A semiempirical model to predict and assign site occupation and sp level of Pb²⁺ in fluorides

Information on the position of A, B, and C bands of Pb²⁺ in 10 different fluoride compounds was collected. Environmental factors h_e of the fluorides were calculated based on the dielectric theory of chemical bond for complex crystals. The relationships between the A, B, and C band energies of Pb²⁺ and h_e were investigated. Three linear formulas were proposed. They allowed us to predict and assign the A, B, and C band energies of Pb²⁺ -doped compounds and were also useful for identifying different Pb²⁺ -occupied lattice sites. The model predicted that the positions of B and C bands for LiCaAlF₆: Pb ²⁺ are 162.9 and 150.9 nm, respectively. In BaY₂ F ₈: Pb²⁺, the excitation spectrum of Pb²⁺ from two different cation sites was identified: the higher energy bands of A, B, and C from the site of Y³⁺ and the lower ones from the site of Ba ²⁺. For KMgF₃: Pb²⁺, the absorption band at 187 nm from the site of K⁺, not Mg²⁺, was confirmed; moreover, the band at 218 nm was assigned to the A band of Pb²⁺ in the Mg²⁺ site. In addition, the origin of the B and C bands for BaY₂ F₈: Pb²⁺ and LiBaF₃: Pb ²⁺ is discussed and reassigned.