Implications of the theory for defect centres having g factors close to the free spin values

The theoretical interpretation of electron spin resonance signals from defect centres with g factors close to those of the free spin value are discussed.It is shown that accounting fully for the observed g shifts has important implications for the theory.These involve a bridging of the gap between the local model approximations of crystal field theory and the more extensive band theory ideas, in addition to questions concerning the expansion or contraction of free-ion one-electron wave functions on formation of a solid.Another aspect concerns evidence for configurational mixing of different free ion-electron configurations by large crystal fields of low symmetry.Experiments are suggested which should be able to form a check on certain of the ideas developed.