Crystal-field model of the Pb⁰(2) centre in SrF₂

A crystal-field model of the Pb 0 (2) centre in SrF 2 accounts for a metastable state which is the source of luminescence, as well as for three peaks observed in its excitation spectrum. Both transition energies and relative intensities are predicted correctly within experimental error. Adjusted values of the spin-orbit constant and a Slater integral are reduced by 21% from their free-atom values. The adjusted values of the axial crystal-field parameter gamma in the relaxed ground state and metastable excited state are 0.6529 eV and 0.5213 eV, respectively. A Huang-Rhys factor S 0 =12 and a phonon energy h(cross) omega =90 cm -1 are inferred from the calculated energy of the metastable state and from the position and width of the observed emission band.