H. U. Güdel, T. Brunold, M. Hazenkamp, M. Herren, U. Oetliker and R. Schenker
Luminescence of Transition Metal Ions in Unusual Oxidation States
Electrochem. Soc. Proceedings (Luminescent Materials VI) 97-29, 225-234 (1998)           

Abstract: The luminescence properties of Ti²⁺, V³⁺, Cr⁴⁺, Mn⁵⁺, Fe⁶⁺, V⁴⁺, Cr⁵⁺, Mn⁶⁺ in insulating host lattices, which have been studied extensively in recent years, are summarized. The luminescence can be tuned from sharp-line to broad-band, from short-lived to long-lived by chemical and structural variation. The materials potential of the new systems is discussed