Synthesis and photoluminescence control of Ca_10.5–1.5xLa_x(PO₄)₇:Eu²⁺ phosphors by aliovalent cation substitution

A range of Ca_10.5-1.5xLa_x(PO₄)₇:Eu²⁺phosphors were synthesized by high temperature solid state method. Subsequently we studied the crystal structures and luminescent properties through X-ray diffraction, photoluminescence and photoluminescence excitation, diffuse reflection spectra, Raman spectra and decay curves systematically. Based on the special crystal structure ofβ-Ca₃(PO₄)₂:Eu²⁺, its emission undergoes a variation from violet–blue to cyan through introducing La³⁺. The substitution of La³⁺ for Ca²⁺ could form some cation vacancies in Ca(4) sites according to the scheme 3Ca²⁺= 2La³⁺+ □ due to the different ion valence, which compels Eu²⁺ to migrate from Ca(4) site to other sites. Additionally, the formation of the cation vacancies can further reduce the thermal stability of phosphors. - Highlights: • Realizing photoluminescence control of Eu²⁺ by introducing relatively larger La³⁺ ion to replace the Ca²⁺ in β-Ca₃(PO₄)₂:Eu²⁺ phosphor. • The mechanism of spectral control is proposed to be due to emptying of Ca²⁺ and migration of Eu²⁺. • The thermal stability reduction is related to the formation of vacancies.