Luminescence and charge carrier trapping in YPO4:Bi

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.