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

Abstract

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 Å) and the spectral overlap method (9.43 Å). Overall, this research indicated that the prepared samples may be potentially applied in white-light-emitting diodes under UV-pumping.