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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.

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Optical absorption and emission spectra are reported for the cubic Cs2NaHoCl6 elpasolite system. Detailed energy and intensity analyses of the high-resolution, variable-temperature spectra allow characterization of the crystal field energy level structure associated with eleven of the Ho3+ term levels. The term levels included in these analyses are 5I8, 5I7, 5F5, 5F4, 5S2, 5F3, 5F2, 3K8, 5G6, 5G5, and 3K7. Intensity calculations are reported for both the pure magnetic dipole transitions and the vibronically induced electric dipole transitions associated with the ν3(t1u), ν4(t1u), and ν6(t2u) vibrational modes of the octahedral (Oh) HoCl63− chromophoric moiety of the Cs2NaHoCl6 system. The electric dipole intensity model used in these calculations includes contributions from both the static-coupling and dynamic-coupling Ho3+-ligand interaction mechanisms. Excellent agreement between observed and calculated intensities is found, and the theoretically calculated intensity results proved crucial to our detailed analysis and assignment of the observed spectra.

Unpolarized and magnetic-field-induced circularly polarized luminescence spectra are reported for Eu3+ doped into the cubic Cs2NaYCl6 host. These spectra were obtained at high resolution under variable temperature conditions, and they span the 5DJ(J = 0–3)→7FJ(J = 0–5) transition regions of Eu3+. A detailed analysis of the spectra leads to a nearly complete location and assignment of the crystal field levels split out of the 7FJ(J = 0–5) and 5DJ(J = 0–3) term levels of Eu3+. Essential to the spectral analysis are crystal field energy level calculations and intensity calculations for both the magnetic dipole origin transitions and the electric dipole (one-phonon) vibronic transitions. The dominant contributions to the vibronic structure in the spectra are assigned to vibronically induced electric dipole transitions which involve coupling between the 4f electrons and the three ungerade vibrational modes localized within the EuCl3−6 chromophoric moiety. Lesser contributions are made by vibronic transitions involving vibrational modes not localized within the EuCl3−6 cluster (e.g., low-frequency lattice modes). Excellent agreement between theory and experiment is achieved for the luminescence intensities and the magnetic-field-induced circularly polarized luminescence spectra associated with the magnetic dipole allowed origin transitions. Very good agreement is also achieved between the calculated and observed vibronic intensity spectra. The latter were calculated using a theoretical model for vibronically induced electric dipole transition intensities which includes contributions from both the static-coupling and dynamic-coupling Eu3+-ligand interaction mechanisms.