Luminescence of Heavily Ce-Doped Alkaline-Earth Fluorides

Luminescent and structural properties of M_1-xCe_xF_2+x (M=Ca, Sr, Ba, 0.15<x<0.35) single crystals were studied. It was found that the solid solutions have fluorite crystal structure with the lattice constant noticeably different from that of MF₂ crystal. A partial deficiency in the fluorine positions as well as excessive fluorine in interstitial sites was revealed. Crystal lattice modification does not strongly affect the basic absorption and emission properties as compared with weakly Ce-doped MF₂. The spectral-kinetic parameters of solid solutions luminescence are similar to those of Ce³⁺ ion in perturbed site in CeF₃ lattice. Low light yield of mixed compounds is connected with the small Stokes shift and reabsorption. The probable model of perturbed Ce³⁺ center in M_1-xCe_xF_2+x crystals assumes the presence of interstitial fluorine in the nearest or next nearest neighborhood of the cerium ion.