A luminescence study of single-crystal EuPO 4 at high pressure

Abstract

The pressure dependence of the luminescence from the 5D 0 → 7F 0–2 transitions in the Eu 3+ ion in singlecrystal EuP04 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 5D 0 level was also measured as a function of pressure via monitoring a peak in the 5D 0 → 7F 1 transition manifold. Abrupt changes in the Eu 3+ 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 Eu 3+ ion in EuPO 4 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 monazitetype monoclinic structure, is retained to at least 20 GPa.