Complexes of rare earths and dipicolinato ions encapsulated in X- and Y-zeolites: Luminescence properties

The complexes {Ln(DP)}Z where Ln(3+) = La3+ or Eu3+, DP is the dipicolinate ion (2,6)-pyridine dicarboxylate: C5H3N(COO-)(2) and Z = one of the faujas ite-type X or Y zeolites have been synthesized and investigated by XRD, Ram an and IR spectroscopy, and Eu3+ luminescence spectroscopy. The rare earth complexes are synthesized inside the super-cages of the zeolites; the degre e of complexation never exceeds 1DP/1Ln. Only the Ln ions, which are in the super-cages, may be complexed. Luminescent europium complexes encapsulated in zeolite matrices were obtained. The D-5(0) --> F-J luminescence observe d under excitation into the lowest-energy ligand-centered absorption band ( 275 nm) indicates that a DP to Eu energy transfer occurs in these systems. The complex versus the zeolite framework conformations influence the europi um emission characteristics: the transfer is more efficient when the comple xed europium [Eu(DP)](+) is directly bonded to the framework oxygen atoms r ather than to a residual water molecule.