Refined analysis of the luminescent centers in the Yb3+:CaF2 laser crystal

A detailed spectroscopic study of various Yb3+:CaF2 crystals with dopant concentrations ranging from 0.03 to 2 at% Yb3+ has been performed. By using site-selective laser excitation, the low-temperature (7 K) excitation and emission spectra recorded in the case of the lower doped samples (0.03% and 0.05%) are found to be dominated by three types of sites with excited state fluorescence lifetimes of about 2, 8 and 10 ms. Confronted with crystal field calculations, these sites have been identified as Yb3+ ions in trigonal (C3v), tetragonal (C4v) and cubic environments, respectively. At higher dopant concentrations (>0.1 at%), evidence is found of a third kind of site, whose contribution increases up to be dominant as dopant concentration is increased above about 1 at%Yb3+ and which gives rise to the lasing center which has been recently discovered and operated.