The present work demonstrates the optimization of the ligand structure in the series of bis-phosphine oxide and carbamoylphosphine oxide representatives for efficient coordination of Tb3+ and Eu3+ ions with the formation of the complexes exhibiting high Tb3+- and Eu3+-centered luminescence. The analysis of the stoichiometry and structure of the lanthanide complexes obtained by XRD method reveals the great impact of the bridging group nature between two phosphine oxide moieties on the coordination mode of the ligands with Tb3+ and Eu3+ ions. The bridging imido-group facilitates the deprotonation of imido-bisphosphine oxide ligand followed by the formation of tris-complexes. The spectral and PXRD analysis of the separated colloids indicates that the high stability of the tris-complexes provides their safe conversion into polystyrenesulfonate-stabilized colloids under the solvent exchange method. The red Eu3+-centered luminescence of the tris-complex exhibits the same specificity in the solutions and the colloids. The pronounced luminescent response on the antibiotics ceftriaxone allows to sense the latter in aqueous solutions with the LOD value equal to 0.974 M.