A5007662208- Luminescence Properties of Advanced Materials
- Radiation Detection and Scintillator Technologies
- Advanced Chemical Physics Studies
- Advanced Semiconductor Detectors and Materials
- Atomic and Molecular Physics
- Magnetic and transport properties of perovskites and related materials
- Electronic and Structural Properties of Oxides
- Atomic and Subatomic Physics Research
- Magnetic Properties of Alloys
- High-pressure geophysics and materials
- Rare-earth and actinide compounds
- Machine Learning in Materials Science
- Semiconductor materials and devices
- Laser-induced spectroscopy and plasma
- Boron and Carbon Nanomaterials Research
- Semiconductor Quantum Structures and Devices
- Metal and Thin Film Mechanics
- Inorganic Chemistry and Materials
- Glass properties and applications
- Semiconductor materials and interfaces
- Magnetic properties of thin films
- Inorganic Fluorides and Related Compounds
- Quantum and electron transport phenomena
- Advanced Condensed Matter Physics
- Advancements in Semiconductor Devices and Circuit Design
Lawrence Livermore National Laboratory
2016-2025
Alstom (Sweden)
2024
Chalmers University of Technology
2017
Mid Sweden University
2001-2006
Uppsala University
2000-2004
We investigate the formation of self-trapped holes (STH) in three prototypical perovskites (SrTiO3, BaTiO3, PbTiO3) using a combination density functional theory (DFT) calculations with local potentials and hybrid functionals. First we construct correction potential for polaronic configurations SrTiO3 that is applied via DFT+U method matches forces from calculations. then use to search configuration space locate lowest energy STH configuration. It demonstrated both yield piece-wise linear...
We apply the compressive sensing lattice dynamics (CSLD) method to calculate phonon dispersion for crystalline solids. While existing methods such as frozen phonon, small displacement, and linear response are routinely applied calculations, they considerable more expensive or cumbersome certain solids, including structures with large unit cells low symmetry, systems that require electronic structure treatment, polar semiconductors/insulators. In latter case, we propose an approach based on a...
Microstructural evolution is a key aspect of understanding and exploiting the processing-structure-property relationship materials. Modeling microstructure usually relies on coarse-grained simulations with principles described by partial differential equations (PDEs). Here we demonstrate that convolutional recurrent neural networks can learn underlying physical rules replace PDE-based in prediction phenomena. Neural nets are trained self-supervised learning image sequences from several...
Opacity model differences with Fe opacity measurements at high temperature (T>180 eV) and electron density (n_{e}>3×10^{22} cm^{-3}) nearly solar interior conditions have remained unresolved [Bailey et al., Nature 517, 56 (2015)10.1038/nature14048 Nagayama Phys. Rev. Lett. 122, 235001 (2019)PRLTAO0031-900710.1103/PhysRevLett.122.235001]. Systematic errors from temporal gradients are one hypothesis for the discrepancy. Past data recorded on x-ray film provided spectral over a time determined...
A broad visible luminescence band and characteristic IR of Yb3+ ions are observed under UV excitation in ytterbium-doped aluminosilicate glass. Samples made both oxidizing reducing conditions analyzed. strong charge-transfer absorption the range is for glass samples containing ytterbium. Additional bands sample conditions, which associated with f-d transitions divalent The attributed to 5d-4f emission from Yb2+ ions, concluded originate a relaxed transition. findings important explain...
We present density-functional theory calculations of the optical absorption spectra silica glass for temperatures up to 2400 K. The calculated exhibit exponential tails near fundamental edge that follow Urbach rule in good agreement with experiments. discuss accuracy our results by comparing hybrid exchange correlation functionals. show holds a frequency interval where is Poisson distributed very large statistical fluctuations. In this regime, direct relation between coefficient and...
Luminescence quenching via nonradiative recombination channels limits the efficiency of optical materials such as phosphors and scintillators therefore has implications for conversion device lifetimes. In Ce-doped yttrium aluminum garnet (YAG:Ce), shows strong dependence on both temperature activator concentration, limiting fabrication high-intensity white-light emitting diodes with high operating temperatures. Here, we reveal by means first-principles calculations an efficient mechanism in...
Using first-principles theory, we have calculated the energy of Gd as a function spin direction, theta, between c and axes found good agreement with experiment for both total magnetic anisotropy its angular dependence. The low temperature direction moment lies at an angle 20 degrees to axis. metal is due unique mechanism involving contribution 7.5 microeV from classical dipole-dipole interaction spins plus 16 spin-orbit conduction electrons. 4f polarizes electrons via exchange interaction,...
The thermodynamic stabilities of various phases the nitrides platinum-metal elements are systematically studied using density functional theory. It is shown that for Rh, Pd, Ir, and Pt two new crystal structures, in which metal ions occupy simple tetragonal lattice sites, have lower formation enthalpies at ambient conditions than any previously proposed structures. region stability with respect to those structures extends 17 GPa ${\mathrm{PtN}}_{2}$. Calculations show ${\mathrm{PtN}}_{2}$...
A first-principles framework for calculating the rates of charge carrier scattering by defects in semiconductors is presented. First a quantitative formalism outlined, followed development an approximate relative that allows rapid assessment effects different on transport given materials. Representative results are presented demonstrate applicability formalism, which achieves three to four orders magnitude reduction computational cost compared full calculation. The differences between two...
We conduct a detailed investigation of the polaron self-interaction (pSI) error in standard approximations to exchange-correlation (XC) functional within density-functional theory (DFT). The pSI leads delocalization wave function and energy, as calculated from Kohn-Sham (KS) potential native charge state polaron. This constitutes origin systematic failure DFT describe formation band insulators. It is shown that these systems is, however, largely absent KS closed-shell neutral state....
We propose a new efficient permanent magnet, SmCoNiFe3, that is breakthrough development of the well-known SmCo5 prototype. More modern neodymium magnets Nd-Fe-B type have an advantage over because their greater maximum energy products due to iron-rich stoichiometry. Our however, removes most this disadvantage while preserving its superior high-temperature efficiency magnets.
We propose approximate and accurate formulas for the number of electron configurations in hot plasmas. Such a quantity is an ingredient algorithms devoted to generation or superconfigurations, which pre-requisite opacity calculations. One main involves Bessel functions fractional order procedure improving accuracy through series expansion explained.
A method is presented for the improved calculation of super-shell partition functions which include repulsive electron-electron interaction energy terms in Boltzmann factor. Heretofore these were approximately treated via use Feynman-Jensen inequalities. Such investigations are particular interest super-transition-array approach hot-plasma radiative opacity.
Calculations within density functional theory on the basis of local approximation are carried out to study properties intrinsic point defects in aluminum antimonide. Special care is taken address finite-size effects, band gap error, and symmetry reduction defect structures. The correction based a set $GW$ calculations. most important identified be interstitial ${\mathrm{Al}}_{i,\mathrm{Al}}^{1+}$, antimony antisites ${\mathrm{Sb}}_{\mathrm{Al}}^{0}$ ${\mathrm{Sb}}_{\mathrm{Al}}^{1+}$,...
Co-doping of Ce-doped LaBr$_3$ 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 rationalizes this enhancement basis first principles electronic structure calculations and point defect thermodynamics. It is shown incorporation creates neutral $V_\text{Br}$-Sr$_\text{La}$ complexes temporarily trap electrons. As result, Auger quenching free carriers reduced, allowing for more linear, albeit...
We investigate the basic quantum-mechanical processes behind nonproportional response of scintillators to incident radiation responsible for reduced resolution. For this purpose, we conduct a comparative first-principles study quasiparticle spectra on basis ${G}_{0}{W}_{0}$ approximation as well absorption and excitonic properties by solving Bethe-Salpeter equation two important systems, NaI ${\mathrm{SrI}}_{2}$. The former is standard scintillator material with well-documented...
Rare-earth based scintillators in general and lanthanum bromide (LaBr_3) particular represent a challenging class of materials due to pronounced spin-orbit coupling subtle interactions between d f states that cannot be reproduced by standard density functional theory (DFT). Here detailed investigation the electronic band structure LaBr_3 using quasi-particle self-consistent GW (QPscGW) method is presented. This parameter-free approach shown yield an excellent description LaBr_3. Specifically...
It was recently shown that the energy resolution of Ce-doped LaBr3 scintillator radiation detectors can be crucially improved by co-doping with Sr, Ca, or Ba. Here, we outline a mechanism for this enhancement on basis electronic structure calculations. We show (i) Br vacancies are primary electron traps during initial stage thermalization hot carriers, prior to hole capture Ce dopants; (ii) isolated associated deep levels; (iii) Sr doping increases vacancy concentration several orders...