Quantum chemical study of 4f→5d excitations of trivalent lanthanide ions doped in the cubic elpasolite Cs2NaYCl6. Ce3+ to Tb3+

Abstract

Wave-function-based ab initio calculations on the lowest states of the 4f n ,4f n−1 5d͑t 2g ͒ 1 , and 4f n−1 5d͑e g ͒ 1 configurations of ͑LnCl 6 ͒ 3− clusters ͑Ln= Ce to Tb͒ embedded in the cubic elpasolite Cs 2 NaYCl 6 have been performed, in an attempt to contribute to a comprehensive understanding of the 4f → 5d excitations of lanthanide ions in crystals. Reliable data are provided on the changes of bond lengths and breathing mode vibrational frequencies upon 4f → 5d͑t 2g ͒ and 4f → 5d͑e g ͒ excitations, as well as on minimum-to-minimum and vertical absorption and emission transitions, and on the Stokes shifts. The available experimental data are discussed and predictions are made. The stabilization of the 4f → 5d͑baricenter͒ excitation of the doped ions with respect to the 4f → 5d excitations of the free ions, which is a key variable for the understanding of these excitations in solid hosts, is analyzed and found to be due, in two-thirds, to dynamic ligand correlation effects and, in one-third, to orbital relaxation, charge transfer, and covalency effects present in a mean-field approximation.

Spectroscopy of High‐Energy States of Lanthanide Ions

“…This has many shortcomings, as discussed in Refs. [21,22,23]. However, our purpose here is to illustrate the method, and this code is quite suitable for that.…”

“…The ab-initio calculations by Seijo and co-workers [21,22,23] have challenged some common assumptions. It is often assumed that the bond lengths always increase when a lanthanide ion is excited from 4f N to 4f N −1 5d.…”

“…First-principles (ab-initio) calculations of the electronic structure of the 4f N and 4f N −1 5d configurations of lanthanide ions in solids are now becoming common [21,24,20,25]. Ishii, Ogasawara and co-workers [40,41,42,20,43] have applied the DV-Xα method for ions across the entire lanthanide series.…”

“…Seijo and co-workers [21,22,23] have concentrated on a smaller number of systems and have used a sophisticated quantum-mechanical embedding scheme to calculate realistic excited-state geometries and potential-energy surfaces.…”

“…It is now possible to make reasonably accurate ab-initio calculations for the 4f N and 4f N −1 5d configurations of lanthanide ions in crystals [20,21,22,23,24,25]. This raises the possibility of determining crystal-field and other parameters from such calculations.…”