Optical Spectra of the Yb(III) Ions in Molten Alkaline Metal Fluorides

The optical spectra of the molten systems MF–YbF 3 (M = Li, Na, K, and Cs) are presented. The spectral data show that complex groups form in these melts. The group is found in the LiF–YbF 3 melt. This group forms due to the partially reductive atmosphere in a furnace combined with an optical cell. The sharp jump of the wavenumber of the electronic transition 2 F 7/2 → Γ 8 2 F 5/2 of the Yb(III) ion on going from the LiF and NaF melts to the KF and CsF melts is assumed to be caused by a decrease in the coordination number from 14 to 13.