Emission quenching induced by intervalence charge transfer in Pr3+- or Tb3+-doped YNbO4 and CaNb2O6

The excitation and emission properties of Pr3+ and Tb3+ ions doped into YNbO4 (hereafter YNB) and CaNb2O6 ( hereafter CNB) have been studied as a function of the temperature in the 10-600 K range. The observed quenching of the luminescence from the P-3(0) (Pr3+) and D-5(3) (Tb3+) states has been related to an electron transfer process from the trivalent rare earth to the Nb5+ ion inducing the formation of an intervalence charge transfer (IVCT) state. On this basis a detailed picture of the excited-state dynamics of the investigated compounds is presented, taking into account the characteristics of the host lattices and of the involved optically active ions.