Vacuum Ultraviolet Excited Photoluminescence Properties of Y2O2S:Eu3+,Bi3+ Phosphor

As an Hg-free lamp using phosphor, the Bi³⁺ and Eu³⁺ co-doped Y₂O₂S phosphors were prepared and their luminescence properties under vacuum ultraviolet(VUV) excitation were investigated. The VUV photoluminescent intensity of Y₂O₂S:Eu³⁺ was weak, however, considerably stronger red emission at 626 nm with good color purity was observed in Y₂O₂S:Eu³⁺,Bi³⁺ systems. Investigation on the photoluminescence reveals that the strong VUV luminescence of Y₂O₂S:Eu³⁺Bi³⁺ at 147 nm is mainly because the Bi³⁺ acts as a medium and effectively performs the energy transfer process: Y³⁺-O^2-→Bi³⁺→Eu³⁺, while the intense emission band at 172 nm is attributed to the absorption of the characteristic ¹S₀-¹P₁ transition of Bi³⁺ and the direct energy transfer from Bi³⁺ to Eu³⁺. The Y₂O₂S:Eu³⁺,Bi³⁺ shows excellent VUV optical properties compared with the commercial (Y, Gd)BO₃:Eu³⁺. Thus, the Y₂O₂S:Eu³⁺,Bi³⁺ can be a potential red VUV-excited candidate applied in Hg-free lamps for backlight of liquid crystal display.