Assignment and vibronic analysis of the 5D0 → 7F2 transition of Eu3+ in hexanitritolanthanate systems

The versatile NO 2 - ligand is a chelating, bidentate ligand in the high symmetry M2M′Eu(NO2)6 (M = Cs, Rb; M′ = Na, Li) systems. The investigation of the vibronic structure and energy levels of these systems is of interest for comparison with the abundant data from Cs2NaEuX6 (X = F, Cl) crystals. The vibrational structure in the electronic emission spectra of the hexanitritolanthanates has been investigated from the analysis of the 10 K and 100 K spectra. Most of the vibronic intensity of the 5D0 → 7F0, 7F2 transitions is due to low energy skeletal modes which correlate with τu (Th) infrared vibrations. The energy levels derived from the vibronic analysis indicate a weak crystal field in these systems.