Study of Mn2+ luminescence in β-PbF2

Highlights: • Multiple centers of Mn²⁺ ions in β–PbF₂ crystal luminescence is studied. • Models of pair-centers of Mn²⁺ ions in β–PbF₂ crystal are proposed. • Energies of transitions in Mn²⁺ ions in β–PbF₂ crystal are calculated. -- Abstract: 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.