A phosphor, Gd0.99Bi0.01Nb1-xPxO4, was synthesized by substituting phosphate, PO43-, into a niobate-based GdNbO4 host lattice. This phosphor showed dramatically improved luminance intensity in the blue region under 254 nm excitation compared to reports for GdNbO4:Bi3+. The band-to-band transitions of PO43- in Gd0.99Bi0.01Nb1-xPxO4 are believed to have a sensitizing function in the host lattice. The partial replacement of NbO43- by PO43- stimulates absorption in the UV region and consequently increases the quantum yield in the blue region. Furthermore, substitution of PO43- in the phosphor improved the surface morphology of the phosphor. (C) 2008 The Electrochemical Society.