Some observations on the luminescence of rare-earth molybdates with β′-Gd2(MoO4)3 structure

Abstract

The luminescence properties of rare-earth activated and unactivated Gd₂(MoO₄)₃ and those of Eu₂(MoO₄)₃ and Tb₂(MoO₄)₃ are reported. Gd₂(MoO₄)₃ shows two different molybdate emissions which are assigned to intrinsic and defect molybdate groups. Energy transfer from the molybdate group to rare-earth activators is not efficient in the diluted samples Gd₂(MoO₄)₃–RE. Time-resolved spectroscopy and decay-curve measurements were not able to demonstrate energy migration in Eu₂(MoO₄)₃. Only one-step transfer processes to centres in the surface were observed. The absence of migration is explained by a structural property, viz. the occurrence of rare-earth sites in pairs. For Tb₂(MoO₄)₃ we were able to demonstrate energy migration through the Tb³⁺ sublattice. The nature of the processes involved is complicated and a detailed analysis was not possible.