Structure and photoluminescence properties of novel Sr6Ca4(PO4)6F2:Re (Re = Eu2+, Mn2+) phosphors with energy transfer for white-emitting LEDs

A series of Sr6Ca4(PO4)6F2:Eu2+,Mn2+ phosphors were synthesized through traditional solid state reaction. The structural and spectroscopic properties of the series samples along with the energy transfer from Eu2+ to Mn2+ ions have been investigated in detail. Under excitation at 295 or 365 nm, Eu2+ singly doped phosphors exhibit a broad emission band centered at 450 nm. When Eu2+ and Mn2+ were co-doped in Sr6Ca4(PO4)6F2, a broad blue emission band peaking at 450 nm and an orange emission band at 570 nm appeared simultaneously upon ultraviolet (365 nm) excitation, which result from the 4f–5d transition of Eu2+ ions and the 4T1–6A1 transition of Mn2+ ions, respectively. By controlling the doping concentration of Mn2+ ions, a series of tunable luminescent colors including white light are obtained with a wide band emission and a correlated color temperature of 6662 K. The possible energy transfer mechanism was proposed to be dipole–quadrupole, with regard to the analysis of photoluminescence spectra and decay curves experimental results of the series samples. The critical distance between the Eu2+ and Mn2+ ions has been calculated by both the concentration quenching method (11.53 A) and the spectral overlap method (9.43 A). Overall, this research indicated that the prepared samples may be potentially applied in white-light-emitting diodes under UV-pumping.