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 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 the excitation of 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. On the same excitation wavelength of 365 nm, the emission peaks of Eu2+-doped Ca3-xSrx(PO4)2 phosphors red-shift 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.