Photoluminescence and Raman Spectroscopy Studies of Eu(OH)₃ Rods at High Pressures

Eu(OH) 3 rods, with diameters of 140 nm and lengths of 100−500 nm were prepared by a hydrothermal method. X-ray diffraction indicated a pure hexagonal phase (space group P 6 3 / m ) of the rods. The relations between structural and optical properties of Eu(OH) 3 rods under high pressures were obtained by photoluminescence (PL) and Raman spectra. Two structural phase-transition points at around 4 and 8 GPa were observed in this work. When a pressure of about 4 GPa was applied to the samples, one new emission peak at 593 nm was observed in the PL spectra, indicating the splitting of the 7 F 1 Stark level in Eu 3+ ions. Such a splitting was attributed to the decrease of site symmetry of Eu 3+ ions from C 3 h to D 2 at high pressures. Two new Raman bands appeared under a pressure up to about 8 GPa due to the pressure-induced amorphization. After the pressure was released, the original PL and Raman spectra were recovered.