Pressure dependences are determined for a number of properties of absorption- and emission-band shapes of vibrationally assisted electronic transitions within impurities in solids. The vibrational coupling of the impurity to the lattice includes both linear and quadratic interaction terms, as well as different pressure couplings in the ground and excited electronic states. The pressure-dependent properties that are examined include the zero-phonon-line energy, the first three moments, the centroid shift from the zero-phonon line, and the Stokes shift. In general, all these properties have pressure dependences that involve the quadratic interaction parameter and the difference in the pressure coupling to the ground and excited electronic states. These pressure-dependent effects are shown to arise through a pressure-dependent Huang-Rhys factor and a pressure-dependent energy separation between the minima of the electronic ground and excited states.

• Received 8 January 1975

DOI:https://doi.org/10.1103/PhysRevB.12.594