Hartree-Fock and second-order Moller-Plesset calculations are reported of the structural and vibrational parameters of some rare earth fluorides LnF(n) neutrals and LnF(n)(+) ions, where Ln is erbium and thulium and n = 1, 2, and 3. Quasi-relativistic pseudopotentials developed by Dolg et al, were applied for a description of the core electrons of the lanthanide atoms. A planar D-3h structure resulted from geometry optimization at both levels of calculation for the ground state of erbium and thulium trifluorides. The vertical and adiabatic ionization energies of LnF(n)(+) are reported and Ln-F bond dissociation energies D-0(LnF(n-1)-F) evaluated. These quantities are compared to available experimental data.