The lanthanide crystal field in cubic Cs₂NaLnCl₆elpasolites

Abstract

The octahedral lanthanide crystal field is calculated for trivalent lanthanide ions (Ln 3+) in the cubic C%NaLnC16 elpasolite structure. These calculations are based on a model which includes two types of Ln3 § interactions: multipole(Lna+)-point charge(ligand) and charge(Lna+)-induced dipole(ligand). The latter interaction mechanism involving ligand dipolar polarization is shown to make the dominant contributions (~ 80-85 per cent of the total) to the B0 t4) and B0 cG) octahedral crystal field coefficients. The calculated values of B0 o) are in good quantitative agreement with empirically determined values, while the calculated B0(6) values are found to be about 2-4 times too small in magnitude. The trends of both B0t4)(calc) and B0<6)(calc) across the lanthanide series are in excellent qualitative agreement with experiment. It is found that the six chloride ions in the first coordination sphere of a Ln 3+ ion contribute > 95 per cent of the calculated Bo C~l and B0 c6) values. The ligand parameters included in the crystal field model (charge, dipolar polarizability, and positional coordinates) are exactly the same as those used in the extant f-[ intensity models for the Cs2NaLnC16 elpasolite systems.

Optical absorption spectra and crystal field analysis of Er3+in the cubic Cs2NaErCl6system

“…Faulkner et al [11] These calculated results accurately reproduce the relative electric dipole versus magnetic dipole character observed for each transition region and they account for the especially strong electric dipole intensity seen in the 4115/2 ~2Hll/2 and 4Gu/2 transition regions. Converting these dipole strengths into intensity quantities and applying Boltzmann statistics to the relative populations of the 4115/2 crystal field levels, the 15 K absorption spectra are predicted to show the following ordering of integrated transition intensities : 4115/2-->4611/2 > 4113/2 > 2//11/~ > 4111/2 > 4F9/2 > $43/2 > 4F7/2 > 2G9/~ > 4F5/2 ,,~ 4F3/2.…”

“…The values of B0 ~4) and B0 ~6) determined in three of these studies [13,15,16] are listed in table 14 along with the values used in the present work. Also listed in table 14 are the values of B0 ~4) and/3o ~6) calculated on the basis of a purely theoretical model for the 4f electron crystal field in Cs2NaLnC1 ~ systems [11]. The parameter sets of [13] and [15] give crystal field energy level orderings identical to those listed in table 2 of the present paper.…”

“…The parameter sets of [13] and [15] give crystal field energy level orderings identical to those listed in table 2 of the present paper. The parameter sets of [11] and [16], however,…”

“…The broad objectives of the work presented here, as well as the experimental procedures and methods of theoretical analysis used, are similar to those described in our previous studies of CsaNaLnC16 systems [1][2][3][4][5][6][7][8][9][10][11]. Spectroscopic measurements were carried out on both pure C%NaErC16 and doped C%NaYC16 : Er 3+ (~ 12 mol per cent) samples over the temperature range 2-300 K. The spectra obtained for the pure and doped samples were found to be identical over the 2-300 K temperature range and all of the temperature-dependent intensity changes observed in the spectra could be accounted for (at least semiquantitatively) in terms of Boltzmann population statistics and/or line broadening (with increasing temperature).…”

“…In pursuit of the latter objective we have used a theoretical model which permits the direct calculation of both magnetic dipole strengths and vibronically-induced electric dipole strengths for the 4[--->4f transitions of the centrosymmetric (Oh point group symmetry) LnC16 z-chromophoric moieties in the cubic C%NaLnC16 systems [8,9]. We have also carried out direct calculations of the 4[ electron crystal field potentials in these systems using a model which admits both multipole (Ln3+)-point charge (ligand) and multipole (LnZ+)-induced dipole (ligand) interactions [10,11]. For each of the C%NaLnC16 systems investigated so far, detailed crystal field energy level and intensity calculations have proved to be essential to making complete assignments of the highresolution, variable temperature optical spectra features.…”