Ab initio calculations for absorption and emission energies of alkali halide crystals doped with thallium

Abstract

The design of new materials capable of yielding optimal performance to detect radiation calls for a deeper theoretical understanding of luminescent properties arising from substitutional defects in solids. Here, the authors calculate transition energies associated with optical properties of thallium doping in alkali halide crystals via an atomic cluster of minimal size where an sp-valence-shell impurity enters as a substitutional defect in the model crystal. Hartree-Fock (HF), density functional theory (DFT), and configuration interaction (CI) [CIS (CI with single excitation) and QCISD (single plus double and quadruple excitation)] calculations are performed to theoretically obtain the absorption and emission energies as vertical transitions evaluated at the ground and first excited-state optimized geometries, respectively, where the optimization is carried out separately with the HF and DFT methods.