Synthesis and luminescence properties of Eu²⁺- and Mn²⁺-activated Mg₂₁Ca₄Na₄(PO₄)₁₈ phosphors

Rare earth-doped phosphates have attracted much attention in recent years because of their interesting optical applications. However, few studies have reported on optical properties of fillowite-like compounds. Eu²⁺ and Mn²⁺ singly doped and Eu²⁺/Mn²⁺-codoped Mg₂₁Ca₄Na₄(PO₄)₁₈ phosphors were synthesized for the first time via combustion-assisted synthesis technique. The Eu²⁺-activated sample emits an intense blue light under 360 nm excitation, while the Eu²⁺/Mn² + -codoped Mg₂₁Ca₄Na₄(PO₄)₁₈ sample exhibits a broad blue emission band and a red emission band, resulting from Eu²⁺ and Mn²⁺, respectively. Energy transfer between Eu²⁺ and Mn²⁺ was discovered and the transfer efficiency was also estimated based on relative intensities of Eu²⁺ and Mn²⁺ emission. Thus, the relative strength of blue and red emission intensities could be tuned by varying the relative concentration of Eu²⁺ and Mn²⁺. Since the photoluminescence excitation spectra of the newly developed Mg₂₁Ca₄Na₄(PO₄)₁₈:Eu²⁺, Mn²⁺ phosphors exhibit a strong absorption in the range of 250–400 nm, they are promising for producing UV-LED-based white LEDs.