Fine structure of 4f–5d absorption spectra of MeF2-Yb³⁺ in the vacuum ultraviolet region under synchrotron excitation

Narrow dips were found in the excitation spectra of crystals of alkaline earth fluorides doped with ErF₃ or/and YbF₃. The positions of the dips are in good agreement with the positions of the narrow absorption lines Er³⁺, Yb³⁺ measured earlier. The absorption lines of the crystals were calculated from the excitation spectra. The observed dips in the excitation spectra are due to the absorption lines of 4f–5d transitions in lanthanide ions.