Defect structure and vibrational states in Eu-doped cubic gadolinium oxide.

We consider an effect of trivalent Eu impurities occupying two different crystallographic positions in cubic gadolinium oxide on its lattice structure and phonon spectrum. The numerical methods employed in the study take into account the shell model to describe interatomic interactions. Using cluster approach, the equilibrium lattice structures and phonon local symmetrized densities of states are calculated. The frequencies of resonant vibrations of various symmetry types induced by europium ions are determined using the Green function method. The participation of ions located around Eu impurities in the symmetrical resonant vibrations is discussed. The calculation results show that europium ions in two non-equivalent structural sites are responsible for the formation of the strongest Raman peak associated with the resonant vibrations at oxygen ions in doped Gd2O3.