On the triplet state of FA(Mg) centres in calcium oxide

Abstract
Electron spin resonance has been observed in the lowest optically excited state of the FA(Mg) centre in CaO by detecting FA(Mg)-band phosphorescence peaking at 689 nm. The ODMR spectrum is axially symmetric about the (100) axis; transferred hyperfine structure due to 25Mg(I=5/2) confirms that a nearest-neighbour cation site of the F-centre is occupied by an Mg2+ impurity ion.