“…Whether Mg directly captures electrons or whether just perturbs the electron centres, characteristic of the host lattice, is to be decided. Several papers (Mort 1965;Nink and Kos 1976;Parfianovich et al 1976;Nink 1977a, b,c,d, 1979, 80;Mehta et al 1977;Kos and Mieke 1978;Kos and Takeuchi 1980;Rao 1980;Jain 1981c;Lakshmanan et al 1983) support the latter view. The idea ofZ centres of Mg started with the suggestion (Mort 1965;Mort and Zimmerman 1966) that the empirical Mollow-Ivey relation for Z 3 centres in alkali halides predicts the Z3 band in LiF:Mg at 225nj.…”