A solid state synthesis route was used to prepare (Gd1−xLnx)2(MoO4)3, Ln=Yb or Tm, compounds with ferroelectric Pba2 crystal structure. It has been observed that this phase is the only one crystallized during 1123K annealing for x≤0.12 for Yb and x≤0.3 for Tm. Above these concentration limits the simultaneous formation of trihydrated Ln2(MoO4)3, Ln=Yb or Tm, is observed. Up to these concentrations Yb and Tm incorporations do not degrade the SHG efficiency. The position of Yb3+ and Tm3+ energy levels involved in laser emission processes were determined by 5K spectroscopy. The 300K pumping and emission spectral distributions and excited level lifetime have been determined with the purpose of future applications as self-activated periodically poled ferroelectric laser and non-linear media.