Pressure induced phase transition and spectroscopy of Mn5+-doped Li3PO4

A pressure induced phase transition from the high temperature to the low temperature form of Li3PO4 was observed and confirmed using Mn5+ luminescence spectroscopy and Raman scattering. The larger 1E splitting and shorter lifetime observed in the low temperature phase are interpreted in terms of a larger distortion of the phosphate group of the low temperature phase from regular tetrahedral symmetry. The results illustrate that a competition between cubic crystal field and non-tetrahedral distortions is crucial to the understanding of the emission properties of d2 systems.