this approach was applied to LaI 3 using density functional theory (DFT) with Hubbard corrections or hybrid exchange-correlation functionals, whereby the Hubbard on-site correction and the fraction of exact exchange were calibrated to experimental data on pure and Ce-doped LaI 3 and then employed to simulate a range of dopants previously untested.…”

Section: Introductionmentioning

confidence: 99%

First-principles search for efficient activators for LaI3

Prange

Gao

et al. 2016

Journal of Luminescence

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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.

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“…9 Lately, codoping of scintillators has also proven to be a successful route to improved scintillation properties. [10][11][12][13][14] Unfortunately, the complex physics underlying the energy resolution of scintillators presently is still only understood at a qualitative level. Better fundamental, quantitative insight is needed, to enable targeted materials design for scintillators.…”

Section: Introductionmentioning

confidence: 99%

“…Modern first-principles and theoretical spectroscopy techniques are clearly advanced enough to thoroughly study some of the mechanisms at play. While we and others started to apply these techniques to scintillator materials, 12,[23][24][25][26][27][28][29][30][31][32][33][34] in most cases, even basic quantities such as the dielectric function, optical absorption, or electronenergy loss function are still unknown. The influence of quasiparticle effects and excitons, for instance, is very well studied, e.g., for transparent conducting oxides, [35][36][37][38][39] but it is largely unknown for scintillator materials.…”

Section: Introductionmentioning

confidence: 99%

Excitons in scintillator materials: Optical properties and electron-energy loss spectra of NaI, LaBr₃, BaI₂, and SrI₂

Schleife

Zhang

et al. 2016

J. Mater. Res.

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Materials for scintillator radiation detectors need to fulfill a diverse set of requirements such as radiation hardness and highly specific response to incoming radiation, rendering them a target of current materials design efforts. Even though they are amenable to cutting-edge theoretical spectroscopy techniques, surprisingly many fundamental properties of scintillator materials are still unknown or not well explored. In this work, we use first-principles approaches to thoroughly study the optical properties of four scintillator materials: NaI, LaBr 3 , BaI 2 , and SrI 2 . By solving the Bethe-Salpeter equation for the optical polarization function we study the influence of excitonic effects on dielectric and electron-energy loss functions. This work sheds light into fundamental optical properties of these four scintillator materials and lays the ground-work for future work that is geared toward accurate modeling and computational materials design of advanced radiation detectors with unprecedented energy resolution.

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Origin of resolution enhancement by co-doping of scintillators: Insight from electronic structure calculations

Cited by 36 publications

References 40 publications

First-principles study of codoping in lanthanum bromide

First-principles study of codoping in lanthanum bromide

First-principles search for efficient activators for LaI3

Excitons in scintillator materials: Optical properties and electron-energy loss spectra of NaI, LaBr₃, BaI₂, and SrI₂

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Origin of resolution enhancement by co-doping of scintillators: Insight from electronic structure calculations

Cited by 36 publications

References 40 publications

First-principles study of codoping in lanthanum bromide

First-principles study of codoping in lanthanum bromide

First-principles search for efficient activators for LaI3

Excitons in scintillator materials: Optical properties and electron-energy loss spectra of NaI, LaBr3, BaI2, and SrI2

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Excitons in scintillator materials: Optical properties and electron-energy loss spectra of NaI, LaBr₃, BaI₂, and SrI₂