Cyclic Phase Transition from Hexagonal to Orthorhombic Then Back to Hexagonal of EuF₃ While Loading Uniaxial Pressure and under High Temperature

The structure and photoluminescence properties are investigated under high pressure and high temperature for pure orthorhombic and hexagonal EuF₃ nanocrystals. Under hydrostatic compression, the hexagonal EuF₃ remains stable at pressures up to 26 GPa. Under nonhydrostatic compression, a cyclic phase transition from hexagonal to orthorhombic and then back to hexagonal is observed for the first time. When loading uniaxial compression, the pure hexagonal EuF₃ partly transforms to orthorhombic at 70 MPa, then the orthorhombic EuF₃ transforms to hexagonal at about 3 GPa, and the transition is completed at about 10 GPa. The cyclic phase transition is also observed during the heating process; the hexagonal transforms to orthorhombic at 550 °C and then to hexagonal at 855 °C. The content phase diagrams are obtained under high pressure and at high temperature

Experimental Determination of the Rotational Constants of High-Lying Vibrational Levels of Ultracold Cs₂ in the 0_g^– Purely Long-Range State

We report on a quantitative experimental determination of the rotational constants for the high-lying vibrational levels of the ultracold pure long-range Cesium molecules formed via photoassociation. The scheme relies on a precise reference of frequency difference in a double photoassociation spectroscopy, which is induced by two laser beams based on an acoustic-optical modulator. The rotational constants are obtained by fitting a nonrigid rotor model into the frequency intervals of the neighboring rotational levels deduced from the reference