Development of persistent phosphor of Eu²⁺ doped Ba₂SiO₄ by Er³⁺ codoping based on vacuum referred binding energy diagram

We have developed the Ba₂SiO₄: Eu²⁺ -Er³⁺ persistent phosphor. The vacuum referred binding energy (VRBE) diagram of the Ba₂SiO₄ host with the 4f ground states of divalent and trivalent lanthanide ions in the host band gap was constructed from the obtained spectroscopic data and the Dorenbos's procedure. From the constructed diagram, the VRBE values of the conduction band (CB) bottom and valence band (VB) top were estimated to be −0.66 and −8.27 eV, respectively. From the energy gap between the CB bottom and 4f ground states of divalent lanthanide ions, we selected the Er³⁺ ion as an efficient co-dopant because the trap depth was estimated to be 0.64 eV, suitable for improving the persistent luminescence duration. The Eu²⁺-Er³⁺-codoped sample showed persistent luminescence intensity of over 0.32 mcd/m² for 7 h duration. The initial persistent luminance intensity of the Eu²⁺-2%Er³⁺-codoped sample was found to be 250 times stronger than that of the only Eu²⁺-doped sample.