Color tuning in Ca3−xMx(PO4)2:Eu2+ (M = Sr, Ba) phosphors via cation substitution
A series of Ca3−xMx(PO4)2:Eu2+ (M = Sr, Ba) phosphors were prepared via a high-temperature solid-state reaction process. The X-ray diffraction and Rietveld refinements were used to verify the incorporations of Eu2+ into Ca3−xMx(PO4)2:Eu2+ (M = Sr, Ba). Upon excitation at 365 nm, the Ca3(PO4)2:Eu2+ phosphors exhibit a relatively narrow-band blue emission peaking at 415 nm attributed to the electric radiation transitions 4f65d1 → 4f7 of Eu2+. Moreover, the structural phase transformation and the unusual emission color variation of Ca3−xMx(PO4)2:Eu2+ (M = Sr, Ba) phosphors via the replacement of cationic M2+ (Sr2+, Ba2+) were reported. Upon excitation at the same wavelength of 365 nm, the emission peaks of Eu2+-doped Ca3−xSrx(PO4)2 phosphors red-shifted from 411 to 524 nm with increasing Sr/Ca ratio. The emission thermal stability of M3(PO4)2:Eu2+ (M = Ca, Sr, Ba) was comparatively characterized and the difference was related to the specific host structural features. The combination of host composition design may provide a novel strategy to obtain white light and tunable luminescence.