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Zusammenfassung:
A model of one-electron states is devised to describe within the strong-field limit the chromium states Cr2+(d4) and Cr+(d5) in tetrahedral crystal fields. The proposed advancement is the inclusion of spin-correlation effects, i.e. a differentiation between the energies of spin-up and spin-down electron configurations. The method comprises the known spin-allowed 5E(D)⇆5T2(D) transitions of Cr2+ and, above all, spin-forbidden transitions. The 4T1(G)→6A1(S) luminescence of ZnSe:Cr+ peaking near v=10 300cm-1 is interpreted as a t2↓→e↑ transition of the d5 configuration. A weak emission band of ZnSe:Cr peaking near 6100 cm− at cryo-temperatures and its analogues in ZnS and other II–VI materials are now assigned to the t2↑t2↓e↑2→t2↑2e↑2 spin-flip process of the Cr2+ (d4) configuration whose Jahn-Teller-stabilised ground state had earlier been proved to participate in this luminescence. The described emission bands provide for the first time direct means to derive from an experiment the spin-flip energy within the one-electron limit.
