Molecular Model Parameters for the Saddle‐Point Configuration of F, F A , F B , and F H Centres in the Alkali Halides

A molecular model for the saddle‐point configuration of F‐type centres, which previously led to the correct prediction of type II emission for F A centres in RbF:Li and RbF:Na, based on an empirical parameter Z , is extended to other impurity F centres in the alkali halides. CsF:Li and CsF:Na are predicted to have type II F A centres, and a number of triangular F B centres in the NaCl structure are also predicted to be type II, particularly in materials with small host anions combined with Li + or Na + impurities. Materials having small Z values, presumed to favour type II behaviour, are also identified, for F H centres with large host anions and H −; or F −; impurities, and for F A and triangular F B centres in the CsCl structure containing Li + or Na + impurities, where the F B centre which has impurities on adjacent corners of a unit‐cube face is strongly favoured.