Lanthanide dopant-induced phase transition and luminescent enhancement of EuF3 nanocrystals

A novel strategy is proposed to prepare hexagonal EuF3 nanocrystals by doping lanthanide ions (Ln3+) with large ionic radius (such as La3+, Ce3+, Pr3+, Nd3+ and Sm3+). Complete phase transition from orthorhombic to hexagonal phase can be achieved with the increase of ionic radius or doping concentration of Ln3+ ions. Meanwhile, the size and self-assembly degree of the product can be reduced dramatically. The possible growth and phase transformation mechanism of EuF3 nanocrystals was proposed. Finally, Eu3+ ion was used as the structural probe to investigate the effect of phase transition on the luminescence. It was found that the emissions of the 5D0 level of Eu3+ are greatly enhanced with the phase transition from orthorhombic to hexagonal phase. The luminescent enhancement is attributed to the larger radiative transition rate of the 5D0 level in the environment with lower symmetry, which can be confirmed by Judd–Ofelt (J–O) theory.