YPO4 doped with Bi³⁺ and/or Tb³⁺ samples were prepared in air. X-ray excited luminescence measurements showed emission from isolated Bi³⁺ and Bi-pairs, and also emission from Bi²⁺ was observed. Based on the obtained spectroscopic data, the electron binding energies in the ground and excited states of Bi³⁺ and Bi²⁺ were placed inside the vacuum referred binding energy (VRBE) scheme, and this was used to explain the luminescence of bismuth doped YPO₄. The VRBE scheme and additional thermoluminescence glow curves show that bismuth can act both as electron and as hole trap in YPO₄.@en