The interaction of trivalent europium and terbium ions with arachidic acid monolayers is reported. The ions are incorporated into the monolayer from the subphase solution, increasing the minimum area per molecule and modifying the pressure-area isotherms. Europium and terbium arachidate bonding in multilayer films transferred to solid supports is evidenced by FTIR and photophysical measurements. The luminescent films are 'Y' type structures, as shown by the X-ray diffraction patterns.