Polarised selective excitation and magnetic circular dichroism of hexavalent uranium in LiF and NaF

Crystals of LiF and NaF doped with uranium and grown in oxygen contain centres with strong fluorescent lines at 527.8 nm and 563.6 nm respectively. The spectroscopic properties of these tetragonal centres have been studied at liquid helium temperature using polarised selective excitation and magnetic circular dichroism techniques. This has enabled the degeneracy of levels to be determined and the phonon coupling from localised vibrations to be described. An E electronic level has been found in each case fairly close in energy to the fluorescent level. The g-values for these E levels and several others in the higher-energy region have been measured.