Effective-Hamiltonian parameters for \emph{ab initio} energy-level calculations of SrCl$_{2}$:Yb$^{2+}$ and CsCaBr$_{3}$:Yb$^{2+}$

TL;DR

This paper derives semi-empirical parameters for a crystal-field Hamiltonian to accurately model the energy levels of Yb$^{2+}$ doped in SrCl$_{2}$ and CsCaBr$_{3}$, based on ab initio calculations.

Contribution

It introduces a method to fit ab initio energy levels with a semi-empirical Hamiltonian, providing parameters that match experimental and atomic data.

Findings

Parameters fit well with experimental data

States with 4f13 6s character approximate impurity-trapped excitons

Range of parameters obtained for different anion-cation separations

Abstract

Calculated energy levels from recent \emph{ab initio} studies of the electronic structure of SrCl$_{2}$:Yb$^{2+}$ and CsCaBr$_{3}$:Yb$^{2+}$ are fitted with a semi-empirical "crystal-field" Hamiltonian, which acts within the model space $4f^{14} + 4f^{13}5d + 4f^{13}6s$. Parameters are obtained for the minima of the potential-energy curves for each energy level and also for a range of anion-cation separations. The parameters are compared with published results parameters fitted to experimental data and to atomic calculations. The states with significant $4f^{13}6s$ character give a good approximation of the impurity-trapped exciton states that appear in the \emph{ab initio} calculations.