Preparation of Ca₂Si₅N₈:Eu²⁺, Tm³⁺ phosphor by calcium hydride and its afterglow properties

Reddish-orange emitting long-lasting phosphorescence phosphor Ca ₂Si₅N₈:Eu²⁺,Tm³⁺ has been prepared by solid-state reaction method using cheaper CaH₂ as calcium source. Upon UV light excitation, Ca₂Si₅N ₈:Eu²⁺,Tm³⁺ phosphor gave a broad band emission peaking at ca. 600 nm. Furthermore, after irradiation by the UV or visible light (in the range of 250-400 nm) for 3 min, the same colored intense afterglow based on the 4f⁶5d¹→4f⁷ transition of Eu²⁺ ion was observed on the phosphor codoped with 0.5 at% of Eu ²⁺ and Tm³⁺ ions, and its afterglow can be seen with the naked eye in the dark clearly for more than 1 h after removal of the excitation source. The afterglow decay curve contained fast decay and slow decay components. The substitution of Mg²⁺ to Ca²⁺ ions or addition of excessive Ca²⁺ ions into the phosphor matrix to modify the defect environment were effective to improve the afterglow properties.