Emission quenching induced by intervalence charge transfer in Pr 3+ - or Tb 3+ -doped YNbO 4 and CaNb 2 O 6

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 3P0 (Pr3+) and 5D3 (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.