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NaEu3(GeO4)2(OH)2: A High-Pressure-Stable Photoluminescent Lanthanide Germanate



The europium germanate NaEu3(GeO4)2(OH)2 was prepared under mild hydrothermal conditions. In situ synchrotron X-ray diffraction analysis and photoluminescence spectroscopic measurement in a diamond anvil cell (DAC) under high pressure were performed to study its structural stability as well as the luminescent properties of the Eu3+ ions. The synchrotron X-ray diffraction analysis revealed that the structure of NaEu3(GeO4)2(OH)2 was stable under pressure that ranged from 1 atm to 20 GPa with only a little distortion, and the unit-cell compression occurred more readily along the a axis than along the c axis. When the pressure was reduced to ambient pressure, the distortion and the unit cell recovered to the original state. Photoluminescence spectroscopic studies under high pressure showed that the redshift of the 5D07FJ (J = 0, 1, 2) transitions and the pressure imposed on the sample had a good linear relationship. Also, the intensity of the red emission lines was independent of the pressure in the range from 9 to about 20 GPa.