A luminescence study of single-crystal EuPO4 at high pressure

The pressure dependence of the luminescence from the D-5(0) --> F-7(0.2) transitions in the Eu3+ ion in single-crystal EuPO4 has been investigated to about 20 GPa using a diamond anvil cell. Based on the level energies derived from the luminescence spectra recorded from the same crystal specimen, the parameterization of the free ion and crystal field effects was carried out with good results, as indicated by the low RMS deviations obtained. The lifetime of the D-5(0) level was also measured as a function of pressure via monitoring a peak in the D-5(0) --> F-7(1) transition manifold. Abrupt changes in the Eu3+ ion luminescence spectra and lifetime were observed between 6 and 8 GPa, while the general spectral pattern remained the same over the entire pressure range investigated. Calculated crystal field parameters also displayed a discontinuity between 6 and 8 GPa. These facts indicate that the site symmetry of the Eu3+ ion in EuPO4 is not changed by the application of pressure to about 20 GPa, but the strength of the crystal field probably changes significantly between 6 and 8 GPa. These observations are consistent with the crystal undergoing an isostructural volume collapse between 6 and 8 GPa. The ambient-pressure phase, which exhibits the monazite-type monoclinic structure, is retained to at least 20 GPa. (C) 1997 Elsevier Science Ltd. All rights reserved.