Abstract
We present ab initio calculations of electron capture and release coefficients as a function of temperature for Tl dopants in the widely used scintillator NaI, which is a soft ionic crystal. The modeled capture and release events occur by transitions mediated by multiple phonon absorption and emission between states with significantly different local geometries around the trapping site. We demonstrate that such transitions are not well-described by the normal harmonic approximation to the nuclear dynamics. We go beyond the harmonic approximation by numerically solving the vibrational Schrödinger equation for the motion along/of a single effective phonon coordinate. The localized trapped state is not correctly described by semilocal density functionals, so we employ a global hybrid functional tuned to reproduce the band gap and lattice constant of the host material. Our calculations, which combine plane-wave and embedded cluster electronic structure methods are in reasonable agreement with available experimental data for detrapping and predict an unusual temperature dependence for trapping rates.
1 More- Received 11 July 2019
- Revised 21 October 2019
DOI:https://doi.org/10.1103/PhysRevB.101.024304
©2020 American Physical Society