On the Eu3+ Fluorescence in Mixed Metal Oxides. III. Energy Transfer in Eu3+-Activated Tungstates and Molybdates of the Type Ln2WO6 and Ln2MoO6

The fluorescence of unactivated and rare-earth-activated materials of the type Ln2WO6, Ln2MoO6, and Y2W1−xMoxO6 (0≤x≤0.1) has been studied. From the experiments on unactivated materials it follows that energy transfer from tungstate to tungstate or mobyldate group takes place, whereas there is no transfer from molybdate to molybdate or tungstate group. Arguments in favor of exchange-regulated energy transfer from tungstate or molybdate group to rare-earth ion are put forward. The efficiencies of the rare-earth-activated tungstates and molybdates can be qualitatively understood assuming a strong dependence of the energy transfer on the angle tungsten (molybdenum)—oxygen—rare earth. In Y2W1−xMoxO6:Eu the molybdate group acts as a killer of the fluorescence under short-wave uv excitation and as a sensitizer under long-wave uv excitation.