Modeling the crystal-field splitting of energy levels of Er3+(4f11) in charge-compensated sites of KPb2Cl5

Abstract

A point-charge lattice-sum model corrected for induced multipoles is used to investigate the crystal-field splitting of the LJ2S+1 energy levels of Er3+(4f11) ions that occupy charge-compensated sites in the laser host crystal KPb2Cl5. Spectroscopic data are reported and analyzed for Er3+ between 1550 and 440nm at cryogenic temperatures. The crystal-field (Stark) splitting of the ground-state manifold I15∕24 and the splitting of individual excited manifolds of Er3+ are established from analyses of temperature-dependent (hot band) absorption spectra. The analyses confirm the Stark splitting of the IJ4 and F9∕24 manifolds that are reported in the literature. From an analysis of the data, it appears that only one of the two possible Pb2+ sites serving as a charge-compensated site for Er3+ is involved in the optical activity of the Er3+ ions. From an examination of the crystallographic data of KPb2Cl5, we identify a possible site for the optically active Er3+ ion in the lattice and calculate the lattice-sum components for that site. These components are used to evaluate the crystal-field splitting of the energy levels of Er3+ at that site. The charge-compensation model assumes that Er3+ substitutes for Pb2+ in the Pb(2) site with a vacancy in a nearby K+ site. To obtain the best overall agreement between calculated and experimental levels, the position of the Er3+ ion is treated as an adjustable parameter along the quantization axis. Individual manifold centroids of the Er3+ ion are also varied. From a least-squares fitting analysis, we obtain a rms deviation of 10cm−1 between 48 calculated-to-observed Stark levels.