Structural phase transition and photoluminescence properties of YF3 and YF3:Eu3+ under high pressure.

We investigate high-pressure induced phase transitions of YF3 and Eu-doped YF3 (YF3:Eu(3+)) by using the angular dispersive synchrotron X-ray diffraction technique at room temperature. It is found that the starting orthorhombic phase transforms into a new high-pressure phase which is identified as hexagonal structure in both YF3 and YF3:Eu(3+). The high-pressure structure of YF3 and YF3:Eu(3+) returned to the orthorhombic phase after release of pressure. The photoluminescence properties of YF3:Eu(3+) have also been studied under high pressure up to 25 GPa. The Eu(3+) ion luminescence lines of (5)D0→(7)F1,2,3,4 transition originating from the orthorhombic phase transform into another group of luminescence lines of hexagonal phase under high pressure, which reveals the pressure-induced structural transition of YF3:Eu(3+). The relative luminescence intensity ratio of (5)D0→(7)F2 to (5)D0→(7)F1 transitions of the Eu(3+) ions is found to increase with increasing pressure before phase transition and decrease after transition finished, indicating reducing and enhancing of the symmetry around the Eu(3+) ions, respectively.