The results of studies of a lithium shallow-donor center and a Fe0 deep donor ( S =1) in mono-isotopic silicon 28Si are presented. Due to considerable narrowing of EPR spectral lines, the article studies the fine spectral structure for both cen- tres which occupy tetrahedral interstitials in a silicon lattice. In the case of the lithium donor center, the experimental data confirm the role of crystal internal strains according to the observations of 1 s (T2) and 1 s (E) states. The strain distribution anisotropy has been investigated by angular dependences of the EPR linewidth, which corresponds to the lithium triplet state T 2z. A similar anisotropy has also been observed in the case of the introduction of Fe0 ions into the initial crystal. This effect has been studied by angular dependences of the EPR linewidth caused by the transitions -1?0 and 0?+1 (? M s=1), as compared with the transition-1?+1 (? M s=2).
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