Binding energies of Eu2+ and Eu3+ ions in β-Ca2SiO4 doped with europium

• Luminescence properties of β-Ca2SiO4 doped with Eu2+ and Eu3+ are studied.
• Short distance compensation model of the Eu3+ replacing Ca2+ is discussed.
• The existence of stable Eu2+ and Eu3+ was discussed in relation to the Fermi level.

β-Ca2SiO4 doped with Eu2+and Eu3+was synthesized by solid state reaction. Europium replaces Ca2+ ions either as Eu2+ or Eu3+, both occupying two not equivalent sites; seven fold and eight fold coordinated by O2−. β-Ca2SiO4:Eu2+, β-Ca2SiO4:Eu3+ and β-Ca2SiO4:Eu2+, Eu3+ samples were investigated by structural and spectroscopic methods. Specifically it has been shown that luminescence spectra of the β-Ca2SiO4:Eu2+, Eu3+ system were a superposition of the Eu2+ and Eu3+ emission and were independent of temperature from 18 K to ambient. To explain this effect the short distance compensation of the Eu3+ replacing Ca2+ in the β-Ca2SiO4 is discussed. It is argued that such compensation has to causes the conduction and valence bands bend. The existence of stable Eu2+ and Eu3+ replacing Ca2+ ion in lattice is discussed by consideration of the energies of the ground states of the Eu2+ and Eu3+, the Fermi energy and the energy necessary for creation of compensation defect.