EPR of iron centres in silicon dioxide

A review is presented of the present status of EPR-based understanding of Fe in SiO₂. As a primary goal, a guide to the literature is given. Quantitative evaluation of all relevant spin-Hamiltonian parameters is discussed, as is computer-based spectral simulation, for single crystals (alpha-quartz), powders and glasses (vitreous quartz). Identification of the numerous centres now known (e.g., for Fe³⁺:[FeO₄/M]⁰ with M=H, Li, Na, …, as well as [FeO₄]^?) is featured, discussing atomic positions, surroundings and dynamic effects. Some general chemical considerations, including comparison between Fe in SiO₂ crystals and glasses, are covered, as are future needs.