Abstract The luminescence of the Bi 3+ ion (6 s 2 ) is studied in the metaphosphates Ln P 3 O 9 ( Ln = Sc, Lu, Y, Gd, La). For Ln = Sc, Lu, Y, Gd the metaphosphates have a monoclinic structure with four slightly different sites for the trivalent cations. For Ln = Sc, Lu, Y the Stokes shift of the Bi 3+ luminescence increased with increasing radius of the host lattice cation. Concentration quenching of the Bi 3+ luminescence is observed. In the case of GdP 3 O 9 -Bi 3+ the excitation energy is transferred to the Gd 3+ ions. LaP 3 O 9 adopts an orthorhombic structure with only one site available for the trivalent cations. The different coordination of the Bi 3+ ion leads to a large increase of the Stokes shift of the Bi 3+ luminescence.