This study present the formation of complex fluoride compounds in binary sy
stems of alkali fluorides (AlkF; Alk=Li, Na, K, Cs, Rb) with trifluorides o
f lanthanides (LnF(3); Ln=La, CE, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, T
m, Yb, Lu). The complex stoichiometry is related to the cation sizes and to
the cation radius ratio.