Colour centre luminescence in KMgF3:Mn crystals

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Abstract
Optical absorption and emission studies of KMgF3 crystals containing various amounts of Mn2+ (0.04-91.2 at%) have been made. Recently, it was determined that when crystals containing about 1.4 at% Mn are irradiated with high energy electrons the absorption spectrum is dominated by a set of five bands originating from a single defect. It was proposed that these bands arise from a defect involving an F centre trapped between adjacent Mn impurity ions. In this work, these observed optical absorption bands are assigned to Mn-pair 3d electron transitions perturbed by the presence of the F centre. Optical excitation at 300 K into any of these five absorption bands (230, 248, 280, 410, and 565 nm) results in an emission band at 630 nm, whereas similar excitation at 77 K or below gives a luminescence at 677 nm which has a much longer lifetime than the 630 nm band. The luminescence is discussed in terms of Mn2+ transitions and the thermal population of energy levels.