Electronic pair excitations of Mn²⁺and Ni²⁺in perovskite fluorides: involvement of the³T1gastate of Ni²⁺

Crystals of KZnF3 and KMgF3 doped with Mn2+ and Ni2+ were used to study the spectroscopic properties of Mn2+-F--Ni2+ pairs. Pair transitions to the doubly excited states 4 Eg a , 4 A 1g (Mn)3 T 1g a (Ni) and 4 Eg b (Mn)3 T 1g a (Ni) were observed. The participation of the spin-allowed 3 A 2g →3 T 1g a excitation on Ni2+ in the pair transition is explained by spin-orbit mixing between 3 T 1g a and 1 Eg . The prominent electronic origins are assigned to the double spin-flip transitions 6 A 1g (Mn)3 A 2g (Ni) →4 Egu(Mn)3 T 1g a (Γ3)v(Ni) and 4 A 1g (Mn)3 T 1g a (Γ3)v(Ni). The former lie at lower energy and are more intense than the corresponding 6 A 1g (Mn)3 A 2g (Ni) →4 Egv(Mn)3 T 1g a (Γ3)u(Ni) transitions involving two orbital jumps. The well-resolved vibronic structure is composed of three basic vibrations of ∼ 150 cm-1, ∼ 294 cm-1 and ∼ 508 cm-1 in the KZnF3 host.