Crystal field spectra of 3dn impurities in zinc selenide

The absorption spectra at liquid helium temperature of divalent impurities Ti d2, V d3, Cr d4, Co d7 and Ni d8 in zinc selenide are presented. Values of the crystal field parameters B and Delta are derived from the spectra. The variation of Delta through the 3dn series has not been explained by present theories: it is suggested that a new approach, based on bond charge, may be more fruitful.