Spectra and energy levels of Yb3+ ions in CaF2 transparent ceramics

Using the calculated Stark energy levels, the majority of the emission lines is attributed to the cubic (Oh), tetragonal (C4v) and trigonal (C3v) site symmetries of Yb3+ in CaF2 ceramics, which are the dominant luminescent centers at low ytterbium concentrations (0.5 at%). For higher dopant concentrations, above the 2.5 at%, these emission lines are related only for one dominant class of Yb3+ centers which corresponds to some hexameric clusters (Yb6F36 and Yb6F37).