Abstract
Energy levels of dilute solutions of valence-pure divalent, trivalent, and tetravalent uranium in fluoride crystals are derived from absorption and fluorescence measurements. Fluorescence is observed which results from transitions between split ground-state and next higher split levels of trivalent uranium and divalent uranium in alkali-earth fluoride lattices. A new explanation is proposed for the fluorescence characteristics of trivalent uranium laser crystals, based upon the competition of energy absorptions of impurity valence states with the fluorescent emission of trivalent uranium ions.