Study of Mn2+ luminescence in β-PbF2

For the first time excitation and luminescence spectra of Mn2+ ions in β-PbF2 crystals at 77 and 300 K, and also the luminescence lifetime are studied. Impurity ions in the crystal form a cubic center and centers of lower symmetry, and also exchange-coupled pairs. The origin of the formation of noncubic centers during the substitution Mn2+ → Pb2+ are the large difference of ionic radii Mn2+(0.80 Å) and Pb2+ (1.26 Å) creating the instability of the local structure around the activator ion, its deformation, and exchange striction. The increase in the impurity concentration enhances these factors leading to the change of the relative concentration of different centers. The strong manifestation of the Jahn-Teller (Ham) effect is found in the luminescence excitation spectra. The importance of using the Trees-Racah α and seniority β corrections in the scheme of the crystal field theory (CFT) calculations is demonstrated. The connection between Trees-Racah corrections values and symmetry of Mn2+ surrounding in homologous crystals MeF2 (Me = Ca, Sr, β - PbF2, Ba) has been revealed.