Magnetic circularly polarized emission and magnetic circular dichroism study of the 7FJ↔5D4 transitions in crystalline Cs2NaTbCl6

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Abstract
Absorption and magnetic circular dichroism (MCD) spectra are reported for the 7 F 6→5 D 4 transition of Tb3+ in crystalline Cs2NaTbCl6. These spectra are interpreted in terms of a crystal-field analysis of Tb3+ situated in an octahedral site with six Cl- nearest neighbours. The extensive, well-resolved vibrational structure in the absorption/MCD spectra is assigned, and these assignments (based on Γ point vibrational modes) are in agreement with previous assignments made for similar elpasolite-hexachloride systems. Total emission and magnetic circularly polarized emission (MCPE) spectra are also reported for the 7 F 6, 7 F 5, 7 F 4, and 7 F 3←5 D 4 transitions of Tb3+ in crystalline Cs2NaTbCl6. These spectra are interpreted in terms of a crystal-field analysis of Tb3+ ions located at octahedral sites in the crystal system. All crystal-field calculations were carried out using a six-parameter weak-field model, and an optimum fit of the spectroscopic observables was achieved with the following parameter set: ζ = 1840 cm-1, F 2 = 417 cm-1, F 4 = 57·60 cm-1, F 6 = 6·30 cm-1, A 4 = + 1900 cm-1, and A 6 = - 200 cm-1. In emission, a large number of magnetic-dipole transitions between (octahedral) crystal-field sub-levels of the various 7 F J (J = 6, 5, 4, and 3) and 5 D 4 states were observed and assigned. The transitions of ΔJ = odd free-ion parentage consisted entirely of pure magnetic-dipole lines with no appearance of vibronically induced electric-dipole components. On the other hand, transitions of ΔJ = even free-ion parentage exhibited both pure magnetic-dipole lines and vibronically induced electric-dipole components with extensive vibrational structure.