Quantum chemical study of the lanthanide bond length contraction on Ln3+-doped Cs2NaYCl6 crystals (Ln=Ce to Lu)

Abstract

The lanthanide-chlorine bond length, R e , and the frequency of the symmetric stretching mode, ¯a 1g , of the (LnCl 6 ) 3Ϫ octahedral defect clusters embedded in Cs 2 NaYCl 6 have been calculated for all 14 Ce 3ϩ to Lu 3ϩ impurities in their ground 4 f n electronic state using wave-function-based ab initio methods of solid state quantum chemistry which include relativistic effects and electron correlation within the (LnCl 6 ) 3Ϫ defect clusters and quantum mechanical interactions between the (LnCl 6 ) 3Ϫ electronic group and the Cs 2 NaYCl 6 embedding host ions. The bond distance values obtained provide useful data to improve the Judd-Morrison model of the 4 f →5d energy separation by explicitly including the local distortions the Ln 3ϩ ions produce in the Cs 2 NaYCl 6 host. The values of the structural parameters R e and ¯a 1g , and their variation across the series have also been studied using simpler models of the embedding host ͑in vacuo and Madelung embeddings͒, which has revealed that host effects, particularly those associated with quantum mechanical interactions, strengthen the Ln-Cl bond ͑decreasing the bond distances and increasing the frequencies of the symmetric bond stretch͒ and are smaller towards the right end of the series. Electron correlation within the (LnCl 6 ) 3Ϫ clusters also reduces the bond distance values, but this reduction increases going right from Ce to Lu; its effects on the frequencies of the symmetric stretching mode are negligible. The comparison of the theoretical results with the few available experiments is very satisfactory.

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

“…We calculated bond lengths, breathing mode vibrational frequencies, minimumto-minimum energy differences, and vertical energy differences ͑including Stokes shifts͒. The results, which are an extension of a previous study on the ground states and lanthanide contraction of the same materials, 12 show the variation across the lanthanide series of the bond-length shortening upon 4f → 5d͑t 2g ͒ excitation and bond-length enlargement upon 4f → 5d͑e g ͒ excitation, the high-spin/lowspin energy differences, and the lowest 4f → 5d͑t 2g ͒ and 4f → 5d͑e g ͒ transition energies. We also present the lowest spin-allowed and spin-forbidden 4f → 5d transitions of the Ln 3+ free ions, which are a necessary reference for discussion.…”

“…[8][9][10][11][12][13] In addition to having given interpretations of spectroscopic measurements in solid hosts doped with lanthanide and actinide ions, 8,[14][15][16] and of energy-transfer mechanisms, 15 ab initio calculations have predicted the distance between f-element ions and their first coordination shell to shorten in the lowest 4f → 5d and 5f → 6d excitations of Ce 3+ ,Pr 3+ ,Pa 4+ ,U 3+ , and U 4+ in sixfold chloride octahedral coordination 8,[14][15][16] and of Ce 3+ in eightfold fluoride cubic coordination. 17 This behavior, which contradicted the widespread assumption that bond length increases upon 4f → 5d and 5f → 6d excitations, has been found to be present in fluorides, chlorides, and bromides of Ce 3+ in solid and liquid solutions.…”

Application of the density functional theory derived orbital-free embedding potential to calculate the splitting energies of lanthanide cations in chloroelpasolite crystals

“…To estimate the magnitude of the possible effect of the geometry, the ligand-field parameters were recalculated using the sum-of-ionic-radii geometries instead of ab initio optimized geometries [21]. The change of the geometry does not affect significantly our results.…”

“…1 represents the investigated system comprising an octahedral arrangement of the lanthanide cation and its ligands (O h symmetry). The lanthanide-ligand distances derived from ab initio (CASSCF or CASPT2) cluster calculations [21] were used.…”

Theoretical study of the effects of F to Cl chemical substitution on the electronic structure and the luminescence properties of Cs2GeF6:Os4+ and Cs2ZrCl6:Os4+ materials

“…This procedure has been successfully applied to transition-metal 34 and f-element impurities. 30,[35][36][37] We will start by describing the spin-free calculations. First, we have performed complete active space selfconsistent field 38 40,41 The CASSCF wave functions were used as a multidimensional zeroth order wave function for the perturbation treatment.…”