Pure Hexagonal Phase of EuF3 Modulated by High Pressure

Abstract

We have performed in situ high-pressure synchrotron X-ray diffraction (XRD) and photoluminescence (PL) measurements to explore the behaviors of europium fluoride (EuF3). At ambient conditions, EuF3 consists of two representative phases of the rare earth trifluorides family. The orthorhombic phase (α-EuF3) evolves into its hexagonal phase (β-EuF3) in the pressure range 2.7–7.8 GPa, which involves the variations of europium positions in one layer and changes in the coordination number of europium from nine to eleven. The existence of pure β-EuF3 at high pressure allows solving detailed structural information of β-EuF3 for the first time. In comparison with the excellent hydrostatic condition in methanol–ethanol–water, a somewhat poor pressure condition in silicon oil contributes to the sluggishness of the phase transition, restrains the compression of lattice constants, and controls the phase content ratio of the quenched sample. Significantly, the PL measurements show that the pressure-induced purity of EuF3 is a benefit to the enhancement of its luminescence intensity. This work provides precise structural and PL information on β-EuF3, getting a deeper insight into the nature of these two typical structures with respect to rare-earth trifluorides.