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+-O2-→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.