The energy transfer of electronic excitations to impurities in dosimetric phosphors BaSO4-Dy

The formation of new radiative states from the combination of ${Dy}^{2+}-{SO}_4^{-}$ and ${SO}_4^{3-}-{SO}_4^{-}$ electron trapping centers in the range of 2.95–3.1 eV has been investigated using VUV and thermal activation spectroscopy. During the excitation process, there is a charge transfer between the oxygen ion of the sulfate anion and ${Dy}^{3+}$ leading to the formation of a combined emissive state ${SO}_4^{3-}\to {SO}_4^{-}$. These states can be formed from the electron-hole trapping centers of ${Dy}^{2+}-{SO}_4^{-}$ and ${SO}_4^{3-}-{SO}_4^{-}$. The combined radiative state at 2.95–3.1 eV and impurity emission at 2.16 eV and 2.56 eV are excited simultaneously by photons of 3.95 eV and 4.5 eV, respectively. During the thermal or optical excitation process, the ${Dy}^{2+}$ and ${SO}_4^{3-}$ electronic centers are ionized. Electrons recombine with a hole trapped by the ground state of the impurity (${SO}_4^{-}$ $-$ ${Dy}^{3+}$), and the released energy is transferred to the ${Dy}^{3+}$ impurities.