The measured optical properties of the Eu chalcogenides are surveyed in an attempt to determine those aspects of the electronic structure of these materials that have been established. Optical absorption as well as optical and magneto-optical reflectivity data are discussed, along with the results of photoconductivity, photoluminescence and photoemission measurements and of magneto-optical measurements in the vicinity of the absorption edge. It is concluded that the fundamental absorption edge is due to the onset of Eu++ 4f to 5d transitions of the type 4f7(8S7/2) → 4f6(7FJ)5d(T2g) and that a higher energy reflectivity peak is primarily due to 4f7(8S7/2) → 4f6(7FJ)5d(Eg) transitions, although anion p-valence band to Eu conduction band transitions may also be involved. The principal unanswered questions involve the relative positions of the Eu 6s and 5d(T2g) states, the breadth of the 5d levels and the role played by exciton effects in the 4f to 5d optical transitions.
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