Magneto-optical properties of the F centre in KMgF₃

A radiation induced optical absorption band (at 275 nm) and a nine-line paramagnetic resonance (described by g=2.00 and A=60 G), that have been attributed previously to the F centre, were investigated in KMgF 3 using combined measurements of the magnetic circular dichroism (MCD) and electron paramagnetic resonance (EPR). The optical band was found to exhibit a temperature dependent MCD which enabled the optical detection of the paramagnetic resonance. This positively confirms that the optical absorption and EPR stem from the same centre. The experimental evidence substantiates the F centre identification, and implies a 2 E u excited state which could, however, be accidentally degenerate with a 2 A 2u state.