Refining spectroscopic calculations for trivalent lanthanide ions: a revised parametric Hamiltonian and open-source solution

Abstract: The historical calculation of spectroscopic properties for trivalent lanthanide ions is a complex multistep process that has been prone to inaccuracies. In this work, we revise the parametric semi-empirical Hamiltonian and address long-standing discrepancies in the literature. We also resurface the distinctions between orthogonal and non-orthogonal operators and use orthogonal operators to provide an alternative parametric description. Based on experimental data available in the literature, a new set of parameter values for the ions in LaF$_3$ and LiYF$_4$ is presented. Additionally, we provide calculations of spontaneous emission rates and oscillator strengths for magnetic dipole transitions in the LaF$_3$ crystal host. To ensure the replicability of our findings, we make available the open-source code $\mathbf{\texttt{qlanth}}$, accompanied by a comprehensive set of electronic files to serve as an updated reference for future calculations.