Optical spectra and crystal field analysis of Nd3+ in the cubic Cs2NaYCl6 host

Abstract

Optical absorption and emission measurements are reported for the Cs2NaYCl6:Nd3+ (∼5 mol %) system under variable-temperature (4.2–296 K) conditions. The absorption measurements span the 12 000–24 000 cm−1 spectral region, and emission spectra are presented throughout the 13 300–18 860 cm−1 region. All the spectra are consistent with the retention of octahedral (Oh) site symmetry for the Nd3+ ions down to 4.2 K. Thirty-four crystal-field levels spanning 14 multiplets of the Nd3+ 4f3 electronic configuration are located and assigned on the basis of the experimental data. The most intense lines observed in each of the multiplet-to-multiplet transition regions are assigned to one-phonon (electric-dipole) vibronic transitions associated with the three odd-parity moiety modes of the NdCl3−6 cluster, ν3(tlu), ν4(tlu), and ν6(t2u). The ν3 lines generally appear as doublets (split by ∼10–15 cm−1) and are displaced from magnetic-dipole origins by ∼245–260 cm−1; the ν4 lines are displaced from origins by ∼100 cm−1, and are generally sharp and symmetric; and the ν6 lines are generally asymmetric in shape (or appear as doublets split by ∼2–6 cm−1), and are displaced from origins by 70–75 cm−1. Additional vibronic lines are observed persistently at displacement energies of ∼40–45 and ∼55–60 cm−1, but these lines are considerably less intense than those assigned to the ν3, ν4, and ν6 moiety-mode vibrations. The energy level data obtained from experiment is rationalized in terms of a 9-parameter model which includes the radial spin-orbit interaction parameter (ζso), the Slater–Condon one-particle electrostatic interaction parameters (F2, F4, and F6), the two-particle electrostatic configuration-interaction parameters (α, β, and γ), and the octahedral (Oh) crystal-field interaction parameters (B(4)0 and B(6)0). The values deduced for the crystal-field parameters are B(4)0 =2400 cm−1 and B(6)0 =−330 cm−1 (expressed with unit-tensor normalization).