Color tuning in Ca3−xMx(PO4)2:Eu2+ (M = Sr, Ba) phosphors via cation substitution

Abstract

A series of Ca_3−xM_x(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 Ca_3−xM_x(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 Ca_3−xM_x(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 Ca_3−xSr_x(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.