Lattice Distortions Around a Tl+ Impurity in NaI:Tl+ and CsI:Tl+ Scintillators. An Ab Initio Study Involving Large Active Clusters

TL;DR

This study uses large-scale ab initio calculations to analyze lattice distortions around Tl+ impurities in NaI and CsI scintillators, revealing complex relaxation patterns and confirming the importance of self-consistent ion responses for accurate absorption energy predictions.

Contribution

It introduces a comprehensive ab initio cluster model with large active clusters to accurately simulate impurity-induced lattice distortions in scintillators.

Findings

Lattice relaxation involves multiple neighbor shells moving concertedly.

Self-consistent wave function adaptation of ions is crucial for accurate modeling.

Calculated absorption energies match well with experimental data.

Abstract

Ab initio Perturbed Ion cluster-in-the-lattice calculations of the impurity centers NaI:Tl+ and CsI:Tl+ are pressented. We study several active clusters of increasing complexity and show that the lattice relaxation around the Tl+ impurity implies the concerted movement of several shells of neighbors. The results also reveal the importance of considering a set of ions that can respond to the geometrical displacements of the inner shells by adapting selfconsistently their wave functions. Comparison with other calculations involving comparatively small active clusters serves to assert the significance of our conclusions. Contact with experiment is made by calculating absorption energies. These are in excellent agreement with the experimental data for the most realistic active clusters considered.