Tunable luminescence for KNaCa2(PO4)2:Eu2+/Mn2+ phosphors due to energy transfer from Eu2+ to Mn2+

A series of KNaCa2(PO4)2:Eu2+/Mn2+ phosphors were synthesized by a solid state reaction. The phase and optical properties of the synthesized phosphors were investigated. The XRD results indicate that the doped Eu2+ and Mn2+ ions do not change the phase of KNaCa2(PO4)2. The emission intensity of KNaCa2(PO4)2:Eu2+ shows obvious dependence on Eu2+ concentration. It was found that the critical concentration for Eu2+ in KNaCa2(PO4)2 is 0.04. The emission intensity of KNaCa2(PO4)2:Eu2+ decreases due to concentration quenching as soon as the Eu2+ concentration is higher than the critical concentration. Due to energy transfer from Eu2+ to Mn2+ in KNaCa2(PO4)2:Eu2+/Mn2+ phosphors, tunable luminescence was obtained by changing the concentration of Mn2+.