Phase transition and multicolor luminescence of Eu2+/Mn2+-activated Ca3(PO4)2 phosphors

Intense blue-green-emitting Eu2+: Ca3(PO4)2 and tunable multicolor-emitting Eu2+/Mn2+: Ca3(PO4)2 phosphors are prepared via a solid-state reaction route. Eu2+-doped orthorhombic Ca3(PO4)2 phosphor exhibits a broad emission band in the wavelength range of 400–700 nm with a maximum quantum yield of 56.7%, and the emission peak red-shifts gradually from 479 to 520 nm with increase of Eu2+ doping content. Broad excitation spectrum (250–420 nm) of Eu2+: Ca3(PO4)2 matches well with the near-ultraviolet LED chip, indicating its potential applications as tri-color phosphors in white LEDs. Interestingly, Mn2+ co-doping into Eu2+: Ca3(PO4)2 leads to its phase transition from orthorhombic to rhombohedral, and subsequently generates tunable multi-color luminescence from green to red via Eu2+ → Mn2+ energy transfer, under 365 nm UV lamp excitation.