  The emission spectra of Ce$^{3+}$ or Pr$^{3+}$ doped CaF$_2$, SrF$_2$,
BaF$_2$ excited by vacuum ultraviolet photons or by x-ray as well as excitation
and absorption spectra in vacuum ultraviolet region (6-13 eV) were studied. The
transfer of exciton energy is the main channel for Ce$^{3+}$ excitation in
alkaline-earth fluorides. Three different stages of energy transfer were
observed. Pr$^{3+}$ excited by two processes, slow f-f luminescence excited by
excitons, fast d-f luminescence excited by some fast process.
