Synthesis, Luminescence, and Energy-Transfer Properties of β‑Na₂Ca₄(PO₄)₂(SiO₄):A (A = Eu²⁺, Dy³⁺, Ce³⁺/Tb³⁺) Phosphors

A series of β-Na₂Ca₄(PO₄)₂(SiO₄) (β-NCPS):A (A = Eu²⁺, Dy³⁺, Ce³⁺/Tb³⁺) phosphors were prepared via a high-temperature solid-state reaction route. The X-ray diffraction, Fourier transform infrared, photoluminescence (PL), cathodoluminescence (CL) properties, fluorescent lifetimes, and absolute quantum yield were exploited to characterize the samples. Under UV radiation, the β-NCPS:Eu²⁺ phosphors present bright green emissions, and the β-NCPS:Ce³⁺ phosphors show strong blue emissions, which are attributed to their 4f⁶5d¹ → 4f⁷ and 5d–4f allowed transitions, respectively. The β-NCPS:Ce³⁺, Tb³⁺ phosphors display intense tunable color from blue to green and high absolute quantum yields (81% for β-NCPS:0.12Ce³⁺ and 83% for β-NCPS:0.12Ce³⁺, 0.08Tb³⁺) when excited at 365 nm. Simultaneously, the energy transfer from Ce³⁺ to Tb³⁺ ions is deduced from the spectral overlap between Ce³⁺ emission and Tb³⁺ excitation spectra and demonstrated by the change of emission spectra and decay lifetimes. Moreover, the energy-transfer mechanism from Ce³⁺ to Tb³⁺ ions is confirmed to be exchange interaction according to the discussion of expression from Dexter and Reisfeld. Under a low-voltage electron-beam excitation, the β-NCPS:A (A = Eu²⁺, Dy³⁺, Ce³⁺/Tb³⁺) phosphors exhibit their characteristic emissions, and the emission profiles of β-NCPS:Ce³⁺,Tb³⁺ phosphors are obviously different from those of the PL spectra; this difference might be ascribed to their different luminescence mechanisms. These results in PL and CL properties suggest that β-NCPS:A (A = Eu²⁺, Dy³⁺, Ce³⁺/Tb³⁺) phosphors are potential candidates for solid-state lighting and field-emission displays