Orange- and Violet-Emitting Long-Lasting Phosphors

Orange phosphorescence from Eu³⁺-activated CaO and SrO and violet phosphorescence from Pb²⁺-activated SrO were clearly observed after the materials had been excited with ultraviolet light. The orange phosphorescence resulted from ⁵ D ₀ to ⁷ F ₁ transitions of the Eu³⁺ ions and the violet from ³ P ₀ to ¹ S ₀ transitions of the Pb²⁺ ions. The phosphorescence lasted >1 h. Trapped-electron centers and hole centers introduced into the CaO and SrO hosts by the ultraviolet light appear to have been responsible for generating the long-lasting phosphorescence.