Multiphonon radiationless phenomena in Mn{sup}(2+)-doped Ca(1-x)Sr{sub}xF{sub}2 and BaF{sub}2 fluorites

摘要

This work investigates the surprising disappearance of the Mn{sup}(2+) photoluminescence on passing from CaF{sub}2:Mn{sup}(2+) to SrF{sub}2:Mn{sup}(2+) or BaF{sub}2:Mn{sup}(2+) using pressure spectroscopy. We show that the loss of luminescence in these systems is associated with non-radiative thermally activated processes whose activation energy and pre-exponential rates strongly depend on the crystal volume irrespective of the chemical composition. A salient feature is the PL enhancement observed in the cotunnite high-pressure phase along the series. This enhancement is explained in terms of the large volume reduction at the phase transition, as well as by the presence of low-symmetry crystal fields attained at the cation sites leading to an increase of the radiative transition rate by the electric-dipole mechanism.