ANALYSIS OF SPECTRAL DATA AND COMPARATIVE ENERGY-LEVEL PARAMETRIZATIONS FOR LN(3+) IN CUBIC ELPASOLITE CRYSTALS

Comparative analyses have been made of the 4f(n) lanthanide ion (Ln(3)) energy level structures in a variety of cubic elpasolite crystals. The systems can be grouped into two sets, namely (i) Ln(3+) in the nea t compounds: Cs(2)NaLnCl(6), (Ln=Ce-Yb, except for Nd, Pm and Sm), Cs2 LiErCl2, Cs(2)NaLnBr(6) (Ln=Pr, Ho, Tm), Cs2KPrF6 and Rb2NaEuF6; and ( ii) Ln(3+) diluted into elpasolite host crystals: Cs2NaYCl6:Ln(3+) (Ln =Pr, Sm, Eu), Cs2NaGdCl6:Ln(3+) (Ln=Ho, Nd) and Cs2KYF6:Eu3+. New ener gy level data obtained from low temperature absorption, emission and e lectronic Raman studies are presented for these systems to provide mor e accurate and extensive data sets. The new energy level data were ana lysed in terms of a 4f(n) ''free-ion'' Hamiltonian and a parametric cr ystal held Hamiltonian model, with octahedral (O-h) site symmetry for the Ln(3+) ion. The empirical energy level data were fitted to the par ametrized total Hamiltonian and the resulting ''best-fit'' parameter s ets are presented and discussed. Examination of the parameter values o btained from least-squares fittings reveals significant differences in the crystal field perturbations experienced by the 4f electrons of Ln (3+) at octahedral sites: the fluoride ligands interact with the 4f el ectrons somewhat more strongly than do the bromide ligands. The phenom enological (fitted) crystal field parameters of Cs(2)NaLnCl(6) do not exhibit a clear trend across the series of lanthanide elements, partly because of the uncertainty in determination due to the term dependenc e. The magnitude of the B-0(k) (k = 4,6) parameters follow different p atterns in the LaCl3:Ln(3+), LaF3:Ln(3+) and LiYF4:Ln(3+) systems. How ever, the magnitudes of the ''free-ion'' parameters resulting from fre e variation in the elpasolite system data fits exhibit clearer trends and the spin-orbit coupling constant is found to fit well to a second- order polynomial in atomic number. The standard deviations of the data fits as defined herein are between 0 and 43 cm(-1), so that the energ y level schemes of the Ln(3+) ions in elpasolite lattices are reasonab ly well reproduced.