EN
The X-band EPR measurements were performed on Gd^{3+}-doped LiErF_{4} and LiDyF_{4} single crystals at room temperature. The spin-lattice relaxation times were evaluated to be 2.7 × 10^{-15} s, 1.0 × 10^{-15} s and 2.2 × 10^{-15} s for LiDyF_{4} , LiErF_{4} and LiYbF_{4}, respectively. Spin-Hamiltonian parameters are determined and discussed in the light of the superposition model in order to determine the distortion of Gd^{3+} ion environment in LiREF_{4} host lattices (RE = Yb, Y, Er, Dy, and Gd).