Color tuning in (Ca1−xSrx)8MgLu(PO4)7:Eu2+,Mn2+ phosphor via host composition design and energy transfer

In this work, a series of Eu2+-doped (Ca1−xSrx)8MgLu(PO4)7 and Eu2+/Mn2+-codoped Ca6.5Sr1.5MgLu(PO4)7 phosphors were prepared via the combustion-assisted solid-state reaction process. XRD patterns and Rietveld refinements were used to verify the incorporations of Sr into Ca8MgLu(PO4)7:Eu2+. Upon the same excitation wavelength of 380 nm, the emission peaks of Eu2+-doped (Ca1−xSrx)8MgLu(PO4)7 (0≤x≤1) phosphors red-shifted from 453 to 519 nm with increasing Sr/Ca ratio. The red-shift of the Eu2+ emission with increasing Sr/Ca ratio was ascribed to the change of Eu2+ emission at different lattice sites. With variation of the Mn2+ content, the emission color of Eu2+/Mn2+ codoped Ca6.5Sr1.5MgLu(PO4)7 phosphors exhibited the luminescence tunable from greenish blue to white and eventually to red. The energy transfer from Eu2+ to Mn2+ in Ca6.5Sr1.5MgLu(PO4)7 host matrix was demonstrated to be of a resonant type via a dipole- dipole mechanism with the critical distance of ∼16.7 Å. By the Sr substitution for Ca and properly tuning by the relative composition change of Eu2+/Mn2+, chromaticity coordinates of (0.329, 0.326) can be reached at near UV light excitation. The combination of host composition design and energy transfer may provide a novel strategy to obtain white light and tunable luminescence.