Infrared reflectivity and Raman spectra of (BaF 2 ) 1 - x (LaF 3 ) x (0.01=<x=<0.47) single crystals are reported. Vibrational modes due to doping have been observed; a number of them can be interpreted as non-centre zone modes activated by loss of translational symmetry. Others are attributed to changes of local structure around clusters of dopant ions, which give rise to modes inherent to LaF 3 . Evolution of infrared spectra with doping rate x is discussed in terms of a percolation model.