Effect of Oxygen Vacancies on the Reduction of Eu3+in Mg3Ca3(PO4)4in Air Atmosphere

The paper reported the synthesis of mixed-valence Eu-doped Mg₃Ca₃(PO₄)₄ by solid-state reaction in the air atmosphere. The luminescence measurements indicated that the obtained phosphors exhibit a broad bluish-green fluorescence of Eu²⁺ and a sharp orange-red emission of Eu³⁺ excited by 395 nm. The abnormal reduction mechanism could be explained by a charge compensation model. A tunable luminescence was realized based on the reduction of Eu³⁺ to Eu²⁺ changed along with increasing the sintering time. The reduction of Eu³⁺ to Eu²⁺ in Mg₃Ca₃(PO₄)₄ host was effected by the oxygen vacancy defects when the samples sintered in different atmosphere and sintered for different lengths of time, and the oxygen vacancies which act as the electron traps were investigated with thermoluminescence. All of the results almost indicated the oxygen vacancy could weaken the reduction of Eu³⁺ to Eu²⁺. Our investigation of Mg₃Ca₃(PO₄)₄:Eu could provide a practical basis and theoretical basis to study the effect of oxygen vacancy on the emission of Eu ions.