Luminescence properties of the layered niobate KCa2Nb3O10 doped with Eu3+ and La3+ ions

In the present work the layered perovskite phase KCa2Nb3O10 was doped with rare earth ions through a solid-state reaction, producing compounds of general formula K(1-x)Ln(x)Ca(2-x)Nb(3)O(10) (where Ln=La3+ or Eu3+ and x=0.02). The photoluminescence properties of the layered oxide doped with rare earth ions in the perovskite-type layers were investigated based on the luminescence data. The KCa2Nb3O10 phase does not exhibit emission bands when excited in the UV region. On the other hand the matrices doped with Ln(3+) ions show a blue emission (lambda(exe)=270 nm) at 298 and 77 K, indicating that the electronic properties of the layered materials are modified by the lanthanide insertion. In the case of K0.98Eu0.02Ca1.98Nb3O10 the characteristic red emission of the trivalent europium ion is also observed under excitation at 270 and 394 nm. The luminescence spectra of the Eu3+-compound show the D-5(0) --> F-7(0) transition split into two peaks, indicating that the Eu3+ ions are located in at least two distinct site symmetries. The results also suggest the occurrence of an energy transfer process between the niobate matrix and the Eu3+ ion. The luminescence decays exhibit biexponential curves corroborating the presence of Eu3+ ions in more than one chemical environment. (C) 2000 Elsevier Science S.A. All rights reserved.